1
DESCRIPTION
HOT ROLLED STEEL SHEET AND METHOD OF PRODUCING SAME
5 Technical Field
[0001]
The present invention relates to a hot rolled steel sheet which has composite
structure and which shows high strength, excellent formability, and excellent fracture
properties, and a method of producing the same.
10 Priority is claimed on Japanese Patent Application No. 2011 -060909, filed in
Japan on March 18, 2011, and Japanese Patent Application No. 2011-064633, filed in
Japan on March 23, 2011, the contents of which are incorporated herein by reference.
Background Art
15 [0002]
In recent years, in order to reduce the weight of automobiles, attempts to
increase the strength of steel sheets have been performed. In general, increasing the
strength of the steel sheet leads to a deterioration of the formability such as a hole
expansibility, and thinning the sheet thickness for weight reduction leads to a decrease in
20 fatigue life. Accordingly, in order to develop a steel sheet which shows the high
strength and which enables the weight reduction of automobiles, it is important to
achieve improvements in the formability such as the hole expansibility and in the fatigue
properties in addition to the increase in the strength of the steel sheet.
[0003]
25 Conventionally, it is known that an excellent fatigue life can be obtained by
2
producing steel which has composite structure consisting of ferrite and martensite. As a
steel sheet which shows the high strength and in which the hole expansibility is intended
to be improved by producing the steel which has the composite structure, Patent
Document 1 discloses a high strength hot rolled steel sheet where a fraction of the
5 microstructure of the steel which consists of the mixed structure of ferrite, martensite,
and residual austenite is appropriately controlled. The characteristic values of the steel
sheet which is obtained by the technique are tensile strength of 590 MPa or more and
hole expanding ratio of approximately 50%.
[0004]
10 Patent Document 2 discloses a high strength hot rolled steel sheet which consists
of a mixed structure of ferrite and martensite, which is precipitation-strengthened by
carbides of Ti or Nb. The characteristic values of the steel sheet which is obtained by
the disclosed technique are tensile strength of 780 MPa or more and hole expanding ratio
of approximately 50%.
15 [0005]
However, for example, for steel sheets which are used as suspension members or
the like of the automobile, a steel sheet which shows excellent coexistence of the tensile
strength with the hole expansibility, such as tensile strength of 590 MPa or more and hole
expanding ratio of 60% or more as the characteristic values thereof, is anticipated. In
20 particular, a steel sheet which has hole expanding ratio of 90% or more when the tensile
strength is 590 MPa to less than 780 MPa and which has hole expanding ratio of 60% or
more when the tensile strength is 780 MPa to 980 MPa is anticipated.
[0006]
In addition, since the variation of each measurement of the hole expanding ratio
25 is comparatively large, it is necessary to reduce a standard deviation a of the hole
3
expanding ratio which is an index representing the variation, in addition to an average
Xave of the hole expanding ratio in order to improve the hole expansibility. As
described above, in the steel sheets which are used as the suspension members of the
automobiles, a steel sheet which has preferably standard deviation a of the hole
5 expanding ratio of 15% or less and which has more preferably standard deviation a of the
hole expanding ratio is 10% or less is anticipated.
[0007]
In addition, for example, in a case where the automobile drives over a curb and a
strong impact load is applied to the suspension parts, fracture may occur from a punching
10 surface of the suspension parts as a starting point. In particular, since the notch
sensitivity increases with an increase in the strength of the steel sheet, the fracture from
the punching end face are strongly concerned. For this reason, for the steel sheets
which are used as structural materials of the suspension parts or the like, it is necessary to
improve the fracture properties. As indices representing the fracture properties,
15 resistance of crack initiation Jc (unit: J/m ) and resistance of crack propagation T. M.
(tearing modulus) (unit: J/m ) which are the characteristic values which are obtained by a
three point bending test with notch, and fracture appearance transition temperature vTrs
(unit: °C) and Charpy absorbed energy E (unit: J) which are obtained by a Charpy impact
test may be exemplified. The resistance of crack initiation Jc represents the resistance
20 to the initiation of cracks (the start of fracture) from the steel sheet which composes the
structural material when the impact load is applied. On the other hand, the resistance of
crack propagation T. M. represents the resistance to large-scale fracture (the propagation
of fracture) of the steel sheet which composes the structural material. In order not to
decrease the safety of the structural material when the impact load is applied, it is
25 important to improve both of the resistances.
4
[0008]
Conventionally, techniques, in which the characteristic values, in particular, the
resistance of crack initiation Jc and the resistance of crack propagation T. M. which are
characteristic values obtained by the three point bending test with notch intend to be
5 improved, have not been disclosed.
[0009]
In addition, repeated stress is applied to the suspension parts for the automobile.
Therefore, since occurrence of the fatigue fracture is concerned, excellent fatigue
properties are also required for the steel sheets which are used as structural materials
10 such as suspension parts.
Related Art Documents
Patent Documents
[0010]
15 [Patent Document 1] Japanese Unexamined Patent Application, First
Publication No. H6-145792
[Patent Document 2] Japanese Unexamined Patent Application, First
Publication No. H9-125194
20 Summary of Invention
Technical Problem
[0011]
The present invention was achieved in consideration of the problems described
above. An object of the present invention is to provide a hot rolled steel sheet, which
25 has an excellent balance between tensile properties and formability and furthermore
5
which has excellent fracture properties and fatigue properties, and a method of producing
the same.
[0012]
Specifically, the present invention is to provide the hot rolled steel sheet which
5 has composite structure and which shows high strength, wherein the hot rolled steel sheet
has the properties such that: the tensile strength TS is 590 MPa or more and the n value
(work hardening coefficient) is 0.13 or more as the tensile properties; the average X.ave of
the hole expanding ratio is 60% or more and the standard deviation a of the hole
expanding ratio is 15% or less as the formability; the resistance of crack initiation Jc is
10 0.5 MJ/m or more, the resistance of crack propagation T. M. is 600 MJ/m or more, the
fracture appearance transition temperature vTrs is -13°C or lower, and the Charpy
absorbed energy E is 16 J or more as the fracture properties; and the fatigue life in plane
bending is 400000 times or more as the fatigue properties.
[0013]
15 In particular, the present invention is to provide the hot rolled steel sheet in
which, when the tensile strength TS is 590 MPa to less than 780 MPa, in the
above-described properties, the average Xave of the hole expanding ratio is 90% or more,
the resistance of crack initiation Jc is 0.9 MJ/m or more, and the Charpy absorbed
energy E is 35 J or more.
20
Solution to Problem
[0014]
An aspect of the present invention employs the following.
[0015]
25 (1) A hot rolled steel sheet according to an aspect of the invention includes, as a
6
chemical composition, by mass %, 0.03% to 0.1% of C, 0.5% to 3.0% of Mn, at least one
of Si and Al so as to satisfy a condition of 0.5% < Si + Al < 4.0%, limited to 0.1% or less
of P, limited to 0.01% or less of S, limited to 0.02% or less of N, at least one selected
from 0.001% to 0.3% of Ti, 0.0001% to 0.02% of Rare Earth Metal, and 0.0001% to
5 0.01 % of Ca, and a balance consisting of Fe and unavoidable impurities, and as a
metallographic structure, a ferrite as a primary phase, at least one of a martensite and a
residual austenite as a secondary phase, and plural inclusions, wherein: amounts
expressed in mass% of each element in the chemical composition satisfy a following
Expression 1; an average grain size of the ferrite which is the primary phase is 2 urn to
10 10 urn; an area fraction of the ferrite which is the primary phase is 90% to 99%; an area
fraction of the martensite and the residual austenite which are the secondary phase is 1%
to 10% in total; when a cross section whose normal direction corresponds to a transverse
direction of the steel sheet is observed at 30 of visual fields by 0.0025 mm2, an average
of a maximum of a ratio of a major axis to a minor axis of each of the inclusions in each
15 of the visual fields is 1.0 to 8.0; when a group of inclusions in which a major axis of each
of the inclusions is 3 jam or more and an interval in a rolling direction between the
inclusions is 50 urn or less are defined as inclusion-cluster, and when an inclusion in
which the interval is more than 50 urn are defined as an independent-inclusion, a total
length in the rolling direction of both the inclusion-cluster whose length in the rolling
20 direction is 30 um or more and the independent-inclusion whose length in the rolling
direction is 30 um or more is 0 mm to 0.25 mm per 1 mm2 of the cross section; a texture
satisfies that an X-ray random intensity ratio of a {211} plane which is parallel to a
rolling surface is 1.0 to 2.4; and a tensile strength is 590 MPa to 980 MPa.
12.0 < (Ti / 48) / (S / 32) + {(Ca / 40) / (S / 32) + (Rare Earth Metal /140) / (S /
7
32)} x 15 < 150 (Expression 1)
(2) The hot rolled steel sheet according to (1) may further includes, as the
chemical composition, by mass %, at least one of 0.001 % to 0.1% of Nb, 0.0001%) to
0.0040% of B, 0.001% to 1.0% of Cu, 0.001% to 1.0% of Cr, 0.001% to 1.0% of Mo,
5 0.001% to 1.0% of Ni, and 0.001% to 0.2% of V.
(3) In the hot rolled steel sheet according to (1) or (2), when the hot rolled steel
sheet includes, as the chemical composition, by mass%, at least one of 0.0001% to 0.02%
of Rare Earth Metal and 0.0001% to 0.01% of Ca, the Ti content may be 0.001% to less
than 0.08%.
10 (4) In the hot rolled steel sheet according to any one of (1) to (3), amounts
expressed in mass% of each element in the chemical composition may satisfy a following
Expression 2; and the average of the maximum in the ratio of the major axis to the minor
axis of each of the inclusions in each of the visual fields may be 1.0 to 3.0.
0.3 < (Rare Earth Metal /140) / (Ca / 40) (Expression 2)
15 (5) In the hot rolled steel sheet according to any one of (1) to (4), an area
fraction of a bainite and a pearlite in the metallographic structure may be 0% to less than
5.0% in total.
(6) In the hot rolled steel sheet according to any one of (1) to (5), a total number
of MnS precipitates and CaS precipitates having a major axis of 3 jam or more may be
20 0% to less than 70% as compared with a total number of the inclusions having the major
axis of 3 um or more.
(7) In the hot rolled steel sheet according to any one of (1) to (6), an average
grain size of the secondary phase may be 0.5 um to 8.0 (am.
(8) A method of producing the hot rolled steel sheet according to any one of (1)
8
to (7) includes: a heating process of heating a steel piece which composed of the
chemical composition according to any one of (1) to (4) to a range of 1200°C to 1400°C;
a first rough rolling process of rough rolling the steel piece in a temperature range of
higher than 1150°C to 1400°C so that a cumulative reduction is 10% to 70% after the
5 heating process; a second rough rolling process of rough rolling in a temperature range of
higher than 1070°C to 1150°C so that a cumulative reduction is 10% to 25% after the
first rough rolling process; a finish rolling process of finish rolling so that a start
temperature is 1000°C to 1070°C and a finish temperature is Ar3 + 60°C to Ar3 + 200°C
to obtain a hot rolled steel sheet after the second rough rolling process; a first cooling
10 process of cooling the hot rolled steel from the finish temperature so that a cooling rate is
20 °C/second to 150 °C/second after the finish rolling process; a second cooling process
of cooling in a temperature range of 650°C to 750°C so that the cooling rate is 1
°C/second to 15 °C/second and a cooling time is 1 second to 10 seconds after the first
cooling process; a third cooling process of codling to a temperature range of 0°C to
15 200°C so that the cooling rate is 20 °C/second to 150 °C/second after the second cooling
process; and a coiling process of coiling the hot rolled steel sheet after the third cooling
process.
(9) In the method of producing the hot rolled steel sheet according to (8), in the
first rough rolling process, the rough rolling may be conducted so that the cumulative
20 reduction is 10% to 65%.
Advantageous Effects of Invention
[0016]
According to the above aspects of the present invention, it is possible to obtain a
9
steel sheet which has an excellent balance between tensile properties and formability and
furthermore which has excellent fracture properties and fatigue properties.
Brief Description of Drawings
[0017]
FIG. 1 is a plan view showing test piece size for evaluation of fatigue properties.
FIG. 2A is an explanatory view for the three point bending test with notch.
FIG. 2B shows a notched test piece before the three point bending test with
notch and is a cross sectional view which includes the notch whose a normal direction
corresponds to a transverse direction of a steel sheet.
FIG. 2C shows a notched test piece which is forcibly fractured after the three
point bending test with notch and shows a fracture surface which includes the notch.
FIG. 3 A is a load displacement curve which is obtained by the three point
bending test with notch.
FIG. 3B is a graph showing a relationship between an amount of crack
propagation Aa and processing energy J per lm .
FIG. 4 A is a schema of an inclusion-cluster which is a group of inclusions.
FIG. 4B is a schema of an independent-inclusion which exists independently.
FIG. 4C is a schema of an inclusion-cluster which includes an inclusion whose
length in a rolling direction is 30 um or more.
FIG. 5 is a diagram which shows a relationship between a total length M in the
rolling direction of the inclusions, an average of a maximum of a ratio of a major axis to
a minor axis of the inclusions, and an average A,ave of the hole expanding ratio.
FIG. 6 is a diagram which shows a relationship between the total length M in the
rolling direction-of the inclusions, the average of the maximum of the ratio of the major
K
10
axis to the minor axis of the inclusions, and a standard deviation a of the hole expanding
ratio.
FIG. 7 is a diagram which shows a relationship between the total length M in the
rolling direction of the inclusions and resistance of crack propagation T. M..
5 FIG. 8 is a diagram which shows a relationship between S content, Ti content,
REM content, and Ca content and the total length M in the rolling direction of the
inclusions.
FIG. 9A is a diagram which shows a relationship between cumulative reduction
in a first rough rolling process and the total length M in the rolling direction of the
10 inclusions.
FIG. 9B is a diagram which shows a relationship between the cumulative
reduction in the first rough rolling process and the average of the maximum of the ratio
of the major axis to the minor axis of the inclusions.
FIG. 9C is a diagram which shows a relationship between cumulative reduction
15 in second rough rolling process and an X-ray random intensity ratio of {211} plane.
FIG. 9D is a diagram which shows a relationship between the cumulative
reduction in the second rough rolling process and an average grain size of ferrite.
Description of Embodiments
20 [0018]
Hereinafter, a preferable embodiment of the present invention will be described
in detail. However, the present invention is not limited only to the configuration which
is disclosed in the embodiment, and various modifications are possible without departing
from the aspect of the present invention.
25 [0019]
11
First, description will be given of the basic research results which have led to the
completion of the present invention. To start with, description will be given of a
measurement method of characteristic values which are required in the hot rolled steel
sheet according to the embodiment.
5 [0020]
The tensile properties were determined from a tensile test with the following
conditions. From a portion of 1/2 in the sheet width of a test steel sheet, test pieces
were prepared so that a tensile direction was parallel to a transverse direction of the test
steel sheet. The tensile test was conducted using the test pieces. Then, tensile strength
10 (TS: Tensile Strength) and yield point (YP: Yield Point) were determined. Here, in a
case where a clear yield point is not observed, 0.2% proof stress was regarded as the
yield point. In addition, n value (work hardening coefficient) is determined as an
approximate value of an n-th power law hardening rule based on true stress and true
strain which were calculated from the tensile test. Here, a range of the strain when the n
15 value is determined is to be 3% to 12%.
[0021]
The hole expansibility was evaluated from a hole expansion test with the
following conditions. From the portion of 1/2 in the sheet width of the test steel sheet,
20 test pieces where the length in the rolling direction was 150 mm and the length in the
20 transverse direction was 150 mm were prepared for each test steel sheet. Using the test
pieces, the hole expansion test was conducted with the following conditions. The
evaluation of the hole expansibility was conducted with the average X,ave of the hole
expanding ratio (unit: %) which was determined by arithmetically averaging 20 test
results and with the standard deviation a (unit: %) which was determined from the
25 following Expression 1. Here, A.i in the following Expression 1 represents the i-th hole
t
12
expanding ratio in the total of 20 tests.
1 20
20 £
(Expression 1)
[0022]
The conditions of the hole expansion test were as follows. In the test piece, a
5 punching hole of 10 mm as an was provided by using a punching punch with a diameter
of 10 mm under condition where a punching clearance which was obtained by dividing
the intervals between the punching punch and the die hole by the sheet thickness of the
test piece was to be 12.5%. Next, in the punching hole in the test piece, a conical punch
with an angle of 60° was inserted from the same direction as the punching punch and the
10 inner hole diameter Df was measured at a point of time where crack which was initiated
in the punching end surface penetrated in the sheet thickness direction of the test piece.
Then, the hole expanding ratio Xi (unit: %) was determined from the following
Expression 2. Here, the penetration of the crack in the sheet thickness was visually
observed.
15 Xi = {(Df - DO) / DO} x 100 (Expression 2)
[0023]
The fatigue properties were evaluated from a fatigue test with the following
conditions. Test pieces with the size shown in FIG. 1 were prepared from the test steel
sheets which were as-hot-rolled. In FIG. 1, the test piece for the fatigue test is shown as
20 11, the rolling direction is shown as RD (Rolling Direction), and the transverse direction
is shown as TD (Transverse Direction). Repeated stress by plane bending was applied
to a neck section of the center of the test pieces and the fatigue life in plane bending,
which was the number of repetitions until the test pieces was fatigue-fractured, was
13
measured. The condition of the repeated stress which was applied to the test pieces in
the fatigue test was completely reversed. Specifically, in a case where the stress
amplitude = ao, the conditions of the fatigue test were controlled so that the stress change
over time was a sine wave where the maximum stress = ao, the minimum stress =-oo, and
5 the average of the stress = 0. The stress amplitude ao was to be within a range of 45% ±
10 MPa as compared with the tensile strength TS of the test steel sheet. In addition, the
fatigue test was conducted at least three times under conditions with the same stress
amplitude ao, and the average of the fatigue life in plane bending by arithmetically
averaging each test result was determined. The fatigue properties were evaluated by the
10 average of the fatigue life in plane bending.
[0024]
The fracture properties were evaluated by the resistance of crack initiation Jc
(unit: J/m2) and the resistance of crack propagation T. M. (unit: J/m3) which were
obtained by the three point bending test with notch to be described later, and the fracture
15 appearance transition temperature vTrs (unit: °C) and the Charpy absorbed energy E
(unit: J) which were obtained by the Charpy impact test.
[0025]
The conditions of the three point bending test with notch were as follows. Five
or more of the notched test pieces shown in FIG. 2 A and FIG. 2B were prepared from one
20 test steel sheet so that the longitudinal direction of the test piece was parallel to the
transverse direction of the test steel sheet and the displacement direction of the three
point bending test with notch corresponded to the rolling direction of the test steel sheet.
FIG. 2A is an explanatory view for the three point bending test with notch. In FIG 2A,
a test piece for the three point bending test with notch is shown as 21, a notch is shown as
14
21, a load point is shown as 22, support points are shown as 23, and the displacement
direction is shown as 24. FIG. 2B is a cross sectional view of the notched test piece 21
before the three point bending test with notch which includes the notch 21a whose the
normal direction corresponds to the transverse direction TD .of the test steel sheet. In
5 FIG. 2B, the sheet thickness direction is shown as ND (Normal Direction). As shown in
the figures, the longitudinal direction of the test piece 21 was 20.8 mm, the thickness in
the displacement direction 24 of the test piece 21 was 5.2 mm, the depth of the
displacement direction 24 of the notch 21a was 2.6 mm, the thickness C (value where the
depth of the displacement direction 24 of the notch 21a was subtracted from the thickness
10 of the displacement direction 24 of the test piece 21) of the displacement direction 24 of
the ligament was 2.6 mm, and the sheet thickness B of the test steel sheet was 2.9 mm.
[0026]
As shown in FIG. 2A, using the test piece 21, both end sections in the
longitudinal direction of the test piece 21 were set as the support points 23 and the central
15 portion thereof was set as the load point 22, and the amount of displacement (stroke) in
the displacement direction 24 of the load point were variously changed, thereby
conducting the three point bending test with notch. The test piece 21 after the three
point bending test with notch was subjected to a heat treatment where the test piece was
held for 30 minutes at 250°C in the atmosphere and then was air-cooled. By the heat
20 treatment, the fracture surface which was derived from the three point bending test with
notch was oxidized and colored. The test piece 21 after the heat treatment was cooled
using liquid nitrogen to the temperature of the liquid nitrogen, and then the test piece 21
was forcibly fractured at the temperature so that the crack propagated along the
displacement direction 24 from the notch 21 a of the test piece 21. FIG. 2C exemplifies
25 a fracture surface which includes the notch in the notched test piece 21 which was
15
forcibly fractured after the three point bending test with notch. In the fracture surface,
as a result of the oxidizing and coloring, it was possible to clearly distinguish the fracture
surface derived from the three point bending test with notch from the fracture surface
derived from the forced fracture. In FIG. 2C, the fracture surface derived from the three
5 point bending test with notch is shown as 21b, the fracture surface derived from the
forced fracture is shown as 21c, the depth of the fracture surface 21b at a position of 1/4
in the sheet thickness of the test steel sheet is shown as LI, the depth of the fracture
surface 21b at a position of 1/2 in the sheet thickness of the test steel sheet is shown as
L2s, and the depth of the fracture surface 21b at a position of 3/4 in the sheet thickness of
10 the test steel sheet is shown as L3. The fracture surface 21b was observed, LI, L2, and
L3 were measured, and then the amount of crack propagation Aa (unit: m) was
determined from the following Expression 3.
Aa = (LI + L2 + L3) / 3 (Expression 3)
[0027]
15 FIG. 3 A exemplifies a load displacement curve obtained by the three point
bending test with notch. As shown in FIG. 3 A, by integrating the load displacement
curve, processing energy A (unit: J) corresponding to the energy which was applied to the
test piece 21 by the test was determined. Then, using the processing energy A, the sheet
thickness B of the test steel sheet before the three point bending test with notch, and the
20 thickness C of the displacement direction 24 of the ligament, processing energy J (unit:
J/m ) per lm was determined from the following Expression 4.
J = (2 x A) / (B x C) (Expression 4)
[0028]
FIG. 3B is a graph showing the relationship between the amount of crack
25 propagation Aa and the processing energy J per lm when the stroke conditions are
16
variously changed in the three point bending test with notch. As shown in FIG. 3B, an
intersection between a linear regression line with respect to Aa and J and a straight line
which passed through an origin and whose inclination was 3 x (YP + TS) / 2 was
determined. The value of the processing energy J per lm2 in the intersection was
5 regarded as the resistance of crack initiation Jc (unit: J/m2) which was a value which
represented the resistance to the initiation of crack of the test steel sheet. In addition, an
inclination of the linear regression line was regarded as the resistance of crack
propagation T. M. (unit: J/m ) which represented the resistance to the propagation of
crack of the test steel sheet. The resistance of crack initiation Jc is an index value which
10 represents the degree of the processing energy which is necessary for initiating the crack.
Specifically, the resistance of crack initiation Jc represents the resistance to the initiation
of the crack (the start of the fracture) from the steel sheet which composes the structural
material when the impact load is applied. The resistance of crack propagation T. M. is
an index value which represents the degree of the processing energy which is necessary
15 for propagating the crack. Specifically, the resistance of crack propagation T. M.
represents the resistance to large-scale fracture (the propagation of the fracture) of the
steel sheet which composes the structural material. The fracture properties of the steel
sheet were evaluated by the resistance of crack initiation Jc and the resistance of crack
propagation T. M.
20 [0029]
The conditions of the Charpy impact test were as follows. V notched test
pieces were prepared so that the longitudinal direction of the test piece was parallel to the
transverse direction of the test steel sheet. Regarding the test piece size, the length of
the test piece in the longitudinal direction was 55 mm, the thickness in the direction
25 where the impact was applied to the test piece was 10 mm, the thickness in a direction
17
which intersected with the longitudinal direction and the impact direction of the test
piece was 2.5 mm, and a depth of the V notch was 2 mm and an angle thereof was 45°.
By conducting the Charpy impact test using the test pieces, the fracture appearance
transition temperature vTrs (unit: °C) and Charpy absorbed energy E (unit: J) were
5 determined. Here, the fracture appearance transition temperature vTrs was to be a
temperature where a fraction of the ductile fracture was 50%, and the Charpy absorbed
energy E was to be a value which was obtained when the test temperature was room
temperature (23°C ± 5°C). The fracture properties of the steel sheet were evaluated by
the fracture appearance transition temperature vTrs and the Charpy absorbed energy E.
10 [0030]
As the above-described characteristic values, the hot rolled steel sheet according
to the embodiment satisfies that the tensile strength TS is 590 MPa or more, the average
A,ave of the hole expanding ratio is 60% or more, the standard deviation a of the hole
expanding ratio is 15% or less, the fatigue life in plane bending is 400000 times or more,
15 the resistance of crack initiation Jc is 0.5 MJ/m2 or more, the resistance of crack
propagation T. M. is 600 MJ/m or more, the fracture appearance transition temperature
vTrs is -13°C or lower, and the Charpy absorbed energy E is 16 J or more.
[0031]
Next, description will be given of the measurement method of the chemical
20 composition, the observation method of the metallographic structure, and the like of the
hot rolled steel sheet according to the embodiment.
[0032]
The chemical composition of the steel sheet was quantitatively analyzed using
EPMA (Electron Probe Micro-Analyzer: electron probe X-ray micro-analysis), AAS
18
(Atomic Absorption Spectrometer: atomic absorption spectrometry), ICP-AES
(Inductively Coupled Plasma-Atomic Emission Spectrometer: inductively coupled
plasma emission spectroscopy spectrometry), or ICP-MS (Inductively Coupled
Plasma-Mass Spectrometer: inductively coupled plasma mass analysis spectrometry).
5 [0033]
The observation of the metallographic structure of the steel sheet was conducted
using the following methods. Test pieces for metallographic structure observation were
cut out from a portion of 1/4 in the sheet width of the steel sheet, so that a cross section
(hereinafter, L cross section) whose normal direction corresponded to the transverse
10 direction was an observed section. Then, the test pieces were mirror-polished. Using
the test pieces after mirror polishing, inclusions which were included in the
metallographic structure were observed at a magnification of 400 -fold by an optical
microscope so that the observed area was at the vicinity of the centeral portion of the
sheet thickness in the above-described L cross section. In addition, Nital etching or Le
15 Pera etching were conducted on the test pieces after mirror polishing, and the observation
was conducted of the metallic phases such as ferrite, martensite, residual austenite,
bainite, pearlite, and the like.
[0034]
The average grain size of ferrite was determined as follows. The crystal
20 orientation distribution was measured by 1 |xm steps using an EBSD (Electron
Back-Scattered diffraction Pattern) method, so that the observed area was at the centeral
portion of the sheet thickness in the L cross section and was an area of 500 urn in the
normal direction and 500 u.m in the rolling direction. Then, points where the
misorientation was 15° or more were connected, which was regarded as high-angle grain
25 boundaries. The arithmetic average of equivalent circle diameters of each crystal grain
19
which was surrounded by the high-angle grain boundaries were determined and were
regarded as the average grain size of the ferrite. At this time, among each of the
measurement points which were measured by the EBSD method, crystal grains where the
IQ (Image Quality) value was 100 or more were regarded as the ferrite, and the crystal
5 grains where the IQ value was 100 or less were regarded as metallic phases with the
exception of the ferrite.
[0035]
Area fractions such as ferrite, martensite, residual austenite, bainite, pearlite, and
the like were determined by image analysis of metallographic micrograph.
10 [0036]
In addition, for the investigation of the inclusions, the total length M (unit:
mm/mm ) in the rolling direction of the inclusions which were defined as described
below was measured.
[0037]
15 The existence of the inclusions causes a deterioration of the hole expansibility,
because the inclusions form voids in the steel during the deformation of steel sheet and
promote the ductile fracture. Moreover, as the shape of the inclusions is elongated in
the rolling direction of the steel sheet, the stress concentration in the vicinity of the
inclusions during plastic deformation of steel sheet increases. Specifically, in addition
20 to the existence of the inclusions, the hole expansibility is drastically influenced by the
shape of the inclusions. Conventionally, it is known that the hole expansibility
drastically deteriorates with an increase in the length in the rolling direction of individual
inclusions.
[0038]
25 The present inventors discover that, when plural inclusions such as elongated
20
inclusions, spherical inclusions, or the like are formed into a group by being distributed
with predetermined intervals in the rolling direction of the steel sheet which is the
direction of crack propagation, the hole expansibility deteriorates in common with the
inclusions which are elongated individually. This seems to be caused by inducing large
5 stress concentrations in the vicinity of the groups, which is derived from the synergistic
effect of the strains which are induced in the vicinity of each inclusion which composes
the groups during the deformation of the steel sheet. Quantitatively, it was discovered
that the hole expansibility deteriorates by the existence of the group of inclusions, in
which a major axis of each of the inclusions is 3 um or more and the inclusions are lined
10 up so that an interval to other adjacent inclusions on a line in the rolling direction of the
steel sheet is 50 um or less, in common with the inclusion which exists independently
and is elongated. Hereinafter, the group of the inclusions in which the respective major
axes are 3 urn or more and the intervals in the rolling direction between the inclusions are
50 um or less is referred to as an inclusion-cluster. In addition, in contrast with the
15 inclusion-cluster, the inclusion which exists independently and in which the interval in
the rolling direction between the inclusions is more than 50 um is referred to as an
independent-inclusion. The above-described major axis represents the longest diameter
in the cross-sectional shape of the observed inclusion and usually corresponds to the
diameter in the rolling direction.
20 [0039]
As described above, in order to improve the hole expansibility of the steel sheet,
it is important to control the shape and distribution of the inclusions as described below.
[0040]
FIG. 4 A is a schema of the inclusion-cluster which is the group of inclusions.
21
In FIG. 4A, the inclusions in which the respective major axes are 3 um or more are
shown as 41a to 41 e, the intervals between inclusions in the rolling direction are shown
as F, the inclusion-cluster is shown as G, and the length of the inclusion-cluster in the
rolling direction is shown as GL. As shown in FIG. 4A, the group of inclusions in
5 which the interval F is 50 um or less along the rolling direction RD of the steel sheet,
specifically, one group which includes the inclusion 41b, the inclusion 41c, and the
inclusion 4Id, is regarded as the inclusion-cluster G The length GL in the rolling
direction of the inclusion-cluster G is measured. The inclusion-cluster G where the
length GL is 30 um or more has an influence on the hole expansibility of the steel sheet.
10 The inclusion-cluster G where the length GL in the rolling direction is less than 30 urn
has a small influence on the hole expansibility. In addition, inclusions in which the
major axis is less than 3 um are not included in the constituent of the inclusion-cluster G
since the influence on the hole expansibility is small even if the interval F is 50 jam or
less. In addition, in FIG. 4A, the inclusion 41a and the inclusion 41 e are respectively
15 regarded as the independent-inclusions.
[0041]
FIG. 4B is a schema of the independent-inclusions. In FIG. 4B, inclusions in
which the respective major axes are 3 jam or more are shown as 41f to 41h, the
independent-inclusions are shown as H, and the length of the independent-inclusion in
20 the rolling direction is shown as HL. As shown in FIG. 4B, the inclusions in which the
interval F is more than 50 jam along the rolling direction RD of the steel sheet,
specifically, the inclusion 4If, the inclusion 41g, and the inclusion 41h, are respectively
regarded as the independent-inclusions H. The length HL in the rolling direction of the
independent-inclusion H is measured. The independent-inclusion H where the length
22
HL is 30 urn or more has an influence on the hole expansibility of the steel sheet. The
independent-inclusion H where the length HL in the rolling direction is less than 30 um
has a small influence on the hole expansibility.
[0042]
5 FIG. 4C is a schema of the inclusion-cluster G which includes the inclusion
where the length in the rolling direction is 30 urn or more. In FIG. 4C, inclusions in
which the respective major axes are 3 um or more are shown as 41 i to 411. In addition,
in FIG. 4C, the inclusion 41j has a length (major axis) in the rolling direction of 30 um or
more. In FIG. 4C, one group which includes the inclusion 41j and the inclusion 41k and
10 in which the interval F is 50 (am or less along the rolling direction RD of the steel sheet is
regarded as the inclusion-cluster G, and the inclusions 41 i and the inclusions 411 are
respectively regarded as the independent-inclusions H,. As described above, since the
inclusion 41k where the interval F to the inclusion 41j is 50 um or less exists even when
the major axis of the inclusion 41j is 30 um or more, the inclusion 41j is regarded as a
15 part of the inclusion-cluster G. In addition, hereafter, the independent-inclusion H
which is not included in the inclusion-cluster G and whose length HL in the rolling
direction is 30 um or more is referred to as elongated inclusion.
[0043]
The length GL in the rolling direction of the inclusion-cluster G and the length
20 HL in the rolling direction of the elongated inclusion (independent-inclusion H where the
length HL in the rolling direction was 30 um or more) were entirely measured in an
observed visual field, and the total length I (unit: mm) of GL and HL was determined by
conducting the measurements for plural visual fields. A total length M (unit: mm/mm2)
which was a converted value per 1 mm of area was determined from the total length I
23
based on the following Expression 5. The total length M has an influence on the hole
expansibility of the steel sheet. Here, S is the total area (unit: mm ) of the observed
visual field.
M = I / S (Expression 5)
5 [0044]
The reason why the total length M which is the converted value per 1 mm of
area from the total length I should be determined, instead of the average of the total
length I which is the length in the rolling direction of the above-described inclusions, is
as follows.
10 [0045]
When the number of the inclusion-clusters G and the elongated inclusions (the
independent-inclusions H where the length HL in the rolling direction is 30 um or more)
in the metallographic structure of the steel sheet is small, the cracks propagate while
voids which are formed at the periphery of the inclusions are interrupted during the
15 deformation of the steel sheet. On the other hand, when the number of the
above-described inclusions is large, voids at the periphery of the inclusions are formed
into long continuous void by being connected without being interrupted, which may
promote the ductile fracture. The influence of the number of the inclusions is not
represented by the average of the total length I but may be represented by the total length
20 M. Accordingly, from this point, the total length M per 1 mm2 of area in the length GL
in the rolling direction of the inclusion-cluster G and in the length HL in the rolling
direction of the elongated inclusions was determined. As described above, the total
length M has an influence on the hole expansibility of the steel sheet.
[0046]
25 The total length M has an influence on the fracture properties of the steel sheet
24
in addition to the hole expansibility of the steel sheet. During the deformation of the
steel sheet, the stress is concentrated on the inclusion-clusters G and elongated inclusions
(independent-inclusions H where the length HL in the rolling direction is 30 um or more)
and the initiation and propagation of cracks occur from the inclusions as a starting point.
5 Therefore, in a case where the value of the total length M is large, the resistance of crack
initiation Jc and the resistance of crack propagation T. M. decrease. In addition, the
Charpy absorbed energy E, which is the energy required to fracture a test piece in a
temperature range where ductile fracture occurs, is an index influenced by both of the
resistance of crack initiation Jc and the resistance of crack propagation T. M. In a case
10 where the value of the total length M is large, the Charpy absorbed, energy E is also
decreased similarly.
[0047]
Furthermore, the total length M also has an influence on the fatigue properties of
the steel sheet. It was found that the fatigue life tended to decrease with an increase in
15 the value of the total length M. The reason for the above seems that the number of the
inclusion-clusters G or the elongated inclusions, which act as the starting point of the
fatigue fracture, increases with an increase in the value of the total length M, so that the
fatigue life decreases as the result.
[0048]
20 From the above point of view, the total length M in the rolling direction of the
inclusions was measured, and therewith, the average Xave of the hole expanding ratio,
the resistance of crack initiation Jc, the resistance of crack propagation T. M, the Charpy
absorbed energy E, the fatigue life, and the like were evaluated.
[0049]
25 In addition to the total length M, as the investigation of the inclusions,
25
measurement was conducted for the ratio of the major axis to the minor axis of the
inclusion, which was represented by dividing the major axis of the inclusion by the minor
axis of the inclusion. The respective ratios of the major axis to the minor axis were
entirely measured for the inclusions in an observed visual field, and a maximum therein
5 was determined. 30 times of the measurements were conducted with different visual
fields. Then, an average of the respective maxima of the ratios of the major axis to the
minor axis which were determined at each visual field was determined. Specifically,
after the cross section (L cross section) where was at a portion of 1/4 in the sheet width of
the steel sheet and whose normal direction corresponded to the transverse direction was
10 mirror-polished, the inclusions were observed using an electron microscope at 30 of
arbitrary visual fields in the vicinity of the centeral portion of the sheet thickness in the L
cross section so that one visual field was to be 0.0025 mm (50 um x 50 um), the
maximum of the ratio of the major axis to the minor axis of the inclusions in each visual
field was determined, and the average of the 30 visual fields was determined.
15 [0050]
In a case where the shape of each of the inclusions is round and the average of
the maximum of the ratio of the major axis to the minor axis is small even when the total
length M in the rolling direction of the inclusions is the same values, the stress
concentration in the vicinity of the inclusions during the deformation of the steel sheet
20 decreases, and the average A,ave of the hole expanding ratio, the resistance of crack
initiation Jc, and the Charpy absorbed energy E are preferably improved. Therefore, the
ratio of the major axis to the minor axis of the inclusions is determined. In addition,
since it was found from experiments that the average of the maximum of the ratio of the
major axis to the minor axis of the inclusions and the standard deviation a of the hole
25 expanding ratio had a correlation, the average in regard to the ratio of the major axis to
26
the minor axis was measured from the point of view of evaluating the standard deviation
a of the hole expanding ratio.
[0051]
In addition to the chemical composition and metallographic structure of the steel
5 sheet, the texture of the steel sheet was measured. The measurement of the texture was
conducted using X-ray diffraction measurement. The X-ray diffraction measurement
was conducted by a diffractometer method or the like using an appropriate X-ray tube.
As a test piece for X-ray diffraction measurement, test pieces in which the length in the
transverse direction was 20 mm and the length in the rolling direction were 20 mm was
10 cut out from a portion of 1/2 in the sheet width of the steel sheet. After mechanically
polishing the test pieces so that a position of 1/2 in the sheet thickness of the steel sheet
was the measurement surface, strain was removed by electrolytic polishing or the like.
The test piece for X-ray diffraction measurement and a reference standard which did not
have the texture in a specific orientation were measured using the X-ray diffraction
15 method or the like under the same conditions, a value where the X-ray intensity of the
steel sheet was divided by the X-ray intensity of the reference standard was regarded as
the X-ray random intensity ratio. Here, the X-ray random intensity ratio is synonymous
with the pole density. In addition, instead of the X-ray diffraction measurement, the
texture may be measured using the EBSD method or an ECP (Electron Channeling
20 Pattern) method. In addition, as the texture of the steel sheet, the X-ray random
intensity ratio of the {211} plane (which was synonymous with the pole density of the
{211} plane or with the {211} reflected intensity) was measured.
[0052]
Next, description will be given of the limitation range and reasons for the
25 limitation relating to the total length M and the average of the ratio of the major axis to
27
the minor axis in order that the properties of the hot rolled steel sheet according to the
embodiment satisfy that the average Xave of the hole expanding ratio is 60% or more, the
standard deviation a of the hole expanding ratio is 15% or less, and the resistance of
crack propagation T. M. is 600 MJ/m or more.
5 [0053]
FIG. 5 is a diagram which shows a relationship between the total length M in the
rolling direction of the inclusions, the average of the maximum of the ratio of the major
axis to the minor axis of the inclusions, and the average Xave of the hole expanding ratio.
FIG. 6 is a diagram which shows a relationship between the total length M in the rolling
10 direction of the inclusions, the average of the maximum of the ratio of the major axis to
the minor axis of the inclusions, and the standard deviation a of the hole expanding ratio.
[0054]
As shown in FIG. 5, the average A,ave of the hole expanding ratio of the steel
sheet is improved with a decrease in the value of the total length M in the rolling
15 direction of the inclusions and with a decrease in the average of the maximum of the ratio
of the major axis to the minor axis. In addition, as shown in FIG. 6, the standard
deviation a of the hole expanding ratio is improved with the decrease in the average of
the maximum of the ratio of the major axis to the minor axis of the inclusions. Here, it
is shown that each data which is plotted in FIG. 5 and FIG. 6 satisfies the configuration of
20 the hot rolled steel sheet according to the embodiment with the exception of a
configuration relating to the total length M in the rolling direction of the inclusions and
the average of the maximum of the ratio of the major axis to the minor axis.
[0055]
From FIG. 5 and FIG. 6, it is understood that the average A-ave of the hole
28
expanding ratio can be controlled to 60% or more and the standard deviation a can be
controlled to 15% or less by controlling the total length M in the rolling direction of the
inclusions to 0 mm/mm2 to 0.25 mm/mm2 and by controlling the average of the
maximum of the ratio of the major axis to the minor axis to 1.0 to 8.0. The reason for
5 the above seems that the stress concentration is relieved in the vicinity of the inclusions
during the plastic deformation of the steel sheet by decreasing the value of the total
length M and the average of the ratio of the major axis to the minor axis as described
above. It is preferable that the total length M in the rolling direction of the inclusions is
0 mm/mm to 0.20 mm/mm , and it is more preferable that the total length M in the
10 rolling direction of the inclusions is 0 mm/mm to 0.15 mm/mm . In addition, it is
understood that the average A.ave of the hole expanding ratio can be controlled to 65% or
more and the standard deviation a can be controlled to 10% or less by preferably
controlling the average of the maximum of the ratio of the major axis to the minor axis to
1.0 to 3.0. It is more preferable that the average of the maximum of the ratio of the
15 major axis to the minor axis is 1.0 to 2.0.
[0056]
FIG. 7 is a diagram which shows a relationship between the total length M in the
rolling direction of the inclusions and the resistance of crack propagation T. M. From
the diagram, it is understood that, in a case where the total length M in the rolling
20 direction of the inclusions is 0 mm/mm2 to 0.25 mm/mm2, in addition to the average
X,ave and the standard deviation a of the hole expanding ratio, the resistance of crack
propagation T. M. of 600 MJ/m or more is also satisfied. In general, in order to prevent
the fracture of the steel sheet which composes the structural material, it is important to
improve the resistance of crack propagation T. M. As mentioned above, the resistance
25 of crack propagation T. M. tends to depend on the total length M in the rolling direction
29
of the inclusions, and it is found that controlling the total length M to the range is
important.
[0057]
As described above, by controlling the total length M in the rolling direction of
5 the inclusions and the average of the maximum of the ratio of the major axis to the minor
axis of the inclusions, it is possible to satisfy the properties such as the average X,ave of
the hole expanding ratio, the standard deviation a of the hole expanding ratio, and the
resistance of crack propagation T. M. In addition, as mentioned above, the total length
M also improves the fatigue properties. Next, description will be given of a method
10 which controls the total length M and the average of the ratio of the major axis to the
minor axis to the ranges.
[0058]
The present inventors found that the inclusion-cluster G and the elongated
inclusion (independent-inclusion H where the length HL in the rolling direction was 30
15 urn or more), which caused the increase in the total length M in the rolling direction of
the inclusions or the average of the maximum of the ratio of the major axis to the minor
axis of the inclusions, were MnS precipitates which were elongated by the rolling or
residues of desulfurizing agent which was added for desulfurization at steel making. In
addition, it was found that, although the influence was not large as compared with the
20 MnS precipitates or the residues of desulfurizing agent, CaS which precipitated without
oxides and sulfides of REM (Rare Earth Metal) as a nucleus and precipitates of calcium
aluminate or the like which was a mixture of CaO and alumina may also increase the
total length M or the average of the ratio of the major axis to the minor axis. Since CaS
- and the precipitates of calcium aluminate or the like may become a shape which is
25 elongated in the rolling direction by rolling, the hole expansibility of the steel sheet, the
30
fracture properties, or the like may deteriorate. As a result of the investigation of the
method which suppressed the inclusions in order to improve the properties such as the
average A,ave of the hole expanding ratio, the standard deviation a of the hole expanding
ratio, and the resistance of crack propagation T. M., it was found that the following was
5 important.
[0059]
First, it is important to reduce the S content which bonds to Mn in order to
suppress the MnS precipitates. From the point of view, in the hot rolled steel sheet
according to the embodiment, in order to totally reduce the entire S content in the steel,
10 the upper limit thereof is to be 0.01 mass%.
[0060]
In addition, since TiS precipitates are formed at a higher temperature than the
MnS formation temperature range when Ti is added, it is possible to reduce the amount
of MnS precipitates. Similarly, since sulfides of REM or Ca are formed when REM or
15 Ca are added, it is possible to reduce the amount of MnS precipitates. Therefore, the
hot rolled steel sheet according to the embodiment contains at least one selected from the
group consisting of, by mass%, Ti: 0.001% to 0.3%, REM: 0.0001% to 0.02%, and Ca:
0.0001% to 0.01%). Although it is possible to reduce the amount of MnS precipitates by
selecting Ca, in order to suppress the precipitation of CaS, calcium aluminate, or the like,
20 the upper limit of the Ca content is to be 0.01 mass%. The limitation range and reasons
for the limitation of the chemical composition of the hot rolled steel sheet will be -
described later in detail.
[0061]
Furthermore, in order to suppress the MnS precipitates, it is necessary to
25 stoichiometrically include the larger amount of Ti, REM, or Ca than that of S.
31
Therefore, the relationship between the S content, the Ti content, the REM content, and
the Ca content and the total length M in the rolling direction of the inclusions was
investigated. FIG. 8 is a diagram which shows a relationship between the S content, the
Ti content, the REM content, and the Ca content and the total length M in the rolling
5 direction of the inclusions. It was found that, when the value of (Ti / 48) / (S / 32) +
{(Ca / 40) / (S / 32) + (REM /140) / (S / 32)} x 15 was 12.0 to 150, the total length M
was 0 mm/mm2 to 0.25 mm/mm2. Specifically, in the hot rolled steel sheet according to
the embodiment, it is necessary that the amounts expressed in mass% of each element in
the chemical composition satisfy the following Expression 6. By satisfying the
10 Expression 6, it is considered that the formation of elongated MnS precipitates is
suppressed. In addition, although not shown in the diagram, it was found that, in a case
where the following Expression 6 was satisfied, the average of the maximum of the ratio
of the major axis to the minor axis of the inclusions was 1.0 to 8.0. Furthermore, it was
found that, even in a case where all of Ti, REM, and Ca were simultaneously included in
15 the steel, or in a case where at least one selected from Ti, REM, and Ca was included in
the steel, the total length M was 0 mm/mm2 to 0.25 mm/mm2 and the average of the
maximum of the ratio of the major axis to the minor axis of the inclusions was 1.0 to 8.0,
when the following Expression 6 was satisfied.
12.0 < (Ti / 48) / (S / 32) + {(Ca / 40) / (S / 32) + (REM /140) / (S / 32)} x 15 <
20 150 (Expression 6)
[0062]
In order to control the total length M to 0 mm/mm2 to 0.25 mm/mm2 and to
control the average of the ratio of the major axis to the minor axis to 1.0 to 8.0, in
addition to satisfying the Expression 6, the cumulative reduction is to be 10% to 70% in a
25 temperature range of higher than 1150 °C to 1400 °C in the first rough rolling process as
32
described later. The method of producing the hot rolled steel sheet according to the
embodiment will be described later in detail.
[0063]
According to the above-described configuration, it is possible to control the total
5 length M and the average of the ratio of the major axis to the minor axis. However, in
order to further improve the properties of the steel sheet, it is preferable to reduce CaS
which precipitates without oxides and sulfides of REM as the nucleus and to reduce the
precipitates of calcium aluminate or the like. In order to reduce the precipitates, the
amounts expressed in mass% of each element in the chemical composition may satisfy
10 the following Expression 7. It was found that, when the following Expression 7 was
satisfied, the average of the maximum of the ratio of the major axis to the minor axis of
the inclusions was preferably 1.0 to 3.0. Moreover, in a case where Ti or REM is added
to steel, since the Ca content may be as small as possible, it is not necessary to determine
an upper limit of the following Expression 7.
15 0.3 < (REM /140) / (Ca / 40) (Expression 7)
[0064]
In a case where REM is sufficiently added as compared with Ca so as to satisfy
the Expression 7, CaS or the like crystallizes or precipitates while spherical REM oxides
or REM sulfides act as the nuclei. On the other hand, since the REM oxides or the
20 REM sulfides which act as the nuclei are reduced when the ratio of REM to Ca is
reduced and the Expression 7 is not satisfied, CaS or the like in which the REM oxides or
the REM sulfides do not act as the nuclei precipitates excessively. The inclusions may
have a shape which is elongated in the rolling direction due to the rolling. As described
above, when the Expression 7 is satisfied, the ratio of the major axis to the minor axis of
25 the inclusions is preferably controlled.
33
[0065]
In order to control the average of the maximum of the ratio of the major axis to
the minor axis of the inclusions to 1.0 to 3.0, in addition to satisfying the Expression 7, it
is preferable that the cumulative reduction is 10% to 65% in a temperature range of
5 higher than 1150°C to 1400°C in the first rough rolling process as described later. The
method of producing the hot rolled steel sheet according to the embodiment will be
described later in detail.
[0066]
Subsequently, description will be given of the base elements of the hot rolled
10 steel sheet according to the embodiment and of the limitation range and reasons for the
limitation. Hereinafter, the % in the description represents mass%.
[0067]
C: 0.03% to 0.1%
C (carbon) is an element which contributes to an improvement in the tensile
15 strength TS. When the C content is insufficient, the fracture appearance transition
temperature vTrs may increase due to the coarsening of the metallographic structure. In
addition, when the C content is insufficient, it may be difficult to obtain the intended area
fraction of martensite and residual austenite. On the other hand, when the C content is
excessive, the average ?i.ave of the hole expanding ratio, the resistance of crack initiation
20 Jc, and the Charpy absorbed energy E may decrease. For this reason, the C content is to
be 0.03% to 0.1 %. Preferably, the C content may be 0.04% to 0.08%. More preferably,
the C content may be 0.04% to 0.07%.
[0068]
Mn: 0.5% to 3.0%
25 Mn (manganese) is an element contributing to an improvement in the tensile
34
strength TS of the steel sheet as an element of solid solution strengthening. In order to
obtain the intended tensile strength TS, the Mn content is to be 0.5% or more. However,
when the Mn content is more than 3.0%, cracking during the hot rolling occurs readily.
For this reason, the Mn content is to be 0.5%) to 3.0%. In addition, when the Mn
5 content is more than 3.0%, ferrite transformation is suppressed and the area fraction of.
the martensite and the residual austenite may increase. To preferably control the area
fraction of the ferrite which is the primary phase and the martensite and the residual
austenite which are the secondary phase, the Mn content may be 0.8% to 2.0%. More
preferably, the Mn content may be 1.0% to 1.5%.
10 [0069]
0.5%, the strength may excessively increase and the average
lave of the hole expanding ratio may decrease. For this reason, preferably, the Al
10 content may be 0.005% to 2.0%.
[0072]
The hot rolled steel sheet according to the embodiment further contains at least
one selected from the group consisting of Ti, REM, and Ca in the following content.
[0073]
15 Ti: 0.001% to 0.3%
Ti (titanium) is an element contributing to an improvement of the tensile
strength TS of the steel sheet by finely precipitating as TiC. In addition, Ti is an
element which suppresses the precipitation of MnS which is elongated during rolling by
precipitating as TiS. Therefore, the total length M in the rolling direction of the
20 inclusions and the average of the maximum of the ratio of the major axis to the minor
axis of the inclusions may decrease. In order to obtain the effect, the Ti content is to be
0.001%) or more. However, when the Ti content is more than 0.3%, the strength may
excessively increase, and the average A,ave of the hole expanding ratio, the resistance of
crack initiation Jc, and the Charpy absorbed energy E may-decrease. For this reason,
25 the Ti content is to be 0.001% to 0.3%. Preferably, the Ti content may be 0.01% to
36
0.3%. More preferably, the Ti content may be 0.05% to 0.18%. Most preferably, the
Ti content may be 0.08% to 0.15%.
[0074]
REM: 0.0001% to 0.02%
5 REM (Rare Earth Metal) is element which suppresses the formation of MnS by
bonding to S in the steel. In addition, REM is element which decreases the average of
the maximum of the ratio of the major axis to the minor axis of the inclusions and the
total length M in the rolling direction by spheroidizing the shape of the sulfides such as
MnS. When the REM content is less than 0.0001%, the effect of suppressing the
10 formation of MnS and the effect of spheroidizing the shape of the sulfides such as MnS
may not be sufficiently obtained. In addition, when the REM content is more than
0.02%, the inclusions which include the REM oxides may excessively form, and the
average X,ave of the hole expanding ratio, the resistance of crack initiation Jc, and the
Charpy absorbed energy E may decrease. For this reason, the REM content is to be
15 0.0001% to 0.02%. Preferably, the REM content may be 0.0005% to 0.005%. More
preferably, the REM content may be 0.001% to 0.004%.
Here, REM represents a generic name for a total of 17 elements, specifically 15
elements from lanthanum with atomic number 57 to lutetium with atomic number 71,
scandium with atomic number 21, and yttrium with atomic number 39. In general,
20 REM is supplied in the state of misch metal which is a mixture of the elements, and is
added to the steel.
[0075]
Ca: 0.0001% to 0.01%
Ca (calcium) is an element which suppresses the formation of MnS by bonding
25 to S in the steel, In addition, Ca is an element which decreases the average of the
37
maximum of the ratio of the major axis to the minor axis of the inclusions and the total
length M in the rolling direction by spheroidizing the shape of the sulfides such as MnS.
When the Ca content is less than 0.0001%, the effect of suppressing the formation of
MnS and the effect of spheroidizing the shape of the sulfides such as MnS may not be
5 sufficiently obtained. In addition, when the Ca content is more than 0.01%, CaS and the
calcium aluminate which tend to be inclusions with an elongated shape may excessively
form, and the total length M and the average of the ratio of the major axis to the minor
axis may increase. For this reason, the Ca content is to be 0.0001% to 0.01%.
Preferably, the Ca content may be 0.0001% to 0.005%). More preferably, the Ca content
10 may be 0.001 % to 0.003%). Furthermore preferably, the Ca content may be 0.0015% to
0.0025%.
[0076]
In the hot rolled steel sheet according to the embodiment, at least one of Ti,
REM, and Ca is included as described above, and simultaneously, the amounts expressed
15 in mass% of each element in the chemical composition satisfy the following Expression
8. Here, detailed description will be given of the impurity S. By satisfying the
following Expression 8, the amount of MnS precipitates in the steel decreases, and it is
possible to obtain an effect of decreasing the average of the maximum of the ratio of the
major axis to the minor axis of the inclusions and the total length M in the rolling
20 direction of the inclusions. Thereby, the total length M in the rolling direction of the
inclusions is controlled to 0 mm/mm2 to 0.25 mm/mm2 and the average of the maximum
of the ratio of the major axis to the minor axis of the inclusions is controlled to 1.0 to 8.0.
As a result, it is possible to obtain an effect of improving the average X,ave of the hole
expanding ratio of the steel sheets, the standard deviation a, the resistance of crack
25 initiation Jc, the resistance of crack propagation T. M., the Charpy absorbed energy E,
38
and the fatigue life. When the value of the following Expression 8 is less than 12.0, the
above effects may not be obtained. Preferably, the above value may be 30.0 or more.
In addition, since it is preferable that the amount of S which is the impurity decreases, it
is not necessary to determine an upper limit of the following Expression 8. However, in
5 a case where the following Expression 8 is 150 or less, the above effect may preferably
obtained.
12.0 < (Ti / 48) / (S / 32) + {(Ca / 40) / (S / 32) + (REM /140) / (S / 32)} x 15 <
150 (Expression8)
[0077]
10 When the large amount of Ti is included within the above range, the tensile
strength TS of the steel sheet is improved. For example, when the Ti content is 0.08%
to 0.3%, it is possible to control the tensile strength TS of the steel sheet to 780 MPa to
980 MPa, and simultaneously, to control the fatigue life in plane bending to 500000 times
or more. The reason for the above is derived from the precipitation strengthening of
15 TiC. On the other hand, when Ti is not added, or when the small amount of Ti is
included within the above range, the formability and the fracture properties of the steel
sheet are improved. For example, when Ti is not added, or when the Ti content is
0.001% to less than 0.08%, although the tensile strength TS of the steel sheet is 590 MPa
to less than 780 MPa, it is possible to control the average A,ave of the hole expanding
20 ratio to 90% or more, the resistance of crack initiation Jc to 0.9 MJ/m or more, and the
Charpy absorbed energy E to 35 J or more. The reason for the above is derived from
the decrease in the amount of TiC precipitates. As described above, depending on the
purpose of the steel sheet, it is preferable to control the Ti content. When Ti is not
added, in order to control the total length M and the average of the ratio of the major axis
25 to the minor axis, it is preferable that at least one of REM and Ca is contained. In
39
addition, when the small amount of Ti is included within the above range, in order to
control the total length M and t average of the ratio of the major axis to the minor axis, it
is preferable that at least one of REM and Ca is contained. Specifically, when at least
one of 0.0001% to 0.02% of REM and 0.0001% to 0.01% of Ca is contained, it is
5 preferable that the Ti content is 0.001 % to less than 0.08%. When at least one of
0.0001% to 0.02% of REM and 0.0001% to 0.005% of Ca is contained, it is more
preferable that the Ti content is 0.01% to less than 0.08%.
[0078]
In addition, from the point of view of suppressing the average of the maximum
10 of the ratio of the major axis to the minor axis of the inclusions, it is preferable that the
amount of Ca and REM satisfies the following Expression 9. When the following
Expression 9 is satisfied, the average of the maximum of the ratio of the major axis to the
minor axis of the inclusions is preferably controlled to 1.0 to 3.0. Specifically, it is
preferable that the amounts expressed in mass% of each element in the chemical
15 composition satisfy the following Expression 9 and the average of the maximum of the
ratio of the major axis to the minor axis of the inclusions is 1.0 to 3.0. More preferably,
the above value may be 1.0 to 2.0. As a result, it is possible to obtain further excellent
effects for the average A,ave of the hole expanding ratio, the standard deviation , the effect is not
obtained. On the other hand, when the Ni content is more than 1.0%, the strength may
excessively increase, and the average Xave of the hole expanding ratio may decrease.
For this reason, preferably, the Ni content may be 0.001%) to 1.0%>. More preferably,,
5 the Ni content may be 0.05%. to 0.2%. In addition, as long as the Ni content is 0% to
1.0%, each of the characteristic values of the hot rolled steel sheet is not negatively
influenced.
[0090]
V: 0.001% to 0.2%
10 Similarly, V is an element which has an effect of improving the tensile strength
TS of the hot rolled steel sheet by precipitation strengthening or solid solution
strengthening. However, when the V content is less than 0.001%>, the effect is not
obtained. On the other hand, when the V content is more than 0.2%>, the strength may
excessively increase, and the average Xave of the hole expanding ratio may decrease.
15 For this reason, preferably, the V content may be 0.001%) to 0.2%>. More preferably, the
V content may be 0.005% to 0.2%. Furthermore preferably, the V content may be
0.01 % to 0.2%. Most preferably, the V content may be 0.01 % to 0.15%. In addition,
as long as the V content is 0% to 0.2%>, each of the characteristic values of the hot rolled
steel sheet is not negatively influenced.
20 [0091]
fn addition, the hot rolled steel sheet according to the embodiment may contain
0% to 1% in total of Zr, Sn, Co, W, and Mg as necessary.
[0092]
Next, description will be given of the metallographic structure and the texture of
25 the hot rolled steel sheet according to the embodiment.
46
[0093]
The metallographic structure of the hot rolled steel sheet according to the
embodiment includes a ferrite as a primary phase, at least one of a martensite and a
residual austenite as a.secondary phase, and plural inclusions. By forming the mixed
5 structure, it is possible to achieve both the high tensile strength TS and elongation (n
value). The reason for the above seems that the ductility is ensured by the ferrite which
is the primary phase and comparatively soft and that the tensile strength TS is ensured by
the secondary phase which is hard. In addition, by forming the mixed structure, the
preferable fatigue properties are obtained. The reason for the above seems that the
10 propagation of the fatigue cracks is suppressed by the martensite and the residual
austenite which are the secondary phase and are comparatively hard. In order to obtain
the effect, in the metallographic structure of the hot rolled steel sheet according to the
embodiment, the area fraction of the primary phase is to be 90% to 99%, and the area
fraction of the martensite and the residual austenite which are the secondary phase is to
15 be 1 % to 10% in total. When the area fraction of the primary phase is less than 90%,
since the metallographic structure is not controlled to the intended mixed structure, it is
not possible to obtain the above effect. On the other hand, it is technically difficult to
control the area fraction of the primary phase to more than 99%. In addition, when the
area fraction of the secondary phase is more than 10% in total, the ductile fracture is
20 promoted, and the average A,ave of the hole expansion value, the resistance of crack
initiation Jc, and the Charpy absorbed energy E deteriorate. On the other hand, when
the area fraction of the secondary phase is less than 1% in total, since the metallographic
structure is not controlled to the intended mixed structure, it is not possible to obtain the
above effect. Preferably, the area fraction of the primary phase may be 95% to 99%,
25 and the area fraction of the martensite and the residual austenite which are the secondary
47
phase may be 1% to 5% in total.
[0094]
In addition, in the metallographic structure, in addition to the ferrite which is the
primary phase, the martensite and the residual austenite which are the secondary phase,
5 and the plural inclusions, a small amount of bainite, pearlite, cementite, or the like may
be included. In the metallographic structure, preferably, the area fraction of the bainite
and the pearlite may be 0% to less than 5.0% in total. As a result, it is preferable that
the metallographic structure is controlled to the intended mixed structure and the above
effect is obtained.
10 [0095]
The average grain size of the ferrite which is the primary phase is to be 2 urn to
10 um. When the average grain size of the ferrite which is the primary phase is 10 urn
or less, it is possible to obtain the intended fracture appearance transition temperature
vTrs. In addition, in order to control the average grain size of the ferrite which is the
15 primary phase to less than 2 urn, it is necessary to select strict producing conditions, and
the load on the producing facility is large. For this reason, the average grain size of the
ferrite which is the primary phase is to be 2 urn to 10 urn. Preferably, the average grain
size may be 2 (am to 7 urn. Furthermore preferably, the average grain size may be 2 um
to 6 um.
20 [0096]
It is preferable that the average grain size of the martensite and the residual
austenite which are the secondary phase is 0.5 um to 8.0 um. When the average grain
size of the secondary phase is more than 8.0 um, the stress concentration which is
induced in the vicinity of the secondary phase may increase, and the properties such as
48
the average A,ave of the hole expanding ratio may decrease. In addition, in order to
control the average grain size of the secondary phase to less than 0.5 urn, it is necessary
to select strict producing conditions, and the load on the producing facility is large. For
this reason, the average grain size of the secondary phase may be 0.5 urn to 8.0 urn.
5 [0097]
In regard to the inclusions which are included in the metallographic structure,
when the L cross section whose normal direction corresponds to the transverse direction
of the steel sheet is observed at 30 of visual fields by 0.0025 mm , the average of the
maximum of the ratio of the major axis to the minor axis of the inclusions in each of the
10 visual fields is to be 1.0 to 8.0. When the above average of the ratio of the major axis to
the minor axis is more than 8.0, the stress concentration in the vicinity of the inclusions
during the deformation of the steel sheet increases, and it is not possible to obtain the
intended properties of the average A,ave of the hole expanding ratio, the standard
deviation a, the resistance of crack initiation Jc, and the Charpy absorbed energy E. On
15 the other hand, although the lower limit of the above average of the ratio of the major
axis to the minor axis is not particularly limited, it is technically difficult to control the
above value to less than 1.0. For this reason, the above average of the ratio of the major
axis to the minor axis is to be 1.0 to 8.0. In addition, preferably, the above average of
the ratio of the major axis to the minor axis may be 1.0 to 3.0. When the above average
20 of the ratio of the major axis to the minor axis is 1.0 to 3.0, it is possible to obtain the
preferable effect for the average X.ave of the hole expanding ratio, the standard deviation
a of the hole expanding ratio, the resistance of crack initiation Jc, and the Charpy
absorbed energy E.
[0098]
49
In addition, in regard to the inclusions which are included in the metallographic
structure, when a group of the inclusions in which a major axis of each of the inclusions
is 3 urn or more and the interval F in the rolling direction between the inclusions is 50
urn or less are defined as the inclusion-cluster G, and when an inclusion in which the
5 interval F is more than 50 jim are defined as the independent-inclusion H, the total length
M in the rolling direction of both the inclusion-cluster G whose length in the rolling
direction GL is 30 um or more and the independent-inclusion H whose length in the
rolling direction HL is 30 jam or more is to be 0 mm to 0.25 mm per 1 mm of the L cross
section whose normal direction corresponds to the transverse direction of the steel sheet.
10 When the inclusions satisfy the above condition, it is possible to obtain the preferable
effect for the average A,ave of the hole expanding ratio, the standard deviation a of the
hole expanding ratio, the resistance of crack initiation Jc, the resistance of crack
propagation T. M., the Charpy absorbed energy E, and the fatigue properties. In
addition, the total length M may be zero. Preferably, the total length M may be 0 mm to
15 0.15 mm per 1 mm of the L cross section whose normal direction corresponds to the
transverse direction of the steel sheet.
[0099]
In addition, in regard to the inclusions which are included in the metallographic
structure, it is preferable that a total number of MnS precipitates and CaS precipitates
20 having the major axis of 3 um or more is 0% to less than 70% as compared with the total
number of the inclusions having the major axis of 3 urn or more. When the total
number of MnS precipitates and CaS precipitates which are included in the inclusions is
0% to less than 70%, it is possible to preferably control the total length M and the
average of the ratio of the major axis to the minor axis. In addition, since the inclusions
50
having the major axis is less than 3 urn have a small influence on the properties such as
the average" Xave of the hole expanding ratio and the like, it is not necessary to take
account of the inclusions.
[0100]
5 In addition, the inclusions as described above mainly indicate the sulfides such
as MnS and CaS, the oxides such as CaO-Al203 compound (calcium aluminate), the
residues of the desulfurizing agent such as CaF2, and or the like in the steel.
[0101]
In regard to the texture of the hot rolled steel sheet according to the embodiment,
10 the X-ray random intensity ratio of the {211} plane ({211} reflected intensity) is to be
1.0 to 2.4. When the {211} reflected intensity is more than 2.4, the anisotropy of the
steel sheet is excessive. Thus, at hole expanding, the reduction of sheet thickness
increases at the end surface in the rolling direction which is subjected to tensile strain in
the transverse direction, high stress is induced in the end surface, and the cracks tend to
15 initiate and propagate. As a result, the average A,ave of the hole expanding ratio
deteriorates. In addition, when the {211} reflected intensity is more than 2.4, the
resistance of crack initiation Jc and the Charpy absorbed energy E also deteriorate. On
the other hand, it is technically difficult to control the {211} reflected intensity to less
than 1.0. For this reason, the {211} reflected intensity is to be 1.0 to 2.4. Preferably,
20 the {211} reflected intensity may be 1.0 to 2.0. In addition, the X-ray random intensity
ratio of the {211} plane, the {211} reflected intensity, and the pole density of the {211}
plane are synonymous. In addition, although the X-ray random intensity ratio of the
{211} plane is basically measured by the X-ray diffraction method, since differences in
the measurement results are not observed even when the measurement is conducted by
25 the EBSD method or the ECP method, the measurement may be conducted by the EBSD
»
51
method or the ECP method.
[0102]
In addition, the measurement method of the chemical composition, the
metallographic structure, and the texture, and the definitions such as the X-ray random
5 intensity ratio, the total length M in the rolling direction of the inclusions, and the
average of the maximum of the ratio of the major axis to the minor axis of the inclusions
are as described above.
[0103]
In the hot rolled steel sheet according to the embodiment, the chemical
10 composition, the metallographic structure, and the texture are satisfied, so that the tensile
strength TS is 590 MPa to 980 MPa. In addition, in the hot rolled steel sheet according
to the embodiment, the chemical composition, the metallographic structure, and the
texture are satisfied, so that the average Xave of the hole expanding ratio is 60% or more,
the standard deviation a of the hole expanding ratio is 15% or less, the fatigue life in
15 plane bending is 400000 times or more, the resistance of crack initiation Jc is 0.5 MJ/m
or more, the resistance of crack propagation T. M. is 600 MJ/m or more, the fracture
appearance transition temperature vTrs is 13°C or lower, and the Charpy absorbed energy
E is 16 J or more.
[0104]
20 In the hot rolled steel sheet according to the embodiment, as described above, it
is preferable to control the tensile strength TS by controlling the Ti content in accordance
with the intended use of the steel sheet. For example, although the tensile strength TS
of the steel sheet is 590 MPa to less than 780 MPa when the Ti content is 0.001 to less
than 0.08%, it is possible to control the average A-ave of the hole expanding ratio to 90%
25 or more, the resistance of crack initiation Jc to 0.9 MJ/m , and the Charpy absorbed
52
energy E to 35 J or more in the above properties. For example, when the Ti content is
0.08% to 0.3%, it is possible to control the tensile strength TS of the steel sheet to 780
MPa to 980 MPa, and it is possible to control the fatigue life in plane bending to 500000
times or more in the above properties. As described above, in a case where the Ti
5 content is changed in accordance with the intended use of the steel sheet, in order to
control the total length M and the average of the ratio of the major axis to the minor axis
to the intended limitation range, the amount of REM and Ca may be controlled as
necessary as described above.
[0105]
10 Next, description will be given of the method of producing the hot rolled steel
sheet according to the embodiment.
[0106]
A method of producing the hot rolled steel sheet according to the embodiment
includes: a heating process of heating a steel piece which consists of the above-described
15 chemical composition to a range of 1200°C to 1400°C; a first rough rolling process of
rough rolling the steel piece in a temperature range of higher than 1150°C to 1400°C so
that a cumulative reduction is 10% to 70% after the heating process; a second rough
rolling process of rough rolling in a temperature range of higher than 1070°C to 1150°C
so that a cumulative reduction is 10% to 25% after the first rough rolling process; a finish
20 rolling process of finish rolling so that a start temperature is 1000°C to 1070°C and a
finish temperature is Ar3 + 60°C to Ar3 + 200°C to obtain a hot rolled steel sheet after
the second rough rolling process; a first cooling process of cooling the hot rolled steel
from the finish temperature so that a cooling rate is 20°C/second to 150°C/second after
the finish rolling process; a second cooling process of cooling in a temperature range of
53
650°C to 750°C so that the cooling rate is l°C/second to 15°C/second and a cooling time
is 1 second to 10 seconds after the first cooling process; a third cooling process of
cooling to a temperature range of 0°C to 200°C so that the cooling rate is 20°C/second to
150°C/second after the second cooling process; and a coiling process of coiling the hot
5 rolled steel sheet after the third cooling process. In addition, Ar3 represents a
temperature where the ferrite transformation starts during cooling.
[0107]
In the heating process, a steel piece which consists of the above-described
chemical composition and which is obtained by continuous casting or the like is heated in
10 a heating furnace. In order to obtain the intended tensile strength TS, the heating
temperature in the process is to be 1200°C to 1400°C. When the temperature is less
than 1200°C, the precipitates which include Ti and Nb are not sufficiently dissolved and
coarsen in the steel piece, so that the precipitation strengthening by the precipitates of Ti
and Nb may not be obtained. Therefore, the intended tensile strength TS may not be
15 obtained. In addition, when the temperature is less than 1200°C, MnS is not sufficiently
dissolved in the steel piece, so that it may not be possible to make S precipitate as the
sulfides with Ti, REM, and Ca. Therefore, the intended properties for the average Xave
of the hole expansion value, the resistance of crack initiation Jc, and the Charpy absorbed
energy E may not be obtained. On the other hand, when the steel piece is heated to
20 more than 1400°C, the above effects are saturated and the heating cost also increases.
[0108]
In the first rough rolling process, rough rolling is conducted to the steel piece
which was taken from the heating furnace. In the first rough rolling, rough rolling is
conducted so that a cumulative reduction is 10% to 70% in a temperature range of higher
54
than 1150°C to 1400°C. When the cumulative reduction in the temperature range is
more than 70%, both the total length M in the rolling direction of the inclusions and the
average of the maximum of the ratio of the major axis to the minor axis of the inclusions
may increase. Therefore, the properties such as the average X,ave of the hole expanding
5 ratio, the standard deviation a, the resistance of crack initiation Jc, the resistance of crack
propagation T. M., the Charpy absorbed energy E, and the fatigue life may deteriorate.
On the other hand, although the lower limit of the cumulative reduction in the first rough
rolling process is not particularly limited, the above value is to be 10% or more in
consideration of production efficiency and the like in the subsequent processes. In
10 addition, preferably, the cumulative reduction in the first rough rolling process may be
10% to 65%. Thereby, under the condition where the composition of the steel piece
satisfies 0.3 < (REM /140) / (Ca / 40), it is possible to control the average of the ratio of
the major axis to the minor axis to 1.0 to 3.0. In addition, by controlling the
temperature range to higher than 1150°C to 1400°C, it is possible to obtain the above
15 effects.
[0109]
In the second rough rolling process, rough rolling is conducted so that a
cumulative reduction is 10% to 25% in a temperature range of higher than 1070°C to
1150°C. When the cumulative reduction is less than 10%, the average grain size of the
20 metallographic structure may coarsen, and the intended average grain size of the ferrite
which is 2 um to 10 urn may not be obtained. As a result, the intended fracture
appearance transition temperature vTrs may not be obtained. On the other hand, when
the cumulative reduction is more than 25%, the {211} reflected intensity as the texture
may increase. As a result, the intended properties such as the average A,ave of the hole
55
expanding ratio, the resistance of crack initiation Jc, and the Charpy absorbed energy E
may not be obtained. In addition, by controlling the temperature range to higher than
1070°C to 1150°C, it is possible to obtain the above effect.
[0110]
5 Here, description will be given of the basic research results relating to the first
rough rolling process and the second rough rolling process. By using the test steels
which consisted of the steel composition a as shown in the following Table 1, steel sheets
were produced by variously changing the cumulative reduction in the first rough rolling
and the second rough rolling, and the properties of the steel sheets were investigated. In
10 addition, the producing conditions with the exception of the cumulative reduction in the
first rough rolling and the second rough rolling of the hot rolled steel sheet according to
the embodiment were satisfied.
[0111]
[Table 1]
15 [0112]
FIG. 9A is a diagram which shows a relationship between the cumulative
reduction in the first rough rolling process and the total length M in the rolling direction
of the inclusions. FIG. 9B is a diagram which shows a relationship between the
cumulative reduction in the first rough rolling process and the average of the maximum
20 of the ratio of the major axis to the minor axis of the inclusions. FIG. 9C is a diagram
which shows a relationship between the cumulative reduction in the second rough rolling
process and the {211} reflected intensity. FIG. 9D is a diagram which shows a
relationship between the cumulative reduction in the second rough rolling process and
the average grain size of the ferrite. In addition, the cumulative reduction represents a
25 ratio of reduction of the steel piece in the first rough rolling process and the second rough
56
rolling process on the basis of the thickness of the steel piece after the heating process.
Specifically, the cumulative reduction of the rough rolling in the first rough rolling
process is defined as {(thickness of the steel piece before first reduction in a temperature
range of higher than 1150°C to 1400°C - thickness of the steel piece after final reduction
5 in a temperature range of higher than 1150°C to 1400°C) / thickness of the steel piece
after the heating process x 100%}. The cumulative reduction of the rough rolling in the
second rough rolling process is defined as {(thickness of the steel piece before first
reduction in a temperature range of higher than 1070°C to 1150°C - thickness of the steel
piece after final reduction in a temperature range of higher than 1070°C to 1150°C) /
10 thickness of the steel piece after the heating process x 100%}.
[0113]
From FIG. 9A, it is understood that, when the cumulative reduction is more than
70% in a temperature range of higher than 1150°C to 1400°C, the total length M in the
rolling direction of the inclusions is excessive, and the total length M of 0 mm/mm2 to
15 0.25 mm/mm2 which is the intended range is not obtained. In addition, from FIG. 9B, it
is understood that, when the cumulative reduction is more than 70% in a temperature
range of higher than 1150°C to 1400°C, the average of the maximum of the ratio of the
major axis to the minor axis of the inclusions is excessive, and the average of the ratio of
the major axis to the minor axis of 1.0 to 8.0 which is the intended range is not obtained.
20 The reason for the above seems that, as the cumulative reduction of the rough rolling
which is conducted in a higher temperature range of higher than 1150°C to 1400°C
increases, the inclusions tend to be elongated by rolling. In addition, from FIG. 9B, it is
understood that, when the cumulative reduction is 65% or less, the average of the ratio of
the major axis to the minor axis of 1.0 to 3.0 is obtained.
57
[0114]
From FIG. 9C, it is understood that, when the cumulative reduction in a
temperature range of higher than 1070°C to 1150°C is more than 25%, the {211}
reflected intensity is excessive, and the intended {211} reflected intensity of 1.0 to 2.4 is
5 not obtained. The reason for the above seems that, when the cumulative reduction of
the rough rolling which is conducted in a temperature range which is a comparatively
low temperature such as higher than 1070°C to 1150°C is excessively large, the
recrystallization does not proceed uniformly after the rough rolling, and a
non-recrystallized structure which leads to increase the {211} reflected intensity remains
10 even after the finish rolling, so that the {211} reflected intensity increases.
[0115]
From FIG. 9D, it is understood that, when the cumulative reduction in a
temperature range of higher than 1070°C to 1150°C is less than 10%, the average grain
size of the ferrite is excessive, and the intended average grain size of 2 urn to 10 urn is
15 not obtained. The reason for the above seems that, as the cumulative reduction of the
rough rolling which is conducted in a temperature range which is a low temperature such
as higher than 1070°C to 1150°C decreases, the grain size of the austenite after
recrystallization increases, and the average grain size of the ferrite of the steel sheet also
increases.
20 [0116]
After the second rough rolling process, as the finish rolling process, finish
rolling is conducted to the steel piece in order to obtain the hot rolled steel sheet. In the
finish rolling process, the start temperature is to be 1000°C to 1070°C. When the start
temperature of the finish rolling is 1000°C to 1070°C, dynamic recrystallization is
58
promoted in the finish rolling. As a result, the rolling texture which is the
non-recrystallized state is relieved, and it is possible to obtain the intended {211}
reflected intensity of 1.0 to 2.4.
[0117]
5 In addition, in the finish rolling process, the finish temperature is to be Ar3 +
60°C to Ar3 + 200°C. In order to obtain the intended {211} reflected intensity of 1.0 to
2.4 by preventing the rolling texture which is the no-recrystallized state and which leads
to increase the {211} reflected intensity from remaining, the finish temperature is
controlled to Ar3 + 60°C or more. Preferably, the temperature may be Ar3 + 100°C or
10 more. In addition, in order to obtain the intended average grain size of the ferrite by
preventing the grain size from excessively coarsening, the finish temperature is
controlled to Ar3 + 200°C or less.
[0118]
In addition, Ar3 is determined from the following Expression 10. In the
15 following Expression 10, the calculation is conducted using the amounts expressed in
mass% of each element in the chemical composition.
Ar3 = 868 - 396 x C + 25 x Si - 68 x Mn - 36 x Ni - 21 x Cu - 25 x Cr + 30 x
Mo (Expression 10)
[0119]
20 Subsequently, the hot rolled steel sheet which is obtained by the finish rolling
process is cooled in a run out table or the like. The cooling of the hot rolled steel sheet
is conducted by the first cooling process to the third cooling process to be described
below. In the first cooling process, the hot rolled steel sheet which is at the finish
temperature of the finish rolling is cooled to a temperature of 650°C to 750°C so that a
59
cooling rate is 20 °C/second to 150 °C/second. Subsequently, in the second cooling
process, the cooling rate is changed to 1 °C/second to 15 °C/second, and cooling is
conducted in a temperature range of 650°C to 750°C for a cooling time of 1 second to 10
seconds. Subsequently, in the third cooling process, the cooling rate is again returned to
5 20 °C/second to 150 °C/second, and cooling is conducted to a temperature range of 0°C
to 200°C. As described above, in the second cooling process, by conducting the cooling
of the hot rolled steel sheet under the cooling rate which is slower than those of the first
cooling process and the third cooling process, it is possible to promote the ferrite
transformation. As a result, it is possible to obtain the hot rolled steel sheet which has
10 the intended mixed structure.
[0120]
When the cooling rate of the first cooling process is less than 20 °C/second, the
grain size of the ferrite may increase, and the fracture appearance transition temperature
vTrs may deteriorate. In addition, due to the restriction of the producing facility, it is
15 difficult to control the cooling rate in the first cooling process to more than 150
°C/second. For this reason, the cooling rate in the first cooling process is to be 20
°C/second to 150 °C/second.
[0121]
In order to promote the ferrite transformation and to control the area fraction of
20 the martensite and the residual austenite which are the secondary phase to the intended
range, the cooling rate in the second cooling process is to be 15 °C/second or less. In
addition, even when the cooling rate in the second cooling process is less than 1
°C/second, the effect is saturated. For this reason, the cooling rate in the second cooling
process is to be 1 °C/secondto 15 °C/second.
60
[0122]
In addition, in order to promote the ferrite transformation and to control the area
fraction of the martensite and the residual austenite to the intended range, the temperature
range where the second cooling process is conducted is to be 750°C or less where the
5 ferrite transformation is promoted. In addition, when the temperature range where the
second cooling process is conducted is less than 650°C, the formation of the pearlite or
the bainite is promoted, and therefore, the fraction of the martensite and the residual
austenite may be excessively small. For this reason, the temperature range where the
second cooling process is conducted is to be 650° to 750°C.
10 [0123]
In addition, when the cooling time in the second cooling process is more than 10
seconds, the formation of the pearlite which causes the deterioration in the tensile
strength TS and the fatigue life is promoted, and therefore, the fraction of the martensite
and the residual austenite may be excessively small. In addition, in order to promote
15 the ferrite transformation, the cooling time in the second cooling process is to be 1
second or more. For this reason, the cooling time in the second cooling process is to be
1 second to 10 seconds.
[0124]
When the cooling rate in the third cooling process is less than 20 °C/second, the
20 formation of the pearlite and the bainite is promoted, and therefore, the fraction of the
martensite and the residual austenite may be excessively small. In addition, due to the
restriction of the producing facility, it is difficult to control the cooling rate in the third
cooling process to more than 150 °C/second. For this reason, the cooling rate in the
third cooling process is to be 20 °C/second to 150 °C/second.
61
[0125]
In addition, when the finish temperature of the cooling in the third cooling
process is higher than 200°C, the formation of the bainite is promoted during the coiling
process which is the subsequent process, and therefore, the fraction of the martensite and
5 the residual austenite may be excessively small. In addition, due to the restriction of the
producing facility, it is difficult to control the finish temperature of the cooling in the
third cooling process to less than 0°C. For this reason, the finish temperature of the
cooling in the third cooling process is to be 0°C to 200°C.
[0126]
10 In addition, for example, the cooling rate of 20 °C/second or more is obtained by
the cooling such as water-cooling or mist-cooling. In addition, for example, the cooling
rate of 15 °C/second or less is obtained by the cooling such as air-cooling.
[0127]
Subsequently, as the coiling process, the hot rolled steel sheet is coiled.
15 [0128]
The above are the producing conditions of the hot rolling method according to
the embodiment. However, as necessary, in order to improve the ductility by the
introduction of moving dislocations and to correct the shape of the steel sheet, the skin
pass rolling may be conducted. In addition, as necessary, in order to remove scale
20 which adheres to the surface of the hot rolled steel sheet, the pickling may be conducted.
In addition, as necessary, by using the obtained hot rolled steel sheet, the skin pass rolling
which is in-line or off-line or the cold rolling may be conducted.
[0129]
In addition, as necessary, in order to improve the corrosion resistance of the steel
62
sheet, the coating such as a hot dip coating may be conducted. In addition to the hot dip
coating, the alloying may be conducted.
Example
5 [0130]
Hereinafter, the effects of an aspect of the present invention will be described in
detail with reference to the following examples. However, the condition in the
examples is an example condition employed to confirm the operability and the effects of
the present invention, so that the present invention is not limited to the example condition.
10 The present invention can employ various types of conditions as long as the conditions
do not depart from the scope of the present invention and can achieve the object of the
present invention.
[0131]
Molten steels having the steel compositions A to MMMM as shown in Tables 2
15 to 4 were obtained. Each of the molten steels was made by conducting converter
smelting and secondary refining. The secondary refining was conducted in a RH
(Ruhrstahl-Hausen) vacuum degasser, and desulfurization was conducted by
appropriately adding CaO-CaF2-MgO based desulfurizing agent. In some of the steel
compositions, in order to suppress the remaining of the desulfurizing agent which tends
20 to be the elongated inclusion, steels having S content which corresponds to that after the
primary refining in the converter were produced without conducting desulfurization.
Steel pieces were obtained by continuous casting using the molten steels, the hot rolling
was conducted under the producing conditions as shown in Tables 5 to 7, and the
obtained steel sheets were coiled. The sheet thickness of the obtained hot rolled steel
25 sheets was to be 2.9 mm.
63
[0132]
The characteristic values of the obtained hot rolled steel sheets, such as the
metallographic structures, the texture, and the inclusions are shown in Tables 8 to 10.
The mechanical properties of the obtained hot rolled steel sheets are shown in Tables 11
5 to 13. The measurement methods of the metallographic structure, the texture, and the
inclusions, and the measurement methods of the mechanical properties are described
above. As the tensile properties, when the tensile strength TS was 590 MPa or more
and the n value was 0.13 or more, it was judged to be acceptable. As the formability,
when the average A,ave of the hole expanding ratio was 60% or more and the standard
10 deviation a of the hole expanding ratio was 15% or less, it was judged to be acceptable.
As the fracture properties, when the resistance of crack initiation Jc was 0.5 MJ/m or
more, the resistance of crack propagation T. M. was 600 MJ/m or more, the fracture
appearance transition temperature vTrs was 13°C or lower, and the Charpy absorbed
energy E was 16 J or more, it was judged to be acceptable. As the fatigue properties,
15 when the bending plane fatigue life was 400000 times or more, it was judged to be
acceptable. In addition, the underlined value in the tables indicates out of the range of
the present invention. In addition, in the tables, by using the amounts expressed in
mass% of each element in the chemical composition, a value of (Ti / 48) / (S / 32) + {(C
/ 40) / (S / 32) + (REM /140) / (S / 32)} x 15 is represented as "*1", and a value of
20 (REM /140) / (Ca / 40) is represented as "*2".
[0133]
In Tables 2 to 13, the producing results and the evaluation results are shown.
All of the Examples satisfied the ranges of the present invention and are excellent in, as
the hot rolled steel sheet, the tensile properties, the formability, the fracture properties,
64
and the fatigue properties. On the other hand, the Comparative Examples did not satisfy
the ranges of the present invention as the hot rolled steel sheet.
[0134]
In Comparative Example 11, since the C content was insufficient, the average ,
5 grain size of the primary phase coarsened. Therefore, the fracture properties of the steel
sheet deteriorated.
In Comparative Example 12, since the C content was insufficient, the average
grain size of the primary phase coarsened and the area fraction of the secondary phase
decreased. Therefore, the tensile properties and the fracture properties of the steel sheet
10 deteriorated.
In Comparative Example 26, since the S content was excessive, the total length
M in the rolling direction of the inclusions increased. Therefore, the formability, the
fracture properties, and the fatigue properties of the steel sheet deteriorated.
In Comparative Example 27, since the value of "*1" was insufficient, the total
15 length M in the rolling direction of the inclusions and the average of the maximum of the
ratio of the major axis to the minor axis of the inclusions increased. Therefore, the
formability and the fracture properties of the steel sheet deteriorated.
In Comparative Example 28, since the Mn content was excessive, the area
fraction of the secondary phase increased. Therefore, the formability and the fracture
20 properties of the steel sheet deteriorated.
In Comparative Example 30, since the reduction in the first rough rolling
process was excessive, the total length M in the rolling direction of the inclusions and the
average of the maximum of the ratio of the major axis to the minor axis of the inclusions
increased. Therefore, the formability, the fracture properties, and the fatigue properties
25 of the steel sheet deteriorated.
65
In Comparative Example 32, since the reduction in the second rough rolling
process was excessive, the {211} reflected intensity increased. Therefore, the
formability and the fracture properties of the steel sheet deteriorated.
In Comparative Example 35, since the reduction in the second rough rolling
5 process was insufficient, the average grain size of the primary phase coarsened.
Therefore, the fracture properties of the steel sheet deteriorated.
In Comparative Example 36, since the start temperature in the finish rolling
process was low, the {211} reflected intensity increased. Therefore, the formability and
the fracture properties of the steel sheet deteriorated.
10 In Comparative Example 37, since the finish temperature in the finish rolling
process was low, the {211} reflected intensity increased. Therefore, the formability and
the fracture properties of the steel sheet deteriorated.
In Comparative Example 38, since the finish temperature in the finish rolling
process was high, the average grain size of the primary phase coarsened. Therefore, the
15 fracture properties of the steel sheet deteriorated.
In Comparative Example 39, since the cooling rate in the first cooling process
was slow, the average grain size of the primary phase coarsened. Therefore, the fracture
properties of the steel sheet deteriorated.
In Comparative Example 40, since the finish temperature of the cooling in the
20 third cooling process was high, the area fraction of the secondary phase decreased.
Therefore, the tensile properties and the fatigue properties of the steel sheet deteriorated.
In Comparative Example 41, since the cooling rate in the third cooling process
was slow, the area fraction of the secondary phase decreased. Therefore, the tensile
properties and the fatigue properties of the steel sheet deteriorated.
25 In Comparative Example 51, since the C content was insufficient, the average
66
grain size of the primary phase coarsened and the area fraction of the secondary phase
decreased. Therefore, the tensile properties, the fracture properties, and the fatigue
properties of the steel sheet decreased.
In Comparative Example 67, since the value of "*1" was insufficient, the total
5 length M in the rolling direction of the inclusions increased. Therefore, the formability,
the fracture properties, and the fatigue properties of the steel sheet deteriorated.
In Comparative Example 68, since the value of "*1" was insufficient, the total
length M in the rolling direction of the inclusions and the average of the maximum of the
ratio of the major axis to the minor axis of the inclusions increased. Therefore, the
10 formability, the fracture properties, and the fatigue properties of the steel sheet
deteriorated.
In Comparative Example 69, since the Mn content was excessive, the area
fraction of the secondary phase increased. Therefore, the formability and the fracture
properties of the steel sheet deteriorated.
15 In Comparative Example 70, since the heating temperature in the heating
process was low, the tensile strength was insufficient.
In Comparative Example 71, since the reduction in the first rough rolling
process was excessive, the total length M in the rolling direction of the inclusions and the
average of the maximum of the ratio of the major axis to the minor axis of the inclusions
20 increased. Therefore, the formability, the fracture properties, and the fatigue properties
of the steel sheet deteriorated.
In Comparative Example 73, since the reduction in the second rough rolling
process was excessive, the {211} reflected intensity increased. Therefore, the
formability and the fracture properties of the steel sheet deteriorated.
25 In Comparative Example 76, since the reduction in the second rough rolling
67
process was insufficient, the average grain size of the primary phase coarsened.
Therefore, the fracture properties of the steel sheet deteriorated.
In Comparative Example 77, since the start temperature in the finish rolling
process was low, the {211} reflected intensity increased. Therefore, the formability and
5 the fracture properties of the steel sheet deteriorated.
In Comparative Example 78, since the finish temperature in the finish rolling
process was low, the {211} reflected intensity increased. Therefore, the formability and
the fracture properties of the steel sheet deteriorated.
In Comparative Example 79, since the finish temperature in the finish rolling
10 process was high, the average grain size of the primary phase coarsened. Therefore, the
fracture properties of the steel sheet deteriorated.
In Comparative Example 80, since the cooling rate in the third cooling process
was slow, the average grain size of the primary phase coarsened and the area fraction of
the secondary phase decreased. Therefore, the tensile properties, the fracture properties,
15 and the fatigue properties of the steel sheet deteriorated.
In Comparative Example 81, since the finish temperature of the cooling in the
third cooling process was high, the area fraction of the secondary phase decreased.
Therefore, the tensile properties and the fatigue properties of the steel sheet deteriorated.
In Comparative Example 84, since all of Ti, REM, or Ca were not contained, the
20 total length M in the rolling direction of the inclusions and the average of the maximum
of the ratio of the major axis to the minor axis of the inclusions increased. Therefore,
the formability, the fracture properties, and the fatigue properties of the steel sheet
deteriorated.
In Comparative Example 85, since the cooling rate in the second cooling process
25 was fast, the area fraction of the secondary phase increased. Therefore, the formability
68
and the fracture properties of the steel sheet deteriorated.
In Comparative Example 86, since the value of "* 1" was insufficient, the total
length M in the rolling direction of the inclusions increased. Therefore, the formability,
the fracture properties, and the fatigue properties of the steel sheet deteriorated.
5 In Comparative Example 91, since the cooling temperature in the second cooling
process was high, the area fraction of the secondary phase increased. Therefore, the
formability and the fracture properties of the steel sheet deteriorated.
In Comparative Example 92, since the cooling time in the second cooling
process was long, the area fraction of the primary phase decreased and the area fraction
10 of the pearlite increased. Therefore, the tensile properties and the fatigue properties of
the steel sheet deteriorated.
In Comparative Example 93, since the cooling time in the second cooling
process was short, the area fraction of the secondary phase increased. Therefore, the
formability and the fracture properties of the steel sheet deteriorated.
15 In Comparative Example 94, since the C content was excessive, the formability
and the fracture properties of the steel sheet deteriorated.
In Comparative Example 95, since the Mn content was insufficient, the tensile
properties of the steel sheet deteriorated.
In Comparative Examples 96 and 97, since the amount of Si + Al was excessive,
20 the formability of the steel sheet deteriorated.
In Comparative Examples 98 and 99, since the amount of Si + Al content wasinsufficient,
the tensile properties and the fracture properties of the steel sheet
deteriorated.
In Comparative Example 100, since the P content was excessive, the formability
25 and the fracture properties of the steel sheet deteriorated.
69
In Comparative Example 101, since the N content was excessive, the tensile
properties of the steel sheet deteriorated.
In Comparative Example 102, since the Ti content was excessive, the
formability and the fracture properties of the steel sheet deteriorated.
5 In Comparative Example 103, since the REM content was excessive, the
formability and the fracture properties of the steel sheet deteriorated.
In Comparative Example 104, since the Ca content was excessive, the total
length M in the rolling direction of the inclusions and the average of the maximum of the
ratio of the major axis to the minor axis of the inclusions increased. Therefore, the
10 formability, the fracture properties, and the fatigue properties of the steel sheet
deteriorated.
In Comparative Example 105, since the Ti content was insufficient, the
formability, the fracture properties, and the fatigue properties of the steel sheet
deteriorated.
15 In Comparative Example 106, since the REM content was insufficient, the
formability, the fracture properties, and the fatigue properties of the steel sheet
deteriorated.
In Comparative Example 107, since the Ca content was insufficient, the
formability, the fracture properties, and the fatigue properties of the steel sheet
20 deteriorated.
In Comparative Example 108, since the Nb content was excessive, the {211}
reflected intensity increased. Therefore, the formability and the fracture properties of
the steel sheet deteriorated.
In Comparative Example 109, since the B content was excessive, the {211}
25 reflected intensity increased. Therefore, the formability and the fracture properties of
70
the steel sheet deteriorated.
In Comparative Example 110, since the Cu content was excessive, the
formability of the steel sheet deteriorated.
In Comparative Example 111, since the Cr content was excessive, the
5 formability of the steel sheet deteriorated.
In Comparative Example 112, since the Mo content was excessive, the
formability of the steel sheet deteriorated.
In Comparative Example 113, since the Ni content was excessive, the
formability of the steel sheet deteriorated.
10 In Comparative Example 114, since the V content was excessive, the formability
of the steel sheet deteriorated.
[0135]
[Table 2]
[0136]
15 [Table 3]
[0137]
[Table 4]
[0138]
[Table 5]
20 [0139]
[Table 6]
[0140]
[Table 7]
[0141]
25 [Table 8]
[0142]
[Table 9]
[0143]
[Table 10]
5 [0144]
[Table 11]
[0145]
[Table 12]
[0146]
10 [Table 13]
Industrial Applicability
[0147]
According to the aspect of the present invention, it is possible to obtain a steel
15 sheet which has an excellent balance between tensile properties and formability and
furthermore which has excellent fracture properties and fatigue properties. Accordingly,
the present invention has significant industrial applicability.
Reference Signs List
20 [0148]
. 41 a to 411 INCLUSIONS IN WHICH MAJOR AXIS OF EACH OF
INCLUSIONS IS 3 ^m OR MORE
F INTERVAL BETWEEN INCLUSIONS IN ROLLING DIRECTION
G INCLUSION-CLUSTER
25 GL LENGTH OF INCLUSION-CLUSTER IN ROLLING DIRECTION
71
72
H INDEPENDENT-INCLUSION
HL LENGTH OF INDEPENDENT-INCLUSION IN ROLLING
DIRECTION
1/-35 \2>
10 Oil
O o
LU
10
CO o
o
o
o
o
in
CO o
o
o
§
CM
O
d
oo.
oo
CO O
o
d
5
5
in
o
I LUGO
1—O
COO.
8
TABLE 2
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
STEEL
COMPOSITION
A
B
C
D
E
F
G
H
I
J
K
L
M
N .
0
P
Q
R
S
T
U
V
W
X
Y
Z
AA
BB
CHEMICAL COMPOSITION
C
0.060
0.055
0.062
0.057
0.065
0.080
0.061
0.060
0.058
0.059
0.028
0.015
0.065
0.068
0.060
0.061
0.062
0.055
0.059
0.060
0.057
0.059
0.062
0.061
0.060
0.061
0.055
0.048
Si
1.25
1.35
1.05
1.95
1.35
1.15
0.50
0.55
1.36
1.17
1.00
1.30
1.09
1.13
1.27
1.35
1.25
1.23
1.20
1.30
1.05
1.04
1.10
1.17
1.15
1.18
1.35
0.51
Mn
1.90
1.85
2.50
1.35
1.70
1.90
1.85
1.87
2.00
1.86
1.90
1.90
1.91
1.80
1.70
1.90
1.80
1.90
1.89
1.83
1.86
1.87
1.83
1.85
1.86
1.87
1.75
3.05
din it'. mass%)
P
0.007
0.008
0.011
0.009
0.010
0.011
0.012
0.008
0.011
0.012
0.012
0.011
0.006
0.005
0.011
0.012
0.009
0.011
0.012
0.014
0.008
0.009
0.011
0.012
0.014
0.009
0.008
0.011
S
0.0030
0.0010
0.0040
0.0010
0.0040
0.0010
0.0030
0.0035
0.0045
0.0035
0.0040
0.0040
0.0040
0.0040
0.0040
0.0040
0.0040
0.0040
0.0040
0.0040
0.0038
0.0040
0.0040
0.0035
0.0043
0.0110
0.0100
0.0040
Al
0.023
0.020
0.029
0.026
0.028
0.025
0.025
0.028
0.027
0.021
0.023
0.021
0.028
0.022
0.025
0.027
0.021
0.029
0.027
0.020
0.022
0.024
0.023
0.024
0.026
0.024
0.025
0.030
N
0.0021
0.0025
0.0029
0.0021
0.0020
0.0029
0.0027
0.0029
0.0028
0.0026
0.0024
0.0020
0.0029
0.0025
0.0022
0.0025
0.0024
0.0023
0.0027
0.0026
0.0020
0.0029
0.0024
0.0023
0.0021
0.0022
0.0021
0.0024
Ti
[0.13
0.13
0.28
0.12
0.25
0.18
0.13
0.13
0.14
0.08
0.12
0.12
0.13
0.14
0.13
0.13
0.12
0.11
0.13
0.14
0.12
0.13
0.11
0.13
0.12
0.13
0.13
0.13
REM
0.0040
0.0025
0.0000
0.0000
0.0000
0.0000
0.0050
0.0050
0.0040
0.0055
0.0040
0.0400
0.0040
0.0180
0.0000
0.0000
0.0010
0.0020
0.0032
0.0034
0.0027
0.0031
0.0055
0.0038
0.0044
0.0034
0.0015
0.0032
Ca
0.0038
0.0020
0.0000
0.0000
0.0003
0.0004
0.0000
0.0003
0.0034
0.0050
0.0037
0.0036
0.0037
0.0000
0.0050
0.0040
0.0031
0.0042
0.0044
0.0040
0.0025
0.0024
0.0040
0.0035
0.0029
0.0041
0.0023
0.0022
• *1
48.66
119.24
46.67
80.00
42.57
124.80
34.60
30.69
32.86
37.39
34.53
65.09
36.20
38.76
36.67
33.67
30.16
32.65
37.61
38.25
31.38
31.52
35.05
40.48
30.21
13.41
11.94
31.01
• *2
0.30
0.36
oo
oo
0.00
0.00
oo
4.76
0.34
0.31
0.31
3.17
0.31
co
0.00
0.00
0.09
0.14
0.21
0.24
0.31
0.37
0.39
0.31
0.43
0.24
0.19
0.42
Si+Al
1.27
1.37
1.08
1.98
1.38
1.17
0.53
0.58
1.39
1.19
1.02
1.32
1.12
1.15
1.30
1.38
1.27
1.26
1.23
1.32
1.07
1.06
1.12
1.19
1.18
1.20
1.38
0.54
OTHER ELEMENTS
V=0.015%
-
V=0.03%
-
-
-
V=0.08%
V=0.08%
Nb=0.019%
-
-
-
B=0.0010%
Cr=0.1XNMo=0.03%
-
-
-
-
-
Cu=0.2%v Ni=0.1%
V=0.02%
. -
-
-
-
-
-
to
s
The underlined value
The m in the table
The ->K2 in the table
in the table indicates out of the range of the present invention
indicates (Ti/48)/(S/32)+{(Ca/40)/(S/32)+(REM/140)/(S/32))x15.
indicates (REM/140)/(Ca/40).
TABLE 3
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
STEEL
COMPOSITION
CC
DD
EE
FF
GG
HH
II
JJ
KK
LL
MM
NN
0 0
PP
QQ
RR
SS
TT
UU
vv
WW
XX
YY
ZZ
AAA
BBB
CCC
DDD
CHEMICAL COMPOSITION ( u n i t : mass%)
C
0.040
0.055
0.062
0.057
0.065
0.090
0.061
0.060
0.040
0.020
0.058
0.031
0.065
0.068
0.060
0.061
0.062
0.055
0.059
0.060
0.057
0.059
0.062
0.061
0.060
0.061
0.055
0.048
Si
1.25
1.35
1.05
1.95
1.35
1.15
0.50
0.55
1.50
1.30
1.36
1.00
1.09
1.13
1.27
1.35
1.25
1.23
1.20
1.30
1.05
1.04
1.10
1.17
1.15
1.18
1.35
0.51
Mn
1.25
1.20
1.48
0.70
1.05
1.25
1.85
1.87
1.51
1.35
1.35
1.25
1.26
1.15
0.83
1.25
1.15
1.25
1.24
1.18
1.21
1.22
1.18
1.20
1.21
1.22
1.10
3.05
P
0.007
0.008
0.011
0.009
0.010
0.011
0.012
0.008
0.007
0.006
0.011
0.012
0.006
0.005
0.011
0.012
0.009
0.011
0.012
0.014
0.008
0.009
0.011
0.012
0.014
0.009
0.008
0.011
S
0.0030
0.0010
0.0040
0.0010
0.0040
0.0010
0.0030
0.0035
0.0015
0.0040
0.0045
0.0040
0.0040
0.0040
0.0040
0.0040
0.0040
0.0040
0.0040
0.0040
0.0038
0.0040
0.0040
0.0035
0.0043
0.0080
0.0100
0.0040
Al
0.023
0.020
0.029
0.026
0.028
0.025
0.025
0.028
0.025
0.021
0.027
0.023
0.028
0.022
0.025
0.027
0.021
0.029
0.027
0.020
0.022
0.024
0.023
0.024
0.026
0.024
0.025
0.030
N
0.0021
0.0025
0.0029
0.0021
0.0020
0.0029
0.0027
0.0029
0.0025
0.0021
0.0028
0.0024
0.0029
0.0025
0.0022
0.0025
0.0024
0.0023
0.0027
0.0026
0.0020
0.0029
0.0024
0.0023
0.0021
0.0022
0.0021
0.0024
Ti
0.05
0.05
0.08
0.04
0.08
0.08
0.05
0.05
0.00
0.05
0.06
0.04
0.05
0.06
0.05
0.05
0.04
0.03
0.05
0.06
0.04
0.05
0.03
0.05
0.04
0.05
0.05
0.05
REM
0.0040
0.0025
0.0000
0.0000
0.0000
0.0000
0.0050
0.0050
0.0034
0.0045
0.0040
0.0040
0.0040
0.0100
0.0000
0.0000
0.0010
0.0020
0.0032
0.0034
0.0027
0.0031
0.0055
0.0038
0.0035
0.0034
0.0015
0.0032
Ca
0.0038
0.0020
0.0000
0.0000
0.0003
0.0004
0.0000
0.0002
0.0028
0.0040
0.0034
0.0037
0.0037
0.0000
0.0050
0.0040
0.0031
0.0042
0.0044
0.0040
0.0025
0.0024
0.0040
0.0035
0.0031
0.0041
0.0023
0.0022
* 1
30.88
65.90
13.33
26.67
13.40
56.80
16.83
15.11
30.17
24.19
21.00
21.20
22.86
18.57
23.33
20.33
16.82
19.31
24.28
24.91
17.35
18.19
21.71
25.25
17.64
11.77
6.61
17.68
• * 2
0.30
0.36
oo
oo
0.00
0.00
00
7.14
0.35
0.32
0.34
0.31
0.31
00
0.00
0.00
0.09
0.14
0.21
0.24
0.31
0.37
0.39
0.31
0.32
0.24
0.19
0.42
Si+A!
1.27
1.37
1.08
1.98
1.38
1.17
0.53
0.58
1.53
1.32
1.39
1.02
1.12
1.15
1.30
1.38
1.27
1.26
1.23
1.32
1.07
1.06
1.12
1.19
1.18
1.20
1.38
0.54
OTHER ELEMENTS
-
-
V=0.02%
-
-
-
V=0.01%
V=0.02%
-
-
Nb=0.012%
B=0.0009%
Cr=0.294v Mo=0.05%
-
-
-
-
"
. -
Cu=0.2%s Ni=0.2%
V=0.01%
-
-
-
-
-
""
"N
The underlined value
The m in the table
The 5K2 in the table
in the table indicates out of the range of the present invention,
indicates (Ti/48)/(S/32)+[(Ca/40)/(S/32)+(REM/140)/(S/32))x15.
indicates (REM/140)/(Ca/40).
•
4/35- ^-£
TABLE 4-1
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
82
83
B4
85
86
87
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
STEEL
COMPOSITION
EEE
FFF
GGG
HHH
JJJ
A
A
KKK
A
A
A
LLL
MMM
NNN
0 00
PPP
QQQ
RRR
SSS
TTT
UUU
VVV
WWW
XXX
YYY
ZZZ
A A A A
BBBB
CCCC
DDDD
EEEE
FFFF
GGGG
HHHH
I1II
JJJJ
KKKK
LLLL
MMMM
CHEMICAL COMPOSITION ( u n i t : mass%)
C
0.060
0.060
0.065
0.078
0.064
0.060
0.060
0.060
0.060
0.060
0.060
0.110
0.040
0.060
0.060
0.031
0.031
0.059
0.055
0.062
0.060
0.060
0.062
0.060
0.060
0.060
0.060
0.060
0.060
0.060
0.060
0.060
0.058
0.065
0.057
0.068
0.068
0.057
0.059
Si
1.10
1.31
1.60
1.50
1.50
1.25
1.25
1.25
1.25
1.25
1.25
1.25
1.25
2.55
1.60
0.47
0.45
1.17
1.35
1.05
1.10
1.31
1.05
1.10
1.31
1.25
1.25
1.25
1.25
1.25
1.25
1.25
1.36
1.09
1.05
1.13
1.13
1.05
1.04
Mn
1.80
1.75
0.50
1.20
1.80
1.90
1.90
1.95
1.90
1.90
1.90
1.90
0.48
1.90
1.90
1.25
1.25
1.86
1.20
2.00
1.80
1.75
1.35
1.80
1.75
1.90
1.90
1.90
1.90
1.90
1.90
1.90
2.00
1.91
1.86
1.80
1.80
1.86
1.87
P
0.010
0.008
0.010
0.010
0.010
0.007
0.007
0.010
0.007
0.007
0.007
0.007
0.007
0.007
0.007
0.012
0.012
0.110
0.008
0.011
0.010
0.008
0.011
0.010
0.008
0.007
0.007
0.007
0.007
0.007
0.007
0.007
0.011
0.006
0.008
0.005
0.005
0.008
0.009
S
0.0010
0.0030
0.0030
0.0025
0.0015
0.0030
0.0030
0.0049
0.0030
0.0030
0.0030
0.0030
0.0030
0.0030
0.0030
0.0040
0.0040
0.0035
0.0010
0.0040
0.0010
0.0030
0.0040
0.0010
0.0030
0.0030
0.0030
0.0030
0.0030
0.0030
0.0030
0.0030
0.0045
0.0040
0.0038
0.0040
0.0040
Al
0.020
0.025
0.028
0.025
0.025
0.023
0.023
0.025
0.023
0.023
0.023
0.023
0.023
1.580
2.430
0.007
0.004
0.021
0.020
0.029
0.020
0.025
0.029
0.020
0.025
0.023
0.023
0.023
0.023
0.023
0.023
0.023
0.027
0.028
0.022
0.022
0.022
0.0038 0.022
0.0040 I 0.024
N
0.0020
0.0025
0.0025
0.0021
0.0031
0.0021
0.0021
0.0040
0.0021
0.0021
0.0021
0.0021
0.0021
0.0021
0.0021
0.0024
0.0024
0.0026
0.0250
0.0029
0.0020
0.0025
0.0029
0.0020
0.0025
0.0021
0.0021
0.0021
0.0021
0.0021
0.0021
0.0021
0.0028
0.0029
0.0020
0.0025
0.0025
0.0020
0.0029
Ti
0.00
0.00
0.00
0.13
0.02
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0.05
0.13
0.13
0.04
0.04
0.08
0.05
0.31
0.00
0.00
0.0008
0.00
0,00
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0.14
0.13
0.12
0.14
0.14
0.12
0.13
The underlined value
The m in the table
The -)K2 in the table
in the table indicates out of the range of the present invention,
indicates (Ti/48)/(S/32)+{(Ca/40)/(S/32)+(REM/140)/(S/32)}x15.
indicates (REM/140)/(Ca/40).
$m 3 ^
TABLE 4-2
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
82
83
84
85
86
87
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
STEEL
COMPOSITION
EEE
FFF
GGG
HHH
JJJ
A
A
KKK
A
A
A
LLL
MMM
NNN
0 0 0
PPP
QQQ
RRR
SSS
TTT
UUU
VVV
WWW
XXX
YYY
ZZZ
A A A A
BBBB
CCGC
DDDD
EEEE
FFFF
GGGG
HHHH
mi
JJJJ
KKKK
LLLL
MMMM
CHEMICAL-COMPOSITION ( u n i t : mass%)
REM
0.0090
0.0000
0.0000
0.0039
0.0001
0.0040
0.0040
0.0040
0.0040
0.0040
0.0040
0.0040
0.0040
0.0040
0.0040
0.0040
0.0040
0.0055
0.0025
Q.OOQQ
0.0250
0.0000
0.0000
0.00008
0.0000
0.0040
0.0040
0.0040
0.0040
0.0040
0.0040
0.0040
0.0040
0.0040
0.0027
0.01800
0.0180
0.0027
0.0031
Ca
0.0000
0.0060
0.0000
0.0038
0.0001
0.0038
0.0038
0.0035
0.0038
0.0038
0.0038
0.0038
0.0038
0.0038
0.0038
0.0037
0.0037
0.0050
0,0020
0,0000
0.0000
0.0130
0.0000
0.0000
o.ooooa
0.0038
0.0038
0.0038
0.0038
0.0038
0.0038
0.0038
0.0034
0.0037
0.0025
0.0000
0.0000
0.0025
0.0024
» 1
30.86
24.00
0.00
58.26
9.92
48.66
48.66
29.19
48.66
48.66
48.66
48.66
30.88
48.66
48.66
21.20
21.20
37.39
65.90
51.67
85.71
52.00
0.13
0.27
0.36
48.66
48.66
48.66
48.66
48.66
48.66
48.66
32.86
36.20
31.38
38.76
38.76
31.38
31.52
* 2
CO
0.00
CO
0.29
0.29
0.30
0.30
0.33
0,30
0.30
0.30
0.30
0.30
0.30
0.30
0.31
0.31
0.31
0.36
00
CO
0.00
oo
CO
0.00
0.30
0.30
0.30
0.30
0.30
0.30
0.30
0.34
0.31
0.31
CO
CO
0.31
0.37
SH-AI
1.12
1.34
1.63
1.53
1.53
1.27
1.27
1.28
1.27
1.27
1.27
1.27
1.27
4.13
4.03
0.48
0.45
1.19
1.37
1.08
1.12
1.34
1.08
1.12
1.34
1.27
1.27
1.27
1.27
1.27
1.27
1.27
1.39
1.12
1.07
1.15
1.15
1.07
1.06
OTHER ELEMENTS
V=0.12%
V=0.13%
V=0.12%
-
V=0.1%
V=0.015%
V=0.015%
-
V=0.015%
V=0.015%
V=0.015%
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Nb=0.11%
B=0.0042%
Cu=1.1X
Cr=1.1%
Mo=1.1%
Ni=1.1%
V=0.22%
Nb=0.0008%
B=0.00009%
Cu=0.0007%N Ni=0.1%
Cr=0.0008%. Mo=0.03«
Cr=0.1«. Mo=0.0008%
Cu=0.2K. Ni=0.0009%
V=0.0008%
The underlined value
The m in the table
The Wl in the table
in the table indicates out of the range of the present invention,
indicates (Ti/48)/(S/32)+{(Ca/40)/(S/32)+(REM/140)/(S/32)]x15.
indicates (REM/140)/(Ca/40).
TABLE 5-1
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
STEEL
COMPOSITION
A
B
C
D
E
F
G
H
I
J
K
L
M
N
0
P
Q
R
S
T
Ar3 TRANSFORMATION
TEMPERATURE
CC)
746
754
700
802
760
736
731
731
743
747
753
765
740
745
760
748
752
748
746
752
PRODUCTION CONDITIONS
USAGE OF REFINING
DESULFURIZING AGENT
IN SECONDARY REFINING
nonuse
use
nonuse
use
nonuse
use
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
• nonuse
HEATING
PROCESS
HEATING
TEMPERATURE
CC)
1200
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
FIRST ROUGH ROLLING PROCESS
START
TEMPERATURE
CC)
1200
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
FINISH
TEMPERATURE
CC)
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
REDUCTION
(%)
65
65
65
65
65
65
65
65
65
65
65
65
65
65
65
65
65
65
65
65
SECOND ROUGH ROLLING PROCESS
START
TEMPERATURE
CC)
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
FINISH
TEMPERATURE
CO
1072
1074
1071
1077
1075
1071
1072
1074
1078
1072
1074
1074
1080
1073
1072
1071
1078
1073
1079
1078
REDUCTION
(»
21
21
21
21
21
21
21
21
21
21
21
21
21
21
21
21
21
21
21
21
TABLE 5-2
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
STEEL
COMPOSITION
A
B
C
D
E
F
G
H
I
J
K
L
M
N
0
P
Q
R
S
T
PRODUCTION CONDITIONS
FINISH
ROLLING
PROCESS
START
TEMPERATURE
(°C)
1012
1014
1011
1017
1015
1011
1012
1014
1018
1012
1014
1014
1020
1013
1012 ,
1011
1018
1013
1019
1018
FINISH
TEMPERATURE
CO
887
889
895
907
888
893
891
891
892
887
892
892
892
892
892
891
891
890
891
893 .
FIRST
COOLING
PROCESS
COOLING
RATE
(°C/sec.)
29
30
33
27
32
35
31
31
27
30
26
25
30
31
28
31
34
30
33
29
SECOND COOLING PROCESS
COOLING
RATE
CC/sec.)
10
10
10
10
10
10
10
10
10
10
10
10
10
5
10
10
10
10
10
10
COOLING
START
TEMPERATURE
(°C)
750
730
720
730
700
750
750
750
750
750
750
750
750
700
750
750
750
750
750
750
COOLING
FINISH
TEMPERATURE
(°C)
670
650
650
650
650
700
690
650
670
670
670
670
670
670
670
670
670
670
670
670
COOLING
TIME
(sec.)
8
8
7
8
5
5
6
10
8
8
8
8
8
6
8
8
8
8
8
B
THIRD COOLING PROCESS
COOLING
RATE
CC/sec.)
29
30
33
27
32
35
31
31
27
30
26
25
30
31
28
31
34
30
33
29
COOLING
FINISH
TEMPERATURE
CO
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
TABLE 5-3
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
STEEL
COMPOSITION
U
V
w
X
Y
Z
AA
BB
A
A
A
A
A
A
A
A
A
A
A
A
A
Ar3 TRANSFORMATION
TEMPERATURE
(°C)
737
743
747
747
747
746
761
654
746
746
746
746
746
746
746
746
746
746
746
746
746
PRODUCTION CONDITIONS
USAGE OF REFINING
DESULFURIZING AGENT
IN SECONDARY REFINING
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
HEATING
PROCESS
HEATING
TEMPERATURE
PC)
1250
1250
1250
1250
1250
1250
1250
1250
1170
1250
1250
1250
1250
1248
1249
1250
1250
1250
1250
1250
1250
FIRST ROUGH ROLLING PROCESS
START
TEMPERATURE
(°C)
1250
1250
1250
1250
1250
1250
1250
1250
1170
1250
1250
1250
1250
1248
1249
1250
1250
1250
1250
1250
1250
FINISH
TEMPERATURE
(°C)
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
REDUCTION
(%)
65
65
65
65
65
65
65
65
65
75
70
58
61
67
70
65
65
65
65
65
65
SECOND ROUGH ROLLING PROCESS
START
TEMPERATURE
(°C)
1150
1150
1150
1150
1150
1150
1150
1150
1120
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
FINISH
TEMPERATURE
(°C)
1070
1077
1072
1079
1072
1073
1070
1070
1078
1079
1072
1080
1072
1076
1072
1070
1074
1070
1075
1075
1075
REDUCTION
(%)
21
21
21
21
21
21
21
21
21
11
16
28
25
10
5
21 •
21
21
21
21
21
TABLE 5-4
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLEj
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
STEL
COMPOSITION
U
V
w
X
Y
Z
AA
BB
A
A
A
A
A
A
A
A
A
A
A
A
A
PRODUCTION CONDITIONS
FINISH
ROLLING
PROCESS
START
TEMPERATURE
CC)
1010
1017
1012
1019
1012
1013
1010
1010
1018
1019
1012
1020
1012
1016'
1012
960
1014
1010
1015
1015
1015
FINISH
TEMPERATURE
CC)
894
892
887
889
893
886
887
845
889
891
885
888
892
886
889
880
800
970
880
880
880
FIRST
COOLING
PROCESS
COOLING
RATE
CC/seo.)
30
32
27
28
33
32
25
28
26
27
35
34
26
27
27
30
34
26
15
30
30
SECOND COOLING PROCESS
COOLING
RATE
Cc/sec.)
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
COOLING
START
TEMPERATURE
CO
750
750
750
750
750
750
750
750
750
750
750
750
750
750
750
750
750
750
750
750
750
COOLING
FINISH
TEMPERATURE
670
670
670
670
670
670
670
670
670
670
670
670
670
670
670
670
670
670
670
670
670
COOLING
TIME
(sec.)
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
THIRD COOLING PROCESS
COOLING
RATE
CC/sec.)
30
32
27
28
33
32
25
28
26
27
35
34
26
27
27
30
34
26
30
30
15
COOLING
FINISH
TEMPERATURE
{"0
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
400
25
TABLE 6-1
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
STEEL
COMPOSITION
cc
DD
EE
FF
QG
HH
n
JJ
KK
LL
MM
NN
OO
PP
QQ
RR
SS
TT
UU
VV
Ar3 TRANSFORMATION
TEMPERATURE
CO
798
798
769
847
805
776
731
731
787
801
787
796
784
788
820
793
796
792
, 790
i 797
PRODUCTION CONDITIONS
USAGE OF REFINING
DESULFURIZING AGENT
IN SECONDARY REFINING
nonuse
use
nonuse
use
nonuse
use
nonuse
nonuse
M?e
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
HEATING
PROCESS
HEATING
TEMPERATURE
(°C)
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
FIRST ROUGH ROLLING PROCESS
START
TEMPERATURE
PC)
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
1250
FINISH
TEMPERATURE
(°C)
1 1 51
1151
1 1 51
1 1 51
1 1 51
1 1 51
1 1 51
1 1 51
1 1 51
1 1 51
1 1 51
1151
1 1 51
1 1 51
1 1 51
1 1 51
1 1 51
1 1 5 1
1 1 51
1 1 51
REDUCTION
(%)
65
65
65
65
65
65
65
65
65
65
65
65
65
65
65
65
65
65
65
65
SECOND ROUGH ROLLING PROCESS
START
TEMPERATURE
PC)
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
FINISH
TEMPERATURE
PC)
1072
1074
1071
1077
1075
1071
1072
1074
1072
1072
1078
1074
1080
1073
1072
1071
1078
1073
1079
1078
REDUCTION
(%)
21
21
21
21
21
21
21
21
21
21
21
21
21
21
21
21
21
21
21
21
TABLE 6-2
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
STEEL
COMPOSITION
cc
DD
EE
FF
GG
HH
II
JJ
KK
LL
MM
NN
OO
PP
QQ
RR
SS
TT
UU
W
PRODUCTION CONDITIONS
FINISH
ROLLING
PROCESS
START
TEMPERATURE
CC)
1012
1014
1011
1017
1015
1011
1012
1014
1012
1012
1018
1014
1020
1013
1012
1011
1018
1013
. 1019
i 1018
FINISH
TEMPERATURE
(°C)
887
889
895
907
888
893
891
891
890
890
892
892
892
892
892
891
891
890
891
893
FIRST
COOLING
PROCESS
COOLING
RATE
(°C/sec.)
29
30
33
27
32
35
31
31
30
30
27
26
30
31
28
31
34
30
33
29
SECOND COOLING PROCESS
COOLING
RATE
(°C/sec.)
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
COOLING
START
TEMPERATURE
PC)
750
750
750
750
750
750
750
750
750
750
750
750
750
750
750
750
750
750
750
750
COOLING
FINISH
TEMPERATURE
(°C)
COOLING
TIME
(sec.)
670 8
670
670
670
670
670
670
670
670
670
670
670
670
670
670
670
670
670
670
670
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
THIRD COOLING PROCESS
COOLING
RATE
CC/sec.)
29
30
33
27
32
35
31
31
30
30
27
26
30
31
28
31
34
30
33
29
COOLING
FINISH
TEMPERATURE
(°C)
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
TABLE 6-3
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
STEEL
COMPOSITION
WW
XX
YY
ZZ
AAA
BBB
CCG
DDD
CC
CO
CC
CC
CC
CC
CC
CC
CC
CC
CC
CC
Ar3 TRANSFORMATION
TEMPERATURE
CC)
778
788
791
791
791
790
805
654
798
798
798
798
798
798
798
798
798
798
798
798
PRODUCTION CONDITIONS
USAGE OF REFINING
DESULFURIZING AGENT
IN SECONDARY REFINING
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
HEATING
PROCESS
HEATING
TEMPERATURE
CC)
1250
1250
1250
1250
1250
1250
1250
1250
1170
1250
1250
1250
1250
1248
1249
1250
1250
1250
1250
1250
FIRST ROUGH ROLLING PROCESS
START
TEMPERATURE
CC)
1250
1250
1250
1250
1250
1250
1250
1250
1170
1250
1250
1250
1250
1248
1249
1250
1250
1250
1250
1250
FINISH
TEMPERATURE
CC)
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
REDUCTION
(%)
65
65
65
65
65
65
65
65
65
75
70
58
61
67
70
65
65
65
65
65
SECOND ROUGH ROLLING PROCESS
START
TEMPERATURE
CC)
1150
1150
1150
1150
1150
1150
1150
1150
1120
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
FINISH
TEMPERATURE
CC)
1070
1077
1072
1079
1072
1073
1070
1070
1078
1079
1072
1080
1072
1076
1072
1070
1074
1070
1075
1075
REDUCTION
21
21
21
21
21
21
21
21
21
11
16
28
25
10
8
21
21
21
21
21
TABLE 6-4
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
STEL
COMPOSITION
WW
XX
YY
ZZ
AAA
BBB
CCC
ODD
CO
CC
OC
CC
CC
CC
CC
CC
CC
CC
CC
CC
PRODUCTION CONDITIONS
FINISH
ROLLING
PROCESS
START ;
TEMPERATURE
CO
1010
1017
1012
1019
1012
1013
1010
1010
1018
1019
1012
1020
1012
1016
1012
960 •
1014
1010
1015
1015
FINISH
TEMPERATURE
• CO
894
892
887
889
893
886
887
850
889
891
885
883
892
886
889
880
820
1015
880
880
FIRST
COOLING
PROCESS
COOLING
RATE
CC/sec.)
30
32
27
28
33
32
25
28
26
27
35
34
26
27
27
30
34
26
25
30
SECOND COOLING PROCESS
COOLING
RATE
CC/sec.)
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
COOLING
START
TEMPERATURE
CO
750
750
750
750
750
750
750
750
750
750
750
750
750
750
750
750
750
750
750
750
COOLING
FINISH
TEMPERATURE
CO
670
670
670
670
670
670
670
670
670
670
670
670
670
670
670
670
670
670
670
670
COOLING
TIME
(sec.)
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
THIRD COOLING PROCESS
COOLING
RATE
CC/sec.)
30
32
27
28
33
32
25
28
26
27
35
34
26
27
27
30
34
26
17
30
COOLING
FINISH
TEMPERATURE
CO
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
400
TABLE 7-1
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
82
83
84
85
86
87
89
90
91
92
93
94
95
96
97
98
99
100
101
STEEL
COMPOSITION
EEE
FFF
GGG
HHH
JJJ
A
A
KKK
A
A
A
LLL
MMM
NNN
0 0 0
PPP
QQQ
RRR
SSS
Ar3 TRANSFORMATION
TEMPERATURE
(°C)
749
758
848
793
758
746
746
743
746
746
746
726
851
779
755
782
782
747
798
PRODUCTION CONDITIONS
USAGE OF REFINING
DESULFURIZING AGENT
IN SECONDARY REFINING
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
use
HEATING
PROCESS
HEATING
TEMPERATURE
(°C)
1200
1200
1200
1200
1200
1200
1200
1200
1200
1200
1200
1200
1250
1248
1248
1250
1250
1250
1250
FIRST ROUGH ROLLING PROCESS
START
TEMPERATURE
CO
1200
1200
1200
1200
1200
1200
1200
1200
1200
1200
1200
1200
1250
1248
1248
1250
1250
1250
1250
FINISH
TEMPERATURE
(°C)
1 1 51
1 1 51
1151
1151
1151
1 1 51
1 1 51
1 1 51
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
REDUCTION
(%)
65
65
65
65
65
65
65
65
65
65
65
65
70
67
67
65
65
65
65
SECOND ROUGH ROLLING PROCESS
START
TEMPERATURE
CO
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
FINISH
TEMPERATURE
CO
1072
1072
1072
1072
1072
1072
1072
1072
1072
1072
1072
1072
1072
1076
1076
1074
1074
1072
1074
REDUCTION
(%)
21
21
21
21
21
13
21
21
21
21
21
21
16
10
10
21
21
21
21
TABLE 7-2
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
82
83
84
85
86
87
89
90
91
92
93
94
95
96
97
98
99
100
101
STEEL
COMPOSITION
EEE
FFF
GGG
HHH
JJJ
A
A
KKK
A
A
A
LLL
MMM
NNN
0 0 0
PPP
QQQ
RRR
SSS
PRODUCTION CONDITIONS
FINISH
ROLLING
PROCESS
START
TEMPERATURE
(°C)
1012
1012
1012
1012
1012
1012
1012
1012
1012
1012
1012
1012
1012
1016
1016
1014
1014
1012
1014
FINISH
TEMPERATURE
(°C)
887
887
910
887
887
911
887
927
887
887
887
887
915
886
886
892
892
887
889
FIRST
COOLING
PROCESS
COOLING
RATE
(°C/sec.)
29
29
29
29
29
25
29
29
29
29
29
29
35
27
27
26
26
30
30
SECOND COOLING PROCESS
COOLING
RATE
(°C/sec.)
10
10
10
25
10
10
8
10
10
6
14
10
10
10
10
10
10
10
10
COOLING
START
TEMPERATURE
PC)
750
750
750
750
750
750
730
750
830
750
740
750
750
750
750
750
750
750
750
COOLING
FINISH
TEMPERATURE
CC)
670
670
670
670
670
670
650
670
751
660
730
670
670
670
670
670
670
670
670
COOLING
TIME
(sec.)
8
8
8
3.2
8
8
10
8
8
15
0.7
8
8
8
8
8
8
8
8
THIRD COOLING PROCESS
COOLING
RATE
CC/sec.)
29
29
29
29
29
29
21
29
29
29
29
29
35
27
27
26
26
30
30
COOLING
FINISH .
TEMPERATURE
PC)
25
25
25
25
25
25
100
25
25
25
25
25
25
25
25
25
25
25
25
TABLE 7-3
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
STEEL
COMPOSITION
TTT
uuu
vw
www
XXX
YYY
ZZZ
AAAA
BBBB
COCO
DDDD
EEEE
FFFF
GGGG
HHHH
IIII
JJJJ
KKKK
LLLL
MMMM
Ar3 TRANSFORMATION
TEMPERATURE
CC)
734
749
758
778
749
758
746
746
723
719
779
707
746
743
740
742
748
744
741
743
PRODUCTION CONDITIONS
USAGE OF REFINING
DESULFURIZING AGENT
IN SECONDARY REFINING
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
nonuse
HEATING
PROCESS
HEATING
TEMPERATURE
CC)
1250
1200
1200
1250
1200
1200
1200
1200
1200
1200
1200
1200
1200
1250
1250
1250
1250
1250
1250
1250
FIRST ROUGH ROLLING PROCESS
START
TEMPERATURE
CC)
1250
1200
1200
1250
1200
1200
1200
1200
1200
1200
1200
1200
1200
1250
1250
1250
1250
1250
1250
1250
FINISH
TEMPERATURE
CO
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
1151
REDUCTION
(%)
65
65
65
65
65
65
65
65
65
65
65
65
65
65
65
65
65
65
65
•65
SECOND ROUGH ROLLING PROCESS
START
TEMPERATURE
CO
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
1150
FINISH
TEMPERATURE
CC)
1071
1072
1072
1071
1072
1072
1072
1072
1072
1072
1072
1072
1072
1078
1080
1070
1073
1073
1070
1077
REDUCTION
«)
21
21
21
21
21
21
21
21
21
21
21
21
21
21
21 .
21
21
21
21
21
TABLE 7-4
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
STEEL
COMPOSITION
TTT
uuu
wv
www
XXX
YYY
ZZZ
AAAA
BBBB
CCCC
DDDD
EEEE
FFFF
GGGG
HHHH
III!
JJJJ
KKKK
LLLL
MMMM
PRODUCTION CONDITIONS
FINISH
ROLLING
PROCESS
START
TEMPERATURE
CO
1011
1012
1012
1011
1012
1012
1012
1012
1012
1012
1012
1012
1012
1018
1020
1010
1013
1013
1010
1017
FINISH
TEMPERATURE
(°C)
895
887
887
895
887
887
887
887
887
887
887
887
887
892
892
894
892
892
894
892
FIRST
COOLING
PROCESS
COOLING
RATE
(0C/sec.)
33
29
29
33
29
29
29
29
29
29
29
29
29
27
30
30
31
31
30
32
SECOND COOLING PROCESS
COOLING
RATE
(°C/sec.)
10
10
10
10
• 10
10
10
10
10
10
10
10
10
10
10
10
5
5
10
10
COOLING
START
TEMPERATURE
(°C)
720
750
750
750
750
750
750
750
750
750
750
750
750
750
750
750
700
700
750
750
COOLING
FINISH
TEMPERATURE
(°C)
650
670
670
670
670
670
670
670
670
670
670
670
670
670
670
670
670
670
670
670
COOLING
TIME
(sec.)
7
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
6
6
8
8
THIRD COOLING PROCESS
COOLING
RATE
(°C/sec.)
33
29
29
33
29
29
29
29
29
29
29
29
29
27
30
30
31
31
30
32
COOLING
FINISH
TEMPERATURE
(°C)
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
TABLE 8-1
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
STEEL
COMPOSITION
A
B
C
D
E
F
G
H
I
J
K
L
M
N
0
P
Q
R
S
T
METALLOGRAPHIC STRUCTURE
CONSTITUENT METALLIC PHASE
ferrite.martensite,residual austenite
ferrite.martensite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite,martensite,residuaI austenite
ferrite.martensite.residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite.residual austenite
ferrite.martensite
ferrite.martensite.residual austenite
ferrite.martensite,residual austenite
ferrite.martensite.residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
PRIMARY PHASE
FERRITE (F)
AREA
FRACTION
F
93.1
93.8
92.8
93.5
92.4
90.5
93.0
93.1
93.4
93.2
97.3
99.1
92.4
92.1
93.1
93.0
92.8
93.8
93.2
93.1
AVERAGE
GRAIN
SIZE
(ym)
4.22
4.25
4.22
4.16
4.19
4.20
4.19
4.20
3.60
4.21
10.04
10.21
3.90
4.21
4.17
4.21
4.18
4.20
4.17
425
SECONDARY PHASE
MARTENSITE (M) AND
RESIDUAL AUSTENITE (r)
AREA FRACTION
M
(%)
5.9
6.2
5.7
4.7
6.1
7.4
5.5
6.1
5.4
5.8
1.9
0.9
7.1
6.4
5.5
5.8
5.9
4.8
5.3
6.0
r
(%)
1.0
0.0
1.5
1.8
1.5
2.1
1.5
0.8
1.2
1.0
0.8
0.0
0.5
1.5
1.4
1.2
1.3
1.4
1.5
0.9
M+r
(%)
6.9
6.2
7.2
6.5
7.6
9.5
7.0
6.9
6.6
6.8
2.7
0.9
7.6
7.9
6.9
7.0
7.2
6.2
6.8
6.9
AVERAGE
GRAIN
SIZE
(#m)
3.4
3.4
3.4
3.3
3.4
3.4
3.4
3.4
2.9
3.4
7.1
7.7
3.1
3.4
3.3
3.4
3.3
3.4
3.3
3.4
AREA
FRACTION
OF BAINITE
(%)
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
AREA
FRACTION
OF
PEARLITE
(%)
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
The underlined value in the table indicates out of the range of the present invention.
TABLE 8-2
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
STEEL
COMPOSITION
A
B
C
D
E
F
G
H
I
J
K
L
M
N
0
P
Q
R
S
T
TEXTURE
X-RAY
RANDOM
INTENSITY
RATIO OF
(211} PLANE
2.31
2.30
2.25
2.32
2.31
2.27
2.00
2.05
2.27
2.32
2.27
2.10
2.27
2.27
2.28
2.29
2.28
2.29
2.28
2.26
INCLUSIONS
AVERAGE OF
MAXIMUM OF
RATIO OF
MAJOR
AXIS TO
MINOR AXIS
3.0
1.5
1.0
1.5
4.5
4.5
1.0
1.0
2.8
2.9
3.0
3.0
3.0
1.0
8.0
8.0
7.0
5.8
4.8
4.0
TOTAL
LENGTH M
IN ROLLING
DIRECTION
(mm/mm2)
0.03
0 . 04
0 . 00
0.02
0.00
0.02
0.00
0.00
0.14
0.18
0.12
0.11
0.12
0.00
0.13
0.19
0.23
0.14
0.12
0.11
NUMBER
PERCENTAGE
OF MnS
AND CaS
(%)
5.00
5.00
-
10.00
-
10.00
-
-
5.00
5.00
4.00
4.00
7.00
-
25.00
25.00
25.00
25.00
25.00
25.00
ELONGATED INCLUSIONS OBSERVED MAINLY
calcium aluminate
calcium aluminate,residual desulfurizing agent
none
residual desulfurizing agent
none
residual desulfurizing agent
none
none
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
none
calcium aluminate,CaS
calcium aluminate,CaS
calcium aluminate,CaS
calcium aluminate,CaS
calcium aluminate.CaS
calcium aluminate.CaS
The underlined value in the table indicates out of the range of the present invention.
TABLE 8-3
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
STEEL
COMPOSITION
U
V
w
X
Y
Z
AA
BB
A
A
A
A
A
A
A
A
A
A
A
A
A
METALLOGRAPHIC STRUCTURE
CONSTITUENT METALLIC PHASE
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residuaI austenite
ferrite.bainite
ferrite.pearlite. bainite
PRIMARY PHASE
FERRITE (F)
AREA
FRACTION
F
93.5
93.2
92.8
93.0
93.1
93.0
93.8
83.7
93.1
93.1
93.1
93.1
93.1
93.1
93.1
93.1
93.1
93.1
93.0
95.5
94.5
AVERAGE
GRAIN
SIZE
4.19
4.22
4.20
4.20
4.20
4.20
4.15
4.15
4.24
4.20
4.20
3.90
4.20
6.00
10.20
3.70
3.70
10.05
10.10
4.90
5.50
SECONDARY PHASE
MARTENSITE (M) AND
RESIDUAL AUSTENITE ( r)
AREA FRACTION
M
(%)
5.3
5.9
6.0
6.4
6.2
5.8
5.6
12.8
5.7
6.1
6.5
5.1
5.5
6.1
5.5
5.7
5.9
5.8
6.0
0.0
0.0
r
(%)
1.2
0.9
1.2
0.6
0.7
1.2
0.6
3.5
1.2
0.8
0.4
1.8
1.4
0.8
1.4
1.2
1.0
1.1
1.0
0.0
0.0
M+r
(%)
6.5
6.8
7.2
7.0
6.9
7.0
6.2
16.3
6.9
6.9
6.9
6.9
6.9
6.9
6.9
6.9
6.9
6.9
7.0
0.0
00
AVERAGE
GRAIN
SIZE
3.3
3.4
3.4
3.4
3.4
3.4
3.3
3.3
3.4
3.4
3.4
3.1
3.4
4.8
7.8
3.0
3.0
7.7
7.5
3.9
4.4
AREA
FRACTION
OF BAINITE
(%)
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
4.50
3.50
AREA
FRACTION
OF
PEARLITE
(%)
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
2.00
The underlined value in the table indicates out of the range of the present invention
TABLE 8-4
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
STEEL
COMPOSITION
U
V
w
X
Y
z
AA
BB
A
A
A
A
A
A
A
A
A
A
A
A
A
TEXTURE
X-RAY
RANDOM
INTENSITY
RATIO OF
{211} PLANE
2.26
2.27
2.31
2.30
2.26
2.32
2.25
2.32
2.30
2.30
2.30
2.50
2.40
2.30
2.25
2.60
3.46
1.84
2.38
2.38
2.38
INCLUSIONS
AVERAGE OF
MAXIMUM OF
RATIO OF
MAJOR
AXIS TO
MINOR AXIS
2.8
2.0
1.0
1.0
3.0
4.0
9.0
1.3
3.0
§£
8.0
3.0
2.9
5.0
7.0
3.0
3.0
3.0
3.0
3.0
3.0
TOTAL
LENGTH M
IN ROLLING
DIRECTION
(mm/mm2)
0 . 21
0.20
0.10
0.00
0.25
0.40
0.30
0.24
0.06
0.48
0.25
0.25
0.24
0.15
0.20
0.06
0.06
0.06
0.06
0.06
0.06
NUMBER
PERCENTAGE
OF MnS
AND CaS
(%)
20.00
20.00
7.00
5-00
20.00
50.00
75.00
10-00
5.00
5.00
5.00
5.00
5.00
5.00
5.00
5.00
5.00
5.00
5.00
5.00
5.00
ELONGATED INCLUSIONS OBSERVED MAINLY
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate.MnS
MnS
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
The underlined value in the table indicates out of the range of the present invention.
TABLE 9-1
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
STEEL
COMPOSITION
CC
DD
EE
FF
GG
HH
II
JJ
KK
LL
MM
NN
00
PP
QQ
RR
SS
TT
UU
W
METALLOGRAPHIC STRUCTURE
CONSTITUENT METALLIC PHASE
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite,martensite, residuaI austenite
ferrite.martensite.residual austenite
ferrite.martensite,residual austenite
ferrite.martensite.residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite.residual austenite
ferrite.martensite,residual austenite
ferrite.martensite.residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
PRIMARY PHASE
FERRITE (F)
AREA
FRACTION
F
95.7
93.8
92.8
93.5
92.4
90.5
93.0
93.1
93.5
99.1
93.4
96.9
92.4
92.1
93.1
93.0
92.8
93.8
93.2
93.1
AVERAGE
GRAIN
SIZE
(um)
5.22
4.25
4.22
4.16
4.19
4.20
4.19
4.20
5.40
10.09
4.30
5.90
4.22
4.21
4.17
4.21
4.18
4.20
4.17
4.25
SECONDARY PHASE
MARTENSITE (M) AND
RESIDUAL AUSTENITE (r)
AREA FRACTION
M
(%)
3.2
4.7
5.4
4.9
5.7
7.1
5.3
5.2
4.9
0/7
5.0
2.3
5.7
6.0
5.2
5.3
5.4
4.7
5.1
5.2
r
(%)
1.1
1.6
1.8
1.6
1.9
2.4
1.8
1.7
1.6
0.2
1.7
0.8
1.9
2.0
1.7
1.8
1.8
1.6
1.7
1.7
M+r
(»
4.3
6.2
7.2
6.5
7.6
9.5
7.0
6.9
6.5
0.9
6.6
3.1
7.6
7.9
6.9
7.0
7.2
62
6.8
6.9
AVERAGE
GRAIN
SIZE
4.2
3.4
3.4
3.3
3.4
3.4
3.4
3.4
4.3
7.7
3.4
4.7
3.4
3.4
3.3
3.4
3.3
3.4
3.3
3.4
AREA .
FRACTION
OF BAINITE
(%)
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
AREA
FRACTION
OF
PEARLITE
(%)
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
o.oo
The underlined value in the table indicates out of the range of the present invention.
TABLE 9-2
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
STEEL
COMPOSITION
CG
DD
EE
FF
GG
HH
II
JJ
KK
LL
MM
NN
00
PP
QQ
RR
SS
TT
UU
W
TEXTURE
X-RAY
RANDOM
INTENSITY
RATIO OF
(211) PLANE
2.31
2.30
2.25
2.32
2.31
2L27
• 2.00
2.05
2.30
2.30
2.27
2.27
2.27
2.27
2.28
2.29
228
229
2.28
2.26
INCLUSIONS
AVERAGE OF
MAXIMUM OF
RATIO OF
MAJOR
AXIS TO
MINOR AXIS
3.0
1.5
1.0
1.5
4.5
4.5
1.0
1.0
2.0
2.0
2.8
3.0
3.0
1.0
8.0
8.0
7.0
5.8
4.8
4.0
TOTAL
LENGTH M
IN ROLLING
DIRECTION
(mm/mm2)
0 . 03
0.04
0.22
0.02
0.24
0.02
0.17
0.18
0.05
0.10
0.14
0.12
0.12
0.18
0.13
0.19
0.23
0.14
0.12
0.11
NUMBER
PERCENTAGE
OF MnS
AND CaS
(%)
5.00
5.00
-
5.00
-
5.00
-
-
17.50
20.00
22.50
20.00
20.00
-
20.00
20.00
20.00
20.00
20.00
20.00
ELONGATED INCLUSIONS OBSERVED MAINLY
calcium aluminate
calcium aluminate,residual desulfurizing agent
none
residual desulfurizing agent
none
residual desulfurizing agent
none
none
residual desulfurizing agent.CaS
calcium aluminate,CaS
calcium aluminate.REM oxide.CaS
calcium aluminate.REM oxide.CaS
calcium aluminate.REM oxide.CaS
none
calcium aluminate,CaS
calcium aluminate,CaS
calcium aluminate,CaS
calcium aluminate,CaS
calcium aluminate,CaS
calcium aluminate,CaS
The underlined value in the table indicates out of the range of the present invention.
TABLE 9-3
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
STEEL
COMPOSITION
WW
XX
YY
ZZ
AAA
BBB
CCC
DDD
CC
CO
CC
CC
CC
CC
CC
CC
CC
CC
CC
CC
METALLOGRAPHIC STRUCTURE
CONSTITUENT METALLIC PHASE
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.nartensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite,martensite,residual austenite
ferrite.martensite.residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite.residual austenite
ferrite.nartensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite.residual austenite
ferrite.martensite,residual austenite
ferrite.pearlite.bainite
ferrite.bainite
PRIMARY PHASE
FERRITE (F)
AREA
FRACTION
F
93.5
93.2
92.8
93.0
93.1
93.0
93.8
83.7
95.7
93.1
93.1
93.1
93.1
93.1
93.1
93.1
93.1
93.1
93.9
95.2
AVERAGE
GRAIN
SIZE
(#m)
4.19
4.22
4.20
4.20
4.20
4.20
4.15
4.15
4.24
4.20
4.20
3.90
4.20
6.00
10.10
3.70
3.70
10.08
10.10
4.90
SECONDARY PHASE
MARTENSITE (M) AND
RESIDUAL AUSTENITE ( r )
AREA FRACTION
M
«)
4.9
5.1
5.4
5.3
5.2
5.3
4.7
12.2
3.2
5.2
5.2
5.2
5.2
5.2
5.2
5.2
5.2
5.2
0.0
0.0
r
(%)
1.6
1.7
1.8
1.8
1.7
1.8
1.6
4.1
1.1
1.7
1.7
1.7
1.7
1.7
1.7
1.7
1.7
1.7
0.0
0.0
M+r
00
6.5
6.8
7.2
7.0
6.9
7.0
6.2
16.3
4.3
6.9
6.9
6.9
6.9
6.9
6.9
6.9
6.9
6.9
0.0
0.0
AVERAGE
GRAIN
SIZE
(um)
3.3
3.4
3.4
3.4
3.4
3.4
3.3
3.3
3.4
3.4
3.4
3.1
3.4
4.8
7.8
3.0
3.0
7.6
7.7
3.9
AREA
FRACTION
OF BAINITE
(%)
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
5.10
4.80
AREA
FRACTION
OF
PEARLITE
(%)
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
1.00
0.00
The underlined value in the table indicates out of the range of the present invention.
TABLE 9-4
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
STEEL
COMPOSITION
WW
XX
YY
ZZ
AAA
BBB
GCC
DDD
CC
CC
CC
CC
CC
CC
CC
CC
CC
CC
CC
CC
TEXTURE
X-RAY
RANDOM
INTENSITY
RATIO OF
(211) PLANE
2.26
2.27
2.31
2.30
2.26
2.32
2.25
2.32
2.30
2.30
2.30
2.50
2.40
2.30
2.25
2.60
3.46
1.84
2.38
2.38
INCLUSIONS
AVERAGE OF
MAXIMUM OF
RATIO OF
MAJOR
AXIS TO
MINOR AXIS
2.8
2.0
1.0
1.0
3.0
4.0
9.0
1.3
3.0
9.0
8.0
3.0
2.9
5.0
7.0
3.0
3.0
3.0
3.0
3.0
TOTAL
LENGTH M
IN ROLLING
DIRECTION
(mm/mm2)
0.21
0.20
0.10
0.00
0.25
0.40
0.45
0.24
0.06
0.48
0.25
0.25
0.24
0.15
0.20
0.06
0.06
0.06
0.06
0.06
NUMBER
PERCENTAGE
OF MnS
AND CaS
(%)
19.00
10.00
10.00
17.50
21.50
40.00
75.00
10.00
5.00
5.00
5.00
5.00
5.00
5.00
5.00
5.00
5.00
5.00
5.00
5.00
ELONGATED INCLUSIONS OBSERVED MAINLY
calcium aluminate.REM oxide,CaS
calcium aluminate
calcium aluminate
calcium aluminate.REM oxide.CaS
calcium aluminate.REM oxide.CaS
calcium aluminate,MnS
MnS
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
The underlined value in the table indicates out of the range of the present invention.
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TABLE 10-1
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
82
83
84
85
86
87
89
90
91
92
93
94
95
96
97
98
99
100
101
STEEL
COMPOSITION
EEE
FFF
GGG
HHH
JJJ
A
A
KKK
A
A
A
LLL
MMM
NNN
OOO
PPP
QQQ
RRR
SSS
METALLOGRAPHIC STRUCTURE
CONSTITUENT METALLIC PHASE
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite, pear lite, bainite
ferrite.martensite,residual austenite
ferrite.martensite.residual austenite
ferrite.martensite,residual austenite.pearlite.bainite
ferrite.martensite.residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
f err ite, martens ite, residua 1 austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite.residual austenite
ferrite.martensite, residual austenite
ferrite.martensite,residual austenite
PRIMARY PHASE
FERRITE (F)
AREA
FRACTION
F
93.1
93.9
93.9
88.5
94.1
92.6
91.0
95.5
S9-X!
89.0
89.0
93.1
93.1
93.1
93.1
88.7
87.6
93.2
93.8
AVERAGE
GRAIN
SIZE
(lim)
4.60
5.10
5.20
4.20
4.50
9.80
4.50
9.40
4.90
5.20
4.00
4.22
4.20
6.00
6.00
5.90
5.90
4.21
4.25
SECONDARY PHASE
MARTENSITE (M) AND
RESIDUAL AUSTENITE ( r)
AREA FRACTION
M
(%)
5.8
5.6
6.1
9.0
5.4
6.4
4-5
4.0
9.0
2.0
8.0
5.9
5.2
6.1
6.1
8.9
9.5
5.8
4.7
r
(%)
1.1
0.5
0.0
2.5
0.5
1.0
0.0
0.5
2.0
1.0
3.0
1.0
1.7
0.8
0.8
2.4
2.9
1.0
1.6
M+r
«)
6.9
6.1
6.1
11.5
5.9
7.4
4,5
4.5
11.0
3.0
Ufl
6.9
6.9
6.9
6.9
11.3
1M
6.8
6.2
AVERAGE
GRAIN
SIZE
(.find
3.7
4.1
4.2
3.4
3.6
7.8
3.6
7.8
3.9
4.2
3.2
3.4
3.4
4.8
4.8
4.7
4.7
3.4
3.4
AREA
FRACTION
OF BAINITE
(%)
0.00
0.00
0.00
0.00
0.00
0.00
2.00
0.00
0.00
2.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
AREA
FRACTION
OF
PEARLITE
(%)
0.00
0.00
0.00
0.00
0.00
0.00
2.50
0.00
0.00
6.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
The underlined value in the table indicates out of the range of the present invention.
TABLE 10-2
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
82
83
84
85
86
87
89
90
91
92
93
94
95
96
97
98
99
100
101
STEEL
COMPOSITION
EEE
FFF
GGG
HHH
JJJ
A
A
KKK
A
A
A
LLL
MMM
NNN
OOO
PPP
QQQ
RRR
SSS
TEXTURE
X-RAY
RANDOM
INTENSITY
RATIO OF
[211) PLANE
2.15
2.00
2.20
2.30
2.20
2.30
2.30
2.00
2.30
2.30
2.30
2.31
2.30
2.30
2.30
2.27
2.27
2.32
2.30
INCLUSIONS
AVERAGE OF
MAXIMUM OF
RATIO OF
MAJOR
AXIS TO
MINOR AXIS
1.0
8.0
1 2 .0
2.9
6.0
3.0
3.0
4.0
3.0
3.0
3.0
3.0
8.0
5.0
5.0
3.0
3.0
2.9
1.5
TOTAL
LENGTH M
IN ROLLING
DIRECTION
(mm/mm2)
0.21
0.20
0.60
0.03
0.45
0.03
0.03
0.25
0.25
0.03
0.03
0.03
0.25
0.15
0.15
0.12
0.12
0.18
0.04
NUMBER
PERCENTAGE
OF MnS
AND CaS
(%)
5.00
5.00
80.00
5.00
65.00
5.00
5.00
50.00
5.00
5.00
5.00
5.00
5.00
5.00
5.00
20.00
20.00
5.00
5.00
ELONGATED INCLUSIONS OBSERVED MAINLY
MnS
calcium aluminate
MnS
calcium aluminate
MnS
calcium aluminate
calcium aluminate
CaS, MnS
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium alum inate, REM oxide, CaS
calcium a I urn inate, REM oxide, CaS
calcium aluminate
calcium aluminate,residual desulfurizing agent
The underlined value in the table indicates out of the range of the present invention.
TABLE 10-3
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
STEEL
COMPOSITION
TTT
UUU
VVV
WWW
XXX
YYY
ZZZ
AAAA
BBBB
CCCC
DDDD
EEEE
FFFF
GGGG
HHHH
mi
JJJJ
KKKK
LLLL
MMMM
METALLOGRAPHIC STRUCTURE
CONSTITUENT METALLIC PHASE
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite, residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite.residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
ferrite.martensite,residual austenite
PRIMARY PHASE
FERRITE (F)
AREA
FRACTION
F
92.8
93.1
93.9
92.8
93.1
93.9
93.1
93.1
93.1
93.1
93.1
93.1
93.1
93.4
92.4
93.5
92.1
92.1
93.5
93.2
AVERAGE
GRAIN
SIZE
0/m)
4.22
4.60
5.10
4.22
4.60
5.10
422
4.22
422
422
4.22
4.22
4.22
3.91
4.23
4.19
4.21
421
4.19
4.22
SECONDARY PHASE
MARTENSITE (M) AND
RESIDUAL AUSTENITE ( r )
AREA FRACTION
M
«)
5.7
5.8
5.6
5.4
5.8
5.6
5.9
5.9
5.9
5.9
5.9
5.9
5.9
5.4
7.1
5.3
6.4
6.4
5.3
5.9
r
00
1.5
1.1
0.5
1.8
1.1
0.5
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.2
0.5
1.2
1.5
1.5
1.2
0.9
M+r
(%)
7.2
6.9
6.1
7.2
6.9
6.1
6.9
6.9
6.9
6.9
6.9
6.9
6.9
6.6
7.6
6.5
7.9
7.9
6.5
6.8
AVERAGE
GRAIN
SIZE
3.4
3.7
4.1
3.4
3.7
4.1
3.4
3.4
3.4
3.4
3.4
3.4
3.4
3.1
3.4
3.3
3.4
3.4
3.3
3.4
AREA
FRACTION
OF BAINITE
00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
o.oo •
0.00
0.00
AREA
FRACTION
OF
PEARLITE
«)
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
The underlined value in the table indicates out of the range of the present invention.
TABLE 10-4
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
STEEL
COMPOSITION
TTT
UUU
VVV
WWW
XXX
YYY
ZZZ
AAAA
BBBB
OCGC
DDDD
EEEE
FFFF
GGGG
HHHH
UH
JJJJ
KKKK
LLLL
MMMM
TEXTURE
X-RAY
RANDOM
INTENSITY
RATIO OF
[211} PLANE
2.25
Z.15
2.00
2.25
2.15
2.00
2.58
2.61
2.31
2.31
2.31
2.31
2.31
2.27
221
2.26
2.27
2.27
2.26
2.27
INCLUSIONS
AVERAGE OF
MAXIMUM OF
RATIO OF
MAJOR
AXIS TO
MINOR AXIS
1.0
1.0
1LQ
mi
10.5
11.2
3.0
3.0
3.0
3.0
3.0
3.0
3.0
2.8
3.0
2.8
1.0
1.0
2.8
2.0
TOTAL
LENGTH M
IN ROLLING
DIRECTION
(mm/mm2)
0.00
0.21
0.51
0.48
0.53
0.49
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.14
0.12
0.21
0.00
0.00
0.21
0.20
NUMBER
PERCENTAGE
OF MnS
AND CaS
(%)
-
5.00
5.00
5.00
5.00
5.00
5.00
5.00
5.00
5.00
5.00
5.00
5.00
5.00
7.00
20.00
-
-
20.00
20.00
ELONGATED INCLUSIONS OBSERVED MAINLY
none
MnS
calcium aluminate
MnS
MnS
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
calcium aluminate
none
none
calcium aluminate
calcium aluminate
The underlined value in the table indicates out of the range of the present invention.
TABLE 11-1
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
STEEL
COMPOSITION
A
B
C
D
E
F
G
H
I
J
K
L
M
N
0
P
Q
R
S
T
MECHANICAL PROPERTIES
TENSILE
PROPERTIES
TENSILE
STRENGTH
TS
(MPa)
820
800
815
790
790
790
824
825
824
704
772
765
815
790
790
790
790
790
790
790
n VALUE
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0.14
0.15
0.14
0.12
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0.13
FORMABILITY
HOLE EXPANSION TEST
AVERAGE
Aave
(%)
68
75
75
75
64
64
90
90
65
75
61
62
65
83
63
62
61
60
61
62
STANDARD
DEVIATION
a
(A)
10
9
7
8
13
11
7
7
9
10
10
9
10
8
15
15
15
13
10
11
FRACTURE PROPERTIES
THREE POINT
BENDING TEST
RESISTANCE
OF CRACK
INITIATION
Jc
(MJ/m3)
0.60
0.69
0.69
0.69
0.55
0.55
0.88
0.88
0.56
0.69
0.51
0.52
0.56
0.79
0.54
0.52
0.51
0.50
0.51
0.52
RESISTANCE
OF CRACK
PROPAGATION
T.M.
(MJ/m3)
893
880
933
906
933
906
933
933
746
693
773
786
773
933
760
680
626
746
773
786
CHARPY TEST
FRACTURE
APPEARANCE
TRANSITION
TEMPERATURE
vTrs
(°C)
ABSORBED
ENERGY
E(J)
-62 23.4
-61
-62
-64
-63
-63
-63
-63
-79
-63
0
6
-71
-63
-64
-63
-63
-63
-64
-62
27.4
27.4
27.4
21.2
21.2
36.0
36.0
21.7
27.4
19.5
20.0
21.7
32.0
20.6
20.0
19.5
18.9
19.5
20.0
FATIGUE
PROPERTIES
FATIGUE
LIFE
(times)
676000
668000
700000
684000
700000
684000
700000
700000
588000
556000
604000
480000
604000
700000
596000
548000
516000
588000
604000
612000
The underlined value in the table indicates out of the range of the present invention.
TABLE 11-2
^©
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
STEEL
COMPOSITION
U
V
w
X
Y
2
AA
BB
A
A
A
A
A
A
A
A
A
A
A
A
A
MECHANICAL PROPERTIES
TENSILE
PROPERTIES
TENSILE
STRENGTH
TS
(MPa)
790
790
790
790
790
790
794
820
774
785
790
790
790
790
790
802
810
785
790
775
774
n VALUE
0.13
0.13
0.13
0.13
0,13
0.13
0.13
0.13
0.14
0.14
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0.11
0.11
FORMABILITY
HOLE EXPANSION TEST
AVERAGE
Aave
00
65
68
80
67
65
50
40
45
66
40
60
52
65
65
62
53
45
60
60
60
60
STANDARD
DEVIATION
a
(A)
9
8
7
8
10
18
20
8
10
18
10
10
9
9
10
10
10
10
10
9
10
FRACTURE PROPERTIES
THREE POINT
BENDING TEST
RESISTANCE
OF CRACK
INITIATION
Jc
(MJ/m3)
0.56
0.60
0.75
0.59
0.56
0.37
0.25
0.31
0.57
025
0.50
6.40
0.56
0.56
0.52
0.41
0.31
0.50
0.50
0.50
0.50
RESISTANCE
OF CRACK
PROPAGATION
T.M.
(MJ/m3)
653
666
800
933
602
400
533
613
853
293
600
600
613
733
666
853
853
853
853
853
853
CHARPY TEST
FRACTURE
APPEARANCE
TRANSITION
TEMPERATURE
vTrs
PC)
-63
-62
-63
-63
-63
-63
-64
-64
-62
-63
-63
-71
-63
-14
-8
-77
-77
-11
-11
-44
-27
ABSORBED
ENERGY
E(J)
21.7
23.4
30.3
22.9
21.7
13.2
7.5
10.3
22.3
7.5
18.9
14.3
21.7
21.7
20.0
14.9
10.3
18.9
18.9
18.9
18.9
FATIGUE
PROPERTIES
FATIGUE
LIFE
(times)
532000
540000
620000
700000
501600
380000
460000
508000
652000
316000
500000
500000
508000
580000 '
540000
652000
652000
652000
652000
360000
350000
The underlined value in the table indicates out of the range of the present invention.
"^p
TABLE 12-1
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
STEEL
COMPOSITION
cc
DD
EE
FF
QG
HH
n
JJ
KK
LL
MM
NN
0 0
PP
QQ
RR
SS
TT
UU
W
MECHANICAL PROPERTIES
TENSILE
PROPERTIES
TENSILE
STRENGTH
TS
(MPa)
600
610
615
600
600
600
610
621
600
575
609
595
600
608
600
600
600
600
600
600
n VALUE
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.12
0.16
0.16
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
FORMABILITY
HOLE EXPANSION TEST
AVERAGE
Aave
(»
98
105
105
105
94
94
120
120
100
100
95
95
95
113
93
92
91
90
91
92
STANDARD
DEVIATION
a
(A)
10
9
7
8
13
11
7
7
8
8
9
10
10
8
15
15
15
13
10
11
FRACTURE PROPERTIES
THREE POINT
BENDING TEST
RESISTANCE
OF CRACK
INITIATION
Jc
(MJ/m3)
1.00
1.09
1.09
1.09
0.95
0.95
1.27
1.27
1.02
1.02
0.96
0.96
0.96
1.19
0.93
0.92
0.91
0.90
0.91
0.92
RESISTANCE
OF CRACK
PROPAGATION
T.M.
(MJ/m3)
893
880
640
906
613
906
706
693
866
800
746
773
773
693
760
680
626
746
773
786
CHARPY TEST
FRACTURE
APPEARANCE
TRANSITION
TEMPERATURE
vTrs
CO
-35
-61
-62
-64
-63
-63
-63
-63
-30
3
-60
-16
-62
-63
-64
-63
-63
-63
-64
-62
ABSORBED
ENERGY
E(J)
41.4
45.4
45.4
45.4
39.2
39.2
54.0
54.0
42.6
42.6
39.7
39,7
39.7
50.0
38.6
38.0
37.5
36.9
37.5
38.0
FATIGUE
PROPERTIES
FATIGUE
LIFE
(times)
576000
568000
424000
584000
408000
584000
464000
456000
560000
310000
488000
504000
504000
456000
496000
448000
416000
488000
504000
512000
CO
i GO
0 r
The underlined value in t he t a b le indicates out of the range of the present invention.
w^^i^^^s^^^^^^^
TABLE 12-2
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
STEEL
COMPOSITION
WW
XX
YY
zz
AAA
BBB
CCC
DDD
cc
cc
cc
cc
cc
cc
cc
cc
cc
cc
cc
cc
MECHANICAL PROPERTIES
TENSILE
PROPERTIES
TENSILE
STRENGTH
TS
(MPa)
610
608
600
600
600
600
604
630
584
595
600
600
600
600
600
612
620
595
585 m
n VALUE
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.16
0.16
0.15
0.15
0.15
0.15
0.15
0.15
0.14
0.15
0.12
0.11
FORMABILITY
HOLE EXPANSION TEST
AVERAGE
Aave
«)
95
98
110
97
95
80
70
58
96
70
90
57
95
95
92
56
58
90
91
90
STANDARD
DEVIATION
a
(A)
9
8
7
8
10
18
20
8
10
18
10
10
9
9
10
10
10
10
8
8
FRACTURE PROPERTIES
THREE POINT
BENDING TEST
RESISTANCE
OF CRACK
INITIATION
Jc
(MJ/m3)
0.96
1.00
1.15
0.98
0.96
0.77
0.64
0.48
0.97
0.64
0.90
0.49
0.96
0.96
0.92
0.47
0.49
0.90
0.91
0.90
RESISTANCE
OF CRACK
PROPAGATION
T.M.
(MJ/m3)
. 653
666
800
933
602
400
333
613
853
293
600
600
613
733
666
853
853
853
853
853
CHARPY TEST
FRACTURE
APPEARANCE
TRANSITION
TEMPERATURE
vTrs ro
-63
-62
-63
-63
-63
-63
-64
-64
-62
-63
-63
-71
-63
-14
-11
-77
-77
-11
-11
-44
ABSORBED
ENERGY
E(J)
39.7
41.4
48.3
40.9
39,7
31.2
25.5
15.6
40.3
25.5
36.9
15.8
39.7
39.7
38.0
15.7
15.9
36.9
37.5
36.9
FATIGUE
PROPERTIES
FATIGUE
LIFE
(times)
432000
440000
520000
600000
401600
280000
240000
408000
552000
216000
400000
400000
408000
480000
440000
552000
552000
-552000
340000
330000
The underlined value in the table indicates out of the range of the present invention.
TABLE 13-1
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
82
83
84
85
86
87
89
90
91
92
93
94
95
96
97
98
99
100
101
STEEL
COMPOSITION
EEE
FFF
GGG
HHH
JJJ
A
A
KKK
A
A
A
LLL
MMM
NNN
OOO
PPP
QQQ
RRR
SSS
MECHANICAL PROPERTIES
• TENSILE
PROPERTIES
TENSILE
STRENGTH
TS
(MPa)
590
600
595
850
600
810
815
820
855
585.
830
820
572
981
983
584
522
704
578
n VALUE
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0.12
0.13
0.13
0.15
0.13
0.13
0.12
0.12
0.15
0.15
FORMABILITY
HOLE EXPANSION TEST
AVERAGE
Aave
«)
69
63
45
55
50
64
65
63
56
65
58
58
90
57
55
95
95
56
105
STANDARD
DEVIATION
a
(A)
8
15
22
13
18
12
10
12
13
13
13
10
10
15
15
10
10
10
9
FRACTURE PROPERTIES
THREE POINT
BENDING TEST
RESISTANCE
OF CRACK
INITIATION
Jc
(MJ/m3)
0.61
0.54
0.31
0.44
0.37
0.55
0.56
0.54
0.45
0.56
0.47
0.46
0.90
0.56
0.56
0.96
0.96
0.44
1.09
RESISTANCE
OF CRACK
PROPAGATION
T.M.
(MJ/m3)
653
666
133
893
333
893
893
600
600
893
893
893
600
733
733
773
773
693
880
CHARPY TEST
FRACTURE
APPEARANCE
TRANSITION
TEMPERATURE
vTrs
(°C)
-77
-66
-64
-86
-79
-14
-79
-14
-70
-64
-90
-62
-63
-14
-14
-16
-16
-63
-61
ABSORBED
ENERGY
E(J)
24.0
20.6
10.3
15.4
13.2
21.2
17.2
20.6
15.7
21.7
15.8
15.6
36.9
21.7
21.7
39.7
39.7
15.3
45.4
FATIGUE
PROPERTIES
FATIGUE
LIFE
(times)
532000
540000
220000
676000
340000
676000
400000
500000
500000
376000
676000
676000
400000
580000
580000
384000
391000
556000
568000
The underlined value in the table indicates out of the range of the present invention.
TABLE 13-2
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
STEEL
COMPOSITION
TTT
UUU
VW
WWW
XXX
YYY
ZZZ
AAAA
BBBB
cccc
DDDD
EEEE
FFFF
GGGG
HHHH
1111
JJJJ
KKKK
LLLL
MMMM
MECHANICAL PROPERTIES
TENSILE
PROPERTIES
TENSILE
STRENGTH
TS
(MPa)
982
595
600
600
590
595
820
820
m.
983
9J2
981
982
791
785
781
782
780
782
781
n VALUE
0.13
0.13
0.13
0.15
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0.13
FORMABILITY
HOLE EXPANSION TEST
AVERAGE
Aave
«)
59
56
57
65
55
57
56
58
54
53
54
52
55
65
65
65
83
83
65
68
STANDARD
DEVIATION
a
(A)
7
8
19
18
20
19
10
10
10
10
10
10
10
9
10
9
8
8
9
8
FRACTURE PROPERTIES
THREE POINT
BENDING TEST
RESISTANCE
OF CRACK
INITIATION
Jc
(MJ/m3)
0.48
0.46
0.44
0.51
0.49
0.48
0.44
0.42
0.60
0.60
0.60
0.60
0.60
0.56
0.56
0.56
0.79
0.79
0.56
0.60
RESISTANCE
OF CRACK
PROPAGATION
T.M.
(MJ/m3)
933
653
297
302
288
300
893
893
893
893
893
893
893
746
773
653
933
933
653
666
CHARPY TEST
FRACTURE
APPEARANCE
TRANSITION
TEMPERATURE
vTrs
CO
-62
-77
-66
-62
-77
-66
-62
-62
-62
-62
-62
-62
-62
-79
-71
-63
-63
-63
-63
-62
ABSORBED
ENERGY
E(J)
15.7
15.5
14.8
16.3
15.8
15.2
15.1
14.9
23.4
23.4
23.4
23.4
23.4
21.7
21.7
21.7
32.0
32.0
21.7
23.4
FATIGUE
PROPERTIES
FATIGUE
LIFE
(times)
700000
532000
213000
230000
222000
232000
676000
676000
676000
676000
676000
676000
676000
588000
604000
532000
700000
700000
532000
540000
The underlined value in the table indicates out of the range of the present invention.