STEEL MATERIAL FOR HARDENING AND METHOD FOR PRODUCING THE
SAME
Technical Field
[0001]
The present invention relates to a steel material for hardening having excellent
machinability and hardening stability, and a method for producing the steel material.
The present application claims priority based on Japanese Patent Application
No. 2010-124536 filed in Japan on May 31, 2010, the contents of which are
incorporated herein by reference.
Background Art
[0002]
In recent years, steels have become increasingly stronger , but this causes a
problem of deterioration in workability. Thus, there is a strong demand for steels
having improved machinability while maintaining the strength. Conventionally, in
order to improve the machinability of the steel, elements such as S, Pb, and Bi have
been added for improving the machinability. Pb and Bi improve the machinability and
have a relatively small effect on the forging, but deteriorate properties related to
strength such as impact properties.
[0003]
Further, the element S forms a soft inclusion such as MnS under cutting
environments, thereby improving the machinability. However, MnS has a size larger
than Pb or other particles, and hence, is likely to form a source of stress concentration.
In particular, when MnS is stretched through forging or rolling, this causes anisotropy in
impact properties and the like, and mechanical properties become significantly weak in
a specific direction. This anisotropy of mechanical properties has to be taken into
consideration in the case of designing a steel structure . Thus, it is necessary to employ
I
a technique for reducing the anisotropy in the mechanical properties in the case when S
is added to the steel.
[0004]
As described above, even if elements effective in improving the machinability
are added, the impact properties deteriorate, and hence, it is difficult to achieve both the
strength and the machinability at the same time. Further, in recent years, from the
viewpoint of environmental protection, there is a tendency to avoid using Pb. Thus,
further technical innovations are required to achieve both the machinability and the
strength of the steel.
[0005]
Conventionally, there are several technical proposals for improving the
machinability without deteriorating the strength. Patent Document I proposes a steel
for a machine structure including: C: 0.05 to 1.2% (mass%, the same applies to the
following elements); Si: 0.03 to 2%; Mn: 0.2 to 1.8%; P: 0.03% or lower (not including
0%); S: 0.03% or lower (not including 0%); Cr: 0.1 to 3%; Al: 0.06 to 0.5%; N: 0.004 to
0.025%; and 0: 0.003% or lower (not including 0%), the steel further including Ca:
0.0005 to 0.02% and/or Mg: 0.0001 to 0.005%, and the steel including solute N:
0.002% or more, with a balance including iron and inevitable impurities, and the steel
satisfying the following relationship of Expression (A).
[0006]
(01 x [Cr] + [AI])/[O] > 150 Expression (A)
where [Cr], [Al] and [ 0] represent amounts (mass% ) of Cr, Al and 0, respectively.
[0007]
Patent Document 2 proposes a steel for a machine structure, the steel including:
C: 0.01 to 0.7%; Si: 0.01 to 2.5%; Mn: 0.1 to 3%; S: 0.01 to 0.16%; and Mg: 0.02% or
lower (not including 0%), the steel satisfying [Mg]/[S] > 7.7 x 10-3, in which, of
sulfide-based inclusions observed in the steel, an average value of an aspect ratio of the
sulfide-based inclusion having a long span of 5 μm or more is 5.2 or lower, and an
2
average value of an aspect ratio of the sulfide-based inclusion having a long span of 50
pm or more is 10.8 or lower, and in which the steel satisfies alb < 0.25, where a
reference character a represents the number of sulfide-based inclusions having a long
span of 20 μm or more, and a reference character b represents the number of
sulfide-based inclusions having a long span of 5 μm or more.
[0008]
Patent Document 3 proposes a steel for carburizing, the steel including:
C: 0.12 to 0.22%; Si: 0.40 to 1.50%; Mn: 0.25 to 0.45%; Ni: 0.50 to 1.50%; Cr: 1.30 to
2.30%; B: 0.0010 to 0.0030%; Ti: 0.02 to 0.06%; Nb: 0.02 to 0.12%; and Al: 0.005 to
0.050%, with a balance substantially consisting of iron, in which a distance from a
quenching end to a position having a hardness corresponding to 50% martensite in an
end quenching test is 20 mm or more, and a component parameter H (H - 106C(%) +
10.8Si(%) + 19.9Mn(%) + 16.7Ni(%) + 8.55Cr(%) + 45.5Mo(%) + 28) is 95 or less.
Related Art Documents
Patent Documents
[0009]
Patent Document 1: Japanese Examined Patent Application, Second
Publication No. 4193998
Patent Document 2: Japanese Examined Patent Application, Second
Publication No. 3706560
Patent Document 3: Japanese Unexamined Patent Application, First
Publication No. 2002-309342
Non-patent Document
[0010]
Non-patent Document 1: "Yakiiresei (Hardening of steels)--Motomekata to
katsuyou (How to obtain and its use)--," (author: OWAKU Shigeo, publisher: Nikkan
Kogyo Shimbun, publishing date: September 25, 1979)
3
Disclosure of the Invention
Problems to be Solved by the Invention
[0011]
The techniques proposed by Patent Documents 1 to 3 have the following
problems, and cannot sufficiently meet the demand to improve the machinability
without deteriorating the strength.
[0012]
The steel proposed by Patent Document 1 improves the lifetime of cutting tools.
However, it contains a relatively large amount of Al, which is an element generating
nitride, of 0.06% to 0.5%, and hence, Nis fixed with Al to be A1N. This makes B
added by 0.005% or lower become a solute state, improving the hardenability according
to the amount of B. However, the solute B significantly achieves the effect of
improving the hardenability even if the amount of B is small. Thus, it is difficult to
suppress the variation in the hardenability (in other words, to achieve stable hardening).
[0013]
With the steel proposed by Patent Document 2, the lifetime of the cutting tool
is not taken into consideration, and hence, there is no mention of characteristics for
avoiding the reduction in the lifetime of the cutting tool.
[0014]
The steel proposed by Patent Document 3 can achieve both the high
hardenability and the low material hardness, and hence, it can be considered that the
machinability can be improved without deteriorating the strength after carburizing.
However, the steel contains B of 0.0010% to 0.0030%. This makes the solute B,
which originally improves the hardenability, become BN due to N entering from the
surface layer at the time of gas carburizing. Thus, this steel cannot solve the problem
that the hardenability does not improve in the carburizing surface layer, and the
imperfect hardened structure increases, thereby reducing the strength.
4
[0015]
In other words, with the steel proposed by Patent Document 3, the desired
hardenability cannot be achieved, and the hardenability varies depending on the amount
of N entering from the surface layer, so that the desired hardenability cannot be
obtained in a stable manner.
[0016]
As described above, the conventional techniques cannot sufficiently meet the
currently demanded strength, in other words, cannot solve the problem of improving the
machinability while stably maintaining the hardenability (hardening stability).
[0017]
In view of the circumstances described above, the present invention aims to
solve the problems and provide a steel material for hardening exhibiting excellent
machinability while maintaining the hardenability in a stable manner.
Means for Solving the Problems
[0018]
The present invention employs the following means for solving the problems
described above.
[0019]
(1) A first aspect of the present invention provides a steel material for
hardening, including chemical components, by mass%, of. C: 0.15 to 0.60%; Si: 0.01 to
1.5%; Mn: 0.05 to 2.5%; P: 0.005 to 0.20%; S: 0.001 to 0.35%; Al: over 0.06 to 0.3%;
and total N: 0.006 to 0.03%, with a balance including Fe and inevitable impurities
including B of not more than 0.0004%, in which R and H satisfy H x 0.948 <_ R _< H x
1.05, where the R is a hardness at a position 5 mm away from a quenching end
measured through a Jominy-type end-quenching method specified in JIS G 0561, and
the H is a calculation hardness at a position 4.763 mm away from the quenching end.
(2) The steel material for hardening according to (1) above may contain the
5
chemical components further including, in mass%, one or more of: Cr: 0.1 to 3.0%; Mo:
0.01 to 1.5%; Cu: 0.1 to 2.0%; Ni: 0.1 to 5.0%; Ca: 0.0002 to 0.005%; Zr: 0.0003 to
0.005%; Mg: 0.0003 to 0.005%; REM: 0.0001 to 0.015%; Nb: 0.01 to 0.1%; V: 0.03 to
1.0%; W: 0.01 to 1.0%; Sb: 0.0005 to 0.0150%; Sn: 0.005 to 2.0%; Zn: 0.0005 to 0.5%;
Te: 0.0003 to 0.2%; Bi: 0.005 to 0.5%; and Pb: 0.005 to 0.5%.
(3) The steel material for hardening according to (1) above may contain the
chemical components further including, in mass%, Ti: 0.001 to 0.05%, in which [total
N] and [Ti] may satisfy 0.006 + [Ti] x (14/48) 5 [total N]< _ 0.03, where [total N] is the
total amount (%) of N, and [Ti] is the amount (%) of Ti.
(4) The steel material for hardening according to (3) above may contain the
chemical components further including, in mass%, one or more of. Cr: 0.1 to 3.0%; Me:
0.01 to 1.5%; Cu: 0.1 to 2.0%; Ni: 0.1 to 5.0%; Ca: 0.0002 to 0.005%; Zr: 0.0003 to
0.005%; Mg: 0.0003 to 0.005%; REM: 0.0001 to 0.015%; Nb: 0.01 to 0.1%; V: 0.03 to
1.0%; W: 0.01 to 1.0%; Sb: 0.0005 to 0.0150%; Sn: 0.005 to 2.0%; Zn: 0.0005 to 0.5%;
Te: 0.0003 to 0.2%; Bi: 0.005 to 0.5%; and Pb: 0.005 to 0.5%.
(5) A second aspect of the present invention provides a method for producing a
steel material for hardening, in which a steel piece having the chemical components
according to any one of (1) to (4) above is subjected to a heat treatment in which
heating at a temperature of not less than 1260°C is applied for not less than 20 minutes.
(6) A third aspect of the present invention provides a method for producing a
steel material for hardening, in which a steel piece having the chemical components
according to (3) or (4) above is subjected to a heat treatment in which heating at a
temperature of not less than 1200°C is applied for not less than 20 minutes in the case
where the amount of Ti is not less than 0.019%, and heating at a temperature of not less
than 1150°C is applied for not less than 20 minutes in the case where the amount of Ti
is not less than 0.025%.
(7) A fourth aspect of the present invention provides a power-transmitting part
obtained by subjecting the steel material for hardening according to any one of (1) to (4)
6
above to a machine work and hardening.
Effects of the Invention
[0020]
According to the present invention, the effect of improving the machinability
prolongs the tool life, thereby reducing the production cost. Further, the stable
hardenability is achieved, thereby suppressing the variations in the deformation caused
by the heat treatment.
Embodiments of the Invention
[0021]
In order to solve the problems described above, the present inventors earnestly
studied a relationship between the hardenability and the machinability of a steel material
for hardening in the case of changing chemical components and thermal history of the
steel material for hardening in an extensive and systematic manner. As a result, the
present inventors reached the following findings (A) to (C). Ilereinbelow, the unit
"%" indicating the amount of component means "mass%" unless otherwise specified.
[0022]
(A) If Al exceeds 0.06%, Al exists in the steel as solute Al, thereby improving
the machinability of the steel material for hardening. In particular, by cutting the steel
material for hardening using a tool coated with a coating containing oxide formed of
metal elements having an affinity with oxygen less than or equal to Al, in other words,
oxide having an absolute value of standard free energy of formation less than or equal to
a value of A12O3, the chemical reaction is more likely to occur at a surface of the tool
that is brought into contact with the steel material for hardening. As a result, A12O3
coating functioning as a tool-protection coating is easily generated on the surface of the
tool, thereby prolonging the lifetime of the tool.
[0023]
7
(B) If Al exceeds 0.06%, N is fixed as nitride (AIN). This makes B become a
solute state, and the solute B makes the hardenability unstable.
[0024]
(C) If Al exceeds 0 .06%, the following conditiohs (a) to (c) need to be satisfied
in order to prevent the B having the inevitable impurity volume from affecting the
hardenability.
[0025]
(a) B in the inevitable impurities is limited to 0.0004 mass% or lower.
[0026]
(b) When the total amount (mass%) of N is denoted by [total N] and the
amount (mass%) of Ti is denoted by [Ti], the [total N] and the [Ti] satisfy the following
Equation (1).
0.006 + [Ti] x (14/48) <_ [total N] <_ 0.03 Equation (1)
[0027]
(c) Before the thermal treatment for hardening , a piece of the steel is heated to
the high temperature of 1260°C (or 1200°C or 1150°C depending on the increase in the
Ti amount) or more, and this high temperature is maintained for at least 20 minutes.
[0028]
Next, a description will be made of a mode for carrying out the present
invention made on the basis of the findings described above.
[0029]
First, chemical components of the steel material for hardening according to an
embodiment of the present invention will be described.
[0030]
C: 0.15 to 0.60%
C is an element largely affecting the strength of the steel. In the case where C
is less than 0.15%, sufficient strength cannot be obtained, and it is necessary to add a
large amount of other alloying elements. On the other hand, in the case where C
8
exceeds 0.60%, the hardness increases, and the machinability significantly deteriorates.
In order to obtain sufficient strength and desired machinability, the amount of C is set to
be in the range of 0.15% to 0.60%. The lower limit of Cis set preferably to be 0.30%.
The upper limit of C is set preferably to be 0.50%.
[0031]
Si: 0.01 to 1.5%
Si is an effective element in deoxidizing the steel, and an effective element in
improving the strength of the ferrite and resistance to temper softening. In the case
where Si is less than 0.01%, the effect obtained from the additive is not sufficient, and
in the case where Si exceeds 1.5%, the steel becomes embrittled and the machinability
significantly deteriorates. Further, carburizing properties are inhibited. Thus, the
amount of Si is set to be in the range of 0.01% to 1.5%. The lower limit of Si is set
preferably to be 0.03%. The upper limit of Si is set preferably to be 1.2%.
[0032]
Mn: 0.05 to 2.5%
Mn is an element that fixes and disperses S in the steel as MnS, and is in solid
solution in a matrix manner, thereby contributing to improvement in hardenability and
securing the strength after hardening. In the case where Mn is less than 0.05%, Sin
the steel bonds to Fe to form FeS, and the steel becomes embrittled. On the other hand,
in the case where Mn exceeds 2.5%, the hardness of the base material increases and the
cold workability deteriorates. Further, the effect on the strength and the hardenability
becomes saturated. Thus, the amount of Mn is set to be in the range of 0.05% to 2.5%.
The lower limit of Mn is set preferably to be 0.10%. The upper limit of Mn is set
preferably to be 2.2%.
[0033]
P: 0.005 to 0.20%
P is an element to make the machinability favorable. In the case where P is
less than 0.005%, the effect of the additive cannot be obtained. On the other hand, in
9
the case where P exceeds 0.20%, the hardness of the base material increases, and the
cold workability, hot workability and the casting property deteriorate. Thus, the
amount of Pis set to be in the range of 0.005% to 0.20%. The lower limit of P is set
preferably to be 0.010%. The upper limit of Pis set preferably to be 0.15%.
[0034]
S: 0.001 to 0.35%
S forms MnS in the steel, and is an element contributing to improvement in the
machinability. In the case where S is less than 0.001%, the effect obtained from the
additive is not sufficient. On the other hand, in the case where S exceeds 0.35%, the
effect obtained from the additive saturates. Further, the excess amount of S causes
grain boundary segregation, leading to grain boundary embrittlement. Thus, the
amount of S is set to be in the range of 0.001% to 0.35%. The lower limit of S is set
preferably to be 0.01%. The upper limit of S is set preferably to be 0.1%.
[0035]
Al: over 0.06% to 0.3%
Al is added for the purpose of deoxidizing the steel. If Al exceeds 0.06% in a
state where N is 0.008% or lower, the solute Al is formed in the steel, which contributes
to improvement in the machinability. However, in the case where Al exceeds 0.3%,
the diameter of the grain of the inclusion A1203 becomes larger, and the fatigue strength
deteriorates in the high cycle range. Thus, the amount of Al is set to be over 0.06% to
0.3%. The lower limit of Al is set preferably to be 0.08%. The upper limit of Al is
set preferably to be 0.15%.
[0036]
Total N (Ti = 0%): 0.006 to 0.03%
Total N (Ti > 0%): 0.006 + [Ti] x (14/48) to 0.03%
N bonds to Al, Ti, Nb and/or V in the steel to form nitride or carbonitride, and
suppresses the coarsening of the crystal grain. Further, N bonds to B contained as an
impurity to form BN, which reduces the amount of B (which causes variation in the
10
hardenability) segregated in the austenite grain boundary.
[0037]
In the case where the total N is less than 0.006% and Ti is not added in the steel,
the effect obtained from the additive does not sufficiently appear. Similarly, in the
case where the total N is less than "0.006 + [Ti] x (14/48)" ([Ti]: mass% of Ti) and Ti
described later is added, the effect obtained from the additive does not sufficiently
appear.
[0038]
On the other hand, in the case where the total N exceeds 0.03%, the effect
obtained from the additive saturates. Further, the carbonitride in non-solid-solution
form remains at the time of heating in the hot rolling or hot forging, which makes it
difficult to increase the fine carbonitride effective in suppressing the coarsening of the
crystal grain.
[0039]
Thus, the amount of the total N is set to be n the range of 0.0060 to 0.03% in
the case where Ti is not added, and is set to be in the range of "0.006 + [Ti] x (14/48)"
to 0.03% in the case where Ti is added. The lower limit of the total Nis set preferably
to be 0.0080%. The upper limit of the total Nis set preferably to be 0.010%.
[0040]
It should be noted that, in the case where Ti is added, the amount of the total
N% ([total N]) is set to be 0.006 + [Ti] x (14/48) or more.
[0041]
In the steel material for hardening according to this embodiment , B in the steel
is segregated around BN or precipitates (TiN, TiCN, MnS and the like) at the time of
hardening to reduce the amount of B segregated in the austenite grain boundary
contributing to improvement in the hardenability , thereby suppressing the increase in
the hardenability resulting from B. The larger amount of [total N] renders the
precipitation of BN easier, and hence, a predetermined amount of [total N] is necessary.
11
However, in the case where Ti exists in the steel, TiN stably exists to the high
temperature range. Thus, the required amount of [total N] is an amount obtained by
adding, to 0.06%, the amount of N: "[Ti] x atomic weight (14/48)," which is obtained
by subtracting the amount of N in TiN. Thus, in the case where Ti is added, the lower
limit of the total N% ([total N]) is set to be 0.006 + [Ti] x (14/48).
[0042]
B: over 0% to 0.0004%
B is segregated in the austenite grain boundary, improving the hardenability of
the steel in an unstable manner. In the steel material for hardening according to this
embodiment, B contained as the inevitable impurity is limited to 0.0004% or lower. B
is an element inevitably contained from the raw material of iron even if not added
intentionally. Thus, the lower limit is set to be over 0%. However, the lower limit
value may be set to be 0.0001% because high cost is required to stably control the
amount of B to be 0.0001 % or lower.
[0043]
In the case where the amount of Al is the general deoxidization agent level,
even if B exists as the inevitable impurity, the effect of B on the hardenability is so
small that it is negligible. However, in the case where Al in the steel exceeds 0.06%,
N is fixed as nitride, the inevitable impurity B becomes the solid-solution state, and the
solute B is segregated in the austenite grain boundary at the time of hardening. This
leads to the significant deterioration in the hardening stability.
[0044]
In the steel material for hardening according to this embodiment, B in the steel
is segregated around BN or precipitations (TiN, TiCN, MnS and the like) at the time of
hardening. This reduces the amount of B segregated in the austenite grain boundary
contributing to improvement in the hardenability, thereby eliminating the effect of B on
the hardenability. However, in the case where B exceeds 0.0004%, the amount of B
segregated in the austenite grain boundary cannot be sufficiently reduced. Thus, the
12
upper limit of B is set to be 0.0004%.
[0045]
Further, Ti may be added to increase BN precipitation/B segregated site for the
purpose of reducing the amount of B segregated in the austenite grain boundary.
[0046]
Ti: 0.001 to 0.05%
Ti serves as a core of MnS, and forms TiN that makes MnS fine. TiN absorbs
solute B and solute N to form composite nitride. This reduces the amount of B
segregated in the austenite grain boundary (in other words, the amount of B improving
the hardenability) causing variations in hardenability. In the case where Ti is less than
0.001%, the effect obtained from the additive does not occur. On the other hand, in
the case where Ti exceeds 0.05%, Ti-based sulfide is generated. This reduces the
amount of MnS that improves the machinability, deteriorating the machinability of the
steel. Thus, the amount of Ti is set to be in the range of 0.001 to 0.05%.
[0047]
The steel material for hardening according to this embodiment may contain at
least one element selected from the group consisting of Cr, Mo, Cu, Ni, Ca, Zr, Mg,
REM, Nb, V, W, Sb, Sn, Zn, Te, Bi, and Pb. These elements are contained optionally
in the steel, and hence, the lower limit values of these elements are 0%. However, in
order to favorably obtain the effect obtained by adding each of the elements, the
following..lower limit values may be set.
[0048]
The steel material for hardening according to this embodiment may contain one
or more elements selected from Cr, Mo, Cu, and Ni for the purpose of improving the
hardenability or strength.
[0049]
Cr: 0.1 to 3.0%
Cr is an element for improving the hardenability and providing resistance to
13
temper softening. This element is added to steel required to have high strength. In
the case where Cr is less than 0.2%, the effect of the additive cannot be obtained, and on
the other hand, in the case where Cr exceeds 3.0%, Cr carbide is generated, and hence,
the steel becomes embrittled. Thus, the amount of Cr is set to be in the range of 0.1 to
3.0%.
[0050]
Me: 0.01 to 1.5%
Mo is an element for providing resistance to temper softening, and improving
the hardenability. This element is added to steel required to have high strength. In
the case where Mo is less than 0.01%, the effect of the additive cannot be obtained, and
on the other hand, in the case where Cr exceeds 1.5%, the effect obtained from the
additive saturates. Thus, the amount of Mo is set to be in the range of 0.01% to 1.5%.
[0051]
Cu: 0.1 to 2.0%
Cu strengthens ferrite, and is effective in improving the hardenability and the
corrosion resistance. In the case where Cu is less than 0.1%, the effect of the additive
cannot be obtained, and on the other hand, in the case where Cu exceeds 2.0%, the
effect of improving the mechanical properties saturates. Thus, the amount of Cu is set
to be in the range of 0.1 to 2.0%. Note that Cu deteriorates the hot rolling property,
and is likely to cause defects at the time of rolling. Thus, it is preferable to add Ni at
the time of adding Cu.
[0052]
Ni: 0.1 to 5.0%
Ni strengthens ferrite, and is effective in improving the rolling property and
improving the hardenability and the corrosion resistance. In the case where Ni is less
than 0.1%, the effect of the additive cannot be obtained. On the other hand, in the case
where Ni exceeds 5.0%, the effect of improving the mechanical properties saturates, and
the machinability deteriorates. Thus, the amount of Ni is set to be in the range of 0.1
14
to 5.0%.
[0053]
Further, the steel material for hardening according to this embodiment may
contain one or more elements selected from Ca, Zr, Mg, and REM for the purpose of
adjusting the deoxidization to control the formation of sulfide.
[0054]
Ca: 0.0002 to 0.005%
Ca is an element for deoxidization, and generates oxide. As is the case with
the steel material for hardening according to this embodiment, a steel containing Al of
over 0.06% as total Al (T-Al) has calcium-aluminate (CaO-A12O3). CaO-A12O3 is an
oxide having a lower melting point as compared with A12O3, and hence, serves as the
coating for protecting the tool at the time of high-speed cutting, thereby improving the
machinability. In the case where Ca is less than 0.0002%, the effect of improving the
machinability cannot be obtained. On the other hand, in the case where Ca exceeds
0.005%, CaS is generated in the steel, thereby deteriorating the machinability. Thus,
the amount of Ca is set to be in the range of 0.0002 to 0.005%.
[0055]
Zr: 0.0003 to 0.005%
Zr is an element for deoxidization, and generates oxide in the steel. Oxide
thereof is considered to be ZrO2. ZrO2 serves as a core of precipitation of MnS, and
thus, increases the precipitation site of the MnS and disperses the MnS in a uniform
manner. Further, Zr is contained in MnS in a solid solution state to form composite
sulfide, lower its deformability, thereby suppressing the stretching of MnS at the time of
rolling or hot forging. As described above, Zr is an element effective in reducing the
anisotropy of the steel.
[0056]
In the case where Zn is less than 0.0003%, the conspicuous effect of the
additive cannot be obtained. On the other hand, in the case where Zr exceeds 0.005%,
15
the yield extremely deteriorates, and a large amount of hard chemical compound such as
Zr02 and ZrS is generated. Thus, the mechanical properties such as machinability,
impact value and fatigue properties deteriorate. For this reason, the amount of Zr is set
to be in the range of 0.0003 to 0.005%.
[0057]
Mg: 0.0003 to 0.005%
Mg is an element for deoxidization, and forms oxide in the steel. The oxide
serves as a core of MnS, and finely disperses MnS. In the case where Al deoxidization
is performed, Mg modifies A1203, which adversely affects the machinability, into MgO
or A1203•MgO which is relatively soft and finely disperses. Further, Mg forms
composite sulfide with MnS, and makes MnS spheroidizing.
[0058]
In the case where Mg is less than 0.0003%, the effect of the additive cannot be
obtained. On the other hand, in the case where Mg exceeds 0.005%, generation of
single MgS is promoted, and thus, the machinability deteriorates. Thus, the amount of
Mg is set to be in the range of 0.0003% to 0.005%.
[0059]
REM: 0.0001 to 0.015%
REM (rare-earth element) is an element for deoxidization, and forms oxide
having a lower melting point. This prevents the nozzle from clogging at the time of
casting. Further, REM is contained in MnS in a solid solution state or bonds to MnS,
and lowers its deformability, thereby preventing the stretching of the MnS shape at the
time of rolling and hot forging. As described above, REM is an element effective in
reducing the anisotropy of the mechanical properties.
[0060]
In the case where REM is less than 0.0001%, the effect obtained from the
additive cannot be sufficiently generated. On the other hand, in the case where Ca
exceeds 0.015%, a large amount of sulfide of REM is generated, and thus, the
16
machinability deteriorates. Thus, the amount of REM is set to be in the range of
0.0001 to 0.015%.
[0061]
Further, the steel material for hardening according to this embodiment may
contain one or more elements selected from Nb, V and W for the purpose of
strengthening resulting from formation of carbonitride, and regulating the grain size of
the austenite grain and making the austenite grain fine resulting from the increase in the
amount of carbonitride.
[0062]
Nb: 0.01 to 0.1%
Nb forms carbonitride, and contributes to strengthening the steel by secondary
precipitation hardening, suppressing the growth of austenite grain and strengthening the
austenite grain. This element is added to steel required to have high strength, and steel
required to have low strain as a grain-size-regulating element for preventing the
coarsening of the grain.
[0063]
In the case where Nb is less than 0.01 %, the effect of increasing the strength
cannot be obtained. On the other hand, in the case where Nb exceeds 0.1%, Nb forms
coarsened carbonitride in non-solid-solution form, which causes hot cracking, and the
mechanical properties deteriorate. Thus, the amount of Nb is set to be in the range of
0.01% to 0.1%.
[0064]
V: 0.03 to 1.0%
V forms carbonitride, and is an element for strengthening the steel by the
secondary precipitation hardening. This element is added, depending on application,
to steel required to have high strength. In the case where V is less than 0.03%, the
effect of increasing the strength cannot be obtained. On the other hand, in the case
where V exceeds 1.0%, V forms the coarsened carbonitride in non-solid-solution form,
17
which causes hot cracking, and the mechanical properties deteriorate. Thus, the
amount of V is set to be in the range of 0.03% to 1.0%.
[0065]
W: 0.01 to 1.0%
W forms carbonitride, and is an element for strengthening the steel by
secondary precipitation hardening. In the case where W is less than 0.01%, the effect
of increasing the strength cannot be obtained. On the other hand, in the case where W
exceeds 1.0%, W forms the coarsened carbonitride in non-solid-solution form, which
causes hot cracking, and the mechanical properties deteriorate. Thus, the amount of W
is set to be in the range of 0,01% to 1.0%.
[0066]
Further, the steel material for hardening according to this embodiment may
contain one or more elements selected from Sb, Sri, Zn, Te, Bi, and Pb for the purpose
of improving the machinability.
[0067]
Sb: 0.0005 to 0.0150%
Sb moderately embrittles ferrite, and improves the machinability. The effect
of Sb is remarkable in the case where the amount of solute Al is large. However, in
the case where Sb is less than 0.0005%, the effect obtained from the additive does not
appear. On the other hand, in the case where Sb exceeds 0.0150%, the macro
segregation of Sb is excessive, which leads to a large reduction in the impact value.
Thus, the amount of Sb is set to be in the range of 0.0005% to 0.0150%.
[0068]
Sri: 0.005 to 2.0%
Sri moderately embrittles ferrite to prolong the lifetime of the tool and improve
the surface roughness. In the case where Sri is less than 0.005%, the effect obtained
from the additive does not appear. On the other hand, in the case where Sri exceeds
2.0%, the effect obtained from the additive saturates. Thus, the amount of Sri is set to
18
be in the range of 0.005% to 2.0%.
[0069]
Zn: 0.0005 to 0.5%
Zn embrittles ferrite to prolong the lifetime of the tool and improve the surface
roughness. In the case where Zn is less than 0.0005%, the effect obtained from the
additive does not appear. On the other hand, in the case where Zn exceeds 0.5%, the
effect obtained from the additive saturates. Thus, the amount of Zn is set to be in the
range of 0.0005% to 0.5%.
[0070]
Te: 0.0003 to 0.2%
Te is an element for improving the machinability. Te forms MnTe, and
coexists with MnS to reduce the deformability of MnS, thereby suppressing stretching
of the MnS shape. As described above, Te is an element effective in reducing the
anisotropy in the mechanical properties. In the case where Te is less than 0.0003%,
the effect obtained from the additive does not appear. On the other hand, in the case
where Te exceeds 0.2%, the effect obtained from the additive saturates, and Te
deteriorates the hot rolling properties, which is likely to cause defects. Thus, the
amount of Te is set to be in the range of 0.0003% to 0.2%.
[0071]
Bi: 0.005 to 0.5%
i is an element for improving the machinability. In the case where Bi is less
than 0.005%, the effect of improving the machinability cannot be obtained. On the
other hand, in the case where Bi exceeds 0.5%, the effect of improving the
machinability saturates, and Bi deteriorates the hot rolling properties, which is likely to
cause defects. Thus, the amount of Bi is set to be in the range of 0.005% to 0.5%.
[0072]
Pb: 0.005 to 0.5%
Pb is an element for improving the machinability. In the case where Pb is less
19
than 0.005%, the effect of improving the machinability cannot be obtained. On the
other hand, in the case where Pb exceeds 0.5%, the effect of improving the
machinability saturates, and Pb deteriorates the hot rolling properties, which is likely to
cause defects. Thus, the amount of Pb is set to be in the range of 0.005% to 0.5%.
[0073]
The remainder of the element composition of the steel material for hardening
according to this embodiment includes inevitable impurities containing B of 0.0004% or
less as described above, and Fe.
The inevitable impurities may include a component other than the
above-described components as long as the component is in an amount that does not
inhibit the effects of the present invention. However, it, is preferable to set the amount
to be 0% as much as possible.
[0074]
Next, a description will be made of the Jominy hardness used as an index
indicating the hardening stability of the steel material for hardening according to this
embodiment.
[0075]
The steel material for hardening according to the present invention is
characterized in that R and H satisfy the following Equation (2), where "R" is a
hardness HRC at a position 5 mm measured from the quenching end and "H" is a
calculation hardness HRC at a position 3/16 inch, in other words, a position 4.763 mm
measured from the quenching end, the R and the H being measured according to the
hardenability test by end quenching (Jominy test) specified by JIS G 0561.
[0076]
H x 0.948 < R<_ H x 1.05 Equation (2)
The above-described "calculation hardness HRC at a position 3/16 inch from
the quenching end" can be obtained through a procedure described in pages 67 to 68 of
"5.3 Method for obtaining the Jominy curve by knowing C% and DI (DI method)" in "5
20
Method for obtaining the Jominy curve through a calculation" of Non-patent Document
1 with a distance measured from a water-cooling end being 3/16 inch (In this procedure,
a D1 value is calculated according to "A-255" of ASTM).
[0077]
Next, a method for obtaining the "IT' defined as "calculation hardness HRC at
a distance of 3/16 inch from the quenching end" will be described.
[0078]
[Procedure 1 ] First, on the basis of C% of the steel, the "50% martensite
hardness" is obtained from Table 1 (Table 5.8 on page 67 in the above-described
Non-patent Document 1).
[0079]
[Table 1]
[0080]
[Procedure 2] Next, a Di value is calculated according to "A-255" of American
Society for Testing and Material (ASTM) using the following Equation (3).
[0081]
Di(inch) = F(C) x F(Mn) x F(Si) x F(Ni) x F(Cr) x F(Mo) x F(Cu) x F(V)
Equation (3),
where
F(Si) = IT00 + 0.7 x [Si],
F(Ni) = 1.00 + 0.363 x [Ni],
F(Cr) = 1.00 + 2.16 x [Cr],
F(Mo) = 1.00 + 3.00 x [Me],
F(Cu) =1.00 + 0.365 x [Cu], and
F(V) = 1.00 + 1.73 x [V].
[0082]
F(C) and F(Mn) are obtained as described below according to the amount of C
21
(mass%) or the amount of Mn (mass%).
[0083]
In the case of [C] 5 0.39 mass%, F(C) = 0.54 x [C]
In the case of 0.39 mass% < [C] 0.55 mass%, F(C) = 0.171 + 0.001 x [C] +
0.265 x [C]2
In the case of 0.55 mass% < [C] 0.65 mass%, F(C) = 0.115 + 0.268 x [C] -
0.038 x [C]2
In the case of 0.65 mass% < [C]< _ 0.75 mass%, F(C) = 0.143 + 0.2 x [C]
In the case of 0.75 mass% < [C], F(C) = 0.062 + 0.409 x [C] - 0.135 x [C]2
In the case of [Mn] <_ 1.20 mass%, F(Mn) = 3.3333 x [Mn] + 1.00
In the case of 1.20 mass% < [Mn], F(Mn) = 5.10 x [Mn] - 1.12
It should be noted that, in the Equations above, the [element] indicates the
amount (mass%) of the element in the steel.
[0084]
From the thus obtained Di values and Table 2 (Table 5.7 on pages 65 to 66 of
the above-described Non-patent Document 1), the "hardness value to be added to the
50% martensite hardness" at a position 3/16 inch away from the water-cooling end is
obtained.
[0085]
[Table 2]
[0086]
It should be noted that the minimum unit for Di values in Table 2 is 0.2 inch,
and hence, the hardness value to be added existing in this minimum unit is obtained
through interpolation using a line. For example, in the case of Di = 1.90 inch, the
hardness number to be added at the position 3/16 inch measured from the water-cooling
end is [7.0 + (9.5 - 7.0) x 0.1/0.2 = 8.25].
[0087]
22
[Procedure 3] The "H" defined as "calculation hardness HRC at a distance of
3/16 inch from the quenching end" is obtained by adding the "hardness value to be
added to the 50% martensite hardness" at the position 3/16 inch measured from the
water-cooling end obtained in the (2) above to the "50% martensite hardness" obtained
in the procedure 2.
[0088]
If the steel having Al of over 0.06% is manufactured with the ordinary method,
N is fixed as nitride, and B having the inevitable impurity volume is in a solid solution
state. In this case, the solute B is segregated in the austenite grain boundary at the time
of hardening, and hence, the hardenability is affected.
[0089]
With the steel material for hardening according to this embodiment, the effect
of B on the hardenability is eliminated as described above, and hence, it is possible to
set the hardness at a position 5 mm measured from the quenching end measured through
the hardenability test by end quenching (Jominy test) to fall within the hardness range
(range indicated by Equation (2) above) under which the amount of Al is not made high.
[0090]
The steel material for hardening according to this embodiment is manufactured
by subjecting a steel piece having the above-described components to a first heat
treatment. Further, after the first heat treatment, it may be possible to apply a second
heat treatment (normalizing).
[0091]
In the first heat treatment, before the hardening heat treatment, the steel
material for hardening is heated to a high temperature of 1260°C or more, and the high
temperature is maintained for at least 20 minutes. However, the heating temperature
can be lowered by increasing the amount of added Ti. That is, by setting the amount
of Ti to more than or equal to 0.19%, it is only necessary to maintain the temperature of
1200°C or more for at least 20 minutes, and by setting the amount of Ti to more than or
23
equal to 0.25%, it is only necessary to maintain the temperature of 1150°C or more for
at least 20 minutes.
If the maintaining time duration is less than 20 minutes, MnS cannot be
sufficiently made fine even if the appropriate heating temperature is applied. In this
case, a large amount of the solute B, which can be segregated in the austenite grain
boundary, remains, and hence, sufficient hardening stability cannot be obtained.
[0092]
The first heat treatment may be applied at the time of heating a steel ingot for
blooming or hot forging, or a continuous casting piece . Further, the first heat
treatment may be applied at a given point in time when heating is applied for rolling the
steel material or after the steel material is rolled. In other words, the first heat
treatment can be applied at any time as long as the first heat treatment is applied before
the hardening heat treatment, and the target of the first heat treatment is not limited to
the metal structure of the steel.
[0093]
It is only necessary to apply the second heat treatment (normalizing) according
to the properties necessary for the part, and there is no specific limitation on the heating
temperature and the maintaining time.
[0094]
In the case where the amount of added Al exceeds 0.06%, N is generally fixed
as nitride,_ and B having the inevitable impurity volume is in a solid solution state,
which affects the hardenability. However, according to the steel material for
hardening according to this embodiment, the following conditions (x) to (z) are satisfied,
whereby it is possible to stabilize the hardenability.
[0095]
[0096]
(x) The amount of B in the inevitable impurities is limited to 0.0004 mass%.
(y) When the total amount (mass%) of N is denoted by [total N], and the
24
amount of Ti (mass%) is denoted by [Ti], the [total N] and the [Ti] satisfy the following
Equation (4).
0.006 + [Ti] x (14/48)< _ [total N] S 0.03 Equation (4)
[0097]
(z) Before the hardening heat treatment, a temperature is raised to a high
temperature of 1260°C or more, and the high temperature is maintained for at least 20
minutes. However, the heating temperature can be lowered in the case where Ti is
added. By setting the amount of Ti to more than or equal to 0.19%, it is only
necessary to maintain the temperature of 1200°C or more for at least 20 minutes, and by
setting the amount of Ti to more than or equal to 0.25%, it is only necessary to maintain
the'temperature of 1150°C or more for at least 20 minutes.
[0098]
The condition (x) limits the total amount of B, which leads to a decrease in the
amount of solute B. Further, the condition (y) enhances the precipitation of BN, which
leads to a decrease in the amount of solute B. Yet further, the condition (z) makes a
part of MnZ become in a solid solution state, and then, the part of MnZ precipitates,
which makes MnS fine and increases the surface area of MnS. With the increase in the
amount of added Ti, TiN increases. This leads to an increase in BN precipitating on
MnS and TiN, or an increase in the amount of B segregated in the interface between
different phases, in other words, between MnS/TiN and Fe-matrix. Therefore, the
segregation amount of the solute B, which is originally segregated in the austenite grain
boundary and has an effect on the hardenability, is reduced, and hence, the hardenability
becomes stabilized.
[0099]
The steel material for hardening described above may be used for a
power-transmitting part such as a gear, a shaft, and a continuously variable transmission
(CVT), by subjecting the steel material to the machine work and hardening.
25
Examples
[0100]
Next, examples of the present invention will be described. The conditions in
the examples are merely examples of those employed for confirming the applicability
and effects of the present invention. Thus, the present invention is not limited to these
examples of the conditions. The present invention may employ various conditions
without departing from the gist of the present invention, provided that the object of the
present invention can be achieved.
[0101]
Test pieces for drill cutting and Jominy test pieces were prepared such that
steel ingots having the chemical components shown in Table 3 and Table 4 were cogged
into a diameter of 35 mm; then, a heat treatment 1 (heating before hardening heat
treatment) and a heat treatment 2 (normalizing) shown in Table 5 were applied; and the
resulting steels were subjected to machine work. For the test No. 31, the heat
treatment 1 was not applied, and the heat treatment 2 was applied such that a heating
temperature of 1250°C was maintained for 0.5 hours, and then, accelerated cooling
(AC) was applied. For the test No. 32, the heat treatment 1 was not applied, and the
heat treatment 2 was applied such that a heating temperature of 1240°C was maintained
for 1.5 hours, and then, accelerated cooling (AC) was applied.
[0102]
or the test Nos. 1, 2, 4 to 12, 14 to 18, 20 to 30, and 33 to 37, the heat
treatment 2 was applied such that the heating temperature of 1250°C was maintained for
0.5 hours, and then, cooling in the air was applied.
[0103]
[Table 3]
[0104]
[Table 4]
[0105]
26
[Table 5]
[0106]
The test pieces for drill cutting were each prepared by cutting out a cylindrical
test piece having a diameter of 30 mm and a height of 21 mm, and applying the milling
finish to the cut-out test piece. For the Jominy test pieces, a test piece having a flange
specified in JIS G 0561 was employed.
[0107]
[Jominy test]
The Jominy test was conducted through an end quenching method based on JIS
G 0561 tinder conditions of a heat treatment 3 shown in Table 5. After grinding was
applied to the test piece in accordance with the requirements of JIS, the Rockwell
hardness with C scale was measured at a position 5 mm away from the hardening end.
[0108]
[Machinability test]
The machinability test was conducted such that each of the test pieces for drill
cutting was subjected to a drill-boring test under the cutting conditions shown in Table
6, and the machinability of each of the steel materials for hardening of Examples and
Comparative Examples was evaluated. As an evaluation index, the drill-boring test
employed the maximum cutting rate VL 1000 (m/min) that enables cutting up to an
accumulated hole depth of 1000 mm.
[0109]
[Table 6]
[0110]
Table 7 shows a hardness R and a hardness after the heat treatment 2 at a
position 5 mm measured from the quenching end of the Jominy test, which are indices
of the hardenability, and the examination results of the maximum cutting rate VL1000
27
(m/min), which is an index of the hardenability. The hardness R was measured with
the number N being 5, and the maximum value, the minimum value, and the standard
deviation of the measured hardness R were obtained.
[0111]
[Table 7]
[0112]
As shown in Table 7, in test Nos. 1 to 27 and Nos. 33 to 37 of Examples of the
present invention, the hardness R [HRC] at the position 5 mm away from the quenching
end measured through the end quenching method (Jominy method) falls, in a stable
manner, within the range between H x 0.948 (lower limit) and H x 1.05 (upper limit)
calculated from the hardness H [HRC] corresponding to 3/16 inch in the Jominy curve
and calculated on the basis of the Di value, the C% and the Di method. Further, the
resulting hardenability is equivalent to a hardenability in the case where the amount of
Al is not increased. Yet further, the machinability (VL1000) exhibits an excellent
value of morethan or equal to 50 m/min.
[0113]
On the other hand, in the test No. 28 of Comparative Example, the hardness R
[HRC] at the position 5 mm measured from the quenching end exceeds the upper limit
calculated from the H, falls outside the range, and exhibits unstable hardenability.
This is because the amount of B in the inevitable impurities exceeds 0.0004 mass%, and
hence, the hardenability increases.
[0114]
In the test No. 29 of Comparative Example, the machinability was poor. This
is because the amount of Al in the steel material for hardening is less than 0.06 mass%,
and hence, the effect of improving the machinability resulting from the solute Al cannot
be obtained.
[0115]
28
In the test No. 30 of Comparative Example, the hardness R [HRC] at the
position 5 mm measured from the quenching end exceeds the upper limit calculated
from the H, falls outside the range, and exhibits unstable hardenability. This is
because the amount of N is lower than 0.0060 mass%, and hence, a sufficient amount of
BN is not generated. Thus, a large amount of the solute B that can be segregated in the
austenite grain boundary remains, and the hardenability increases.
[0116]
In the tests Nos. 31 and 32 of Comparative Example, the hardness R [HRC] at
the position 5 mm away from the quenching end exceeds the upper limit calculated
from. the H, falls outside the range, and exhibits unstable hardenability. This is
because no heat treatment having the condition corresponding to the heat treatment 1
was applied, and hence, MnS is not sufficiently made finer. Thus, a large amount of
the solute B that can be segregated in the austenite grain boundary remains, and the
hardenability increases.
Industrial Applicability
[0117]
As described above, according to the present invention, the effect of improving
the machinability prolongs the tool life, thereby reducing the production cost. Further,
stable hardenability is achieved, thereby suppressing variations in the deformation
caused by heat treatment. Thus, the present invention is highly applicable in the steel
industry.
29
Table 7
8
33
34
35
Calculation value
45.0 38.0 36.0 39.9
52.3 41.7 39.5 43.8
40.6 35.6 33.7 37.3
46.2 39.0 37. 0 41.0
41.8 36.5 34.6 38.3
41.4 36.3 34.4 38
39.3 34.7 32.8 36.4
50.4 40.8 38.6 42.8
53.2 44.4 42 46.6
51.4 42.1 39.9 44.2
49.9 43.0 40.8 45.2
45.2 38.8 36.7 40.7
49.2 42.0 39.8 44.1
37.9 33.3 31.6 35.0
41.8 36.5 34.6 38.3
40.3 35.6 33.7 37.3
39.9 35.1 33.3 36.9
43.0 37.0 35. 1 38.9
63.1 43.2 41.0 45.4
67.1 44.1 41.8 46.3
if
37.0 35.1 38.9
41.7 36.5 34.6 38.3
40.9 36.0 34.1 37.8
41.7 36.5 34.6 38.3
42.2 36.8 34.8 38.6
43.9 38.0 36.0 39.9
41.2 36.3 34.4 38.1
42.3 37.3 35.3 39.1
43.0 37.0 35.1 38.9
53.5 44.5 42.2 46.7
Experimental value
R (average) Maximum value Minimum value
Standard
deviation
Hardness after
heat treatment 2
VLI000
HRC) HRC HRC a-5 (HV) mlmin
37.1 37.4 36.8 0.2 155 55
37.0 37.3 36.6 0.2 163 55
37.5 37.9 37.1 0.3 164 55
39.4 39.7 39.0 0.3 166 50
37.1 37.5 36.4 0.4 163 55
43.1 43.7 42.6 0.5 178 50
38.7 39.5 38.0 0.5 166 50
38.4
IN
38.1 0.3 163 55
41.9 42.1 41.4 0.2 164 55
36.4 37.2 35.0 0.8 162 55
40.1 40.4 39.0 0.5 165 55
36.8 37.1 36.5 0.2 163 55
36.6 37.1 36.0 0.4 163 55
34.8 35.1 34.4 0.2 161 60
41.1 41.7 40.5 0.4 163 55
44.5 45.1 44.0 0.4 168 50
42.3 42.8 42.0 0.3 167 50
43.2 43.4 43.0 0.2 166 50
39.5 40.0 39.2 0.3 164 55
43.0 43.5 42.4 0.4 166 50
34.1 34.5 33.8 02 161 60
36.5 37.0 36.1 0.3 163 60
35.7 36.0 35 0 162 60
35.2 35.9 34.6 0.4 162 60
37.0 37.2 36.5 0.2 163 60
43.1 43.7 42.8 0.3 171 55
44.0 44.8 43.0 0.6 172 55
40.1 42.3 37.2 2.1 163 55
36.3 37.0 35.9 0.4 163 40
38.6 41.0 36.7 1.4 162 55
39.2 43.1 36.8 22 163 55
40.2 44.2 37.0 3.1 163 55
38.0 39.1 37.5 06. 164 55
36.2 37.1 351 0.7 162 55
37.3 37.9 36.9 0.4 163 55
37.0 38.1 36.5 0.6 163 55
44.4 45.5 43.6 0.7 168 50
Table 2
Di value
1.00
1.20
1.40
1.60
1.80
2.00
2.20
2.40
2.60
2.80
3.00
3.20
140
3.60 91.44
3.80 96.52
4.00 101.60
4.20 1 106.68
440
4.60
4.80
5.00
5.20
5.40
5.60
5.80
6.00
6.20
6.40
6.60
Di value
(mm)
25.40
30.48
35.56
40.64
45.72
50.80
55.88
60.96
66.04
71.12
76.20
81.28
86.36
111.76 1
116.84
121.92
127.00
132.08
137.16
142.24
147.32
152.40
157.48
162.56
167.64
Distance ( 1/16 inch) from water-cooling end and hardness value to be added to 50% martensite hardness
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 29 30 31 32
u.5 1 0
13,0 4.5
140 90 00
140 11,0 4.5
24,0 1?0 ]0 0,0
14.0 12.5 9.5 3.5
140 130 10.5 65
14.0 13,5 11.0 s.0 3,0
140 135 11.5 95 5,5 15
14.0 135 120 100 7,5 4,0 Lo
14.0 13,5 12.5 11 . 0 9.0 6,0 30 1.0
14,0 14,0 13.0 11.5 9. 5 75 5,0 2,5 05
14.0 14.0 13.0 120 10,5 9.0 7.0 45 2.5 0,0
140 140 130 120 11.0 9,5 8.0 65 45 2,5 0.0
14,0 too 130 12.5 11.5 10,0 9,0 Bo 6,0 40 20 00
140 140 135 125 120 11.0 100 90 75 60 4.0 2.0 00
140 14,0 13.5 3 . 0
'
12.0 11.0 10.5 9.5 8.5 75 5 , 5 4.0 20 05
140 140 13 5 1 3 0 25 11.5 11.0 100 90 8.0 7.0 5.5 40 20 05
14.0 1410 13.5 12.0 125 12.0 11.5 110 10,0 90 8.0 7.0 5.0 4.0 20 05
140 140 135 130 130 12.5 12.0 11.0 10.5 10.0 9.0 8.0 7,0 5,5 40 25 1.0
14.0 14.0 13.5 13.5 130 12,5 12.0 11.5 11,0 10.5 9.5 9.0 8.0 7.0 55 4.0 3 0 15- 00
14,0 14.0 13.5 13.5 130 125 120 120 11.5 ILO 100 95 8,5 8,0 7.0 55 4,5 3.5 2.0 0,5
140 140 13,5 13.5 130 130 125 120 11.5 11.0 105 100 00 8,5 8,0 6,5 55 4,5 35 25 LO 0.0
140 140 140 13 . 5 13.0 130 125 120 120 11.5 110 105 100 9,0 85 71 TO 6 . 0 5.0 4 . 0 30 2,0 1,0
14.0 14.0 14.0 13.5 13,0 13,0 12,5 12 2 120 115 110 10,5 10.0 95 9 ,0 8.5 8 ,0 7.0 60 50 40 35 25 1.5 0.5
14.0 14.0 14.0 t3.5 13.0 13,0 13.0 12,5 120 120 115 110 105 100 95 9,0 8_5 8,0 7.0 6.0 55 45 35 3.0 20 1.0 0.0
140 140 140 140 135 130 13,0 13.0 125 12.0. 12.0 11.5 110 105 100 95 9,0 8,5 8.0 7,0 65 6,0 5.0 40 35 25 20 L0 0,5
14.0 140 140 14,0 13 , 5 13,0 13 , 0 13.0 110 12 . 5 12.0 12 .0 115 11,0 105 10,0 9.5 9,0 85 8.0 75 7,0 60 55 50 0 3 . 5 25 2.0 05
140 140 140 140 135 130 13,0 130 13,0 12.5 12.0 110 115 110 105 100 9.5 9.0 9,0 8,5 8.0 7 , 5 6,5 60 55
1
4. 5 4.0 3.0 2,5
Table 3
20 0.23 0.29
21 0.20 0.33
22 0.20 0.2
23 0.20 0.25
24 0.20 0.24
25 0.20 0.26
26 0.2 0.27
27 l 0.22 0.2
28 0.20 0.24
29 0.20 0.22
30 0.20 0.19
3 0.20 0.22
32 0.20 0.24
33 0.21 0.24
34 0.20 0.2
35 0.21 0.23
36 0.20 0.23
37 0.25 0.22
Chemical component (mass%)
n p s -- as i Al Ti B C
0.81 0.014 0.015 0.0081 0.0081 0.100 0.0002 1.20
0.79 0.013
0.80 0.010
0.81 0.011
0.74 0.012
0.80 0.013
0.79 0.014
0.80 0.015
0.73 0.013
0.82 0.016
0.83 0.014
0.91 0.015
0.79 0.016
0.79 0.015
0.79 0.013
0.73 0.012
0.8 0.014
0.75 0.0
0.74 0.012
0.80 0.016
0.74 0.0
0.81 0.015
0.81 0.015
0.80 0.013
0.80 0.0
0.80 0.012
0.80 0.013
0.79 0.014
0.80 0.015
0.75 0.013
0.82 0.016
0.83 0.016
0.015 0.0085 0.0085 0.102 0.0002 1.19
0.015 0.0090 0.0090 0.110 0.0002 1.21
0.016 0.0126 0.0082 0.098 0-015 0.0003 1.23
0.017 0.0119 0.0081 0.087 0.013 0.0002 1.24
0.015 0.0091 0.0091 0.095 0.0002 0.0
0.016 0.0081 0:0081 0.104 0.0002 0.75
0.014 0.0092 0.0092 0.089 0.0002 1.19
0.015 0.0083 0.0083 0.120 0.0002 1.23
0.015 0-0079 0.0079 0.099 0.0003 120
0.020 0.0081 0.0081 0.098 0.0002 1.20
0.014 0.0082 0.0082 0.115 0.0002 1.20
0.014 0.0079 0.0079 0.123 0.0002 1.20
0.014 0.0078 0.0078 0.15
0.016 0.0099 0.0099 0.142
0.015 0.0094 0.0094 0.123 0.0003 1.19
0.016 0.0082 0.0082 0.116
0.015 0.0080 0.0080 0.132
0.015 0.0081 0.0081 0.145
0.015
0.016
0.015
0.0083
0.0078
0.0083
0.0078
0.0081
0
0.097
0.0081
0.014 0.0079
0.016 0.0078
0.012 0.0077
0.013 0.0118
0.014 0.0114
0.015 0.0086
0.015 0.0085
0.016 0.004
0.015 0.0089
0.014 0.0084
0.015 0.0155
0.014 0.0146
0.014 0.0221
0.
0.101
0.0079 0.099
0.0078 0.098
0.0077 0.103
0.0002 1.21
0.0002
0.0002
0.0002
0.0002
9
1.05
20
19
0.0002 1.20
0.0002 1.21
0.0077 0.110 0.014 0.0003
0.0079 0.102 0.012 0.0002
0.0086 0.102 0.0006
20
2
2
0.0085 0.040 0.0002 1.20
0.0041 0.111 0.0002 1.20
0.0089 0.110 0.0002 1.20
0.0084 0-096 0.0002
0.0091 0.099 0.022 0.0002
0.0070 0.103 0.026 0.0003
20
20
0.0084 0.102 0.047 0.0002 1.21
0.016 0.0099 0.0099 { 0.1 1 1 0.0004 1.2
0.015 0.0098 0.0098 0.098 0.0001 1.20
Table 4
Table 5
Test Heat treatment
No. Heat treatment 1 Heat treatment 2 Heat treatment 3
1 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x 1 hour and then, cooling in the air
2 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x 1 hour and then, cooling in the air
3 1300°C x 2 hours and then, cooling in the air Not applied 925°C x 1 hour and then, cooling in the air
4 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x 1 hour and then, cooling in the air
5 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x 1 hour and then, cooling in the air
6 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 900°C x 1 hour and then, cooling in the air
7 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x I hour and then, cooling in the air
8 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x 1 hour and then, cooling in the air
9 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x 1 hour and then, cooling in the air
10 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x 1 hour and then, cooling in the air
1 I 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x 1 hour and then, cooling in the air
12 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x I hour and then, cooling in the air
13 1300°C x 2 hours and then, cooling in the air Not applied 925°C x 1 hour and then, cooling in the air
14 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x 1 hour and then, cooling in the air
15 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x I hour and then, cooling in the air
16 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x 1 hour and then, cooling in the air
17 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x 1 hour and then, cooling in the air
18 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x 1 hour and then, cooling in the air
19 1300°C x 2 hours and then, cooling in the air Not applied 925°C x I hour and then, cooling in the air
20 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x 1 hour and then, cooling in the air
21 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x 1 hour and then, cooling in the air
22 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x 1 hour and then, cooling in the air
23 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x I hour and then, cooling in the air
24 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x 1 hour and then, cooling in the air
25 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x 1 hour and then, cooling in the air
26 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x 1 hour and then, cooling in the air
27 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x 1 hour and then, cooling in the air
28 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x 1 hour and then, cooling in the air
29 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x I hour and then, cooling in the air
30 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x 1 hour and then, cooling in the air
31 Not applied 1250°C x 0.5 hours and then, AC 925°C x I hour and then, cooling in the air
32 Not applied 1240°C x 1 - 5 hours and then, AC 925°C x 1 hour and then, cooling in the air
33 1200°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x I hour and then, cooling in the air
34 1200°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x 1 hour and then, cooling in the air
35 1150°C x 2 hours and then, coolie in the air 1250°Cx 0.5 hours and then, cooling in the air 925°C x I hour and then, cooling in the air
36 1300°C x 2 hours and Then, cooling in the a r 1250°C x 0.5 hours and then, cooling in the air 925°C x I hour and then, cooling in the air
37 1300°C x 2 hours and then, cooling in the air 1250°C x 0.5 hours and then, cooling in the air 925°C x 1 hour and then, cooling in the air
Table 6
Lubricant for cutting
Water-soluble
cutting oil
Drill diameter cp 3 mm
NACHI normal drill
Protruding amount 45 mm
Tool lifetime Until tool breaks
(NACHI normal drill refers to a drill with a model type SD3.0 made by NACHI-FUJIKOSHI CORP. The outermost surface of this tool is made of iron-based oxide.)
Table 7
Di value H
mm HRC
42.8 37.0
42.3 3 386.8
45.0 .0
48.4 39.8
Calculation "value
H x 0.948 1 H x 1.05
HRC HRC
35.1 38.9
34.8 38.6
36.0 39.9
37.7 41.7
37.1
37.0
37.5
39.4
37.4
37.3
37.9
39.7
36.8
36.6
37.1
39.0
0.2
0.2
0.3
0.3
155
163
164
166
5
37
43.3
44.5
35.3
40.3
36.7
36.0
42.2
39.1
44.6
40.7
39.9
46.7
37.1
44.4
375
45.5
36.4
42.6
38.0
38.1
43.6
0.4 163
32
33
34
35
36
52.3
40.6
46.2
41.8
41.4
39.3
50.4
53.2
51.4
49.9
45.2
49.2
37.9
41.8
40.3
39.9
43.0
63.1
67.1
42.8
41.7
40.9
41.7
42.2
43.9
41.2
423
43.0
36.8
38.0
36.3
37.3
37.0
41.7 39.5
35.6 33.7
39.0 37.0
36.5 34.6
36.3 34.4
34.7 32.8
40.8 38.6
44.4 42.1
42.1 39.9
43.0 40.8
38.8 36.7
42.0 39.8
33.3 31.6
36.5 34.6
35.6 33.7
35.1 33.3
37.0 35.1
43.2 41.0
44.1 41.8
37.0 35.1
36.5 34.6
36.0 34.1
36.5 34.6
34.8
36.0
34.4
35.3
35.1
43.8
37.3
41.0
38.3
38.1
36.4
42.8
46.6
44.2
45.2
40.7
44.1
35.0
38.3
373
36.9
38.9
45.4
46.3
38w9
383
37.8
38.3
38.6
39.9
38.1
39.1
38.9
41.9
36.4
40.1
36.8
36.6
34.8
41.1
44.5
42.3
43.2
39.5
43.0
34.1
36.5
35.7
35.2
37.0
43.1
44.0
40.1
36.3
38.6
39.2
40.2
38.0
36.2
37.3
37.0
43.5
34.5
37.0
36.0
35.9
372
43.7
44.8
42.3
37.0
41.0
43.1
44.2
39.1
37.1
37.9
38.1
41.4
35.0
39.0
36.5
36.0
34.4
40.5
44.0
42.0
43.0
39.2
42.4
33.8
36.1
35.1
34.6
36.5
42.8
43.0
37.2
35.9
36.7
36.8
37.0
37.5
35.1
36.9
36.5
0.2
00=8
0.5
0.2
0.4
0.2
0.4
0.4
0.3
0.2
0.3
0.4 166
02 161
0.3 163
0.3 162
0.4 162
0.2 163
0.3 171
0.6 172
2.1 163
0.4 163
1.4 162
2.2 163
3.1 163
164
162
0.6
0.7
0.4
0.6
178 50
166 50
163
155
164
162
165
163
163
161
163 55
168 50
167 50
166 50
164 55
163
163
0.7 168
55
55
55
50
55
55
55
55
55
55
55
50

CLAIMS
1. A steel material for hardening, including chemical components, by mass%, of:
C: 0.15 to 0.60%;
Si: 0.01 to 1.5%;
Mn: 0.05 to 2.5%;
P: 0.005 to 0.20%;
S: 0.001 to 0.35%;
Al: over 0.06 to 0.3%; and
total N: 0.006 to 0.03%,
with a balance including Fe and inevitable impurities including B of not more
than 0.0004%, wherein
R and H satisfy following Equation (1), where the R is a hardness at a position
5 mm away from a quenching end measured through a Jominy-type end-quenching
method specified in JIS G 0561, and the H is a calculation hardness at a position 4.763
mm away from the quenching end.
H x 0.948 <_R