DESCRIPTION
TITLE OF INVENTION: GRAIN-ORIENTED ELECTRICAL STEEL
SHEET AND MANUFACTURING METHOD THEREOF
TECHNICAL FIELD
[0001] The present invention relates to a
manufacturing method for improving a coating film
property and a magnetic property of a grain-oriented
electrical steel sheet. This application is based
upon and claims the benefit of priority of the prior
Japanese Patent Application No. 2011-4359, filed on
January 12, 2011, the entire contents of which are
incorporated herein by reference.
BACKGROUND ART
[0002] A grain-oriented electrical steel sheet is
mainly used for a transformer core material for
electric power and thus is required to be low in core
loss. In a manufacturing method of a grain-oriented
electrical steel sheet, a cold-rolled steel sheet
having a final sheet thickness is subjected to
decarburization annealing, and then is subjected to
finish annealing aimed at secondary recrystallization
and purification, and then is subjected to a process
of forming a coating film on the steel sheet surface.
The grain-oriented electrical steel sheet obtained in
this manner is composed of a Si containing steel
sheet having a sharp (110) [001] texture (Goss
orientation) and a several micron inorganic coating
film formed on the surface. The steel sheet has the
Goss orientation, which is an essential condition for
!
*
achieving a low core loss property of the grainoriented
electrical steel sheet, and for making this
structure, grain growth called secondary
recrystallization in which Goss oriented grains
selectively grow during finish annealing is used.
[0003] For stably causing the secondary
recrystallization, in the grain-oriented electrical
steel sheet, fine precipitates in the steel called
inhibitors are used. The inhibitor suppresses the
grain growth in a low-temperature portion during
finish annealing and at a certain temperature or
higher, loses its pinning effect by decomposition or
coarsening to cause the secondary recrystallization,
and sulfide or nitride is generally used. For
obtaining the desirable structure, it is necessary to
keep the inhibitor up to a certain temperature, and
if being sulfide, a sulfur component partial pressure
in the finish annealing is controlled, and if being
nitride, a nitrogen partial pressure is controlled or
the like, and thereby the object of the desirable
structure is accomplished. Sulfide and nitride used
as the inhibitor are needed for the secondary
recrystallization to occur in the middle of i
increasing the temperature during the finish
annealing, but when they are retained in a product,
they significantly deteriorate a core loss of the
product. In order to remove an effect of sulfide and
nitride from the steel sheet, after the secondary
recrystallization is completed, the steel sheet is
- 2 -
retained for a long time in pure hydrogen at around
1200°C. This is referred to as purification annealing.
Thus, in the purification annealing, the steel sheet
is in a state of being retained at a high temperature
during the finish annealing.
I •
[0004] On the other hand, the coating film of the
grain-oriented electrical steel sheet is composed of
a glass coating film and a secondary coating film,
and by tension that these coating films apply to the
steel sheet, a magnetic domain control effect is
obtained and the low-core loss property is improved.
As described in Patent Literature 1, if this tension
is high, a core loss improving effect is high, and
thus the secondary coating film in particular is
required to have capability of generating high
tens ion.
[0005] Generally, at the time of finish annealing,
Si02 in the steel sheet and MgO of an annealing
separating agent main component react and thereby the
glass coating film is formed on the steel sheet. The
glass coating film has two functions. As the first
function, the glass coating film tightly adheres to
the steel sheet and the glass coating film itself has
an effect of applying tension to the steel sheet and
works as an intermediate layer to secure adhesiveness
to the steel sheet when the secondary coating film to
be formed in a process after the finish annealing is
formed. When the adhesiveness of the glass coating
film is good, the secondary coating film to generate
- 3 -
high tension can be formed, and thus by the higher
magnetic domain control effect, the low core loss can
be achieved. Further, as the second function, the
glass coating film has a function of preventing an
i
excessive reduction in strength by the inhibitor
during the finish annealing and stabilizing the
secondary recrystaliization. Thus, in order to
stably manufacture a grain-oriented electrical steel
sheet having a good magnetic property, the glass
coating film having good adhesiveness to the steel
sheet is reguired to be formed.
[0006] In order to improve the adhesiveness between
the glass coating film and the steel sheet in the
grain-oriented electrical steel sheet, it is
necessary to optimize an interface structure between
the glass coating film and the steel sheet. However,
in a conventional grain-oriented electrical steel
sheet, the sufficient adhesiveness is not necessarily
secured when tension higher than ever before is
desired to be applied, or the like.
CITATION LIST
PATENT LITERATURE
[0007] Patent Literature 1: Japanese Laid-open j
Patent Publication No. 07-207424
Patent Literature 2: Japanese Laid-open Patent
Publication No. 2003-27196
Patent Literature 3: Japanese Laid-open Patent
Publication No. 2004-76143
Patent Literature 4: Japanese Laid-open Patent
- -4 -
Publication No. 2000-204450
Patent Literature 5: Japanese Laid-open Patent
Publication No. 06-17261
Patent Literature 6: International Publication
Pamphlet No. WO2011/7771
Patent .Literature 7: Japanese Examined Patent
Application Publication No. 60-55570
Patent Literature 8 : Japanese Laid-open Patent
Publication No. 2008-1977
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0008] An object of the present invention is to
provide a grain-oriented electrical steel sheet
capable of forming a coating film to generate high
tension, having a glass coating film excellent in
coating film adhesiveness, and having a good magnetic
property, and a manufacturing method thereof.
SOLUTION TO PROBLEM
[0009] The gist of the present invention is as
follows.
(1) A grain-oriented electrical steel sheet being a
grain-oriented electrical steel sheet containing Si
of 0.8 mass% to 7 mass%, Mn of 0.05 mass% to 1 mass%,
B of 0.0005 mass% to 0.0080 mass%, Al of 0.025 mass%
or less in a content ratio, each content of C, N, S,
and Se of 0.005 mass% or less, and a balance being
composed of Fe and inevitable impurities and having a
glass coating film made of composite oxide mainly
composed of forsterite on the steel sheet surface, in
- 5 -
•
which
when on a condition that a secondary coating film
having a thickness of not less than 1 \i m nor more
than 2 p and formed in a manner that a coating
solution containing 26 to 38 mass% of colloidal
silica, 4 to 12 mass% of one type or two types
selected from a group consisting of chromic anhydride
and chromate, and a balance being composed of
aluminum biphosphate is applied and dried and then is
baked at 800°C to 900°C is formed on the surface of
the glass coating film, glow discharge optical
emission spectrometry (GDS) to the surface of the
secondary coating film is performed, a peak, of B, in
emission intensity having a peak position in emission
intensity different from a peak position, of Mg, in
emission intensity is obtained and the peak position,
of B, in emission intensity from the steel sheet
surface is deeper than the peak position, of Mg, in
emission intensity, and
further, out of the peaks, of B, in emission
intensity observed by the glow discharge optical
emission spectrometry (GDS), a peak occurrence time
tB of the peak that is the farthest from the steel
sheet surface is expressed by Expression (1) below.
tMg X 1.6 ^ tB ^ tMg X 5- • • (1)
Here, tMg represents a peak occurrence time of Mg.
(2) A manufacturing method of a grain-oriented
electrical steel sheet, includes:
at a predetermined temperature, heating an
- 6 -
%
electrical steel sheet material containing Si of 0.8
mass% to 7 mass%, acid-soluble Al of 0.01 mass% to
0.065 mass%, N of 0.004 mass% to 0.012 mass%, Mn of
0.05 mass% to 1 mass%, B of 0.0005 mass% to 0.0080
mass%, at least one type selected from a group
consisting of S and Se of 0.003 mass% to 0.015 mass%
in total amount, a C content of 0.085 mass% or less,
and a balance being composed of Fe and inevitable
impurities;
performing hot rolling of the heated silicon
steel material to obtain a hot-rolled steel strip;
performing annealing of the hot-rolled steel
strip to obtain an annealed steel strip;
performing cold rolling of the annealed steel
strip one time or more to obtain a cold-rolled steel
strip;
performing decarburization annealing of the coldrolled
steel strip to obtain a decarburizationannealed
steel strip in which primary
recrystallization has been caused;
applying an annealing separating agent having MgO
as its main component on the decarburization-annealed
steel strip;
finish annealing the decarburization-annealed
steel strip and thereby causing secondary
recrystallization; and
further performing a nitriding treatment in which
an N content in the decarburization-annealed steel
strip is increased between start of the
~ 7 ~
decarburization annealing and occurrence of the
secondary recrystallization in the finish annealing,
in which
the predetermined temperature, when S and Se are
contained in the silicon steel material, is a
temperature Tl (°C) expressed by Expression (2) below
or lower, a temperature T2 (°C) expressed by
Expression (3) below or lower, and a temperature T3
(°C) expressed by Expression (4) below or lower, when
no Se is contained in the silicon steel material, the
predetermined temperature is the temperature Tl (°C)
expressed by Expression (2) below or lower and the
temperature T3 (°C) expressed by Expression (4) below
or lower, when no S is contained in the silicon steel
material, the predetermined temperature is the
temperature T2 (°C) expressed by Expression (3) below
or lower and the temperature T3 (°C) expressed by
Expression (4) below or lower, and a finishing
temperature Tf of finish rolling in the hot rolling
satisfies Expression (5) below, amounts of BN, MnS,
and MnSe in the hot-rolled steel strip satisfy
Expressions (6), (7), and (8) below, and at the time
of finish annealing, a temperature falls within a
temperature range of 800°C to 1100°C and an atmosphere
satisfies Expressions (9) and (10) below.
Tl = 14855/(6.82 - log([Mn] X [S])) - 273 ...(2)
T2 = 10733/(4.08 - log([Mn] X [Se])) -
273 ... (3)
T3 = 16000/(5.92 - log([B] X [N])) - 273 ...(4)
- 8 -
Tf ^ 1000 - 10000 X [B] ... • (5)
BasBN ^ 0. 0005 ... (6)
[ B ] - Ba s B N ^ 0 . 0 0 1 . . . (7)
SasMnS + 0 . 5 X Sea s M n s e = 0 . 0 0 2 . . . ( 8)
0. 75 ^ PN2 ^ 0 . 2 . . ' . • • • (9)
-0.7 ^ Log[PH2o/PH2] (10)
Here, [Mn] represents the Hn content (mass%) of
the silicon steel material, [S] represents the S
content (mass%) of the silicon steel material, [Se]
represents the Se content (mass%) of the silicon
steel material, [B] represents the B content (mass%)
of the silicon steel material, [N] represents the N
content (mass%) of the silicon steel material, BaSBN
represents an amount of B (mass%) that has
precipitated as BN in the hot-rolled steel strip,
SasMns represents an amount of S (mass%) that has
precipitated as MnS in the hot-rolled steel strip,
and SeasMnse represents an amount of Se (mass%) that
has precipitated as MnSe in the hot-rolled steel
strip. Further, PN2 represents a nitrogen partial
pressure, and PH2o and PH2 represent a water vapor
partial pressure and a hydrogen partial pressure
respectively.
(3) The manufacturing method of the grain-oriented
electrical steel sheet according to the previous
clause (2), in which the temperature at the time of
finish annealing falls within the temperature range
of 800°C to 1100°C and the atmosphere at the time of
finish annealing satisfies (11) Expression.
- 9 -
4Log[PN2] = 3Log[PH2o/PH2] + A + 3455/T- • • • (11)
Here, -3.72 ^ 3Log [ PH20/ PH2 ] + A ^ -5.32 and -0.7
^ Log [ PH2O/PH2] are satisfied and A represents a
constant determined in such a manner that
3Log[PH2O/PH2] + A falls within a predetermined range
according to Log [ PH2O/PH2] , and T represents the
absolute temperature.
(4) The manufacturing method of the grain-oriented
electrical steel sheet according to the previous
clause (2), in which at the time of finish annealing,
an atmosphere at 1100°C or higher satisfies (12)
Expression and (13) Expression.
0.1 ^ PN2 (12)
-2 ^ Log[PH20/PH2] (13)
(5) The manufacturing method of the grain-oriented
electrical steel sheet according to the previous
clause (2), in which the electrical steel sheet
material further contains at least one type selected
from a group consisting of Cr: 0.3 mass% or less, Cu:
0.4 mass% or less, Ni: 1 mass% or less, P: 0.5 mass%
or less, Mo: 0.1 mass% or less, Sn: 0.3 mass% or less,
Sb: 0.3 mass% or less, and Bi: 0.01 mass% or less.
ADVANTAGEOUS EFFECTS OF INVENTION
[0010] According to the present invention, it is
possible to obtain a grain-oriented electrical steel
sheet capable of forming coating films to generate
high tension, having a glass coating film excellent
in coating film adhesiveness, and having a good
magnetic property.
- 10 -
BRIEF DESCRIPTION OF DRAWINGS
[0011] [Fig. 1] Fig. 1 is a view showing a schematic
dialog of a result of glow discharge optical emission
spectrometry (GDS) of a surface of a grain-oriented
electrical steel sheet;
[Fig. 2] Fig. 2 shows the relationship between
precipitate amounts in a hot-rolled steel strip and a
magnetic property after finish annealing;
[Fig. 3] Fig. 3 is a view showing the
relationship between the precipitate amounts in the
hot-rolled steel strip and coating film adhesiveness
after the finish annealing;
[Fig. 4] Fig. 4 is a view showing the
relationship between an amount of B that has not
precipitated as BN and the magnetic property after
the finish annealing;
[Fig. 5] Fig. 5 is a view showing the
relationship between the amount of B that has not
precipitated as BN and the coating film adhesiveness
after the finish annealing;
[Fig. 6] Fig. 6 is a view showing the
relationship between a condition of hot rolling and
the magnetic property after the finish annealing;
[Fig. 7] Fig. 7 is a view showing the
relationship between the condition of the hot rolling
and the magnetic property after the finish annealing;
[Fig. 8] Fig. 8 is a view showing the
relationship between the condition of the hot rolling
and the coating film adhesiveness after the finish
- 11 -
annealing;
[Fig. 9] Fig. 9 is a view showing the
relationship between the condition of the hot rolling
and the coatiri'g film adhesiveness after the finish
annealing;
[Fig. 10] Fig. 10 is a view showing the
relationship between a finishing temperature of
finish rolling in the hot rolling and the magnetic
property after the finish annealing;
[Fig. 11] Fig. 11 is a view showing the
relationship between the finishing temperature of the
finish rolling in the hot rolling and the coating
film adhesiveness after the finish annealing;
[Fig. 12] Fig. 12 is a view showing the
relationship between precipitates of hot rolling and
a magnetic property after finish annealing;
[Fig. 13] Fig. 13 is a view showing the
relationship between the precipitates of the hot
rolling and coating film adhesiveness after the
finish annealing;
[Fig. 14] Fig. 14 is a view showing the
relationship between an amount of B that has not
precipitated as BN and the magnetic property after
the finish annealing;
[Fig. 15] Fig. 15 is a view showing the
relationship between the amount of B that has not
precipitated as BN and the coating film adhesiveness
after the finish annealing;
[Fig. 16] Fig. 16 is a view showing the
- 12 -
relationship between a condition of the hot rolling
and the magnetic property after the finish annealing;
[Fig. 17] Fig. 17 is a view showing the
relationship between the condition of the hot rolling
and the magnetic property after the finish annealing;
[Fig. 18] Fig. 18 is a view showing the
relationship between the condition of the hot rolling
and the coating film adhesiveness after the finish
annealing;
[Fig. 19] Fig. 19 is a view showing the
relationship between the condition of the hot rolling
and the coating film adhesiveness after the finish
annealing;
[Fig. 20] Fig. 20 is a view showing the
relationship between a finishing temperature of
finish rolling in the hot rolling and the magnetic
property after the finish annealing;
[Fig. 21] Fig. 21 is a view showing the
relationship between the finishing temperature of the
finish rolling in the hot rolling and the coating
film adhesiveness after the finish annealing;
[Fig. 22] Fig. 22 is a view showing the
relationship between precipitate amounts in a hotrolled
steel strip and a magnetic property after
finish annealing;
[Fig. 23] Fig. 23 is a view showing the
relationship between the precipitate amounts in the
hot-rolled steel strip and coating film adhesiveness
after the finish annealing;
- 13 -
[Fig. 24] Fig. 24 is a view showing the
relationship between an amount of B that has not
precipitated as BN and the magnetic property after
the finish annealing;
[Fig. 25] Fig. 25 is a view showing the
relationship between the amount of B that has not
precipitated as BN and the coating film adhesiveness
after the finish annealing;
[Fig. 26] Fig. 26 is a view showing the
relationship between a condition of hot rolling and
the magnetic property after the finish annealing;
[Fig. 27] Fig. 27 is a view showing the
relationship between the condition of the hot rolling
and the magnetic property after the finish annealing;
[Fig. 28] Fig. 28 is a view showing the
relationship between the condition of the hot rolling
and the coating film adhesiveness after the finish
annealing;
[Fig. 29] Fig. 29 is a view showing the
relationship between the condition of the hot rolling
and the coating film adhesiveness after the finish
annealing;
[Fig. 30] Fig. 30 is a view showing the
relationship between a finishing temperature of
finish rolling in the hot rolling and the magnetic
property after the finish annealing;
[Fig. 31] Fig. 31 is a view showing the
relationship between the finishing temperature of the
finish rolling in the hot rolling and the coating
- 14 -
film adhesiveness after the finish annealing; and
[Fig. 32] Fig. 32 is a view showing the
relationship between a ratio tB/tMg of a GDS analysis
result and the coating film adhesiveness.
DESCRIPTION OF EMBODIMENTS
[0012] Conventionally, B has been used as an
additive of an annealing separating agent of a grainoriented
electrical steel sheet, but the present
inventors found that in the case of B being added
into a steel sheet, there is sometimes a case that
coating film adhesiveness is improved together with a
magnetic property. Then, as a result of a detailed
examination of a sample exhibiting good properties,
it became clear that there are characteristics in
distribution of B in an interface between a glass
coating film and a steel sheet. That is, it was
found that an interface structure between the glass
coating film and the steel sheet is optimized,
thereby making it possible to improve the magnetic
property and the coating film adhesiveness. This
interface structure includes the following
characteristics. Thatis, in a grain-oriented
electrical steel sheet containing, as an entire steel
sheet, Si of 0.8 mass% to 7 mass%, Mn of 0.05 mass%
to 1 mass%, B of 0.0005 mass% to 0.0080 mass%, Al of
0.025 mass% or less in a content ratio, each content
of C, N, S, and Se of 0.005 mass% or less, and a
balance being composed of Fe and inevitable
impurities, a layer made of composite oxide mainly
- 15 -
composed of forsterite is provided on the steel sheet
surface.
[0013] The meaning that it is mainly composed of
forsterite here indicates that forsterite occupies
70% by weight or more of a constituent of a coating
film as a forming compound of the coating film. Then,
it is characterized in that when glow discharge
optical emission spectrometry (GDS) to the steel
sheet surface is performed, a peak, of B, in emission
intensity is obtained at a position different from a
peak position of Mg and the position of the peak from
the steel sheet surface is deeper than that of Mg.
Concretely, as shown in Fig. 1, it is characterized
in that out of the peaks of B observed by the GDS,
the distance from the surface to the peak that is the
farthest from the steel sheet surface is a certain
distance or more from the peak position of Mg.
[0014] This peak of Mg was examined on samples made
under various conditions of the following first
experiment and the relationship with the adhesiveness
was examined, and thereby results shown in Fig. 32
were obtained. Here, the peak position of Mg was set
to tMg, and out of the peaks of B, the position of
the peak positioned in the deepest portion from the
steel sheet surface was set to tB. Further, in Fig.
32, with regard also to the magnetic property,
results arranged according to a ratio tB/tMg of
values tMg and tB are shown. Incidentally, Fig. 32
shows that as a peeled area is smaller, the
- 16 -
adhesiveness is improved.
[0015] As shown in Fig. 32, it is found that when tB
^ tMq X 1.6 is satisfied, the peeled area of the
coating film is 5% or less, which is minor, and the
adhesiveness is improved. On the other hand, the
magnetic property is also improved when the value tB
is large, but when the value tB is too large, there
is also a case that the magnetic property rather
deteriorates, and thus the ratio tB/tMg is set to 5
or less.
[0016] Incidentally, when the values tB and tMg are
measured by the GDS, the measurement is performed in
a manner that the thickness of a secondary coating
film on a glass coating film is set to a certain
condition. For example, when a secondary coating
film having a thickness of not less than 1 /jm nor
more than 2 ix m and formed in a manner that a coating
solution containing 26 to 38% by weight of colloidal
silica, 4 to 12 mass% of one type or two types
selected from a group consisting of chromic anhydride
and chromate, and a balance being composed of
aluminum biphosphate is applied and dried and then is
baked at 800°C to 900°C is formed, the values tB and
tMg can be measured by the GDS without change.
However, when the composition and thickness of the
secondary coating film are unclear, the secondary
coating film is removed by an aqueous sodium
hydroxide solution or the like to expose the surface
of the glass coating film, and then, as described
.- 17 -
above, a secondary coating film having a thickness of
not less than 1 /im nor more than 2 /i m and formed in
a manner that a coating solution containing 26 to 38%
by weight of colloidal silica, 4 to 12 mass% of one
type or two types selected from a group consisting of
chromic anhydride and -chromate, and a balance being
composed of aluminum biphosphate is applied and dried
and then is baked at 800°C to 900°C is formed, and in
such a state, the values tb and tMg are measured by
the GDS. The secondary coating film in such a
composition range and in such a thickness range is
formed, thereby making it possible to measure the
values tB and tMg with sufficient accuracy.
[0017] From this result, an electrical steel sheet
is characterized in that the peak position of Mg is
expressed by (1) Expression when in the event that
the GDS analysis is performed from the surface of the
glass coating film, the peak position, of B, of
concentration in the deepest portion is expressed by
a discharge time, each of the peak positions of B is
set to tB (second), and the peak position of Mg is
set to tMg (second).
tMg X 1.6 ^ tB ^ tMg X 5 • • • (1)
[0018] Almost all Mg is derived from the glass
coating film. Thus, in the event that the secondary
coating film is thick, as the peak position of Mg
changes, the peak position of B changes. In order to
avoid this effect, in the present invention, the
thickness of the secondary coating film at the time
- 18 -
of GDS measurement is defined. Further, when a large
amount of Mg is contained in the secondary coating
film of a product sheet, the peak of Mg derived from
the glass coating film becomes unclear. Therefore,
in order to evaluate (1) Expression, the value
measured after the secondary coating film is removed
is needed to be used. Incidentally, the definitions
of thickness, composition, and forming conditions of
the secondary coating film are pretreatment
conditions where the GDS measurement is performed,
and the states of the secondary coating film and the
like of the product sheet are not defined.
[0019] In order to make the structure determined in
(1) Expression, as described in (3) described
previously, components such as Si may be defined and
this electrical steel sheet material may be treated
at a predetermined temperature, or the methods
described in (4) and (5) described previously may
also be followed.
[0020]
The contents of tests leading to obtaining of the
knowledge as above will be described below. First,
with regard to the relationship between precipitates
and a magnetic property and coating film adhesiveness,
tests to examine a silicon steel material having a
composition containing S were performed.
[0021] First, various silicon steel slabs each
containing Si: 3.3 mass%, C: 0.06 mass%, acid-soluble
Al: 0.027 mass%, N: 0.008 mass%, Mn: 0.05 mass% to
- 19 -
0.19 massl, S: 0.007 mass%, and B: 0.0010 mass% to
0.0035 massl, and a balance being composed of Fe and
inevitable impurities were obtained. Next, the
silicon steel slabs were heated at a temperature of
1100°C to 1250°C and ware subjected to hot rolling.
In the hot rolling, rough rolling was performed ,at
1050°C and then finish rolling was performed at 1000^C,
and thereby hot-rolled steel strips each having a
thickness of 2.3 mm were obtained. Then, a cooling
water was jetted onto the hot-rolled steel strips to
then let the hot-rolled steel strips cool down to
550°C, and thereafter the hot-rolled steel strips were
cooled down in the atmosphere. Subsequently,
annealing of the hot-rolled steel strips was
performed. Next, cold rolling was performed, and
cold-rolled steel strips each having a thickness of
0.22 mm were obtained. Thereafter, the cold-rolled
steel strips were heated at a speed of 15°C/s, and
were subjected to decarburization annealing at a
temperature of 840°C, and decarburization-annealed
steel strips were obtained. Subsequently, the
decarburization-annealed steel strips were annealed
in an ammonia containing atmosphere to increase
nitrogen in the steel strips up to 0.022 mass%. Next,
an annealing separating agent having MgO a-s its main
component was applied on the steel strips and finish
annealing was performed. With regard to the
atmosphere of the finish annealing, of the atmosphere
from 800°C to 1100°C, a nitrogen partial pressure PN2
- 20 -
was set to 0.5 and an oxygen potential Log[PH2O/?H2 ]
was set to -1.0, and of the atmosphere at 1100°C or
higher, the nitrogen partial- pressure PN2 was set to
0.1 or less and the oxygen potential Log[PH2O/PH2 ] was
set to -2 or less, and various samples were
manufactured.
[0022] Then, the relationship between precipitates
in the hot-rolled steel strip and a magnetic property
after the finish annealing was examined. This result
is shown in Fig. 2. The vertical axis indicates a
value (mass!) obtained by converting a precipitation
amount of BN into B. The horizontal axis corresponds
to an amount of S that has precipitated as MnS
(mass%). Further, white circles each indicate that a
magnetic flux density B8 was 1.88 T or more, and
black squares each indicate that the magnetic flux
density B8 was less than 1.88 T. As shown in Fig. 2,
in the samples each having the precipitation amount
of MnS or BN being less than a certain value, the
magnetic flux density B8 was low. This indicates
that secondary recrystallization was unstable.
[0023] On the other hand, the relationship between
the state of precipitates and coating film
adhesiveness after the finish annealing was examined.
In order to make an adhesiveness improving effect
clear, an evaluation was performed with a secondary
coating film amount larger than a normal areal weight.
When the areal weight of a secondary coating film is
increased, high tension is applied to a steel sheet,
I - 21 -
*
and if the adhesiveness of a glass coating film is
not sufficient, coating film peeling occurs easily.
For this test, as the secondary coating film, first,
a coating solution containing 100 g of aluminum
phosphate having a solid content concentration of 50%,
102 g of colloidal silica having a solid content
concentration of 20%, and 5.4 g of chromic anhydride
was made. Then, this coating solution was applied on
a steel sheet having a glass coating film obtained
after the finish annealing to be 10 g/m2 per one side
and was dried, and then was baked at 900°C. This
steel sheet was wound around a round bar having 20 4> ,
and then when a peeled area of the coating film to
expose the steel sheet on the inner side of the bent
portion was 5% or less, the adhesiveness was
determined to be good. This result is shown in Fig.
3. In Fig. 3, white circles each indicate one having
good adhesiveness, and black squares each indicate
one having coating film peeling and having
adhesiveness substantially equal to that of a
conventional one. As shown in Fig. 3, in the samples
each having the precipitation amounts of MnS arid BN
being certain values or more, the improvement of the
coating film adhesiveness is confirmed.
[0024] Further, with regard to the samples in which
certain amounts or more of MnS and BN are
precipitated, the relationship between an amount of B
that has not precipitated as BN and the magnetic
property after the finish annealing was examined.
- 22 -
I This result is shown in Fig. 4. In Fig. 4, the
horizontal axis indicates the B content (mass%), and
the vertical axis indicates the value (mass%)
obtained by converting the precipitation amount of BN
into B. Further, white circles each indicate that
the magnetic flux density B8 was 1.88 T or more, and
black squares each indicate that the magnetic flux
density B8 was less than 1.88 T. As shown in Fig. 4,
in the samples in which the amount of B that has not
precipitated as BN is a certain value or more, the
magnetic flux density B8 was low. This indicates
that the secondary recrystallization was unstable.
[0025] Similarly, with regard to the samples in
which certain amounts or more of MnS and BN are
precipitated, the relationship between the amount of
B that has not precipitated as BN and the coating
film adhesiveness after the finish annealing was
examined. This result is shown in Fig. 5. The
evaluation of the adhesiveness was performed by the
same method as that described in the explanation in
Fig. 3. As shown in Fig. 5, in the samples each
having the precipitation amount of BN being a certain
value or more, the improvement of the coating film
adhesiveness is confirmed.
[0026] Further, as a result of examination of a form
of the precipitates in the samples each having the
good magnetic property and coating film adhesiveness,
it turned out that MnS becomes a nucleus and BN
compositely precipitates around MnS. Such composite
- 23 -
i
precipitates are effective as inhibitors that
stabilize the secondary recrystallization. Further,
by making the atmosphere of the finish annealing
appropriate, BN is decomposed in an appropriate
temperature region during the finish annealing to
supply B to an interface between the steel sheet and
the glass coating film at the time of the glass
coating film being formed, which contributes to the
improvement of the coating film adhesiveness finally.
[0027] Further, the relationship between a condition
of the hot rolling and the magnetic property after
the finish annealing was examined. This result is.,
shown in Fig. 6 and Fig. 7.
[0028] In Fig. 6, the horizontal axis indicates the
Mn content (mass%) and the vertical axis indicates
the slab heating temperature (°C) at the time of hot
rolling. In Fig. 7, the horizontal axis indicates
the B content (mass%) and the vertical axis indicates
the slab heating temperature (°C) at the time of hot
rolling. Further, white circles each indicate that
the magnetic flux density B8 was 1.88 T or more, and
black squares each indicate that the magnetic flux
density B8 was less than 1.88 T. Further, the curve
in Fig. 6 indicates a solution temperature Tl (°C) of
MnS expressed by Expression (2) below, and the curve
in Fig. 7 indicates a solution temperature T3 (°C) of
BN expressed by Expression (4) below. As shown in
Fig. 6, it turned out that in the samples in which
the slab heating is performed at a temperature
- 24 -
•
determined according to the Mn content or lower, the
high magnetic flux density B8 is obtained. Further,
it also turned out that this temperature
approximately agrees with the solution temperature Tl
of MnS. Further, as shown in Fig. 7, it also turned
out that in the samples in which the slab heating is
performed at a temperature determined according to
the B content or lower, the high magnetic flux
density B8 is obtained. Further, it also turned out
that this temperature approximately agrees with the
solution temperature T3 of BN. That is, it turned
out that it is effective to perform the slab heating
in the temperature region where MnS and BN are not
completely solid-dissolved.
Tl = 14855/(6.82 - log([Mn] X [S])) - 273 ...(2)
T3 = 16000/(5.92 - log([B] X [N])) - 273 ...(4)
[0029] Here, [Mn] represents the Mn content (mass%),
[S] represents the S content (mass%), [B] represents
the B content (mass%), and [N] represents the N
content (mass%).
[0030] Further, as a result of examination of
precipitation behavior of BN, it turned out that a
precipitation temperature region of BN is 800°C to
1000°C.
[0031] Similarly, the relationship between the
condition of the hot rolling and the coating film
adhesiveness after the finish annealing was examined.
The evaluation of the adhesiveness was performed by
I the same method as that described in the explanation
- 25 -
in Fig. 3. This result is shown in Fig. 8 and Fig. 9.
In Fig. 8, the horizontal axis indicates the Mn
content (mass%) and the vertical axis indicates the
slab heating temperature (°C) at the time of hot
rolling. Further, white circles each indicate that
there was no problem in terms of the coating film
adhesiveness, and black squares each indicate that
coating film peeling occurred. Further, the curve in
Fig. 8 indicates the solution temperature Tl (°C) of
MnS expressed by Expression (2), and the curve in Fig.
9 indicates the solution temperature T3 (°C) of BN
expressed by Expression (4). As shown in Fig. 8, it
turned out that in the samples in which the slab
heating is performed at a temperature determined
according to the Mn content or lower, a coating film
adhesiveness improving effect is obtained. Further,
it also turned out that this temperature
approximately agrees with the solution temperature Tl
of MnS. Further, as shown in Fig. 9, it also turned
out that in the samples in which the slab heating is
performed at a temperature determined according to
the B content or lower, the coating film adhesiveness
improving effect is obtained. Further, it also
turned out that this temperature approximately agrees
with the solution temperature T3 of BN.
[0032] Further, the present inventors examined a
finishing temperature of the finish rolling in the
hot rolling. In this examination, first, various
silicon steel slabs each containing Si: 3.3 mass%, C:
- 26 -
0.06 mass%, acid-soluble Al: 0.027 mass%, N: 0.008
mass%, Mn: 0.1 mass%, S: 0.007 mass%, and B: 0.001
mas's% to 0.004 mass%, and a balance being composed of
Fe and inevitable impurities were obtained. Next,
the silicon steel slabs were heated at a temperature
of 1200°C and were subjected to hot rolling. In the
hot rolling, rough rolling was performed at 1050°C and
then finish rolling was performed at 1020 °C to 90 0 °C,
and thereby hot-rolled steel strips each having a
thickness of 2.3 mm were obtained. Then, a cooling
water was jetted onto the hot-rolled steel strips to
then let the hot-rolled steel strips cool down to
550°C, and thereafter the hot-rolled steel strips were
cooled down in the atmosphere. Subsequently,
annealing of the hot-rolled steel strips was
performed. Next, cold rolling was performed, and
cold-rolled steel strips each having a thickness of
0.22 mm were obtained. Thereafter, the cold-rolled
steel strips were heated at a speed of 15°C/s, and
were subjected to decarburization annealing at a
temperature of 840°C, and decarburization-annealed
steel strips were obtained. Subsequently, the
decarburization-annealed steel strips were annealed
in an ammonia containing atmosphere to increase
nitrogen in the steel strips up to 0.022 mass%. Next,
an annealing separating agent having MgO as its main
component was applied on the steel strips and finish
annealing was performed. With regard to the
atmosphere of the finish annealing, of the atmosphere
- 27 -
from 800°C to 1100°C, the nitrogen partial pressure PN2 j
was set to 0.5 and the oxygen potential Log[PH2o/PH2 ]
was set to -1.0, and of the atmosphere at 1100°C or
higher, the nitrogen partial pressure.PN2 was set to
0.1 or less and the oxygen potential Log [ PH2O/PH2] was
set to -2 or less, and various samples were
manufactured.
[0033] Then, the relationship between the finishing
temperature of the finish rolling in the hot rolling
and the magnetic property after the finish annealing
was examined. This result is shown in Fig. 10. In
Fig. 10, the horizontal axis indicates the B content
(mass%), and the vertical axis indicates a finishing
temperature Tf of the finish rolling. Further, white
circles each indicate that the magnetic flux density
B8 was 1.91 T or more, and black squares each
indicate that the magnetic flux density B8 was less
than 1.91 T. As shown in Fig. 10, it turned out that
when the finishing temperature Tf of the finish
rolling satisfies Expression (5) below, the high
magnetic flux density B8 is obtained. This is
conceivably because by controlling the finishing
temperature Tf of the finish rolling, the
precipitation of BN was further promoted.
Tf ^ 1000 - 10000 X [B] ...(5)
[0034] Further, the relationship between the
finishing temperature of the finish rolling in the
hot rolling and the coating film adhesiveness after
the finish annealing was examined. The evaluation of
- 28 -
the adhesiveness was performed by the same method as
that described in the explanation in Fig. 3. This
result is shown in Fig. 11. In Fig. 11, the
horizontal axis indicates the B content (mass%) and
the vertical axis indicates the finishing temperature
Tf of the finish rolling. Further, white circles
each indicate that the coating film adhesiveness was
good, and black squares each indicate that coating
film peeling occurred. As shown in Fig. 11, it
turned out that the finishing temperature Tf of the
finish rolling satisfies Expression (5) and the
atmosphere of the finish annealing is made
appropriate, and thereby the coating film
adhesiveness improving effect is obtained.
[0035]
Next, with regard to the relationship between the
precipitates and the magnetic property and the
coating film adhesiveness, tests to examine a silicon
steel material having a composition containing Se
were performed.
[0036] First, various silicon steel slabs each
containing Si: 3.3 mass%, C: 0.06 mass%, acid-soluble
Al: 0.028 mass%, N: 0.007 mass%, Mn: 0.05 mass% to
0.20 mass%, Se: 0.007 mass%, and B: 0.0010 mass% to
0.0035 mass%, and a balance being composed of Fe and
inevitable impurities were obtained. Next, the
silicon steel slabs were heated at a temperature of
1100°C to 1250°C and were subjected to hot rolling.
In the hot rolling, rough rolling was performed at
- 29 -
t
1050°C and then finish rolling was performed at 1000°C,
and thereby hot-rolled steel strips each having a
thickness of 2.3 mm were obtained. Then, a cooling
water was jetted onto the hot-rolled steel strips to
then let the hot-rolled steel strips cool down to
550°C, and thereafter the hot-rolled steel strips were
cooled down in the atmosphere. Subsequently,
annealing of the hot-rolled steel strips was
performed. Next, cold rolling was performed, and
cold-rolled steel strips each having a thickness of
0.2 2 mm were obtained. Thereafter, the cold-rolled
steel strips were heated at a speed of 15°C/s, and
were subjected to decarburization annealing at a
temperature of 850°C, and decarburization-annealed
steel strips were obtained. Subsequently, the
decarburization-annealed steel strips were annealed
in an ammonia containing atmosphere to increase
nitrogen in the steel strips up to 0.023 mass%. Next,
an annealing separating agent having MgO as its main
component was applied on the steel strips and finish
annealing was performed in a manner that of the
atmosphere from 800°C to 1100°C, the nitrogen partial
pressure PN2 was set to 0.5 and the oxygen potential
Log [ PH2O/PH2] was set to -1.0, and of the atmosphere at
1100°C or higher, the nitrogen partial pressure PN2
was set to 0.1 or less and the oxygen potential
Log [ PH2O/PH2 ] wis set to -2 or less, and various
samples were manufactured.
[0037] Then, the relationship between precipitates
- 30 -
in the hot-rolled steel strip and a magnetic property
after the finish annealing was examined. This result
is shown in Fig. 12. In Fig. 12, the horizontal axis
indicates a value (mass%) obtained by converting a
precipitation amount of MnSe into an amount of Se,"
and the vertical axis indicates a value (mass%)
obtained by converting a precipitation amount of BN
into B. Further, white circles each indicate that
the magnetic flux density B8 was 1.88 T or more, and
black squares each indicate that the magnetic flux
density B8 was less than 1.88 T. As shown in Fig. 12,
in the samples each having the precipitation amount
of MnSe or BN being less than a certain value, the
magnetic flux density B8 was low. This indicates
that secondary recrystallization was unstable.
[0038] Similarly, the relationship between the
precipitates in the hot-rolled steel strip and
coating film adhesiveness after the finish annealing
was examined. The evaluation of the coating film
adhesiveness was performed by the same method as that
described in the explanation in Fig. 3. This result
is shown in Fig. 13. In Fig. 13, the horizontal axis
indicates the value (mass%) obtained by converting
the precipitation amount of MnSe into the amount of
Se, and the vertical axis indicates the value (mass%)
obtained by converting the precipitation amount of BN
into B. Further, white circles each indicate that
the coating film adhesiveness is good and black
squares each indicate that coating film peeling
- 31 -
•
;
•i
occurred. As shown in Fig. 13, it is found that in i
the case of the samples in which the precipitation
amounts of MnSe and BN are certain values or more and
the atmosphere of the finish annealing being
appropriate, the coating film adhesiveness improving
effect is obtained.
[0039] Further, with regard to the samples in which
certain amounts or more of MnSe and BN are
precipitated, the relationship between an amount of B
that has not precipitated as BN and the magnetic
property after the finish annealing was examined.
This result is shown in Fig. 14. In Fig. 14, the
horizontal axis indicates the B content (mass%), and
the vertical axis indicates the value (mass%)
obtained by converting the precipitation amount of BN
into B. Further, white circles each indicate that
the magnetic flux density B8 was 1.88 T or more, and
black squares each indicate that the magnetic flux
density B8 was less than 1.88 T. As shown in Fig. 14,
in the samples in which the amount of B that has not
precipitated as BN is a certain value or more, the
magnetic flux density B8 was low. This indicates
that the secondary recrystallization was unstable.
[0040] Similarly, with regard to the samples in
which certain amounts or more of' MnSe and BN are
precipitated, the relationship between the amount of
B that has not precipitated as BN and the coating
film adhesiveness after the finish annealing was
examined. The evaluation of the coating film
- 32 -
9
adhesiveness was performed by the same method as that
described in the explanation in Fig. 3. This result
is shown in Fig. 15. In Fig. 15, the horizontal axis
indicates the B content (mass%), and the vertical
axis indicates the value (mass%) obtained by
converting the precipitation amount of BN into B.
Further, white circles each indicate that the
improvement effect was seen in the coating film
adhesiveness, and black squares each indicate that
coating film peeling occurred and there was no
improvement effect in the coating film adhesiveness.
As shown in Fig. 15, in the case of the samples in
which the amount of B that has not precipitated as BN
is a certain value or less and the atmosphere of the
finish annealing being the appropriate condition, the
improvement effect of the coating film adhesiveness
is seen.
[0041] Further, as a result of examination of a form
of the precipitates in the samples each having the
good magnetic property and coating film adhesiveness,
it turned out that MnSe becomes a nucleus and BN
compositely precipitates around MnSe. Such composite
precipitates are effective as inhibitors that
stabilize the secondary recrystallization. Further,
when the atmosphere of the finish annealing is
appropriate, BN is decomposed in an appropriate
temperature region during the finish annealing to
supply B to an interface between a steel sheet and a
glass coating film at the time of the glass coating
- 33 -
film being formed, which contributes to the
improvement of the coating film adhesiveness finally.
[0042] Further, the relationship between a condition
•
of the hot rolling and the magnetic property after
the finish annealing was examined. This result is
shown in Fig. 16 and Fig. 17.
[0043] In Fig. 16, the horizontal axis indicates the
Mn content (mass%) and the vertical axis indicates
the slab heating temperature (°C) at the time of hot
rolling. In Fig. 17, the horizontal axis indicates
the B content (mass%) and the vertical axis indicates
the slab heating temperature (°C) at the time of hot
rolling. Further, white circles each indicate that
the magnetic flux density B8 was 1.88 T or more, and
black squares each indicate that the magnetic flux
density B8 was less than 1.88 T. Further, the curve
in Fig. 16 indicates a solution temperature T2 (°C) of
MnSe expressed by Expression (3) below, and the curve
in Fig. 17 indicates the solution temperature T3 (°C)
of BN expressed by Expression (4). As shown in Fig.
16, it turned out that-in the samples in which the
slab heating is performed at a temperature determined
according to the Mn content or lower, the high
magnetic flux density B8 is obtained. Further, it
also turned out that this temperature approximately
agrees with the solution temperature T2 of MnSe.
Further, as shown in Fig. 17, it also turned out that
in the samples in which the slab heating is performed
at a temperature determined according to the B
- 34 -
•
content or lower, the high magnetic flux density B8
is obtained. Further, it also turned out that this
temperature approximately agrees with the solution
temperature T3 of BN . That is, it turned out that it
is effective to perform the slab heating in the
temperature region where MnSe and BN are not
completely solid-dissolved.
[0044] T2 = 10733/(4.08 - log([Mn] X [Se] ) ) -
273 ... (3)
Here, [Se] represents the Se content (mass%).
[0045] Similarly, the relationship between the
condition of the hot rolling and the coating film
adhesiveness after the finish annealing was examined.
This result is shown in Fig. 18 and Fig. 19. The
evaluation of the coating film adhesiveness was
performed by the same method as that described in the
explanation in Fig. 3.
[0046] In Fig. 18, the horizontal axis indicates the
Mn content (mass%) and the vertical axis indicates
the slab heating temperature (°C) at the time of hot
rolling. In Fig. 19, the horizontal axis indicates
the B content (mass%) and the vertical axis indicates
the slab heating temperature (°C) at the time of hot
rolling. Further, white circles each indicate that
the coating film adhesiveness improved, and black
squares each indicate that coating film peeling
occurred and the adhesiveness did not improve.
Further, the curve in Fig. 18 indicates the solution
temperature T2 (°C) of MnSe expressed by Expression
- 35 -
(3), and the curve in Fig. 19 indicates the solution
temperature T3 (°C) of BN expressed by Expression (4).,.
As shown in Fig. 18, it turned out that in the
samples in which the slab heating is performed at a
temperature determined according to the Mn content or
lower, the coating film adhesiveness improves.
Further, it also turned out that this temperature
approximately agrees with the solution temperature T2
of MnSe. Further, as shown in Fig. 19, it turned out
that in the samples in which the slab heating is
performed at a temperature determined according to
the B content or lower, the coating film adhesiveness
improving effect is obtained. Further, it also
turned out that this temperature approximately agrees
with the solution temperature T3 of BN. That is, it
turned out that it is effective to perform the slab
heating in the temperature region where MnSe and BN
are not solid-dissolved completely and to perform the
finish annealing in the • appropriate atmosphere.
[0047] Further, as a result of examination of
precipitation behavior of BN, it turned out that a
precipitation temperature region of BN is 800°C to
10 0 0°C.
[0048] Further, the present inventors examined a
finishing temperature of the finish rolling in the
hot rolling. In this examination, first, various
silicon steel slabs each containing Si: 3.3 mass%, C:
0.06 mass%, acid-soluble Al: 0.028 mass%, N: 0.007
mass%, Mn: 0.1 mass%, Se: 0.007 mass%, and B: 0.001
- 36 -
mass% to 0.004 mass%, and a balance being composed of
I Fe and inevitable impurities were obtained. Next,
the silicon steel slabs were heated at a temperature
of 1200°C and were subjected to hot rolling. ,In the
hot rolling, rough rolling was performed at 1050°C and
then finish rolling was performed at 102 0°C to 900°C,
and thereby hot-rolled steel strips each having a
thickness of 2.3 mm were obtained. Then, a cooling
water was jetted onto the hot-rolled steel strips to
then let the hot-rolled steel strips cool down to
5 5 0 °C, and thereafter the hot-rolled steel strips were
cooled down in the atmosphere. Subsequently,
annealing of the hot-rolled steel strips was
performed. Next, cold rolling was performed, and
cold-rolled steel strips each having a thickness of
0.22 mm were obtained. Thereafter, the cold-rolled
steel strips were heated at a speed of 15°C/s, and
were subjected to decarburization annealing at a
temperature of 850°C, and decarburization-annealed
steel strips were obtained. Subsequently, the
decarburization-annealed steel strips were annealed
in an ammonia containing atmosphere to increase
nitrogen in the steel strips up to 0.023 mass%. Next,
an annealing separating agent having MgO as its main
component was applied on the steel strips, and finish
annealing was performed in a manner that of the
atmosphere from 800°C to 1100°C, the nitrogen partial
pressure PN2 is set to 0.5 and the oxygen potential
Log [ PH2O/PH2] is set to -1, and of the atmosphere at
- 37 -
1100°C or higher, the nitrogen partial pressure PN2 is
set to 0.1 or less and the oxygen potential
Log [ PH2O/PH2] is set to -2, and various samples were
manufactured.
[0049] Then, the relationship between the finishing
temperature of the finish rolling in the hot rolling
and the magnetic property after the finish annealing
was examined. This result is shown in Fig. 20. In
Fig. 20, the horizontal axis indicates the B content
(mass%), and the vertical axis indicates the
finishing temperature Tf of the finish rolling.
Further, white circles each indicate that the
magnetic flux density B8 was 1.91 T or more, and
black squares each indicate that the magnetic flux
density B8 was less than 1.91 T. As shown in Fig. 20,
it turned out that when the finishing temperature Tf
of the finish rolling satisfies Expression (13)
described previously, the high magnetic flux density
B8 is obtained. This is conceivably because by
controlling the finishing temperature Tf of the
finish rolling, the precipitation of BN was further
promoted.
[0050] Similarly, the relationship between the
finishing temperature of the finish rolling in the
hot rolling and the coating film adhesiveness after
the finish annealing was examined. This result is
shown in Fig. 21. In Fig. 21, the horizontal axis
indicates the B content (mass%) and the vertical axis
indicates the finishing temperature Tf of the finish
- 38 -
*
rolling. Further, white circles each indicate that
the coating film adhesiveness improved, and black
squares each indicate that coating film peeling
occurred and no adhesiveness improving effect was
obtained. As shown in Fig. 21, it turned out that
when the finishing temperature Tf of the finish
rolling satisfies Expression (13) and the finish
annealing is performed in the appropriate atmosphere,
the coating film adhesiveness improving effect is
obtained.
[0051]
Further, with regard to the relationship between
the magnetic property and the coating film
adhesiveness, tests to examine a silicon steel
material having a composition containing S and Se
were performed.
[0052] First, various silicon steel slabs each
containing Si: 3.3 mass%, C: 0.06 mass%, acid-soluble
Al: 0.026 mass%, N: 0.009 mass%, Mn: 0.05 mass% to
0.20 mass%, S: 0.005 mass%, Se: 0.007 mass%, and B:
0.0010 mass% to 0.0035 mass%, and a balance being
composed of Fe and inevitable impurities were
obtained. Next, the silicon steel slabs were heated
at a temperature of 1100°C to 1250°C and were
subjected to hot rolling. In the hot rolling, rough
rolling was performed at 1050°C and then finish
rolling was performed at 1000°C, and thereby hotrolled
steel strips each having a thickness of 2.3 mm
were obtained. Then, a cooling water was jetted onto
- 39 -
the hot-rolled steel strips to then let the hotrolled
steel strips cool down to 550°C, and thereafter
the hot-rolled steel strips were cooled down in the
atmosphere. Subsequently, annealing of the hotrolled
steel strips was performed. Next, cold
rolling was performed, and cold-rolled steel strips
each having a thickness of 0.22 mm were obtained.
Thereafter, the cold-rolled steel strips were heated
at a speed of 15°C/s, and were subjected to
decarburization annealing at a temperature of 850°C,
and decarburization-annealed steel strips were
obtained. Subsequently, the decarburization-annealed
steel strips were annealed in an ammonia containing
atmosphere to increase nitrogen in the steel strips
up to 0.021 mass%. Next, an annealing separating
agent having MgO as its main component was applied on
the steel strips, and.finish annealing was performed
in a manner that of the atmosphere from 800°C to
1100°C, the nitrogen partial pressure PN2 is set to
0.5 and the oxygen potential Log[PH2O/PH2 ] is set to -1,
and of the atmosphere at 1100°C or higher, the
nitrogen partial pressure PN2 is set to 0.1 or less
and the oxygen potential Log [ PH2O/PH2] is set to -2 or
less, and various samples were manufactured.
[0053] Then, the relationship between precipitates
in the hot-rolled steel strip and the magnetic
property after the finish annealing was examined.
This result is shown in Fig. 22. In Fig. 22, the
horizontal axis indicates the sum (mass%) of a value
- 40 -
obtained by converting a precipitation amount of MnS
into an amount of S and a value obtained bymultiplying
a value obtained by converting a
precipitation amount of MnSe into an amount of Se by
0.5, and the vertical axis indicates a value (mass%)
obtained by converting a precipitation amount of BN
into B. Further, white circles each indicate that
the magnetic flux density B8 was 1.88 T or more, and
black squares each indicate that the magnetic flux
density B8 was less than 1.88 T. As shown in Fig. 22,
in the samples each having the precipitation amount
of MnS, MnSe, or BN being less than a certain value,
the magnetic flux density B8 was low. This indicates
that secondary recrystallization was unstable.
[0054] Similarly, the relationship between the
precipitates in the hot-rolled steel strip and the
coating film adhesiveness after the finish annealing
was examined. The evaluation of the coating film
adhesiveness was performed by the same method as that
described in the explanation in Fig. 3. This result
is shown in Fig. 23. In Fig. 23, the horizontal axis
indicates the sum (mass%) of the value obtained by
converting the precipitation amount of MnS into the
amount of S and the value obtained by multiplying the
value obtained by converting the precipitation amount
of MnSe into the amount of Se by 0.5, and the
vertical axis indicates the value (massl) obtained by
converting the precipitation amount of BN into B.
Further, white circles each indicate that the coating
- 41 -
film adhesiveness improved and black squares each
indicate that coating film peeling occurred and no
coating film adhesiveness improving effect was
obtained. As shown in Fig. 23, when the
precipitation amounts of MriS, MnSe and BN were
certain values or more and the atmosphere of the
finish annealing was the appropriate condition, the
coating film adhesiveness improved.
[0055] Further, with regard to the samples in which
certain amounts or more of MnS, MnSe and BN are
precipitated, the relationship between an amount of B
that has not precipitated as BN and the magnetic
property after the finish annealing was examined.
This result is shown in Fig. 24. In Fig. 24, the
horizontal axis indicates the B content (mass%), and
the vertical axis indicates the value (mass%)
obtained by converting the precipitation amount of BN
into B. Further, white circles each indicate that
the magnetic flux density B8 was 1.88 T or more, and
black squares each indicate that the magnetic flux
density B8 was less than 1.88 T. As shown in Fig. 24,
in the samples in which the amount of B that has not
precipitated as BN is a certain value or more, the
magnetic flux density B8 was low. This indicates
that the secondary recrystallization was unstable.
[0056] Similarly, with regard to the samples in
which certain amounts or more of MnS, MnSe and BN are
precipitated, the relationship between the amount of
B that has not precipitated as BN and the coating
- 42 -
film adhesiveness after the finish annealing was
examined. The evaluation method of the coating film
adhesiveness is the same as that used in Fig. 3.
This result is shown in Fig. 25. In Fig. 25, the
horizontal axis indicates the B content (mass%), and
the vertical axis indicates the value (mass%)
obtained by converting the precipitation amount of BN
into B. Further, white circles each indicate that
the coating film adhesiveness improved, and black
squares each indicate that coating film peeling
occurred and the coating film adhesiveness did not
improve. As shown in Fig. 25, in the case of the
samples in which the amount of B that has not
precipitated as BN is a certain value or less and the
atmosphere of the finish annealing being appropriate,
the coating film adhesiveness improved.
[0057] Further, as a result of examination of a form
of the precipitates in the samples each having the
good magnetic property and coating film adhesiveness,
<
it turned out that MnS or MnSe becomes a nucleus and
BN compositely precipitates around MnS or MnSe. Such
composite precipitates are effective as inhibitors
that stabilize the secondary recrystallization.
Further, when the atmosphere of the finish annealing
is set to an appropriate condition, BN is decomposed
in an appropriate temperature region during the
finish annealing to supply B to an interface between
a steel sheet and a glass coating film at the time of
the glass coating film being formed, which
- 43 -
I
1'
I
1:
contributes to the improvement of the coating film
adhesiveness finally.
[0058] Next, the relationship between a condition of
the hot rolling and the magnetic property after the
finish annealing was examined. This result is shown
in Fig. 26 and Fig. 27.
[0059] In Fig. 26, the horizontal axis indicates the
Mn content (mass%) and the vertical axis indicates
the slab heating temperature (°C) at the time of hot
rolling. In Fig. 27, the horizontal axis indicates
the B content (mass%) and the vertical axis indicates
the slab heating temperature (°C) at the time of hot
rolling. Further, white circles each indicate that
the magnetic flux density B8 was 1.88 T or more, and
black squares each indicate that the magnetic flux
density B8 was less than 1.88 T. Further, the two
curves in Fig. 26 indicate the solution temperature
Tl (°C) of MnS expressed by Expression (2) and the
solution temperature T2 (°C) of MnSe expressed by
Expression (3), and the curve in Fig. 27 indicates
the solution temperature T3 (°C) of BN expressed by
Expression (4). As shown in Fig. 26, it turned out
that in the samples in which the slab heating is
performed at a temperature determined according to
the Mn content or lower, the high magnetic flux
density B8 is obtained. Further, it also turned out
that this temperature approximately agrees with the
solution temperature Tl of MnS and the solution
temperature T2 of MnSe. Further, as shown in Fig. 27,
- 44 -
i.
!•
it also turned out that in the samples in which the j
[
slab heating is performed at a temperature determined
according to the B content or lower, the high
magnetic flux density B8 is obtained. Further, it
also turned out that this temperature approximately
agrees with the solution temperature T3 of BN . That
is, it turned out that it is effective to perform the
slab heating in the temperature region where MnS,
MnSe, and BN are not completely solid-dissolved.
[0060] Similarly, the relationship between the
condition of the hot rolling and the coating film
adhesiveness after the finish annealing was examined.
This result is shown in Fig. 28 and Fig. 29. In Fig.
28, the horizontal axis indicates the Mn content
(mass%) and the vertical axis indicates the slab
heating temperature (°C) at the time of hot rolling.
In Fig. 29, the horizontal axis indicates the B
content (mass%) and the vertical axis indicates the
slab heating temperature (°C) at the time of hot
rolling. Further, white circles each indicate that
the coating film adhesiveness improved, and black
squares each indicate that coating film peeling
occurred and the coating film adhesiveness did not
improve. Further, the two curves in Fig. 28 indicate
the solution temperature Tl (°C) of MnS expressed by
Expression (2) and the solution temperature T2 (°C) of
MnSe expressed by Expression (3), and the curve in
Fig. 29 indicates the solution temperature T3 (°C) of
BN expressed by Expression (4). As shown in Fig. 28,
- 45 -
it turned out that in the samples in which the slab
heating is performed at a temperature determined
according to the Mn content or lower and the
atmosphere of the finish annealing is the appropriate
condition, the coating film adhesiveness improves.
Further, it also turned out that this temperature
approximately agrees with the solution temperature Tl
of MnS and the solution temperature T2 of MnSe.
Further, as shown in Fig. 29, it also turned out that
in the samples in which the slab heating is performed
at a temperature determined according to the B
content or lower and the atmosphere of the finish
annealing is the appropriate condition, the coating
film adhesiveness improves. Further, it also turned
out that this temperature approximately agrees with
the solution temperature T3 of BN . That is, it
turned out that it is effective that the slab heating
is performed in the temperature region where MnS,
MnSe, and BN are not solid-dissolved completely and
the atmosphere of the finish annealing is appropriate.
[0061] Further, as a result of examination of
precipitation behavior of BN, it turned out that a
precipitation temperature region of BN is 800°C to
100 0°C.
[0062] Further, the present inventors examined a
finishing temperature of the finish rolling in the
hot rolling. In this examination, first, various
silicon steel slabs each containing Si: 3.3 mass%, C:
0.06 mass%, acid-soluble Al: 0.026 mass%, N: 0.009
- 46 -
mass%, Mn: 0.1 mass%, S: 0.005 mass%, Se: 0.007 mass%,
and B: 0.001 mass% to 0.004 mass%, and a balance
being composed of Fe and inevitable impurities were
obtained. Next, the silicon steel slabs were heated
at a temperature of 1200°C and were subjected to hot
rolling. In the hot rolling, rough rolling was
performed at 1050°C and then finish rolling was
performed at 1020°C to 90 0°C, and thereby hot-rolled
steel strips each having a thickness of 2.3 mm were
obtained. Then, a cooling water was jetted onto the
hot-rolled steel strips to then let the hot-rolled
steel strips cool down to 550°C, and thereafter the
hot-rolled steel strips were cooled down in the
atmosphere. Subsequently, annealing of the hotrolled
steel strips was performed. Next, cold
rolling was performed, and cold-rolled steel strips
each having a thickness of 0.22 mm were obtained.
Thereafter, the cold-rolled steel strips were heated
.at a speed of 15°C/s, and were subjected to
decarburization annealing at a temperature of 850°C,
and decarburization-annealed steel strips were
obtained. Subsequently, the decarburization-annealed
steel strips were annealed in an ammonia containing
atmosphere to increase nitrogen in the steel strips
up to 0.021 mass%. Next, an annealing separating
agent having MgO as its main component was applied on
the steel strips, and finish annealing was performed
in a manner that of the atmosphere from 800°C to
1100°C, the nitrogen partial pressure PN2 is set to
- 47 -
'i
0.5 and the oxygen potential Log[PH2O/PH2 ] is set to -1, j
and of the atmosphere at 1100°C or higher, the
nitrogen partial pressure PN2 is set to 0.1 or less
and the oxygen potential Log [ PH2O/PH2] is set to -2 or
less, and various samples were manufactured.
i
[0063] Then, the relationship between the finishing
temperature of the finish rolling in the hot rolling
and the magnetic property after the finish annealing
was examined. This result is shown in Fig. 30. In
Fig. 30, the horizontal axis indicates the B content
(mass%), and the vertical axis indicates the
finishing temperature Tf of the finish rolling.
Further, white circles each indicate that the
magnetic flux density B8 was 1.91 T or more, and
black squares each indicate that the magnetic flux
density B8 was less than 1.91 T. As shown in Fig. 30,
it turned out that when the finishing temperature Tf
of the finish rolling satisfies Expression (5), the
high magnetic flux density B8 is obtained. This is
conceivably because by controlling the finishing
temperature Tf of the finish rolling, the
precipitation of BN was further promoted.
[0064] Similarly, the relationship between the
finishing temperature of the finish rolling in the
hot rolling and the coating film adhesiveness after
the finish annealing was examined. This result is
shown in Fig. 31. In Fig. 31, the horizontal axis
indicates the B content (mass%) and the vertical axis
indicates the finishing temperature Tf of the finish
- 48 -
rolling. Further, white circles each indicate that
the coating film adhesiveness improved, and black
squares each indicate that coating film peeling
occurred and the coating film adhesiveness did not
improve. As shown in Fig. 31, it turned out that
when the finishing temperature Tf of the finish
rolling satisfies Expression (5) and the atmosphere
of the finish annealing is the appropriate condition,
the coating film adhesiveness improves.
[0065] From the results of the first to third
experiments, it is found that the precipitated form
of BN and the atmosphere of the finish annealing are
controlled as above, and thereby the magnetic
property and coating film adhesiveness of the grainoriented
electrical steel sheet improve stably.
Incidentally, when the atmosphere of the finish
annealing was not set to the values by Expressions
(9) and (10), the magnetic property was good but the
coating film adhesiveness improving effect was not
obtained. The detailed reason why when B does not
compositely precipitate with MnS or MnSe as BN, the
secondary recrystallization becomes unstable, thereby
making it impossible to obtain the good magnetic
property and unless the atmosphere of the finish
annealing is controlled, the coating film
adhesiveness improving effect does not appear has not
been clarified yet so for, but is conceived as - follows .
[0066] First, the magnetic property is as follows.
- 49 - 1
Generally, B in a solid solution state is likely to
segregate in grain boundaries, and BN that has
precipitated independently after the hot rolling is
often fine. B in a solid solution state and fine BN
suppress grain growth at the time of primary
recrystallization as strong inhibitors in a lowtemperature
region where the decarburization
annealing is performed, and in a high-temperature
region where the finish annealing is performed, B in
a solid solution state and fine BN do not function as
inhibitors locally, thereby turning the crystal grain
structure of the steel into a mixed grain structure.
Thus, when a primary recrystallization temperature is
in the low-temperature region, primary recrystallized
grains are small, so that the magnetic flux density
of the grain-oriented electrical steel sheet becomes
low. Further, in the high-temperature region, the
crystal grain structure is turned into the mixed
grain structure, so that the secondary
recrystallization becomes unstable.
[0067] Next, the coating film adhesiveness is as
follows. First, with regard to the.state of B after
the purification annealing, it is conceivable that B j
existing in the interface between the glass coating
film and the steel sheet exists as oxide. It is 1
conceivable that B exists as BN before the
purification occurs, but BN is decomposed by the
purification and B in the steel sheet diffuses to the
vicinity of the surface of the steel sheet to form
- 50 -
oxide. Details of the oxide are not clarified, but
the present inventors presume that B forms composite
oxide with Mg, Si, and Al existing in the glass
coating film and at the bottom of the glass coating
film.
[0068] BN is decomposed at a later stage of the
finish annealing and B is concentrated on the surface
of the steel sheet, but when the concentration of B
occurs at an early stage of the.glass coating film
being formed, the interface structure after the
completion of the finish annealing is in a state
where B is concentrated in a portion, of the glass
coating film, shallower than the bottom. For this
reason, the interface between the glass coating film
and the steel sheet is not brought into the structure
provided with the characteristics of the present
invention. On the other hand, when the decomposition
of BN is started in a state where the formation of
the glass coating film has advanced to a
predetermined extent, B is concentrated in the
vicinity of the bottom of the glass coating film and
the interface between the glass coating film and the
steel sheet is brought into the.v structure provided
with the characteristics of the present invention.
Here, the state where the formation of the glass
coating film has advanced to a predetermined extent
is a situation where the formation of the bottom of
the glass coating film has started, and a temperature
region of the situation is about 1000°C or higher.
- 51 -
Thus, in order to make the interface structure
between the glass coating film and the steel sheet of
the present invention, B is concentrated at this
temperature or higher, which may be set as the
condition, but for this, the precipitate of BN in the
steel sheet needs to exist stably until the
temperature becomes high.
[0069] Unless BN is fine and is compositely
precipitated with MnS or MnSe, the decomposition
temperature in the finish annealing decreases and
solid-dissolved B is concentrated on the interface
between the glass coating film and the steel sheet
before the bottom of the glass coating film is formed,
which does not contribute to improvement of an anchor
effect of the interface between the glass coating
film and the steel sheet. For this reason, it is
conceivable that the coating film adhesiveness
improving effect disappear.
[0070] Thus, in order to make B function effectively,
it is necessary to control the atmosphere of the
finish annealing in a high temperature region. In
order to achieve this, the inventors found that it is
effective to suppress the decomposition of BN from
800°C to 1100°C and at 1100°C or higher, promote the
decomposition of BN and make the atmosphere where the
purification is advanced.
[0071] Incidentally, B is also used as an additive
of the annealing separating agent, and thus in the
grain-oriented electrical steel sheet that has been
- 52 -
t
subjected to the finish annealing, segregation of B
is sometimes observed in the vicinity of the
interface between the glass coating film and the
steel sheet. However, B derived from the annealing
separating agent makes it difficult to obtain the
interface structure between the glass coating film
and the steel sheet in the present invention. In
order to make the concentration situation such as the
interface structure between the glass coating film
and the steel sheet of the present invention by B
derived from the annealing separating agent, B in
sufficient amount needs to diffuse in the steel sheet
from the surface of the steel sheet. It is
conceivable that the oxide of B has a relatively high
oxygen equilibrium dissociation pressure among the
elements constituting the glass coating film, and
thus the situation where B diffuses to the bottom of
the glass coating film that is supposed to be lower
in the oxygen potential than the surface layer of the
glass coating film to form oxide does not occur
easily. Thus, it is difficult to make the interface
structure between the glass coating film and the
steel sheet in the present invention by using B
derived from the annealing separating agent.
[0072] Next, there will be explained reasons for
limiting respective conditions of the present
invention below.
[0073] First, with regard to the interface structure
between the glass coating film and the steel sheet,
- 53 -
when in the deepest portion, the concentration
position of B is deeper than a concentration position
of Mg, the adhesiveness of the glass coating film
improves. As for a value, in the event that the GDS
analysis is performed from the surface of the glass
coating film, the peak position, of B, of the
concentration in the deepest portion is expressed by
a discharge time to be set to tB (second) and the
peak position of Mg is set to tMg (second), and in
this case, the following condition is set, thereby
making it possible to obtain a good result.
tMg X 1.6 ^ tB ^ tMg X 5 • • • (1)
[0074] On the other hand, when the value tB is too
large, the magnetic property tends to deteriorate.
For this reason, the value tB is preferably set to
tMg X 5.0 or less .
[0075] Next, there will be described reasons for
limiting the atmosphere of the finish annealing.
While the temperature is 800°C to 1100°C, the nitrogen
partial pressure PN2 is maintained to 0.75 to 0.2 and
the oxygen potential Log[PH2O/PH2 ] is set to 0.7 or
less. This is to suppress the decomposition of BN in
the temperature region of 800 to 1100°C. Unless the
decomposition of BN is suppressed in this temperature
region, it makes impossible to obtain the good
adhesiveness. This is because unless the
decomposition of BN is suppressed sufficiently in the
case of the inappropriate atmosphere, B diffuses to
the surface of the steel sheet since the early period
- 54 -
of the finish annealing and is concentrated in the
shallow position from the surface of the steel sheet.
[0076] Details of the condition of the atmosphere of
the finish annealing are as follows. That is, the
nitrogen partial pressure PN2 is set to the value of
0.2 or more in order to suppress the decomposition of
BN appropriately. On the other hand, when it exceeds
0.75 to be too large, the decomposition of BN is
suppressed excessively and the good secondary
recrystallization does not occur. Further, when the
oxygen potential Log[PH2O/PH2 ] exceeds -0.7, oxidation
of B occurs, to thereby promote the decomposition of
BN consequently. Thus, in order to suppress the
decomposition of BN in the temperature region of 800 "
to 1100°C, the atmosphere of the finish annealing
satisfies the above-described conditions of the
nitrogen partial pressure PN2 and the oxygen potential
Log [PH2O/PH2] •
[0077] Further, as for control of the atmosphere of
the finish annealing, when the oxygen partial
pressure and the nitrogen partial pressure are
controlled according to (11) Expression, the better
result can be obtained.
4Log[PN2] = 3Log[PH2o/PH2] + A + 3455/T- • • • (11)
Here, -3.72 ^ 3Log [ PH2o/ PH2 ] + A ^ -5.32 and -0.7
^ Log [ PH2O/PH2] are satisfied and T represents the
absolute temperature.
[0078] Further, the temperature region where the
above-described atmosphere conditions are set is set
- 55 -
to 800°C to 1100°C. If the temperature region is
lower than 800°C, it overlaps with a temperature
region of the early stage of the formation of the
glass coating film, and when in this region, the
above-described oxygen potential Log [ PH2O/PH2 ] is set,
the sound glass coating film cannot be obtained and
the coating film adhesiveness is likely to be
adversely affected. When the lower limit temperature
is too low, the adhesiveness is adversely affected,
and when it is too high, the decomposition of BN
cannot be suppressed sufficiently, and thus in this
embodiment, the lower limit temperature is set to
800°C. On the other hand, when the upper limit
temperature is too high, the secondary
recrystallization becomes unstable, and when the
upper limit temperature is too low, B is easily
concentrated in the vicinity of poles of the steel
sheet surface and the adhesiveness improving effect
is likely to disappear. Thus, in this embodiment,
the atmosphere of the above-described conditions is
made from 800°C to 1100°C.
[0079] With regard to the nitrogen partial pressure
PN2, a method of adjusting the atmosphere of the
finish annealing can be performed by controlling a
mixed ratio of a nitrogen gas and a gas that does not
react with the steel sheet such as hydrogen. Further,
with regard to.the oxygen potential Log[PH2O/PH2 ] , it
can be performed by controlling the dew point of the
atmosphere, or the like.
- 56 -
[0080] Further, in the atmosphere at a temperature
in excess of 1100°C, the nitrogen partial pressure PN2
is preferably set to 0.1 or less and the oxygen
potential Log[PH2O/PH2] is preferably set to -2 or less.
This is to concentrate B in a predetermined position
as oxide and to further advance the purification
after the secondary recry's talli zat ion . The reason
why the upper limit of the oxygen potential
Log[PH2O/PH2] is set to -2 is to further concentrate B
in the vicinity of the surface of the steel sheet as
oxide. When this value is too high, the
concentration of oxide of B occurs in the deep
portion of the steel sheet to make it difficult to
obtain the good magnetic property. Further, the
reason why the nitrogen partial pressure PN2 is set to
0.1 or less is because when the nitrogen partial
pressure PN2 is too high, the concentration of oxide
of B occurs in the vicinity of the surface of the
steel sheet to make it impossible to obtain the. good
adhesiveness. Further, this is also because there is
sometimes a case that the purification does not
advance easily and an annealing time period becomes
long to be uneconomic. As has been described above
in detail, in order to make B function effectively so
as to improve the coating film adhesiveness, it is
necessary to control the nitrogen partial pressure PN2
and' the oxygen potential Log [ PH2O/PH2] in the high
temperature region during the finish annealing.
[0081] Next, there will be described reasons for
- 57 -
limiting the component ranges.
[0082] The silicon steel material used in this
embodiment contains Si: 0.8 mass% to 7 mass%, acidsoluble
Al: 0.01 mass% to 0.065 mass%, N: 0.004 mass%
to 0.012 mass%, Mn: 0.05 mass% to 1 mass%, and S and
Se: 0.003 mass% to 0.015 mass% in total amount, B:
0.0005 mass% to 0.0080 mass%, and a C content being
0.085 mass% or less, and a balance being composed of
Fe and inevitable impurities.
[0083] Further, the grain-oriented electrical steel
sheet obtained finally contains Si of 0.8 mass% to 7
mass%, Mn of 0.05 mass% to 1 mass%, B of 0.0005 mass%
to 0.0080 mass%, each content of Al, C, N, S, and Se
of 0.005 mass% or less, and a balance being composed
of Fe and inevitable impurities.
[0084] Si increases electrical resistance to reduce
a core loss. However, when the Si content exceeds 7
mass%, the cold rolling becomes difficult to be
performed, and a crack is likely to be caused at the
time of cold rolling. Thus, the Si content is set to
7 mass% or less, and is preferably 4.5 mass% or less,
and is further preferably 4 mass% or less. Further,
when the Si content is less than 0.8 mass%, a y
transformation is caused at the time of finish
annealing to thereby make a crystal orientation of
the grain-oriented electrical steel sheet deteriorate.
For this reason, the Si content is set to 0.8 mass%
- 58 -
; •
or more, and is preferably 2 mass% or more, and is
further preferably 2.5 mass% or more.
[0085] C is an element effective for controlling the
primary recrystallized structure, but adversely
affects the magnetic property. For this reason, in
this embodiment, before the finish annealing, the
decarburization annealing is performed. However,
when the C content exceeds 0.085 mass%, the time
taken for the decarburization annealing becomes long,
and productivity in industrial production is impaired.
For this reason, the C content is set to 0.085 mass%
or less, and is preferably 0.07 mass% or less.
[0086] Further, when exceeding 0.005 mass% in the
grain-oriented electrical steel sheet to be obtained
finally, C adversely affects the magnetic property,
and thus the C content in the grain-oriented
electrical steel sheet to be obtained finally is set
to 0.005 mass% or less.
[0087] Acid-soluble Al bonds to N to precipitate as
(Al, Si)N and functions as an inhibitor. When the
content of acid-soluble Al falls within a range of
0.01 mass% to 0.065 mass%, the secondary
recrystallization is stabilized. For this reason,
the content of acid-soluble Al is set to not less
than 0.01 mass% nor more than 0.065 mass%. Further,
the content of acid-soluble Al is preferably 0.02
mass% or more, and is further preferably 0.025 mass%
or more. Further, the content of acid-soluble Al is
.
- 59 -
preferably 0.04 mass% or less, and is further
preferably 0.03 mass% or less.
[0088] Further, when exceeding 0.005 mass% in the
grain-oriented electrical steel sheet to be obtained
finally, Al adversely affects the magnetic property,
and thus the Al content in the grain-oriented
electrical steel sheet to be obtained finally is set
to 0.005 mass% or less.
[0089] B bonds to N to compos itely precipitate with
MnS or MnSe as BN and functions as an inhibitor.
When the B content falls within a range of 0.0005
mass% to 0.0080 mass%, the secondary
recrystallization is stabilized. For this reason,
the B content is set to not less than 0.0005 mass%
nor more than 0.0080 mass%. Further, the B content
is preferably 0.001 mass% or more, and is further
preferably 0.0015 mass% or more. Further, the B
content is preferably 0.0040 mass% or less, and is
further preferably 0.0030 mass% or less.
[0090] Further, to the grain-oriented electrical
steel sheet to be obtained finally, B is added
because of being derived from the annealing
separating agent, or the like. When exceeding 0.0080
mass%, B adversely affects the magnetic property, and
thus the B content in the grain-oriented electrical
steel sheet to be obtained finally is set to 0.0005
mass% to 0.0080 mass%.
- 60 -
[0091] N bonds to B or Al to function as an
inhibitor. When the N content is less than 0.004
mass%, it is not possible to obtain a sufficient
amount of the inhibitor. For this reason, the N
content is set to 0.004 mass% or more, and is
preferably 0.006 mass% or more, and is further
preferably 0.007 mass% or more. On the other hand,
when the N content exceeds 0.012 mass%, a hole called
a blister occurs in the steel strip at the time of
cold rolling. For this reason, the N content is set
to 0.012 mass% or less, and is preferably 0.010 mass%
or less, and is further preferably 0.009 mass% or
less .
[0092] Further, when exceeding 0.005 mass% in the
grain-oriented electrical steel sheet to be obtained
finally, N adversary affects the magnetic property,
and thus the N content in the grain-oriented
electrical steel sheet to be obtained finally is set
to 0.005 mass% or less.
[0093] Mn, S and Se produce MnS and MnSe to be a
nucleus around which BN compositely precipitates, and
composite precipitates function as inhibitors. When
the Mn content falls within a range of 0.05 mass% to
1 mass%, the secondary recrystallization is
stabilized. For this reason, the Mn content is set
to not less than 0.05 mass% nor more than 1 mass%.
Further, the Mn content is preferably 0.08 mass% or
more, and is further preferably 0.09 mass% or more.
- 61 -
#
Further, the Mn content is preferably 0.50 mass% or
less, and is further preferably 0.2 mass% or less.
[0094] Further, when Mn falls outside the range of
0.05 mass% to 1 mass% even in the grain-oriented
electrical steel sheet to be obtained finally, the
secondary recrystallization becomes unstable to
adversely affect the magnetic property, and thus the
Mn content in the grain-oriented electrical steel
sheet to be obtained finally is set to 0.05 mass% to
1 mass%.
[0095] Further, when the content of S and Se falls
within a range of 0.003 mass% to 0.015 mass% in total
amount, the secondary recrystallization is stabilized.
For this reason, the content of S and Se is set to
not less than 0.003 mass% nor more than 0.015 mass%
in total amount. Further, in terms of preventing
occurrence of a crack in the hot rolling, Expression
(14) below is preferably satisfied. Incidentally,
only either S or Se may be contained in the silicon
steel material, or both S and Se may also be
contained in the silicon steel material. When both S
and Se are contained, it is possible to promote the
precipitation of BN more stably and to improve the
magnetic property stably.
[Mn]/([S] + [Se]) ^ 4 ...(14)
[0096] Further, when exceeding 0.005 mass% in the
grain-oriented electrical steel sheet to be obtained
finally, S and Se adversary affect the magnetic
- 62 -
property, and thus the content of S and Se in the
grain-oriented electrical steel sheet to be obtained
finally is set to 0.005 mass% or less.
[0097] Ti forms coarse TiN to affect the
precipitation amounts of BN and (Al, Si)N functioning
as inhibitors. When the Ti content exceeds 0.004
mass%, the good magnetic property is not easily
obtained. For this reason, the Ti content is
preferably 0.004 mass% or less.
[0098] Further, one type or more selected from a
group consisting of Cr, Cu, Ni, P, Mo, Sn, Sb, and Bi
may also be contained in the silicon steel material
in ranges below.
[0099] Cr improves an oxide layer formed at the time
of decarburization annealing, and is effective for
forming the glass coating film. However, when the Cr
content exceeds 0.3 mass%, decarburization is
noticeably prevented. For this reason, the Cr
content is set to 0.3 mass% or less.
[0100] Cu increases specific resistance to reduce a
core loss. However, when the Cu content exceeds 0.4
mass%, this effect is saturated. Further, a surface
flaw called "copper scab" is sometimes caused at the
time of hot rolling. For this reason, the Cu content
is set to 0.4 mass% or less.
[0101] Ni increases specific resistance to reduce a
core loss. Further, Ni controls a metallic structure
of the hot-rolled steel strip to improve the magnetic
_
- 63 -
•
property. However, when the Ni content exceeds 1
mass%, the secondary recrystallization becomes
unstable. For this reason, the Ni content is set to
1 mass% or less.
[0102] P increases specific resistance to reduce a
core loss. However, when the P content exceeds 0.5
mass%, there is caused a problem in a rolling
property. For this reason, the P content is set to
0.5 mass% or less.
[0103] Mo improves a surface property at the time of
hot rolling. However, when the Mo content exceeds
0.1 mass%, this effect is saturated. For this reason,
the Mo content is set to 0.1 mass% or less.
[0104] Sn and Sb are grain boundary segregation
elements. The silicon steel material used in this
embodiment contains Al, so that there is sometimes a
case that Al is oxidized by moisture released from
the annealing separating agent depending on the
condition of the finish annealing. In this case,
variations occur in inhibitor strength depending on
the position in the grain-oriented electrical steel
sheet, and the magnetic property also sometimes
varies. However, when the grain boundary segregation
elements are contained, the oxidation of Al can be
suppressed. That is, Sn and Sb suppress the
oxidation of Al to suppress the variations in the
magnetic property. However, when the content of Sn
and Sb exceeds 0.30 mass% in total amount, the oxide
- 64 -
i
layer is not easily formed at the time of
decarburization annealing, thereby making the
formation of the glass coating film insufficient.
Further, the decarburization is noticeably prevented.
For this reason, the content of Sn and Sb is set to
0.3 mass% or less in total amount.
[0105] Bi stabilizes precipitates such as sulfides
to strengthen the function as an inhibitor. However,
when the Bi content exceeds 0.01 mass%, the formation
of the glass coating film is adversely affected. For
this reason, the Bi content is set to 0.01 mass% or
less .
[0106] Next, each treatment in this embodiment will
'* be explained.
[0107] The silicon steel material (slab) having the
above-described components can be manufactured in a
manner that, for example, steel is melted in a
converter, an electric furnace, or the like, and the
molten steel is subjected to a vacuum degassing
treatment according to need, and next is subjected to
continuous casting. Further, the silicon steel
material can also be manufactured in a manner that in
place of the continuous casting, an ingot is made to
then be bloomed. The thickness of the silicon steel
slab is set to, for example, 150 mm to 350 mm, and is
preferably set to 220 mm to 280 mm. Further, what is
called a thin slab having a thickness of 30 mm to 70
mm may also be manufactured. When the thin slab is
- 65 -
manufactured, the rough rolling performed when
obtaining the hot-rolled steel strip can be omitted.
[0108] After the silicon steel slab is manufactured,
the slab heating is performed, and the hot rolling is
performed. Then, in this embodiment, BN is made to
compositely precipitate with MnS and/or MnSe, and the
conditions of the slab heating and the hot rolling
are set in such a manner that the precipitation
amounts of BN, MnS, and MnSe in the hot-rolled steel
strip satisfy Expressions (6) to (8) below.
[0109] BasBN ^ 0. 0005 ... (6)
[B] - BasBN ^ 0.001 ... (7)
SasMnS + 0 . 5 X SeasMnSe ^ 0 . 0 0 2 . . . ( 8)
Here, "BaSBN" represents the amount of B that has
precipitated as BN (mass%), vSaSMns" represents the
amount of S that has precipitated as MnS (mass%), and
"SeaSMnse" represents the amount of Se that has
precipitated as MnSe (mass%).
[0110] As for B, a precipitation amount and a solid
solution amount of B are controlled in such a manner
that Expression (6) and Expression (7) are satisfied.
A certain amount or more of BN is made to precipitate
in order to secure an amount of the inhibitors.
Further, when the amount of solid-dissolved B is
large, there is sometimes a case that unstable fine
;. precipitates are formed in the subsequent processes
to adversely affect the primary recrystallized
structure.
- 66 -
[0111] MnS and MnSe each function as a nucleus
around which BN compositely precipitates. Thus, in
order to make BN precipitate sufficiently to thereby
improve the magnetic property, the precipitation
amounts of MnS and MnSe are controlled in such a
manner that Expression (8) is satisfied.
[0112] The condition expressed in Expression (6) is
derived from Fig. 4, Fig. 14, and Fig. 24. It is
found from Fig. 4, Fig. 14, and Fig. 24 that in the
case of [B] - BasBN being 0.001 mass% or less, the good
magnetic flux density, being the magnetic flux
density B8 of 1.88 T or more, is obtained.
[0113] The conditions expressed in Expression (6)
and Expression (8) are derived from Fig. 2, Fig. 12,
and Fig. 22. It is found from Fig. 2 that when BasBN
is 0.0005 mass% or more and SaSMns is 0.002 mass% or
more, the good magnetic flux density, being the
magnetic flux density B8 of 1.88 T or more, is
obtained.
[0114] Similarly, it is found from Fig. 12 that when
BasBN is 0.0005 mass% or more and SeaSMnse is 0.004
mass% or more, the good magnetic flux density, being
the magnetic flux density B8 of 1.88 T or more, is
obtained. Similarly, it is found from Fig. 22 that
when BaSBN is 0.0005 mass% or more and SasMnS + 0.5 X
SeasMnSe is 0.002 mass% or more, the good magnetic flux
density, being the magnetic flux density B8 of 1.88 T
or more, is obtained. Then, as long as SaSMns is 0.002
- 67 -
•
mass% or more, SaSMns + 0.5 X SeaSMnse becomes 0.002
mass% or more inevitably, and as long as SeaSMnse is
0.004 mass% or more, SasMnS + 0.5 X SeasMnse becomes
0.002 mass% or more inevitably. Thus, it is
important that SasMnS + 0.5 X SeasMnSe is 0.002 mass% or
more .
[0115] Further, the slab heating temperature is set
so as to satisfy the following conditions.
[0116] (i) in the case of S and Se being contained
in the silicon steel slab
the temperature Tl (°C) expressed by Expression
(2) or lower, the temperature T2 (°C) expressed by
Expression (3) or lower, and the temperature T3 (°C)
expressed by Expression (4) or lower
(ii) in the case of no Se being contained in the
silicon steel slab
the temperature Tl (°C) expressed by Expression
(2) or lower and the temperature T3 (°C) expressed by
Expression (4) or lower
(iii) in the case of no S being contained in the
silicon steel slab
the temperature T2 (°C) expressed by Expression
(3) or lower and the temperature T3 (°C) expressed by
Expression (4) or lower
Tl = 14855/(6.82 - log([Mn] X [S])) - 273 ...(2)
T2 = 10733/(4.08 - log([Mn] X [Se])) -
273 ...(3)
T3 = 16000/(5.92 - log([B] X [N])) - 273 ...(4)
- .68 -
This is because when the slab heating is
performed at such temperatures, BN, MnS, and MnSe are
not completely solid-dissolved at the time of slab
heating, and the precipitations of BN, MnS, and MnSe
are promoted during the hot rolling. As is clear
from Fig. 6, Fig. 16, and Fig. 26, the solution
temperatures Tl and T2 approximately agree with the
upper limit of the slab heating temperature capable
of obtaining the magnetic flux density B8 of 1.88T or
more. Further, as is clear from Fig. 7, Fig. 17, and
Fig. 27, the solution temperature T3 approximately
agrees with the upper limit of the slab heating
temperature capable of obtaining the magnetic flux
density B8 of 1.88T or more.
[0117] Further, the slab heating temperature is
further preferably set so as to satisfy the following
conditions as well. This is to make a preferable
amount of MnS or MnSe precipitate during the slab
heating.
(i) in the case of no Se being contained in the
silicon steel slab
a temperature T4 (°C) expressed by Expression
(15) below or lower
(ii) in the case of no S being contained in the
silicon steel slab
a temperature T5 (°C) expressed by Expression
(16) below or lower
- 6 9 -
T 4 = 14855/(6.82-1og([Mn -0.0034] X [S -
0.002] ) ) - 273 . . . (15)
T5 = 10733/(4.08 - log( [Mn - 0.0034] X [Se -
0.004] ) ) - 273 ... (16)
When the slab heating temperature is too high, BN,
MnS, and/or MnSe are sometimes solid-dissolved
completely. In this case, it becomes difficult to
make BN, MnS, and/or MnSe precipitate at the time of
hot rolling. Thus, the slab heating is preferably
performed at the temperature Tl and/or the
temperature T2 or lower, and at the temperature T3 or
lower. Further, if the slab heating temperature is
the temperature T4 or T5 or lower, a preferable
amount of MnS or MnSe precipitates during the slab
heating, and thus it becomes possible to make BN
compositely precipitate around MnS or MnSe to form
effective inhibitors easily.
[0118] Further, as for B, the finishing temperature
Tf of the finish rolling in the hot rolling is set in
such a manner that Expression (5) below is satisfied.
This is to further promote the precipitation of BN.
[0119] Tf ^ 1000 - 10000 X [B] ...(5)
As is clear from Fig. 10, Fig. 20, and Fig. 30,
the condition expressed in Expression (5)
approximately agrees with the condition capable of
obtaining the magnetic flux density B8 of 1.88 T or
more. Further, the finishing temperature Tf of the
- 70 -
finish rolling is further preferably set to 8 00°C or
higher in terms of the precipitation of BN.
[0120] After the hot rolling, the annealing of the
hot-rolled steel strip is performed. Next, the cold
rolling is performed. As described above, the cold
rolling may be performed only one time, or may also
be performed a plurality of times with the
intermediate annealing being performed therebetween.
In the cold rolling, the final cold rolling rate is
preferably set to 80% or more. This is to develop a
good primary recrystalii zed texture.
[0121] Thereafter, the decarburization annealing is
performed. As a result, C contained in the steel
strip is removed. The decarburization annealing is
performed in a moist atmosphere, for example.
Further, the decarburization annealing is preferably
performed for a time such that, for example, a
crystal grain diameter obtained by the primary
recrystallization in a temperature region of 770°C to
950°C becomes 15 fj. m or more. This is to obtain the
good magnetic property. Subsequently, the
application of the annealing separating agent and the
finish annealing are performed. As a result, the
crystal grains oriented in the {110}<001> orientation
preferentially grow by the secondary
recrystallization.
[0122] Further, the nitriding treatment is performed
between start of the decarburization annealing and
- 71 -
occurrence of the secondary recrystallization in the
finish annealing. This is to form inhibitors of (Al,
Si)N. This nitriding treatment' may be performed
during the decarburization annealing, or, may also be
performed during the finish annealing. When the
nitriding treatment is performed during the
decarburization annealing, the annealing is only
necessary to be performed in an atmosphere containing
a gas having nitriding capability such as ammonia,
for example. Further, the nitriding treatment may be
performed during a heating zone or a soaking zone in
a continuous annealing furnace, or the nitriding
treatment may also be performed at a stage after the
soaking zone. When the nitriding treatment is
performed during the finish annealing, a powder
having nitriding capability such as MnN, for example,
is only necessary to be added to the annealing
separating agent.
[0123] In the method of the finish annealing, the
temperature falls within the temperature range of
800°C to 1100°C and the atmosphere satisfies (9) and
(10) Expressions as described previously.
0.75 ^ PN2 ^ 0.2 (9)
-0.7 ^ Log[PH2o/PH2] (10)
[0124] The finish annealing is normally performed in
a mixed atmosphere of nitrogen and hydrogen, so., that
the nitrogen partial pressure in this atmosphere is
controlled and thereby the condition of (9)
- 72 -
I *
Expression is achieved. Further, the oxygen
potential can be controlled by containing water vapor
in the atmosphere, thereby making it possible to
satisfy the condition of (10) Expression.
[0125] Here, when further, the condition of (11)
Expression is satisfied and the atmosphere at 1100°C
or higher satisfies (12) Expression and (13)
Expression, the better results can be obtained.
4Log[PN2] = 3Log1PH2o/PH2] + A + 3345/T- • • • (11)
0.1 ^ PN2 (12)
-2 ^ Log[PH20/PH2] (13)
Here, -3.72 ^ 3Log [ PH2o/ PH2 ] + A ^ -5.32 and -0.7
sS Log [ PH2O/PH2] are satisfied and PN2 represents the
nitrogen partial pressure, PH2O and PH2 represent a
water vapor partial pressure and a hydrogen partial
pressure respectively, A represents a constant
determined in such a manner that 3Log[PH2O/PH2 ] + A
falls within a predetermined range according to
Log [ PH2O/PH2] r and T represents the absolute
temperature.
[0126] In this embodiment, the inhibitors are
strengthened by BN, so that a heating speed in a
temperature range of 1000°C to 1100°C is preferably
set to 15°C/h or less in a heating process of the
finish annealing. Further, in place of controlling
the heating speed, it is also effective to perform
isothermal annealing in which the steel strip is
- 73 -
maintained in the temperature range of 1000°C to
1100°C for 10 hours or longer.
[0127] According to this embodiment as above, it is
possible to stably manufacture the grain-oriented
electrical steel sheet excellent in the magnetic
property.
Example
[0128] Next, experiments conducted by the present
inventers will be explained. The conditions and so
on in the experiments are examples employed for
confirming the practicability and the effects of the
present invention, and the present invention is not
limited to those examples.
[0129]
Slabs each having a composition shown in Table 1
and a balance being composed of Fe and inevitable
impurities were made. Next, the slabs were heated at
1100°C, and thereafter were subjected to finish
rolling at 900°C. Incidentally, the heating
temperature of 1100°C was a value falling below all
the values of the temperatures Tl, T2, and T3
calculated from the composition in Table 1. In this
manner, hot-rolled steel strips each having a
thickness of 2.3 mm were obtained. Subsequently,
annealing of the hot-rolled steel strips was
performed at 1100°C. Next, cold rolling was performed,
and thereby cold-rolled steel strips each having a
thickness of 0.22 mm were obtained. Thereafter,
decarburization annealing was performed in a moist
- 74 -
I •
atmosphere gas at 830°C for 100 seconds, and
decarburization-annealed steel strips were obtained.
Subsequently, the decarburization-annealed steel
strips were annealed in an ammonia containing
atmosphere to increase nitrogen in the steel strips
up to 0.023 mass%. Next, an annealing separating
agent having MgO as its main component was applied on
the steel strips, and of the atmosphere up to 800°C,
the nitrogen partial pressure PN2 was set to 0.5 and
the oxygen potential Log [ PH2O/PH2 ] was set to -0.5, and
of the atmosphere from 800°C to 1100°C, the nitrogen
partial pressure PN2 was set to 0.5 and the oxygen
potential Log [ PH2O/PH2] was set to -1, and of the
atmosphere at 1100°C or higher, the nitrogen partial
pressure PN2 was set to 0.1 or less and the oxygen
potential Log[PH2O/PH2 ] was set to -2 or less, and the
steel strips were heated up to 12 0 0°C at a speed of
15°C/h and were subjected to finish annealing.
[0130] Steel sheets obtain in this manner had
compositions shown in Table 2. On each of such
samples obtained after the finish annealing, the
situation of coating films and the magnetic property
(magnetic flux density B8) were measured. First,
with regard to the situation of coating films, the
proportion of forsterite in a glass coating film and
peak positions of Mg and B by the GDS were examined.
Incidentally, before performing the measurement by
the GDS, a coating solution composed of 100 g of an
aluminum biphosphate solution having a solid content
- 75 -
concentration of 50%, 102 g of colloidal silica
having a solid content concentration of 20%, and 5.4
g of chromic anhydride was made. Then, the coating
solution was applied on the steel sheet, having the
glass coating film obtained after the finish
annealing to be 5 g/m2 per one side after being baked
and was dried, and then was baked at 9 0 0°C . The
thickness of- a secondary coating film was 1.5 p. m in
this case.
[0131] Further, the magnetic property (magnetic flux
density B8) was measured based on JIS C2556. Further,
the coating film adhesiveness was also tested by the
following procedures. First, a coating solution
composed of 100 g of an aluminum biphosphate solution
having a solid content concentration of 50%, 102 g of
colloidal silica having a solid content concentration
of 20%, and 5.4 g of chromic anhydride was made.
Then, the coating solution was applied on the steel
sheet having the glass coating film obtained after
the finish annealing to be 10 g/m2 per one side after
i being baked and was dried, and then was baked at 900°C.
Next, this steel sheet was wound around a round bar
having a diameter of 20 4> and then a peeled area of
the coating film to expose the steel sheet on the
inner side of the bent portion was measured. When
the peeled area was 5% or less, the adhesiveness was
determined to be good. Results of the above test are
shown in Table 3.
[0132] [Table 1]
- 76 -
t
TABLE 1
S T E E L CHEMICAL COMPOSITION(mass%)
MAT ERIAL •
No, SI I B I C I N I S I SB I Al - I' Mn
A1 2.5 0.0025 0.06 0.008 0.007 0.03 0.1
m A2 4 0.0025 0.05 0.008 0.007 0.03 0.1
gJ A3 3.4 0.0005 0.06 0.008 0.007 0.03 0.1
2 A4 3.4 0.008 0.06 0.008 0.007 0.03 0.1
X A5 3.4 0.0025 0.06 0.008 0.007 0.04 0.1
2 A6 3.4 0.0025 0.06 0.008 0.007 0.03 0.3
O A7 3.4 O'.OCES $.08 0.008 0.007 0.03 0.1
t? AS 3.4 0.0025 0.06 0.008 0.012 0.03 0.1
^ A9 3.4 0.0025 0.06 0.008 0.007 0.006 0.03 0.1
2 MO 3.4 0.002 0.06 0.008 0.007 - O03 0.1
A11 3.4 0.002 0.06 0.008 0.007 0.03 0.15
A12 ~ 3.4 0.0025 0.06 0.011 0.007 - 0.03 0.1
A13 0.6 0.0025 0.06 0.008 0.007 = O03 0.1
A14 7.5 O.0025 0.06 0.008 0.007 - 0.03 0.1
> A15 3.4 0.0002 0.06 0.008 0.007 0.03 0.1
P y A16 3.4 0.01 0.06 0.008 0.007 0.03 0.1
5 S A17 3.4 0.0025 0.06 0.008 0.007 0.07 0.1
a < A18 3.4 0.0025 0.06 0.008 0.007 0.03 0.1
O Q A19 3.4 0.0025 0.086 0.008 0.007 0.03 0.1
° A20 3.4 0.0025 0.06 0.014 0.007 0.03 0.1
A21 3.4 0.0025 0.06 0.008 0.016 0.03 0.1
• I A22 | 3.4 | 0.0025 I 0.06 I 0.008 I 0.009 I 0.007 I 0.03 I 0.1 I
[ 0 1 3 3 ] [Table 2]
TABLE 2
TTCT o i m CHEMICAL COMPOSITION(mass%)
No. Si I B I C I N I S I Se I Al I Mn
A1 2.5 0.002 0.0005 0.001 0.001 < 0.0005 0.002 0.1
^ A2 4 0.002 0.0005 0.001 0.001 < 0.0005 0.002 0.1
^ A3 3.3 0.0001 0.0005 0.001 0.001 < 0.0005 0.002 0.1
J A4 3.3 0.008 0.0005 0.001 0.001 < 0.0005 0.002 0.1
g A5 3.3 0.002 0.0005 0.001 0.001 < 0.0005 0.005 0.1
2 A6 3.3 0.002 0.0005 0.001 0.001 < 0.0005 0.002 0.3
O A7 3.3 0.002 0.005 0.001 0.001 < 0.0005 0.002 0.1
£ AB 3.3 0.002 0.0005 0.003 0.005 < 0.0005 0.002 0.1
£ A9 3.3 0.002 0.0005 0.001 0.001 0.005 0.002 0.1
S A10 3.3 0.0015 0.0005 0.001 0.001 < 0.0005 0.002 0.1
A11 3.3 0.0015 0.0005 0.001 0.001 < 0.0005 0.002 0.15
A12 3.3 0.005 0.0005 0.005 0.001 <0.0005~ 0.002 0.1
A13 0.5 0.008 0.0005 0.0005 0.001 < 0.0005 0.002 0.1
A14 7.1 0.002 0.0005 0.001 0.001 < 0.0005 0.002 0.1
•> A15 3.3 <0.0001 0.0005 0.001 0.001 < 0.0005 0.002 01
i- !J A16 33 0.01 0.0005 0.001 0.001 <0.0005 0.002 0.1
a !| A17 3.3 0.001 0.0005 0.001 0.001 < 0.0005 0.008 0.1
Q- 5 A1B 3.3 0.001 0.0005 0.001 < 0.0005 0.002 1.1
o " ^ A19 3.3 0.001 0.008 0.0005 0.001 < 0.0005 0.002 0.1
° A20 3.3 0.005 0.0005 0.01 0.004 < 0.0005 0.002 0.1
A21 3.3 0.002 0.0005 0.001 0.007 < 0.0005 0.002 0.1
I A22 I 3.3 I 0.002 I 0.0005 I 0.001 | 0.Q01 I 0.007 I 0.002v I 0.1 I
[0134] [Table 3]
- 77 -
TABLE 3
OOATING FILM FORMING GDS EMISSION INTENSITY COATING FILM MAGNETIC
STEEL COMPOUND PEAK POSITION ADHESIVENESS PROPERTY
TEST T No. SHEET FORSTERITE OCCURRENCE TIME COATING FILM MAGNETIC FLUX
^ (mass%) tB/tMeft PEELED AREA (X) DENSITY BB (T)
B1 AJ 70 17 5 1.893
B2 A2 90 VB 5 1.900
gJ B3 A3 95 U 5 1.91 B
^ B4 A4 90 1.9 0 1.905
X B5 A5 95 35 5 1.922 .
^ B6 A6 95 35 5_ 1.891
O B7 ,A7 90 1J5 0 1.926
£ B8 A8 95. 36 0 1.920
£ B9 A9 90 3A Q 1.906
5 B10 A1 0 95 25 0 1.902
B11 A11 95 . 3J 0 1.924
B12 A12 95 5 0 1.925
b1 A1 3 65 OB 1_5 1.875
b2 AM 90 05 40 1.660
j> b3 M5 70 CO 20 1.861
^ y b4 A16 90_ 15 0^ 1.752
a | b5 AT7 §0 UNCLEAR 6J) 1.653
°- S b6 A18 9C) OB 10 1.752
Ofl b7 M9 95^ JOJ 6J) 1.788
° b8 A20 95^ 8J3 0^ 1746
b8 A21 90 4J 5 1.658
I b10 I A22 I 90 I 3.2 | 10 I 1.685 I
[0135] As shown in Table 2 and Table 3, it is found
that when the steel sheet has the composition falling
within the range of the present invention, an amount
of forsterite of the glass coating film is 70% or
more, and tB/tMg of the peak positions of Mg and B in
a GDS profile is 1.6 or more, the adhesiveness and
the magnetic flux density are good. Particularly,
when tB/tMg is 2.0 or more, the adhesiveness is
particularly good. On the other hand, when tB/tMg
exceeds 5.0, the magnetic property deteriorates, and
thus the upper limit of tB/tMg is 5. As for the
amount of forsterite, 70% or more of the amount
cannot -be obtained when the amounts of Si and Al each
do not fall within the range of the present invention.
[0136]
- 78 -
Slabs each having a composition shown in Table 4
and a balance being composed of Fe and inevitable
impurities were made. Further, under the temperature
conditions shown in Table 5, slab heating and finish
rolling were performed, and hot-rolled steel strips
each having a thickness of 2.3 mm were obtained.
Analysis results of B, BN, MnS, and MnSe of hotrolled
sheets that were subjected to such heat
treatments are as shown in Table 6. Subsequently,
annealing of the hot-rolled steel strips was
performed at 1100°C. Next, cold rolling was performed,
and thereby cold-rolled steel strips each having a
thickness of 0.22 mm were obtained. Thereafter,
decarburization annealing was performed in a moist
atmosphere gas at 830°C for 100 seconds, and
decarburization-annealed steel strips were obtained.
Subsequently, the decarburization-annealed steel
strips were annealed in an ammonia containing
atmosphere to increase nitrogen in the steel strips
up to 0.023 mass%. Next, an annealing separating
agent having MgO as its main component was applied on
the steel strips, and the atmosphere up to 800°C was
set to be the same as that in Example 1, and of the
atmosphere from 800°C to 1100°C, the nitrogen partial
pressure PN2 was set to 0.5 and the oxygen potential
Log [ PH2O/PH2] was set to -1, and of the atmosphere at
1100°C or higher, the nitrogen' partial pressure PN2
was set to 0.1 or less and the oxygen potential
Log [ PH2O/PH2] was set to -2 or less, and the steel
- 79 -
strips were heated up to 1200°C at a speed of 15°C/h
and were subjected to finish annealing. Then, in the
same manner as that in Example 1, the evaluation of
tB and tMg was performed by the GDS and further the
magnetic property (magnetic flux -density B8) was
measured. Further, the test of the coating film
adhesivaness was also performed. The above results
are shown in Table 7.
[0137] [Table 4]
TABLE 4
TEST LMERIALI CHEMICAL COMPQSITION(massX) 1
No. SI I B I C I N I S I SB I Al" I Mn
m B1 3.3 0.002 0.06 0.00B 0.007 0.03 0.1
gJ B2 3.3 0.002 0.05 0.008 0.006 0.006 0.03 0.1
5 B3 3.3 0.002 0.06 0.008 0.007 0.03 0.1
X B4 3.3 0.002 0.06 0.008 0.006 0.03 0.1
2 B5 3.3 0.002 0.06 0.008 0.006 0.03 0.1
O B6 3.3 0.001 0.06 0.008 0.007 0.03 0.1
i B7 3.3 0.002 0.06 0.008 0.007 0.03 0.1
£ B8 3.3 0.002 0.06 0.008 0.005 0.03 0.1
S B9 3.3 0.002 0.06 0.008 0.007 0.03 0.1
B10 3.3 0.002 0.06 0.008 0005 0.006 ~ 0.03 0.1
B11 3.3 0.002 0.06 0.008 0.007 0.03 0.1
> B12 3.3 0.002 0.05 0.008 0.006 0.006 0.03 0.1
P y B13 3.3 0.002 0.06 0.008 0.007 0.03 0.1
£ 5 B14 3.3 0.002 0.06 0.008 0.006 0.03 0.1
£ 5 B15 3.3 0.002 0.06 0.008 0.006 0.03 0.1
O w B16 3.3 0.001 0.06 0.008 0.007 0.03 0.1
° B17 3.3 0.002 0.06 0.008 0.007 0.03 0.1
I B18 I 3.3 I 0.002 I 0.06 I 0.008 I 0.002 I 0.002 I 0.03 I 0.1 |
[ 0 1 3 8 ] [Table 5]
- 80 -
TABLE 5
I I I SLAB HEATING FINISH ROLLING
HEATING I ~ I ~ I ~ FINISHING 1 000~1 0000
TEST MATERIAL TEST No. TEMPERATURE T1 T2 T3 TEMPERATURE Tf * [B]
^ (°C) CO CO CO CO
B1 Dl 1216 1216 = 1220 . 900 980
gJ B2 D2 1197 1206 1197 1220 900 980
S B3 D3 1220 1 21 6 = 1220 900 980
X B4 D4 1150 1206 - 1220 980 980
^ B5 D5 1150 1206 1220 800 980
O B6 D6 1150 1216 = HJ9 900 990
| B7 D7 1150 1216 - 1220 900 980
£ B8 D8 11 50 1195 = 1220 900 980
5 B9 D9 11 50 1 21 6 = 1220 900 980
B10 D10 1150 1195 1197 1220 900 980
B11 dl 1230 1216 1220 900 980
> B12 d2 1210 1206 1197 1220 900 980
P y B13 d3 1240 1216 - 1220 900 980 .
5 | B14 d4 11 50 1 206 = 1 220 1 000 980
CL 5 B15 d5 1150 1206 - 1220 780 980
O S B16 d6 1280 1 216 1T79 900 990
° B17 d7 1280 1216 - 1220 900 980
| | B18 I d8 I 1280 I 1139 I - I 1220 I 900 I 980 |
[ 0 1 3 9 ] [Table 6]
TABLE 6
I STEEL I I PRECIPITATES IN HOT-ROLLED STEEL STRIP I
TEST MATERIAL TEST No. B as BN I [ B ] - B as BN I S as MnS + 0.5XSe as MnSe
No, (%) 00 (%)
^ B1 D1 0.0015 0.0005 0.005
gj B2 D2 0.001 5 0.0005 O01
| B3 D3 0.001 5 0.0005 0.004
X B4 D4 0.0015 0.0005 0.005
2 B5 D5 0.0015 0.0005 0.005
O B6 D6 0.0005 0.0005 0.005
£ B7 D7 0.001 O001 0.005
£ B8 D8 0.001 5 0.0005 0.002
S B9 D9 0.001 7 0.0005 0.006
B10 D10 0.0018 0.0005 0.009
B11 dl 0.0011 0.0009 0.005
> B12 d2 0.0013 0.0007 0.005
P y B13 d3 0.0011 0.0009 0.006
a ^ B14 d4 0.001 2 0.0008 0.004
S < B15 d5 0.0011 0.0009 0.005
O m B16 d6 0.0003 0.0007 0.005
° B17 d7 0.0005 0.0015 0.005
I B18 I d8 I 0.0013 I 0.0007 I 0.001 I
[ 0 1 4 0 ] [ T a b l e 7]
- 81 -
TABLE 7
COATING FILM FORMING GDS EMISSION INTENSITY COATING FLM MAGNETIC
STEEL COMPOUND PEAK POSITION ADHESIVENESS PROPERTY
TEST MATERIAL TEST No. —
FORSTERITE OCCURRENCE TIME COATING FILM MAGNETIC FLUX
_ (mass%) tB/tMgfcb PEELED AREA QQ DENSITY B8 (T)
m B1 Dl 90 2J 5 1.901
g| B2 D2 95 25 0_ 1.923
5 B3 D3 90 2J 0 1.904
X B4 D4 95 25 5 1.91 B
2 B5 D5 95 25 5 1.921
O B6 D6 90 3J 0 1.906
g B7 D7 95 26 0 1.923
£ ' BB D8 90 2A 0 1.914
5 B9 D9 95 3E 0 1.920
flIO DIP 95 2.8 0 1.922
B11 dl 95 1 15_ 1.876
> B12 d2 95 1 20 1.875
P !J B13 d3 90^ 05 15 1.870
cc | B14 d4 90 OB 20 1.877
oZ < B15 d5 95 1 20 1.795
O m B16 d6 9C) UNCLEAR 3J) 1.865
° B17 d7 90 1 20 1.874
I B1B | d8 I 90 I 0.9 I 10 I 1.870 [
[0141] As shown in Table 1, in the case of Test No.
dl to Test No. d3, the slab heating temperature was
higher than Tl, so that the coating film adhesiveness
was poor and the magnetic flux density was also low.
Further, in the case of Test No. d4, the finishing
temperature Tf of the finish rolling was higher than
1000 - 10000 X [B] , so that the coating film
adhesiveness was poor. Further, in the case of Test
No. d5, the finishing temperature Tf of the finish
rolling did not reach 800°C, so that the coating film
adhesiveness was poor and the magnetic flux density
was also low. In the case of Test No. d6 and Test No.
d7, the slab heating temperature was higher than Tl
and T3, and further BasBN was less than 0.0005 and [B]
- BasBN was greater than 0.001, so that the coating
film adhesiveness was poor and the magnetic flux
density was also low. In the case of Test No. d8,
- 8.2 -
t
the value of SaSMns + SeaSMnse was less than 0.002, so
that the magnetic flux density was low. On the other
hand, in the case of Test No. Dl to Test No. D10 each
being an invention example in which the slab heating
temperature is equal to or lower than the
temperatures Tl, T2, and T3 in the slab heating
temperature, the good coating film adhesiveness and
magnetic flux density were obtained.
[0142] As is clear from the above, according to the
operation conditions in the range of the present
invention, it is possible to obtain the grainoriented
electrical steel sheet having the good
magnetic property and coating film adhesiveness.
[0143]
Slabs each having a composition shown in Table 8
and a balance being composed of Fe and inevitable
impurities were made. Next, under the conditions
shown in Table 9, the slabs were heated and then were
subjected to finish rolling at 900°C. In this manner,
hot-rolled steel strips each having a thickness of
2.3 mm were obtained. Subsequently, annealing of the
hot-rolled steel strips was performed at 1100°C. Next,
cold rolling was performed, and thereby cold-rolled
steel strips each having a thickness of 0.22 mm were
obtained. Thereafter, decarburization annealing was
performed in a moist atmosphere gas at 830°C for 100
seconds, and decarburization-annealed steel strips
were obtained. Subsequently, the decarburizationannealed
steel strips were annealed in an ammonia
- 83 -
containing atmosphere to increase nitrogen in the
steel strips up to 0.022 mass%. Next, an annealing
separating agent having MgO as its main component was
applied on the steel strips, and the atmosphere up to
800°C was set to be the same as that' in Example 1, and
of the atmosphere from 800°C to 1100°C, the nitrogen
partial pressure PN2 was set to 0.5 and the oxygen
potential Log [ PH2O/PH2] was set to -1, and of the
atmosphere at 1100°C or higher, the nitrogen partial
pressure PN2 was set to 0.1 or less and the oxygen
potential Log[PH2O/PH2] was set to -2, and the steel
strips were heated up to 1200°C at a speed of 15°C/h
and were subjected to finish annealing. Then, in the
same manner as that in Example 1, the evaluation of
tB and tMg was performed by the GDS and further the
coating film adhesiveness and the magnetic property
(magnetic flux density B8) were measured. The above
results are shown in Table 10.
[0144] [Table 8]
- 84 -
m l l l l l l l l l l l l l l l l l l l l l l Q l l l l l l l o
° d
5 i i i i i i i i i i i i i i i i i i i- i i 2 i i i i i i i S !
OT I I I I I I I I I I I I I I I I I I I I O I I I I I I I 5 ' '
J l l l l l l l l l l l l l l l l l l l o ' l l l l l l l o ' l l l
D - l l l l l l l l l l l l l l l l l l g l l l l l l l g l l l l
2 I I I I I ! I I I I I I I I I I I - I I I I I I I ^ | | | I I
-gi
CO
§ O I I I I I I I I I I I I I I I I £- I I I I I I I o* I I I I I I
"z ;
g
t j o i i i i i i i i i i i i i i i g i i i i i i i g i i i i i i i
o
a.
O 2 0 O O O O O O o O O O 0 0 O O 0 0 0 0 0 O 0 0 0 0 0 0 O O O O
_1
<
S $ I 8 I I I I I I I 8 I I 8 8 I I I I I I I I I I I I I I I I I
i d o dd
o
" 8 8 8 8 8 8 8 8 8 8 5 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8
d d d d d d d d o o o o o o o o o o o o o o o o o o o d d o o
S G O C p G O C s l ^ " C O G P 0 P 0 C ) C p C D 0 O G O G O 0 O 0 O C D 'GO O D G O O D G O C D C D G O G Q C P O O O P GO
O O O ^ - O O O O O O O O O O O O O O O O O O O O O O O O Q O • ^ - o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o
d d d d d d d o d o o o o o o o o o o o o o o o o d o d d o o
< D U ^ « 3 < 0 < D < p < D < O t O < D < D < D < D < o ! G ( D ( 0 < D < D < 0 < D < 0 < 0 < D < D < D ( D < D < 0 ( 0 < 0
Q O O O O O O O O O O O O O O g O O O O O O O O O O O O O O O O
d d d d d d d d d d o o o o 0 o o o o o o d o d o o d d d o o
t D o o o o o o o o o g o o o o o o o o o o o o o o o o o o o o o
d d d d d d d d d 0 - o o o d o o o o o o d o o o d d d d d d d
3 0 0 g O 0 O 0 O 0 0 0 0 0 0 0 O 0 O 0 0 0 0 0 0 0 O 0 0 0 0 0
d d ^ d d d d d d d d d d d d d d d d d d d d d d d d d d d d .
-i £
( - 1 - 2 0 0 0 0 0 0 0 0 0 Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q
CD <
2 | .
•Z muJLJLUmmliJfflffl[j[jj3j[yj2iIJiIJiIiiIiiIJ[uSjUmSj m a) cu m a> a)
CD
3 ™«V)G N0UN3ANI 3Af l C ^ 00
?l J I J
- 85 -
h
[ 0 1 4 5 ] [Table 9]
TABLE 9
I I gT D = L I SLAB HEATING I
TEST TEST No. MATERIAL T E M P I £ ^ U R E
T1 T2 T3
N°- CO CO (°C) CO)
E1 CI 1170 1216 1220
E2 C2 1170 1206 1197 1220
E3 C3 1170 1216 1220
E4 C4 11 70 1 206 1220
E5 C5 1170 1206 1245
E6 C6 1170 1216 1179
E7 C7 1170 1291 = 1220
w EB C8 1100 1152 1220
| E9 C9 1170 1216 1309
< E10 010 1100 1195 1197 1141
ft E11 C11 1170 1267 - 1220
g E12 C12 1100 1163 1220
P E13 01 3 11 70 = 1282 1220
g E1 4 01 4 11 00 = 1139 1220
2 E15 C15 1170 1195 - 1220
E16 016 1170 1195 1220
E17 017 1170 1195 - 1220
El B C18 1170 1195 - 1220
E19 C19 1170 1195 1220
E20 020 1170 1195 1220
E21 C21 1170 1195 - 1220
E22 C22 1170 1195 1220
I E23 I C23 I 1170 I 1195 I - I 1220
e1 024 1170 1195 1220
> e2 025 1170 1195 - 1220
B ^ e3 C26 1170 1195 - 1220
a I e4 C27 1170 1195 1220
^ X e5 028 1170 1195 - 1220
O m e6 029 1170 1195 1220 !.
° e7 030 1170 1195 - 1220
I e8 I 031 I 1170 I 1195 I - I 1220 I
[ 0 1 4 6 ] [ T a b l e 10]
- 86 - |
t
TABLE 1 Q -
COATING FILM FORMING GDS EMISSION INTENSITY COATING FLM MAGNETIC
STEEL COMPOUND PEAK POSITION ADHESIVENESS PRDPFRTY
TEST TEST No MATERIAL
F 0 R S T E R I T E OCCURRENCE TIME COATING FILM MAGNETIC FLUX
Jj°J (mass%) tB/tMtfcb PEELED AREA CO DENSITY B8 (T)
E1 CI 95 3J 5 1.920
E2 C2 90 32 0 1.883
E3 03 95 2J3 0 1.919
E4 04 90 32 5 1.891
E5 05 95 3.3 5 1.918
E6 . C6 95 3_i 0_ 1.921
E7 C7 90 23 0 1.900
w EB C8 95 29 0_ 1.917
| E9 C9 90 2J3 0 1.918
< E1 0 01 0 95 35 p 1.924
w E11 C11 95 32 5 1.916
§ E1 2 01 2 95 23 0 1.922
P E1 3 013 90 3,4 0 1.886
Lu Et4 C14 95 3J 0 1.91 0
^ E1 5 C1 5 95 33 5 1.923
E1 6 01 6 9C) 29 0 1.917
E1 7 C1 7 60^ 3A C) 1.902
E1 8 C1 8 EX) E) CI 1.916
E1 9 C1 9 95 29 E> 1.919
E20 C20 9J 22 5^ 1.921
E21 C21 9C) 35 _0^ 1.886
E22 C22 9j) 3A 5^ 1.925
E23 C23 95 3.3 5 1 9 2 3
e1 C24 95 1 5 1.876
> e2 025 9J) 09 10 1.876
P j e3 026 9j> 1 30 1.870
| 2 e4 C27 95 OJ 20 1.872
£ < e5 C2E) SO OJ 10 1.795
O m e6 C29 9J OJ 10 1.865
° e7 C30 9j> 1 . 20 1.878
I e8 I 031 I 90 I 1 I 20 | 1.755 |
[0147] As is clear from Table 8 and Table 10, in
comparative examples each having the composition of
the material falling outside the range of the present
invention, the coating film adhesiveness deteriorated
and the magnetic flux density was low. However, in
invention examples El to E 23 each having the
composition of the material falling within the range
of the present invention, .the good coating film
adhesiveness and magnetic flux density were obtained.
[0148]
- 87 -
The following experiment was performed with the
aim of examining effects of the atmosphere from 800°C
to 1100°C and a switching temperature. First, slabs
each having a composition composed of Si: 3.4 mass%,
B: 0.0025 mass%, C: 0.06 mass%, N: 0.008 mass%, S:
0.007 mass%, and Al 0.03 mass% and having a balance
being composed of Fe and inevitable impurities were
made. Next, the slabs were heated at 1100°C, and
thereafter were subjected to finish rolling at 900°C.
The heating temperature of 1100°C was a value falling
below all the values of the temperatures Tl, T2, and
T3 calculated from the above-described composition.
In this manner, hot-rolled steel strips each having a
thickness of 2.3 mm were obtained. Subsequently,
annealing of the hot-rolled steel strips was
performed at 1100°C. Next, cold rolling was performed,
and thereby cold-rolled steel strips each having a
thickness of 0.22 mm were obtained. Thereafter,
decarburization annealing was performed in a moist
atmosphere gas at 830°C for 100 seconds, and
decarburization-annealed steel strips were obtained.
Subsequently, the decarburization-annealed steel
strips were annealed in an ammonia containing
atmosphere to increase nitrogen in the steel strips
up to 0.023 mass%. Next, an annealing separating
agent having MgO as its main component was applied on
the steel strips, and the atmosphere up to a
temperature of Al in Table 11 was set to be the same
as that in Example 1, and at switching temperatures
- 88 - ;
Al and A2 in Table 11, the atmosphere in Table 11 was
made, and at a temperature higher than the
temperature A2, the nitrogen partial pressure PN2 was
set to 0.05 and the oxygen potential Log[PH2O/PH2] was
set to -2 or less, and the steel strips were heated
up to 1200°C at a speed of 15°C/h and after reaching
1200°C, the steel strips were subjected to finish
annealing in an atmosphere of 100% hydrogen.
[0149] On each of such samples obtained after the
finish annealing, the situation of coating films and
the magnetic property (magnetic flux density B8) were
measured. First, with regard to the situation of
coating films, an amount of forsterite of a glass
coating film and peak positions of Mg and B by the
GDS were examined. The amount of forsterite was 70%
or more in all the samples. Before performing the
measurement by the GDS, a coating solution composed
of 100 g of an aluminum biphosphate solution having a
solid content concentration of 50%, 102 g of
colloidal silica having a solid content concentration
of 20%, and 5.4 g of chromic anhydride was made.
Then, the coating solution was applied on a steel
sheet having the glass coating film obtained after
the finish annealing to be 5 g/m2 per one side after
being baked and was dried, and then was baked at 900°C.
The thickness of a secondary coating film was 1.5 p.m
i n t h i s c a s e.
[0150] Further, the magnetic property (magnetic flux
density B8) was measured based on JIS C2556. Further,
- 89 -
the coating film adhesiveness was also tested by the
following procedures. First, a coating solution
composed of 100 g of an aluminum biphosphate solution
having a solid content concentration of 50%, 102 g of
colloidal silica having a solid content concentration
of 20%, and 5.4 g of chromic anhydride was made..
Then, the coating solution was applied on the steel
sheet having the glass coating film obtained after
the finish annealing to be 10 g/m2 per one side after
being baked and was dried, and then was baked at 900°C.
This steel sheet was wound around a round bar having
a diameter of 20 § F3 800 1100 0.5 lOT 3.4 1.931 Q
" F4 800 1100 0.5 -1 3.6 1.932 O
m f1 800 1100 0.1 02 0.7 1.890 X
£ LU f2 BOO 1100 0.9 H 5.6 1.872 Q
< a. f3 800 11 00 0.5 =05 0.8 1.892 X
<3 f4 700 1100 0.5 J 0.9 1.909 X
I § f5 900 11 00 0.5 H 0.7 1.879 X
§ f6 800 1 000 0.5 H 1 1.889 X
I n I 800 I 1150 I 0.5 I -1 I 5.2 I 1.869 I Q I
[0152"] As shown in Table 11, in the case of Test No.
fl, the nitrogen partial pressure PN2 from 800°C to
1100°C was too small, so that the decomposition of BN
- 90 - -
advanced, B was concentrated in the vicinity of the
surface, and the ratio tB/tMg became small to make it
impossible to obtain the coating film adhesiveness
improving effect. Further, in the case of Test No.
f2, the nitrogen partial pressure PN2 was too high, so
that the coating film adhesiveness was good but it
was impossible to obtain the good magnetic property.
In the case of Test No. f3, the oxygen potential
Log[PH2O/PH2] was too high, so that the decomposition
of BN advanced, the magnetic flux density was poor,
and the ratio tB/tMg became too small to make it
impossible to obtain, the coating film adhesiveness
improving effect.
[0153] On the other hand, in Test No. f4 in which
the atmosphere switching temperature was changed, the
switching temperature Al was too low to thus make it
impossible to obtain the adhesiveness improving
effect. In Test No. f5, the switching temperature Al
was too high, so that the decomposition of BN by
oxidation was accelerated, the ratio tB/tMg became an
inappropriate value, and the magnetic flux density B8
was also pdor. In Test No. f6, the switching
temperature A2 was too low, so that the decomposition
of BN was accelerated, the ratio tB/tMg became an
inappropriate value, and the magnetic flux density B8
w a s a l s o p o o r . In Test No. f 7, the switching
temperature A2 was too high, so that the
decomposition of BN was slow, the ratio tB/tMg was
too large, and the magnetic property was poor.
- 91 -
[0154] As is clear from the above, when the
operation conditions of the present invention are set,
it is possible to obtain the grain-oriented
electrical steel sheet having the good magnetic
property and coating film adhesiveness.
[0155]
The following experiment was performed with the
aim of examining better conditions of the atmosphere
from 800°C to 1100°C. First, slabs each having a
composition composed of Si: 3.4 mass%, B: 0.0025
mass%, C: 0.06 mass%, N: 0.008 mass%, S: 0.007 mass%,
and Al 0.03 mass% and having a balance being composed
of Fe and inevitable impurities were made. Next, the
slabs were heated at 1100°C, and thereafter were
subjected to finish rolling at 900°C. The heating
temperature of 1100°C was a value falling below all
the values of Tl, T2, and T3 calculated from the
above-described composition. In this manner, hotrolled
steel strips each having a thickness of 2.3 mm
were obtained. Subsequently, annealing of the hotrolled
steel strips was performed at 1100°C. Next,
cold rolling was performed, and thereby cold-rolled
steel strips each having a thickness of 0.22 mm were
obtained. Thereafter, decarburization annealing was
performed in a moist atmosphere gas at 830°C for 100
seconds, and decarburization-annealed steel strips
were obtained. Subsequently, the decarburizationannealed
steel strips were annealed in an ammonia
containing atmosphere to increase nitrogen in the
- 92 -
steel strips up to 0.023 mass%. Next, an annealing
separating agent having MgO as its main component was
applied on the steel strips, and the atmosphere up to
the temperature of Al in Table 12 was set to be the
same as that in Example 1, and at the switching
temperatures Al and A2 in Table 12, the atmosphere in
Table 12 was made, and at a temperature higher than
the temperature A2, the nitrogen partial pressure PN2
was set to 0.05 and the oxygen potential Log[PH 2O/PH2]
was set to -2 or less, and the steel strips were
heated up to 1200°C at a speed of 15°C/h and after
reaching 1200°C, the steel strips were subjected to
finish annealing in an atmosphere of 100% hydrogen.
[0156] On each of such samples obtained after the
finish annealing, the situation of coating films and
the magnetic property (magnetic flux density B8) were
measured. First, with regard to the situation of
coating films, an amount of forsterite of a glass
coating film layer and peak positions of Mg and B by
the GDS were examined. The amount of forsterite was
70% or more in all the samples. Before performing
the measurement by the GDS, a coating solution
composed of 100 g of an aluminum biphosphate solution
having a solid content concentration of 50%, 102 g of
colloidal silica having a solid content concentration
of 20%, and 5.4 g of chromic anhydride was made.
Then, the coating solution was applied on a steel
sheet having the glass coating film obtained after
the finish annealing to be 5 g/m2 per one side after
- 93 - '
J
being baked and was dried, and then was baked at 900°C.
The thickness of a secondary coating film was 1.5 p
in this case.
[0157] Further, the magnetic property (magnetic flux
density B8) was measured based on JIS C2556. Further,
the coating film.adhesiveness was also tested by the
following procedures. First, a coating solution
composed of 100 g of an aluminum biphosphate solution
having a solid content concentration of 50%, 102 g of
colloidal silica having a solid content concentration
of 20%, and 5.4 g of chromic anhydride was made.
Then, in order to obtain particularly high tension,
the coating solution was applied on the steel sheet
having the glass coating film obtained after the
finish annealing to be 12 g/m2 per one side after
being baked and was dried, and then was baked at 900°C.
This steel sheet was wound around a round bar having
a diameter of 20 <& and then a peeled area of the
coating film to expose the steel sheet on the inner
side of the bent portion was measured. When the
peeled area was 5% or less, the adhesiveness was
determined to be good. Results of the above test are
shown in Table 12.
[0158] [Table 12]
- 94 -
TABLE 1 2
I I I SWITCHING I ATMOSPHERE I I I I
TEST No. TEMPERATURE CO ™_ tMg/tB B8 ADHESIVENESS
A1 I A2 SLogCPHso/Pj+A LogCPHK/Pn,]
g u j G1 800 11 00 ±37 H 3.9 1.925 Q
g i G2 800 11 00 i5J3 _^1 4.1 1.931 Q
^ | G3 800 1100 zhZ d 3.8 1.929 Q
5 L l J G4 800 1100 -4.2 -0.7 4.2 1.919 O
gl BOO 11 00 ^53 H 1.7 1.905 X
aj g2 800 11 00 T33 H 5.8 1.879 Q
£ tu £3 800 11 00 -4.2 . 02 1.0 1.896 X
g a g4 800 1100 ^3A 02 0.9 1.874 X
< 5 g5 800 11 00 l55 02 0.9 1.875 X
1 2 g6 700 11 00 z±2 =1 0.7 1.91 0 X
g g7 900 11 00 l4J H 0.8 1.869 X
g8 800 1 000 Z43 ll 0.9 1.871 X
I g9 | 800 I 1150 I -4.2 I -1 I 6.0 | 1.872 I O I
[0159] As shown in Table 12, in the case of Test No.
gl, 3Log [PH2O/PH2] + A in (11) Expression from 800°C to
1100°C was lower than the best condition, so that the
decomposition of BN advanced easily, and as compared
to the best condition, B was concentrated in the
vicinity of the surface and the ratio tB/tMg became
small, and in the case of this embodiment example
having high coating film tension in particular, the
coating film adhesiveness was not good. Further, in
the case of Test No. g2, 3Log [ P H 2O/PH2 ] + A in (11)
Expression was too high, so that the coating film
adhesiveness was good, but it was impossible to
obtain the good magnetic property. In the case of
Test No. g3, the oxygen potential Log [ PH2O/PH2] was too
high, so that the ratio tb/tMg became an
inappropriate value to make it impossible to obtain
the good adhesiveness. In the case of Test No. g4
and Test No. g5, the oxygen potential Log[PH2O/PH2 ] was
too high and the value of 3Log [ PH2O/PH2] + A was
inappropriate, so that it was impossible to obtain - 95 - the good magnetic property in both cases, and further
in the case of Test No. g5, it was impossible to
obtain the good adhesiveness.
[0160] On the other hand, in Test No. g6 in which
the atmosphere switching temperature was changed, the
switching temperature Al was too low to thus make it
impossible to obtain the adhesiveness improving
effect. In Test No. g7, the switching temperature Al
was too high, so that the decomposition of BTST by
f oxidation was accelerated, the ratio tB/tMg became an
inappropriate value, and the magnetic flux density B8
was poor. In Test No. g8, the switching temperature
A2 was too low, so that the decomposition of BN was
accelerated, the ratio tB/tMg became an inappropriate
value, and the magnetic flux density B8 was also poor.
In Test No. g9, the switching temperature A2 was too
high, so that the decomposition of BN was slow, the
ratio tB/tMg was too large, and the magnetic property
was poor.
[0161] As is clear from the above, when the
operation condition of the finish annealing of the
present invention is set to the particularly good
nitrogen partial pressure range, it is possible to
obtain the grain-oriented electrical steel sheet that
has the good coating film adhesiveness in addition to
the good magnetic property even though the coating
films to generate particularly high tension are
formed.
t
[0162] ••
- 96 -
The following experiment was performed with the
aim of examining conditions of the atmosphere at
1100°C or higher. First, slabs each having a
composition composed of Si: 3.4 mass%, B: 0.0025
mass%, C: 0.06 mass%, N: 0.008 mass%, S: 0.007 mass%,
and Al 0.03 mass% and having a balance being composed
of Fe and inevitable impurities were made. Next, the
slabs were heated at 1100°C, and thereafter were
subjected to finish rolling at 900°C. The heating
temperature of 1100°C was a value falling below all
the values of Tl, T2, and T3 calculated from the
above-described composition. In this manner, hotrolled
steel strips each having a thickness of 2.3 mm
were obtained. Subsequently, annealing of the hotrolled
steel strips was performed at 1100°C. Next,
cold rolling was performed, and thereby cold-rolled
steel strips each having a thickness of 0.22 mm were
obtained. Thereafter, decarburization annealing was
performed in a moist atmosphere gas at 830°C for 100
seconds, and decarburization-annealed steel strips
were obtained. Subsequently, the decarburizationannealed
steel strips were annealed in an ammonia
containing atmosphere to increase nitrogen in the
steel strips up to 0.023 mass%. Next, an annealing
separating agent having MgO as its main component was
applied on the steel strips, and of the atmosphere up
to 800°C, the nitrogen partial pressure PN2 was set to
0.5 and the oxygen potential Log[PH2O/PH2 ] was set to -
0.5, and of the atmosphere from 800°C to 1100°C, the
!
- 97 -
nitrogen partial pressure PN2 was set to 0.5 and the
oxygen potential Log[PH2O/PH2] was set to -1, and at
1100°C or higher, the atmosphere shown in Table 13 was
made, and the steel strips were heated up to 1200°C at
a speed of 15°C/h and after reaching 1200°C, the steel
strips were subjected to finish annealing in an
atmosphere of 100% hydrogen.
[0163] On each of such samples obtained after the
finish annealing, the situation of coating films and
the magnetic property (magnetic flux density B8) were
measured. First, with regard to the state of coating
films, an amount of forsterite of a glass coating
film layer and peak positions of Mg and B by the GDS
were examined. The amount of forsterite was 70% or
more in all the samples. Before performing the
measurement by the GDS, a coating solution composed
of 100 g of an aluminum biphosphate solution having a
solid content concentration of 50%, 102 g of
colloidal silica having a solid content concentration
of 20%, and 5.4 g of chromic anhydride was made.
Then, the coating solution was applied on a steel
sheet having the glass coating film obtained after
the finish annealing to be 5 g/m2 per one side after
being baked and was dried, and then was baked at 900°C.
The thickness of a secondary coating film was 1.5 \i m
in this case.
[0164] Further, the magnetic property (magnetic flux
density B8) was measured based on JIS C2556. Further,
the coating film adhesiveness was also tested by the f
- 98 - ' i
following procedures. First, a coating solution
composed of 100 g of an aluminum biphosphate solution
having a solid content concentration of 50%, 102 g of
colloidal silica having a solid content concentration
of 20%, and 5.4 g of chromic anhydride was made.
Then, in order to apply particularly high tension,
the coating solution was applied on the steel sheet
having the glass coating film obtained after the
finish annealing to be 12 g/m2 per one side after
being baked and was dried, and then was baked at 900°C.
This steel sheet was wound around a round bar having
a diameter of 20 4> and then a peeled area of the
coating film to expose the steel sheet on the inner
side of the bent portion was measured. When the
peeled area was 5% or less, the adhesiveness was
determined to be good. Results of the above test are
shown in Table 13.
•
[ 0 1 6 5 ] [Table 13]
TABLE 13
I I SWITCHING I ATMOSPHERE I I I I
TEST No. TEMPERATURE 2 Z _ _ _ _ tMg/tB B8 ADHESIVENESS
A2 PN2 |Log(PH20/PH2T
t k l w c i m r tU H1 UOO O05 ^2 3.1 1.924 O
I N
EJ™N _ H 2 UOO 0.05 -3 3.2 1.917 O
H3 1100 0.1 -2 3.1 1.901 Q
" hi 1100 0.15 -1 5.5 1.874 Q
COMPARATIVE ' TT^Z ~
E X A M p L E h2 U00 OJ 0 5.4 1.872 O
I h3 I 1100 I 02 \ -2 I 1.7 I 1.880 I X |
[0166] As shown in Table 13, in the case of Test No.
hi, the nitrogen partial pressure PN2 and the oxygen
potential Log [ PH2O/PH2 ] at 1100°C or higher were too
high, so that the decomposition of BN did not advance,
the ratio tB/tMg was too large, and the magnetic
- 99 -
property was poor. Further, in the case of Test No.
h2, the oxygen potential Log[PH2O/PH2 ] was too high, so
that the ratio tb/tMg was too large and the magnetic
property was poor. In the case of Test No. h3, the
nitrogen partial pressure PN2 was too high, so that
the ratio tB/tMg was too small and when the coating
films to generate particularly high tension were
formed as was in this embodiment example, it was
impossible to obtain the adhesiveness improving
effect.
[0167] As is clear from the above, when the
operation condition of the present invention is set
in terms of the finish annealing, it is possible to
obtain the grain-oriented electrical steel sheet that
has the good coating film adhesiveness in addition to
the good magnetic property even though particularly
high tension is applied.
INDUSTRIAL APPLICABILITY
[0168] The present invention can be utilized in an
industry of manufacturing electrical steel sheets and
in an industry of utilizing electrical steel sheets,
for example.
i
- 100 -

CLAIMS
[Claim 1] A grain-oriented electrical steel sheet
being a grain-oriented electrical steel sheet
containing Si of 0.8 mass% to 7 mass%, Mn of 0.05
mass% to 1 mass%, B of 0.0005 mass% to 0.0080 mass%,
each content of Al, C, N, S, and Se of 0.005 mass% or
less, and a balance being composed of Fe and
inevitable impurities and having a glass.coating film
made of composite oxide mainly composed of forsterite
on the steel sheet surface, wherein
when on a condition that a secondary coating film
containing 26 to 38 mass% of colloidal silica, 4 to
12 mass% of one type or two types selected from a
group consisting of chromic anhydride and chromate,
and a balance being composed of aluminum biphosphate
and having a thickness of not less than 1 um nor more
than 2 ix m is formed on the surface of the glass
coating film, glow discharge optical emission
spectrometry (GDS) to the surface of the secondary
coating film is performed, a peak, of B, in emission
intensity having a peak position in emission
intensity different from a peak position,, of Mg, in
emission intensity is obtained and the peak position,
of B, in emission intensity from the steel sheet
surface is deeper than the peak position, of Mg, in
emission intensity, and
further, out of the peaks, of B, in emission
intensity observed by the glow discharge optical
emission spectrometry (GDS), a peak occurrence time
- 101 -
tB of the peak that is the farthest from the steel
sheet surface is expressed by Expression (1) below.
tMg X 1.6 ^ tB ^ tMg X 5 • • • (1)
Here, tMg represents a peak occurrence time of Mg.
[Claim 2] A manufacturing method of a grain-oriented
electrical steel sheet, comprising:
at a predetermined temperature, heating an
electrical steel sheet material containing Si of 0.8
mass% to 7 mass%, acid-soluble Al of 0.01 mass% to
0.0065 mass%, N of 0.004 mass% to 0.012 mass%, Mn of
0.05 mass% to 1 mass%, B of 0.0005 mass% to 0.0080
mass%, at least one type selected from a group
consisting of S and Se of 0.003 mass% to 0.015 mass%
in total amount, a C content of 0.085 mass% or less,
and a balance being composed of Fe and inevitable
impurities;
performing hot rolling of the heated silicon
steel material to obtain a hot-rolled steel strip;
performing annealing of the hot-rolled steel
strip to obtain an annealed steel strip;
performing cold rolling of the annealed steel
strip one time or more to obtain a cold-rolled steel
strip;
performing decarburization annealing of the coldrolled
steel strip to obtain a decarburizationannealed
steel strip in which primary '•
recrystallization has been caused;
applying an annealing separating agent having MgO
as its main component on the decarburization-annealed
- 102 -
l
I:
steel strip;
finish annealing the decarburization-annealed
steel strip and thereby causing secondary
recrystallization; and
further performing a nitriding treatment in which
an N content in the decarburization-annealed steel
strip is increased between start of the
decarburization annealing and occurrence of the
secondary recrystallization in the finish annealing,
wherein
the predetermined temperature, when S and Se are
contained in the silicon steel material, is a
temperature Tl (°C) expressed by Expression (2) below
or lower, a temperature T2 (°C) expressed by
Expression (3) below or lower, and a temperature T3
(°C) expressed by Expression (4) below or lower,
when no Se is contained in the silicon steel
material, the predetermined temperature is the
temperature Tl (°C) expressed by Expression (2) below
or lower and the temperature T3 (°C) expressed by
Expression (4) below.or lower,
when no S is contained in the silicon steel
material, the predetermined temperature is the
temperature T2 (°C) expressed by Expression (3) below
or lower and the temperature T3 (°C) expressed by
Expression (4) below or lower, and a finishing
temperature Tf of finish rolling in the hot rolling
satisfies Expression (5) below,
amounts of BN, MnS, and MnSe in the hot-rolled
- 103 -
steel strip satisfy Expressions (6), (7), and (8)
below, and at the time of finish annealing, a
temperature falls within a temperature range of 800°C
to 1100°C and an atmosphere satisfies Expressions (9)
and (10) below.
Tl = 14855/(6.82 - log([Mn] X [S])) - 273 ...(2)
T2 = 10733/(4.08 - log([Mn] X [Se])) -
273 ... (3)
T3 = 16000/(5.92 - log([B] X [N])) - 273 ...(4)
Tf ^ 1000 - 10000 X [B] ...(5)
BasBN ^ 0. 0005 ... (6)
[ B ] - Ba s B N ^ 0 . 0 0 1 . . . (7)
SasMnS + 0 . 5 X SeasMnSe ^ 0 . 0 0 2 . . . ( 8)
0.7 5 ^ PN2 ^ 0.2 (9)
-0.7 ^ Log[PH2o/PH2] (10)
Here, [Mn] represents the Mn content (mass%) of
the silicon steel material, [S] represents the S
content (mass%) of the silicon steel material, [Se]
represents the Se content (mass%) of the silicon
steel material, [B] represents the B content (mass%)
of the silicon steel material, [N] represents the N
content (mass%) of the silicon steel material, BasBN
represents an amount of B (mass%) that has
precipitated as BN in the hot-rolled steel strip, SasMns represents an amount of S (mass%) that has v '<
precipitated as MnS in the hot-rolled steel strip,
and SeaSMnse represents an amount of Se (mass%) that
has precipitated as MnSe in the hot-rolled steel
strip. Further, PN2 represents a nitrogen partial
- 104 - '
pressure, and PH2O and PH2 represent a water vapor
partial pressure and a hydrogen partial pressure
respectively.
[Claim 3] The manufacturing method of the grainoriented
electrical steel sheet according to claim 2,
wherein
at the time of finish annealing, the temperature
falls within the temperature range of 800°C to 1100°C
and the atmosphere satisfies Expression (11) below.
4Log[PN2] = 3Log[PH2o/PH2] + A + 3455/T- • • • (11)
Here, -3.72 ^ 3Log [ PH2o/ PH2 ] + A ^ -5.32 and -0.7
^ Log[PH2O/PH2 ] are satisfied and A represents a
constant determined in such a manner that
3Log [PH2O/PH2] + A falls within a predetermined range
according to Log [ PH2O/PH2 ] / and T represents the
absolute temperature.
[Claim 4] The manufacturing method of the grainoriented
electrical steel sheet according to claim 2,
wherein
at the time of finish annealing, an atmosphere at
1100°C or higher satisfies Expressions (12) and (13)
below.
0.1 ^ PN2 ' ' * •- (12)
-2 ^ Log[PH2o/PH2] (13)
[Claim 5] The manufacturing method of the grainoriented
electrical steel sheet according to claim 2,
wherein
the electrical steel sheet material further
contains at least one type selected from a group • I
i-
- 105 - !
. . . ,
I
i ft
I • i
I ' .
j consisting of Cr: 0.3 mass% or less, Cu: 0,4 mass! or
| less, Ni: 1 jriass% or less, P: 0.5 mass% or less, Mo:
•i _ .
0.1 mass% or less, Sn: 0-3 mass% or less, Sb: 0.3
mass% or less, and Bi: 0.01 mass% or less.