TITLE
PRODUCTION METHOD FOR GRAIN-ORIENTED ELECTRICAL STEEL SHEET
5 FIELD
[0001]
The present invention relates to a method for producing grain-oriented electrical steel sheet.
BACKGROUND
10 [0002]
Grain-oriented electrical steel sheet is steel sheet which contains Si in 2 mass% to 5 mass%
or so and has crystal grains of the steel sheet integrated in orientation to a high degree to the
{110}<001> orientation called the "Goss orientation". Grain-oriented electrical steel sheet is
excellent in magnetic characteristics, so, for example, is utilized as the core material of
15 transformers and other stationary induction apparatus etc. In the past, various techniques have
been developed for improving the magnetic characteristics of electrical steel sheet. In particular,
along with the demands for energy-saving in recent years, further reduction of the core loss has
been sought in grain-oriented electrical steel sheet. For reducing the core loss of grain-oriented
electrical steel sheet, raising the integration degree of the orientation of the crystal grains of the
20 steel sheet to the Goss orientation to improve the magnetic flux density and reduce the hysteresis
loss is effective. In the production of grain-oriented electrical steel sheet, the crystal orientation
is controlled by utilizing the catastrophic grain growth phenomenon called "secondary
recrystallization". To suitably control the crystal orientation by secondary recrystallization, it is
important to secure uniform precipitation and thermal stability of the microprecipitates in the
25 steel called "inhibitors".
[0003]
The art of suitably controlling the secondary recrystallization to produce low core loss
grain-oriented electrical steel sheet has been variously proposed. For example, PTL 1 discloses
the art of controlling the heat pattern in the temperature raising process in primary
30 recrystallization annealing to produce grain-oriented electrical steel sheet lowered in core loss
over the entire length of the coil. Furthermore, PTL 2 discloses the art of strictly controlling the
average grain size of the crystal grains after secondary recrystallization and the angle of
deviation from the ideal orientation to reduce the core loss of grain-oriented electrical steel sheet.
35 [CITATIONS LIST]
[PATENT LITERATURE]
2
[0004]
[PTL 1] WO2014/049770
[PTL 2] Japanese Unexamined Patent Publication No. 7-268567
5 SUMMARY
[TECHNICAL PROBLEM]
[0005]
The success of secondary recrystallization of grain-oriented electrical steel sheet is
determined by the balance of the frequency of Goss orientation and the thermal stability of
10 precipitates in the steel (inhibitors) in the steel sheet after decarburization and before finish
annealing. In general, if raising the rate of temperature rise at the time of primary
recrystallization annealing, the amount of Goss-oriented grains increases and the magnetic
characteristics are improved. However, according to studies of the inventors, in thin materials (in
one aspect, sheets of thickness of 0.23 mm or less), compared with thick materials, the effect of
15 improvement of the magnetic characteristics due to the increase in the rate of temperature rise
tends to be small. In the past, no method for producing grain-oriented electrical steel sheet
excellent in magnetic characteristics in which, while thin, the effect of improvement of the
magnetic characteristic due to the increase in the rate of temperature rise has been manifested
well has been provided.
20 [0006]
Therefore, the present invention has as its object to solve the above problem and provide a
method for producing grain-oriented electrical steel sheet enabling production of grain-oriented
electrical steel sheet which is thin and yet excellent in magnetic characteristics.
25 [SOLUTION TO PROBLEM]
[0007]
The present invention encompasses the following aspects:
[1] A method for producing grain-oriented electrical steel sheet including
a hot rolling process of heating and hot rolling a slab having a slab composition comprising,
30 by mass%, C: 0.02% or more and 0.10% or less, Si: 2.5% or more and 4.5% or less, Mn: 0.01%
or more and 0.30% or less, a total of one or both of S and Se: 0.001% or more and 0.050% or
less, acid soluble Al: 0.01% or more and 0.05% or less, N: 0.002% or more and 0.020% or less,
P: 0.0400% or less, and Cu: 0.05% or more and 0.50% or less and having a balance of Fe and
impurities to obtain hot rolled steel sheet,
35 a process of dipping the hot rolled steel sheet in a pickling solution or annealing the hot
rolled steel sheet to obtain hot rolled annealed sheet, then dipping the hot rolled annealed sheet in
3
a pickling solution to obtain a pickled sheet,
a cold rolling process of cold rolling the pickled sheet to obtain a cold rolled steel sheet,
a primary recrystallization annealing process of annealing the cold rolled steel sheet for
primary recrystallization to obtain a primary recrystallized annealed sheet,
5 a finish annealing process of coating a surface of the primary recrystallized annealed sheet
by an annealing separator containing MgO, then finish annealing the sheet to obtain a finish
annealed sheet, and
a flattening annealing process of coating the finish annealed sheet with an insulation
coating, then annealing it for flattening,
10 the pickling solution containing Cu in 0.0001 g/L or more and 5.00 g/L or less,
a thickness of the cold rolled steel sheet being 0.15 mm or more and 0.23 mm or less, and
the primary recrystallization annealing process including a temperature raising process and
a decarburization annealing process, an average rate of temperature rise of a temperature region
of 30℃ to 400℃ in the temperature raising process being more than 50℃/s and 1000℃/s or
15 less.
[2] A method for producing grain-oriented electrical steel sheet according to [1], wherein a
total content of Cu and Mn in the pickling solution is 0.01 g/L or more and 5.00 g/L or less.
[3] A method for producing grain-oriented electrical steel sheet according to [1] or [2], wherein
in the pickling process, a pH of the pickling solution is -1.5 or more and less than 7.0, a solution
20 temperature is 15℃ or more and 100℃ or less, and the dipping is performed for 5 seconds or
more and 200 seconds or less.
[4] A method for producing grain-oriented electrical steel sheet according to any one of [1] to
[3], wherein the pickling solution contains Ni: 0.01 g/L or more and 5.00 g/L or less.
[5] A method for producing grain-oriented electrical steel sheet according to any one of [1] to
25 [4], wherein in the temperature raising process in the primary recrystallization annealing process,
a dew point in the temperature region of 30℃ to 800℃ is -50℃ to 0℃.
[6] A method for producing grain-oriented electrical steel sheet according to any one of [1] to
[5], wherein an average rate of temperature rise in a temperature region of 550℃ to 700℃ in the
temperature raising process is 100℃/s or more and 3000℃/s or less.
30 [7] A method for producing grain-oriented electrical steel sheet according to any one of [1] to
[6] wherein an average rate of temperature rise in a temperature region of 700℃ to 800℃ in the
temperature raising process is 400℃/s or more and 2500℃/s or less.
[8] A method for producing grain-oriented electrical steel sheet according to any one of [1] to
[7], where the decarburization annealing process includes soaking treatment performed at a
35 temperature of 750℃ to 900℃ in an atmosphere of an oxygen potential (PH 2 O /PH 2 ) of 0.2 to
0.6.
4
[9] A method for producing grain-oriented electrical steel sheet according to [8], wherein the
decarburization annealing process includes a first soaking treatment performed at a temperature
of 750℃ to 900℃ in an atmosphere of an oxygen potential (PH 2 O /PH 2 ) of 0.2 to 0.6 and a
second heat treatment performed after the first heat treatment at a temperature of 900℃ to
5 1000℃ in an atmosphere of an oxygen potential (PH 2 O /PH 2 ) of less than 0.2.
[10] A method for producing grain-oriented electrical steel sheet according to any one of [1] to
[9], performing nitriding after the cold rolling process and before the finish annealing process.
[11] A method for producing grain-oriented electrical steel sheet according to any one of [1] to
[10], wherein the slab composition contains, in place of part of the Fe, by mass%, one or more
10 elements selected from the group consisting of
Sn: 0.50% or less,
Cr: 0.500% or less,
Bi: 0.0200% or less,
Sb: 0.500% or less,
15 Mo: 0.500% or less, and
Ni: 0.500% or less.
[ADVANTAGEOUS EFFECTS OF INVENTION]
[0008]
20 According to one aspect of the present invention, a method for producing grain-oriented
electrical steel sheet which is thin and yet excellent in magnetic characteristics can be provided.
DESCRIPTION OF EMBODIMENTS
[0009]
25 Below, an illustrative embodiment of the present invention will be explained, but the
present invention is not limited to the following embodiment. Note that, unless otherwise
indicated, the expression "A to B" for the numerical values A and B will mean "A or more and B
or less".
[0010]
30 One aspect of the present invention provides a method for producing grain-oriented
electrical steel sheet including
a hot rolling process of heating and hot rolling a slab having a slab composition comprising,
by mass%, C: 0.02% or more and 0.10% or less, Si: 2.5% or more and 4.5% or less, Mn: 0.01%
or more and 0.30% or less, a total of one or both of S and Se: 0.001% or more and 0.050% or
35 less, acid soluble Al: 0.01% or more and 0.05% or less, N: 0.002% or more and 0.020% or less,
P: 0.0400% or less, and Cu: 0.05% or more and 0.50% or less and having a balance of Fe and
5
impurities to obtain hot rolled steel sheet,
a process of dipping the hot rolled steel sheet in a pickling solution or annealing the hot
rolled steel sheet to obtain hot rolled annealed sheet, then dipping the hot rolled annealed sheet in
a pickling solution to obtain a pickled sheet,
5 a cold rolling process of cold rolling the pickled sheet to obtain a cold rolled steel sheet,
a primary recrystallization annealing process of annealing the cold rolled steel sheet for
primary recrystallization to obtain a primary recrystallized annealed sheet,
a finish annealing process of coating a surface of the primary recrystallized annealed sheet
by an annealing separator containing MgO, then finish annealing the sheet to obtain a finish
10 annealed sheet, and
a flattening annealing process of coating the finish annealed sheet with an insulation
coating, then annealing it for flattening.
[0011]
In one aspect, the pickling solution contains Cu in 0.0001 g/L or more and 5.00 g/L or less.
15 In one aspect, a total content of Cu and Mn in the pickling solution is 0.01 g/L or more and 5.00
g/L or less.
[0012]
If establishing the presence of constituents functioning as inhibitors at the time of finish
annealing (typically, MnS, MnSe, and AlN) in the steel, holding the inhibitors without breaking
20 down until a predetermined temperature at the time of finish annealing is important for the
desired secondary recrystallization. However, according to the study of the inventors, if the
thickness of the steel sheet supplied for the finish annealing is small (that is, if the sheet is thin),
the effect of increase of the Goss orientation by raising the rate of temperature rise at the time of
the primary recrystallization annealing tends to be small. While not desirable to be bound by
25 theory, in a thin material, a reaction breaking down the inhibitors easily occurs due to the size of
the surface area and there is a good possibility that the effect of increase of the Goss orientation
will not be able to be sufficiently enjoyed. That is, to make the effect of increase of the Goss
orientation be sufficiently obtained in a thin material, just raising the rate of temperature rise at
the time of the primary recrystallization annealing is not sufficient. It is necessary to take
30 measures for stabilizing the inhibitors. For example, MnS is broken down by a reaction of
MnS→Mn+S whereby S is discharged outside of the system as a gas, so at the time of finish
annealing, control for reducing the gas permeability is required.
[0013]
The inventors realized improvement in the magnetic characteristics (magnetic flux density
35 and core loss) of thin materials, the object of the present invention, by making the slab contain
Cu in 0.05% or more and by controlling the pickling conditions of the hot rolled steel sheet or
6
hot rolled annealed sheet. The inventors analyzed the steel slab after hot rolled annealing and
after pickling, whereupon they discovered the possibility that a layer of Cu or Mn or in some
cases Ni segregated at the surface (below, sometimes referred to as a "3d transition metal
segregated layer") is formed at the surface of the sample. More specifically, the inventors
5 analyzed the steel slab by glow discharge emission spectroscopy (GDS) whereupon, at the
surface of the sample, emission intensities derived from the above such 3d transition metals were
observed by the peaks, so the presence of the surface segregated layer was surmised. Note that in
this analysis, emission peaks of light elements which might conceivably bond with the 3d
transition metals, such as oxygen or nitrogen, could not be confirmed at the sample surface, so it
10 is surmised that the 3d transition metals were segregated there not as compounds, but as metals
alone. This 3d transition metal segregated layer may conceivably result from the Cu or Mn or
other 3d transition metals contained in the steel dissolving out into the acid solution during
pickling and then reprecipitating due to some reason or another. If there is a 3d transition metal
segregated layer present at the surface of the steel sheet, the gas permeability of the steel sheet
15 may be remarkably decreased. Conversely speaking, the release of gas from inside the steel is
also suppressed. For example, the inhibitor MnS breaks down as MnS→Mn+S and S is released
outside of the steel as a gas. Here, if there is a 3d transition metal segregated layer present at the
surface of the steel sheet and reducing the gas permeability, the generation of S gas will be
suppressed (that is, the active amount of S dissolved in the steel will increase). At the same time
20 as the generation of S gas being suppressed, the above reaction of MnS→Mn+S is also
suppressed. This in turn leads to thermal stability of the MnS.
[0014]
As the metal constituents made to be contained in the pickling solution, from the viewpoint
of the ease of precipitation at the surface of the steel sheet and the lighter load on the
25 environment, 3d transition metals (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) are advantageous.
The particularly preferable 3d transition metals are Cu, Mn, and/or Ni, but if 3d transition metals,
the effect of thermal stabilization of the MnS can be exhibited, so Sc, Ti, V, Co, Cr, and Zn are
also preferable as 3d transition metals. Therefore, the pickling solution, in one aspect, includes
one or more types of metal selected from the group consisting of Sc, Ti, V, Cu, Mn, Ni, Co, Cr,
30 and Zn, more advantageously includes one or more types of metal selected from the group
consisting of Cu, Mn, and Ni, still more advantageously includes one or both types of metal
selected from the group consisting of Cu and Mn, particularly advantageously includes Cu and
optionally Mn. Where the 3d transition metals in the pickling solution are derived from does not
matter. That is, they may be constituents in the steel dissolved into the pickling solution or may
35 be 3d transition metals intentionally made to be contained in the pickling solution.
[0015]
7
In one aspect, the Cu content in the pickling solution is 0.0001 g/L or more from the
viewpoint of the effect of its precipitating well at the surface of the steel sheet and suppressing
breakdown of the inhibitors being exhibited well. Further, in one aspect, it is 5.00 g/L or less
from the viewpoint of preventing inconveniences at the time of primary recrystallization due to
5 excessive precipitation of metal constituents (insufficient decarburization, insufficient formation
of oxide film, etc.) That is, the Cu content in the pickling solution is, in one aspect, 0.0001 g/L or
more and 5.00 g/L or less, preferably 0.005 g/L or more and 5.00 g/L or less, more preferably
0.01 g/L or more and 5.00 g/L or less, still more preferably 0.02 g/L or more and 4.00 g/L or
less, and further preferably 0.03 g/L or more and 2.00 g/L or less.
10 [0016]
In one aspect, the total content of the Cu and Mn in the pickling solution is preferably 0.01
g/L or more from the viewpoint of the effect of their precipitating well at the surface of the steel
sheet and suppressing breakdown of the inhibitors being exhibited well. Preferably it is 5.00 g/L
or less from the viewpoint of preventing inconveniences at the time of primary recrystallization
15 due to excessive precipitation of metal constituents (insufficient decarburization, insufficient
formation of oxide film, etc.) The total content of the Cu and Mn in the pickling solution is
preferably 0.01 g/L or more and 5.00 g/L or less, more preferably 0.02 g/L or more and 4.00 g/L
or less, and still more preferably 0.03 g/L or more and 2.00 g/L or less.
[0017]
20 The Ni content in the pickling solution is preferably 0.01 g/L or more and 5.00 g/L or less,
more preferably 0.02 g/L or more and 4.00 g/L or less, and further preferably 0.03 g/L or more
and 2.00 g/L or less.
[0018]
The amounts of the metal constituents in the pickling solution can be measured using ICP25 AES (Inductively Coupled Plasma-Atomic Emission Spectrometry).
[0019]
According to the method of the present embodiment, it is possible to achieve excellent
thermal stability of the inhibitors not only in thick materials, but also in thin materials, so the
advantages due to the method of the present embodiment are particularly remarkable in the
30 production of grain-oriented electrical steel sheet using thin materials. The thickness of the cold
rolled steel sheet in the method of the present embodiment is, in one aspect, 0.23 mm or less, less
than 0.23 mm, or 0.22 mm or less. The thickness of the cold rolled steel sheet can be made 0.15
mm or more, 0.16 mm or more, 0.17 mm or more, or 0.18 mm or more in one aspect in
accordance with the desired application of the grain-oriented electrical steel sheet.
35 [0020]
Below, the method for producing the grain-oriented electrical steel sheet according to the
8
present embodiment will be specifically explained.
[0021]
Chemical Composition of Slab
First, the chemical composition of the slab used for the grain-oriented electrical steel sheet
5 according to the present embodiment will be explained. Note that, below, unless otherwise
indicated, the expression "%" will be assumed to express "mass%". Further, the balance of the
slab other than the elements explained below is Fe and impurities.
[0022]
The content of C (carbon) is 0.02% or more and 0.10% or less. C plays various roles, but if
10 C is less than 0.02%, at the time of heating the slab, the grain size becomes excessively large,
whereby the core loss value of the final grain-oriented electrical steel sheet is made to increase,
so this is not preferable. If the content of C is more than 0.10%, at the time of decarburization
after cold rolling, the decarburization time becomes long and the production costs increase, so
this is not preferable. Further, if the content of C is more than 0.10%, the decarburization easily
15 becomes incomplete and there is a possibility of magnetic aging occurring in the final grainoriented electrical steel sheet, so this is not preferable. Therefore, the content of C is 0.02% or
more and 0.10% or less, preferably 0.04% or more and 0.09% or less, more preferably 0.05% or
more and 0.09% or less.
[0023]
20 The content of Si (silicon) is 2.5% or more and 4.5% or less. Si raises the electrical
resistance of the steel sheet to thereby reduce the eddy current loss - which is one of the causes
of core loss. If the content of Si is less than 2.5%, it becomes difficult to sufficiently suppress the
eddy current loss of the final grain-oriented electrical steel sheet, so this is not preferable. If the
content of Si is more than 4.5%, the workability of the grain-oriented electrical steel sheet falls,
25 so this is not preferable. Therefore, the content of Si is 2.5% or more and 4.5% or less, preferably
2.7% or more and 4.0% or less, more preferably 3.2% or more and 3.7% or less.

CLAIMS
[Claim 1]
A method for producing grain-oriented electrical steel sheet including
a hot rolling process of heating and hot rolling a slab having a slab composition comprising,
by mass%, C: 0.02% or more and 0.10% or less, Si: 2.5% or more and 4.5% or less, Mn: 0.01%
or more and 0.30% or less, a total of one or both of S and Se: 0.001% or more and 0.050% or
less, acid soluble Al: 0.01% or more and 0.05% or less, N: 0.002% or more and 0.020% or less,
P: 0.0400% or less, and Cu: 0.05% or more and 0.50% or less and having a balance of Fe and
impurities to obtain hot rolled steel sheet,
a process of dipping the hot rolled steel sheet in a pickling solution or annealing the hot
rolled steel sheet to obtain hot rolled annealed sheet, then dipping the hot rolled annealed sheet in
a pickling solution to obtain a pickled sheet,
a cold rolling process of cold rolling the pickled sheet to obtain a cold rolled steel sheet,
a primary recrystallization annealing process of annealing the cold rolled steel sheet for
primary recrystallization to obtain a primary recrystallized annealed sheet,
a finish annealing process of coating a surface of the primary recrystallized annealed sheet
by an annealing separator containing MgO, then finish annealing the sheet to obtain a finish
annealed sheet, and
a flattening annealing process of coating the finish annealed sheet with an insulation
coating, then annealing it for flattening,
the pickling solution containing Cu in 0.0001 g/L or more and 5.00 g/L or less,
a thickness of the cold rolled steel sheet being 0.15 mm or more and 0.23 mm or less, and
the primary recrystallization annealing process including a temperature raising process and
a decarburization annealing process, an average rate of temperature rise of a temperature region
of 30℃ to 400℃ in the temperature raising process being more than 50℃/s and 1000℃/s or
less.
[Claim 2]
A method for producing grain-oriented electrical steel sheet according to claim 1, wherein a
total content of Cu and Mn in the pickling solution is 0.01 g/L or more and 5.00 g/L or less.
[Claim 3]
A method for producing grain-oriented electrical steel sheet according to claim 1 or 2,
wherein in the pickling process, a pH of the pickling solution is -1.5 or more and less than 7.0, a
solution temperature is 15℃ or more and 100℃ or less, and the dipping is performed for 5
25
seconds or more and 200 seconds or less.
[Claim 4]
A method for producing grain-oriented electrical steel sheet according to any one of claims
1 to 3, wherein the pickling solution contains Ni: 0.01 g/L or more and 5.00 g/L or less.
[Claim 5]
A method for producing grain-oriented electrical steel sheet according to any one of claims
1 to 4, wherein in the temperature raising process in the primary recrystallization annealing
process, a dew point in the temperature region of 30℃ to 800℃ is -50℃ to 0℃.
[Claim 6]
A method for producing grain-oriented electrical steel sheet according to any one of claims
1 to 5, wherein an average rate of temperature rise in a temperature region of 550℃ to 700℃ in
the temperature raising process is 100℃/s or more and 3000℃/s or less.
[Claim 7]
A method for producing grain-oriented electrical steel sheet according to any one of claims
1 to 6, wherein an average rate of temperature rise in a temperature region of 700℃ to 800℃ in
the temperature raising process is 400℃/s or more and 2500℃/s or less.
[Claim 8]
A method for producing grain-oriented electrical steel sheet according to any one of claims
1 to 7, wherein the decarburization annealing process includes soaking treatment performed at a
temperature of 750℃ to 900℃ in an atmosphere of an oxygen potential (PH 2 O /PH 2 ) of 0.2 to
0.6.
[Claim 9]
A method for producing grain-oriented electrical steel sheet according to claim 8, wherein
the decarburization annealing process includes a first soaking treatment performed at a
temperature of 750℃ to 900℃ in an atmosphere of an oxygen potential (PH 2 O /PH 2 ) of 0.2 to
0.6 and a second heat treatment performed after the first heat treatment at a temperature of 900℃
to 1000℃ in an atmosphere of an oxygen potential (PH 2 O /PH 2 ) of less than 0.2.
[Claim 10]
A method for producing grain-oriented electrical steel sheet according to any one of claims
26
1 to 9, performing nitriding after the cold rolling process and before the finish annealing process.
[Claim 11]
A method for producing grain-oriented electrical steel sheet according to any one of claims
1 to 10, wherein the slab composition contains, in place of part of the Fe, by mass%, one or more
elements selected from the group consisting of
Sn: 0.50% or less,
Cr: 0.500% or less,
Bi: 0.0200% or less,
Sb: 0.500% or less,
Mo: 0.500% or less, and
Ni: 0.500% or less.