FIELD
[0001]
The present invention relates to a method for producing grain-oriented electrical steel sheet.
BACKGROUND
[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
15 excellent in magnetic characteristics and, for example, is utilized as the core material of
transformers and other stationary induction apparatus etc.
[0003]
In such grain-oriented electrical steel sheet, various techniques have been developed for
improving the magnetic characteristics. In particular, along with the demands for energy-saving
20 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 degree
of integration of the orientation of the crystal grains of the steel sheet to the Goss orientation to
improve the magnetic flux density and reduce the hysteresis loss is effective.
[0004]
25 Here, in the production of grain-oriented electrical steel sheet, the crystal orientation is
controlled by utilizing the catastrophic grain growth phenomenon called "secondary
recrystallization". However, to suitably control the crystal orientation by secondary
recrystallization, it is important to improve the heat resistance of the microprecipitates in the
steel called "inhibitors".
30 [0005]
For example, the method of making the inhibitors completely dissolve at the time of heating
the steel slab before hot rolling, then making them finely precipitate in the hot rolling and later
annealing process may be mentioned. Specifically, the method such as illustrated in the
following PTL 1 of using MnS and AIN as inhibitors and rolling by a rolling reduction rate of
35 more than 80% in the final cold rolling process or the method such as illustrated in the following
PTL 2 of using MnS and MnSe as inhibitors and performing a cold rolling process two times
may be mentioned.
[0006]
Further, PTLs 3 and 4 disclose the art of controlling the conditions of the hot rolled
annealing and pickling treatment conditions to produce grain-oriented electrical steel sheet
5 excellent in coating characteristics. Furthermore, PTL 5 discloses the art of controlling the
pickling treatment conditions, additive conditions of annealing separators, and finish annealing
conditions to produce grain-oriented electrical steel excellent in coating characteristics. PTL 6
discloses the art of controlling carbides by heat treatment before cold rolling to produce grainoriented
electrical steel sheet excellent in magnetic characteristics. Furthermore, PTL 7 discloses
10 the art of controlling the temperature raising process in primary recrystallization annealing and
introducing microstrain during the temperature raising process to thereby produce grain-oriented
electrical steel excellent in magnetic characteristics.
[0007]
Further, the following PTL 8 discloses the art of controlling the heat pattern in the
15 temperature raising process in primary recrystallization annealing to produce grain-oriented
electrical steel sheet lowered in core loss over the entire length of the coil. Furthermore, the
following PTL 9 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.
20
[CITATIONS LIST]
[PATENT LITERATURE]
[0008]
[PTL 1] Japanese Examined Patent Publication No. 40-15644b
25 [PTL 2] Japanese Examined Patent Publication No. 51-13469
[PTL 3] Japanese Unexamined Patent Publication No. 2019-99827
[PTL 4] Japanese Unexamined Patent Publication No. 2003-193141
[PTL 5] Japanese Unexamined Patent Publication No. 2014-196559
[PTL 6] Japanese Unexamined Patent Publication No. 2016-156068
30 [PTL 7] Japanese Unexamined Patent Publication No. 6-212274
[PTL 8] W02014/049770
[PTL 9] Japanese Unexamined Patent Publication No. 7-268567
35 [TECHNICAL PROBLEM]
[0009]
SUMMARY
2
Along with the increasing global regulation of the efficiency of transformers, demand for
reduction of core loss in grain-oriented electrical steel sheet has grown much larger. On the other
hand, transformers are important equipment supporting social infrastructure over the long term,
so continued stable operation is important. For this reason, greater reliability contributing to
5 stabler operation of transformers is being sought from the grain-oriented electrical steel sheet
forming the main members. In particular, uniform appearance of grain-oriented electrical steel
sheet free from uneven color etc. has become an important element in obtaining trust from users.
[0010]
The above-mentioned PTLs 3 to 5 disclose art creating a difference in concentration ofMn
10 or Cu at the surface of steel sheet and center of sheet thickness to improve the coating film
adhesion. However, the art of causing concentration of a specific constituent at the surface of
steel sheet is art aiming at only improvement of the coating characteristics. Art for stably
obtaining excellent magnetic characteristics was not studied.
[0011]
15 The above-mentioned PTL 6 promotes a change from cementite to graphite by heat
treatment before cold rolling to improve the texture obtained by the subsequent primary
recrystallization. However, the temperature raising process in primary recrystallization annealing
and the pickling are based on the conventional methods and are not newly studied.
[0012]
20 Further, as disclosed in the above-mentioned PTL 7, it is confirmed that the magnetic
characteristics of the grain-oriented electrical steel sheet are greatly affected by rapidly raising
the temperature to a temperature of 700°C or more by 1 00°C/s or more in the temperature raising
process in primary recrystallization annealing and introducing microstrain of a nominal strain of
0.1% or more during this rapid heating. Further, in the above-mentioned PTL 8, it is confirmed
25 that the magnetic characteristics of the grain-oriented electrical steel sheet are greatly affected by
rapidly raising the temperature to between 500°C to 600°C by 1 00°C/s or more in the
temperature raising process in primary recrystallization annealing. The above-mentioned PTL 9
discloses setting the temperature of temperature rise to 850°C by 300°C/s or 450°C/s in the
temperature raising process of the primary recrystallization annealing.
30 [0013]
However, in the above-mentioned PTLs 7 to 9, what kind of affect there is on the magnetic
characteristics of grain-oriented electrical steel sheet if making the inhibitors change in the
thickness direction of steel sheet was not studied in detail.
[0014]
35 Therefore, the present invention was made in consideration of the above problem. An object
of the present invention is to provide a new and improved method for producing grain-oriented
3
electrical steel sheet enabling production of grain-oriented electrical steel sheet realizing high
magnetic flux density and excellent in magnetic characteristics.
[SOLUTION TO PROBLEM]
5 [0015]
To solve the above problem, according to one aspect of the present invention,
there is provided a method for producing grain-oriented electrical steel sheet comprising
a process of heating and hot rolling a slab containing, by mass%, C: 0.01% or more and
0.10% or less, Si: 2.5% or more and 4.5% or less, Mn: 0.01% or more and 0.50% or less, a total
10 of one or more ofS, Se, and Te: 0.001% or more and 0.050% or less, acid soluble Al: more than
0% and 0.05% or less, and N: more than 0% and 0.015% or less and having a balance of Fe and
impurities to obtain a hot rolled steel sheet or annealing the hot rolled steel sheet to obtain a hot
rolled annealed sheet,
a process of cold rolling the hot rolled steel sheet or the hot rolled annealed sheet to obtain a
15 cold rolled steel sheet,
a process of annealing the cold rolled steel sheet for primary recrystallization to obtain a
primary recrystallized annealed sheet,
a process of coating a surface of the primary recrystallized annealed sheet by an annealing
separator including MgO, then finish annealing it to obtain a finish annealed sheet,
20 at least one steel sheet among the hot rolled steel sheet, the hot rolled annealed sheet, the
cold rolled steel sheet, and the primary recrystallized annealed sheet being treated by shot
blasting and treated by contact with a solution, and
a process of coating the finish annealed sheet with an insulation coating, then annealing it
for flattening,
25 in the shot blasting treatment, an average particle size of the shot material being 0.1 mm or
more and 5.0 mm or less and a shot speed being 10 m/s or more and 150 m/s or less,
the solution containing one or more elements from among Cu, Hg, Ag, Pb, Cd, Co, Zn, and
Ni, having a total concentration of the elements of 0.00001% or more and 1.0000% or less,
having a pH of -1.5 or more and less than 7, and having a solution temperature of 15°C or more
30 and 1 00°C or less, the time during which the steel sheet is dipped in the solution being 5 seconds
or more and 200 seconds or less.
[0016]
Further, according to another aspect of the present invention,
there is provided a method for producing grain-oriented electrical steel sheet wherein
35 leveling treatment may be performed instead of the above-mentioned shot blasting treatment or
in addition to the shot blasting treatment,
4
in the leveling treatment, the number of bending operations of the hot rolled steel sheet
being two or more, a bending angle being 10 degrees or more and 90 degrees or less, and a
bending radius being 10 mm or more and 200 mm or less.
[0017]
5 Furthermore, according to another aspect of the present invention,
there is provided a method for producing grain-oriented electrical steel sheet wherein in the
rapid temperature rise of the primary recrystallization annealing, an average rate of temperature
rise in the temperature region of 550°C to 700°C is 1 00°C/s or more and 3000°C/s or less.
[0018]
10 Furthermore, according to another aspect of the present invention,
there is provided a method for producing grain-oriented electrical steel sheet wherein the
slab contains, in place of part of the Fe, one or more elements selected from the group
comprising Cu: 1.0% or less, Sn: 1.0% or less, Ni: 1.0% or less, Cr: 1.0% or less, Sb: 1.0% or
less, and Bi: 1.0% or less.
15 [0019]
Furthermore, according to another aspect of the present invention,
there is provided a method for producing grain-oriented electrical steel sheet wherein the
primary recrystallization annealing includes a process of temperature rise, a process of
intermediate treatment from temperature rise to decarburization annealing, and a process of
20 decarburization annealing,
in the intermediate treatment, a dew point temperature of the atmosphere is -40°C or more
and ooc or less and a dwell time at a steel sheet temperature of700°C or more and 950°C or less
is 1 second or more and 20 seconds or less, and
in the decarburization annealing, an oxygen partial pressure ratio (PH 2 o 1PH 2 ) of the
25 atmosphere is 0.35 or more and 0.60 or less.
[ADVANTAGEOUS EFFECTS OF INVENTION]
[0020]
According to the present invention, a solution containing one or more elements from among
30 Cu, Hg, Ag, Pb, Cd, Co, Zn, and Ni (in this Description, these will sometimes be referred to as
"Cu etc.") and the electrical steel sheet are made to contact each other. The electrical steel sheet
includes MnS, MnSe, and MnTe as precipitates (in this Description, these will sometimes be
referred to as "MnS etc.") MnS and other precipitates act as inhibitors. In the present invention,
if MnS etc. contact a solution containing Cu etc., part of the Mn at the MnS etc., in particular the
35 Mn of the surface layers ofMnS etc., is substituted by Cu etc. By utilizing this phenomenon to
improve the heat resistance of the precipitates, it is possible to improve the inhibitor strength of
5
the grain-oriented electrical steel sheet. Due to this mechanism of action, it is possible to provide
a new and improved method for producing grain-oriented electrical steel sheet enabling
production of grain-oriented electrical steel sheet realizing high magnetic flux density and
excellent in magnetic characteristics.
5 [0021]
According to another aspect of the present invention, it is possible to further raise the
magnetic flux density by combination of the art of increasing the Goss oriented grains near the
surface layer by rapid heat treatment in the temperature raising process in the primary
recrystallization annealing.
10 [0022]
Further, according to another aspect of the present invention, it is possible to further raise
the magnetic flux density by adding additional elements to the slab to stabilize the secondary
recrystallization.
[0023]
15 Furthermore, the inventors discovered that the phenomenon of substitution of the Mn of the
surface layer of the MnS etc. by Cu etc. sometimes causes uneven color of the final product, but
can be resolved by controlling the atmospheric and temperature conditions in the intermediate
treatment and the atmospheric conditions in the decarburization annealing in the primary
recrystallization annealing (rapid heat treatment and intermediate treatment and decarburization
20 annealing). Based on this discovery, it is possible to suppress uneven color by another aspect of
the present invention.
25
DESCRIPTION OF EMBODIMENTS
[0024]
Below, preferred embodiments of the present invention will be explained in detail. 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". If assigning units to only the numerical value B in such an
expression, the units shall also apply to the numerical value A.
[0025]
30 Method for Producing Grain-Oriented Electrical Steel Sheet
The inventors discovered the following as a result of intensive study of the method for
producing grain-oriented electrical steel sheet for improving the magnetic characteristics of
grain-oriented electrical steel sheet.
[0026]
35 Specifically, the inventors discovered that if making electrical steel sheet including MnS
etc. contact a solution containing Cu etc. to improve the heat resistance of the MnS etc., part of
6
the Mn at the MnS etc., in particular the Mn of the surface layers of the MnS etc., is substituted
with Cu etc. and by making use of this phenomenon, it is possible to improve the inhibitor
strength and improve the magnetic characteristics. ln addition, they discovered that it is possible
to improve the magnetic characteristics more by modifying the pretreatment of the shot blasting
5 treatment or leveling treatment so to control the inhibitors in the thickness direction of the steel
sheet when bringing the solution into contact with the sheet.
Furthermore, they discovered that by increasing the Goss oriented grains in the vicinity of
the surface layer by rapid heat treatment in the temperature raising process in the primary
recrystallization annealing, it is possible to further improve the magnetic characteristics.
I 0 Further, they discovered that by adding additional elements to the slab to stabilize
secondary crystallization, it is possible to further improve the magnetic characteristics.
Furthermore, they discovered that the phenomenon of the Mn of the surface layers of the
MnS etc. being substituted with Cu etc. sometimes causes uneven color of the final product, but
this can be eliminated by controlling and improving the atmospheric and temperature conditions
15 in the intermediate treatment and the atmospheric conditions in the decarburization annealing in
the primary recrystallization annealing (rapid heat treatment and intermediate treatment and
decarburization annealing).
[0027]
The inventors considered the above discoveries and came up with the present invention. An
20 embodiment of the present invention is a method for producing grain-oriented electrical steel
sheet provided with the following constitution.
[0028]
a process of heating and hot rolling a slab containing, by mass%, C: 0.01% or more and
0.10% or less, Si: 2.5% or more and 4.5% or less, Mn: 0.01% or more and 0.50% or less, a total
25 of one or more of S, Se, and Te: 0.001% or more and 0.050% or less, acid soluble Al: more than
0% and 0.05% or less, and N: more than 0% and 0.015% or less and having a balance of Fe and
impurities to obtain a hot rolled steel sheet or annealing the hot rolled steel sheet to obtain a hot
rolled annealed sheet,
a process of cold rolling the hot rolled steel sheet or the hot rolled annealed sheet to obtain a
30 cold rolled steel sheet,
a process of annealing the cold rolled steel sheet for primary recrystallization to obtain a
primary recrystallized annealed sheet,
a process of coating a surface of the primary recrystallized annealed sheet by an annealing
separator including MgO, then finish annealing it to obtain a fmish annealed sheet,
35 a process of coating the finish annealed sheet with an insulation coating, then annealing it
for flattening,
7
at least one steel sheet among the hot rolled steel sheet, the hot rolled annealed sheet, the
cold rolled steel sheet, and the primary recrystallized annealed sheet being treated by shot
blasting and treated by contact with a solution, and
in the shot blasting treatment, an average particle size of the shot material being 0.1 mm or
5 more and 5.0 mm or less and a shot speed being 10 rnls or more and 150 rnls or less,
the solution containing one or more elements from among Cu, Hg, Ag, Pb, Cd, Co, Zn, and
Ni, having a total concentration of the elements of 0.00001% or more and 1.0000% or less,
having a pH of -1.5 or more and less than 7, and having a solution temperature of l5°C or more
and 1 00°C or less, the time during which the steel sheet is dipped in the solution being 5 seconds
10 or more and 200 seconds or less.
[0029]
It is also possible to perform leveling treatment instead of the above-mentioned shot
blasting treatment or in addition to the shot blasting treatment. In the leveling treatment, the
number of bending operations of the steel sheet is two or more, the bending angle is 10 degrees
15 or more and 90 degrees or less, and the bending radius is 10 mm or more and 200 mm or less.
[0030]
Furthermore, the temperature raising process in the primary recrystallization annealing may
be made a rapid temperature rise as well. In the rapid temperature rise, the average rate of
temperature rise of the temperature region of 550°C to 700°C is 1 00°C/s or more and 3000°C/s
20 or less.
[0031]
Further, the primary recrystallization annealing may also include a process of temperature
rise, a process of intermediate treatment from temperature rise to decarburization annealing, and
a process of decarburization annealing,
25 in the intermediate treatment, a dew point temperature of the atmosphere is -40°C or more
and ooc or less and a dwell time at a steel sheet temperature of 700°C or more and 950°C or less
is 1 second or more and 20 seconds or less, and
in the decarburization annealing, an oxygen partial pressure ratio (PH 2 o fPH 2 ) of the
atmosphere is 0.35 or more and 0.60 or less.
30 [0032]
Below, the method for producing the grain-oriented electrical steel sheet according to the
present embodiment will be specifically explained.
[0033]
Chemical Composition of Slab
35 First, the chemical composition of the slab used for the grain-oriented electrical steel sheet
according to the present embodiment will be explained. Note that, below, unless otherwise
8
indicated, the expression"%" will be assumed to express "mass%". Further, the balance of the
slab other than the elements explained below consists of Fe and impurities. Here, "impurities"
indicate constituents contained in the raw materials or constituents entering in the process of
production which are not intentionally contained in the steel sheet. Further, the chemical
5 composition of the slab of the material of the grain-oriented electrical steel sheet is basically
based on the composition of the grain-oriented electrical steel sheet. However, in the production
of general grain-oriented electrical steel sheet, part of the contained elements is discharged
outside of the system due to the decarburization annealing and purification annealing in the
production process, so the chemical composition of the material slab and the final product grain-
1 0 oriented electrical steel sheet becomes different. The slab composition can be suitably adjusted
considering the effects of the decarburization annealing and purification annealing in the
production process so that the characteristics of the grain-oriented electrical steel sheet become
the desired ones.
[0034]
15 The content of C (carbon) is 0.01% or more and 0.10% or less. C plays various roles, but if
the content of C is less than 0.01 %, 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 0.1 0%, at the time of
decarburization after cold rolling, the decarburization time becomes long and the production
20 costs increase, so this is not preferable. Further, if the content of C is more than 0.1 0%, the
decarburization easily becomes incomplete and there is a possibility of magnetic aging occurring
in the final grain-oriented electrical steel sheet, so this is not preferable. Therefore, the content of
Cis 0.01% or more and 0.10% or less, preferably 0.05% or more and 0.09% or less.
[0035]
25 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 - 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,
30 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.
[0036]
The content ofMn (manganese) is 0.01% or more and 0.50% or less. Mn forms the
inhibitors MnS, MnSe, MnTe, etc. governing the secondary recrystallization. If the content of
35 Mn is less than 0.01 %, the absolute amounts ofMnS, MnSe, and MnTe causing the secondary
recrystallization become insufficient, so this is not preferable. If the content of Mn is more than
9
0.50%, at the time of slab heating, the Mn becomes difficult to dissolve, so this is not preferable.
Further, if the content ofMn is more than 0.15%, the precipitated size of the inhibitors MnS,
MnSe, and MnTe easily becomes coarser and the optimal distribution of size as inhibitors is
detracted from, so this is not preferable. Therefore, the content ofMn is 0.01% or more and
5 0.50% or less, preferably 0.01% or more and 0.30% or less, more preferably 0.03% or more and
0.15% orless.
[0037]
The total content of the one or more elements from among S (sulfur), Se (selenium), and Te
is a total ofO.OOl% or more and 0.050% or less. S, Se, and Te form inhibitors together with the
10 above-mentionedMn. Two or more ofS, Se, and Te maybe included in the slab, but it is
sufficient that at least one of any of them be contained in the slab. If the total of the contents of
S, Se, and Te is outside the above range, a sufficient inhibitor effect cannot be obtained, so this is
not preferable. Therefore, the contents ofS, Se, and Teare a tots! ofO.OOl% or more and
0.050% or less, preferably 0.002% or more and 0.040% or less.
15 [0038]
The content of acid soluble AI (acid soluble aluminum) is more than 0% and 0.05% or less.
The acid soluble AI forms the inhibitors required for producing high magnetic flux density grainoriented
electrical steel sheet. If the content of acid soluble Al is 0, sometimes no AIN is present,
the inhibitor strength becomes insufficient, and good magnetic characteristics cannot be
20 obtained, so this is not preferable. If the content of acid soluble AI is more than 0.05%, the AlN
precipitating as inhibitors becomes coarser and causes the inhibitor strength to drop, so this is not
preferable. Therefore, the content of acid soluble AI is more than 0% and 0.05% or less,
preferably more than 0% and 0.04% or less.
[0039]
25 The content ofN (nitrogen) is more than 0% and 0.015% or less. N forms the inhibitor AlN
together with the above-mentioned acid soluble AI. If the content ofN is outside the above
range, a sufficient inhibitor effect cannot be obtained, so this is not preferable. Therefore, the
content ofN is more than 0% and 0.015% or less, preferably more than 0% and 0.012% or less.
[0040]
30 P (phosphorus) may be contained in more than 0% and 1.0% or less. P has the action of
raising the strength without causing a drop in the magnetic flux density. However, if causing P to
be excessively contained, the toughness of the steel becomes impaired and the steel sheet easily
breaks. For this reason, the upper limit of the amount ofP is made 1.0%. Preferably it is 0.150%
or less, more preferably 0.120% or less. The lower limit of the amount ofP is not particularly
35 limited, but if considering the production costs, it becomes 0.001% or more.
[0041]
10
Further, the slab used for the production of the grain-oriented electrical steel sheet
according to the present embodiment may contain one or more elements of any of Cu, Sn, Ni, Cr,
Sb, or Bi as elements stabilizing the secondary recrystallization in addition to the abovementioned
elements. If the slab contains the above elements, the magnetic flux density of the
5 grain-oriented electrical steel sheet produced can be further improved.
[0042]
The slab is formed by casting molten steel adjusted to the chemical composition explained
above. Note that, the method of casting the slab is not particularly limited. Further, in R&D, even
if a steel ingot is formed by a vacuum melting furnace etc., a similar effect as the case where the
I 0 slab is formed for the above constituents can be confirmed.
[0043]
Process for Forming Hot Rolled Steel Sheet
Next, the slab is heated and hot rolled to work it into a hot rolled steel sheet. The slab
heating temperature is not particularly limited. If making the inhibitor constituents in the slab
15 completely dissolve, for example, it may be heated to 1280°C or more. Note that, the upper limit
value of the heating temperature of the slab at this time is not particularly prescribed, but from
the viewpoint of protection of the facilities, 1450°C is preferable. For example, the heating
temperature of the slab may be 1280°C or more and 1450°C or less. On the other hand, if not
making the inhibitor constituents in the slab completely dissolve, for example, the heating
20 temperature of the slab may be less than 1280°C. In this case, in the hot rolling process or any
process from the hot rolled annealing process to the fmish annealing process, the steel sheet may
also be nitrided.
[0044]
Next, the heated slab is hot rolled to work it to a hot rolled steel sheet. The thickness of the
25 worked hot rolled steel sheet may, for example, be 1.8 mm or more and 3.5 mm or less. If the
thickness of the hot rolled steel sheet is less than 1.8 mm, sometimes the shape of the steel sheet
after hot rolling becomes poor, so this is not preferable. If the thickness of the hot rolled steel
sheet is more than 3.5 mm, the rolling load in the process of cold rolling becomes larger, so this
is not preferable.
30 The hot rolled steel sheet may also be annealed to obtain a hot rolled annealed sheet. If
annealing the hot rolled sheet, the shape of the steel sheet becomes better, so it is possible to
reduce the possibility of the steel sheet breaking in the later cold rolling.
[0045]
Process for Forming Cold Rolled Steel Sheet
35 Next, the obtained hot rolled steel sheet or hot rolled annealed sheet is worked into a cold
rolled sheet by a single cold rolling operation or several cold rolling operations with process
11
annealing interposed. Note that, if rolling by a plurality of cold rolling operations with process
annealing and/or pickling interposed, it is also possible to omit the previous stage hot rolled
annealing. From the viewpoint of decreasing roll wear in cold rolling, pickling treatment is
preferably performed before the individual cold rolling processes. Further, both hot rolled
5 annealing and process annealing may be performed.
[0046]
Further, the steel sheet may be heat treated at 300°C or so or less between passes of cold
rolling, between rolling stands, or during rolling. In such a case, the magnetic characteristics of
the fmal grain-oriented electrical steel sheet can be improved. Note that, the hot rolled steel sheet
I 0 may be rolled by cold rolling three times or more, but a large number of cold rolling operations
increases the production costs, so the hot rolled steel sheet is preferably rolled by one or two cold
rolling operations. If performing the cold rolling by Sendzimir or other reverse rolling, the
number of passes in the cold rolling operations is not particularly limited, but from the viewpoint
of production costs, nine passes or less is preferable.
15 [0047]
Process for Primarv Recrvstallization Annealing
Next, the cold rolled steel sheet is raised in temperature, then annealed for decarburization.
These processes are called ''primary recrystallization annealing" and are preferably performed
consecutively. The temperature rise of the primary recrystallization annealing can be made a
20 rapid temperature rise whereby, in a cold rolled steel sheet, it becomes possible to increase the
Goss oriented grains before the secondary recrystallization and, in the secondary recrystallization
process, the oriented grains closer to the ideal Goss orientation recrystallize secondarily.
[0048]
Temperature Raising Process
25 In the present invention, in the temperature raising process in the primary recrystallization
annealing, the average rate of temperature rise from 550°C to 700°C may be made a rapid one of
1 00°C/s or more and 3000°C/s or less. Due to this, it is possible to increase the Goss oriented
grains before secondary recrystallization of the cold rolled steel sheet and possible to improve
the magnetic flux density of the fmal grain-oriented electrical steel sheet. The temperature range
30 of the rapid temperature rise is 550°C to 700°C. If the start temperature of the rapid temperature
rise is more than 550°C, the recovery of the dislocations in the steel sheet greatly proceeds and
the primary recrystallization of the oriented grains other than the Goss oriented grains ends up
starting, so the effect of increasing the Goss oriented grains is decreased, therefore this is not
preferable. If the end temperature of the rapid temperature rise is less than 700°C, the primary
3 5 recrystallization of the other oriented grains ends up fmishing before the primary
recrystallization of the Goss oriented grains fmishes, so the effect of increasing the Goss oriented
12
grains is decreased, therefore this is not preferable.
[0049]
Further, if making the average rate of temperature rise from 550°C to 700°C 400°C/s or
more, it is possible to further increase the Goss oriented grains before the secondary
5 recrystallization and further improve the magnetic flux density of the final grain-oriented
electrical steel sheet, so this is more preferable. If making the average rate of temperature rise
from 550°C to 700°C 700°C/s or more, it is possible to better improve the magnetic flux density
of the grain-oriented electrical steel sheet, so this is very preferable. If the average rate of
temperature rise from 550°C to 700°C is less than 100°C/s, sufficient Goss oriented grains for
I 0 improving the magnetic characteristics are not obtained by secondary recrystallization, so this is
not preferable. On the other hand, the upper limit of the average rate of temperature rise from
550°C to 700°C is not particularly prescribed, but from the viewpoint of the facilities and
production costs, for example it may be made 3000°C/s. Note that, the start temperature of
temperature rise of the primary recrystallization annealing and the heat pattern and peak
15 temperature other than the rapid temperature rise from 550°C to 700°C are not particularly
limited.
[0050]
The rise in the inhibitor strength at the surface layer side of the steel sheet and a certain
range of depth of the surface layer of the steel sheet due to the treatment making a solution
20 contact the steel sheet (solution contact treatment) explained later and the increase in the Goss
oriented grains due to the rapid temperature rise in the primary recrystallization annealing have a
synergistic effect on improvement of the magnetic characteristics. As this mechanism, it may be
that the inhibitor strength rises, so in the fmish annealing temperature raising process, abnormal
grain growth other than the Goss oriented grains in the vicinity of the surface layer is suppressed
25 and as a result abnormal grain growth of a large number of Goss oriented grains is promoted.
[0051]
Such a rapid temperature rise can be obtained by, for example, using the ohmic heating
method or the induction heating method.
[0052]
30 Here, the temperature raising process may be performed by several apparatuses. For
example, recovery of the steel sheet, that is, holding at a temperature lower than the 550°C at
which a decrease of dislocation density in the steel occurs or gradual cooling, also can improve
the temperature evenness of the steel sheet before the temperature rise, so this may be performed.
Furthermore, the temperature raising process raising the temperature from 550°C to 700°C may
35 also be performed by one or more apparatuses.
[0053]
13
The point at which the temperature rise is started is the point of transition at the low
temperature side of 550°C or less from the state where the temperature of the steel sheet falls to
the state where the temperature of the steel sheet rises (that is, the point where the change in
temperature becomes the local minimum value). Further, the point at which the temperature rise
5 is ended is the point of transition at the high temperature side of 700°C or more from the state
where the temperature of the steel sheet rises to the state where the temperature of the steel sheet
falls (that is, the point where the change in temperature becomes the local maximum value).
[0054]
However, due to the provision of a plurality of temperature raising apparatuses, at the high
10 temperature side from the temperature raising process including 700°C, there is a possibility that
the temperature of the steel sheet will continue rising. In such a case, for example, the end point
of the rapid temperature rise may be made 700°C or more or the point where the rate of change
of the rate of temperature rise becomes the local minimum value at a negative value.
[0055]
15 Here, the method of judging the start point of temperature rise and the end point of rapid
temperature rise is not particularly prescribed, but, for example, it is possible to use a radiant
thermometer etc. to measure the steel sheet temperature. Note that, the method of measurement
of the steel sheet temperature is not particularly limited. Further, whether the end temperature of
the temperature rise of the primary recrystallization continues to be lower than the
20 decarburization annealing temperature or to be higher, the effect of the present invention remains
intact. If the end temperature of the temperature rise of the primary recrystallization becomes
lower than the decarburization annealing temperature, the sheet may also be heated in the
decarburization annealing process. If the end temperature of the temperature rise of the primary
recrystallization becomes higher than the decarburization annealing temperature, the sheet may
25 also be treated to dissipate the heat or treated by gas cooling etc. so as to cool the steel sheet
temperature. Furthermore, it is possible cool down to a temperature lower than the
decarburization annealing temperature, then reheat in the decarburization annealing process.
[0056]
However, if measurement of the steel sheet temperature is difficult and estimation of the
30 accurate locations of the start point of temperature rise and the end point of rapid temperature
rise is difficult, it is also possible to estimate these locations by estimating the heat patterns of
the temperature raising process and cooling process. Further, the entry side temperature and exit
side temperature of the steel sheet at the temperature raising apparatus in the temperature raising
process may also be deemed the start point of temperature rise and the end point of rapid
3 5 temperature rise.
[0057]
14
Intermediate Treatment
Further, in another aspect of the present invention, an intermediate treatment process may
be provided between the temperature raising process and decarburization annealing process in
the primary recrystallization annealing, the dew point temperature of the atmosphere in the
5 intermediate treatment process may be -40°C or more and ooc or less, and the dwell time at the
steel sheet temperature of 700°C or more and 950°C or less may be I second or more and 20
seconds or less.
[0058]
As explained in detail later, by modifying the conditions of the solution contact treatment, it
I 0 is possible to control the inhibitors in the thickness direction of the steel sheet to improve the
magnetic characteristics. On the other hand, by modifying the solution contact treatment, the
demerit of uneven color of the appearance of the steel sheet sometimes newly arises. Uneven
color of the appearance of the steel sheet is due to the state of formation of the oxide film after
decarburization annealing. More specifically, uneven color is caused in the appearance of steel
15 sheet if the internal oxidation becomes uneven. The inventors discovered that it is possible to
suppress the occurrence of uneven color by controlling the atmospheric and temperature
conditions before the decarburization annealing, that is, the intermediate treatment.
[0059]
If the dew point temperature of the atmosphere in the intermediate treatment process is less
20 than -40°C, in the following decarburization annealing, the oxide film is unevenly formed and
uneven color occurs in the appearance of the grain-oriented electrical steel sheet obtained as a
fmal product, so this is not preferable. Even if the dew point temperature of the atmosphere in
the intermediate treatment process is more than 0°C, in the following decarburization annealing,
the oxide film is unevenly formed and uneven color occurs in the appearance of the grain-
25 oriented electrical steel sheet obtained as a fmal product, so this is not preferable.
If the dwell time at the temperature of the steel sheet of 700°C or more and 950°C or less in
the intermediate treatment is less than I second, the oxide film is unevely formed in the
following decarburization annealing and uneven color occurs in the appearance of the grainoriented
electrical steel sheet obtained as a fmal product, so this is not preferable. The upper
30 limit of the dwell time at the temperature of the steel sheet of 700°C or more and 950°C or less
in the intermediate treatment is not particularly prescribed, but if more than 20 seconds, the
facility becomes long and large, so this is not preferable.
[0060]
The mechanism by which the intermediate treatment affects the formation of an oxide film
35 in the following decarburization annealing is not necessarily clear, but is guessed to be as
follows. If performing the treatment for bringing a solution containing one or more elements
15
from among Cu, Hg, Ag, Pb, Cd, Co, Zn, and Ni (Cu etc.) into contact with a steel sheet
(solution contact treatment), the Mn of part of the MnS, MnSe, or MnTe at the surface side of the
steel sheet is substituted by these elements. Cu, Hg, Ag, Pb, Cd, Co, Zn, and Ni are not
uniformly distributed at the surface of the steel sheet, but become locally present at locations of
5 presence of MnS etc., so at the locations where these elements are locally present, the internal
oxidation at the following decarburization annealing is obstructed and a difference ends up
arising in the amount of internal oxidation from locations where Cu, Hg, Ag, Pb, Cd, Co, Zn, and
Ni are not present. Here, if a predetermined set amount of an oxide film is formed before the
decarburization annealing due to the intermediate treatment, sites for internal oxidation in the
10 following decarburization annealing are formed over the entire surface of the steel sheet, so it is
believed that the internal oxidation proceeds relatively uniformly.
If the dew point temperature in the intermediate treatment is less than -40°C, in particular,
at locations where Cu, Hg, Ag, Pb, Cd, Co, Zn, or Ni is locally present, the amount of formation
of an oxide film in the intermediate treatment becomes insufficient, so this is not preferable. On
15 the other hand, if the dew point temperature in the intermediate treatment is more than 0°C, in
the intermediate treatment, an external oxidation type of silica film ends up being formed and
after that in the decarburization annealing, progression of internal oxidation is suppressed and
the oxide film ends up becoming thinner, so it is guessed that a shortage will arise in the amount
of oxidation at the locations where Cu, Hg, Ag, Pb, Cd, Co, Zn, or Ni is locally present and
20 uneven color will end up remaining in the fmal product.
Even if the dwell time at the steel sheet temperature of 700°C or more and 950°C or less in
the intermediate treatment is less than 1 second, the amount of formation of the oxide film in the
intermediate treatment becomes insufficient, so this is not preferable. If the dwell time is more
than 20 seconds, the facility becomes long and large, so this not preferable.
25 [0061]
Decarburization Annealing
Next, the cold rolled steel sheet is annealed for decarburization. From the viewpoint of
decarburization ability, the decarburization annealing may be performed in a wet atmosphere
containing hydrogen and nitrogen at a temperature of 900°C or less. Here, to keep the
30 decarburization from being obstructed, the oxygen partial pressure ratio of the decarburization
annealing, that is, the ratio PH 2 o IPH 2 of the water vapor partial pressure PH 2 o and the
hydrogen partial pressure PH 2 in the atmosphere, may be made 0.35 or more.
[0062]
Further, from the viewpoint of suppressing the occurrence of uneven color, the ratio
35 PH 2 o IPH 2 of the water vapor partial pressure PH 2 o and the hydrogen partial pressure PH 2 in
the atmosphere may be made 0.35 or more and 0.60 or less. If the oxygen partial pressure ratio of
16
the atmosphere of the decarburization annealing is less than 0.35, the oxide film becomes thinner
and a shortage arises in the amount of oxygen at the locations where Cu, Hg, Ag, Pb, Cd, Co, Zn,
or Ni is present and uneven color ends up remaining in the final product, so this is not preferable.
If the oxygen partial pressure ratio of the atmosphere of the decarburization annealing is more
5 than 0.60, the magnetic characteristics deteriorate, so this is not preferable. Therefore, the
oxygen partial pressure ratio of the atmosphere of the decarburization annealing is 0.35 or more
and 0.60 or less.
[0063]
Note that, in the process of primary recrystallization annealing, reduction annealing may be
I 0 performed after decarburization annealing for the purpose of improving the magnetic
characteristics and coating characteristics of the cold rolled steel sheet.
[0064]
Process of Finish Annealing
After that, the cold rolled steel sheet after the primary recrystallization annealing is treated
15 by finish annealing. At this time, an annealing separator containing MgO as its main constituent
may be coated before the finish annealing for the purpose of preventing the steel sheets from
sticking to each other, forming a primary coating, controlling the behavior of the secondary
recrystallization, etc. The annealing separator is generally coated on the surface of the steel sheet
in the state of an aqueous slurry and dried, but the electrostatic coating method etc. may also be
20 used.
[0065]
Next, finish annealing is performed for the purpose of forming the primary coating and
secondary recrystallization. The finish annealing may, for example, be performed by heat
treating the steel sheet in the coil state using a batch type heating furnace etc. Furthermore, to
25 better reduce the core loss value of the final grain-oriented electrical steel sheet, purification
treatment may be performed raising the temperature of the steel sheet in the coil state up to
1200°C or so in temperature, then holding it there.
[0066]
In finish annealing, the temperature is generally raised from room temperature or so.
30 Further, there are various rates of temperature rise in fmish annealing, but the rate is not
particularly limited in the present invention. The conditions of general finish annealing can be
used. For example, from the viewpoint of the productivity and general restriction on facilities,
5°C/h to 1 00°C/h is also possible. Further, this may be performed by other known heat patterns.
In the cooling process as well, the heat pattern is not particularly limited.
35 [0067]
The composition of the atmospheric gas in the finish annealing is not particularly limited. In
17
the process of progression of secondary recrystallization, the gas may also be a mixed gas of
nitrogen and hydrogen. The atmosphere may be a dry atmosphere or may be a wet atmosphere.
The purification annealing may be performed in dry hydrogen gas.
[0068]
5 Process of Flattening Annealing
Next, for the purpose of imparting insulation ability and tension to the steel sheet after the
fmish annealing, for example, an insulation coating having aluminum phosphate or colloidal
silica etc. as its main constituent is coated on the surface of the steel sheet. After that, flattening
annealing is performed for the purpose of baking on the insulation coating and flattening the
10 shape of the steel sheet resulting from the finish annealing. Note that, the constituents of the
insulation coating are not particularly limited so long as an insulation ability and tension are
imparted to the steel sheet. Note that, in the present embodiment, needless to say, depending on
the purpose of the user, the grain-oriented electrical steel sheet may also be treated to control the
magnetic domains.
15 [0069]
Process of Treating Steel Sheet by Shot Blasting and/or Leveling and Making it Contact
Solution
In the present process, at least one steel sheet of hot rolled steel sheet, hot rolled annealed
sheet, cold rolled steel sheet, and primary recrystallized annealed sheet is treated by shot blasting
20 and/or leveling, then dipped in a solution. The treatment for contact with a solution (below,
sometimes called "solution contact treatment") is performed at least once after the hot rolling
and before the finish annealing for the later explained control of inhibitors in the thickness
direction. Note that, the process of treatment by shot blasting and/or leveling and contact with a
solution may be performed by separate processes.
25 [0070]
Solution Contact Treatment
The order of the procedure may change, but first the solution contact treatment will be
explained. The solution contains one or more elements from among Cu, Hg, Ag, Pb, Cd, Co, Zn,
and Ni (in this Description, these will sometimes be called "Cu etc."). The total of the
30 concentrations of these elements is, by mass%, 0.00001% or more and 1.0000% or less, the pH is
-1.5 or more and less than 7, the solution temperature is 15°C or more and 1 oooc or less, and the
time during which the steel sheet is dipped in the solution is 5 seconds or more and 200 seconds
or less.
If the total of the concentrations of the one or more elements from among Cu, Hg, Ag, Pb,
35 Cd, Co, Zn, and Ni of the solution is less than 0.00001%, the effect of the control of inhibitors in
the thickness direction becomes insufficient, so this is not preferable. If the total of the
18
concentrations of the one or more elements from among Cu, Hg, Ag, Pb, Cd, Co, Zn, and Ni of
the solution is more than 1.0000%, the effect of improvement of the magnetism is saturated and
also the cost of the solution increases, so this is not preferable. Therefore, the total of the
concentrations of the one or more elements from among Cu, Hg, Ag, Pb, Cd, Co, Zn, and Ni of
5 the solution is 0.00001% or more and 1.0000% or less.
Further, if the pH of the solution is less than -1.5, the acidity becomes too strong and
handling of the solution becomes difficult, so this is not preferable. If the pH of the solution is 7
or more, the effect of control of the inhibitors in the thickness direction due to the solution
contact treatment becomes insufficient, so this is not preferable. Therefore, the pH of the solution
10 is less than -1.5 or more and less than 7.
Further, if the temperature of the solution is less than 15°C, the effect of control of the
inhibitors in the thickness direction due to the solution contact treatment becomes insufficient, so
this is not preferable. If the temperature of the solution is more than 1 00°C, handling of the
solution becomes difficult, so this is not preferable. Therefore, the temperature of the solution is
15 l5°C or more and 1 oooc or less.
Further, in solution contact treatment, if the time during which the steel sheet is dipped in
the solution is less than 5 seconds, the effect of the control of inhibitors in the thickness direction
by solution contact treatment becomes insufficient, so this is not preferable. If the time during
which the steel sheet is dipped in the solution is more than 200 seconds, the facilities become
20 long and large, so this is not preferable. Therefore, the time during which the steel sheet is
dipped in the solution is 5 seconds or more and 200 seconds or less.
[0071]
The mechanism by which control of inhibitors in the thickness direction becomes possible
by solution contact treatment is guessed to be as follows: If the solution contains one or more
25 elements from among Cu, Hg, Ag, Pb, Cd, Co, Zn, and Ni (in this Description, these sometimes
being referred to as "Cu etc."), since the affinity of these elements with S, Se, and Te in the
solution is extremely high, these are substituted for the Mn in the MnS, MnSe, and MnTe (in this
Description, these sometimes being referred to as "MnS etc.") precipitates exposed at the surface
of the steel sheet to form compounds. This reaction easily occurs at the surface sides contacting
30 the solution in particular in the MnS and other precipitates. If Mn is substituted by other metal
elements (Cu etc.) at the surface sides of the MnS and other precipitates, these surface side
compounds become barriers suppressing dissolution of the Mn and S, Se, and Teat the center
sides of the MnS and other precipitates in the steel, so it is believed that the Ostwald ripening of
MnS etc. in the fmish annealing process is suppressed and the heat resistance, that is, inhibitor
35 strength, of the MnS and other precipitates rises. This reaction occurs when a solution containing
one or more elements from among Cu, Hg, Ag, Pb, Cd, Co, Zn, and Ni (Cu etc.) contacts the
19
MnS, MnSe, or MnTe (MnS etc.) Therefore, if cracks, voids, and other defects are present at the
surface of the steel sheet due to the shot blasting treatment and leveling treatment, the solution
passes through these spaces to infiltrate the steel sheet whereby the solution reacts with not only
the MnS etc. exposed at surface-most part of the steel sheet, but also the MnS etc. in the range
5 down over a range of a certain depth of the surface layer of the steel sheet and causes the
inhibitor strength to rise.
[0072]
Shot Blasting Treatment
Due to the shot blasting treatment and other treatment, cracks, voids, and other defects are
I 0 introduced into the surface of the steel sheet. In the solution contact treatment after that, the
solution passes through these spaces to infiltrate the steel sheet whereby the solution reaches not
only the surface-most part of the steel sheet, but also down over a range of a certain depth. Due
to the above-mentioned solution treatment, it is possible to increase the heat resistance of the
inhibitors by the Mn on the surfaces of the precipitates of MnS, MnSe, and MnTe (in this
15 Description, these sometimes being referred to as "MnS etc.") acting as inhibitors being
substituted by Cu etc. Therefore, due to the shot blasting, it is possible to make the solution
penetrate not only at the surface-most layer of the steel sheet, but also down to a certain depth of
the steel sheet and increase the strength of the MnS and other inhibitors present there.
[0073]
20 The conditions of the shot blasting are an average particle size of the shot material of 0.1
mm or more and 5.0 mm or less and a shot speed of 10 rn!s or more and !50 rn!s or less. Due to
this, microcracks allowing infiltration of the solution are introduced in the surface of steel sheet.
As the blast material (shot material), a general one can be used. Steel balls of a hardness of
Hv500 or so may be used. If the average particle size of the shot material is less than 0.1 mm,
25 microcracks cannot be sufficiently obtained. If the average particle size of the shot material is
more than 5.0 mm, the steel sheet deforms in shape and uniform deformation by cold rolling
becomes difficult and good magnetic characteristics cannot be obtained. Further, if the shot
speed is less than 10 rn!s, microcracks cannot be sufficiently obtained. If the shot speed is more
than 150 rn!s, the steel sheet deforms in shape and uniform deformation by cold rolling becomes
30 difficult and good magnetic characteristics cannot be obtained. The shape of the blasting material
is generally roughly classified into spherical shapes and angular shapes. In general, an angular
shape blast material has a high grinding ability and enables rapid introduction of cracks at the
surface of the steel sheet. In the present invention, either of an angular shaped blasting material
or spherical shaped blast material can be used. An angular shaped blast material and a spherical
35 shaped blast material may also be used mixed together.
[0074]
20
Leveling Treatment
As the method of introducing cracks, voids, or other defects in the surface of the steel sheet,
aside from shot blasting, it is possible to use leveling treatment. Instead of shot blasting, leveling
treatment may also be used. Further, shot blasting and leveling may also be jointly used.
5 Leveling secures the flatness of the steel sheet by imparting tension to the steel sheet while
bending and rebending it along a leveler roller. Through the bending and rebending by this
leveling, it is possible to introduce cracks, voids, and other defects at the surface of the steel
sheet. Therefore, due to the subsequent solution contact treatment, the solution can pass through
the cracks, voids, and other spaces to infiltrate the steel sheet so that the solution reaches not
10 only at the surface-most layer of the steel sheet, but also down to a certain depth of the steel
sheet.
[0075]
The leveling conditions are a number of times of bending of the steel sheet of two times or
more, a bending angle of 10 degrees or more and 90 degrees or less, and a bending radius of 10
15 mm or more and 200 mm or less. Due to this, microcracks through which the solution can
penetrate are introduced into the surface of the steel sheet. If the number of times of bending is
less than two, microcracks cannot be sufficiently obtained. Further, if the bending angle is less
than 10°, microcracks cannot be sufficiently obtained. If the bending angle is more than 90°, the
steel sheet deforms in shape, uniform deformation by the cold rolling becomes difficult, and
20 good magnetic characteristics cannot be obtained. Furthermore, if the bending radius is less than
10 mm, the steel sheet deforms in shape, uniform deformation by the cold rolling becomes
difficult, and good magnetic characteristics cannot be obtained. If the bending radius is more
than 200 mm, microcracks cannot be sufficiently obtained.
[0076]
25 Method for Confirming Surfaces of"MnS Etc." Precipitates Substituted by "Cu Etc."
The method for confirming that the surfaces of the MnS and other precipitates are
substituted by Cu etc. will be explained. First, the steel sheet sample to be confirmed is polished
to a mirror finish and examined by an SEM-EDX. In the observed image obtained by the SEM,
the presence of MnS and other precipitates can be confirmed. At the examined image, element
30 mapping ofEDX of the Cu etc., for example, Mn, S, and Cu, and the strength ratio are
superposed. Due to this, it is possible to confirm the constituent elements of the precipitate
particles. In a typical example, if examining the precipitate particles and their vicinities, the
mapping strength ratio of the Mn and S rises at the parts of the precipitate particles, so it can be
confirmed that the particles are MnS particles. Furthermore, if the mapping strength ratio of Cu
35 also rises at the part near the surface of the particles, it is estimated that the surface of the
precipitates is substituted by Cu.
21
[0077]
Furthermore, the state of distribution of elements in the precipitate particles is confirmed by
Auger electron spectroscopy. More specifically, by sputtering by Ar the surface layers of the
MnS and other precipitates by Auger electron spectroscopy at several run intervals (typically 1
5 run intervals) while analyzing the elements, it is possible to confirm the distribution of
constituent elements from the surface layer parts of the precipitated particles toward the inside. If
Cu etc. is detected at a high concentration only at the surface layer parts of the MnS or other
precipitates and the concentration of Cu etc. falls at the insides of the precipitates, it is possible
to deem that the surfaces of the precipitates have been substituted by Cu etc.
10 [0078]
Further, in the present embodiment, it is believed that cracks, voids, etc. are formed in the
surface layer of the steel sheet by the shot blasting treatment or leveling treatment, so the
solution passes through these spaces to infiltrate the steel sheet and reacts with not only the MnS
etc. exposed at the surface-most layer of the steel sheet, but also the MnS etc. in a range of a
15 certain depth of the surface layer of the steel sheet. By the above method of configuration, it is
possible to confirm if to what extent of depth from the surface layer of the steel sheet the
surfaces of the "MnS etc." precipitates have been substituted by "Cu etc." From the viewpoint of
increasing the strength of the inhibitors, preferably the surfaces of the "MnS etc." precipitates are
substituted by "Cu etc." down to a deep range. Typically, preferably it is substituted in a range of
20 a depth of 10 to 500 J.1ffi from the surface of the steel sheet.
[0079]
The apparatus and the measurement conditions used for the SEM, EDS, and Auger electron
spectroscopy can be suitably selected in accordance with the measured object. In the analysis in
this Description, for the SEM apparatus, an FE-SEM Model JEOL7001F made by JEOL is used
25 by a WD of 10 mm and acceleration voltage of 15 kV. For the Auger electron spectroscopy
analyzer, an FE-AES Pill-700 made by PHI is used by an electron beam: 10 kV, 10 nA, and ion
beam: Ar/2 kV.
[0080]
In general, in the process of production of steel sheet, pickling treatment is performed
30 before the later processes for the pmpose of removing scale, cleaning the surface of the steel
sheet, etc. Typically, from the viewpoint of decreasing roll wear in cold rolling, the pickling
treatment may also be performed before the individual cold rolling processes. Further, from the
viewpoint of controlling the oxidation of the surface of the steel sheet in the primary
recrystallization annealing, the pickling treatment may also be applied before the primary
35 recrystallization annealing. Furthermore, from the viewpoint of improvement of the coatability
of the annealing separator, pickling treatment may also be applied before the fmish annealing.
22
These pickling treatments may also be applied combined.
Along with this, the solution contact treatment may be included in the pickling process of
the steel sheet. As pickling conditions, the above pH value, solution temperature, and contact
time (pickling time) may be employed. Note that, the effect of improvement of the heat
5 resistance of the inhibitors (precipitates) due to the present art etc. can also be obtained in
application to other types of steel. For example, they may also be applied to non-oriented
electrical steel sheet. In the case of application to other types of steel, the slab constituents and
process conditions are not limited to the above.
10
[0081]
It is possible to produce the final grain-oriented electrical steel sheet by the above
processes. According to the method of production according to the present embodiment, it is
possible to produce grain-oriented electrical steel sheet excellent in magnetic characteristics.
[0082]
In the grain-oriented electrical steel sheet according to the present embodiment, further, the
15 magnetic flux density B8 value may also be controlled. Specifically, in the grain-oriented
electrical steel sheet according to the present embodiment, the magnetic flux density B8 value
maybe made 1.91T or more, preferably 1.92T or more, more preferably 1.93T or more, still
more preferably 1.94T or more, and even more preferably 1.95T or more. Here, the magnetic
flux density B8 value is the magnetic flux density when applying a magnetic field of 800A/m by
20 50 Hz to the grain-oriented electrical steel sheet. If the magnetic flux density B8 value is low, the
core loss value of the grain-oriented electrical steel sheet (in particular, the hysteresis loss) ends
up becoming larger, so this is not preferable. The upper limit value of the magnetic flux density
B8 value is not particularly limited, but practically it may be, for example, 2.0T. Note that, the
magnetic flux density and other magnetic characteristics of grain-oriented electrical steel sheet
25 can be measured by known methods. For example, the magnetic characteristics of grain-oriented
electrical steel sheet can be measured by using the method based on the Epstein test prescribed in
JIS C2550 or the single sheet magnetic characteristic test method prescribed in JIS C2556
(Single Sheet Tester: SST) etc. Note that, in R&D, if a steel ingot is formed in a vacuum melting
furnace etc., it becomes difficult to obtain a test piece of an equivalent size as actual production.
30 In this case, for example, it is also possible to obtain a test piece of a width 60 mmxlength 300
mm and measure the characteristics based on the single sheet magnetic characteristic test
method. Furthermore, it is also possible to multiply the obtained results by a correction
coefficient so that measurement values equal to the method based on the Epstein test are
obtained. In the present embodiment, measurement is performed by a measurement method by
3 5 the single sheet magnetic characteristic test method.
[0083]
23
The thus obtained grain-oriented electrical steel sheet is worked into a wound core or
stacked core when producing a transformer. Here, a uniform appearance of the grain-oriented
electrical steel sheet free from uneven color etc. has become an important factor in obtaining
trust from users. In an embodiment of the present invention, when preparing color samples
5 dividing the levels of colors from white to black into eight equal parts, dividing a 50 mmx50 mm
area of the steel sheet, judging the levels of the colors of the divided regions by the eight-level
color samples, and two or more stages of color difference arise between these regions, it may be
judged that there is uneven color. For example, it is possible to prepare color samples by
simultaneously scanning steel sheet samples provided with various tones and white and black
I 0 color samples and using commercially available image processing software to classify the
samples equally dividing the luminances from white to black into eight equal levels. By
comparing these color samples and steel sheet, it is possible to analyze if two or more stages of
color difference occur in the 50 mmx50 mm area of the steel sheet.
[0084]
15 Above, the grain-oriented electrical steel sheet according to the present embodiment was
20
explained. The grain-oriented electrical steel sheet according to the present embodiment can be
produced by the method for producing grain-oriented electrical steel sheet of the abovementioned
present embodiment. However, the invention is not limited to only this method.
EXAMPLES
[0085]
Below, while showing examples, a method for producing grain-oriented electrical steel
sheet and grain-oriented electrical steel sheet according to embodiments of the present invention
will be explained in more detail. Note that, the examples shown below are just illustrations of the
25 grain-oriented electrical steel sheet according to the embodiments. The grain-oriented electrical
steel sheet according to the present embodiment is not limited to the examples shown below.
[0086]
Example 1
Production of Grain-Oriented Electrical Steel Sheets
30 First, a steel ingot containing C: 0.04%, Si: 3.3%, Mn: 0.09%, S: 0.002%, Se: 0.001%, Te:
0.001%, acid soluble Al: 0.005%, and N: 0.003% and having a balance of Fe and impurities was
prepared. The steel ingot was annealed at 1200°C for 1 hour, then was hot rolled to thereby
obtain thickness 2.3 mm hot rolled steel sheets. The obtained hot rolled sheet sheets were
annealed at a peak temperature of 1 000°C for 140 seconds, pickled, then process annealed and
35 treated by shot blasting and treated by solution contact between two cold rolling processes to
thereby obtain thickness 0.23 mm cold rolled steel sheets. Here, the conditions of the shot
24
blasting treatment and conditions of the solution contact treatment after process annealing are the
conditions shown in Table 1.
[0087]
Next, the obtained cold rolled steel sheets were annealed for primary recrystallization in a
5 wet hydrogen atmosphere and 850°C for 180 seconds. Here, the rates of temperature rise were
made the conditions shown in Table 1. Next, the surfaces of the steel sheets after the primary
recrystallization annealing were coated with an annealing separator containing MgO in the state
of an aqueous slurry and then dried. After that, these were fmish annealed and the finish
annealed steel sheets were rinsed. After that, the surfaces of the steel sheets were coated with an
10 insulation coating having aluminum phosphate and colloidal silica as its main constituents, then
was annealed for flattening for the purpose of baking on the insulation coating and flattening the
steel sheets.

CLAIMS
[Claim 1]
A method for producing grain-oriented electrical steel sheet comprising
5 a process of heating and hot rolling a slab containing, by mass%, C: 0.01% or more and
0.10% or less, Si: 2.5% or more and 4.5% or less, Mn: 0.01% or more and 0.50% or less, a total
of one or more of S, Se, and Te: 0.001% or more and 0.050% or less, acid soluble Al: more than
0% and 0.05% or less, and N: more than 0% and 0.015% or less and having a balance of Fe and
impurities to obtain a hot rolled steel sheet or annealing the hot rolled steel sheet to obtain a hot
10 rolled annealed sheet,
a process of cold rolling the hot rolled steel sheet or the hot rolled annealed sheet to obtain a
cold rolled steel sheet,
a process of annealing the cold rolled steel sheet for primary recrystallization to obtain a
primary recrystallized annealed sheet,
15 a process of coating a surface of the primary recrystallized annealed sheet with an annealing
separator including MgO, then fmish annealing it to obtain a finish annealed sheet,
a process of coating the finish annealed sheet with an insulation coating, then annealing it
for flattening,
at least one steel sheet among the hot rolled steel sheet, the hot rolled annealed sheet, the
20 cold rolled steel sheet, and the primary recrystallized annealed sheet being treated by shot
blasting and treated by contact with a solution,
in the shot blasting treatment, an average particle size of the shot material being 0.1 rnm or
more and 5.0 rnm or less and a shot speed being 10 m/s or more and 150 m/s or less,
the solution containing one or more elements from among Cu, Hg, Ag, Pb, Cd, Co, Zn, and
25 Ni, having a total concentration of the elements ofO.OOOOl% or more and 1.0000% or less,
having a pH of -1.5 or more and less than 7, and having a solution temperature of 15°C or more
and 100°C or less, the time during which the steel sheet is dipped in the solution being 5 seconds
or more and 200 seconds or less.
30 [Claim 2]
A method for producing grain-oriented electrical steel sheet comprising
a process of heating and hot rolling a slab containing, by mass%, C: 0.01% or more and
0.10% or less, Si: 2.5% or more and 4.5% or less, Mn: 0.01% or more and 0.50% or less, a total
of one or more of S, Se, and Te: 0.001% or more and 0.050% or less, acid soluble AI: more than
35 0% and 0.05% or less, and N: more than 0% and 0.015% or less and having a balance of Fe and
impurities to obtain a hot rolled steel sheet or annealing the hot rolled steel sheet to obtain a hot
35
rolled annealed sheet,
a process of cold rolling the hot rolled steel sheet or the hot rolled annealed sheet to obtain a
cold rolled steel sheet,
a process of annealing the cold rolled steel sheet for primary recrystallization to obtain a
5 primary recrystallized annealed sheet,
a process of coating a surface of the primary recrystallized annealed sheet with an annealing
separator including MgO, then fmish annealing it to obtain a finish annealed sheet, and
a process of coating the finish annealed sheet with an insulation coating, then annealing it
for flattening,
I 0 at least one steel sheet among the hot rolled steel sheet, the hot rolled annealed sheet, the
cold rolled steel sheet, and the primary recrystallized annealed sheet being treated by leveling
and treated by contact with a solution,
in the leveling treatment, the number of bending operations of the steel sheet being two or
more, a bending angle being 10 degrees or more and 90 degrees or less, and a bending radius
15 being 10 mm or more and 200 mm or less,
the solution containing one or more elements from among Cu, Hg, Ag, Pb, Cd, Co, Zn, and
Ni, having a total concentration of the elements ofO.OOOOI% or more and 1.0000% or less,
having a pH of -1.5 or more and less than 7, and having a solution temperature of 15°C or more
and 1 00°C or less, the time during which the steel sheet is dipped in the solution being 5 seconds
20 or more and 200 seconds or less.
[Claim 3]
A method for producing grain-oriented electrical steel sheet according to claim 1 or 2,
wherein in the rapid temperature rise of the primary recrystallization annealing, an average rate
25 of temperature rise in the temperature region of 550°C to 700°C is I 00°C/s or more and
3000°C/s or less
[Claim4]
A method for producing grain-oriented electrical steel sheet according to any one of claims
30 1 to 3, wherein the slab contains, in place of part of the Fe, one or more elements selected from
the group comprising Cu: 1.0% or less, Sn: 1.0% or less, Ni: 1.0% or less, Cr: 1.0% or less, Sb:
1.0% or less, and Bi: 1.0% or less.
35
[Claim 5]
A method for producing grain-oriented electrical steel sheet according to any one of claims
I to 4, wherein
36
the primary recrystallization annealing includes a process of temperature rise, a process of
intermediate treatment from temperature rise to decarburization annealing, and a process of
decarburization annealing,
in the intermediate treatment, a dew point temperature of the atmosphere is -40°C or more
5 and ooc or less and a dwell time at a steel sheet temperature of 700°C or more and 950°C or less
is 1 second or more and 20 seconds or less, and
in the decarburization annealing, an oxygen partial pressure ratio (PH 2 o 1PH 2 ) of the
atmosphere is 0.35 or more and 0.60 or less.