DESCRIPTION
TITLE OF INVENTION: METHOD OF MANUFACTURING GRAINORIENTED
ELECTRICAL STEEL SHEET
TECHNICAL FIELD
[0001] The present invention relates to a method of
manufacturing a grain-oriented electrical steel sheet
in which the variation in magnetic property is
suppressed.
BACKGROUND ART
[0002] A grain-oriented electrical steel sheet is a
steel sheet which contains Si and in which crystal
grains are highly integrated in a {110}<001>
orientation, and is used as a material of a wound
core of a stationary induction apparatus such as a
transformer. The control of the orientation of the
crystal grains is conducted with catastrophic grain
growth phenomenon called secondary recrystallization.
[0003] As a method of controlling the secondary
recrystallization, the following two methods can be
cited. In one method, heating is performed on a slab
at a temperature of 1280°C or higher to almost
completely solid-solve fine precipitates called
inhibitors, and thereafter hot rolling, cold rolling,
annealing and so on are performed to cause the fine
precipitates to precipitate during the hot rolling
and the annealing. In the other method, heating is
performed on a slab at a temperature of lower than
- 1 -
1280°C, and thereafter hot rolling, cold rolling,
decarburization annealing, nitriding, finish
annealing and so on are performed to cause AlN (Al,
Si)N and the like to precipitate as inhibitors during
the nitriding. The former method is sometimes called
a high-temperature slab heating method, and the
latter method is sometimes called a low-temperature
slab heating method.
[0004] In the low-temperature slab heating method,
nitridation annealing is normally performed after
decarburization annealing also serving as primary
recrystallization annealing is performed, and the
decarburization annealing and the nitridation
annealing are tried to be simultaneously performed in
recent years. If it becomes possible to
simultaneously perform the decarburization annealing
and the nitridation annealing, it becomes possible to
perform them in one furnace and use existing
annealing facilities, and to reduce the total
treatment time required for annealing and suppress
the energy consumption.
[0005} However, simultaneously performing the
decarburization annealing and the nitridation
annealing causes a remarkable variation in magnetic
property (magnetic property deviation) depending on
site, after the finish annealing performed with the
steel being coiled.
CITATION LIST
PATENT LITERATURE
[0006] Patent Literature 1: Japanese Laid-open
Patent Publication No. 3-122227
Patent Literature 2: Korean Registered Patent
Publication No. 817168
Patent Literature 3: Japanese Laid-open Patent
Publication No. 2009-209428
Patent Literature 4: Japanese Laid-open Patent
Publication No. 7-252351
Patent Literature 5: Japanese National
Publication of International Patent Application No.
2 00 1-5 1554 0
Patent Literature 6: Japanese Laid-open Patent
Publication No, 2007-254829
SUMMARY OF THE INVENTION
TECHNICAL PROBLEM
[0007] An object of the present invention is to
provide a method of manufacturing a grain-oriented
electrical steel sheet, capable of suppressing the
variation in magnetic property.
SOLUTION TO PROBLEM
[0008] It turned out that the above-described
variation in magnetic properties after the finish
annealing is remarkable when using a slab containing
a low C content, in particular, when the C content is
0.06 mass% or less. The reason when the slab
containing a low C content is that a reduction in
time period used for the decarburization annealing in
a manufacturing process of the grain-oriented
electrical steel sheet is required from the viewpoint
- 3 -
of reducing CO2 emissions in recent years. Although
the cause of the variation in magnetic property after
the finish annealing is not exactly known, the
variation is considered to occur because the crystal
grains sometimes do not uniformly grow during the
finish annealing even if the crystal grains seem to
be uniform before the finish annealing. Further, the
conceivable reason why the crystal grains do not
uniformly grow is that when the decarburization
annealing and the nitridation annealing are
simultaneously performed, the primary
recrystallization and the nitridation proceed during
the decarburization annealing, thereby causing a
difference in size of a precipitate in the thickness
direction of the steel sheet. More specifically, the
primary recrystallized grain is less likely to grow
on the surface layer portion of the 'steel sheet due
to the formation of the precipitate with the
nitridation, whereas the primary recrystallized grain
is more likely to grow at the central portion because
the precipitate is not formed before a certain amount
of nitrogen diffuses. Accordingly, it is conceivable
that there occurs variation in the grain diameter of
the primary recrystallized grain to make the grain
diameter (secondary recrystallization grain diameter)
obtained through secondary recrystallization nonuniform,
resulting in a large variation in magnetic
property.
[0009] The present inventors thought, based on such
- 4 -
knowledge, that it is possible to uniformly cause the
secondary recrystaliization through forming an
effective precipitate in order to make the crystal
grain growth uniform during the finish annealing in
the low-temperature slab heating method in which the
decarburization annealing and the nitridation
annealing are simultaneously performed. Then, the
present inventors repeatedly carried out an
experiment of measuring the magnetic properties of
the grain-oriented electrical steel sheets obtained
through adding various kinds of elements to slabs.
As a result, the present inventors found that
addition of Ti and Cu was effective to make the
secondary recrystallization uniform.
[0010] The present invention has been made based on
the above-described knowledge, and a.summary thereof
is as follows.
[0011] (1) A method of manufacturing a grainoriented
electrical steel sheet, including:
performing hot rolling on a steel containing Si:
2.5 mass% to 4.0 mass%, C: 0.02 masso to 0.10 masso,
Mn: 0.05.masso to 0.20 masso, acid-soluble Al: 0.020
mass% to 0.040 mass%, N: 0.002 mass% to 0.012 mass%,
S: 0.001 masso to 0.010 mass%, and P: 0.01 masso to
0.08 masso, further containing at least one kind
selected from a group consisting of Ti: 0.0020 mass%
to 0.010 mass% and Cu: 0.010 mass% to 0.50 masso, and
a balance composed of Fe and inevitable impurities,
to obtain a hot-rolled sheet;
- 5 -
performing annealing on the hot-rolled steel
sheet to obtain an annealed steel sheet;
performing cold roiling on the annealed steel
sheet to obtain a cold-rolled steel sheet;
performing decarburization annealing and
nitr.idation annealing on the cold-rolled steel sheet
to obtain a decarburized nitrided steel sheet; and
performing finish annealing on the decarburized
nitrided steel sheet,
wherein the obtaining the decarburized nitrided
steel sheet includes:
starting heating on the cold-rolled steel sheet
in a decarburizing and nitriding atmosphere;
then performing first annealing at a first
temperature within a range of 700°C to 950°C; and
then, performing second annealing at a second
temperature within a range of 850°C to 950°C when the
first temperature is lower than 800°C and within a
range of 800°C to 950°C when the first temperature is
800°C or higher.
[0012] (2) The method of manufacturing a grainoriented
electrical steel sheet according to (1),
wherein
the first temperature falls within a range of
700°C to 850°C, and
the second temperature falls within a range of
850°C to 950°C.
[0013] (3) The method of manufacturing a grainoriented
electrical steel sheet according to (1) or
- 6 -
(2), wherein the steel further contains at least one
kind selected from a group consisting of Cr: 0.010
mass% to 0.20 mass%, Sn: 0.010 mass% to 0.20 masso,
Sb: 0.010 mass% to 0.20 mass%, Ni: 0.010 mass% to
0.20 mass%, Se: 0.005 mass° to 0.02 mass%, Bi: 0.005
mass% to 0.02 mass%, Pb: 0.005 masso to 0.02 mass%,
B: 0.005 mass° to 0.02 mass%, V: 0.005 mass% to 0.02
mass%, Mo: 0.005 mass% to 0.02 mass%, and As: 0.005
masso to 0.02 mass
[0014] (4) The method of manufacturing a grainoriented
electrical steel sheet according to any one
of (1) to (3), wherein
a Ti content in the steel is 0.0020 mass% to
0.0080 masso,
a Cu content in the steel is 0.01 mass% to 0.10
mass%, and
a relation of "20x[Ti]+[Cu]=0.18" is established
where the Ti content (mass%) in the steel is
expressed as [Ti] and the Cu content (masso) is
expressed as [Cu]
[0015] (5) The method of manufacturing a grainoriented
electrical steel sheet according to (4),
wherein a relation of !!10x [Ti]+[Cu]<0 07!! is
established.
[0016] (6) The method of manufacturing a grainoriented
electrical steel sheet according to any one
of (1) to (5), wherein the hot roiling on the steel
is performed after heating the steel to a temperature
of 1250°C or lower.
- 7 -
[0017] (7) The method of manufacturing a grain
oriented electrical steel sheet according to any one
of (1) to (6), wherein time periods of the first
annealing and the second annealing are 15 seconds or
more.
ADVANTAGEOUS EFFECTS OF INVENTION
[0018] According to the present invention,
appropriate amounts of Ti and/or Cu are contained in
the steel, and clecarburization annealing and
nitridation annealing is performed at appropriate
temperatures, thereby making it possible to suppress
the variation in magnetic property.
BRIEF DESCRIPTION OF DRAWINGS
[0019] [Fig. 1] Fig. 1 is a chart representing the
relation between a Ti content and a Cu content and
the magnetic flux density and the evaluation of its
variation.
[Fig. 2] Fig. 2 is a flowchart illustrating a
method of manufacturing a grain-oriented electrical
steel sheet according to an embodiment of the present
invention.
DESCRIPTION OF EMBODIMENTS
[0020] As described above, the present inventors
repeatedly conducted the experiments of measuring the
magnetic properties of grain-oriented electrical
steel sheets obtained through adding various kinds of
elements to slabs and found out that addition of Ti
and Cu is effective to make the secondary
recrystallization uniform.
- 8 -
[0021] In the experiment, silicon steel with a
composition used for manufacturing a grain-oriented
electrical steel sheet based on a low-temperature
slab heating method was used, for example. Eurther,
Ti and Cu were contained at various ratios into the
steel to produce steel ingots with various
compositions. Further, the steel ingots were heated
at a temperature of 1250°C or lower and subjected to
hot rolling, and then subjected to cold rolling.
Furthermore, decarburization annealing and
nitridation annealing were simultaneously performed
after the cold rolling, and then finish rolling was
performed. Then, the magnetic flux densities B8 of
the obtained grain-oriented electrical steel sheets
were measured and the variations in the magnetic flux
densities B8 in coils after the finish annealing were
checked. The magnetic flux density BS is the
magnetic flux density occurring in the grain-oriented
electrical steel sheet when a magnetic field of 800
Aim at 50 Hz is applied thereto.
[0022] As a result of the experiment, it was found
out that the variation in the magnetic flux density
B8 in the coil after the finish annealing is
remarkably reduced when the steel ingot contains
0.0020 mass% to 0.010 mass% of Ti and/or 0.010 masso
to 0.50 masso of Cu.
[0023] An example of the results, obtained through
the above-described experiments is illustrated in
Fig. 1. Though details of the experiments will be
described later, an open circle mark in Fig. 1
indicates that the average value of the magnetic flux
densities B8 of five single-plate samples was 1.90 T
or more and the difference between the maximum value
and the minimum value of the magnetic flux density B8
was 0.030 T or less. Further, a filled circle mark
in Fig. 1 indicates that at least the average value
of the magnetic flux densities BE of five singleplate
samples was less than 1.90 T or the difference
between the maximum value and the minimum value of
the magnetic flux density BE was more than 0.030 T.
It is apparent from Fig. 1 that when the steel ingot
contains 0.0020 mass% to 0.010 mass% of Ti and/or
0.010 mass% to 0.50 mass% of Cu, the average value of
the magnetic flux densities BE is high and the
variation in the magnetic flux density BE is small.
[0024] Next, a method of manufacturing a grainoriented
electrical steel sheet according to an
embodiment of the present invention will be
described. Fig. 2 is a flowchart illustrating the
method of manufacturing •a grain-oriented electrical
steel sheet according to the embodiment of the
present invention.
[0025] In the present embodiment, first, a slab is
produced through casting of molten steel for a grainoriented
electrical steel sheet with a predetermined
composition (Step 1). The casting method therefor is
not particularly limited. The molten steel contains,
for example, Si: 2.5 mass% to 4.0 mass%, C: 0.02
- 10 -
mass% to 0.10 mass%, Mn: 0.05 mass% to 0.20 mass%,
acid-soluble Al: 0.020 mass% to 0.040 mass%, N: 0.002
mass% to 0.012 mass%, S: 0.001 mass% to 0.010 mass%,
and P: 0.01 mass% to 0.08 mass%. The molten steel
further contains at least one kind selected from a
group consisting of Ti: 0.0020 mass% to 0.010 mass%
and Cu: 0.010 mass% to 0.50 mass%. In short, the
molten steel contains one or both of Ti and Cu in
ranges of Ti: 0.010 mass% or less and Cu: 0.50 mass%
or less to satisfy at least one of Ti: 0.0020 mass%
or more or Cu: 0.010 mass% or more. The balance of
the molten steel may be composed of Fe,and inevitable
impurities. Note that the inevitable impurities may
include an element(s) forming an inhibitor in the
manufacturing process of the grain-oriented
electrical steel sheet and remaining. in the grainoriented
electrical steel sheet after purification is
performed through high-temperature annealing.
[0026] Here, reasons for numerical limitations of
the composition of the above-described molten steel
will be explained.
[0027]- Si is an element that is extremely effective
to enhance the electrical resistance of the grainoriented
electrical steel sheet to reduce the eddy
current loss constituting a part of the core loss.
When the Si content is less than 2.5 mass%, the eddy
current loss cannot be sufficiently suppressed. On
the other hand, when the Si content is more than 4.0
mass%, the processability is lowered. Accordingly,
- 11 -
the Si content is set to 2.5 mass% to 4.0 masso.
[00281 C is an element that is effective to control
the structure (primary recrystallization structure)
obtained through primary recrystallization. When the
C content is less than 0.02 mass%, the effect cannot
be sufficiently obtained. On the other hand, when
the C content is more than 0.10 mass, the time
required for decarburization annealing increases,
resulting in a larger exhaust amount of CO2. NoI-.e
that when the decarburization annealing is
insufficient, the grain-oriented electrical steel
sheet with excellent magnetic properties is less
likely to be obtained. Accordingly, the C content is
set to 0.02 mass% to 0.10 mass%. Further, since the
variation in magnetic property after finish annealing
is particularly prominent when the C content is 0.06
mass% or less in the conventional technique as
described above, the embodiment is particularly
effective in the case where the C content is 0.06
mass% or less.
[0029] Mn increases the specific resistance of the
grain-oriented electrical steel sheet to reduce the
core loss. Mn also functions to prevent occurrence
of cracks in the hot rolling. When the Mn content is
less than 0.05 mass%, the effects cannot be
sufficiently obtained. On the other hand, when the
Mn content is more than 0.20 mass%, the magnetic flux
density of the grain-oriented electrical steel sheet
is lowered. Accordingly, the Mn content is set to
- 12 -
0.05 mass% to 0.20 mass%.
[0030] Acid-soluble Al is an important element
forming A1N serving as an inhibitor. When the acidsoluble
Al content is less than 0.020 mass%, a
sufficient amount of A1N cannot be formed, resulting
in insufficient inhibitor strength. On the other
hand, when the acid-soluble Al content is more than
0.040 mass%, A1N becomes coarse, resulting in a
decrease in inhibitor strength. Accordingly, the
acid-soluble Al content is set to 0.020 mass% to
0.040 mass%.
[0031] N is an important element forming A1N through
reacting with the acid-soluble Al. Though a large
amount of N does not need to be contained in the
grain-oriented electrical steel sheet because
nitridation annealing is performed after the cold
rolling as will be described later,,a great load may
be required in steelmaking in order to make the N
content less than 0.002 mass%. On the other hand,
when the N content is more than 0.012 mass%, a hole
called blister is generated in the steel sheet in the
cold rolling. Accordingly , the N content is set to
0.002 mass% to 0.012 mass%. The N content is
preferably 0.010% mass% or less in order to further
reduce the blister.
[0032] S is an important element forming a MnS
precipitate through reacting with Mn. The MnS
precipitate mainly affects the primary
recrystallization and functions to suppress the
13 -
variation depending on site in grain growth in the
primary recrystallization due to the hot rolling-
When the Mn content is less than 0.001 mass%, the
effect cannot be sufficiently obtained. On the other
hand, when the Mn content is more than 0.010 mass%,
the magnetic property is likely to decrease.
Accordingly, the Mn content is set to 0.001 mass% to
0.010 mass The Mn content is preferably 0.009 mass%
or less in order to further improve the magnetic
property.
[0033] P increases the specific resistance of the
grain-oriented electrical steel sheet to reduce the
core loss. When the P content is less than 0.01
mass%, the effect cannot be sufficiently obtained.
On the other hand, when the P content is more than
0.08 mass%, the cold rolling may become difficult to
perform. Accordingly, the P content is set to 0.01
mass% to 0.08 mass%.
[0034] Ti forms a TiN precipitate through reacting
with N. Further, Cu forms a CuS precipitate through
reacting with S. These precipitates function to make
the growth of the crystal grains in the finish
annealing uniform irrespective of the site of the
coil and suppress the variation in magnetic property
of the grain-oriented electrical steel sheet. In
particular, the TiN precipitate is considered to
suppress the variation in grain growth in a high
temperature region in the finish annealing to
decrease the deviation of the magnetic property of
- 14 -
the grain-oriented electrical steel sheet. Further,
the CuS precipitate is considered to suppress the
variation in grain growth in a low temperature region
in the decarburization annealing and the finish
annealing to decrease the deviation of the magnetic
property of the grain-oriented electrical steel
sheet. When the Ti content is less than 0.0020 mass%
and the Cu content is less than 0.010 mass%, the
effects cannot be sufficiently obtained. On the
other hand, when the Ti content is more than 0.010
mass%, the TiN precipitate is excessively formed and
remains even after the finish annealing. Similarly,
when the Cu content is more than 0.50 mass%, the CuS
precipitate is excessively formed and remains even
after the finish annealing." If these precipitates
remain in the grain-oriented electrical steel sheet,
it is difficult to obtain a high magnetic property.
Accordingly, the molten steel contains one or both of
Ti and Cu in ranges of Ti: 0.010 mass% or less and
Cu: 0.50 mass% or less to satisfy at least one of Ti:
0.0020"mass% or more or Cu: 0.010 mass% or more. In
short, the molten steel contains at least one kind
selected from a group consisting of Ti: 0.0020 mass%
to 0.010 mass% and Cu: 0.010 mass% to 0.50 mass%.
[0035] Note that the lower limitof the Ti content
is preferably 0.0020 mass%, and the upper limit of
the Ti content is preferably 0.0080 mass%. Further,
the lower limit of the Cu content is preferably 0.01
- 15 -
mass%, and the upper limit of the Cu content is
preferably 0.10 mass%. Further, where the Ti content
(mass%) is expressed as [Ti] and the Cu content
(mass%) is expressed as [Cu], it is more preferable
that the relation of "20x[Ti]+[Cu]<0.18" is
established and, preferably, the relation of
"l0x[Ti]+[Cu] 0.07" is established.
[0036] Note that at least one kind of the following
various kinds of elements may be contained in the
molten steel.
[0037] Cr and Sn improve the quality of an oxide
layer to be formed in the decarburization annealing
and improve the quality of a glass film to be formed
of the oxide layer in the finish annealing. In other
words, Cr and Sn improve the magnetic property
through stabilization of the formation of the oxide
layer and the glass film to suppress the variation in
the magnetic property. However, when the Cr content
is more than 0.20 mass%, the formation of the glass
film may be unstable. Further, when the Sn content
is more than 0.20 mass%, the surface of the steel
sheet may be less likely to be oxidized to result in
insufficient formation of the glass film.
Accordingly, each of the Cr content and the Sn
content is preferably 0.20 mass% or less. Further,
in order to sufficiently obtain the above effects,
each of the Cr content and the Sn content is
preferably 0.01 mass% or more. Note that Sn is a
grain boundary segregation element and thus also has
- 16 -
an effect to stabilize secondary recrystallization.
[0038] Further, the molten steel may contain Sib:
0.010 mass% to 0.20 mass%, Ni: 0.010 mass% to 0.20
mass%, Se: 0.005 mass% to 0.02 mass%, Bi: 0.005 mass%
to 0.02 mass%, Pb: 0.005 mass% to 0.02 mass%, B:
0.005 mass% to 0.02 mass%, V: 0.005 mass% to 0.02
mass%, Me: 0.005 mass% to 0.02 mass %, and/or As:
0.005 mass% to 0.02 mass%. These elements may be
inhibitor strengthening elements.
[0039] In the embodiment, after the slab is produced
from the molten steel with the composition, the slab
is heated (Step S2). The temperature of the heating
is preferably set to 1250°C or lower from the
viewpoint of energy saving.
[0040] Next, hot rolling is performed on the slab to
obtain a hot-rolled steel sheet (Step S3). The
thickness of the hot-rolled steel sheet is not
particularly limited, and may be set to 1.8 mm to 3.5
mm.
[0041] Thereafter, annealing is performed on the
hot-rolled steel sheet to obtain an annealed steel
sheet (Step S4). The condition of the annealing is
not particularly limited, and the annealing may be
performed, for example, at a temperature of 750°C to
1200°C for 30 seconds to 10 minutes. The annealinq
improves the magnetic property.
[0042] Subsequently, cold rolling is performed on
the annealed steel sheet to obtain a cold-rolled
steel sheet (Step S5). The cold rolling may be
- 17 -
performed only once or a plurality of times while an
intermediate annealing is performed therebetween.
The intermediate annealing is preferably performed at
a temperature of 750°C to 1200°C for 30 seconds to 10
minutes.
[0043] Note that if the cold rolling is performed
without performing the above-described intermediate
annealing, it may be difficult to obtain uniform
properties. On the other hand, if the cold rolling
is performed a plurality of times while the
intermediate annealing is performed therebetween, the
uniform properties are easily obtained but the
magnetic flux density may decrease. Accordingly, it
is preferable to determine the number of times of the
cold rolling and the presence or absence of the
intermediate annealing according to the property
required for and the cost of the finally obtained
grain-oriented electrical steel sheet.
[0044] Further, in any case, it is preferable to set
the rolling reduction at the final cold rolling to
80% to 95%.
[0045] _.The decarburization annealing and nitridation
annealing (decarburization and nitridation annealing)
is performed on the cold-rolled steel sheet in a
decarburizing and nitriding atmosphere after the cold
rolling to obtain a decarburized nitrided steel sheet
(Step S6). The decarburization annealing removes
carbon in the steel sheet and causes primary
recrystallization. Further, the nitridation
- 18 -
annealing increases the nitrogen content in the steel
sheet. An example of the decarburiz"ing and nitriding
atmosphere is a moist atmosphere containing hydrogen,
nitrogen, water vapor and gas (ammonia or the like)
having a nitriding capability.
[0046] In the decarburization and nitridation
annealing, at least the heating of the cold-rolled
steel sheet is started in the decarburizing and
nitriding atmosphere, then a first annealing is
performed at a temperature T1 within a range of 700°C
to 950°C, and then a second annealing is performed at
a temperature T2. More specifically, the atmosphere
containing the gas having the nitriding capability is
prepared prior to the generation of decarburization,
and the decarburization and the nitridation are
simultaneously performed. The temperature T2 here is
a temperature within a range of 850°CC to 950°C when
the temperature T1 is lower than 800°C, and is a
temperature within a range of 800°C to 950°C when the
temperature Ti is 800°C or higher. Further, it is
preferable to keep the cold-rolled steel sheet at the
tempera-ture Ti and at the temperature T2 for 15
seconds or more each. The decarburization, primary
recrystallization, and nitridation may occur in both
of the annealing at the temperature Ti and the
annealing at the temperature T2, and the annealing at
the temperature Ti mainly contributes to nitridation
and the annealing at the temperature T2 mainly
contributes to appearance of the primary
- 19 -
recrystallization.
[0047] When the temperature Ti is lower than 700°C,
the crystal grain obtained through the primary
recrystallization (primary recrystallized grain) is
small so that the subsequent secondary
recrystallization does not sufficiently appear. On
the other hand, when the temperature Ti is higher
than 950°C, the primary recrystallized grain is large
so that the subsequent secondary recrystallization
does not sufficiently appear. Further, when the
temperature T2 is lower than 850°C when the
temperature Ti is lower than 800°C, the crystal grain
(primary recrystallized grain) obtained through the
primary recrystallization is small so that the
subsequent secondary recrystallization does not
sufficiently appear. Similarly, when the temperature
T2 is lower than 800°C, even when the temperature Ti
is higher than 800°C, the crystal grain (primary
recrystallized grain) obtained through the primary
recrystallization is small so that the subsequent
secondary recrystallization does not sufficiently
appear. On the other hand, when the temperature T2
is higher than 950°C, the primary recrystallized grain
is large so that the subsequent secondary
recrystallization does not sufficiently appear.
Further, when the temperature Tl is lower than 700°C
or when the temperature Ti and the temperature T2 are
higher than 950°C, nitrogen is less likely to diffuse
inside the steel sheet, so that the subsequent
- 20 -
secondary recrystallization does not sufficiently
appear.
[0048] Further, when each holding time at the
temperatures Ti and T2 is shorter than 15 seconds,
the nitridation may be insufficient or the primary
recrystallized grain may be small. In particular,
when the holding time at the temperature Ti is
shorter than 15 seconds, the nitridation is likely to
insufficient, and when the holding time at the
temperature T2 is shorter than 15 seconds, the
primary recrystallized grain with a sufficient size
is less likely to be obtained.
[0049] Note that the temperature T2 may be made
equal to the temperature Ti. In other words, if the
temperature Ti is 800°C or higher, the annealing at
the temperature Ti and the annealing, at the
temperature T2 may be continuously performed.
Further, when the temperature Tl and the temperature
T2 are made different, it is preferable to set the
temperature Ti to a temperature suitable for
nitridation and set the temperature T2 to a
temperature suitable for appearance of the primary
recrystallization. Setting the temperature Ti and
the second temperature T2 as described above makes it
possible to further increase the magnetic flux
density and further suppress the variation in
magnetic flux density. For example, it is preferable
to set the temperature Ti to a temperature in a range
of 700°C to 850°C, and to set the temperature T2 to a
- 21 -
temperature in a range of 850°C to 950°C.
[0050] When the temperature Ti falls within the
range of 700°C to 850°C, it is possible to
particularly effectively diffuse the nitrogen
entering the surface of the steel sheet to the
central portion of the steel sheet. Accordingly, the
secondary recrystallization sufficiently appears and
an excellent magnetic property is obtained. Further,
when the temperature T2 falls within the range of
850°C to 950°C, it is possible to adjust the primary
recrystallized grain to a particularly preferable
size. Accordingly, the secondary recrystallization
sufficiently appears and an excellent magnetic
property is obtained.
[0051] After the decarburization and nitridation
annealing, an annealing separating agent containing
MgO as a main component is applied,•in a water
slurry, to the surface of the decarburized nitrided
steel sheet, and the decarburized nitrided steel
sheet is coiled. Then, batch-type finish annealing
is performed on the coiled decarburized nitrided
steel sheet to obtain a coiled finish-annealed steel
sheet (Step S7). The finish annealing causes
secondary recrystallization.
[0052] Thereafter, the coiled finish-annealed steel
sheet is uncoiled, and the annealing separating agent
is removed. Subsequently, a coating solution
containing aluminum phosphate and colloidal silica as
main components is applied to the surface of the
- 22 -
finish-annealed steel sheet, and baking is performed
thereon to form an insulating film (Step S8).
[0053] In the above manner, the grain-oriented
electrical steel sheet can be manufactured.
[0054] Note that the steel being an object for the
hot rolling is not limited to the slab obtained
through casting of the molten steel; but a so-called
thin slab may be used. Further, when using the thin
slab, it is not always necessary to, perform the slab
heating at 1250°C or lower.
EXAMPLE
[0055] Next, the experiments carried out by the
present inventers will be described. The conditions
and so on in the experiments are examples employed to
verify the practicability and the effects of the
present invention, and the present invention is not
limited to those examples.
[0056] (First Experiment)
First, 15 kinds of steel ingots each containing
Si: 3.1 mass%, C: 0.06 mass%, Mn: 0.10 mass%, acidsoluble
Al: 0.029 mass%, N: 0.008 mass%, S: 0.0060
mass -and P: 0.030 mass%, further containing Ti and
Cu in amounts listed in Table 1, and the balance
composed of Fe and inevitable impurities were
produced using a vacuum melting furnace. Then,
annealing was performed on the steel ingots at 1150°C
for one hour, and then hot rolling was performed
thereon to obtain hot-rolled steel sheets with a
thickness of 2.3 mm.
- 23 -
[0057] Subsequently, annealing was performed on the
hot-rolled steel sheets at 1100°C for 120 seconds to
obtain annealed steel sheets. Then, acid pickling
was performed on the annealed steel sheets, and then
cold rolling was performed on the annealed steel
sheets to obtain cold-rolled steel sheets with a
thickness of 0.23 mm. Subsequently, decarburization
annealing and nitridation annealing (decarburization
and nitridation annealing) was performed on the coldrolled
steel sheets in an atmosphere containing water
vapor, hydrogen, nitrogen and ammonia to obtain
decarburized nitrided steel sheets. In the
decarburization and nitridation annealing, annealing
was performed at a temperature T1 of 800°C to 840°fi -f-b-
40 seconds, and then annealing was performed at 870°C
for 70 seconds.
[0058] Thereafter, an annealing separating agent
containing MgO as a main component was applied, in a
water slurry, to the surfaces of the decarburized
nitrided steel sheets. Then, finish annealing was
performed on them at 1200°C for 20 hours to obtain
finish--annealed steel sheets. Subsequently, the
finish-annealed steel sheets were washed with water,
and then cutout into a single-plate magnetic
measurement size with a width of 60 mm and a length
of 300 mm. Subsequently, a coating solution
containing aluminum phosphate and colloidal silica as
main components was applied to the surfaces of the
finish-annealed steel sheets, and baking was
- 24 -
performed thereon to form an insulating film. In
this manner, samples of the grain-oriented electrical
steel sheets were obtained.
[0059] Then, the magnetic flux density B8 of each of
the grain-oriented electrical steel sheets was
measured. The magnetic flux density B8 is the
magnetic flux density occurring in the grain-oriented
electrical steel sheet when a magnetic field of 800
A/m at 50 Hz is applied thereto as described above.
Note that the magnetic flux densities B8 of five
single-plate samples for measurement were measured
for each of the samples. Then, for each sample, the
average value "average B8," the maximum value
"B8max," and the minimum value "B8min" were obtained.
The difference "AB8" between the maximum value
"B8max" and the minimum value "B8min" was also
obtained. The difference "AB8" is an index
indicating the fluctuation range of the magnetic
property. These results are listed in Table 1
together with the Ti contents and the Cu contents.
Further, the evaluation results based on the average
value "-average B8" and the difference "AB8" are
indicated in Fig. 1. As described above, an open
circle mark in Fig. 1 indicates that the average
value "average B8" was 1.90 T or more and the
difference "AB8" was 0.030 T or less. Further, a
filled circle mark in Fig. 1 indicates that the
average value "average B8" was less than 1.90 T or
the difference "AB8" was more than 0.030 T.
- 25 -
[0060] [Table 1]
TABLE 1
SAMPLE
No.
Ti CONTENT
(MASS%)
Cu CONTENT
(MASS%)
20X[Ti]+[Cul 10XCTi7+CCu] AVERAGE 68
(T)
BBmax
(T)
B8min
(T)
ADS
(T)
NOTE
1 0.0010 0.005 0.025 0.015 1 2909 1.926 1 .872 0.054 COMPARATIVE EXAMPLE
2 0.0022 0.006 0.050 0.028 1.918 1.925 1.891 0.034 EMBODIMENT
3 0.0049 0,005 0103 0.054 1.916 1 .924 1.892 0.032 EMBODIMENT
4 0.0088 0.007 J 0.183 0.095 1.905 1.922 1391 0.031 EMBODIMENT
5 0.0105 0.004 0.214 0.109 1 .882 1.892 1.862 0.030 COMPARATIVE EXAMPLE
6 0.0012 0.032 0.056 0.044 1 1.919 1 929 1.893 0036 EMBODIMENT
7 0.0013 0.080 0.106 0.093 1.918 1927 1.892 0.D35 EMBODIMENT
8 0.0015 0.131 0.161 0.146 1.916 1.924 1.891 0.033 EMBODIMENT
9 0.0014 0.412 0A40 0.426 1.903 1.911 1.880 0.031 EMBODIMENT
10 0.0011 0.582 0.604 0.593 1 .681 1 .889 1.859 0030 COMPARATIVE EXAMPLE
11 0.0035 0.061 0.151 0.116 1.915 1.923 1.896 0.027 EMBODIMENT
12 00058 0.083 0199 0.141 1 904 1.911 1985 0.026 EMBODIMENT
13 0.0069 0.014 0.152 0.083 1.912 1.920 1.893 0.027 EMBODIMENT
14 0.0085 0.420 0.590 0.505 1.901 1.909 1.884 0.025 EMBODIMENT
15 0.0027 0.022 0.076 0.049 1.920 1 .930 1.902 0.028 EMBODIMENT
[0061] As presented in Table 1 and Fig- 1, in the
samples No. 2 to No. 4, No. 6 to No. 9, and No. 11 to
No. 15, in each of which the Ti content and the Cu
content were within the range of the present
invention, the average value "average B8" was large
to be 1.90 T or more and the difference "8B8" was
small to be 0.030 T or less. In short, high magnetic
property was obtained and the variation in magnetic
property was smal.l.
[0062) In particular, the balance between the
average value "average B8" and the difference "4B8"
was excellent in the samples No. 11, No. 13, and No.
15, in which the relation of "20x[Ti]+[Cu]<0.18" was
established where the Ti content (mass%) was
expressed as [Ti] and the Cu content (mass%) was
expressed as [Cu]. Among them, the balance between
the average value "average B8" and the difference
"/1B8" was extremely excellent in the sample No. 15,
in which the relation of "l0x[Ti]+[Cu];^0.07" was
established.
[0063] On the other hand, in the sample No. 1, in
which the Ti content was less than 0.0020 mass% and
the Cu content was less than 0.010 mass%, the
difference "4B8" was large to be more than 0.030 T.
In short, the variation in the magnetic property was
large. Further, in the sample No. 5, in which the Ti
content was more than 0.010 masses and the sample No.
1.0, in which the Cu content was more than 0.50 mass%,
a large amount of precipitate was contained to affect
- 28 -
the finish annealing, with the result that the
average value "average B8" was small to be less than
1.90 T. In short, a sufficiently high magnetic
property could not be obtained.
[0064] (Second Experiment)
First, 3 kinds of steel ingots each containing
Si: 3.1 mass%, C: 0.04 mass%, Mn: 0.10 mass%, acidsoluble
Al: 0.030 mass%, N: 0.003 mass%, S: 0.0055
mass%, and P: 0.028 mass%, further containing Ti and
Cu in amounts listed in Table 2, and the balance
composed of Fe and inevitable impurities were
produced using a vacuum melting furnace. Then,
annealing was performed on the steel ingots at 1150°C
for one hour, and then hot rolling was performed
thereon to obtain hot-rolled steel sheets with a
thickness of 2.3 mm.
[0065] Subsequently, annealing was .performed on the
hot-rolled steel sheets at 1090°C for 120 seconds to
obtain annealed steel sheets. Then, acid pickling
was performed on the annealed steel sheets, and then
cold rolling was performed on the annealed steel
sheets-to obtain cold-rolled steel sheets with a
thickness of 0.23 mm. Subsequently, steel sheets for
annealing were cutout from the cold-rolled steel
sheets, and decarburization annealing and nitridation
annealing (decarburization and nitridation annealing)
was performed on the steel sheets in an atmosphere
containing water vapor, hydrogen, nitrogen and
ammonia to obtain decarburized nitrided steel sheets.
- 29 -
In the decarburization and nitridation annealing,
annealing was performed at 800°C for 50 seconds, and
then annealing was performed at temperatures T2
listed in Table 2 for 80 seconds.
[0066] Thereafter, an annealing separating agent
containing MgO as a main component was applied, in a
water slurry, to the surfaces of the decarburized
nitrided steel sheets. Then, finish annealing was
performed on them at 1200°C for 20 hours to obtain
finish-annealed steel sheets. Subsequently,
treatments from the water washing to the formation of
the insulating film were performed similarly to the
first experiment to obtain samples of the grainoriented
electrical steel sheets.
[0067] Then, for each of the samples, the average
value "average B8," the maximum value "BBmax," the
minimum value "BBmin," and the difference "OB8" were
obtained similarly to the first experiment. These
results are listed in Table 2 together with the Ti
contents, the Cu contents, and the temperatures T2.
[0068] [Table 2]
TABLE2
SAMPLE
No.
Ti CONTENT
(MASS%)
Cu CONTENT
(MASS% )
20:<[T i]+CC u] 10X[71]+[C u]
TEMPERATURE T2
(°C)
AVERAGE B8
(T)
BBmax
(T)
68min
(T)
E68
(T)
I NOTE
21 00013 0.005 1 0.031 0.018 780 1 B42 1.861 1.829 0031 COMPARATIVE EXAMPLE
22 0.0013 0.005 0.031 0018 820 1 903 1,916 1.879 0037 COMPARATIVE EXAMPLE
23 0.0013 0,005 0.031 0016 870 1910 1.928 1.884 0.044 COMPARATIVE EXAMPLE
24 0.0013 0.005 0.031 0018 920 1.902 1.934 1.863 0.071 COMPARATIVE EXAMPLE
25 0.0013 0.005 0.031 0.018 960 1,723 1.872 1 .621 0.251 COMPARATIVE EXAMPLE
26 0.0025 0 .028 0.078 0.053 780 1.841 1,659 1 ,833 0026 COMPARATIVE EXAMPLE
27 00025 0.028 0.078 0 .053 820 1,910 1.918 1 896 0022 EMBODIMENT
26 00025 0.028 0.078 0.053 670 1 .922 1.931 1.906 0025 EMBODIMENTS
29 00025 0.028 0.078 0 .053 920 1,924 1236 12508 0 .026 EMBODIMENT
30 00025 0.028 0.078 0 .053 960 1 822 1371 1372 0.099 COMPARATIVE EXAMPLE
31 0.0072 0142 0286 0.214 780 1 846 1.662 1.834 0028 COMPARATIVE EXAMPLE
32 0.0072 0,142 0286 0.214 820 1.912 12920 1.898 00022 EMBODIMENT
33 0.0072 0142 0.286 0.214 870 1,924 1 932 1206 0026 EMBODIMENT
34 0.0072 0 1 42 0286 0.214 920 1,925 1,934 1.908 0026 EMBODIMENT
35 00072 0142 0,286 0.214 960 1 825 1 .878 1.781 0.097 COMPARATIVE EXAMPLE
[0069] As presented in Table 2, in the samples No.
27 to No. 29 and No. 32 to No. 34, in each of which
the Ti content, the Cu content, and the temperature
T2 were within the range of the present invention,
the average value "average B8" was large to be 1.90 T
or more and the difference "AB8" was small to be
0.030 T or less. In short, a high magnetic property
was obtained and the variation in the magnetic
property was small.
[0070] On the other hand, in the samples No. 21 to
No. 25, in each of which the Ti content was less than
0.0020 mass% and the Cu content was less than 0.010
mass%, the difference "AB8" was large to be more than
0.030 T. In short, the variation in the magnetic
property was large.
[0071] Further, in the samples No. 26 and No. 31, in
each of which the temperature T2 was lower than 800°C,
the average value "average B8" was small to be less
than 1.90 T. In the samples No. 30 and No. 35 in
each of which the temperature T2 was higher than
950°C, the difference "AB8" was large to be more than
0.030 T--and the average value "average B8" was small
to be less than 1.90 T.
[0072] (Third Experiment)
First, 9 kinds of steel ingots each containing
Si: 3.1 mass%, C: 0.04 mass%, Mn: 0.10 mass%, acidsoluble
Al: 0.030 mass%, N: 0.003., mass%, S: 0.0055
mass%, P; 0.028 mass%, Ti; 0.025 mass%, and Cu: 0.028
mass%, and the balance composed of Fe and inevitable
- 32 -
impurities were produced using a vacuum melting
furnace. Then, annealing was performed on the steel
ingots at 1150°C for one hour, and then hot rolling
was performed thereon to obtain hot-rolled steel
sheets with a thickness of 2.3 mm.
[0073] Subsequently, annealing was performed on the
hot-rolled steel sheets at 1070°C for 120 seconds to
obtain annealed steel sheets. Then, acid pickling
was performed on the annealed steel sheets, and then
cold rolling was performed on the annealed steel
sheets to obtain cold-rolled steel sheets with a
thickness of 0.23 mm. Subsequently, steel sheets for
annealing were cutout from the cold-rolled steel
sheets, and decarburization annealing and nitridation
annealing (decarburization and nitridation annealing)
was performed on the steel sheets in an atmosphere
containing water vapor, hydrogen, nitrogen and
ammonia to obtain decarburized nitrided steel sheets.
In the decarburization and nitridation annealing,
annealing was performed at temperatures Ti within a
range of 680°C to 860°C listed in Table 3 for 20
seconds-, and then annealing was performed at
temperatures T2 within a range of 830°C to 960°C
listed in Table 3 for 90 seconds.
[0074] Thereafter, an annealing separating agent
containing MgO as a main component was applied, in a
water slurry, to the surfaces of the decarburized
nitrided steel sheets. Then, finish annealing was
performed on them at 1200°C for 20 hours to obtain
- 33 -
finish-annealed steel sheets. Subsequently,
treatments from the water washing to the formation of
the insulating film were performed similarly to the
first experiment to obtain samples of the grainoriented
electrical steel sheets.
[0075] Then, for each of the samples, the average
value "average B8," the maximum value "B8max," the
minimum value "BBmin," and the difference "hB8" were
obtained similarly to the first experiment. These
results are listed in Table 3 together with the
temperatures Tl and the temperatures T2.
[0076] [Table 3]
TABLE3
SAMPLE
No.
TEMPERATURE T1 TEMPERATURE T2 AVERAGE 08
(T)
B8 max
(T)
BBmin
(T)
A BB
(T)
NOTE
41 680 880 1.894 1.905 1.874 0 .031 COMPARATIVE EXAMPLE
42 730 880 1 .920 1,929 1.907 0.022 - EMBODIMENT
43 780 880 1.921 1.931 1 .908 0 .023 EMBODIMENT
44 830 880 1.919 1.929 1 .904 0.025 EMBODIMENT
45 880 880 1.909 1.921 1.893 0.028 EMBODIMENT
46 780 790 1 .870 1.898 1 232 0.066 COMPARATIVE EXAMPLE
47 780 830 1,895 1.908 1.881 0.027 COMPARATIVE EXAMPLE
48 780 920 1.925 1.933 1.908 0.025 EMBODIMENT
49 780 960 1,824 1.873 1 .776 0.097 COMPARATIVE EXAMPLE
[0077] As presented in Table 3, in the samples No.
42 to No. 45 and No. 48, in each of which the
temperature Tl and the temperature T2 were within the
range of the present invention, the average value
"average B8" was large to be 1.90 T or more and the
difference "AB8" was small to be 0.030 T or less. In
short, a high magnetic property was obtained and the
variation in the magnetic property was small.
[0078] Further, in the samples No. 42 to No. 44 and
No. 48, in each of which the temperature Ti falls
within a range of 700°C to 850°C and the temperature
T2 falls within a range of 850°C to 950°C, the average
value "average B8" was particularly large to be 1.91T
or more and the difference "A98" was particularly
small to be 0.025T or less.
[0079] On the other hand, in the sample No. 41, in
which the temperature Ti was lower than 700°C, the
difference "AB8" was large to be more than 0.030 T
and the average value "average B8" was small to he
less than 1.90 T. Also in the sample No. 46, in
which the temperature T2 was lower than 800°C, the
difference "OB8" was large to be more than 0.030 T
and the average value "average B8" was small to be
less than 1.90 T. Further, also in the sample No.
49, in which the temperature T2 was higher than 950°C,
the difference "AB8" was large to be more than 0.030
T and the average value "average 138" was small to be
less than 1.90 T. Furthermore, in the sample No. 47,
in which the temperature Ti was lower than 800°C and
- 36 -
the temperature T2 was lower than 850°C, the average
value "average B8" was small to be less than 1.90 T.
[0080] (Fourth Experiment)
First, 10 kinds of steel ingots each containing
Si: 3.2 mass%, C: 0.048 mass%, Mn: 0.08 mass%, acidsoluble
Al: 0.028 mass%, N: 0.004 mass%, S: 0.0061
mass%, P: 0.033 mass%, Ti: 0.0024 mass%, and Cu:
0.029 mass%, further containing Cr and Sn in amounts
listed in Table 4, and the balance composed of Fe and
inevitable impurities were produced using a vacuum
melting furnace. Then, annealing was performed on
the steel ingots at 1.100°C for one hour, and then hot
rolling was performed thereon to obtain hot-rolled
steel sheets with a thickness of 2.3 mm.
[0081] Subsequently, annealing was performed on the
hot-rolled steel sheets at 1100°C for 120 seconds to
obtain annealed steel sheets. Then, acid pickling
was performed on the annealed steel sheets, and then
cold rolling was performed on the annealed steel
sheets to obtain cold-rolled steel sheets with a
thickness of 0.23 mm. Subsequently, decarburization
annealing and nitridation annealing ( decarburization
and nitridation annealing) was performed on the coldrolled
steel sheets in an atmosphere containing water
vapor, hydrogen , nitrogen and ammonia to obtain
decarburized nitrided steel sheets. In the
decarburization and nitridation annealing , annealing
was performed at temperatures Ti of 800°C to 840°0 -r'
30 seconds , and then annealing was performed at 860°C
- 37 -
for 80 seconds.
[0082] Thereafter, an annealing separating agent
containing MgO as a main component was applied, in a
water slurry, to the surfaces of the decarburized
nitrided steel sheets. Then, finish annealing was
performed on them at 1200°C for 20 hours to obtain
finish-annealed steel sheets. Subsequently,
treatments from the water washing to the formation of
the insulating film were performed similarly to the
first experiment to obtain samples of the grainoriented
electrical steel sheets.
[0083] Then, for each of the samples, the average
value "average B8," the maximum value "B8max," the
minimum value "BBmin," and the difference "/1B8" were
obtained similarly to the first experiment. These
results are listed in Table 4 together with the Cr
contents and the Sn contents.
[0084] [Table 4]
E O
to Cu E o
7 m O of
H H (P
Di CD
w E ti CD
Di
l O CD 2 I-
(D 0 Cl)
`t Cu) It Cn
5 0 'O
o fu n
CS Cn (D
0 co
ri CD
o ft H Cl-
10 0 • 0 ct
(D CO (D
h tT o m R
rt CD o
'< 13 H
o
0 ft
a o ^3- y
w (D w
o E c
O
Y H
O
ti
Di
C
H
(D
rt CD CD
Di 0 Fl
(D H -a (D H-
0. CD 7
CD rt
v CD co w
CD h
¢ r K
1 CD
rt H H- 0
7 M Ft
(D I-h W
CD CD C rt
C C- ti CD 01
D 0 CD ti (D
h ri N
H. It 0 Lq
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Cf
pl. w
TABLE 4
SAMPLE
No.
Cr CONTENT
(MASS%)
Sn CONTENT
...-%)
AVERAGE B8
(T)
B8 max
(T)
B8min
(T)
LB8
(T)
NOTE
51 0.005 0.006 1.909 1.917 1.890 0.027 EMBODIMENT
52 0.070 0.005 1.916 1.927 1.904 0.023 EMBODIMENT
53 0.140 0.007 1.915 1.926 1 .902 0.024 EMBODIMENT
54 0.212 0.004 1.908 1.918 1.889 0.029 EMBODIMENT
55 0.005 0.044 1.919 1.929 1 .906 0.023 EMBODIMENT
56 0.004 0.085 1.918 1.927 1.904 0.023 EMBODIMENT
57 0.005 0.253 1.907 1.916 1.888 0.028 EMBODIMENT
58 0.072 0.122 1.913 1 .923 1.899 0.024 EMBODIMENT
59 0.160 0.038 1.913 1.923 1.899 0.024 EMBODIMENT
60 0.180 0.161 1 .911 1.922 1 .897 0.025 EMBODIMENT
0
in the magnetic property was small. Among them, in
the samples No. 52, No. 53, No. 55, No. 56, and No.
58 to No. 60, each of which contains 0.010 masso to
0.20 mass% of Cr and/or 0.010 mass% to 0.20 mass% of
Sn, the average value "average B8" was particularly
large to be 1.91 T or more and the difference "ABB"
was particularly small to be 0.025 T or less.
INDUSTRIAL APPLICABILITY
[0086] The present invention is applicable, for
example, in electrical steel sheet manufacturing
industries and electrical steel sheet using
industries.
CLAIMS
[Claim 1] A method of manufacturing a grain-oriented
electrical steel sheet, comprising:
performing hot rolling on a steel containing Si:
2.5 mass% to 4.0 mass%, C: 0.02 mass% to 0.10 mass%,
Mn: 0.05 mass% to 0.20 masso-, acid-soluble Al: 0.020
mass% to 0.040 mass%, N: 0.002 masso to 0.012 mass%,
S: 0.001 mass% to 0.010 mass%, and P: 0.01 mass% to
0.08 mass%, further containing at least one ]rind
selected from a group consisting of Ti: 0.0020 mass%
to 0.010 mass% and Cu: 0.010 mass% to 0.50 mass%, and
a balance composed of Fe and inevitable impurities,
to obtain a hot-rolled sheet;
performing annealing on the hot-rolled steel
sheet to obtain an annealed steel sheet;
performing cold rolling on the annealed steel
sheet to obtain a cold-rolled steel sheet;
performing decarburization annealing and
nitridation annealing on the cold-rolled steel sheet
to obtain a decarburized nitrided steel sheet; and
performing finish annealing on the decarburized
nitride-d steel sheet,
wherein the obtaining the decarburized nitrided
steel sheet comprises:
starting heating on the cold-rolled steel sheet
in a decarburizing and nitriding atmosphere;
then performing first annealing at a first
temperature within a range of 700°C to 950°C; and
then, performing second annealing at a second
- 41 -
temperature within a range of 850°C to 950°C when the
first temperature is lower than 800°C and within a
range of 800°C to 950°C when the first temperature is
800°C or higher.
[Claim 2] The method of manufacturing a grainoriented
electrical steel sheet according to claim 1,
wherein
the first temperature falls within a range of
700°C to 850°C, and
the second temperature falls within a range of
850°C to 950°C.
[Claim 3] The method of manufacturing a grainoriented
electrical steel sheet according to claim 1,
wherein the steel further contains at least one kind
selected from a group consisting of Cr: 0-010 mass%
to 0.20 mass%, Sn: 0.010 mass% to 0.20 mass%, Sb:
0.010 mass% to 0.20 mass%, Ni: 0.010 mass% to 0.20
mass%, Se: 0.005 mass% to 0.02 mass%, Bi: 0.005 mass%
to 0 . 0 2 mass%, Pb: 0 . 0 0 5 mass% to 0.02 mass%, B
0.005 mass% to 0.02 mass%, V: 0.005 mass% to 0.02
mass%, Moe 0.005 mass% to 0.02 mass%, and As: 0.005
mass% t-o 0.02 mass%.
[Claim 4] The method of manufacturing a grainoriented
electrical steel sheet according to claim 2,
wherein the steel further contains at least one kind
selected from a group consisting of Cr: 0.010 mass%
to 0.20 mass%, Sn: 0.010 mass% to 0.20 mass%, Sb:
0.010 mass% to 0.20 mass%, Ni„ 0.010 mass% to 0.20
mass%, Se: 0.005 mass% to 0.02 mass%, Bi: 0.005 mass%
- 42 -
to 0.02 mass%, Pb: 0.005 mass% to 0.02 mass%, B:
0.005 mass'. to 0.02 mass%, V: 0.005 mass% to' 0.02
mass%, Mo: 0.005 mass% to 0.02 mass%, and As: 0.005
mass% to 0.02 mass%.
[Claim 5] The method of manufacturing a grainoriented
electrical steel sheet according to claim 1,
wherein
a Ti content in the steel is 0.0020 mass% to
0.0080 mass%,
a Cu content in the steel is 0.01 mass% to 0-10
mass%, and
a relation of "20x[Ti]+[Cu]'0.18" is established
where the Ti content (mass%) in the steel is
expressed as [Ti] and the Cu content (mass%) is
expressed as [Cu].
[Claim 6] The method of manufacturing a grainoriented
electrical steel sheet according to claim 2,
wherein
a Ti content in the steel is 0.0020 mass% to
0.0080 mass%,
a Cu content in the steel is 0.01 mass% to 0,10
masso, -and
a relation of "20x[Ti]+[Cu]<0.18" is established
where the Ti content (mass%) in the steel is
expressed as [Ti] and the Cu content (mass%) is
expressed as [Cu].
[Claim 7] The method of manufacturing a grainoriented
electrical steel sheet according to claim 3,
wherein
- 43 -
a Ti content in the steel is 0.0020 mass% to
0.000 mass%,
a Cu content in the steel is 0.01 mass% to 0.10
mass%, and
a relation of "20x[Ti]+[Cu]:E^0,18" is established
where the Ti content (mass%) in the steel is
expressed as [Ti] and the Cu content (mass%) is
expressed as [Cu],
[Claim 8] The method of manufacturing a grainoriented
electrical steel sheet according to claim 4,
-wherein
a Ti content in the steel is 0.0020 mass% to
0.0080 mass%,
a Cu content in the steel is 0.01 mass% to 0.10
mass%, and
a relation of "20x[Ti]+[Cu]c0.18" is established
where the Ti content (mass%) in the steel is
expressed as [Ti] and the Cu content (mass%) is
expressed as [Cu],
[Claim 9] The method of manufacturing a grainoriented
electrical steel sheet according to claim 5,
wherein, a relation of "l0x[Ti]+[Cu]C0.07" is
established.
[Claim 10] The method of manufacturing a grainoriented
electrical steel sheet according to claim 6,
wherein a relation of "10x[Ti]+[Cu]<_0,07" is
established,
[Claim 11] The method of manufacturing a grainoriented
electrical steel sheet according to claim 7,
- 44 -
wherein a relation of "10x[Ti]+[Cu]:!^0.07" is
established.
[Claim 12] The method of manufacturing a grainoriented
electrical steel sheet according to claim 8,
wherein a relation of "l0x[Ti]+[Cu]-0.07" is
established.
[Claim 13] The method of manufacturing a grainoriented
electrical steel sheet according to claim 1,
wherein the hot rolling on the steel is performed
after heating the steel to a temperature of 1250°C or
lower.
[Claim 14] The method of manufacturing a grainoriented
electrical steel sheet according to claim 2,
wherein the hot rolling on the steel is performed
after heating the steel to a temperature of 1250°C or
lower.
[Claim 15] The method of manufacturing a grainoriented
electrical steel sheet according to claim 3,
wherein the hot rolling on the steel is performed
after heating the steel to a temperature of 1250°C or
lower.
[Claim -16] The method of manufacturing a grainoriented
electrical steel sheet according to claim 5,
wherein the hot rolling on the steel is performed
after heating the steel to a temperature of 1250°C or
lower.
[Claim 17] The method of manufacturing a grainoriented
electrical steel sheet according to claim 9,
wherein the hot rolling on the steel is performed
- 45 -
after heating the steel to a temperature of 1250°C or
lower.
[Claim 18] The method of manufacturing a grainoriented
electrical steel sheet according to claim 1,
wherein time periods of the first annealing and the
second annealing are 15 seconds or more.
[Claim 19] The method of manufacturing a grainoriented
electrical steel sheet according to claim 2,
wherein time periods of the first annealing and the
second annealing are 15 seconds or more.
[Claim 20] The method of manufacturing a grainoriented
electrical steel sheet according to claim 3,
wherein time periods of the first annealing and the
second annealing are 15 seconds or more.
[Claim 21] The method of manufacturing a grainoriented
electrical steel sheet according to claim 5,
wherein time periods of the first annealing and the
second annealing are 15 seconds or more.
[Claim 22] The method of manufacturing a grainoriented
electrical steel sheet according to claim 9,
wherein time periods of the first annealing and the
second annealing are 15 seconds or more.
[Claim 23] The method of manufacturing a grainoriented
electrical steel sheet according to claim
13, wherein time periods of the first annealing and
the second annealing are 15 seconds or more.