[0001]The present invention relates to a method for manufacturing a grain-oriented
electrical steel sheet.
Priority is claimed on Japanese Patent Application No. 2019-005060, filed
10 January 16, 2019, the content of which is incorporated herein by reference.
[Background Art]
[0002]
Grain-oriented electrical steel sheets are soft magnetic materials and are mainly
used as iron core materials for transformers. For this reason, grain-oriented electrical
15 steel sheets are required to have magnetic properties such as high magnetization
characteristics and a low iron loss. Magnetization characteristics include magnetic flux
densities induced when an iron core is excited. When magnetic flux densities increase,
sizes of iron cores can be reduced, which is advantageous in terms of device constitutions
of transformers and also in terms of the manufacturing costs of transformers.
20 [0003]
In order to improve magnetization characteristics, it is necessary to control a
texture to the crystal orientation (Goss orientation) in which the { 110} plane is aligned
parallel to the steel sheet surface and the <1 00> axis is aligned with the rolling direction.
In order to accumulate crystal orientations in the Goss orientation, in general, the
25 inhibitors such as AlN, MnS, and MnSe are finely precipitated in steel, and thereby, the
1
secondary recrystallization is controlled.
[00041
Also, as magnetic properties, a high magnetic flux density (represented by a
magnetic flux density B8 value when a magnetic field of 800 Aim is applied) and a low
5 iron loss (represented by an energy loss W17150 (W/kg) with a magnetic flux density of 1.7
teslas (T) at a frequency of 50 hertz (Hz)) are required.
[00051
Iron loss is an electric power loss consumed as heat energy when iron cores are
excited by an alternating-current magnetic fields. In view of energy saving, iron loss is
10 required to be as low as possible. A level of iron loss is influenced by the magnetic
susceptibility, sheet thickness, film tension, amount of impurities, electrical resistivity,
grain size, magnetic domain size, and the like. Now that various technologies for
electrical steel sheets have been developed, research and development to reduce iron loss
are continuously performed to improve energy efficiency.
15 [0006]
Patent Document 1 (Japanese Examined Patent Application, Second Publication
No. S58-26405) discloses a method for reducing iron loss by irradiating a steel sheet
which has been subjected to final annealing with a laser beam to provide local minute
strain to the steel sheet so that a magnetic domain is subdivided when an electrical steel
20 sheet is used as a laminated iron core.
[0007]
Also, Patent Document 2 (Japanese Unexamined Patent Application, First
Publication No. S62-86175) discloses a method in which the magnetic domain
refinement effect does not disappear even if an electrical steel sheet has been subjected to
25 processing to iron core and then subjected to stress relief annealing when an electrical
2
5
steel sheet is used as a wound iron core. When a magnetic domain is subdivided using
these technical means, iron loss is significantly reduced.
[0008]
However, when the inventors of the present invention observed the movement of
the magnetic domain when the magnetic domain was subdivided as described above, it
was found that there were some magnetic domains which did not move. Thus, the
inventors of the present invention have come to the recognition that, in order to further
reduce an iron loss value of a grain-oriented electrical steel sheet, eliminating the pinning
10 effect which hinders the movement of the magnetic domain caused by a glass film on a
surface of the steel sheet is important as well as subdividing the magnetic domain ..
[0009]
In order to facilitate the movement of the magnetic domain as described above,
it is effective not to form a glass film on the surface of a steel sheet. As a means for
15 this, Patent Document 3 (Specification of United States Patent No. 3785882) discloses a
method for preventing a glass film from being formed on a surface of a steel sheet using
coarse high-purity alumina as an annealing separator. However, this method cannot
eliminate inclusions directly below a surface and a margin of improvement in iron loss is
only 2% at most at W 15/60-
20 [0010]
Patent Document 4 (Japanese Unexamined Patent Application, First Publication
No. S64-83620) discloses a method for performing chemical polishing or electrolytic
polishing after final annealing as a method for controlling inclusions directly below a
surface and achieving mirror finishing of the surface. However, although it is possible
25 to process a sample material at a laboratory level using a method such as chemical
3
polishing and electrolytic polishing, in order to carry out the above method on an
industrial scale, the problems concerning managing of a concentration and a temperature
of a chemical solution and installing of a pollution control facility or the like need to be
resolved. Furthermore, in view of productivity, it is very difficult to put the above
5 method into practical use.
[0011]
As a method for resolving this problem, Patent Document 5 (Japanese
Unexamined Patent Application, First Publication No. H07-118750) discloses a method
in which decarburization annealing is performed in an atmosphere gas having an
10 oxidation degree at which Fe-based oxides (Fe2Si04, FeO, and the like) are not formed
and alumina is used as an annealing separator between sheets. However, even if this
process were to be carried out industrially, it can be seen that it would be difficult to
obtain good magnetic properties while decarburization is stably performed.
[Prior Art Document]
15 [Patent Document]
[0012]
20
[Patent Document 1]
Japanese Examined Patent Application, Second Publication No. S58-026405
[Patent Document 2]
Japanese Unexamined Patent Application, First Publication No. S62-86175
[Patent Document 3]
Specification of United States Patent No. 3785882
[Patent Document 4]
Japanese Unexamined Patent Application, First Publication No. S64-083620
25 [Patent Document 5]
4
5
Japanese Unexamined Patent Application, First Publication No. H07-118750
[Summary of the Invention]
[Problems to be Solved by the Invention]
[0013]
The present invention was made in view of the above-described problems and an
object of the prevent invention is to provide a method for manufacturing a grain-oriented
electrical steel sheet having good magnetic properties while satisfactorily performing
decarburization in decarburization annealing.
[Means for Solving the Problem]
10 [0014]
( 1) A method for manufacturing a grain-oriented electrical steel sheet according
to an aspect of the present invention includes: a silicon steel material production process
of producing a silicon steel material; a hot rolling process of obtaining a hot rolled sheet
by subjecting the silicon steel material to hot rolling; a cold rolling process of obtaining a
15 steel sheet of a final sheet thickness by subjecting the hot rolled sheet to a single cold
rolling process or multiple cold rolling processes having intermediate annealing
performed between the cold rolling processes; a decarburization annealing process of
subjecting the steel sheet to decarburization annealing; and a final annealing process of
applying an annealing separator containing alumina as a main component to the steel
20 sheet and subjecting the steel sheet to final annealing, wherein the silicon steel material
contains: in terms of mass%, Si: 0.8 to 7.0%; C: 0.085% or less; acid-solubleAl: 0.010 to
0.065%; N: 0.004 to 0.012%; Mn: 1.00% or less; S: 0.050% or less; a total of 0.01 to
0.20% of one or both of Sn and Sb; and the remainder: Fe and impurities.
[0015]
25 (2) In the method for manufacturing a grain-oriented electrical steel sheet
5
according to (1), the decarburization annealing process may include: performing the
decarburization annealing using a decarburization annealing furnace including a heating
area and a soaking area, an oxidation degree P1 of an atmosphere gas in the heating area
may satisfy the following Expression 1, and an oxidation degree P2 of an atmosphere gas
5 in the soaking area may satisfy the following Expression 2:
0.01,:5Pl,:50.15 (Expression 1); and
0.01,:5P2,:50.15 (Expression 2).
[0016]
(3) In the method for manufacturing a grain-oriented electrical steel sheet
10 according to (1) or (2), the silicon steel material may further contain, in terms of mass%,
Cr: 0.02 to 0.50%.
[0017]
(4) In the method for manufacturing a grain-oriented electrical steel sheet
according to (2) or (3), the P1 and the P2 described above may sati sfy the following
15 Expression 3:
P1>P2 (Expression 3).
[0018]
(5) In the method for manufacturing a grain-oriented electrical steel sheet
according to any one of (1) to (4), the silicon steel material may further contain, in terms
20 of mass%, Cu: 0% or more and 0.4% or less; P: 0% or more and 0.5% or less; Ni: 0% or
more and 1.0% or less; B: 0% or more and 0.008% or less; V: 0% or more and 0.15% or
less; Nb: 0% or more and 0.20% or less; Mo: 0% or more and 0.10% or less; Ti: 0% or
more and 0.015% or less; and Bi: 0% or more and 0.010% or less.
[0019]
25 (6) In the method for manufacturing a grain-oriented electrical steel sheet
6
according to any one of (1) to (5), the method for manufacturing a grain-oriented
electrical steel sheet may further include: a nitriding treatment process from before the
decarburization annealing process to before secondary recrystallization initiation in the
final annealing process.
5 [0020]
(7) In the method for manufacturing a grain-oriented electrical steel sheet
according to any one of (1) to (6), the method for manufacturing a grain-oriented
electrical steel sheet may further include: a hot-band annealing process of subjecting the
hot rolled sheet obtained in the hot rolling process to annealing after the hot rolling
10 process and before the cold rolling process.
[Effects of the Invention]
[0021]
According to the above aspect of the present invention, it is possible to provide a
method for manufacturing a grain-oriented electrical steel sheet having good magnetic
15 properties while satisfactorily performing decarburization in decarburization annealing.
[Brief Description of Drawing]
[0022]
Fig. 1 is a flowchart for explaining a method for manufacturing a grain-oriented
electrical steel sheet according to an embodiment of the present invention.
20 [Embodiments for implementing the Invention]
25
[0023]
Although the above-described research has been conducted to improve magnetic
properties of grain-oriented electrical steel sheets in the related art, there are still issues
such as those mentioned above which need to be resolved.
The inventors of the present invention have conducted various experiments to
7
resolve such problems. As a result, it is found that, when an appropriate amount of Sn
and/or Sb is included as steel components, a grain-oriented electrical steel sheet having
good magnetic properties can be manufactured while satisfactorily performing
decarburization. Furthermore, it is found that the above effect was improved by
5 controlling oxidation degrees (PH2o/PH2) of atmosphere gases in a heating area and a
soaking area of a decarburization annealing process.
[0024]
Preferred embodiments of the present invention will be described below. Here,
it is obvious that the present invention is not limited to the constitutions disclosed in
10 these embodiments and various modifications are possible without departing from the
gist of the present invention.
15
It is also obvious that the independent elements of the following embodiments
can be combined with each other within the scope of the present invention.
[0025]
Also, in the following embodiments, a numerically limited range includes a
lower limit value and an upper limit value. However, numerical values indicated using
the term "exceeding" and the expression "less than" are not included in this numerical
range.
In addition, unless otherwise specified, "%" of a chemical component in the
20 following embodiments means "mass%".
25
[0026]
A method for manufacturing a grain-oriented electrical steel sheet according to
an embodiment of the present invention will be described below.
[0027]
A method for manufacturing a grain-oriented electrical steel sheet according to
8
the following embodiments includes: a silicon steel material production process of
producing a silicon steel material; a hot rolling process of obtaining a hot rolled sheet by
subjecting the silicon steel material to hot rolling; a cold rolling process of obtaining a
steel sheet of a final sheet thickness by subjecting the hot rolled sheet to a single cold
5 rolling process or multiple cold rolling processes having intermediate annealing
performed between cold rolling processes; a decarburization annealing process of
subjecting the steel sheet to decarburization annealing; and a final annealing process of
applying an annealing separator having alumina as a main component to the steel sheet
and subjecting the steel sheet to final annealing, in which the silicon steel material
10 contains, in terms of mass%, Si: 0.8 to 7.0%; C: 0.085% or less; acid-soluble Al: 0.010 to
0.065%; N: 0.004 to 0.012%; Mn: 1.00% or less; S: 0.050% or less; a total of 0.01 to
0.20% of one or both of Sn and Sb; and the remainder: Fe and impurities. Furthermore,
in the method for manufacturing a grain-oriented electrical steel sheet according to the
above-described embodiment, a hot-band annealing process of subjecting the hot rolled
15 sheet which has been obtained in the hot rolling process to annealing may be further
provided after the hot rolling process and before the cold rolling process.
[0028]
[Chemical components of silicon steel material]
If the Si content increases, the electrical resistance increases and iron loss
20 characteristics are improved. However, if the Si content exceeds 7 .0%, cold rolling is
extremely difficult and a steel material may crack during rolling. For this reason, an
upper limit of the Si content is 7 .0%. The upper limit of the Si content is preferably
4.5%, and more preferably 4.0%.
Also, if the Si content is less than 0.8%, y transformation occurs during final
25 annealing and a crystal orientation of a steel sheet is impaired. For this reason, a lower
9
limit of the Si content is 0.8%. The lower limit of the Si content is preferably 2.0%, and
more preferably 2.5%.
[0029]
Cis an element which is effective in controlling a primary recrystallization
5 structure, but adversely affects the magnetic properties. Thus, C needs to be removed
by performing a decarburization process before final annealing.
If the C content of the silicon steel material is more than 0.085%, a
decarburization annealing time increases and the productivity in industrial production is
impaired. For this reason, an upper limit of the C content is 0.085%. The upper limit
10 of the C content is more preferably 0.070%.
[0030]
In the method for manufacturing a grain-oriented electrical steel sheet according
to this embodiment, acid-soluble Al is an essential element for functioning as an inhibitor
as (Al, Si)N by binding with N. The acid-solubleAl content is 0.010 to 0.065% in
15 which secondary recrystallization is stable.
20
A lower limit of the acid-soluble Al content is preferably 0.020%, and more
preferably 0.025%. An upper limit of the acid-solubleAl content is preferably 0.040%,
and more preferably 0.030%.
[0031]
If theN content exceeds 0.012%, voids called blisters occur in a steel sheet
during cold rolling. Thus, it is desirable that theN content do not exceed 0.012%.
Furthermore, in order to bind withAl and function as an inhibitor, the N content needs to
be 0.004% or more. A lower limit of theN content is preferably 0.006%, and more
preferably 0.007%. An upper limit of theN content is preferably 0.010%, and more
25 preferably 0.009%.
10
[0032]
It is desirable that Mn and S be added within a range such that Mn/(S+Se)~4 is
satisfied in view of preventing the occurrence of cracks in hot rolling. If the Mn content
increases, a saturation magnetic flux decreases. Thus, the Mn content is preferably
5 1.00% or less. The S content is preferably 0.050% or less, more preferably 0.015% or
less, still more preferably 0.010% or less, and still yet more preferably 0.007% or less.
Also, a part of S can be partially replaced with Se. For this reason, when Se is
included, S+Se: 0.050% or less is preferable and it is desirable that a range be set to
satisfy Mn/(S+Se)~4.
10 [0033]
Mn and S may be utilized as inhibitors for secondary recrystallization in some
cases. In these cases, the Mn content at which stable secondary recrystallization is
provided is within the range of 0.02 to 0.30%. A lower limit of the Mn content is
preferably 0.05%, and more preferably 0.07%. An upper limit of the Mn content is
15 preferably 0.15%, and more preferably 0.10%. Furthermore, in this case, the preferred
S content is within the range of 0.010 to 0.050%. The S content is preferably 0.015% or
more, and more preferably 0.020% or more. The S content is more preferably 0.040%
or less. In addition, S can also be replaced with Se.
20
[0034]
In the manufacturing method of Taguchi, Sakakura et al. (for example, Japanese
Examined Patent Application, Second Publication No. S40-15644), Mn and S are utilized
as inhibitors for secondary recr ystallization. On the other hand, in the manufacturing
method of Komatsu et al. (for example, Japanese Examined Patent Application, Second
Publication No. S62-45285), Mn and S are not utilized as inhibitors for secondary
25 recrystallization.
11
[0035]
Sn and Sb are well-known grain boundary segregation elements. Also in a
grain-oriented electrical steel sheet, until now, it has been known that, Sb and Sn enhance
the sealing properties of the surface and prevent oxidation in a high dew point
5 atmosphere, but it has not been known that Sb and Sn promote decarburization in a low
dew point atmosphere.
[0036]
In order to obtain the decarburization promoting effect of Sn and/or Sb, it is
necessary to contain one or both of Sn and Sb in a total amount of 0.01% or more. A
10 lower limit of the total content of Sn and/or Sb is preferably 0.03%, and more preferably
0.05%. An upper limit of the total content of Sn and/or Sb is 0.20%. Even if a total of
Sn and/or Sb to be contained exceeds 0.20%, the decarburization promoting effect is
substantially saturated.
15
[0037]
Cr is an element which has an influence on an oxide layer formation behavior in
decarburization annealing, improves decarburization properties, and promotes subsequent
surface smoothing. For this reason, Cr may be contained. When Cr is contained, the
Cr content is preferably 0.02 to 0.50% in which the effect of improving decarburization
properties is obtained. More preferably, a lower limit of the Cr content is 0.05%. In
20 addition, an upper limit of the Cr content is more preferably 0.39%.
[0038]
Also, in this embodiment, the silicon steel material may contain a selective
element in addition to the above-described basic elements and impurities. For example,
instead of a part of Fe which is the remainder described above, one or more selective
25 elements selected from the group consisting of Cu, P, Ni, B, V, Nb, Mo, Ti, and Bi may
12
be contained.
These selective elements may be contained in accordance with the purpose
thereof. Thus, it is not necessary to limit the lower limits of these selective elements
and the lower limits may be 0%. Furthermore, even if these selective elements are
5 contained as impurities, the above effects are not impaired.
[0039]
Cu: 0% or more and 0.4% or less
Copper (Cu) is an element which is effective in increasing electric resistance and
reducing iron loss. Therefore, Cu may be contained within the range of the content of
10 0.4% or less. If the Cu content exceeds 0.4%, the effect of reducing iron loss is
saturated and it may cause a surface defect called a "copper scab" during hot rolling in
some cases. A lower limit of the Cu content is preferably 0.05%, and more preferably
0.1 %. An upper limit of the Cu content is preferably 0.3%, and more preferably 0.2%.
[0040]
15 P: 0% or more and 0.5% or less
Phosphorus (P) is an element which is effective in increasing electric resistance
and reducing iron less. Therefore, P may be contained within the range of the content of
0.5% or less. If the P content exceeds 0.5%, there may be a problem in the rollability of
a silicon steel sheet in some cases. A lower limit of the P content is preferably 0.005%,
20 and more preferably 0.01 %. An upper limit of the P content is preferably 0.2%, and
more preferably 0. 15%.
[0041]
Ni: 0% or more and 1.0% or less
Nickel (Ni) is an element which is effective in increasing electric resistance and
25 reducing iron loss. Furthermore, Ni is an effective element for controlling a
13
metallographic structure of a hot rolled sheet and improving magnetic properties.
Therefore, Ni may be contained within the range of the content of 1.0% or less. If the
Ni content exceeds 1.0%, secondary recrystallization may be unstable in some cases. A
lower limit of the Ni content is preferably 0.01 %, and more preferably 0.02%. An
5 upper limit of the Ni content is preferably 0.2%, and more preferably 0.1 %.
[0042]
B: 0% or more and 0.008% or less
Boron (B) is an element which is effective for exerting an inhibitor effect as BN.
Therefore, B may be contained within the range of the content of 0.008% or less. If the
10 B content exceeds 0.008%, there is a concern concerning deterioration of magnetic
properties. A lower limit ofthe B content is preferably 0.0005%, and more preferably
0.001%. An upper limit of the B content is preferably 0.005%, and more preferably
0.003%.
15
[0043]
V: 0% or more and 0.15% or less
Nb: 0% or more and 0.20% or less
Ti: 0% or more and 0.015% or less
Vanadium (V), niobium (Nb ), and titanium (Ti) are elements which are effective
for functioning as inhibitors by binding with N or C. Therefore, V, Nb, and/or Ti may
20 be contained within the ranges ofthe content of0.15% or less, 0.20% or less, and/or
0.015% or less, respectively. If these elements remain in a final product and the V
content exceeds 0.15%, the Nb content exceeds 0.20%, or the Ti content exceeds 0.015%,
there is a concern concerning deterioration of magnetic properties.
A lower limit of the V content is preferably 0.002%, and more preferably 0.01 %.
25 An upper limit of the V content is preferably 0.10%, and more preferably 0.05%.
14
A lower limit of the Nb content is preferably 0.005%, and more preferably
0.02%. An upper limit of the Nb content is preferably 0.10%, and more preferably
0.08%.
A lower limit of the Ti content is preferably 0.002%, and more preferably
5 0.004%. An upper limit of the Ti content is preferably 0.010%, and more preferably
0.008%.
[0044]
Mo: 0% or more and 0.10% or less
Molybdenum (Mo) is also an effective element for increasing electric resistance
10 and reducing iron loss. Therefore, Mo may be contained within the range of 0.10% or
less. If the Mo content exceeds 0.1 0%, a problem may occur in the rollability of the
steel sheet in some cases. A lower limit of the Mo content is preferably 0.005%, and
more preferably 0.01 %. An upper limit of the Mo content is preferably 0.08%, and
more preferably 0.05%.
15 [0045]
Bi: 0% or more and 0.010% or less
Bismuth (Bi) is an element which is effective for stabilizing precipitates such as
sulfide and strengthening a function as an inhibitor. Therefore, Bi may be contained
within the range of 0.010% or less. If the Bi content exceeds 0.010%, the magnetic
20 properties rna y deteriorate in some cases. A lower limit of the Bi content is preferably
0.001%, and more preferably 0.002%. An upper limit of the Bi content is preferably
0.008%, and more preferably 0.006%.
[0046]
[Method for manufacturing grain-oriented electrical steel sheet]
25 In order to manufacture a grain-oriented electrical steel sheet having a texture
15
developed in a { 110} <001> orientation from the silicon steel material having the abovedescribed
chemical composition, the following steps are performed.
[0047]
First, molten steel having the above-described chemical component is cast
5 (S 100) to obtain a silicon steel material and a hot rolled sheet obtained from this silicon
steel material using a normal hot rolling step (S 1 02). Alternatively, instead of the hot
rolling step (S 102), molten steel may be continuously cast to form a thin strip.
[0048]
The hot rolled sheet or the continuously cast thin strip i s subjected to the cold
10 rolling step (S 106) immediately or after the hot-band annealing step (S 104 ).
The annealing in the hot-band annealing step (S104) may be performed within a
temperature range of 750 to 1200 oc for 30 seconds to 30 minutes.
[0049]
The hot-band annealing step is effective for enhancing the magnetic properties
15 of a product. The presence or absence of the hot-band annealing step may be
determined in accordance with the properties and the manufacturing costs required for
the grain-oriented electrical steel sheet to be finally manufactured and the hot-band
annealing step may be omitted.
20
[0050]
The cold rolling in the cold rolling step (S 1 06) is performed once or through
multiple cold rolling steps having annealing performed between the cold rolling steps.
When a single cold rolling step is performed, the rolling reduction is preferably 80% or
more. Furthermore, when the multiple cold rolling steps having annealing performed
between the cold rolling steps are performed, the rolling reduction of the final cold
25 rolling after the last annealing is more preferably 80% or more. A cold rolled sheet
16
obtained through this step is a steel sheet having a final sheet thickness.
[0051]
The material which has been subjected to cold rolling is subjected to the
decarburization annealing step (S 1 08) to remove carbon contained in the steeL
5 [0052]
In the method for manufacturing a grain-oriented electrical steel sheet according
to this embodiment, in the decarburization annealing step (S 1 08), decarburization
annealing is performed in a moist hydrogen atmosphere. Annealing is performed by
controlling an atmosphere gas in the decarburization annealing step (S 108) to an
10 oxidation degree at which iron (Fe)-based oxide is not formed.
[0053]
In the decarburization annealing step (S 108), when decarburization annealing is
performed using a decarburization annealing furnace including a heating area and a
soaking area, it is desirable that an oxidation degree P1 of an atmosphere gas in the
15 heating area satisfy the following Expression 1:
20
25
0.01~P1~0.15 (Expression 1).
[0054]
It is desirable that an oxidation degree P2 of an atmosphere gas in the soaking
area in the decarburization annealing step (S 108) satisfy the following Expression 2:
O.Ol~P2~0 . 15 (Expression 2).
[0055]
The oxidation degree P1 and the oxidation degree P2 are oxidation degrees
represented by a ratio "PH2o/PH2" of a partial pressure of water vapor to a partial pressure
of hydrogen in an atmosphere gas containing hydrogen, nitrogen, and water vapor.
When the oxidation degree P1 of the atmosphere gases in the heating area and
17
the oxidation degree P2 in the decarburization annealing step (S 1 08) are defined using
the foregoing Expressions 1 and 2, it is considered that Sn and/or Sb segregates on the
surface during heating to alter an initial oxide film on the outermost surface and the
decarburization properties are improved.
5 [0056]
In order to apply an annealing separator containing alumina as a main
component in a subsequent process, to laminate a steel sheet, and to smooth a surface of
the steel sheet which has been subjected to a final annealing, it is desirable to perform
annealing at an oxidation degree at which Fe-based oxides (Fe2Si04, FeO, and the like)
10 are not formed in this decarburization annealing. For example, in a temperature range
of 800 to 850 oc in which decarburization annealing is normally performed, it is possible
to suppress the formation of Fe-based oxides by adjusting the oxidation degree P1 of the
atmosphere gas in the heating area and the oxidation degree P2 of the atmosphere gas in
the soaking area to 0.15 or less.
15 [0057]
When the oxidation degree Pl or the oxidation degree P2 are greater than 0.15,
inclusions are generated below a surface of a product, which hinders the reduction of iron
loss. Here, if any of the oxidation degrees decreases too much, a decarburization rate
will decrease. When both of these are taken into account, in this temperature range, the
20 oxidation degree P1 and the oxidation degree P2 (Pmo/Pm) are preferably within the
range of0.01 to 0.15.
[0058]
Also, in view of that carbon is further reduced and even better iron loss can be
obtained in the decarburization annealing process, it is more desirable that the oxidation
25 degree Pl of the atmosphere gas in the heating area and the oxidation degree P2 of the
18
atmosphere gas in the soaking area satisfy the following Expression 4:
P1>P2 (Expression 3).
[0059]
In the decarburization process, a heating rate from room temperature to a
5 temperature of the soaking area (a heating rate in the heating area) is preferably 7
°C/second or faster on average, and more preferably 9 oc/second or faster. If the
heating rate is too slow, the decarburization properties deteriorate. Furthermore, it is
not necessary to specify an upper limit, but if the heating rate is too fast, it will be
difficult to control a soaking temperature.
10 [0060]
A temperature of the soaking area and a retention time in the soaking area are
preferably 750 to 900 oc and 10 to 600 seconds. If a temperature (an annealing
temperature) of the soaking area is lower than 750 °C, the decarburization rate decreases
and the productivity decreases. On the other hand, if the temperature of the soaking
15 area is higher than 900 oc, a primary recrystallization grain size exceeds a desired size
and thus the magnetic properties after the final annealing deteriorate. Furthermore, if
the retention time is shorter than 10 seconds, decarburization cannot be sufficiently
performed. On the other hand, if the retention time is longer than 600 seconds, the
productivity decreases.
20 [0061]
25
A nitriding treatment step (SilO) may be provided from before the
decarburization annealing step (S 1 08) to the start of secondary recrystallization in the
final annealing step (S 112).
[0062]
The method for this nitriding treatment is not particularly limited. There are a
19
method to be performed in an atmosphere gas having a nitriding ability such as ammonia,
a method in which a nitride having a nitriding ability is added to an annealing separator,
and the like.
For example, it is desirable that, in the nitriding treatment step (S 11 0), the
5 nitriding treatment of a manufacturing method of Komatsu et al. in which (Al, Si)N is
utilized as a main inhibitor (Japanese Examined Patent Application, Second Publication
No. S62-45285 or the like) be used.
[0063]
In the final annealing step (S 112), an annealing separator containing alumina as
10 a main component (containing 50 mass% or more of alumina) is used. It is desirable
that the annealing separator contain 5 to 50 mass% of magnesia in addition to alumina.
When magnesia is contained, the formation of inclusions such as mullite (3Ah03·2Si02)
on the surface of the steel sheet is suppressed and the iron loss is stably improved.
In the final annealing, the above-described annealing separator containing
15 alumina as a main component is applied to the surface of the steel sheet having an oxide
layer and dried. After dried, the steel sheet is wound in a coil shape and subjected to
final annealing (secondary recrystallization annealing).
[0064]
When an annealing separator containing alumina (Ah03) as a main component
20 is used, even if the steel sheet is subjected to final annealing, it is possible to suppress the
formation of a film of an inorganic mineral substance such as forsterite on the surface of
the steel sheet.
[0065]
With regard to the application of the annealing separator, when a decarburized
25 annealed sheet is laminated (coiled), the surface which has been subjected to final
20
annealing can be mirror-finished and iron loss can be significantly reduced by applying
an annealing separator containing alumina as a main component which does not easily
react with silica in the form of a water slurry, through an electrostatic coating method, or
the like.
5 [0066]
This laminated decarburized annealed sheet is subjected to the final annealing to
occur secondary recrystallization and purification of a nitride, a sulfide, or the like.
Performing the secondary recrystallization within a prescribed temperature range using a
means such as holding the secondary recrystallization at a constant temperature is
10 effective in increasing a magnetic flux density.
Although the final annealing may be performed, for example, under the
conditions that a temperature is raised to 1150 to 1250 ac and annealing is performed for
10 to 30 hours in an atmosphere gas containing hydrogen and nitrogen, when purification
or the like of a nitride and a sulfide or the like is performed, after the completion of the
15 secondary recrystallization, it is desirable to perform annealing at a temperature of 1100
ac or higher in 100% hydrogen.
[0067]
After the final annealing step (S 112), in an insulation coating forming step
(S 114), an insulation coating configured to apply tension to the steel sheet may be
20 formed on the surface of the steel sheet.
[0068]
Also, if necessary, magnetic domain refinement processing may be performed
between the above-described processes through a mechanical method using a tooth
profile or the like, a chemical method using etching or the like, laser irradiation, electron
25 beam irradiation, or the like.
21
[0069]
As described above, in the decarburization annealing process in which the
decarburization annealing is performed in the moist hydrogen atmosphere to remove
carbon contained in the steel which has been subjected to cold rolling, the annealing to be
5 performed through the controlling of the atmosphere gas to have the oxidation degree in
which the iron-based oxide is not formed is a main characteristic of the method for
manufacturing a grain-oriented electrical steel sheet according to the embodiment of the
present invention.
10
[0070]
Also, in the method for manufacturing a grain-oriented electrical steel sheet
according to the above-described embodiment, the nitriding treatment process may be
further provided from before the decarburization annealing process to before the
secondary recrystallization initiation in the final annealing (for example, within a
temperature range of 600 to 1000 °C). To be specific, the nitriding treatment process
15 may be performed independently before the decarburization annealing process, carried
out in one or more stages of a heating stage, a soaking stage, and a cooling stage in the
decarburization annealing process, carried out independently after a decarburization
annealing process, or carried out before the secondary recrystallization initiation in the
final annealing process by adding a nitrogen compound to an annealing separator.
20 [0071]
The grain-oriented electrical steel sheet obtained through the manufacturing
method in the above-described embodiment can be mainly utilized as an iron core of a
transformer or other electric devices.
[Examples]
25 [0072]
22
Although examples of the present invention will be described below, it is
obvious that the conditions adopted in the examples are embodiments in which the
feasibility and the effects of the present invention can be confirmed and the present
invention is not limited to these embodiments.
5 [0073]
The inventors of the present invention considered that the oxide layer formed at
an initial stage of decarburization annealing has a significant influence on a subsequent
decarburization behavior with respect to the decarburization behavior on the surface of
the silicon steel sheet and conducted various experiments associated with this.
10 [0074]
The inventors of the present invention have examined about stability of a
decarburization reaction in the decarburization annealing step in which decarburization
annealing is performed in a moist hydrogen atmosphere to remove carbon contained in
steel which has been subjected to cold rolling when Sn or Sb i s contained as a component
15 of a silicon steel material and Cr is further contained.
[0075]

A silicon steel slab containing, in terms of mass obtained through casting, Si:
3.3%; Mn: 0.14%; C: 0.05%; S: 0.007%; acid-solubleAl: 0.027%; N: 0.008%; and the
20 remainder: Fe and impurities was heated and then subjected to hot rolling to have a sheet
thickness of2.0 mm. The hot rolled sheet was heated to 1100 oc, a temperature of the
hot rolled sheet decreased to 900 oc, and was held for 30 seconds, and then subjected to
one cold rolling to a final sheet thickness of 0.22 mm.
[0076]
25 The cold rolled sheet was subjected to decarburization annealing in which an
23
oxidation degree (PH2o/PH2) was changed by changing a dew point in an atmosphere gas
containing 75% hydrogen and 25% nitrogen and a temperature was rai sed to 830 oc at a
heating rate of 7 °C/second and held for 120 seconds. In Example 1, the oxidation
degree in the heating area is equal to the oxidation degree in the soaking area.
5 [0077]
After that, an amount of nitrogen in the steel was increased to 0.02 mass% in an
ammonia gas and an inhibitor was strengthened.
[0078]
The decarburized annealed sheet was subjected to the final annealing in which
10 an annealing separator (80 mass% of alumina+20 mass% of magnesia) containing
alumina as a main component was applied in the form of a water slurry, a temperature
was raised to 1200 oc in an atmosphere gas containing 75% hydrogen and 25% nitrogen,
the atmosphere gas was changed to a 100% hydrogen atmosphere gas, and then annealing
was performed at 1200 oc for 20 hours.
15 [0079]
The samples prepared through the above steps were washed with water and then
were sheared, were subjected to stress relief annealing, had an insulation coating formed
to provide tension to the steel sheet (had a tension coating to be applied), were subjected
to laser irradiation, and were subjected to magnetic measurement through an SST
20 method. Table 1 shows the amounts of carbon after the decarburization annealing and the
values of iron loss (W17!so) obtained through the above magnetic measurement.
[0080]
[Table 1]
Sample Oxidation Amount of Evaluation Iron loss Evaluation Comprehensive
No. degree of carbon of of amount (Wmso) of iron loss evaluation
decarburization decarburized of carbon (Wikg)
annealing sheet £ppm)
24
1 0.01 66 B 0.63 Ex B
2 0.04 57 B 0.64 Ex B
3 0.06 45 B 0.66 Ex B
4 0.11 38 B 0.67 Ex B
5 0.15 31 B 0.67 Ex B
6 0.20 19 Ex 0.74 B G
7 0.25 7 Ex 0.81 B G
[0081]
In Table 1, "Ex" means an excellent result, "G" means a good range (allowable),
and "B" means a bad result.
[0082]
5 From Table 1, when annealing was performed in a wet gas (a water vaporhydrogen-
nitrogen mixed gas) atmosphere with an oxidation degree of 0.01 to 0.15, the
amount of carbon was reduced to 0.02% or less. Thus, the crystal orientation was not
impaired through transformation during final annealing and a good iron loss of 0.70
W/kg or less was obtained. However, since the amount of carbon in the steel was
10 greater than 0.0030% (30 ppm), there is a concern that magnetic aging occur
(deterioration of magnetic properties due to aging).
Also, when annealing was performed in a wet gas atmosphere having an
oxidation degree of 0.20 or more, the amount of carbon in the steel was 0.0030% or less,
but good iron loss is not obtained.
15 [0083]
It is considered that the reason why the amount of carbon was not reduced to
0.0030% or less depended on a quality and a morphology of an oxide formed on the
surface of the steel sheet in a heating process of decarburization annealing. On the
surface subjected to decarburization annealing, generally, a decarburization (oxidation of
20 carbon in the steel) reaction and an oxide formation (oxidation of silicon in the steel)
reaction of a silica or the like were competing with the moisture in the atmosphere.
From the results of Example 1, it is considered that, when annealing was
25
performed in an atmosphere gas with a low oxidation degree which does not form ironbased
oxides, silica on the surface of the steel sheet was generally generated in the form
of a dense film, which inhibits decarburization.
[0084]
5
10
Influences of surface-segregation-forming elements and oxide-forming elements
on the silica forming reaction were investigated. The results will be shown below as
Example 2.
[0085]
A silicon steel slab containing, in terms of mass% obtained through casting, Si:
3.3%; Mn: 0.14%; C: 0.05%; S: 0.007%; acid-soluble AI: 0.027%; N: 0.008%; Sn:
0.07%; and the remainder: Fe and impurities was heated and then subjected to hot rolling
to have a sheet thickness of 2.0 mm. The hot rolled sheet was heated to 1100 °C, cooled
to 900 °C, was held for 30 seconds, and then subjected to one cold rolling so that a final
15 sheet thickness was 0.22 mm.
[0086]
The cold rolled sheet was subjected to decarburization annealing in which an
oxidation degree (PH2oiPH2) was changed by changing a dew point in an atmosphere gas
containing 75% hydrogen and 25% nitrogen and a temperature was raised to 830 oc at a
20 heating rate of 7 °C/second and held for 120 seconds. In Example 2, the oxidation
degree in the heating area is equal to the oxidation degree in the soaking area.
[0087]
After that, an amount of nitrogen in the steel was increased to 0.02 mass% (a
nitriding treatment) in an ammonia gas to strengthen an inhibitor.
25 [0088]
26
The decarburized annealed sheet was subjected to the final annealing in which
an annealing separator (50 mass% of alumina+50 mass% of magnesia) containing
alumina as a main component was applied in the form of a water slurry, a temperature
was raised to 1200 oc in an atmosphere gas containing 75% hydrogen and 25% nitrogen,
5 the atmosphere gas was changed to a 100% hydrogen atmosphere gas, and then annealing
was performed at 1200 ac for 20 hours. The samples prepared through the above steps
were washed with water and then were sheared, were subjected to stress relief annealing,
had an insulation coating formed to provide tension to the steel sheet (had a tension
coating to be applied), were subjected to laser irradiation, and were subjected to magnetic
10 measurement using through an SST method. Table 2 shows the amounts of carbon after
the decarburization annealing and the values of iron loss (W mso) obtained through the
above magnetic measurement.
[0089]
[Table 2]
Sample Oxidation Amount of Evaluation Iron loss Evaluation Comprehensive
No. degree of carbon of of amount (Wmso) of iron loss evaluation
decarburization decarburized of carbon (Wikg)
annealing sheet (ppm)
1 O.Ql 43 B 0.63 Ex G
2 0.04 26 Ex 0.63 Ex Ex
3 0.06 21 Ex 0.64 Ex Ex
4 0.11 19 Ex 0.65 Ex Ex
5 0.15 16 Ex 0.65 Ex Ex
6 0.20 18 Ex 0.72 B G
7 0.25 9 Ex 0.77 B G
15 [0090]
In Table 2, "Ex" means an excellent result, "G" means a good range, and "B"
means a bad result.
It can be seen from Table 2 that, when annealing was performed in a wet gas (a
water vapor-hydrogen-nitrogen mixed gas) atmosphere with an oxidation degree of 0.01
20 to 0.15, good iron loss is obtained and the amount of carbon in the steel is 0.0030% or
27
less.
[0091]
It can be seen from the above experiment that, when an appropriate amount of
Sn is contained, the decarburization reaction is promoted when decarburization annealing
5 is performed in an atmosphere gas with a low oxidation degree in which an iron oxide is
not formed. Even when Sb is contained, the same effect as that of Sn is obtained and
the effect can be arranged with the total amount of Sb and Sn. It is presumed that Sb
and Sn are segregation elements and both segregate on the surface of the steel sheet to
suppress the diffusion of Si to the surface and suppress the formation of the surface silica
10 film.
[0092]

In Example 3, the stabilization of the decarburization reaction when an
appropriate amount of Cr was contained together with Sn and Sb (segregation elements)
15 in Example 2 was investigated.
[0093]
A silicon steel slab containing, in terms of mass obtained through casting, Si:
3.3%; Mn: 0.14%; C: 0.05%; S: 0.007%; acid-solubleAl: 0.027%; N: 0.008%; Sn:
0.05%; Sb: 0.01 %, Cr: 0.12%; and the remainder: Fe and impurities was heated and then
20 subjected to hot rolling to have a sheet thickness of 2.0 mm. The hot rolled sheet was
heated to 1100 oc, was held for 30 seconds, and then subjected to one cold rolling to a
final sheet thickness of 0.22 mm.
[0094]
The cold rolled sheet was subjected to decarburization annealing in which an
25 oxidation degree (PH2o/PH2) was changed by changing a dew point in an atmosphere gas
28
5
containing 75% hydrogen and 25% nitrogen and a temperature was raised to 830 oc at a
heating rate of 7 °C/second and held at 830 oc for 120 seconds. In Example 3, the
oxidation degree in the heating area is equal to the oxidation degree in the soaking area.
[0095]
After that, an amount of nitrogen in the steel was increased to 0.02 mass% in
ammonia gas to strengthen the inhibitor.
[0096]
The decarburized annealed sheet was subjected to the final annealing in which
an annealing separator (70 mass% of alumina+30 mass% of magnesia) containing
10 alumina as a main component was applied in the form of a water slurry, a temperature
was raised to 1200 oc in an atmosphere gas containing 75% hydrogen and 25% nitrogen,
the atmosphere gas was changed to a 100% hydrogen atmosphere gas, and then annealing
was performed at 1200 oc for 20 hours.
15
[0097]
The samples prepared through the above steps were washed with water and then
were sheared, were subjected to stress relief annealing, had an insulation coating formed
to provide tension to the steel sheet (had a tension coating to be applied), were subjected
to laser irradiation, and were subjected to magnetic measurement using through an SST
method.
20 [0098]
Table 3 shows the amounts of carbon after decarburization annealing and a value
of iron loss (W mso) obtained through the above magnetic measurement.
[0099]
[Table 3]
I Sample I Oxidation I Amount of I Evaluation I Iron loss I Evaluation I Comprehensive I
29
No. degree of carbon of of amount (Wmso) of iron loss evaluation
decarburization decarburized of carbon (Wik.g)
annealing sheet (ppm)
1 O.Ql 18 Ex 0.63 Ex Ex
2 0.04 13 Ex 0.63 Ex Ex
3 0.06 8 Ex 0.62 Ex Ex
4 0.11 3 Ex 0.65 Ex Ex
5 0.15 2 Ex 0.65 Ex Ex
6 0.20 2 Ex 0.70 Ex Ex
7 0.25 2 Ex 0.74 B G
[0100]
In Table 3, "Ex" means an excellent result, "G" means a good range, and "B"
means a bad result.
It can be seen from Table 3 that, when annealing was performed in a wet gas (a
5 water vapor-hydrogen-nitrogen mixed gas) atmosphere with an oxidation degree of 0.01
to 0.20, good iron loss is obtained and the amount of carbon in the steel is 0.0030% or
less. When Cr is contained, an upper limit of an oxidation degree can be expanded.
Unlike Sn and Sb, it is presumed that the contained Cr affects the formation of film-like
silica and promotes the decarburization reaction when an oxide is formed in the heating
10 process of decarburization annealing.
[0101]

In Example 4, the stabilization of the decarburization reaction when the
oxidation degree in the heating area and the oxidation degree in the soaking area were
15 changed was investigated.
[0102]
A silicon steel slab containing, in terms of mass% obtained through casting, Si:
3.3%; Mn: 0.14%; C: 0.05%; S: 0.007%; acid-solubleAl: 0.027%; N: 0.008%; Sn:
0.05%; and Sb: 0.01% and the remainder: Fe and impurities was heated and then
20 subjected to hot rolling to have a sheet thickness of 2.0 mm. The hot rolled sheet was
30
5
subjected to annealing in which the hot rolled sheet was heated to 1120 oc and then
cooled to 950 oc and held for 30 seconds, and then subjected to one cold rolling so that a
final sheet thickness was 0.22 mm.
[0103]
The cold rolled sheet was subjected to decarburization annealing in which an
oxidation degree (PH2o/PH2) was changed by changing a dew point in an atmosphere gas
containing 75% hydrogen and 25% nitrogen, a temperature was raised to 830 oc at a
heating rate of 7 oC/second and held at 830 oc for 120 seconds. In Example 4, the
oxidation degree in the soaking area was set to 0.08 and the oxidation degree in the
10 heating area was changed.
15
[0104]
After that, an amount of nitrogen in the steel was increased to 0.02 mass% in
ammonia gas to strengthen the inhibitor.
[0105]
The decarburization annealing sheet was subjected to final annealing in which
an annealing separator (70 mass% of alumina+30 mass% of magnesia) containing
alumina as a main component was applied in the form of a water slurry, a temperature
was raised to 1200 oc in an atmosphere gas containing 75% hydrogen and 25% nitrogen,
the atmosphere gas was changed to a 100% hydrogen atmosphere gas, and then annealing
20 was performed at 1200 oc for 20 hours.
[0106]
The samples prepared through the above steps were washed with water and then
were sheared, were subjected to stress relief annealing, had an insulation coating formed
to provide tension to the steel sheet (had a tension coating to be applied), were subjected
25 to laser irradiation, and were subjected to magnetic measurement through an SST
31
method.
[0107]
Table 4 shows the amounts of carbon after the decarburization annealing and the
values of iron loss (W17!so) obtained through the above magnetic measurement.
5 [0108]
[Table 4]
Sample Oxidation Amount of Evaluation Iron Evaluation Comprehensive
No. degree of carbon of of amount loss of iron loss evaluation
decarburization decarburized of carbon (Wmso)
annealing sheet (ppm) (Wikg)
1 0.08 7 Ex 0.63 Ex Ex
2 0.10 2 Ex 0.62 Ex Ex
3 0.15 1 Ex 0.62 Ex Ex
[0109]
It can be seen from Table 4 that, when the oxidation degree of a wet gas (a water
vapor-hydrogen-nitrogen mixed gas) in the heating area is higher than the oxidation
10 degree (0.08) in the soaking area, an amount of carbon is further reduced and even better
iron loss is obtained.
[0110]

Furthermore, the cold rolling process was reviewed. The results will be
15 explained below as Example 5.
[0111]
A silicon steel slab containing, in terms of mass obtained through casting, Si:
3.2; Mn: 0.1 %; C: 0.05%; S: 0.006%; acid-solubleAl: 0.028%; N: 0.008%; Sn: 0.05%;
Cr: 0.11 %; and the remainder: Fe and impurities was heated and then subjected to hot
20 rolling to have a sheet thickness of 2.6 mm. A part of the hot rolled sheet was annealed
(subjected to hot-band annealing) at 1100 °C, was subjected to annealing in which cold
32
rolling was performed to have a sheet thickness of2.0 mm, and was heated to 1120°C,
and then was subjected to annealing in which a temperature was cooled to 950°C and
held for 30 seconds (intermediate annealing), and then was subjected to cold rolling to
have a final sheet thickness of 0.22 mm (Process A). The remaining hot rolled sheet
5 was subjected to annealing in which cold rolling was performed to have a sheet thickness
of 2.0 mm without performing hot-band annealing, was heated to 1120oc and was
subjected to annealing in which a temperature was cooled to 950°C and held for 30
seconds and then subjected to cold rolling so that a final sheet thickness is 0.22 mm
(process B). A cold rolling rate after final annealing was 89% in each case.
10 [0112]
The cold rolled sheet was subjected to decarburization annealing in which a
temperature was raised to 830 oc at a heating rate of 30 oc/second at an oxidation degree
(PHZoiPHZ) of 0.06 in an atmosphere gas containing 75% hydrogen and 25% nitrogen and
held for 120 seconds. In Example 5, the oxidation degree in the heating area is equal to
15 the oxidation degree in the soaking area.
20
[0113]
After that, an amount of nitrogen in the steel was increased to 0.025 mass% in
ammonia gas to strengthen the inhibitor.
[0114]
The decarburized annealed sheet was subjected to final annealing in which an
annealing separator (90 mass% of alumina+ 10 mass% of magnesia) containing alumina
as a main component was applied in the form of a water slurry, a temperature was raised
to 1200 oc in an atmosphere gas containing 75% hydrogen and 25% nitrogen, the
atmosphere gas was changed to a 100% hydrogen atmosphere gas, and then annealing
25 was performed at 1200 oc for 20 hours.
33
The samples prepared through the above steps were washed with water and then
were sheared, were subjected to stress relief annealing, had an insulation coating formed
to provide tension to the steel sheet (had a tension coating to be applied), were subjected
to laser irradiation, and were subjected to magnetic measurement through an SST
5 method.
Table 5 shows the amounts of carbon after the decarburization annealing and the
values of iron loss (W17!so) obtained through the above magnetic measurement.
[0115]
[Table 5]
Process Amount of Evaluation Iron Evaluation Comprehensive
carbon of of amount loss of iron evaluation
decarburized of carbon (Wmso) loss
sheet (ppm) (W/kg)
A 13 Ex 0.66 Ex Ex
B 10 Ex 0.65 Ex Ex
10 [0116]
In Table 5, "Ex" means an excellent result.
As shown in Table 5, regardless of which step was passed, when the amount of
carbon in the steel which has been subjected to decarburization was 0.0030% (30 ppm) or
less, good iron loss was obtained.
15 [0117]

A silicon steel slab containing the components shown in Table 6 and the
remainder: Fe and impurities, and obtained by casting was heated and then subjected to
hot rolling to have a sheet thickness of 2.3 mm. The hot rolled sheet was subjected to
20 annealing in which a temperature was rai sed to 1100 °C, held for 60 seconds and then
was subjected to one cold rolling to have a final sheet thickness of 0.22 mm.
[011 8]
34
The cold rolled sheet was subjected to decarburization annealing in which a
temperature was raised to 830 oc at a heating rate of 30 °C/second at an oxidation degree
(PH2o!PH2) ofO.lO in an atmosphere gas containing 75% hydrogen and 25% nitrogen and
the oxidation degree (PHZoiPH2) was changed to an oxidation degree (PHZoiPHZ) of 0.06
5 and held for 120 seconds.
10
[011 9]
After that, the amount of nitrogen in the steel was increased to 0.025 mass% in
ammonia gas to strengthen the inhibitor.
[0120]
The decarburized annealed sheet was subjected to the final annealing in which
an annealing separator (60 mass% of alumina+40 mass% of magnesia) containing
alumina as a main component was applied in the form of a water slurry, a temperature
was raised to 1200 oc in an atmosphere gas containing 75% hydrogen and 25% nitrogen,
the atmosphere gas was changed to a 100% h ydrogen atmosphere gas, and then annealing
15 was performed at 1200 oc for 20 hours. The samples prepared through the above steps
were washed with water and then were sheared, were subjected to stress relief annealing,
had an insulation coating formed to provide tension to the steel sheet (had a tension
coating to be applied), were subjected to laser irradiation, and were subjected to magnetic
measurement using through an SST method. Table 6 shows the amounts of carbon after
20 the decarburization annealing and the values of iron loss (yY mso) obtained through the
above magnetic measurement
35
[0121]
[Table 6]
Mass%: (remainder: Fe and impurities)
Sample Acid-
No. Si Mn c s so1ub1e N Sn Sb Cr Cu p Ni B v Nb Mo Ti Bi
Al
1 3.20 0.10 0.05 0.006 0.027 0.008 0.05 - - - - - - - - - - -
2 3.30 0.11 0.06 0.005 0.028 0.007 - 0.01 - - - - - - - - - -
3 3.20 0.10 0.05 0.006 0.027 0.008 0.05 0.01 - - - - - - - - -
4 3.20 0.10 0.05 0.005 0.028 0.007 0.05 - 0.10 - - - - - - - - -
5 3.30 0.11 0.06 0.006 0.027 0.008 - 0.01 0.10 - - - - - - - - -
6 3.20 0.10 0.05 0.006 0.027 0.008 0.05 0.01 0.10 - - - - - - - - -
7 3.20 0.10 0.05 0.006 0.027 0.008 0.05 0.01 0.02 - - - - - - - - -
8 3.20 0.10 0.05 0.006 0.027 0.008 0.05 0.01 0.50 - - - - - - - - -
9 2.70 0.12 0.05 0.005 0.028 0.008 0.04 - 0.11 - - - - - - - - -
10 3.80 0.12 0.06 0.005 0.028 0.008 0.04 - 0.11 - - - - - - - - -
11 3.20 0.14 0.05 0.007 0.027 0.007 0.06 - 0.12 - - - - - - - - -
36
12 3.20 0.45 0.05 0.007 0.027 0.007 0.06 - 0.12 - - - - - - - - -
13 3.30 0.11 0.04 0.006 0.026 0.008 0.05 - 0.09 - - - - - - - - -
14 3.20 0.11 0.07 0.006 0.026 0.008 0.05 - 0.09 - - - - - - - - -
15 3.30 0.13 0.06 0.004 0.027 0.007 - 0.02 0.12 - - - - - - - - -
16 3.20 0.13 0.05 O.Dl5 0.027 0.007 - 0.02 0.12 - - - - - - - - -
17 3.30 0.10 0.06 0.005 0.025 0.008 0.03 0.01 0.13 - - - - - - - - -
18 3.30 0.10 0.06 0.005 0.035 0.008 0.03 0.01 0.13 - - - - - - - - -
19 3.20 0.11 0.05 0.006 0.027 0.004 0.07 0.12 - - - - - - - - -
20 3.20 0.11 0.05 0.006 0.027 0.010 0.07 0.12 - - - - - - - - -
21 3.30 0.12 0.06 0.005 0.029 0.008 0.05 - 0.10 0.2 - - - - - - - -
22 3.20 0.11 0.05 0.006 0.027 0.008 0.05 - 0.11 - 0.2 - - - - - - -
23 3.20 0.14 0.06 0.006 0.026 0.008 - 0.02 0.12 - - 0.3 - - - - - -
24 3.30 0.11 0.05 0.005 0.027 0.008 0.01 0.11
- - - - 0.00
3
- - - - -
25 3.20 0.10 0.05 0.006 0.025 0.009 0.03 0.01 0.12 - - - - 0.07 - - - -
37
26 3.30 0.11 0.06 0.006 0.026 0.009 0.02 0.01 0.13 - - - - - 0.05 - - -
27 3.30 0.11 0.05 0.006 0.027 0.008 0.04 - 0.11 - - - - - - 0.05 - -
28 3.20 0.14 0.06 0.008 0.027 0.007 - 0.02 0.12 - - - - - - - 0.005 -
29 3.20 0.10 0.05 0.006 0.028 0.008 0.05 - 0.12 - - - - - - - - 0.005
(Continuation of table 6)
Sample No. Amount of carbon of Evaluation of amount of Iron Joss (W 17150) Evaluation of iron Joss Comprehensive evaluation
decarburized sheet (ppm) carbon (W/kg)
1 12 Ex 0.66 Ex Ex
2 14 Ex 0.66 Ex Ex
3 11 Ex 0.65 Ex Ex
4 10 Ex 0.65 Ex Ex
5 11 Ex 0.64 Ex Ex
6 8 Ex 0.64 Ex Ex
7 10 Ex 0.65 Ex Ex
8 10 Ex 0.65 Ex Ex
9 8 Ex 0.64 Ex Ex
10 17 Ex 0.61 Ex Ex
11 7 Ex 0.65 Ex Ex
12 8 Ex 0.67 Ex Ex
13 8 Ex 0.66 Ex Ex
14 12 Ex 0.69 Ex Ex
15 9 Ex 0.69 Ex Ex
16 8 Ex 0.68 Ex Ex
17 7 Ex 0.67 Ex Ex
18 9 Ex 0.63 Ex Ex
19 8 Ex 0.69 Ex Ex
20 7 Ex 0.63 Ex Ex
38
21 8 Ex 0.63 Ex Ex
22 10 Ex 0.65 Ex Ex
23 9 Ex 0.64 Ex Ex
24 7 Ex 0.64 Ex Ex
25 10 Ex 0.65 Ex Ex
26 9 Ex 0.63 Ex Ex
27 8 Ex 0.65 Ex Ex
28 9 Ex 0.67 Ex Ex
29 8 Ex 0.64 Ex Ex
39
[0122]
As shown in Table 6, regardless of the composition of the silicon steel slab to be
used, when the amount of carbon in the steel which has been subjected to decarburization
was 0.0030% (30 ppm) or less, good iron loss was obtained.
5 [0123]
It can be seen from the above results that a decarburization reaction is stably
performed and a product with good iron loss characteristics can be manufactured by
promoting smoothing of the surface of the steel sheet when Sn and Sb are contained as
components of the silicon steel slab and an appropriate amount of Cr is contained, in the
10 decarburization annealing step of performing decarburization annealing in a moist
hydrogen atmosphere to remove carbon contained in the steel which has been subjected
to cold rolling.
15
[Industrial Applicability]
[0124]
According to the present invention, it is possible to provide a method for
manufacturing a grain-oriented electrical steel sheet having good magnetic properties
while satisfactorily performing decarburization in decarburization annealing.
Therefore, the present invention has high industrial applicability.

WE CLAIMS

1. A method for manufacturing a grain-oriented electrical steel sheet, comprising:
a silicon steel material production process of producing a silicon steel material;
a hot rolling process of obtaining a hot rolled sheet by subj ecting the silicon
5 steel material to hot rolling;
a cold rolling process of obtaining a steel sheet of a final sheet thickness by
subjecting the hot rolled sheet to a single cold rolling process or multiple cold rolling
processes having intermediate annealing performed between the cold rolling processes;
a decarburization annealing process of subjecting the steel sheet to
10 decarburization annealing; and
15
20
a final annealing process of applying an annealing separator containing alumina
as a main component to the steel sheet and subjecting the steel sheet to final annealing,
wherein the silicon steel material contains: in terms of mass%,
Si: 0.8 to 7.0%;
C: 0.085% or less;
acid-solubleAl: 0.010 to 0.065%;
N: 0.004 to 0.012%;
Mn: 1.00% or less;
S: 0.050% or less;
a total of 0.01 to 0.20% of one or both of Sn and Sb; and
the remainder: Fe and impurities.
2. The method for manufacturing a grain-oriented electrical steel sheet according to
claim 1, wherein the decarburization annealing process includes: performing the
25 decarburization annealing using a decarburization annealing furnace including a heating
41
area and a soaking area,
an oxidation degree P1 of an atmosphere gas in the heating area satisfies the
following Expression 1, and
an oxidation degree P2 of an atmosphere gas in the soaking area satisfies the
5 following Expression 2:
O.Ol:SP1:S0.15 (Expression 1); and
O.Ol:SP2:S0.15 (Expression 2).
3. The method for manufacturing a grain-oriented electrical steel sheet according to
10 claim 1 or 2, wherein the silicon steel material further contains, in terms of mass%, Cr:
0.02 to 0.50%.
4. The method for manufacturing a grain-oriented electrical steel sheet according to
claim 2 or 3, wherein the P1 and the P2 described above satisfy the following Expression
15 3:
P1>P2 (Expression 3).
5. The method for manufacturing a grain-oriented electrical steel sheet according to any
one of claims 1 to 4, wherein the silicon steel material further contains, in terms of
20 mass%,
25
Cu: 0% or more and 0.4% or less;
P: 0% or more and 0.5% or less;
Ni: 0% or more and 1.0% or less;
B: 0% or more and 0.008% or less;
V: 0% or more and 0.15% or less;
42
5
10
Nb: 0% or more and 0.20% or less;
Mo: 0% or more and 0.10% or less;
Ti: 0% or more and 0.015% or less; and
Bi: 0% or more and 0.010% or less.
6. The method for manufacturing a grain-oriented electrical steel sheet according to any
one of claims 1 to 5, further comprising:
a nitriding treatment process from before the decarburization annealing process
to before secondary recrystallization initiation in the final annealing process.
7. The method for manufacturing a grain-oriented electrical steel sheet according to any
one of claims 1 to 6, further comprising:
a hot-band annealing process of subjecting the hot rolled sheet obtained in the
hot rolling process to annealing after the hot rolling process and before the cold rolling
15 process.