[0001]The present invention relates to a method for producing a grain oriented
electrical steel sheet.
Priority is claimed on Japanese Patent Application No. 2019-005203, filed on
January 16, 2019, and the content of which is incorporated herein by reference.
10
Background Art
[0002]
A grain oriented electrical steel sheet is used mainly in a transformer. A
transformer is continuously excited over a long period of time from installation to disuse
15 such that energy loss continuously occurs. Therefore, energy loss occurring when the
transformer is magnetized by an alternating current, that is, iron loss is a main index that
determines the performance of the transformer.
[0003]
In order to reduce iron loss of a grain-oriented electrical steel sheet, various
20 methods have been developed. Examples of the methods include a method of highly
aligning grains in the {110}<001> orientation called Goss orientation in a crystal
structure, a method of increasing the content of a solid solution element such as Si that
increases electric resistance in a steel sheet, and a method of reducing the thickness of a
steel sheet.
25 [0004]
2
In addition, it is known that a method of applying tension to a steel sheet is
effective for reducing iron loss. Thus, in general, in order to reduce the iron loss, an
insulation coating is formed on a surface of the grain oriented electrical steel sheet. The
coating applies the tension to the grain oriented electrical steel sheet, and thereby,
reduces the iron loss as a single steel sheet. 5 Moreover, the coating ensures interlaminar
electrical insulation when the grain oriented electrical steel sheets are utilized after being
laminated, and thereby, reduces the iron loss as an iron core.
[0005]
For instance, as the grain oriented electrical steel sheet with the coating, a
10 forsterite film which is an oxide film including Mg is formed on a surface of a base steel
sheet, and then, the insulation coating is formed on a surface of the forsterite film. In
the case, the coating on the base steel sheet includes the forsterite film and the insulation
coating. The forsterite film and the insulation coating respectively have a function of
increasing the electrical insulation and applying the tension to the base steel sheet.
15 [0006]
The forsterite film which is the oxide film including Mg is formed, during final
annealing which is a heat treatment at 900 to 1200C for 30 hours or more to make the
steel sheet be secondary-recrystallized, by reacting an annealing separator mainly
including magnesia (MgO) with silicon dioxide (SiO2) formed on the base steel sheet
20 during decarburization annealing.
[0007]
The insulation coating is formed by applying coating solution including, for
instance, phosphoric acid or phosphate, colloidal silica, and chromic anhydride or
chromate to the base steel sheet after final annealing, and by baking and drying it at 300
25 to 950C for 10 seconds or more.
3
[0008]
In order that the coating ensures the function of increasing the insulation and
applying the tension to the base steel sheet, sufficient adhesion is required between the
coating and the base steel sheet.
5 [0009]
Conventionally, the above adhesion has been mainly ensured by the anchor
effect derived from the unevenness of an interface between the base steel sheet and the
forsterite film. However, in recent years, it has been found that the unevenness of the
interface becomes an obstacle of movement of a magnetic domain wall when the grain
10 oriented electrical steel sheet is magnetized, and thus, the unevenness is also a factor that
hinders the reduction of iron loss.
[0010]
For instance, Japanese Unexamined Patent Application, First Publication No.
S49-096920 (Patent Document 1) and PCT International Publication No.
15 WO2002/088403 (Patent Document 2) disclose a technique to ensure the adhesion of the
insulation coating even in a state in which the forsterite film which is the oxide film
including Mg does not exist and the interface is smooth in order to further reduce the iron
loss.
[0011]
20 In the method for producing the grain oriented electrical steel sheet as disclosed
in the Patent Document 1, the forsterite film is removed by pickling or the like and then
the surface of the base steel sheet is smoothened by chemical polishing or electrolytic
polishing. In the method for producing the grain oriented electrical steel sheet as
disclosed in the Patent Document 2, the formation of the forsterite film itself is
25 suppressed by using an annealing separator containing alumina (Al2O3) for the final
4
annealing and thereby the surface of the base steel sheet is smoothened.
[0012]
However, in the producing methods as disclosed in the Patent Document 1 and
the Patent Document 2, there is a problem that the insulation coating is difficult to adhere
to the surface of the base steel shee 5 t (sufficient adhesion is not obtained) in a case where
the insulation coating is formed in contact with the surface of the base steel sheet
(directly on the surface of the base steel sheet).
Related Art Documents
10 Patent Documents
[0013]
[Patent Document 1] Japanese Unexamined Patent Application, First
Publication No. S49-096920
[Patent Document 2] PCT International Publication No. WO2002/088403
15
Summary of Invention
Technical Problem to be Solved
[0014]
The present invention has been made in consideration of the above mentioned
20 situations. An object of the invention is to provide a method for producing a grain
oriented electrical steel sheet without the forsterite film and excellent in magnetic
characteristics (in particular, iron loss) and the coating adhesion.
Solution to Problem
25 [0015]
5
The present inventors have investigated a technique to improve the adhesion
(coating adhesion) between the steel sheet and the insulation coating even in a case
where the forsterite film is not formed for reducing the iron loss and the insulation
coating is formed on the surface of the grain oriented electrical steel sheet in which the
5 surface of the steel sheet is smoothened.
[0016]
As a result, it has been found that it is possible to produce the grain oriented
electrical steel sheet without the forsterite film and excellent in the magnetic
characteristics and the coating adhesion by appropriately combining predetermined
10 processes.
[0017]
An aspect of the present invention employs the following.
(1) A method for producing a grain oriented electrical steel sheet according to
an aspect of the present invention includes:
15 a hot rolling process of hot-rolling a steel piece to obtain a hot rolled steel sheet,
the steel piece including, as a chemical composition, by mass%,
0.030 to 0.100% of C,
0.80 to 7.00% of Si,
0.01 to 1.00% of Mn,
20 0 to 0.060% in total of S and Se,
0.010 to 0.065% of acid soluble Al,
0.004 to 0.012% of N,
0 to 0.30% of Cr,
0 to 0.40% of Cu,
25 0 to 0.50% of P,
6
0 to 0.30% of Sn,
0 to 0.30% of Sb,
0 to 1.00% of Ni,
0 to 0.008% of B,
5 0 to 0.15% of V,
0 to 0.20% of Nb,
0 to 0.10% of Mo,
0 to 0.015% of Ti,
0 to 0.010% of Bi, and
10 a balance consisting of Fe and impurities;
a cold rolling process of cold-rolling the hot rolled steel sheet to obtain a cold
rolled steel sheet;
a decarburization annealing process of decarburization-annealing the cold rolled
steel sheet to obtain a decarburization annealed sheet;
15 an annealing separator applying process of applying and drying an annealing
separator including Al2O3 and MgO to the decarburization annealed sheet;
a final annealing process of final-annealing the decarburization annealed sheet
after applying the annealing separator to obtain a final annealed sheet;
an annealing separator removing process of removing a redundant annealing
20 separator from a surface of the final annealed sheet; and
an insulation coating forming process of forming an insulation coating on the
surface of the final annealed sheet,
wherein, in the decarburization annealing process,
PH2O/PH2 which is an oxidation degree of an atmosphere is 0.18 to 0.80, an
25 annealing temperature is 750 to 900C, a holding is 10 to 600 seconds, and after
7
decreasing a temperature, an oxide layer of a steel sheet surface is removed by being
pickled in a mixed solution of a hydrofluoric acid and a sulfuric acid,
wherein, in the annealing separator applying process,
MgO / (MgO + Al2O3) which is a mass ratio of MgO and Al2O3 is 5 to 50%, and
a hydration water is 1.5 5 mass% or less in the annealing separator,
wherein, in the final annealing process,
an oxidation degree is 0.00010 to 0.2 when an atmosphere includes a hydrogen,
or a dew point is 0C or less when an atmosphere consists of an inert gas without a
hydrogen,
10 wherein, in the annealing separator removing process,
the final annealed sheet is water-washed using a solution with an inhibitor which
is at least one of a triethanolamine, a rosinamine, or a mercaptan in order to remove the
redundant annealing separator from the surface thereof, and an amount of an iron
hydroxide and an iron oxide on the surface thereof is controlled to 0.9 g/m2 or less per a
15 side, and
wherein, in the insulation coating forming process,
an insulation coating forming solution in which a phosphoric acid and a metal
compound are included and in which a mass ratio of the phosphoric acid and the metal
compound is 2:1 to 1:2 is applied and is baked at 600 to 1150C, and after decreasing a
20 temperature, an insulation coating forming solution in which a phosphate and a colloidal
silica are included and in which a metal compound is not included is applied and is baked
at 600 to 1150C, in order to form the insulation coating.
(2) The method for producing the grain oriented electrical steel sheet
according to (1) may include,
25 between the hot rolling process and the cold rolling process,
8
at least one of a hot band annealing process of annealing the hot rolled steel
sheet or a hot band pickling process of pickling the hot rolled steel sheet.
(3) In the method for producing the grain oriented electrical steel sheet
according to (1) or (2),
in the decarburization annealing 5 process, a nitriding treatment may be conducted
by annealing the cold rolled steel sheet in an atmosphere including ammonia.
(4) The method for producing the grain oriented electrical steel sheet
according to any one of (1) to (3) may include,
between the cold rolling process and the decarburization annealing process,
10 between the decarburization annealing process and the annealing separator applying
process, between the annealing separator removing process and the insulation coating
forming process, or after the insulation coating forming process,
a magnetic domain refining process of conducting a magnetic domain refining
treatment.
15 (5) In the method for producing the grain oriented electrical steel sheet
according to any one of (1) to (4),
in the annealing separator removing process, a pickling may be conducted after
water-washing using an acidic solution whose volume concentration is less than 20%.
(6) In the method for producing the grain oriented electrical steel sheet
20 according to any one of (1) to (5),
the steel piece may include, as the chemical composition, by mass%, at least one
selected from a group consisting of
0.02 to 0.30% of Cr,
0.05 to 0.40% of Cu,
25 0.005 to 0.50% of P,
9
0.02 to 0.30% of Sn,
0.01 to 0.30% of Sb,
0.01 to 1.00% of Ni,
0.0005 to 0.008% of B,
5 0.002 to 0.15% of V,
0.005 to 0.20% of Nb,
0.005 to 0.10% of Mo,
0.002 to 0.015% of Ti, and
0.001 to 0.010% of Bi.
10
Effects of Invention
[0018]
According to the above aspects of the present invention, it is possible to provide
the method for producing the grain oriented electrical steel sheet without the forsterite
15 film and excellent in the magnetic characteristics and the coating adhesion.
Brief Description of Drawings
[0019]
Fig. 1 is a flow chart illustrating a method for producing a grain oriented
20 electrical steel sheet according to an embodiment of the present invention.
Detailed Description of Preferred Embodiments
[0020]
Hereinafter, a preferable embodiment of the present invention is described in
25 detail. However, the present invention is not limited only to the configuration which is
10
disclosed in the embodiment, and various modifications are possible without departing
from the aspect of the present invention. In addition, the limitation range as described
in the embodiment includes a lower limit and an upper limit thereof. However, the
value expressed by ''more than'' or ''less than'' does not include in the limitation range.
''%'' of the amount 5 of respective elements expresses ''mass%''.
[0021]
A method for producing a grain oriented electrical steel sheet according to an
embodiment of the present invention (hereinafter, referred to as ''the method for
producing the grain oriented electrical steel sheet according to the embodiment'') is the
10 method for producing the grain oriented electrical steel sheet without a forsterite film and
includes the following processes.
( i ) Hot rolling process of hot-rolling a steel piece including predetermined
chemical composition to obtain a hot rolled steel sheet.
( ii ) Cold rolling process of cold-rolling the hot rolled steel sheet by cold-rolling
15 once or by cold-rolling plural times with an intermediate annealing to obtain a cold rolled
steel sheet.
( iii ) Decarburization annealing process of decarburization-annealing the cold
rolled steel sheet to obtain a decarburization annealed sheet.
( iv ) Annealing separator applying process of applying and drying an annealing
20 separator including Al2O3 and MgO to the decarburization annealed sheet.
( v ) Final annealing process of final-annealing the decarburization annealed
sheet after applying the annealing separator to obtain a final annealed sheet.
( vi ) Annealing separator removing process of removing a redundant annealing
separator from a surface of the final annealed sheet.
25 ( vii ) Insulation coating forming process of forming an insulation coating on the
11
surface of the final annealed sheet.
[0022]
In addition, the method for producing the grain oriented electrical steel sheet
according to the embodiment may further include the following processes.
( I ) Hot band annealing 5 process of annealing the hot rolled steel sheet.
( II ) Hot band pickling process of pickling the hot rolled steel sheet.
( III ) Magnetic domain refining process of conducting a magnetic domain
refining treatment.
[0023]
10 In the method for producing the grain oriented electrical steel sheet according to
the embodiment, it is necessary to control not only one process in the above processes
but each of the above processes comprehensively and inseparably. Only when the
predetermined conditions in each of all processes as explained above are controlled, it is
possible to reduce the iron loss and improve the coating adhesion.
15 [0024]
Hereinafter, each process is described in detail.
[0025]
< Hot rolling process >
In the hot rolling process, the steel piece is hot-rolled to obtain the hot rolled
20 steel sheet, the steel piece including, as the chemical composition, by mass%,
0.030 to 0.100% of C,
0.80 to 7.00% of Si,
0.01 to 1.00% of Mn,
0 to 0.060% in total of S and Se,
25 0.010 to 0.065% of acid soluble Al,
12
0.004 to 0.012% of N,
0 to 0.30% of Cr,
0 to 0.40% of Cu,
0 to 0.50% of P,
5 0 to 0.30% of Sn,
0 to 0.30% of Sb,
0 to 1.00% of Ni,
0 to 0.008% of B,
0 to 0.15% of V,
10 0 to 0.20% of Nb,
0 to 0.10% of Mo,
0 to 0.015% of Ti,
0 to 0.010% of Bi, and
a balance consisting of Fe and impurities. In the embodiment, the steel sheet
15 after the hot rolling process is referred to as the hot rolled steel sheet.
[0026]
The method for making the steel piece (slab) to be used in the hot rolling
process is not limited. For instance, molten steel with predetermined chemical
composition may be made, and the slab may be made by using the molten steel. The
20 slab may be made by continuous casting. An ingot may be made by using the molten
steel, and then, the slab may be made by blooming the ingot. Moreover, the slab may
be made by other methods.
[0027]
A thickness of the slab is not particularly limited. The thickness of the slab
25 may be 150 to 350 mm for instance. The thickness of the slab is preferably 220 to 280
13
mm. The slab with the thickness of 10 to 70 mm which is a so-called thin slab may be
used.
[0028]
Limitation reasons of the chemical composition of the steel piece are explained.
Hereinafter, "%" 5 of the chemical composition represents "mass%".
[0029]
( 0.030 to 0.100% of C )
C (carbon) is an element effective in controlling the primary recrystallized
structure, but negatively affective in the magnetic characteristics. Thus, C is the
10 element to be removed by decarburization annealing before final annealing. When the
C content is more than 0.100%, a time for decarburization annealing needs to be
prolonged, and the productivity decreases. Thus, the C content is to be 0.100% or less.
The C content is preferably 0.085% or less, and more preferably 0.070% or less.
[0030]
15 It is favorable that the C content is lower. However, when considering the
productivity in industrial production and the magnetic characteristics of the product, the
lower limit of the C content is substantially 0.030%.
[0031]
( 0.80 to 7.00% of Si )
20 Si (silicon) increases the electric resistance of grain oriented electrical steel sheet,
and thereby, reduces the iron loss. When the Si content is less than 0.80%, γ
transformation occurs during the final annealing and the crystal orientation of grain
oriented electrical steel sheet is impaired. Thus, the Si content is to be 0.80% or more.
The Si content is preferably 2.00% or more, and more preferably 2.50% or more.
25 On the other hand, when the Si content is more than 7.00%, the cold workability
14
deteriorates and the cracks tend to occur during cold rolling. Thus, the Si content is to
be 7.00% or less. The Si content is preferably 4.50% or less, and more preferably
4.00% or less.
[0032]
5 ( 0.01 to 1.00% of Mn )
Mn (manganese) increases the electric resistance of grain oriented electrical
steel sheet, and thereby, reduces the iron loss. Moreover, Mn forms MnS and/or MnSe
which act as the inhibitor by bonding to S and/or Se. When the Mn content is within
0.01 to 1.00%, the secondary recrystallization becomes stable. Thus, the Mn content is
10 to be 0.01 to 1.00%. The lower limit of the Mn content is preferably 0.08%, and more
preferably 0.09%. The upper limit of the Mn content is preferably 0.50%, and more
preferably 0.20%.
[0033]
( 0 to 0.060% in total of one or both of S and Se )
15 S (sulfur) and Se (selenium) are elements to form MnS and/or MnSe which act
as the inhibitor by bonding to Mn.
When the total amount of one or both of S and Se (S + Se) is more than 0.060%,
the dispersion state of precipitation of MnS and/or MnSe becomes uneven. In the case,
the desired secondary recrystallized structure cannot be obtained, and the magnetic flux
20 density may decrease. Moreover, MnS remains in the steel after purification annealing,
and the hysteresis loss may increase. Thus, the total amount of S and Se is to be
0.060% or less.
The lower limit of the total amount of S and Se is not particularly limited, and
may be 0%. The lower limit thereof may be 0.003%. When the inhibitor thereof is
25 used, the lower limit is preferably 0.015%.
15
[0034]
( 0.010 to 0.065% of acid soluble Al (Sol. Al) )
The acid soluble Al (aluminum) is an element to form (Al, Si)N which acts as
the inhibitor by bonding to N. When the amount of acid soluble Al is less than 0.010%,
the effect of addition is not sufficiently 5 obtained, and the secondary recrystallization does
not proceed sufficiently. Thus, the amount of acid soluble Al is to be 0.010% or more.
The amount of acid soluble Al is preferably 0.015% or more, and more preferably
0.020% or more.
[0035]
10 On the other hand, when the amount of acid soluble Al is more than 0.065%, the
dispersion state of precipitation of AlN and/or (Al, Si)N becomes uneven, the desired
secondary recrystallized structure cannot be obtained, and the magnetic flux density
decreases. Thus, the amount of acid soluble Al (Sol. Al) is to be 0.065% or less. The
amount of acid soluble Al is preferably 0.055% or less, and more preferably 0.050% or
15 less.
[0036]
( 0.004 to 0.012% of N )
N (nitrogen) is an element to form AlN and/or (Al, Si)N which act as the
inhibitor by bonding to Al. When the N content is less than 0.004%, the formation of
20 AlN and/or (Al, Si)N becomes insufficient. Thus, the N content is to be 0.004% or
more. The N content is preferably 0.006% or more, and more preferably 0.007% or
more.
On the other hand, when the N content is more than 0.012%, the blisters (voids)
may be formed in the steel sheet. Thus, the N content is to be 0.012% or less.
25 [0037]
16
The steel piece includes, as the chemical composition, the above elements, and
the balance consists of Fe and impurities. However, in consideration of the influence on
the magnetic characteristics and the improvement of the inhibitors functions by forming
compounds, the steel piece may include at least one of optional elements as substitution
for a part of Fe. For instanc 5 e, the optional elements included as substitution for a part
of Fe may be Cr, Cu, P, Sn, Sb, Ni, B, V, Nb, Mo, Ti, and Bi. However, the optional
elements do not need to be included, the lower limits thereof may be 0% respectively.
Moreover, even if the optional elements may be included as impurities, the above
mentioned effects are not affected. Herein, the impurities correspond to elements which
10 are contaminated during industrial production of steel from ores and scrap that are used
as a raw material of steel, or from environment of a production process.
[0038]
( 0 to 0.30% of Cr )
Cr (chrome) is an element effective in increasing the electric resistance, and
15 thereby, reducing the iron loss, in common with Si. Thus, Cr may be included. In
order to obtain the above effects, the Cr content is preferably 0.02% or more, and more
preferably 0.05% or more.
On the other hand, when the Cr content is more than 0.30%, the magnetic flux
density may deteriorate. Thus, the upper limit of the Cr content is preferably 0.30%,
20 more preferably 0.20%, and further more preferably 0.12%.
[0039]
( 0 to 0.40% of Cu )
Cu (copper) is also an element effective in increasing the electric resistance, and
thereby, reducing the iron loss. Thus, Cu may be included. In order to obtain the
25 above effects, the Cu content is preferably 0.05% or more, and more preferably 0.10% or
17
more.
On the other hand, when the Cu content is more than 0.40%, the improvement
effect of reducing the iron loss may be saturated, and surface defects called ''copper scab''
may be incurred during hot rolling. Thus, the upper limit of the Cu content is preferably
0.40%, more preferably 5 0.30%, and further more preferably 0.20%.
[0040]
( 0 to 0.50% of P )
P (phosphorus) is also an element effective in increasing the electric resistance,
and thereby, reducing the iron loss. Thus, P may be included. In order to obtain the
10 above effects, the P content is preferably 0.005% or more, and more preferably 0.010%
or more.
On the other hand, when the P content is more than 0.50%, the rollability may
deteriorate. Thus, the upper limit of the P content is preferably 0.50%, more preferably
0.20%, and further more preferably 0.15%.
15 [0041]
( 0 to 0.30% of Sn )
( 0 to 0.30% of Sb )
Sn (tin) and Sb (antimony) are elements effective in stabilizing the secondary
recrystallization, and thereby, developing the {110}<001> orientation. Thus, Sn and Sb
20 may be included. In order to obtain the above effects, the Sn content is preferably
0.02% or more, and more preferably 0.05% or more. Moreover, the Sb content is
preferably 0.01% or more, and more preferably 0.03% or more.
On the other hand, when the Sn content is more than 0.30% or when the Sb
content is more than 0.30%, the magnetic characteristics may deteriorate. Thus, the
25 upper limits of the Sn content and the Sb content are preferably 0.30% respectively.
18
The upper limit of the Sn content is preferably 0.15%, and more preferably 0.10%.
Moreover, the upper limit of the Sb content is preferably 0.15%, and more preferably
0.10%.
[0042]
5 ( 0 to 1.00% of Ni )
Ni (nickel) is also an element effective in increasing the electric resistance, and
thereby, reducing the iron loss. Moreover, Ni is an element effective in controlling the
metallographic structure of the hot rolled steel sheet, and thereby, improving the
magnetic characteristics. Thus, Ni may be included. In order to obtain the above
10 effects, the Ni content is preferably 0.01% or more, and more preferably 0.02% or more.
On the other hand, when the Ni content is more than 1.00%, the secondary
recrystallization may be unstable. Thus, the Ni content is preferably 1.00% or less,
more preferably 0.20% or less, and further more preferably 0.10% or less.
[0043]
15 ( 0 to 0.008% of B )
B (boron) is an element effective in forming BN which acts as the inhibitor by
bonding to N. Thus, B may be included. In order to obtain the above effects, the B
content is preferably 0.0005% or more, and more preferably 0.0010% or more.
On the other hand, when the B content is more than 0.008%, the magnetic
20 characteristics may deteriorate. Thus, the upper limit of the B content is preferably
0.008%, more preferably 0.005%, and further more preferably 0.003%.
[0044]
( 0 to 0.15% of V )
( 0 to 0.20% of Nb )
25 ( 0 to 0.015% of Ti )
19
V (vanadium), Nb (niobium), and Ti (titanium) are elements which act as the
inhibitor by bonding to N, C, and the like. Thus, V, Nb, and Ti may be included. In
order to obtain the above effects, the V content is preferably 0.002% or more, and more
preferably 0.010% or more. The Nb content is preferably 0.005% or more, and more
preferably 0.020% or more. 5 The Ti content is preferably 0.002% or more, and more
preferably 0.004% or more.
On the other hand, when the V content is more than 0.15%, when the Nb content
is more than 0.20%, or when the Ti content is more than 0.015% in the steel piece, there
elements may remain in the final product. In the case, as the final product, the V
10 content may be more than 0.15%, the Nb content may be more than 0.20%, or the Ti
content may be more than 0.015%. As a result, the magnetic characteristics of the final
product (grain oriented electrical steel sheet) may deteriorate.
Thus, the upper limit of the V content is preferably 0.15%, more preferably
0.10%, and further more preferably 0.05%. The upper limit of the Ti content is
15 preferably 0.015%, more preferably 0.010%, and further more preferably 0.008%. Thus,
the upper limit of the Nb content is preferably 0.20%, more preferably 0.10%, and further
more preferably 0.08%.
[0045]
( 0 to 0.10% of Mo )
20 Mo (molybdenum) is also an element effective in increasing the electric
resistance, and thereby, reducing the iron loss. Thus, Mo may be included. In order to
obtain the above effects, the Mo content is preferably 0.005% or more, and more
preferably 0.01% or more.
On the other hand, when the Mo content is more than 0.10%, the rollability of
25 the steel sheet may deteriorate. Thus, the upper limit of the Mo content is preferably
20
0.10%, more preferably 0.08%, and further more preferably 0.05%.
[0046]
( 0 to 0.010% of Bi )
Bi (bismuth) is an element effective in stabilizing precipitates such as sulfide,
and thereby, improving 5 the inhibitors functions. Thus, Bi may be included. In order to
obtain the above effects, the Bi content is preferably 0.001% or more, and more
preferably 0.002% or more.
On the other hand, when the Bi content is more than 0.010%, the magnetic
characteristics may deteriorate. Thus, the upper limit of the Bi content is preferably
10 0.010%, more preferably 0.008%, and further more preferably 0.006%.
[0047]
The chemical composition as described above may be measured by typical
analytical methods for the steel. For instance, the chemical composition may be
measured by using ICP-AES (Inductively Coupled Plasma-Atomic Emission
15 Spectrometer: inductively coupled plasma emission spectroscopy spectrometry).
Herein, the acid soluble Al may be measured by ICP-AES using filtrate after heating and
dissolving the sample in acid. In addition, C and S may be measured by the infrared
absorption method after combustion, N may be measured by the thermal conductometric
method after fusion in a current of inert gas, and O may be measured by, for instance, the
20 non-dispersive infrared absorption method after fusion in a current of inert gas.
[0048]
Next, conditions for hot-rolling the above steel piece are explained.
The conditions of the hot rolling are not particularly limited. For instance, the
conditions are as follows.
25 The slab is heated before the hot rolling. The slab is put and heated in a known
21
heating furnace or a known soaking furnace. As one method, the slab is heated to
1280C or less. By setting the heating temperature of the slab to 1280C or less, for
instance, it is possible to avoid various problems when the heating temperature is more
than 1280C (a dedicated high temperature heating furnace is required, the melt scale
amount rapidly increases, and the like) 5 . The lower limit of the heating temperature of
the slab is not particularly limited. However, when the heating temperature is
excessively low, the hot rolling may become difficult and the productivity may be
decreased. Thus, the heating temperature may be in the range of 1280C or less in
consideration of the productivity. The lower limit of the heating temperature of the slab
10 is preferably 1100C. The upper limit of the heating temperature of the slab is
preferably 1250C.
[0049]
In addition, as another method, the slab is heated to higher temperature of
1320C or more. By heating the slab to higher temperature of 1320C or more, it is
15 possible to stabilize the secondary recrystallization by solutionizing AlN and Mn(S, Se)
and by finely precipitating them in the subsequent processes.
The slab heating in itself may be omitted, and the hot rolling may be conducted
after casting and before decreasing the temperature of the slab.
[0050]
20 The heated slab is hot-rolled by a hot rolling mill, and thereby, the hot rolled
steel sheet is obtained. The hot rolling mill includes, for instance, a rough rolling mill
and a final rolling mill which is arranged downstream of the rough rolling mill. The
rough rolling mill includes rough rolling stands which are in a row. Each of the rough
rolling stands has plural rolls arranged one above the other. In the same way, the final
22
rolling mill includes final rolling stands which are in a row. Each of the final rolling
stands has plural rolls arranged one above the other. The heated steel piece is rolled by
the rough rolling mill and then by the final rolling mill, and thereby, the hot rolled steel
sheet is obtained.
A final temperature 5 in the hot rolling process (the temperature of the steel sheet
at outlet side of the final rolling stand by which the steel sheet is finally rolled in the final
rolling mill) may be 700 to 1150C. The hot rolled steel sheet is produced by the hot
rolling process explained above.
[0051]
10 < Hot band annealing process >
In the hot band annealing process, as necessary, the hot rolled steel sheet
obtained by the hot rolling process is annealed (hot band annealed) to obtain the hot band
annealed sheet. In the embodiment, the steel sheet after the hot band annealing process
is referred to as the hot band annealed sheet.
15 [0052]
The hot band annealing is conducted in order to homogenize the nonuniform
structure after hot rolling, to control the precipitation of AlN which is the inhibitor
(precipitate finely), and to control secondary phase, solid-soluted carbon, and the like.
As the annealing conditions, known conditions may be applied according to the purpose.
20 For instance, in order to homogenize the nonuniform structure after hot rolling, the hot
rolled steel sheet is hold at 750 to 1200C of the heating temperature (furnace
temperature in a hot band annealing furnace) for 30 to 600 seconds.
The hot band annealing is not always necessary. The hot band annealing may
be conducted as a result of considering the characteristics and the producing cost required
25 for the grain oriented electrical steel sheet finally produced.
23
[0053]
< Hot band pickling process >
In the hot band pickling process, as necessary, the hot rolled steel sheet after the
hot rolling process or the hot band annealed sheet after the hot band annealing process in
a case where the hot band annealing 5 has been conducted is pickled in order to remove
surface scale. The pickling conditions are not particularly limited, and known
conditions may be appropriately applied.
[0054]
< Cold rolling process >
10 In the cold rolling process, the hot rolled steel sheet or the hot band annealed
sheet after the hot rolling process, the hot band annealing process, or the hot band
pickling process is cold-rolled by once or by plural times with an intermediate annealing
to obtain the cold rolled steel sheet. In the embodiment, the steel sheet after the cold
rolling process is referred to as the cold rolled steel sheet.
15 [0055]
A cold rolling reduction rate in final cold rolling (cumulative cold rolling
reduction rate without intermediate annealing or cumulative cold rolling reduction rate
after intermediate annealing) is preferably 80% or more, and more preferably 90% or
more. The upper limit of the final cold rolling reduction rate is preferably 95%.
20 [0056]
Herein, the final cold rolling reduction rate (%) is defined as follows.
Final cold rolling reduction rate (%) = ( 1 - Sheet thickness of steel sheet after
final cold rolling / Sheet thickness of steel sheet before final cold rolling ) × 100
[0057]
25 < Decarburization annealing process >
24
In the decarburization annealing process, the cold rolled steel sheet after the cold
rolling process is subjected to the magnetic domain refining treatment as necessary, and
then, is decarburization-annealed to promote the primary recrystallization. Moreover, in
the decarburization annealing, C which negatively affective in the magnetic
characteristics is re 5 moved from the steel sheet. In the embodiment, the steel sheet after
the decarburization annealing process is referred to as the decarburization annealed sheet.
[0058]
For the above purposes, in the decarburization annealing, the oxidation degree
PH2O/PH2 in atmosphere is to be 0.18 to 0.80, an annealing temperature is to be 750 to
10 900C, and a holding is to be 10 to 600 seconds. The oxidation degree PH2O/PH2 is
defined as the ratio of water vapor partial pressure PH2O (atm) to hydrogen partial
pressure PH2 (atm) in the atmosphere.
[0059]
When the oxidation degree (PH2O/PH2) is less than 0.18, dense silicon dioxide
15 (SiO2) is quickly formed as an externally oxidized layer, it is suppressed to release C
outside the system, and thus, the decarburization does not occur properly. On the other
hand, when the oxidation degree is more than 0.80, the oxidized layer of the steel sheet
surface is thickened, and it becomes difficult to remove the oxidized layer.
When the annealing temperature is less than 750C, the decarburization speed
20 slows down, and thereby, the productivity decreases. In addition, the decarburization
does not occur properly, and thereby, the magnetic characteristics after the final
annealing deteriorate. On the other hand, when the annealing temperature is more than
900C, the grain size after the primary recrystallization exceeds favorable size, and
thereby, the magnetic characteristics after the final annealing deteriorate.
25 When the holding time is less than 10 seconds, the decarburization does not
25
occur sufficiently. On the other hand, when the holding time is more than 600 seconds,
the productivity decreases. In addition, the grain size after the primary recrystallization
exceeds favorable size, and thereby, the magnetic characteristics after the final annealing
deteriorate.
5 [0060]
Depending on the above oxidation degree (PH2O/PH2), a heating rate in a
heating stage to the annealing temperature may be controlled. For instance, in a case
where the heating including an induction heating is conducted, an average heating rate
may be 5 to 1000 C/second. Moreover, in a case where the heating including an
10 electric heating is conducted, an average heating rate may be 5 to 3000 C/second.
[0061]
After conducting the decarburization annealing and then decreasing the
temperature, the oxidized layer of the steel sheet surface is removed.
As a method for removing the oxidized layer of the steel sheet surface, there is
15 mechanical polishing such as brush polishing, sandpaper polishing, grinding, and the like.
However, it is preferable to use pickling solution (solution for pickling) from an
industrial standpoint. In the case, since the oxidized layer formed on the steel sheet
surface is the oxide which is mainly SiO2, it is difficult to dissolve the oxide only by
mineral acid such as hydrochloric acid, sulfuric acid, nitric acid, and the like. When
20 hydrofluoric acid is mixed with the above acid, it is possible to efficiently and quickly
remove the oxidized layer. Thus, it is preferable to conduct pickling using the mixed
solution of a hydrofluoric acid and a sulfuric acid.
[0062]
In addition, in the decarburization annealing process, the nitriding treatment may
25 be conducted. In the nitriding treatment, the cold rolled steel sheet may be annealed in
26
the atmosphere including ammonia after the above holding. In a case where the
temperature for heating the slab is lower, it is preferable that the nitriding treatment is
conducted in the decarburization annealing process. By additionally conducting the
nitriding treatment in the decarburization annealing process, the inhibitor such as AlN
and (Al, Si)N is formed prior to the secondary 5 recrystallization in the final annealing
process, and thus, it is possible to make the secondary recrystallization occur stably.
[0063]
Although the conditions for the nitriding treatment are not particularly limited, it
is preferable to conduct the nitriding treatment so that the nitrogen content increases by
10 0.003% or more, preferably 0.005% or more, and more preferably 0.007% or more.
When the nitrogen (N) content is more than 0.030%, the effects are saturated. Thus, the
nitriding treatment may be conducted so that the nitrogen content becomes 0.030% or
less.
[0064]
15 The conditions for the nitriding treatment are not particularly limited, and
known conditions may be appropriately applied.
For instance, in a case where the nitriding treatment is conducted after the
holding at 750 to 900C for 10 to 600 seconds in the oxidation degree (PH2O/PH2) of
0.01 to 0.15, the nitriding treatment may be conducted such that the cold rolled steel
20 sheet is not cooled to the room temperature but held in the cooling stage in the
atmosphere including the ammonia. It is preferable that the oxidation degree
(PH2O/PH2) in the cooling stage is within the range of 0.0001 to 0.01. Moreover, in a
case where the nitriding treatment is conducted during the holding at 750 to 900C for 10
to 600 seconds in the oxidation degree (PH2O/PH2) of 0.01 to 0.15, the ammonia may be
25 included in the atmospheric gas with the above oxidation degree.
27
[0065]
< Annealing separator applying process >
In the annealing separator applying process, the decarburization annealed sheet
after the decarburization annealing process (or the decarburization annealed sheet after
the nitriding treatment) is s 5 ubjected to the magnetic domain refining treatment as
necessary, and then, the annealing separator including Al2O3 and MgO is applied to the
decarburization annealed sheet. Thereafter, the applied annealing separator is dried.
[0066]
In a case where the annealing separator includes MgO but does not include
10 Al2O3, the forsterite film is formed on the steel sheet in the final annealing process. On
the other hand, in a case where the annealing separator includes Al2O3 but does not
include MgO, mullite (3Al2O3･2SiO2) is formed on the steel sheet. The mullite
becomes the obstacle of movement of the magnetic domain wall, and thus, causes the
deterioration of the magnetic characteristics of the grain oriented electrical steel sheet.
15 [0067]
Thus, in the method for producing the grain oriented electrical steel sheet
according to the embodiment, as the annealing separator, the annealing separator
including Al2O3 and MgO is utilized. By utilizing the annealing separator including
Al2O3 and MgO, the forsterite film is not formed on the surface of the steel sheet, and it
20 is possible to smoothen the surface of the steel sheet after the final annealing.
[0068]
For the annealing separator, MgO / (MgO + Al2O3) which is the mass ratio of
MgO and Al2O3 is to be 5 to 50%, and the hydration water is to be 1.5 mass% or less.
When MgO / (MgO + Al2O3) is less than 5%, the mullite is excessively formed,
25 and thus, the iron loss deteriorates. On the other hand, when MgO / (MgO + Al2O3) is
28
more than 50%, the forsterite is formed, and thus, the iron loss deteriorates.
When the hydration water in the annealing separator is more than 1.5 mass%,
the secondary recrystallization may be unstable, and it may be difficult to smoothen the
surface of the steel sheet because the surface of the steel sheet is oxidized (SiO2 is
formed) in the final annealing. The 5 lower limit of the hydration water is not particularly
limited, but may be 0.1 mass% for instance.
[0069]
The annealing separator is applied by water slurry or by electrostatic spray. In
the annealing separator applying process, the annealing separator may further include
10 nitrides such as manganese nitride, iron nitride, and chromium nitride which are
decomposed before the secondary recrystallization in the final annealing process and
which nitride the decarburization annealed sheet or the decarburized and nitrided sheet.
[0070]
< Final annealing process >
15 The decarburization annealed sheet after applying the above annealing separator
is final-annealed to obtain the final annealed sheet. By conducting the final annealing
for the decarburization annealed sheet after applying the above annealing separator, the
secondary recrystallization proceeds, and the crystal orientation aligns in the {110}<001>
orientation. In the embodiment, the steel sheet after the final annealing process is
20 referred to as the final annealed sheet.
[0071]
In the final annealing, in a case where the atmosphere (furnace atmosphere)
includes hydrogen, the oxidation degree (PH2O/PH2) is to be 0.00010 to 0.2. In a case
where the atmosphere consists of the inert gas (nitrogen, argon, and the like) without the
25 hydrogen, the dew point is to be 0C or less.
29
By controlling the oxidation degree or the dew point to be within the above
range depending on the atmosphere, it is possible to stably proceed the secondary
recrystallization and to increase the alignment degree of the orientation.
[0072]
When the oxidation degree 5 is less than 0.00010 in a case where the atmosphere
includes the hydrogen, the dense surface silica film formed by the decarburization
annealing is reduced before the secondary recrystallization in the final annealing, and
thereby, the secondary recrystallization becomes unstable. On the other hand, when the
oxidation degree is more than 0.2, the dissolution of the inhibitor such as AlN and (Al,
10 Si)N is promoted, and thereby, the secondary recrystallization becomes unstable.
Moreover, when the dew point is more than 0C in a case where the atmosphere consists
of the inert gas without the hydrogen, the dissolution of the inhibitor such as AlN and (Al,
Si)N is promoted, and thereby, the secondary recrystallization becomes unstable. The
lower limit of the dew point is not particularly limited, but may be -30C for instance.
15 [0073]
< Annealing separator removing process >
In the annealing separator removing process, the redundant annealing separator
is removed from the surface of the steel sheet after the final annealing (the final annealed
sheet) by water-washing. Here, the redundant annealing separator indicates, for
20 instance, the unreacted annealing separator which has not reacted with the steel sheet
during the final annealing.
[0074]
In the case, in order to prevent the iron after water-washing from corroding, the
redundant annealing separator is removed by washing using the solution including the
25 inhibitor (corrosion prevention agent) which is at least one of triethanolamine,
30
rosinamine, or mercaptan. It is important to control the total amount of iron hydroxide
and iron oxide on the steel sheet surface to 0.9 g/m2 or less per a side, by conducting the
above washing.
[0075]
When the r 5 emoval of the redundant annealing separator on the steel sheet
surface is insufficient and when the total amount of the iron hydroxide and the iron oxide
on the steel sheet surface is more than 0.9 g/m2 per a side, the exposure of the base steel
sheet surface may be insufficient, and thus, the steel sheet surface may not be controlled
to be a mirror like surface sufficiently. The lower limit of the amount of the iron
10 hydroxide and the iron oxide is not particularly limited, but may be 0.01 g/m2 for
instance.
[0076]
In order to remove the redundant annealing separator, a scrubber may be utilized
in addition to the washing using the solution including the above inhibitor. By utilizing
15 the scrubber, it is possible to reliably remove the redundant annealing separator which
deteriorates the wettability in the insulation coating forming process.
[0077]
Moreover, in a case where the redundant annealing separator is not sufficiently
removed even when the above washing is conducted, the pickling may be conducted
20 using the acidic solution whose volume concentration is less than 20%. For instance,
the pickling may be conducted after water-washing. In a case where the pickling is
conducted, it is preferable to utilize the solution including less than 20 volume% in total
of at least one of sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, chloric
acid, chromium oxide in aqueous solution, chromate acid mixture, permanganic acid,
25 peroxosulfuric acid, and peroxophosphoric acid. It is more preferable to utilize the
31
solution including less than 10 volume% thereof. The lower limit of the volume
concentration is not particularly limited, but may be 0.1 volume% for instance. By
utilizing the above solution, it is possible to efficiently remove the redundant annealing
separator from the surface of the steel sheet. Herein, the above volume% may be the
concentration ba 5 sed on the volume at room temperature.
[0078]
Moreover, in a case where the pickling is conducted, the temperature of the
solution is preferably 20 to 80C. By controlling the temperature of the solution to be
within the above range, it is possible to efficiently remove the redundant annealing
10 separator from the surface of the steel sheet.
[0079]
< Insulation coating forming process >
In the insulation coating forming process, the final annealed sheet after the
annealing separator removing process is subjected to the magnetic domain refining
15 treatment as necessary, and then, the insulation coating is formed on the surface of the
final annealed sheet. In the embodiment, the steel sheet after the insulation coating
forming process is referred to as the grain oriented electrical steel sheet.
[0080]
The coating applies the tension to the grain oriented electrical steel sheet, and
20 thereby, reduces the iron loss as the single steel sheet. Moreover, the coating ensures
interlaminar electrical insulation when the grain oriented electrical steel sheets are
utilized after being laminated, and thereby, reduces the iron loss as an iron core.
[0081]
In order to form the insulation coating on the surface of the final annealed sheet,
25 the insulation coating forming solution (insulation coating forming solution 1) in which
32
phosphoric acid and metal compound are included and in which a mass ratio of the
phosphoric acid and the metal compound is 2:1 to 1:2 is applied and is baked at 600 to
1150C, and after decreasing a temperature, the insulation coating forming solution
(insulation coating forming solution 2) in which phosphate and colloidal silica are
5 included and in which the metal compound is not included is applied and is baked at 600
to 1150C.
[0082]
The metal compound is preferably the compound which reacts with the
phosphoric acid to form metallic phosphide. For instance, the metal compound is
10 chloride, sulfate, carbonate, nitrate, phosphate, metal, and the like. The metallic
phosphide is preferably at least one of Fe3P, Fe2P, and FeP, in order to ensure the
excellent adhesion with the steel sheet. Therefore, the metal compound which reacts
with the phosphoric acid to form the metallic phosphide is preferably the compound
including Fe. When considering the reactivity with the phosphoric acid, FeCl3 is
15 preferable. Herein, when organic phosphoric acid or phosphate is used as a source of
phosphorus in the metallic phosphide, the amount of the metallic phosphide may be
insufficient. Thus, the insulation coating forming solution 1 needs to include the
phosphoric acid.
[0083]
20 The mass ratio of the phosphoric acid and the metal compound in the insulation
coating forming solution 1 is controlled to 2:1 to 1:2, preferably to 1:1 to 1:1.5. By
controlling the mass ratio of the phosphoric acid and the metal compound to be within
the above range, it is possible to sufficiently improve the adhesion of the insulation
coating.
25 [0084]
33
Except for controlling the phosphoric acid and the metal compound as explained
above, the insulation coating forming solution 1 may be the same solution as the
insulation coating forming solution 2. For instance, the insulation coating forming
solution 1 may mainly include the phosphate and the colloidal silica.
5 [0085]
The baking temperature and the holding time for the insulation coating forming
solution 1 are not particularly limited. In order to promote the reaction of the
phosphoric acid and the metal compound, the baking temperature is preferably 600 to
1150C. When the metal compound is FeCl3, the baking temperature is preferably 700
10 to 1150C. Moreover, the baking time is preferably 10 to 600 seconds.
[0086]
After baking the insulation coating forming solution 1 and then decreasing the
temperature to the room temperature (approximately 25C), the insulation coating
forming solution (insulation coating forming solution 2) in which the phosphate and the
15 colloidal silica are included and in which the metal compound is not included is applied
and is baked at 600 to 1150C.
[0087]
The phosphate included in the insulation coating forming solution 2 is favorably
the phosphate of Ca, Al, Sr, and the like. Among these, the aluminum phosphate is
20 more preferable. The above colloidal silica is not particularly limited to the colloidal
silica having specific properties. Moreover, the particle size thereof is not particularly
limited to specific particle size, but is preferably 200 nm or less (mean number diameter).
For instance, the particle size may be 5 to 30 nm. When the particle size thereof is more
than 200 nm, the particles may settle in the insulation coating forming solution 2.
25 Moreover, the insulation coating forming solution 2 may further include the chromic
34
anhydride or the chromate.
[0088]
The baking temperature and the holding time for the insulation coating forming
solution 2 are not particularly limited. In order to promote the reaction of the phosphate
and the colloidal silica, the baking temperature 5 is preferably 600 to 1150C. Moreover,
the baking time is preferably 10 to 600 seconds. Moreover, an atmosphere is not
particularly limited, but the nitrogen atmosphere is preferable.
[0089]
The insulation coating forming solution 1 and the insulation coating forming
10 solution 2 may be applied to the surface of the steel sheet, for instance, by the wet
applying method such as roll coater.
[0090]
< Magnetic domain refining process >
The method for producing the grain oriented electrical steel sheet according to
15 the embodiment may include the magnetic domain refining process of conducting the
magnetic domain refining treatment at appropriate timing of (first) between the cold
rolling process and the decarburization annealing process, (second) between the
decarburization annealing process and the annealing separator applying process, (third)
between the annealing separator removing process and the insulation coating forming
20 process, or (fourth) after the insulation coating forming process.
[0091]
By conducting the magnetic domain refining treatment, it is possible to reduce
the iron loss of the grain oriented electrical steel sheet. In a case where the magnetic
domain refining treatment is conducted between the cold rolling process and the
25 decarburization annealing process, between the decarburization annealing process and
35
the annealing separator applying process, or between the annealing separator removing
process and the insulation coating forming process, the groove may be formed lineally or
punctiformly so as to extend in the direction intersecting the rolling direction and so as to
have the predetermined interval in the rolling direction. By forming the above groove,
the width of 180° domain ma 5 y be narrowed (180° domain may be refined).
[0092]
In a case where the magnetic domain refining treatment is conducted after the
insulation coating forming process, the stress-strain or the groove may be applied or
formed lineally or punctiformly so as to extend in the direction intersecting the rolling
10 direction and so as to have the predetermined interval in the rolling direction. By
applying the above stress-strain or forming the above groove, the width of 180° domain
may be narrowed (180° domain may be refined).
[0093]
The above stress-strain may be applied by irradiating laser beam, electron beam,
15 and the like. The above groove may be formed by a mechanical groove forming
method such as toothed gear, by a chemical groove forming method such as electrolytic
etching, by a thermal groove forming method such as laser irradiation, and the like. In a
case where the insulation coating is damaged and the performance such as electrical
insulation deteriorates by applying the above stress-strain or forming the above groove,
20 the insulation coating may be formed again, and thereby, the damage may be repaired.
[0094]
Fig. 1 shows an instance of the method for producing the grain oriented
electrical steel sheet according to the embodiment. In the figure, the processed
surrounded by the solid line indicates the essential processed, and the processed
25 surrounded by the broken line indicates the optional processes.
36
[0095]
The grain oriented electrical steel sheet produced by the method according to the
embodiment does not include the forsterite film. Specifically, the grain oriented
electrical steel sheet includes a base steel sheet, an intermediate layer which is arranged
in contact with the base 5 steel sheet, and the insulation coating which is arranged in
contact with the intermediate layer to be an outermost surface.
[0096]
Whether or not the grain oriented electrical steel sheet includes the forsterite
film may be confirmed by X-ray diffraction method. For instance, the X-ray diffraction
10 may be conducted for the surface after removing the insulation coating from the grain
oriented electrical steel sheet, and the obtained X-ray diffraction spectrum may be
collated with PDF (Powder Diffraction File). The forsterite (Mg2SiO4) may be
identified by JCPDS No. 34-189. In the embodiment, when the primal constituent
phase in the above X-ray diffraction spectrum is not the forsterite, the grain oriented
15 electrical steel sheet is judged not to include the forsterite film.
[0097]
In order to only remove the insulation coating from the grain oriented electrical
steel sheet, the grain oriented electrical steel sheet with the coating may be immersed in
hot alkaline solution. Specifically, it is possible to remove the insulation coating from
20 the grain oriented electrical steel sheet by immersing the steel sheet in sodium hydroxide
aqueous solution which includes 30 mass% of NaOH and 70 mass% of H2O at 80C for
20 minutes, washing it with water, and then, drying it. In general, only insulation
coating is removed by the alkaline solution, and the forsterite film is removed by the
acidic solution such as hydrochloric acid.
25 [0098]
37
In the grain oriented electrical steel sheet produced by the method according to
the embodiment, since the forsterite film is not included, the magnetic characteristics (the
iron loss characteristics) are improved. In addition, since each of the processes is
optimally controlled, the coating adhesion is improved.
5
Examples
[0099]
Hereinafter, the examples of the present invention are explained. However, the
condition in the examples is an example condition employed to confirm the operability
10 and the effects of the present invention, so that the present invention is not limited to the
example condition. The present invention can employ various types of conditions as
long as the conditions do not depart from the scope of the present invention and can
achieve the object of the present invention.
[0100]
15 In steel slabs having the chemical composition shown in Table 1, the steel slabs
of No. A13 and No. a11 were heated to 1350°C, and then hot-rolled to obtain the hot
rolled steel sheets having the sheet thickness of 2.6 mm. The hot rolled steel sheets
were cold-rolled once or cold-rolled plural times with the intermediate annealing to
obtain the cold rolled steel sheets having the final sheet thickness of 0.22 mm. The cold
20 rolled steel sheets having the final sheet thickness of 0.22 mm were
decarburization-annealed in the decarburization annealing process under conditions
shown in Tables 2 to 4. After conducting the decarburization annealing and then
decreasing the temperature to the room temperature, the oxide layer of the steel sheet
surface was removed by being pickled in the mixed solution of the hydrofluoric acid and
25 the sulfuric acid.
38
[0101]
Moreover, in the steel slabs having the chemical composition shown in Table 1,
the steel slabs except for No. A13 and No. a11 were heated to 1150°C, and then
hot-rolled to obtain the hot rolled steel sheets having the sheet thickness of 2.6 mm.
The hot rolled steel sheets were cold-5 rolled once or cold-rolled plural times with the
intermediate annealing to obtain the cold rolled steel sheets having the final sheet
thickness of 0.22 mm. The cold rolled steel sheets having the final sheet thickness of
0.22 mm were decarburization-annealed in the decarburization annealing process under
conditions shown in Tables 2 to 4. After conducting the decarburization annealing and
10 then decreasing the temperature to the room temperature, the oxide layer of the steel
sheet surface was removed by being pickled in the mixed solution of the hydrofluoric
acid and the sulfuric acid. Thereafter, the nitriding treatment was conducted during
cooling by being held in the atmosphere including the ammonia.
[0102]
15 In No. B5, the hot rolled steel sheet after the hot rolling was subjected to the hot
band annealing in which the annealing was conducted at 1100°C and then at 900°C.
Thereafter, the pickling was conducted in order to remove the surface scale, and then, the
cold rolling was conducted.
[0103]
20 In the decarburization annealing, the average heating rate in the heating stage to
the annealing temperature was less than 15 C/second.
[0104]
For the decarburization annealed sheets after the above decarburization
annealing, the annealing separator was applied and dried. The conditions of the ratio of
25 MgO and Al2O3 (MgO / (MgO + Al2O3)) and the hydration water are shown in Tables 2
39
to 4.
[0105]
The decarburization annealed sheets after applying the annealing separator were
final-annealed at 1100°C or 1200°C for 20 hours. At the time, as shown in Tables 5 to 7,
the oxidation degree was controlled whe 5 n the atmosphere included the hydrogen (H2),
and the dew point was controlled when the atmosphere did not include the hydrogen.
[0106]
After the final annealing, as shown in Tables 5 to 7, the redundant annealing
separator was removed by water-washing from the surface of the final annealed sheet
10 using the solution including the inhibitor which was at least one of triethanolamine,
rosinamine, or mercaptan.
[0107]
After the water-washing, the pickling was conducted as necessary. For
instance, in the examples of the pickling ''Yes'' shown in Tables, the redundant annealing
15 separator was removed by being pickled. In the pickling, the steel sheets were
immersed in the sulfuric acid aqueous solution (volume concentration of sulfuric acid : 1
volume%).
[0108]
Thereafter, the insulation coating forming solution (insulation coating forming
20 solution 1) including the phosphoric acid and the metal compound (FeCl3) in the ratio
thereof shown in Tables 8 to 10 was applied, and was baked at the temperature shown in
Tables 8 to 10. After decreasing the temperature, the insulation coating forming
solution (insulation coating forming solution 2) mainly including the phosphate and the
colloidal silica and including the chromic anhydride as necessary was applied, and was
25 baked at the temperature shown in Tables 8 to 10. By conducting the above baking, the
40
insulation coating was formed.
[0109]
Moreover, in the examples, as shown in Tables 11 to 13, the magnetic domain
refining treatment was conducted at any timing of (first) between the cold rolling process
and the decarburization annealing 5 process, (second) between the decarburization
annealing process and the annealing separator applying process, (third) between the
annealing separator removing process and the insulation coating forming process, or
(fourth) after the insulation coating forming process. For the magnetic domain
refinement, the groove was formed mechanically or chemically, or the stress-strain or the
10 groove was applied or formed by the laser.
[0110]
For the obtained grain oriented electrical steel sheets Nos. B1 to B46 and b1 to
b33, the iron loss and the coating adhesion were evaluated.
[0111]
15 < Iron loss >
The samples were taken from the obtained grain oriented electrical steel sheets,
and the iron loss W17/50 (W/kg) was measured under the conditions of 50 Hz of AC
frequency and 1.7 T of excited magnetic flux density on the basis of the epstein test
regulated by JIS C2550-1: 2000. As for the grain oriented electrical steel sheets in
20 which the magnetic domain refinement was conducted, when the iron loss W17/50 was
less than 0.7 W/kg, it was judged to as acceptable. As for the grain oriented electrical
steel sheets in which the magnetic domain refinement was not conducted, when the iron
loss W17/50 was less than 1.0 W/kg, it was judged to as acceptable.
[0112]
25 < Coating adhesion >
41
The samples were taken from the obtained grain oriented electrical steel sheets,
and the coating adhesion of the insulation coating was evaluated by rolling the sample
around the cylinder with 20 mm of diameter (180° bending) and by measuring the area
fraction of remained coating after bending back. In the evaluation of the coating
adhesion of the insulation c 5 oating, the presence or absence of delamination of the
insulation coating was visually evaluated. When the area fraction of remained coating
which was not delaminated from the steel sheet was 90% or more, it was regarded as ◎
(Very Good). When the area fraction was 85% or more and less than 90%, it was
regarded as ○ (Good). When the area fraction was 80% or more and less than 85%, it
10 was regarded as △ (Poor). When the area fraction was less than 80%, it was regarded as
× (NG). When the area fraction of remained coating was 85% or more (the above ◎ and
○), it was judged to as acceptable.
The results are shown in Tables 11 to 13.
[0113]
15 [Table 1]
42
[0114]
[Table 2]
43
[0115]
[Table 3]
44
[0116]
[Table 4]
45
[0117]
[Table 5]
46
[0118]
[Table 6]
47
[0119]
[Table 7]
48
[0120]
[Table 8]
49
[0121]
[Table 9]
50
[0122]
[Table 10]
51
[0123]
[Table 11]
52
[0124]
[Table 12]
53
[0125]
[Table 13]
54
[0126]
As shown in Tables 1 to 13, in the inventive examples Nos. B1 to B46, all
process conditions satisfied the range of the present invention, and thus, the iron loss was
low. Moreover, the c 5 oating adhesion was excellent.
On the other hand, in the comparative examples Nos. b1 to b33, at least one of
the process conditions was out of the range of the present invention, and thus, the iron
loss and/or the coating adhesion was insufficient. Herein, in the comparative example
55
No. b25, the rolling could not be conducted, and thus, the evaluation thereafter was not
conducted. Moreover, in the comparative example No. b26, the secondary
recrystallization did not occur because of being transformed during the final annealing
process, and thus, the evaluation thereafter was not conducted.
5
Industrial Applicability
[0127]
According to the above aspects of the present invention, it is possible to provide
the method for producing the grain oriented electrical steel sheet without the forsterite
10 film and excellent in the magnetic characteristics and the coating adhesion. The
obtained grain oriented electrical steel sheet is excellent in the magnetic characteristics
and the coating adhesion, and therefore, the present invention has significant industrial
applicability.

CLAIMS

1. A method for producing a grain oriented electrical steel sheet,
5 the method comprising:
a hot rolling process of hot-rolling a steel piece to obtain a hot rolled steel sheet,
the steel piece including, as a chemical composition, by mass%,
0.030 to 0.100% of C,
0.80 to 7.00% of Si,
10 0.01 to 1.00% of Mn,
0 to 0.060% in total of S and Se,
0.010 to 0.065% of acid soluble Al,
0.004 to 0.012% of N,
0 to 0.30% of Cr,
15 0 to 0.40% of Cu,
0 to 0.50% of P,
0 to 0.30% of Sn,
0 to 0.30% of Sb,
0 to 1.00% of Ni,
20 0 to 0.008% of B,
0 to 0.15% of V,
0 to 0.20% of Nb,
0 to 0.10% of Mo,
0 to 0.015% of Ti,
25 0 to 0.010% of Bi, and
57
a balance consisting of Fe and impurities;
a cold rolling process of cold-rolling the hot rolled steel sheet to obtain a cold
rolled steel sheet;
a decarburization annealing process of decarburization-annealing the cold rolled
steel shee 5 t to obtain a decarburization annealed sheet;
an annealing separator applying process of applying and drying an annealing
separator including Al2O3 and MgO to the decarburization annealed sheet;
a final annealing process of final-annealing the decarburization annealed sheet
after applying the annealing separator to obtain a final annealed sheet;
10 an annealing separator removing process of removing a redundant annealing
separator from a surface of the final annealed sheet; and
an insulation coating forming process of forming an insulation coating on the
surface of the final annealed sheet,
wherein, in the decarburization annealing process,
15 PH2O/PH2 which is an oxidation degree of an atmosphere is 0.18 to 0.80, an
annealing temperature is 750 to 900C, a holding is 10 to 600 seconds, and after
decreasing a temperature, an oxide layer of a steel sheet surface is removed by being
pickled in a mixed solution of a hydrofluoric acid and a sulfuric acid,
wherein, in the annealing separator applying process,
20 MgO / (MgO + Al2O3) which is a mass ratio of MgO and Al2O3 is 5 to 50%, and
a hydration water is 1.5 mass% or less in the annealing separator,
wherein, in the final annealing process,
an oxidation degree is 0.00010 to 0.2 when an atmosphere includes a hydrogen,
or a dew point is 0C or less when an atmosphere consists of an inert gas without a
25 hydrogen,
58
wherein, in the annealing separator removing process,
the final annealed sheet is water-washed using a solution with an inhibitor which
is at least one of a triethanolamine, a rosinamine, or a mercaptan in order to remove the
redundant annealing separator from the surface thereof, and an amount of an iron
hydroxide and a 5 n iron oxide on the surface thereof is controlled to 0.9 g/m2 or less per a
side, and
wherein, in the insulation coating forming process,
an insulation coating forming solution in which a phosphoric acid and a metal
compound are included and in which a mass ratio of the phosphoric acid and the metal
10 compound is 2:1 to 1:2 is applied and is baked at 600 to 1150C, and after decreasing a
temperature, an insulation coating forming solution in which a phosphate and a colloidal
silica are included and in which a metal compound is not included is applied and is baked
at 600 to 1150C, in order to form the insulation coating.
15 2. The method for producing the grain oriented electrical steel sheet according to
claim 1,
the method including, between the hot rolling process and the cold rolling
process,
at least one of a hot band annealing process of annealing the hot rolled steel
20 sheet or a hot band pickling process of pickling the hot rolled steel sheet.
3. The method for producing the grain oriented electrical steel sheet according to
claim 1 or 2,
wherein, in the decarburization annealing process, a nitriding treatment is
25 conducted by annealing the cold rolled steel sheet in an atmosphere including ammonia.
59
4. The method for producing the grain oriented electrical steel sheet according to
any one of claims 1 to 3,
the method including, between the cold rolling process and the decarburization
annealing process, between the decarburization a 5 nnealing process and the annealing
separator applying process, between the annealing separator removing process and the
insulation coating forming process, or after the insulation coating forming process,
a magnetic domain refining process of conducting a magnetic domain refining
treatment.
10
5. The method for producing the grain oriented electrical steel sheet according to
any one of claims 1 to 4,
wherein, in the annealing separator removing process, a pickling is conducted
after water-washing using an acidic solution whose volume concentration is less than
15 20%.
6. The method for producing the grain oriented electrical steel sheet according to
any one of claims 1 to 5,
wherein, the steel piece includes, as the chemical composition, by mass%, at
20 least one selected from a group consisting of
0.02 to 0.30% of Cr,
0.05 to 0.40% of Cu,
0.005 to 0.50% of P,
0.02 to 0.30% of Sn,
25 0.01 to 0.30% of Sb,
60
0.01 to 1.00% of Ni,
0.0005 to 0.008% of B,
0.002 to 0.15% of V,
0.005 to 0.20% of Nb,
5 0.005 to 0.10% of Mo,
0.002 to 0.015% of Ti, and
0.001 to 0.010% of Bi.