[0001]The present invention relates to a grain oriented electrical steel sheet, a forming
10 method for an insulation coating of a grain oriented electrical steel sheet, and a producing
method for a grain oriented electrical steel sheet.
Priority is claimed on Japanese Patent Application No. 2019-005237, filed on
January 16, 2019, and the content of which is incorporated herein by reference.
15 Background Art
[0002]
A grain oriented electrical steel sheet is the steel sheet where silicon (Si ) of
approximately 0.5 to 7 mass% is included and crystal orientation is aligned with
{110}<001> orientation (Goss orientation) by utilizing a phenomenon called secondary
20 recrystallization. Herein, the {110}<001> orientation represents that {110} plane of
crystal is aligned parallel to a rolled surface and <001> axis of crystal is aligned parallel
to a rolling direction.
[0003]
The grain oriented electrical steel sheet is mainly used for an iron core of a
25 transformer and the like as a soft magnetic material. Since the grain oriented electrical
2
steel sheet significantly influences a performance of the transformer, investigation has
been eagerly carried out in order to improve excitation characteristics and iron loss
characteristics of the grain oriented electrical steel sheet.
[0004]
A typical method for producing 5 the grain oriented electrical steel sheet is as
follows.
A steel piece with a predetermined composition is heated and hot-rolled to
obtain a hot rolled steel sheet. The hot rolled steel sheet is hot-band-annealed as
necessary, and then is cold-rolled to obtain a cold rolled steel sheet. The cold rolled
10 steel sheet is decarburization-annealed to activate primary recrystallization. A
decarburization annealed steel sheet after the decarburization annealing is final-annealed
to activate the secondary recrystallization.
[0005]
After the decarburization annealing and before the final annealing, aqueous
15 slurry including an annealing separator whose main component is MgO is applied to a
surface of the decarburization annealed steel sheet, and then is dried. The
decarburization annealed steel sheet is coiled, and then is final-annealed. During the
final annealing, MgO included in the annealing separator is reacted to SiO2 included in
an internally oxidized layer formed on a surface of the steel sheet by the decarburization
20 annealing, and thereby, a primary layer (referred to as "glass film" or "forsterite film")
which mainly includes forsterite (Mg2SiO4) is formed on the surface of the steel sheet.
In addition, after forming the glass film (that is, after the final annealing), a solution
which mainly includes colloidal silica and phosphate for instance is applied to the surface
of the final annealed steel sheet and is baked, and thereby, a tension-insulation coating
25 (referred to as "secondary layer") is formed.
3
[0006]
The above glass film functions as an insulator and also improves adhesion of the
tension-insulation coating formed on the glass film. The tension is imparted to the base
steel sheet by adhering the glass film, the tension-insulation coating, and the base steel
sheet. As a result, the iron loss as the grain orien 5 ted electrical steel sheet decreases.
[0007]
However, since the glass film is a non-magnetic material, the existence of the
glass film is unfavorable from a magnetic standpoint. Moreover, an interface between
the base steel sheet and the glass film has intruding structure such that the glass film is
10 intricately intertwined therewith, and the intruding structure tends to suppress domain
wall motion when the grain oriented electrical steel sheet is magnetized. Thus, the
existence of the glass film may cause an increase in the iron loss.
[0008]
For instance, in a case where the formation of the glass film is suppressed, the
15 formation of the intruding structure may be suppressed, and thus, the domain wall may
easily move during being magnetized. However, in a case where the formation of the
glass film is simply suppressed, the adhesion of the tension-insulation coating is not
ensured, and thus, the sufficient tension is not imparted to the base steel sheet. As a
result, it is difficult to reduce the iron loss.
20 [0009]
As described above, at present, in a case where the glass film is removed from
the grain oriented electrical steel sheet, the domain wall may be easily moved, and thus,
it is expected that the magnetic characteristics are improved. On the other hand, in the
above case, the tension is hardly imparted to the base steel sheet, and thus, it is
25 unavoidable that the magnetic characteristics (especially, the iron loss characteristics)
4
deteriorate. Therefore, in a case where the grain oriented electrical steel sheet in which
the glass film is removed whereas the coating adhesion is ensured is realized, it is
expected that the magnetic characteristics are improved.
[0010]
In the 5 past, it has been investigated to improve the adhesion of the
tension-insulation coating for the grain oriented electrical steel sheet without the glass
film.
[0011]
For instance, Patent Document 1 discloses technique to wash a steel sheet by
10 being immersed in aqueous solution of 2 to 30% as sulfuric acid concentration with
sulfuric acid or sulfate before forming a tension-insulation coating. Patent Document 2
discloses technique to conduct pretreatment for a steel sheet surface using oxidizing acid
before forming a tension-insulation coating. Patent Document 3 discloses a grain
oriented silicon steel sheet where an externally oxidized layer containing mainly silica is
15 included and where metallic iron of 30% or less in cross-sectional area fraction is
included in the externally oxidized layer. Patent Document 4 discloses a grain oriented
electrical steel sheet where fine linear grooves are directly formed on a base steel surface
of the grain oriented electrical steel sheet and where the fine linear grooves are with
depth of 0.05 to 2 m and with an interval of 0.05 to 2 m.
20
Related Art Documents
Patent Documents
[0012]
[Patent Document 1] Japanese Unexamined Patent Application, First
25 Publication No. H05-311453
5
[Patent Document 2] Japanese Unexamined Patent Application, First
Publication No. 2002-249880
[Patent Document 3] Japanese Unexamined Patent Application, First
Publication No. 2003-313644
[Patent Document 4] Japanese 5 Unexamined Patent Application, First
Publication No. 2001-303215
Summary of Invention
Technical Problem to be Solved
10 [0013]
As described above, the grain oriented electrical steel sheet without the glass
film is inferior in the adhesion of the tension-insulation coating. For instance, in a case
where the above grain oriented electrical steel sheet is held for long time, the
tension-insulation coating may be delaminated. In the case, the tension is not imparted
15 to the base steel sheet. For the grain oriented electrical steel sheet, it is exceedingly
important to improve the adhesion of the tension-insulation coating.
[0014]
The techniques disclosed in Patent Document 1 to Patent Document 4 intend to
improve the adhesion of the tension-insulation coating respectively. However, in the
20 techniques, it is unclear that the adhesion is stably obtained and that the effect in
improving the iron loss is obtained thereby. The above techniques are not enough to
obtain the effect.
[0015]
The present invention has been made in consideration of the above mentioned
25 situations. An object of the invention is to provide the grain oriented electrical steel
6
sheet excellent in the adhesion of the tension-insulation coating even without the glass
film (forsterite film). In addition, an object of the invention is to provide the method for
forming the above insulation coating and for producing the above grain oriented
electrical steel sheet.
5
Solution to Problem
[0016]
An aspect of the present invention employs the following.
[0017]
10 (1) A grain oriented electrical steel sheet according to an aspect of the present
invention, the grain oriented electrical steel sheet without a forsterite film includes:
a base steel sheet;
an oxide layer arranged in contact with the base steel sheet; and
a tension-insulation coating arranged in contact with the oxide layer,
15 wherein the base steel sheet includes, as a chemical composition, by mass%,
2.5 to 4.0% of Si,
0.05 to 1.00% of Mn,
0 to 0.01% of C,
0 to 0.005% of S+Se,
20 0 to 0.01% of sol.Al,
0 to 0.005% of N,
0 to 0.03% of Bi,
0 to 0.03% of Te,
0 to 0.03% of Pb,
25 0 to 0.50% of Sb,
7
0 to 0.50% of Sn,
0 to 0.50% of Cr,
0 to 1.0% of Cu, and
a balance consisting of Fe and impurities,
5 the oxide layer is an iron oxide layer,
when the iron oxide layer is analyzed by a fourier transform infrared
spectroscopy, when A650 is an absorbance of an absorption peak detected at 650 cm-1 in
an infrared absorption spectrum, and when A1250 is an absorbance of an absorption peak
detected at 1250 cm-1 in the infrared absorption spectrum,
10 the A650 and the A1250 satisfy 0.2 ≤ A650 / A1250 ≤ 5.0, and
a magnetic flux density B8 in a rolling direction of the grain oriented electrical
steel sheet is 1.90 T or more.
(2) In the grain oriented electrical steel sheet according to (1), an average
thickness of the iron oxide layer may be 200 to 500 nm.
15 (3) A forming method for an insulation coating of a grain oriented electrical
steel sheet according to an aspect of the present invention, the forming method for the
insulation coating of the grain oriented electrical steel sheet without a forsterite film
includes an insulation coating forming process of forming a tension-insulation coating on
a steel substrate,
20 wherein, in the insulation coating forming process,
a solution for forming the tension-insulation coating is applied to an oxide layer
of the steel substrate and the solution is baked,
wherein the steel substrate includes a base steel sheet and the oxide layer
arranged in contact with the base steel sheet,
25 the base steel sheet includes, as a chemical composition, by mass%,
8
2.5 to 4.0% of Si,
0.05 to 1.00% of Mn,
0 to 0.01% of C,
0 to 0.005% of S+Se,
5 0 to 0.01% of sol.Al,
0 to 0.005% of N,
0 to 0.03% of Bi,
0 to 0.03% of Te,
0 to 0.03% of Pb,
10 0 to 0.50% of Sb,
0 to 0.50% of Sn,
0 to 0.50% of Cr,
0 to 1.0% of Cu, and
a balance consisting of Fe and impurities,
15 the oxide layer is an iron oxide layer, and
when the iron oxide layer is analyzed by a fourier transform infrared
spectroscopy, when A650 is an absorbance of an absorption peak detected at 650 cm-1 in
an infrared absorption spectrum, and when A1250 is an absorbance of an absorption peak
detected at 1250 cm-1 in the infrared absorption spectrum,
20 the A650 and the A1250 satisfy 0.2 ≤ A650 / A1250 ≤ 5.0.
(4) In the forming method for the insulation coating of the grain oriented
electrical steel sheet according to (3), an average thickness of the iron oxide layer may be
200 to 500 nm.
(5) A producing method for a grain oriented electrical steel sheet according to
25 an aspect of the present invention, the producing method for the grain oriented electrical
9
steel sheet without a forsterite film includes
a hot rolling process of heating and thereafter hot-rolling a steel piece to obtain a
hot rolled steel sheet,
a hot band annealing process of optionally annealing the hot rolled steel sheet to
5 obtain a hot band annealed steel sheet,
a cold rolling process of cold-rolling the hot rolled steel sheet or the hot band
annealed steel sheet by cold-rolling once or by cold-rolling plural times with an
intermediate annealing to obtain a cold rolled steel sheet,
a decarburization annealing process of decarburization-annealing the cold rolled
10 steel sheet to obtain a decarburization annealed steel sheet,
a final annealing process of applying an annealing separator to the
decarburization annealed steel sheet and thereafter final-annealing the decarburization
annealed steel sheet to obtain a final annealed steel sheet,
an oxidizing process of conducting a washing treatment, a pickling treatment,
15 and a heat treatment in turn for the final annealed steel sheet to obtain an oxidized steel
sheet,
an insulation coating forming process of applying a solution for forming a
tension-insulation coating to a surface of the oxidized steel sheet and of baking the
solution,
20 wherein, in the hot rolling process,
the steel piece includes, as a chemical composition, by mass%,
2.5 to 4.0% of Si,
0.05 to 1.00% of Mn,
0.02 to 0.10% of C,
25 0.005 to 0.080% of S+Se,
10
0.010 to 0.07% of sol.Al,
0.005 to 0.020% of N,
0 to 0.03% of Bi,
0 to 0.03% of Te,
5 0 to 0.03% of Pb,
0 to 0.50% of Sb,
0 to 0.50% of Sn,
0 to 0.50% of Cr,
0 to 1.0% of Cu, and
10 a balance consisting of Fe and impurities, and
wherein, in the oxidizing process,
as the washing treatment, a surface of the final annealed steel sheet is washed,
as the pickling treatment, the final annealed steel sheet is pickled using a sulfuric
acid of 5 to 20 mass%, and
15 as the heat treatment, the final annealed steel sheet is held in a temperature range
of 700 to 850C for 10 to 50 seconds in an atmosphere where an oxygen concentration is
5 to 21 volume% and a dew point is -10 to 30C.
(6) In the producing method for the grain oriented electrical steel sheet
according to (5), in the final annealing process,
20 the annealing separator may include MgO and Al2O3 of 85 mass% or more in
total,
MgO : Al2O3 which is a mass ratio of MgO and Al2O3 may satisfy 3 : 7 to 7 : 3,
and
the annealing separator may include a bismuth chloride of 0.5 to 15 mass% as
25 compared with a total amount of MgO and Al2O3.
11
(7) In the producing method for the grain oriented electrical steel sheet
according to (5), in the final annealing process,
the annealing separator may include MgO of 60 mass% or more, and
a forsterite film formed on a surface may be removed by grinding or pickling the
surface 5 of the final annealed steel sheet after final annealing.
(8) In the producing method for the grain oriented electrical steel sheet
according to according to any one of (5) to (7), in the decarburization annealing process,
when S1 is an average heating rate in units of C/second in a temperature range
of 500C or more and less than 600C during raising a temperature of the cold rolled
10 steel sheet and when S2 is an average heating rate in units of C/second in a temperature
range of 600C or more and 700C or less during raising the temperature of the cold
rolled steel sheet,
the S1 and the S2 may satisfy 300 ≤ S1 ≤ 1000, 1000 ≤ S2 ≤ 3000, and 1.0 < S2
/ S1 ≤ 10.0.
15 (9) In the producing method for the grain oriented electrical steel sheet
according to according to any one of (5) to (8), in the hot rolling process,
the steel piece may include, as the chemical composition, by mass%, at least one
selected from a group consisting of
0.0005 to 0.03% of Bi,
20 0.0005 to 0.03% of Te, and
0.0005 to 0.03% of Pb.
Effects of Invention
[0018]
25 According to the above aspects of the present invention, it is possible to provide
12
the grain oriented electrical steel sheet excellent in the adhesion of the tension-insulation
coating even without the glass film (forsterite film). In addition, it is possible to
provide the method for forming the above insulation coating and for producing the above
grain oriented electrical steel sheet.
5 [0019]
Specifically, according to the above aspects of the present invention, the glass
film is not included, the formation of the intruding structure is suppressed, and thereby,
the domain wall can easily move. In addition, the morphology of the iron oxide layer is
controlled, the adhesion of the tension-insulation coating is ensured, and thereby, the
10 sufficient tension can be imparted to the base steel sheet. As a result, it is possible to
obtain the excellent magnetic characteristics as the grain oriented electrical steel sheet.
Brief Description of Drawings
[0020]
15 Fig. 1A is a cross-sectional illustration showing a grain oriented electrical steel
sheet according to an embodiment of the present invention.
Fig. 1B is a cross-sectional illustration showing a modification of the grain
oriented electrical steel sheet according to the embodiment.
Fig. 2A is an infrared absorption spectrum of a fourier transform infrared
20 spectroscopy.
Fig. 2B is an infrared absorption spectrum of a fourier transform infrared
spectroscopy.
Fig. 3 is a flow chart illustrating a producing method for the grain oriented
electrical steel sheet according to the embodiment.
25
13
Detailed Description of Preferred Embodiments
[0021]
Hereinafter, a preferred embodiment of the present invention is described in
detail. However, the present invention is not limited only to the configuration which is
5 disclosed in the present embodiment, and various modifications are possible without
departing from the aspect of the present invention. In addition, the limitation range as
described below includes a lower limit and an upper limit thereof. However, the value
represented by ''more than'' or ''less than'' does not include in the limitation range.
Unless otherwise noted, ''%'' of the chemical composition represents ''mass%''.
10 [0022]
Moreover, in the embodiment and the drawings, duplicate explanations in regard
to the component which has the substantial same function are omitted by adding the same
reference sign.
[0023]
15 The present inventors have made a thorough investigation to improve the
adhesion of the tension-insulation coating for the grain oriented electrical steel sheet
without the glass film (forsterite film). As a result, it has been found that, even without
the glass film, the coating adhesion can be ensured by forming a favorable iron oxide
layer, the favorable iron oxide layer being formed by the following treatments.
20 Specifically, a final annealed steel sheet without the glass film after final annealing is
subjected to washing treatment of washing a surface thereof, to pickling treatment using
sulfuric acid, and then to heat treatment in predetermined atmosphere.
[0024]
Moreover, it has been found that, in the grain oriented electrical steel sheet with
25 the above specific iron oxide layer, alignment degree of crystal orientation of the base
14
steel sheet considerably influences the magnetic characteristics after forming the
tension-insulation coating and after magnetic domain refining treatment, and that the
above influence is more than expected. The present inventors have also found that it is
possible to preferably improve the magnetic characteristics by controlling a heating rate
for decarburization annealing 5 and/or by including an element increasing inhibitor
intensity as chemical composition of a steel piece.
[0025]
< Grain Oriented Electrical Steel Sheet >
The main features of the grain oriented electrical steel sheet according to the
10 embodiment are described with reference to Figure 1A and Figure 1B. Figure 1A and
Figure 1B are illustrations schematically showing the structure of grain oriented
electrical steel sheet according to the embodiment.
[0026]
As schematically shown in Figure 1A, the grain oriented electrical steel sheet 10
15 according to the embodiment includes the base steel sheet 11, the iron oxide layer 13
arranged in contact with the base steel sheet 11, and the tension-insulation coating 15
arranged in contact with the iron oxide layer 13. In the grain oriented electrical steel
sheet 10, the glass film (forsterite film) does not exist between the base steel sheet 11 and
the tension-insulation coating 15. In the grain oriented electrical steel sheet 10, the iron
20 oxide layer 13 and the tension-insulation coating 15 may be formed on at least one sheet
surface of the base steel sheet 11. In general, the iron oxide layer 13 and the
tension-insulation coating 15 are formed on both sheet surfaces of the base steel sheet 11
as schematically shown in Figure 1B.
[0027]
25 Hereinafter, the grain oriented electrical steel sheet 10 according to the
15
embodiment is explained focusing on its characteristic features. In the following
description, detailed description of known features and features which can be
accomplished by the skilled person may be omitted.
[0028]
5 ( Base Steel Sheet 11 )
The base steel sheet 11 is obtained by using steel piece with a predetermined
chemical composition and applying predetermined production conditions, and thus, the
chemical composition and the texture are controlled. The chemical composition of the
base steel sheet 11 is described in detail below.
10 [0029]
( Iron Oxide Layer 13 )
The iron oxide layer 13 is the oxide layer which acts as an intermediate layer
between the base steel sheet 11 and the tension-insulation coating 15 in the grain oriented
electrical steel sheet 10 according to the embodiment. The iron oxide layer 13 mainly
15 includes iron oxides. The constituent phase therein is not particularly limited. In the
grain oriented electrical steel sheet 10 according to the embodiment, the iron oxide layer
13 is defined as the oxide layer which satisfies 0.2 ≤ A650 / A1250 ≤ 5.0 described later.
On the other hand, the forsterite film, the oxide layer except for the iron oxide layer, and
the like do not satisfy 0.2 ≤ A650 / A1250 ≤ 5.0.
20 [0030]
The iron oxide layer 13 mainly includes iron oxides such as magnetite (Fe3O4),
hematite (Fe2O3), fayalite (Fe2SiO4). In addition to the above iron oxides, silicon oxide
(SiO2) and the like may be included. The existence of the iron oxide layer 13 can be
confirmed by conducting the fourier transform infrared spectroscopy on the surface
25 where the tension-insulation coating 15 is not formed (surface where the
16
tension-insulation coating 15 is removed).
[0031]
The iron oxides are formed, for instance, by reacting oxygen with the surface of
the final annealed steel sheet. The iron oxide layer 13 mainly includes the iron oxides,
and thereby, the adhesion with the 5 base steel sheet 11 is improved. In general, it is
difficult to improve the adhesion between metals and ceramics. However, in the grain
oriented electrical steel sheet 10 according to the embodiment, the iron oxide layer 13 is
arranged between the base steel sheet 11 and the tension-insulation coating 15 which is a
kind of ceramic, and thereby, the adhesion of the tension-insulation coating 15 is
10 improved even without the glass film.
[0032]
The average thickness of the iron oxide layer 13 (the average thickness d1 in
Figure 1A and Figure 1B) is preferably in the range of 200 to 500 nm, for instance.
When the average thickness d1 of the iron oxide layer 13 is 200 nm or more, the adhesion
15 can be favorably improved. On the other hand, when the average thickness d1 of the
iron oxide layer 13 is more than 500 nm, the iron oxide layer 13 may be excessively thick,
and the delamination may partially occur. The average thickness d1 of the iron oxide
layer 13 is preferably 220 nm or more, and more preferably 250 nm or more. Moreover,
the average thickness d1 of the iron oxide layer 13 is preferably 480 nm or less, and more
20 preferably 450 nm or less.
[0033]
The above average thickness d1 of the iron oxide layer 13 may be measured by
observing the distribution of bond between iron and oxygen using X-ray photoelectron
spectroscopy (XPS) for instance. Specifically, the XPS spectrum is measured while
25 sputtering from the surface, and the average thickness d1 of the iron oxide layer 13 may
17
be regarded as the range from the position where the Fe-O peak which is appeared at 712
eV is detected in the spectrum to the position where the above Fe-O peak is substituted
for the metallic Fe peak which is appeared at 708 eV in the spectrum.
[0034]
When the measured s 5 ample has the tension-insulation coating 15 as the
outermost layer, XPS analysis may be conducted after reducing the thickness of the
tension-insulation coating 15. For instance, the thickness of the tension-insulation
coating 15 is preliminary confirmed from the cross section along the thickness direction
of the grain oriented electrical steel sheet 10, and then, the surface of the grain oriented
10 electrical steel sheet 10 is mechanically parallel-polished so that the thickness of the
tension-insulation coating 15 becomes less than 0.1 m. Thereafter, XPS analysis may
be conducted using the above grain oriented electrical steel sheet 10. The spectrum
originated from the tension-insulation coating 15 may be detected immediately after
starting XPS analysis (immediately after starting sputtering). With the passage of time,
15 the Fe-O peak which is appeared at 712 eV and which is originated from the iron oxide
layer 13 is detected. With more passage of time, the metallic Fe peak which is appeared
at 708 eV and which is originated from the base steel sheet 11 is detected. Based on the
above Fe-O peak and the above metallic Fe peak, the average thickness d1 of the iron
oxide layer 13 may be measured as described above.
20 [0035]
The constituent phase in the iron oxide layer 13 is not particularly limited. As
necessary, it is possible to identify the constituent phase by X-ray crystallography, XPS
analysis, and the like.
[0036]
25 ( Tension-Insulation Coating 15 )
18
The tension-insulation coating 15 is arranged on the surface of the iron oxide
layer 13. The tension-insulation coating 15 ensures the electrical insulation for the
grain oriented electrical steel sheet 10, and thereby, the eddy current loss is reduced. As
a result, the iron loss characteristics are improved. In addition to the electrical
insulation, the tension-insulation coating 5 15 improves corrosion resistance, heat
resistance, slippage, and the like for the grain oriented electrical steel sheet 10.
[0037]
Moreover, the tension-insulation coating 15 applies the tension to the base steel
sheet 11. When the tension is applied to the base steel sheet 11, the magnetic domain
10 wall motion becomes easier during the magnetization process, and thus, the iron loss
characteristics of the grain oriented electrical steel sheet 10 are improved.
[0038]
The average thickness of the tension-insulation coating 15 is not particularly
limited, but may be 0.1 to 10 m for instance.
15 [0039]
Moreover, the continuous wave laser beam or the electron beam may be
irradiated on the surface of the tension-insulation coating 15, in order to refine the
magnetic domain.
[0040]
20 For instance, the tension-insulation coating 15 is formed by applying the
insulation coating forming solution which mainly includes metal phosphate and colloidal
silica to the surface of the iron oxide layer 13 arranged in contact with the base steel
sheet 11 and by baking the above solution.
[0041]
25 < Thickness of Grain Oriented Electrical Steel Sheet 10 >
19
The average thickness of the grain oriented electrical steel sheet 10 according to
the embodiment (the average thickness t in Figure 1A and Figure 1B) is not particularly
limited, but may be 0.17 to 0.35 mm for instance.
[0042]
< Chemical C 5 omposition of Base Steel Sheet 11 >
The chemical composition of the base steel sheet 11 of the grain oriented
electrical steel sheet 10 according to the embodiment is described in detail. Hereinafter,
''%'' of the amount of respective elements as described below expresses ''mass%'' unless
otherwise mentioned.
10 [0043]
In the grain oriented electrical steel sheet 10 according to the embodiment, the
base steel sheet 11 includes, as the chemical composition, base elements, optional
elements as necessary, and a balance consisting of Fe and impurities.
[0044]
15 In the embodiment, the base steel sheet 11 includes Si and Mn as the base
elements (main alloying elements).
[0045]
( 2.5 to 4.0% of Si )
Si (silicon) is an element which increases the electric resistance of steel and
20 which reduces the eddy current loss. When the Si content is less than 2.5%, the above
effect to reduce the eddy current loss is not sufficiently obtained. On the other hand,
when the Si content is more than 4.0%, the cold workability of steel deteriorates. Thus,
in the embodiment, the Si content of the base steel sheet 11 is to be 2.5 to 4.0%. The Si
content is preferably 2.7% or more, and more preferably 2.8% or more. Moreover, the
25 Si content is preferably 3.9% or less, and more preferably 3.8% or less.
20
[0046]
( 0.05 to 1.0% of Mn )
Mn (manganese) forms MnS and MnSe in the production processes by bonding
to S and/or Se explained later. These precipitates act as the inhibitor (inhibitor of
normal grain growth) and induce 5 the secondary recrystallization in steel during final
annealing. Moreover, Mn is an element which improves the hot workability of steel.
When the Mn content is less than 0.05%, the above is not sufficiently obtained. On the
other hand, when the Mn content is more than 1.0%, the secondary recrystallization does
not occur and the magnetic characteristics of steel deteriorate. Thus, in the embodiment,
10 the Mn content of the base steel sheet 11 is to be 0.05 to 1.0%. The Mn content is
preferably 0.06% or more. Moreover, the Mn content is preferably 0.50% or less.
[0047]
In the embodiment, the base steel sheet 11 may include the impurities. The
impurities correspond to elements which are contaminated during industrial production
15 of steel from ores and scrap that are used as a raw material of steel, or from environment
of a production process.
[0048]
Moreover, in the embodiment, the base steel sheet 11 may include the optional
elements in addition to the base elements and the impurities. For example, as
20 substitution for a part of Fe which is the balance, the silicon steel sheet may include the
optional elements such as C, S, Se, sol. Al (acid-soluble Al), N, Bi, Te, Pb, Sb, Sn, Cr,
and Cu. The optional elements may be included as necessary. Thus, a lower limit of
the respective optional elements does not need to be limited, and the lower limit may be
0%. Moreover, even if the optional elements may be included as impurities, the above
25 mentioned effects are not affected.
21
[0049]
( 0 to 0.01% of C )
C (carbon) is an optional element. C is the element effective for microstructure
control until the completion of the decarburization annealing process in the production
processes, and thereby, the magnetic characteristics for 5 the grain oriented electrical steel
sheet are improved. However, as the final product, when the C content of the base steel
sheet 11 is more than 0.01%, the magnetic characteristics for the grain oriented electrical
steel sheet 10 deteriorate. Thus, in the embodiment, the C content of the base steel
sheet 11 is to be 0.01% or less. The C content is preferably 0.005% or less. On the
10 other hand, the lower limit of the C content of the base steel sheet 11 is not particularly
limited, but may be 0%. It is preferable that the C content is as low as possible.
However, even when the C content is reduced to less than 0.0001%, the effect for the
microstructure control is saturated, and the producing cost increases. Thus, the C
content is preferably 0.0001% or more.
15 [0050]
( 0 to 0.005% in total of S+Se )
S (sulfur) and Se (selenium) are optional elements. S and Se form MnS and
MnSe which act as the inhibitor by bonding to Mn in the production processes.
However, when the total amount of S and Se of the base steel sheet 11 is more than
20 0.005%, the inhibitor remains in the base steel sheet 11, and the magnetic characteristics
deteriorate. Thus, in the embodiment, the total amount of S and Se of the base steel
sheet 11 is to be 0.005% or less. On the other hand, the lower limit of the total amount
of S and Se of the base steel sheet 11 is not particularly limited, but may be 0%. It is
preferable that the total amount of S and Se is as low as possible. However, even when
25 the total amount of S and Se is reduced to less than 0.0001%, the producing cost
22
increases. Thus, the total amount of S and Se is preferably 0.0001% or more.
[0051]
( 0 to 0.01% of sol.Al )
Sol. Al (acid soluble Al) is an optional element. Al forms AlN which acts as
the inhibitor by bonding 5 to N in the production processes. However, when the sol.Al
content is more than 0.01%, the inhibitor excessively remains in the base steel sheet 11,
and the magnetic characteristics deteriorate. Thus, in the embodiment, the sol.Al
content of the base steel sheet 11 is to be 0.01% or less. The sol.Al content is preferably
0.005% or less, and more preferably 0.004% or less. The lower limit of the sol.Al
10 content of the base steel sheet 11 is not particularly limited, but may be 0%. However,
in order to reduce the sol.Al content to less than 0.0001%, the producing cost increases.
Thus, the sol.Al content is preferably 0.0001% or more.
[0052]
( 0 to 0.005% of N )
15 N (nitrogen) is an optional element. N forms AlN which acts as the inhibitor
by bonding to Al in the production processes. However, when the N content is more
than 0.005%, the inhibitor excessively remains in the base steel sheet 11, and the
magnetic characteristics deteriorate. Thus, in the embodiment, the N content of the base
steel sheet 11 is to be 0.005% or less. The N content is preferably 0.004% or less. The
20 lower limit of the N content of the base steel sheet 11 is not particularly limited, but may
be 0%. However, in order to reduce the N content to less than 0.0001%, the producing
cost increases. Thus, the N content is preferably 0.0001% or more.
[0053]
( 0 to 0.03% of Bi )
25 ( 0 to 0.03% of Te )
23
( 0 to 0.03% of Pb )
Bi (bismuth), Te (tellurium), and Pb (lead) are optional elements. When the
amount of each of these elements included in the base steel sheet 11 is 0.03% or less, it is
possible to favorably improve the magnetic characteristics for the grain oriented
electrical steel sheet 10. However, whe 5 n the amount of each of these elements is more
than 0.03% respectively, the steel sheet may become brittle in the higher temperature
range. Thus, in the embodiment, the amount of each of these elements included in the
base steel sheet 11 is to be 0.03% or less. The lower limit of the amount of each of
these elements included in the base steel sheet 11 is not particularly limited, but may be
10 0%. The lower limit of the amount of each of these elements may be 0.0001%.
[0054]
( 0 to 0.50% of Sb )
( 0 to 0.50% of Sn )
( 0 to 0.50% of Cr )
15 ( 0 to 1.0% of Cu )
Sb (antimony), Sn (tin), Cr (chrome), and Cu (copper) are optional elements.
When these elements are included in the base steel sheet 11, it is possible to favorably
improve the magnetic characteristics for the grain oriented electrical steel sheet 10.
Thus, in the embodiment, it is preferable to control the amount of each of these elements
20 included in the base steel sheet 11 to 0.50% or less of Sb, 0.50% or less of Sn, 0.50% or
less of Cr, and 1.0% or less of Cu. The lower limit of the amount of each of these
elements included in the base steel sheet 11 is not particularly limited, but may be 0%.
In order to favorably obtain the above effect, the amount of each of these elements is
preferably 0.0005% or more, and more preferably 0.001% or more.
25 [0055]
24
Herein, at least one of Sb, Sn, Cr, and Cu may be included in the base steel sheet
11. Specifically, the base steel sheet 11 may be include at least one of 0.0005 to 0.50%
of Sb, 0.0005 to 0.50% of Sn, 0.0005 to 0.50% of Cr, and 0.0005 to 1.0% of Cu.
[0056]
In the grain oriented electrical st 5 eel sheet, the chemical composition changes
relatively drastically (the amount of alloying element decreases) through the
decarburization annealing and through the purification annealing during secondary
recrystallization. Depending on the element, the amount of the element may decreases
through the purification annealing to an undetectable level (1 ppm or less) using the
10 typical analysis method. The above mentioned chemical composition is the chemical
composition as the final product (the base steel sheet 11 of the grain oriented electrical
steel sheet 10). In general, the chemical composition of the final product is different
from the chemical composition of the steel piece (slab) as the starting material.
[0057]
15 The chemical composition of the base steel sheet 11 of the grain oriented
electrical steel sheet 10 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 Spectrometer: inductively coupled plasma emission
spectroscopy spectrometry). Specifically, it is possible to obtain the chemical
20 composition by conducting the measurement by Shimadzu ICPS-8100 and the like
(measurement device) under the condition based on calibration curve prepared in
advance using samples with 35mm square taken from the base steel sheet 11. In
addition, C and S may be measured by the infrared absorption method after combustion,
and N may be measured by the thermal conductometric method after fusion in a current
25 of inert gas.
25
[0058]
The above chemical composition is the composition of the base steel sheet 11 of
the grain oriented electrical steel sheet 10. When the grain oriented electrical steel sheet
10 used as the measurement sample has the tension-insulation coating 15 and the iron
oxide layer 13 on the surface 5 thereof, the chemical composition is measured after
removing the coating and the like by the typical methods.
[0059]
< Surface Analysis by Fourier Transform Infrared Spectroscopy >
In the grain oriented electrical steel sheet 10 according to the embodiment, the
10 iron oxide layer 13 is arranged between the base steel sheet 11 and the tension-insulation
coating 15, and thereby, the iron oxide layer 13, the tension-insulation coating 15, and the
base steel sheet 11 adhere tightly, even without the glass film (forsterite film).
[0060]
It is possible to judge whether or not the iron oxide layer 13 is included in the
15 grain oriented electrical steel sheet 10 by the surface analysis using the fourier transform
infrared spectroscopy. Specifically, the fourier transform infrared spectroscopy is
conduced, and then, the absorbance of specific peak may be confirmed. Hereinafter, the
surface analysis by the fourier transform infrared spectroscopy is explained in detail with
reference to Figure 2A and Figure 2B. Figure 2A and Figure 2B show the infrared
20 absorption spectrum of the fourier transform infrared spectroscopy.
[0061]
When the tension-insulation coating 15 is not included in the grain oriented
electrical steel sheet 10 (when the steel sheet is after the oxidizing process and before the
insulation coating forming process in the method for producing the grain oriented
25 electrical steel sheet according to the embodiment), the surface of the iron oxide layer 13
26
is analyzed by known fourier transform infrared spectrophotometer which is
commercially available (for instance, Frontier of PERKIN ELMER Frontier and the
like).
[0062]
When the te 5 nsion-insulation coating 15 is included, the fourier transform
infrared spectroscopy may be conducted while reducing the thickness of the
measurement sample. For instance, the thickness of the tension-insulation coating 15 is
preliminary confirmed from the cross section along the thickness direction of the grain
oriented electrical steel sheet 10, and then, the surface of the grain oriented electrical
10 steel sheet 10 is mechanically parallel-polished so that the thickness of the
tension-insulation coating 15 becomes less than 0.1 m. The fourier transform infrared
spectroscopy is conducted using the above grain oriented electrical steel sheet 10 after
polishing. Thereafter, the measured surface of the measurement sample is mechanically
parallel-polished so that the thickness of the analyzed measurement sample is further
15 reduced by approximately 0.05 m. The fourier transform infrared spectroscopy is
conducted again using the measurement sample after polishing. The above analysis and
polishing are repeated until the base steel sheet 11 is exposed in the measurement sample.
By the above procedure, the iron oxide layer 13 is analyzed by the fourier transform
infrared spectrophotometer.
20 [0063]
The result of the fourier transform infrared spectroscopy is not affected by the
presence or absence of the tension-insulation coating 15. Specifically, it is confirmed
that the result of the fourier transform infrared spectroscopy is equivalent between the
analysis using the measurement sample where the tension-insulation coating 15 is not
25 included and where the iron oxide layer 13 is the outermost layer and the analysis using
27
the measurement sample where the tension-insulation coating 15 is included and where
the iron oxide layer 13 is exposed by the above procedure.
[0064]
When the fourier transform infrared spectroscopy is conducted, for instance, it is
preferable to measure 5 the infrared absorption spectrum of the iron oxide layer 13 by
reflection absorption spectroscopy. At this time, the absorption peak detected at 650
cm-1 in the infrared absorption spectrum is observed as the absorption peak originated
from iron oxides included in the iron oxide layer 13. On the other hand, the absorption
peak detected at 1250 cm-1 in the infrared absorption spectrum is observed as the
10 absorption peak originated from SiO2. In some case, the position of the wavenumber at
which these absorption peaks are detected may shift by about 1 to 2 cm-1 from the above
wavenumber. However, as shown in Figure 2A and Figure 2B, the spectral waveform
of the above two absorption peaks is specific, and thus, the skilled person can easily
identify the above two absorption peaks from the infrared absorption spectrum.
15 [0065]
It is possible to define the absorbance Ak of each absorption peak as following
(formula 11), using the intensity Ik (for instance, transmittance Tk (unit: %)) of each
absorption peak and the intensity I0
k (for instance, transmittance T0
k (unit: %)) of the base
line of each absorption peak as shown in Figure 2A for instance. Moreover, if the
20 fourier transform infrared spectrophotometer used for the surface analysis is the device
which can directly output the absorbance, it is also possible to define the absorbance Ak
of each absorption peak as following (formula 11'), using the absorbance A'k (no unit) of
each absorption peak and the absorbance A0
k (no unit) of the base line of each absorption
peak as shown in Figure 2B for instance.
25 [0066]
28
Ak = log(I0
k / Ik) ---(formula 11)
Ak = A'k - A0
k ---(formula 11')
[0067]
Based on the above formula 11 and the above formula 11', A650 is defined as the
absorbance of the absorption peak detected a 5 t 650 cm-1 of the wavenumber in the infrared
absorption spectrum, and A1250 is defined as the absorbance of the absorption peak
detected at 1250 cm-1 of the wavenumber in the infrared absorption spectrum.
[0068]
The absorption peak detected at 650 cm-1 is originated from the iron oxides, and
10 the absorption peak detected at 1250 cm-1 is originated from SiO2. Thus, the value of
the above A650 and the value of the above A1250 correspond to the amount of formed iron
oxides and the amount of formed SiO2 respectively.
[0069]
In the case of observing the infrared absorption spectrum which is the relation
15 between the wavenumber (cm-1) and the transmittance T (%) as shown in Figure 2A, it is
possible to define the above base line as follows.
The base line of the absorption peak detected at 650 cm-1 : the line connecting
the maximum of the transmittance T in the wavenumber range of 510 to 560 cm-1 and the
maximum of the transmittance T in the wavenumber range of 720 to 820 cm-1.
20 The base line of the absorption peak detected at 1250 cm-1 : the line connecting
the maximum of the transmittance T in the wavenumber range of 1000 to 1100 cm-1 and
the maximum of the transmittance T in the wavenumber range of 1280 to 1350 cm-1.
[0070]
In the case of observing the infrared absorption spectrum which is the relation
25 between the wavenumber (cm-1) and the absorbance A (no unit) as shown in Figure 2B, it
29
is possible to define the above base line as follows.
The base line of the absorption peak detected at 650 cm-1 : the line connecting
the minimum of the absorbance A in the wavenumber range of 510 to 560 cm-1 and the
minimum of the absorbance A in the wavenumber range of 720 to 820 cm-1.
The base line of the absorption peak de 5 tected at 1250 cm-1 : the line connecting
the minimum of the absorbance A in the wavenumber range of 1000 to 1100 cm-1 and the
minimum of the absorbance A in the wavenumber range of 1280 to 1350 cm-1.
[0071]
In the grain oriented electrical steel sheet 10 according to the embodiment, the
10 following (formula 101) is satisfied when the iron oxide layer 13 is analyzed by the
fourier transform infrared spectroscopy.
[0072]
0.2 ≤ A650 / A1250 ≤ 5.0 ---(formula 101)
[0073]
15 In the grain oriented electrical steel sheet 10 according to the embodiment, when
the infrared absorption spectrum satisfies the above formula 101, it is judged that the iron
oxide layer 13 is included in the grain oriented electrical steel sheet 10. For instance, in
regard to the grain oriented electrical steel sheet 10 including the tension-insulation
coating 15, when at least one infrared absorption spectrum satisfying the above formula
20 101 is observed in plural analyses of the fourier transform infrared spectroscopy where
the above analysis and polishing are repeated, it is judged that the iron oxide layer 13 is
included in the grain oriented electrical steel sheet 10. On the other hand, the forsterite
film and the oxide layer except for the iron oxide layer 13 do not satisfy the above
formula 101.
25 [0074]
30
When the absorbance ratio A650 / A1250 is less than 0.2, the amount of formed
iron oxides is excessively small as compared with the amount of formed SiO2, the
formation of the iron oxide layer 13 is insufficient, and thus, the adhesion of the
tension-insulation coating cannot be sufficiently improved. In addition, when the
absorbance ratio A650 / A1250 5 is more than 5.0, the adhesion of the tension-insulation
coating 15 decreases, which is unfavorable. The reason why the adhesion decreases
when the absorbance ratio A650 / A1250 is more than 5.0 is not entirely clear. In a case
where the holding time is shorter or the holding temperature is lower in the heat
treatment of the oxidizing process explained later, the above situation is occasionally
10 observed. Thus, it is presumed that both the amount of formed iron oxides and the
amount of formed SiO2 are insufficient and that the formation of the iron oxides for
ensuring the adhesion is insufficient.
[0075]
In the grain oriented electrical steel sheet 10 according to the embodiment, the
15 absorbance ratio A650 / A1250 is preferably 0.4 or more, and more preferably 0.6 or more.
Moreover, the absorbance ratio A650 / A1250 is preferably 4.5 or less, and more preferably
4.0 or less.
[0076]
< Forsterite Film >
20 The grain oriented electrical steel sheet 10 according to the embodiment does
not include the forsterite film. In the embodiment, it may be judged by the following
procedure whether or not the grain oriented electrical steel sheet 10 includes the forsterite
film
[0077]
25 Whether or not the grain oriented electrical steel sheet 10 includes the forsterite
31
film may be confirmed by X-ray diffraction method. For instance, the X-ray diffraction
may be conducted for the surface after removing the tension-insulation coating 15 and
the like from the grain oriented electrical steel sheet 10, and the obtained X-ray
diffraction spectrum may be collated with PDF (Powder Diffraction File). The
forsterite (Mg2SiO4) may 5 be identified by JCPDS No. 34-189. In the embodiment,
when the main constituent phase in the above X-ray diffraction spectrum is not the
forsterite, the grain oriented electrical steel sheet 10 is judged not to include the forsterite
film.
[0078]
10 In order to only remove the tension-insulation coating 15 from the grain oriented
electrical steel sheet 10, the grain oriented electrical steel sheet 10 with the coating may
be immersed in hot alkaline solution. Specifically, it is possible to remove the
tension-insulation coating 15 and the like from the grain oriented electrical steel sheet 10
by immersing the steel sheet in sodium hydroxide aqueous solution which includes 30
15 mass% of NaOH and 70 mass% of H2O at 80C for 20 minutes, washing it with water,
and then by 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. Thus, in a case where the forsterite film is included, by immersing in the above
alkaline solution, the tension-insulation coating 15 is removed, and the forsterite film is
20 exposed.
[0079]
< Magnetic Characteristics >
The magnetic characteristics of the grain oriented electrical steel sheet may be
measured on the basis of the epstein test regulated by JIS C2550: 2011, the single sheet
25 tester (SST) method regulated by JIS C 2556: 2015, and the like. In the grain oriented
32
electrical steel sheet 10 according to the embodiment, the magnetic characteristics may
be evaluated by adopting the single sheet tester method regulated by JIS C 2556: 2015
among the above methods.
[0080]
In the grain oriented e 5 lectrical steel sheet 10 according to the embodiment, the
magnetic flux density B8 in the rolling direction (the magnetic flux density under the
magnetizing field of 800A/m) may be 1.90 T or more. The upper limit of the magnetic
flux density is not particularly limited, but may be 2.02 T for instance.
[0081]
10 As described above, the magnetic characteristics of the grain oriented electrical
steel sheet may be measured on the basis of the epstein test regulated by JIS C2550: 2011,
the single sheet tester (SST) method regulated by JIS C 2556: 2015, and the like. When
a steel ingot is formed in vacuum furnace and the like for the research and development,
it is difficult to take a test piece with the same size as that industrially produced. In the
15 case, for instance, the test piece with a width of 60 mm and a length of 300 mm may be
taken, and the measurement may be conducted in accordance with the single sheet tester
method. Moreover, the measured value may be multiplied by the correction factor in
order to obtain the measured value equivalent to that based on the epstein test. In the
embodiment, the measurement is conducted in accordance with the single sheet tester
20 method. The test piece may be taken so that the longitudinal direction is the rolling
direction, and the magnetic flux density B8 in the rolling direction may be measured.
[0082]
< Producing Method for Grain Oriented Electrical Steel Sheet >
Next, a producing method for the grain oriented electrical steel sheet according
25 to a preferred embodiment of the present invention is described in detail with reference to
33
Figure 3. Fig. 3 is a flow chart illustrating an instance of the producing method for the
grain oriented electrical steel sheet according to the embodiment.
[0083]
Herein, the producing method for the grain oriented electrical steel sheet 10 is
not limited to t 5 he following method. The following method is just an instance for
producing the grain oriented electrical steel sheet 10.
[0084]
< Overall Flow of Producing Method for Grain Oriented Electrical Steel Sheet >
The producing method for the grain oriented electrical steel sheet according to
10 the embodiment is for producing the grain oriented electrical steel sheet without the
forsterite film, and the overall flow thereof is as follows.
[0085]
The producing method for the grain oriented electrical steel sheet according to
the embodiment includes the following processes, which are shown in Figure 3.
15 (S101) Hot rolling process of heating and thereafter hot-rolling a steel piece
(slab) including predetermined chemical composition to obtain a hot rolled steel sheet.
(S103) Hot band annealing process of optionally annealing the hot rolled steel
sheet to obtain a hot band annealed steel sheet.
(S105) Cold rolling process of cold-rolling the hot rolled steel sheet or the hot
20 band annealed steel sheet by cold-rolling once or by cold-rolling plural times with an
intermediate annealing to obtain a cold rolled steel sheet.
(S107) Decarburization annealing process of decarburization-annealing the cold
rolled steel sheet to obtain a decarburization annealed steel sheet.
(S109) Final annealing process of applying an annealing separator to the
25 decarburization annealed steel sheet and thereafter final-annealing the decarburization
34
annealed steel sheet to obtain a final annealed steel sheet.
(S111) Oxidizing process of conducting a washing treatment, a pickling
treatment, and a heat treatment in turn for the final annealed steel sheet to obtain an
oxidized steel sheet.
(S113) Insulation coating forming 5 process of applying a solution for forming a
tension-insulation coating to a surface of the oxidized steel sheet and of baking the
solution.
[0086]
The above processes are respectively described in detail. In the following
10 description, when the conditions of each process are not described, known conditions
may be appropriately applied.
[0087]
< Hot Rolling Process >
The hot rolling process (step S101) is the process of heating and thereafter
15 hot-rolling the steel piece (for instance, steel ingot such as slab) including predetermined
chemical composition to obtain the hot rolled steel sheet. In the hot rolling process, the
steel piece is heat-treated. The heating temperature of the steel piece is preferably in the
range of 1200 to 1400C. The heating temperature of the steel piece is preferably
1250C or more, and preferably 1380C or more. Subsequently, the heated steel piece
20 is hot-rolled to obtain the hot rolled steel sheet. The average thickness of the hot rolled
steel sheet is preferably in the range of 2.0 to 3.0 mm for instance.
[0088]
In the producing method for the grain oriented electrical steel sheet according to
the embodiment, the steel piece includes, as the chemical composition, base elements,
25 optional elements as necessary, and a balance consisting of Fe and impurities.
35
Hereinafter, ''%'' of the amount of respective elements as described below expresses
''mass%'' unless otherwise mentioned.
[0089]
In the producing method for the grain oriented electrical steel sheet according to
the e 5 mbodiment, the steel piece (slab) includes Si, Mn, C, S+Se, sol. Al, and N as the
base elements (main alloying elements).
[0090]
( 2.5 to 4.0% of Si )
Si is the element which increases the electric resistance of steel and which
10 reduces the eddy current loss. When the Si content of the steel piece is less than 2.5%,
the above effect to reduce the eddy current loss is not sufficiently obtained. On the
other hand, when the Si content of the steel piece is more than 4.0%, the cold workability
of steel deteriorates. Thus, in the embodiment, the Si content of the steel piece is to be
2.5 to 4.0%. The Si content of the steel piece is preferably 2.7% or more, and more
15 preferably 2.8% or more. Moreover, the Si content of the steel piece is preferably 3.9%
or less, and more preferably 3.8% or less.
[0091]
( 0.05 to 1.0% of Mn )
Mn forms MnS and MnSe in the production processes by bonding to S and/or Se
20 explained later. These precipitates act as the inhibitor and induce the secondary
recrystallization in steel during final annealing. Moreover, Mn is an element which
improves the hot workability of steel. When the Mn content of the steel piece is less
than 0.05%, the above is not sufficiently obtained. On the other hand, when the Mn
content of the steel piece is more than 1.0%, the secondary recrystallization does not
25 occur and the magnetic characteristics of steel deteriorate. Thus, in the embodiment,
36
the Mn content of the steel piece is to be 0.05 to 1.0%. The Mn content of the steel
piece is preferably 0.06% or more. Moreover, the Mn content of the steel piece is
preferably 0.50% or less.
[0092]
5 ( 0.02 to 0.10% of C )
C is the element effective for microstructure control until the completion of the
decarburization annealing process in the production processes, and thereby, the magnetic
characteristics for the grain oriented electrical steel sheet are improved. When the C
content of the steel piece is less than 0.02%, or when the C content of the steel piece is
10 more than 0.10%, the above effect in improving the magnetic characteristics are not
sufficiently obtained. The C content of the steel piece is preferably 0.03% or more.
Moreover, the C content of the steel piece is preferably 0.09% or less.
[0093]
( 0.005 to 0.080% in total of S+Se )
15 S and Se form MnS and MnSe which act as the inhibitor by bonding to Mn in
the production processes. When the total amount of S and Se of the steel piece is less
than 0.005%, it is difficult to obtain the effect for forming MnS and MnSe. On the other
hand, when the total amount of S and Se is more than 0.080%, the magnetic
characteristics deteriorate, and the steel sheet may become brittle in the higher
20 temperature range. Thus, in the embodiment, the total amount of S and Se of the steel
piece is to be 0.005 to 0.080%. The total amount of S and Se of the steel piece is
preferably 0.006% or more. Moreover, the total amount of S and Se of the steel piece is
preferably 0.070% or less.
[0094]
25 ( 0.01 to 0.07% of sol.Al )
37
Sol. Al forms AlN which acts as the inhibitor by bonding to N in the production
processes. When the sol.Al content of the steel piece is less than 0.01%, AlN does not
form sufficiently, and thus, the magnetic characteristics deteriorate. On the other hand,
when the sol.Al content of the steel piece is more than 0.07%, the magnetic
characteristics deteriorate, a 5 nd the cracks tend to occur during cold rolling. Thus, in the
embodiment, the sol.Al content of the steel piece is to be 0.01 to 0.07%. The sol.Al
content of the steel piece is preferably 0.02% or more. Moreover, the sol.Al content of
the steel piece is preferably 0.05% or less.
[0095]
10 ( 0.005 to 0.020% of N )
N forms AlN which acts as the inhibitor by bonding to Al in the production
processes. When the N content of the steel piece is less than 0.005%, AlN does not
form sufficiently, and thus, the magnetic characteristics deteriorate. On the other hand,
when the N content of the steel piece is more than 0.020%, AlN becomes difficult to act
15 as the inhibitor, and thus, the secondary recrystallization becomes difficult to occur. In
addition, the cracks tend to occur during cold rolling. Thus, in the embodiment, the N
content of the steel piece is to be 0.005 to 0.020%. The N content of the steel piece is
preferably 0.012% or less, and more preferably 0.010% or less.
[0096]
20 In the producing method for the grain oriented electrical steel sheet according to
the embodiment, the steel piece (slab) may include the impurities. The impurities
correspond to elements which 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.
25 [0097]
38
Moreover, in the embodiment, the steel piece may include the optional elements
in addition to the base elements and the impurities. For example, as substitution for a
part of Fe which is the balance, the silicon steel sheet may include the optional elements
such as Bi, Te, Pb, Sb, Sn, Cr, and Cu. The optional elements may be included as
necessary. Thus, a 5 lower limit of the respective optional elements does not need to be
limited, and the lower limit may be 0%. Moreover, even if the optional elements may
be included as impurities, the above mentioned effects are not affected.
[0098]
( 0 to 0.03% of Bi )
10 ( 0 to 0.03% of Te )
( 0 to 0.03% of Pb )
Bi, Te, and Pb are optional elements. When the amount of each of these
elements included in the steel piece is 0.03% or less, it is possible to favorably improve
the magnetic characteristics for the grain oriented electrical steel sheet. However, when
15 the amount of each of these elements is more than 0.03% respectively, the steel sheet
may become brittle in the higher temperature range. Thus, in the embodiment, the
amount of each of these elements included in the steel piece is to be 0.03% or less. The
lower limit of the amount of each of these elements included in the steel piece is not
particularly limited, but may be 0%. In order to favorably obtain the above effect, the
20 amount of each of these elements is preferably 0.0005% or more, and more preferably
0.001% or more.
[0099]
Herein, at least one of Bi, Te, and Pb may be included in the steel piece.
Specifically, the steel piece may be include at least one of 0.0005 to 0.03% of Bi, 0.0005
25 to 0.03% of Te, and 0.0005 to 0.03% of Pb.
39
[0100]
( 0 to 0.50% of Sb )
( 0 to 0.50% of Sn )
( 0 to 0.50% of Cr )
5 ( 0 to 1.0% of Cu )
Sb, Sn, Cr, and Cu are optional elements. When these elements are included in
the steel piece, it is possible to favorably improve the magnetic characteristics for the
grain oriented electrical steel sheet. Thus, in the embodiment, it is preferable to control
the amount of each of these elements included in the steel piece to 0.50% or less of Sb,
10 0.50% or less of Sn, 0.50% or less of Cr, and 1.0% or less of Cu. The lower limit of the
amount of each of these elements included in the steel piece is not particularly limited,
but may be 0%. In order to favorably obtain the above effect, the amount of each of
these elements is preferably 0.0005% or more, and more preferably 0.001% or more.
[0101]
15 Herein, at least one of Sb, Sn, Cr, and Cu may be included in the steel piece.
Specifically, the steel piece may be include at least one of 0.0005 to 0.50% of Sb, 0.0005
to 0.50% of Sn, 0.0005 to 0.50% of Cr, and 0.0005 to 1.0% of Cu.
[0102]
The chemical composition of the steel piece may be measured by typical
20 analytical methods for the steel. For instance, the chemical composition may be
measured on the basis of the above analytical method.
[0103]
< Hot Band Annealing Process >
The hot band annealing process (step S103) is the process of optionally
25 annealing the hot rolled steel sheet after the hot rolling process to obtain the hot band
40
annealed steel sheet. By conducting the annealing for the hot rolled steel sheet, the
recrystallization occurs in steel, and finally, the excellent magnetic characteristics can be
obtained.
[0104]
The heating method is 5 not particularly limited, and known heating method may
be adopted. Moreover, the annealing conditions are not particularly limited. For
instance, the hot rolled steel sheet may be held in the temperature range of 900 to 1200C
for 10 seconds to 5 minutes.
[0105]
10 The hot band annealing process may be omitted as necessary.
Moreover, after the hot band annealing process and before the cold rolling
process explained below, the surface of the hot rolled steel sheet may be pickled.
[0106]
< Cold Rolling Process >
15 The cold rolling process (step S105) is the process of cold-rolling the hot rolled
steel sheet after the hot rolling process or the hot band annealed steel sheet after the hot
band annealing process by cold-rolling once or by cold-rolling plural times with the
intermediate annealing to obtain the cold rolled steel sheet. Since the sheet shape of the
hot band annealed steel sheet is excellent due to the hot band annealing, it is possible to
20 reduce the possibility such that the steel sheet is fractured in the first cold rolling. The
cold rolling may be conducted three or more times, but the producing cost increases.
Thus, it is preferable to conduct the cold rolling once or twice.
[0107]
In the cold rolling process, the cold rolling method for the steel sheet is not
25 particularly limited, and known method may be adopted. For instance, the cold rolling
41
reduction in final cold rolling (cumulative cold rolling reduction without intermediate
annealing or cumulative cold rolling reduction after intermediate annealing) may be in
the range of 80 to 95%.
[0108]
Herein, 5 the final cold rolling reduction (%) is defined as follows.
Final cold rolling reduction (%) = ( 1 - Sheet thickness of steel sheet after final
cold rolling / Sheet thickness of steel sheet before final cold rolling ) × 100
[0109]
When the final cold rolling reduction is less than 80%, the Goss nuclei may not
10 be formed favorably. On the other hand, when the final cold rolling reduction is more
than 95%, the secondary recrystallization may be unstable in the final annealing process.
Thus, it is preferable that the cold rolling reduction in final cold rolling is 80 to 95%.
[0110]
When conducting the cold rolling plural times with the intermediate annealing,
15 the reduction in first cold rolling may be 5 to 50%, and the holding in the intermediate
annealing may be conducted in the temperature range of 950 to 1200C for 30 seconds to
30 minutes.
[0111]
The average thickness of the cold rolled steel sheet (thickness after cold rolling)
20 is different from the thickness of the grain oriented electrical steel sheet which includes
the thickness of the tension-insulation coating. For instance, the average thickness of
the cold rolled steel sheet may be 0.10 to 0.50 mm. In the embodiment, even when the
cold rolled steel sheet is the thin sheet whose average thickness is less than 0.22 mm, the
adhesion of the tension-insulation coating is favorably improved. Thus, the average
25 thickness of the cold rolled steel sheet may be 0.20 mm or less.
42
[0112]
In the cold rolling process, the aging treatment may be conducted in order to
favorably improve the magnetic characteristics of the grain oriented electrical steel sheet.
For instance, since the thickness of the steel sheet is reduced by plural passes in the cold
rolling, the steel sheet may 5 be held in the temperature range of 100C or more for 1
minute or more at least once in the interval of plural passes. By the aging treatment, it
is possible to favorably control the primary recrystallized texture in the decarburization
annealing process, and as a result, it is possible to obtain the secondary recrystallized
texture where the {110}<001> orientation is favorably developed in the final annealing
10 process.
[0113]
< Decarburization Annealing Process >
The decarburization annealing process (step S107) is the process of
decarburization-annealing the cold rolled steel sheet after the cold rolling process to
15 obtain the decarburization annealed steel sheet. In the decarburization annealing
process, the cold rolled steel sheet is annealed under predetermined conditions in order to
control the primary recrystallized structure.
[0114]
In the producing method for the grain oriented electrical steel sheet according to
20 the embodiment, the decarburization annealing process includes two stages which are a
heating stage and a holding stage in order to obtain the desired primary recrystallized
structure. The conditions in the heating stage and the holding stage are not particularly
limited, and known conditions may be adopted.
[0115]
25 In the heating stage, the heating rate to reach the decarburization annealing
43
temperature may influence the primary recrystallized texture, and thus, may influence the
alignment degree to the Goss orientation after the secondary recrystallization. In grain
oriented electrical steel sheet without the glass film according to the embodiment, the
alignment degree to the Goss orientation of the base steel sheet considerably influences
the magnetic characteristics after forming 5 the tension-insulation coating and after
magnetic domain refining treatment. Thus, it is preferable to appropriately control the
heating rate of the decarburization annealing as necessary.
[0116]
Specifically, when the cold rolled steel sheet is heated in the heating stage, it is
10 preferable to control the heating rate in the temperature range of 500 to 700C in order to
improve the primary recrystallized texture. In particular, it is more preferable to
separately control the heating rate in the temperature range of 500C or more and less
than 600C and the heating rate in the temperature range of 600C or more and 700C or
less. From the viewpoint of the effect on the oxide layer formed in the decarburization
15 annealing, the favorable range is different between the average heating rate S1 in the
temperature range of 500C or more and less than 600C and the average heating rate S2
in the temperature range of 600C or more and 700C or less. In the temperature range
of 500C or more and less than 600C, the formation of Mn oxides is influenced in
addition to the primary recrystallized texture. In the temperature range of 600C or
20 more and 700C or less, the formation of SiO2 is influenced in addition to the primary
recrystallized texture.
[0117]
In the embodiment, the average heating rate S1 in the temperature range of
500C or more and less than 600C is preferably 300 C/second or more and 1000
44
C/second or less. Moreover, in the temperature range of 600C or more and 700C or
less where SiO2 influencing the reaction to form the glass film (forsterite film) is formed,
it is preferable that the detention time of the steel sheet is shortened. Thus, the average
heating rate S2 in the temperature range of 600C or more and 700C or less is preferably
5 1000 C/second or more and 3000 C/second or less.
[0118]
It is preferable that the average heating rate S2 is faster than the average heating
rate S1. For instance, it is preferable that ratio S2 / S1 is more than 1.0 and 10.0 or less.
[0119]
10 Specifically, it is preferable that the average heating rate S1 and the average
heating rate S2 satisfy all of the following (formula 111) to (formula 113). When all of
the following (formula 111) to (formula 113) are satisfied, it is possible to more
favorably improve the magnetic characteristics (iron loss characteristics) of the grain
oriented electrical steel sheet.
15 [0120]
300 ≤ S1 ≤ 1000 ---(formula 111)
1000 ≤ S2 ≤ 3000 ---(formula 112)
1.0 < S2 / S1 ≤ 10.0 ---(formula 113)
[0121]
20 In regard to the above formula 111, when the average heating rate S1 is less than
300 C/second, the primary recrystallized texture may be affected, and thus, the magnetic
characteristics may deteriorate. On the other hand, when the average heating rate S1 is
more than 1000 C/second, the adhesion of the tension-insulation coating may be
insufficient. The average heating rate S1 in the temperature range of 500C or more
45
and less than 600C is more preferably 350 C/second or more. The average heating
rate S1 is more preferably 900 C/second or less.
[0122]
In regard to the above formula 112, when the average heating rate S2 is less than
1000 C/second, the formation of Si 5 O2 influencing the reaction to form the glass film
may not be sufficiently suppressed. On the other hand, when the average heating rate
S2 is more than 3000 C/second, the decarburization annealing temperature may be
overshot. The average heating rate S2 in the temperature range of 600C or more and
700C or less is more preferably 1200 C/second or more. The average heating rate S2
10 is more preferably 2500 C/second or less.
[0123]
In regard to the above formula 113, when the ratio S2 / S1 of the average heating
rates is 1.0 or less, the magnetic characteristics may deteriorate. On the other hand,
when the ratio S2 / S1 of the average heating rates is more than 10.0, the temperature
15 control may be difficult. The ratio S2 / S1 of the average heating rates is more
preferably 1.2 or more. The ratio S2 / S1 is more preferably 9.0 or less.
[0124]
It is preferable that the cold rolled steel sheet is heated to the decarburization
annealing temperature of 750 to 950C by the above average heating rates.
20 [0125]
Other conditions in the heating stage (for instance, heating atmosphere and the
like) are not particularly limited. The cold rolled steel sheet may be heated in known
moist atmosphere including hydrogen and nitrogen according to common procedure.
[0126]
46
In the decarburization annealing process, following the above heating process,
the cold rolled steel sheet is held in the decarburization annealing temperature as the
holding stage. The conditions in the holding stage are not particularly limited. For
instance, the cold rolled steel sheet may be held in the temperature range of 750 to 950C
for 1 to 5 minutes. Moreover, the atmosphere 5 in the holding stage is not particularly
limited. The holding stage may conducted in known moist atmosphere including
hydrogen and nitrogen according to common procedure.
[0127]
< Final Annealing Process >
10 The final annealing process (step S109) is the process of applying the annealing
separator to the decarburization annealed steel sheet after the decarburization annealing
process and thereafter final-annealing the decarburization annealed steel sheet to obtain
the final annealed steel sheet. In the final annealing, the coiled steel sheet may be held
at a higher temperature for a long time in general. Thus, in order to suppress the seizure
15 between the inside and outside of the coiled steel sheet, the annealing separator is applied
to the decarburization annealed steel sheet and is dried before the final annealing.
[0128]
In the final annealing process, the annealing separator applied to the
decarburization annealed steel sheet is not particularly limited, and known annealing
20 separator may be adopted. The producing method for the grain oriented electrical steel
sheet according to the embodiment is the method for producing the grain oriented
electrical steel sheet without the glass film (forsterite film), and thus, the annealing
separator which does not form the forsterite film may be adopted. In a case where the
annealing separator which forms the forsterite film is adopted, the forsterite film may be
25 removed by grinding or pickling after the final annealing.
47
[0129]
( Annealing Separator which does not form Forsterite Film )
As the annealing separator which does not form the glass film (forsterite film),
the annealing separator which mainly includes MgO and Al2O3 may be utilized. For
instance, it is preferable that the annealing 5 separator includes MgO and Al2O3 of 85
mass% or more in total as percent solid, MgO : Al2O3 which is the mass ratio of MgO
and Al2O3 satisfies 3 : 7 to 7 : 3, and the annealing separator includes the bismuth
chloride of 0.5 to 15 mass% as compared with the total amount of MgO and Al2O3 as
percent solid. The range of the above mass ratio of MgO and Al2O3 and the amount of
10 the above bismuth chloride are determined from the viewpoint of obtaining the base steel
sheet excellent in the surface smoothness without the glass film.
[0130]
In regard to the above mass ratio of MgO and Al2O3, when the amount of MgO
exceeds the above range, the glass film may be formed and remained on the steel sheet
15 surface, and thus, the surface of the base steel sheet may not be smoothed. Moreover, in
regard to the above mass ratio of MgO and Al2O3, when the amount of Al2O3 exceeds the
above range, the seizure of Al2O3 may occur, and thus, the surface of the base steel sheet
may not be smoothed. It is more preferable that MgO : Al2O3 which is the mass ratio of
MgO and Al2O3 satisfies 3.5 : 6.5 to 6.5 : 3.5.
20 [0131]
In a case where the bismuth chloride is included in the annealing separator, the
glass film is easily removed from the steel sheet surface even when the glass film is
formed in the final annealing. When the amount of the bismuth chloride is less than 0.5
mass% as compared with the total amount of MgO and Al2O3, the glass film may be
25 remained. On the other hand, when the amount of the bismuth chloride is more than 15
48
mass% as compared with the total amount of MgO and Al2O3, the effect to suppress the
seizure between the steel sheets may not be obtained as the annealing separator. The
amount of the bismuth chloride is more preferably 3 mass% or more, and more
preferably 7 mass% or less, as compared with the total amount of MgO and Al2O3.
5 [0132]
The type of the bismuth chloride is not particularly limited, and known bismuth
chloride may be adopted. For instance, bismuth oxychloride (BiOCl), bismuth
trichloride (BiCl3), and the like may be used. Moreover, compounds which can form
the bismuth oxychloride by reaction in the annealing separator during the final annealing
10 process may be used. For instance, as the compounds which can form the bismuth
oxychloride during the final annealing, a mixture of bismuth compound and metal
chloride may be used. For instance, as the bismuth compound, bismuth oxide, bismuth
hydroxide, bismuth sulfide, bismuth sulfate, bismuth phosphate, bismuth carbonate,
bismuth nitrate, organobismuth compound, bismuth halide, and the like may be used.
15 For instance, as the metal chloride, iron chloride, cobalt chloride, nickel chloride, and the
like may be used.
[0133]
After applying the above annealing separator which does not form the forsterite
film to the surface of the decarburization annealed steel sheet and drying the annealing
20 separator, the final annealing is conducted. The annealing conditions in the final
annealing process are not particularly limited, and known conditions may be adopted.
For instance, the steel sheet may be held in the temperature range of 1100 to 1300C for
10 to 30 hours. Moreover, furnace atmosphere may be known nitrogen atmosphere or
mixed atmosphere of nitrogen and hydrogen. After the final annealing, it is preferable
25 that the redundant annealing separator is removed from the steel sheet surface by
49
water-washing or pickling.
[0134]
( Annealing Separator which forms Forsterite Film )
As the annealing separator which forms the glass film (forsterite film), the
annealing separator which mainly includes 5 MgO may be utilized. For instance, it is
preferable that the annealing separator includes MgO of 60 mass% or more as percent
solid.
[0135]
After applying the annealing separator to the surface of the decarburization
10 annealed steel sheet and drying the annealing separator, the final annealing is conducted.
The annealing conditions in the final annealing process are not particularly limited, and
known conditions may be adopted. For instance, the steel sheet may be held in the
temperature range of 1100 to 1300C for 10 to 30 hours. Moreover, furnace atmosphere
may be known nitrogen atmosphere or mixed atmosphere of nitrogen and hydrogen.
15 [0136]
In a case where the annealing separator which forms the forsterite film is used,
MgO in the annealing separator reacts with SiO2 of the steel sheet surface during the
final annealing, whereby the forsterite (Mg2SiO4) is formed. Thus, it is preferable that
the forsterite film formed on the surface is removed by grinding or pickling the surface of
20 the final annealed steel sheet after the final annealing. The method for removing the
forsterite film from the surface of the final annealed steel sheet is not particularly limited,
and known grinding or known pickling may be adopted.
[0137]
For instance, in order to remove the forsterite film by pickling, the final
25 annealed steel sheet may be immersed in hydrochloric acid of 20 to 40 mass% at 50 to
50
90C for 1 to 5 minutes, be water-washed, and then be dried. Moreover, the final
annealed steel sheet may be pickled in mixed solution of fluorinated ammonium and
sulfuric acid, be chemically polished in mixed solution of hydrofluoric acid and
hydrogen peroxide solution, be water-washed, and then be dried.
5 [0138]
< Oxidizing Process>
The oxidizing process (step S111) is the process of conducting the washing
treatment, the pickling treatment, and the heat treatment in turn for the final annealed
steel sheet after the final annealing process (final annealed steel sheet without the
10 forsterite film) to obtain the oxidized steel sheet. Specifically, the surface of the final
annealed steel sheet is washed as the washing treatment, the final annealed steel sheet is
pickled using sulfuric acid of 5 to 20 mass% as the pickling treatment, and the final
annealed steel sheet is held in the temperature range of 700 to 850C for 10 to 50 seconds
in the atmosphere where the oxygen concentration is 5 to 21 volume% and the dew point
15 is -10 to 30C as the heat treatment.
[0139]
( Washing Treatment )
The surface of the final annealed steel sheet after the final annealing process is
washed. The method for washing the surface of the final annealed steel sheet is not
20 particularly limited, and known washing method may be adopted. For instance, the
surface of the final annealed steel sheet may be water-washed.
[0140]
( Pickling Treatment )
The final annealed steel sheet after the washing treatment is pickled using the
25 sulfuric acid of 5 to 20 mass%. When the sulfuric acid is less than 5 mass%, the iron
51
oxide layer satisfying the above formula 101 is not formed. Also, when the sulfuric
acid is more than 20 mass%, the iron oxide layer satisfying the above formula 101 is not
formed. The concentration of the sulfuric acid is preferably 6 mass% or more. The
concentration of the sulfuric acid is preferably 15 mass% or less. Moreover, the
temperature of the sulfuric acid used 5 for pickling is not particularly limited, but may be
70C or more for instance.
[0141]
The time for the pickling treatment is not particularly limited. For instance, the
final annealed steel sheet may be passed at general line speed in the pickling bath where
10 the above sulfuric acid is included.
[0142]
( Heat Treatment )
The final annealed steel sheet after the pickling treatment is held in the
temperature range of 700 to 850C for 10 to 50 seconds in the atmosphere where the
15 oxygen concentration is 5 to 21 volume% and the dew point is -10 to 30C. By the heat
treatment, the surface of the final annealed steel sheet after the pickling treatment is
oxidized, and thereby, the iron oxide layer is formed. The oxidized steel sheet after
conducting the washing treatment, the pickling treatment, and the heat treatment satisfies
the above formula 101.
20 [0143]
When the oxygen concentration is less than 5%, when the dew point is less than
-10C, or when the holding temperature is less than 700C, the iron oxide layer satisfying
the above formula 101 is not formed. Also, when the oxygen concentration is more
than 21% or when the dew point is more than 30C, the iron oxide layer satisfying the
52
above formula 101 is not formed. When the holding temperature is more than 850C,
the effect is saturated, and the heating cost increases.
[0144]
When the holding time is less than 10 seconds, the iron oxide layer satisfying
the a 5 bove formula 101 is not formed. On the other hand, when the holding time is more
than 50 seconds, the effect is saturated, and the heating cost increases.
[0145]
The oxygen concentration is preferably 6 volume% or more, and is preferably
21 volume% or less. The dew point is preferably 0C or more, and is preferably 30C
10 or less. The holding temperature is preferably 720C or more, and is preferably 850C
or less. The holding time is preferably 15 seconds or more, and is preferably 50
seconds or less.
[0146]
< Insulation Coating Forming Process >
15 The insulation coating forming process (step S113) is the process of applying the
solution for forming the tension-insulation coating to the surface of the oxidized steel
sheet after the oxidizing process and of baking the solution to obtain the grain oriented
electrical steel sheet. In the insulation coating forming process, the tension-insulation
coating may be formed on one sheet surface or both sheet surfaces of the oxidized steel
20 sheet.
[0147]
Before applying the solution, the surface of the oxidized steel sheet where the
insulation coating is formed may be subjected to optional pretreatment such as
degreasing treatment with alkaline, pickling treatment with hydrochloric acid, sulfuric
25 acid, phosphoric acid, and the like. The pretreatment may not be conducted.
53
[0148]
The conditions for forming the tension-insulation coating are not particularly
limited, and known conditions may be adopted. Moreover, the tension-insulation
coating may mainly include inorganics and may further include organics. For instance,
the tension-insulation c 5 oating may mainly include at least one of metal chromate, metal
phosphate, colloidal silica, Zr compound, Ti compound, and the like as the inorganics,
and fine particles of organic resin may be dispersed in the tension-insulation coating.
From the viewpoint of reducing the environmental loading during producing, the
tension-insulation coating may be produced from starting material such as metal
10 phosphate, coupling agents of Zr or Ti, carbonates thereof, ammonium salts thereof.
[0149]
< Other Processes >
( Flattening Annealing Process )
Following the insulation coating forming process, the flattening annealing may
15 be conducted for straightening. By conducting the flattening annealing for the grain
oriented electrical steel sheet after the insulation coating forming process, it is possible to
favorably reduce the iron loss characteristics.
[0150]
( Magnetic Domain Refining Process)
20 The magnetic domain refining treatment may be conducted for the produced
grain oriented electrical steel sheet. Herein, the magnetic domain refining treatment is
the treatment such that the laser beam which refines the magnetic domain is irradiated to
the surface of the grain oriented electrical steel sheet or the groove is formed on the
surface of the grain oriented electrical steel sheet. By conducting the magnetic domain
25 refining treatment, it is possible to favorably reduce the magnetic characteristics.
54
[0151]
< Forming Method for Insulation Coating of Grain Oriented Electrical Steel Sheet >
Next, a forming method for the insulation coating of the grain oriented electrical
steel sheet according to a preferred embodiment of the present invention is described.
The forming method for the insulation c 5 oating of the grain oriented electrical steel sheet
according to the embodiment includes the insulation coating forming process. In the
insulation coating forming process, the solution for forming the tension-insulation
coating is applied to a steel substrate, and the solution is baked, in order to form the
tension-insulation.
10 [0152]
The above steel substrate includes the base steel sheet and the oxide layer
arranged in contact with the base steel sheet.
[0153]
The base steel sheet includes, as the chemical composition, by mass%,
15 2.5 to 4.0% of Si,
0.05 to 1.0% of Mn,
0 to 0.01% of C,
0 to 0.005% of S+Se,
0 to 0.01% of sol.Al,
20 0 to 0.005% of N,
0 to 0.03% of Bi,
0 to 0.03% of Te,
0 to 0.03% of Pb,
0 to 0.50% of Sb,
25 0 to 0.50% of Sn,
55
0 to 0.50% of Cr,
0 to 1.0% of Cu, and
a balance consisting of Fe and impurities.
[0154]
The oxide layer is the iron oxide la 5 yer. When the iron oxide layer is analyzed
by the fourier transform infrared spectroscopy, when A650 is the absorbance of the
absorption peak detected at 650 cm-1 in the infrared absorption spectrum, and when A1250
is the absorbance of the absorption peak detected at 1250 cm-1 in the infrared absorption
spectrum,
10 the A650 and the A1250 satisfy 0.2 ≤ A650 / A1250 ≤ 5.0.
[0155]
In the insulation coating forming process, the solution for forming the
tension-insulation coating is applied to the iron oxide layer of the steel substrate, and the
solution is baked.
15 [0156]
It is preferable that the average thickness of the iron oxide layer is 200 to 500
nm.
[0157]
The forming method for the insulation coating of the grain oriented electrical
20 steel sheet according to the embodiment is substantially the same as the insulation
coating forming process in the producing method for the grain oriented electrical steel
sheet described above. For instance, the steel substrate in the forming method for the
insulation coating of the grain oriented electrical steel sheet according to the embodiment
corresponds to the oxidized steel sheet in the producing method for the grain oriented
25 electrical steel sheet described above. Moreover, the steel substrate in the forming
56
method for the insulation coating of the grain oriented electrical steel sheet according to
the embodiment corresponds to the base steel sheet 11 and the iron oxide layer 13 shown
in Figure 1A and Figure 1B of the grain oriented electrical steel sheet described above.
Thus, the detail explanation for the forming method for the insulation coating of the grain
oriented electrical st 5 eel sheet according to the embodiment is omitted.
Examples
[0158]
Hereinafter, the effects of an aspect of the present invention are described in
10 detail with reference to the following examples. However, the condition in the
examples is an example condition employed to confirm the operability 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
15 present invention.
[0159]
(Example 1)
A steel slab A (steel piece A) and a steel slab B (steel piece B) were heated to
1350C, and then were hot-rolled to obtain the hot rolled steel sheets having the average
20 thickness of 2.3 mm, herein the steel slab A including 0.082 mass% of C, 3.3 mass% of
Si, 0.082 mass% of Mn, 0.023 mass% of S, 0.025 mass% of sol.Al, 0.008 mass% of N,
and the balance consisting of Fe and impurities, and the steel slab B including. 0.081
mass% of C, 3.3 mass% of Si, 0.083 mass% of Mn, 0.022 mass% of S, 0.025 mass% of
sol.Al, 0.008 mass% of N, 0.0025 mass% of Bi, and the balance consisting of Fe and
25 impurities.
57
[0160]
The obtained hot rolled steel sheets were annealed at 1100C for 120 seconds,
and then were pickled. The steel sheets after pickling were cold-rolled to obtain the
cold rolled steel sheets having the average thickness of 0.23 mm.
5 [0161]
The obtained cold rolled steel sheets were decarburization-annealed. In the
decarburization annealing, the cold rolled steel sheets were heated under the conditions
such that the average heating rate S1 in the heating stage of 500C or more and less than
600C was 400 C/second and the average heating rate S2 in the heating stage of 600C
10 or more and 700C or less was 1100 C/second (S2 ÷ S1 = 2.75), and then were held at
850C for 120 seconds.
[0162]
Subsequently, the annealing separator was applied and dried. In the annealing
separator, MgO and Al2O3 of 95 mass% in total as percent solid were included, the
15 mixing ratio of MgO and Al2O3 was 50% : 50% in mass% (1 :1 as mass ratio), and
BiOCl of 5 mass% as compared with the total amount of MgO and Al2O3 was included.
Thereafter, the final annealing was conducted at 1200C for 20 hours.
[0163]
The redundant annealing separator is removed by water-washing from the
20 obtained final annealed steel sheet. In any steel sheets, the glass film (forsterite film)
was not formed when confirmed by X-ray diffraction method.
[0164]
The steel sheets after removing the redundant annealing separator by
water-washing were subjected to the pickling treatment using the sulfuric acid whose
58
temperature was 70C and whose concentration was shown in the following Table 1.
Thereafter, the heat treatment was conducted by changing oxygen concentration, dew
point, temperature, and time.
[0165]
5 [Table 1]
59
[0166]
The aqueous solution which mainly included aluminum phosphate and colloidal
silica was applied to the steel sheets after the oxidizing process, the solution was baked at
850C for 1 minute, and thereby, the tension-5 insulation coating whose coating weight
60
was 4.5 g/m2 was formed on the surface of the test piece. The laser beam was irradiated
on the test piece in order to refine the magnetic domain.
[0167]
The base steel sheets of the grain oriented electrical steel sheets were chemically
analyzed on the basis of the above method. The 5 steel sheets made from the steel slab A
included, as the chemical composition, by mass%, 0.002% or less of C, 3.30% of Si,
0.082% Mn, 0.005% or less of S (0.005% or less of S + Se), 0.005% or less of sol.Al,
0.005% or less of N, and the balance consisting of Fe and impurities. The steel sheets
made from the steel slab B included, as the chemical composition, by mass%, 0.002% or
10 less of C, 3.30% of Si, 0.083% Mn, 0.005% or less of S (0.005% or less of S + Se),
0.005% or less of sol.Al, 0.005% or less of N, 0.0001 mass% of Bi, and the balance
consisting of Fe and impurities.
[0168]
< Evaluation >
15 The fourier transform infrared spectroscopy, the average thickness of the iron
oxide layer, the magnetic characteristics, and the adhesion of the tension-insulation
coating were evaluated. The evaluation methods were as follows.
[0169]
( Magnetic Characteristics )
20 The magnetic flux density B8 in the rolling direction (unit : T) (magnetic flux
density in 800A/m) and the iron loss W17/50 (unit : W/kg) (iron loss when excited to
1.7T at 50Hz) were evaluated on the basis of the method regulated by JIS C 2556: 2015,
using a single test piece with a length of 300 mm and a width of 60 mm. When the
magnetic flux density B8 was 1.90 T or more, it was judged to as acceptable.
25 [0170]
61
( Fourier Transform Infrared Spectroscopy )
The steel sheet surface after oxidizing and before forming the tension-insulation
coating was analyzed by the reflection absorption spectroscopy of the fourier transform
infrared spectroscopy, using Frontier of PERKIN ELMER Frontier. Form the obtained
infrared absorption spectrum, the absorbance ratio A650 5 / A1250 was calculated on the basis
of the above method. When the absorbance ratio A650 / A1250 was 0.2 to 5.0, it was
judged to as acceptable.
[0171]
( Adhesion of Tension-Insulation Coating )
10 The test piece whose longitudinal direction corresponded to the rolling direction
was taken from the obtained grain oriented electrical steel sheets, and the bend tests of
bending diameter ϕ 10 and bending diameter ϕ 20 were conducted using cylindrical
mandrel bend tester. The surface of the test piece after the bend tests was observed, the
fraction of the area where the insulation coating was remained without delamination in
15 the area of the bended part (fraction of remained coating) was calculated, and thereby, the
adhesion of the tension-insulation coating was evaluated. When the fraction of
remained coating was grade A, it was judged to as acceptable.
[0172]
Grade A : the fraction of remained coating is 90% or more.
20 Grade B : the fraction of remained coating is 70% or more and less than 90%. .
Grade C : the fraction of remained coating is less than 70%.
[0173]
( Average Thickness of Iron Oxide Layer )
The test piece for XPS was taken from the obtained grain oriented electrical
25 steel sheets, and the average thickness of the iron oxide layer was measured on the basis
62
of the above method.
[0174]
The obtained results are summarized in the following Table 2.
[0175]
5 [Table 2]
63
[0176]
As clearly shown in the Tables 1 & 2, since the oxidizing conditions were
satisfied in the test numbers 1-2, 1-3, 1-5, 1-6, 1-8, 1-15, 1-16, 1-18, 1-19, and 1-21, the
absorbance ratio A650 / A1250 was satisfied, and both magnetic characteristics and
adhesion of the tension-5 insulation coating were excellent.
Moreover, since the chemical compositions of the steel slabs were favorable in
the test numbers 1-15, 1-16, 1-18, 1-19, and 1-21 among the above test numbers, the
magnetic characteristics were further excellent.
[0177]
10 On the other hand,
since the holding time for oxidizing was shorter in the test number 1-1 and the
holding temperature for oxidizing was lower in the test number 1-4, the absorbance ratio
A650 / A1250 was not satisfied, and the adhesion of the tension-insulation coating was
inferior.
15 Since the concentration of sulfuric acid was lower in the test number 1-7 and the
oxygen concentration for oxidizing was higher in the test number 1-9, the adhesion of the
tension-insulation coating was inferior.
Since the dew point for oxidizing was lower in the test number 1-10 and the
oxygen concentration for oxidizing was lower in the test number 1-11, the adhesion of
20 the tension-insulation coating was inferior.
Since the dew point for oxidizing was higher in the test number 1-12, the
adhesion of the tension-insulation coating was inferior.
Since the concentration for pickling was higher and the temperature for
oxidizing was lower in the test number 1-13, the adhesion of the tension-insulation
25 coating was inferior.
64
Since the holding time for oxidizing was shorter in the test number 1-14 and the
holding temperature for oxidizing was lower in the test number 1-17, the absorbance
ratio A650 / A1250 was not satisfied, and the adhesion of the tension-insulation coating was
inferior.
Since the concentration o 5 f sulfuric acid was lower in the test number 1-20 and
the oxygen concentration for oxidizing was higher in the test number 1-22, the adhesion
of the tension-insulation coating was inferior.
Since the dew point for oxidizing was lower in the test number 1-23 and the
oxygen concentration for oxidizing was lower in the test number 1-24, the adhesion of
10 the tension-insulation coating was inferior.
Since the dew point for oxidizing was higher in the test number 1-25, the
adhesion of the tension-insulation coating was inferior.
Since the concentration for pickling was higher and the temperature for
oxidizing was lower in the test number 1-26, the adhesion of the tension-insulation
15 coating was inferior.
[0178]
(Example 2)
Steel slabs (steel pieces) with chemical compositions shown in the following
Table 3 were heated to 1380C, and then were hot-rolled to obtain the hot rolled steel
20 sheets having the average thickness of 2.3 mm. Some steels were cracked, and thus
could not be subjected to subsequent processes.
[0179]
[Table 3]
65
[0180]
The hot rolled steel sheets which could be subjected to subsequent processes
were annealed at 1120C for 120 seconds, and then were pickled. The steel sheets after
pickling were cold-rolled to obtain t 5 he cold rolled steel sheets having the average
thickness of 0.23 mm. Some steels were cracked during cold rolling, and thus could not
be subjected to subsequent processes.
[0181]
The steel sheets which could be subjected to subsequent processes were
10 decarburization-annealed. In the decarburization annealing, the cold rolled steel sheets
66
were heated under the conditions such that the average heating rate S1 in the heating
stage of 500C or more and less than 600C was 900 C/second and the average heating
rate S2 in the heating stage of 600C or more and 700C or less was 1600 C/second (S2
÷ S1 = 1.78), and then were held at 850C for 150 seconds.
5 [0182]
Subsequently, the annealing separator was applied and dried. In the annealing
separator, MgO and Al2O3 of 94 mass% in total as percent solid were included, the
mixing ratio of MgO and Al2O3 was 50% : 50% in mass% (1 :1 as mass ratio), and
BiOCl of 6 mass% as compared with the total amount of MgO and Al2O3 was included.
10 Thereafter, the final annealing was conducted at 1200C for 20 hours.
[0183]
The redundant annealing separator is removed by water-washing from the
obtained final annealed steel sheet. In any steel sheets, the glass film (forsterite film)
was not formed when confirmed by X-ray diffraction method.
15 [0184]
The steel sheets after removing the redundant annealing separator by
water-washing were subjected to the pickling treatment using the sulfuric acid whose
temperature was 70C and whose concentration was 10%. Thereafter, the heat
treatment was conducted by holding under conditions such as 21% of the oxygen
20 concentration, 10C of the dew point, 800C of the temperature, and 20 seconds of time.
Herein, in the test number 2-24 shown below, the heat treatment was not conducted, and
the test number 2-24 was as pickled.
[0185]
Subsequently, the aqueous solution which mainly included aluminum phosphate
67
and colloidal silica was applied, the solution was baked at 850C for 1 minute, and
thereby, the tension-insulation coating whose coating weight was 4.5 g/m2 was formed on
the surface of the test piece.
[0186]
The base steel sheets of the grain oriented e 5 lectrical steel sheets were chemically
analyzed on the basis of the above method. The chemical compositions are shown in
Table 4. In regard to Table 3 and Table 4, the element whose value is blanc in the tables
indicates the element in which the purposeful control is not conducted for the amount
thereof during production.
10 [0187]
[Table 4]
[0188]
68
< Evaluation >
The fourier transform infrared spectroscopy, the average thickness of the iron
oxide layer, the magnetic characteristics, and the adhesion of the tension-insulation
coating were evaluated. The evaluation methods for the fourier transform infrared
spectroscopy, the average 5 thickness of the iron oxide layer, and the adhesion of the
tension-insulation coating were the same as those in the above Example 1. The
magnetic characteristics were evaluated as follows.
[0189]
( Magnetic Characteristics )
10 The magnetic characteristics in the rolling direction were evaluated on the basis
of the method regulated by JIS C 2556: 2015, using the single test piece with the length
of 300 mm and the width of 60 mm. When the magnetic flux density B8 was 1.90 T or
more, it was judged to as acceptable. For the steel sheets whose magnetic flux density
B8 was acceptable, the laser beam was irradiated in order to refine the magnetic domain.
15 The iron loss W17/50 of the steel sheets for which the laser beam was irradiated was
evaluated.
[0190]
The obtained results are summarized in the following Table 5.
[0191]
20 [Table 5]
69
[0192]
As clearly shown in the Tables 3 to 5, since the chemical compositions of the
base steel sheets were satisfied in the test numbers 2-1 to 2-11, the absorbance ratio A650 /
A1250 was satisfied, and both magnetic 5 characteristics and adhesion of the
tension-insulation coating were excellent.
Moreover, since the chemical compositions of the steel slabs were favorable in
the test numbers 2-3 to 2-11 among the above test numbers, the magnetic characteristics
were further excellent.
70
[0193]
On the other hand,
since the Si content was excessive in the test number 2-12, the steel sheet was
fractured during cold rolling.
Since 5 the Si content was insufficient in the test number 2-13, the magnetic
characteristics were inferior.
Since the C content was insufficient in the test number 2-14 and the C content
was excessive in the test number 2-15, the magnetic characteristics were inferior.
Since the sol.Al content was insufficient in the test number 2-16, the magnetic
10 characteristics were inferior.
Since the sol.Al content was excessive in the test number 2-17, the steel sheet
was fractured during cold rolling.
Since the Mn content was insufficient in the test number 2-18 and the Mn
content was excessive in the test number 2-19, the magnetic characteristics were inferior.
15 Since the total amount of S and Se was insufficient in the test number 2-20, the
magnetic characteristics were inferior.
Since the total amount of S and Se was excessive in the test number 2-21, the
steel sheet was fractured during hot rolling.
Since the N content was excessive in the test number 2-22, the steel sheet was
20 fractured during cold rolling.
Since the N content was insufficient in the test number 2-23, the magnetic
characteristics were inferior.
Since the heat treatment in the oxidizing process was not conducted in the test
number 2-24, the adhesion of the tension-insulation coating was inferior. In the test
25 number 2-24, the coating just after being baked had been delaminated even in the frat
71
part except for the bended part in addition to the bended part.
[0194]
(Example 3)
Steel slabs (steel pieces) with chemical compositions shown in the following
Table 6 were heated to 1380C, and then were 5 hot-rolled to obtain the hot rolled steel
sheets having the average thickness of 2.3 mm.
[0195]
[Table 6]
10 [0196]
The hot rolled steel sheets were annealed at 1120C for 120 seconds, and then
were pickled. The steel sheets after pickling were cold-rolled to obtain the cold rolled
steel sheets having the average thickness of 0.23 mm.
[0197]
15 The obtained cold rolled steel sheets were decarburization-annealed. In the
decarburization annealing, the cold rolled steel sheets were heated by changing the
average heating rate S1 (C/second) in the heating stage of 500C or more and less than
72
600C and the average heating rate S2 (C/second) in the heating stage of 600C or more
and 700C or less as shown in the following Table 7, and then were held at 850C for 150
seconds.
[0198]
5 [Table 7]
[0199]
Subsequently, the annealing separator was applied and dried. In the annealing
separator, MgO and Al2O3 of 94 mass% in total as percent solid were included, the
10 mixing ratio of MgO and Al2O3 was 50% : 50% in mass% (1 :1 as mass ratio), and
BiOCl of 6 mass% as compared with the total amount of MgO and Al2O3 was included.
Thereafter, the final annealing was conducted at 1200C for 20 hours.
73
[0200]
The redundant annealing separator is removed by water-washing from the
obtained final annealed steel sheet. In any steel sheets, the glass film (forsterite film)
was not formed when confirmed by X-ray diffraction method.
5 [0201]
The steel sheets after removing the redundant annealing separator by
water-washing were subjected to the pickling treatment using the sulfuric acid whose
temperature was 85C and whose concentration was 8%. Thereafter, for the test
numbers 3-1 to 3-12 and 3-16, the heat treatment was conducted by holding under
10 conditions such as 21% of the oxygen concentration, 10C of the dew point, 800C of the
temperature, and 30 seconds of time. Moreover, for the test number 3-13, the heat
treatment was conducted by holding under conditions such as 1% of the oxygen
concentration, 10C of the dew point, 700C of the temperature, and 5 seconds of time.
Moreover, for the test numbers 3-14 and 3-15, the heat treatment was conducted by
15 holding under conditions such as 21% of the oxygen concentration, 10C of the dew
point, 650C of the temperature, and 5 seconds of time.
[0202]
The aqueous solution which mainly included aluminum phosphate and colloidal
silica was applied to the steel sheets after the oxidizing process, the solution was baked at
20 850C for 1 minute, and thereby, the tension-insulation coating whose coating weight
was 4.5 g/m2 was formed on the surface of the test piece. The laser beam was irradiated
on the test piece in order to refine the magnetic domain.
[0203]
The base steel sheets of the grain oriented electrical steel sheets were chemically
74
analyzed on the basis of the above method. Any steel sheets included, as the chemical
composition, by mass%, 0.002% or less of C, 0.005% or less of S (0.005% or less of S +
Se), 0.005% or less of sol.Al, and 0.005% or less of N. Moreover, the Si content, the
Mn content, and the Pb content of any steel sheets were the same as those of the steel
slabs (steel pieces). Moreover, in any 5 steel sheets including Bi or Te, the Bi content was
0.0001% and the Te content was 0.0001%. Moreover, in any steel sheets, the balance of
the above elements consisted of Fe and impurities.
[0204]
< Evaluation >
10 The fourier transform infrared spectroscopy, the average thickness of the iron
oxide layer, the magnetic characteristics, and the adhesion of the tension-insulation
coating were evaluated. The evaluation methods were the same as those in the above
Example 1.
[0205]
15 The obtained results are summarized in the following Table 8.
[0206]
[Table 8]
75
[0207]
As clearly shown in the Tables 6 to 8, since the chemical compositions of the
base steel sheets were satisfied and the production conditions were satisfied in the test
numbers 3-1 to 3-12 and 3-16, both magnetic 5 characteristics and adhesion of the
tension-insulation coating were excellent.
Moreover, since the oxidizing conditions were favorable in the test numbers 3-1
to 3-3 among the above test numbers although the steel number and the heating rate of
the decarburization annealing in the test numbers 3-1 to 3-3 were the same as those in the
10 test numbers 3-13 to 3-15, both magnetic characteristics and adhesion of the
tension-insulation coating were excellent as compared with those in the test numbers
76
3-13 to 3-15.
Moreover, since the chemical compositions of the steel slabs were favorable in
the test numbers 3-4 to 3-12 among the above test numbers, the magnetic characteristics
were further excellent.
In particular, since the average heating rate S1 a 5 nd the average heating rate S2 in
the heating stage of the decarburization annealing were favorable in addition to the steel
slabs having the favorable chemical compositions in the test numbers 3-6 to 3-12 among
the above test numbers, the magnetic characteristics were further excellent.
[0208]
10 On the other hand, since the conditions for the oxidizing process were not
favorable in the test numbers 3-13 to 3-15, the adhesion of the tension-insulation coating
was inferior. The coating thereof had been delaminated before conducting the bend test.
[0209]
(Example 4)
15 Steel slabs (steel pieces) with chemical compositions shown in the following
Table 9 were heated to 1350C, and then were hot-rolled to obtain the hot rolled steel
sheets having the average thickness of 2.3 mm.
[0210]
[Table 9]
77
[0211]
The obtained hot rolled steel sheets were annealed at 1100C for 120 seconds,
and then were pickled. The steel sheets after pickling were cold-rolled to obtain the
cold rolled steel sheets having 5 the average thickness of 0.23 mm.
[0212]
The obtained cold rolled steel sheets were decarburization-annealed. In the
decarburization annealing, the cold rolled steel sheets were heated under the conditions
such that the average heating rate S1 in the heating stage of 500C or more and less than
10 600C was 400 C/second and the average heating rate S2 in the heating stage of 600C
or more and 700C or less was 1100 C/second (S2 ÷ S1 = 2.75), and then were held at
850C for 120 seconds.
[0213]
78
Subsequently, the final annealing was conducted under conditions shown in the
following Table 10. In the Table 10, the amount of main materials in the annealing
separator is shown as percent solid. Moreover, the amount of the bismuth chloride is
shown as the amount compared with the total amount of MgO and Al2O3.
5 [0214]
[Table 10]
[0215]
The redundant annealing separator is removed by water-washing from the
10 obtained final annealed steel sheet. In any steel sheets except for the test numbers 4-3
and 4-4, the glass film (forsterite film) was not formed when confirmed by X-ray
diffraction method. In the steel sheets of the test numbers 4-3 and 4-4, the forsterite
79
film formed on the surface was removed by grinding or pickling the surface of the final
annealed steel sheet after the final annealing. Thereafter, in any steel sheets, the glass
film (forsterite film) was not formed when confirmed by X-ray diffraction method.
[0216]
The steel sheets after 5 removing the redundant annealing separator by
water-washing (the steel sheets after removing the glass film in the test numbers 4-3 and
4-4) were subjected to the pickling treatment under conditions shown in the following
Table 11. Herein, in the test numbers 4-1 and 4-2 shown in the Table 11, the pickling
treatment in the oxidizing process was not conducted, and the oxygen concentration in
10 the atmosphere during the heat treatment was 0 volume% (25 volume% of nitrogen and
75 volume% of hydrogen).
[0217]
[Table 11]
80
[0218]
The aqueous solution which mainly included aluminum phosphate and colloidal
silica was applied to the steel sheets after the oxidizing process, the solution was baked at
850C for 1 minute e 5 xcept for the test numbers 4-1 and 4-2, the solution was baked at
850C for 30 minutes in the test numbers 4-1 and 4-2, and thereby, the tension-insulation
coating whose coating weight was 4.5 g/m2 was formed on the surface of the test piece.
The laser beam was irradiated on the test piece in order to refine the magnetic domain.
[0219]
10 The base steel sheets of the grain oriented electrical steel sheets were chemically
81
analyzed on the basis of the above method. The chemical compositions are shown in
Table 12. In regard to Table 9 and Table 12, the element whose value is blanc in the
tables indicates the element in which the purposeful control is not conducted for the
amount thereof during production.
5 [0220]
[Table 12]
[0221]
< Evaluation >
10 The fourier transform infrared spectroscopy, the average thickness of the iron
oxide layer, the magnetic characteristics, and the adhesion of the tension-insulation
coating were evaluated. The evaluation methods were the same as those in the above
Example 1.
[0222]
82
The obtained results are summarized in the following Table 13.
[0223]
[Table 13]
5 [0224]
As clearly shown in the Tables 9 to 13, since the chemical compositions of the
base steel sheets were satisfied and the production conditions were satisfied in the test
numbers 4-3 to 4-14, both magnetic characteristics and adhesion of the tension-insulation
coating were excellent. On the other hand, since the production conditions were not
10 favorable in the test numbers 4-1 and 4-2, the adhesion of the tension-insulation coating
was inferior.
Reference Signs List
83
[0225]
10 Grain oriented electrical steel sheet
11 Base steel sheet
13 Iron oxide layer
5 15 Tension-insulation coating

CLAIMS

1. A grain oriented electrical steel sheet without a forsterite film characterized in
that
the gr 5 ain oriented electrical steel sheet comprises:
a base steel sheet;
an oxide layer arranged in contact with the base steel sheet; and
a tension-insulation coating arranged in contact with the oxide layer,
wherein the base steel sheet includes, as a chemical composition, by mass%,
10 2.5 to 4.0% of Si,
0.05 to 1.00% of Mn,
0 to 0.01% of C,
0 to 0.005% of S+Se,
0 to 0.01% of sol.Al,
15 0 to 0.005% of N,
0 to 0.03% of Bi,
0 to 0.03% of Te,
0 to 0.03% of Pb,
0 to 0.50% of Sb,
20 0 to 0.50% of Sn,
0 to 0.50% of Cr,
0 to 1.0% of Cu, and
a balance consisting of Fe and impurities,
the oxide layer is an iron oxide layer,
25 when the iron oxide layer is analyzed by a fourier transform infrared
85
spectroscopy, when A650 is an absorbance of an absorption peak detected at 650 cm-1 in
an infrared absorption spectrum, and when A1250 is an absorbance of an absorption peak
detected at 1250 cm-1 in the infrared absorption spectrum,
the A650 and the A1250 satisfy 0.2 ≤ A650 / A1250 ≤ 5.0, and
a magnetic flux density B8 in a r 5 olling direction of the grain oriented electrical
steel sheet is 1.90 T or more.
2. The grain oriented electrical steel sheet according to claim 1,
wherein an average thickness of the iron oxide layer is 200 to 500 nm.
10
3. A forming method for an insulation coating of a grain oriented electrical steel
sheet without a forsterite film characterized in that
the forming method for the insulation coating includes an insulation coating
forming process of forming a tension-insulation coating on a steel substrate,
15 wherein, in the insulation coating forming process,
a solution for forming the tension-insulation coating is applied to an oxide layer
of the steel substrate and the solution is baked,
wherein the steel substrate includes a base steel sheet and the oxide layer
arranged in contact with the base steel sheet,
20 the base steel sheet includes, as a chemical composition, by mass%,
2.5 to 4.0% of Si,
0.05 to 1.00% of Mn,
0 to 0.01% of C,
0 to 0.005% of S+Se,
25 0 to 0.01% of sol.Al,
86
0 to 0.005% of N,
0 to 0.03% of Bi,
0 to 0.03% of Te,
0 to 0.03% of Pb,
5 0 to 0.50% of Sb,
0 to 0.50% of Sn,
0 to 0.50% of Cr,
0 to 1.0% of Cu, and
a balance consisting of Fe and impurities,
10 the oxide layer is an iron oxide layer, and
when the iron oxide layer is analyzed by a fourier transform infrared
spectroscopy, when A650 is an absorbance of an absorption peak detected at 650 cm-1 in
an infrared absorption spectrum, and when A1250 is an absorbance of an absorption peak
detected at 1250 cm-1 in the infrared absorption spectrum,
15 the A650 and the A1250 satisfy 0.2 ≤ A650 / A1250 ≤ 5.0.
4. The forming method for the insulation coating of the grain oriented electrical
steel sheet according to claim 3,
wherein an average thickness of the iron oxide layer is 200 to 500 nm.
20
5. A producing method for a grain oriented electrical steel sheet without a forsterite
film characterized in that
the producing method includes
a hot rolling process of heating and thereafter hot-rolling a steel piece to obtain a
25 hot rolled steel sheet,
87
a hot band annealing process of optionally annealing the hot rolled steel sheet to
obtain a hot band annealed steel sheet,
a cold rolling process of cold-rolling the hot rolled steel sheet or the hot band
annealed steel sheet by cold-rolling once or by cold-rolling plural times with an
intermediate 5 annealing to obtain a cold rolled steel sheet,
a decarburization annealing process of decarburization-annealing the cold rolled
steel sheet to obtain a decarburization annealed steel sheet,
a final annealing process of applying an annealing separator to the
decarburization annealed steel sheet and thereafter final-annealing the decarburization
10 annealed steel sheet to obtain a final annealed steel sheet,
an oxidizing process of conducting a washing treatment, a pickling treatment,
and a heat treatment in turn for the final annealed steel sheet to obtain an oxidized steel
sheet,
an insulation coating forming process of applying a solution for forming a
15 tension-insulation coating to a surface of the oxidized steel sheet and of baking the
solution,
wherein, in the hot rolling process,
the steel piece includes, as a chemical composition, by mass%,
2.5 to 4.0% of Si,
20 0.05 to 1.00% of Mn,
0.02 to 0.10% of C,
0.005 to 0.080% of S+Se,
0.010 to 0.07% of sol.Al,
0.005 to 0.020% of N,
25 0 to 0.03% of Bi,
88
0 to 0.03% of Te,
0 to 0.03% of Pb,
0 to 0.50% of Sb,
0 to 0.50% of Sn,
5 0 to 0.50% of Cr,
0 to 1.0% of Cu, and
a balance consisting of Fe and impurities, and
wherein, in the oxidizing process,
as the washing treatment, a surface of the final annealed steel sheet is washed,
10 as the pickling treatment, the final annealed steel sheet is pickled using a sulfuric
acid of 5 to 20 mass%, and
as the heat treatment, the final annealed steel sheet is held in a temperature range
of 700 to 850C for 10 to 50 seconds in an atmosphere where an oxygen concentration is
5 to 21 volume% and a dew point is -10 to 30C.
15
6. The producing method for the grain oriented electrical steel sheet according to
claim 5,
wherein, in the final annealing process,
the annealing separator includes MgO and Al2O3 of 85 mass% or more in total,
20 MgO : Al2O3 which is a mass ratio of MgO and Al2O3 satisfies 3 : 7 to 7 : 3, and
the annealing separator includes a bismuth chloride of 0.5 to 15 mass% as
compared with a total amount of MgO and Al2O3.
7. The producing method for the grain oriented electrical steel sheet according to
25 claim 5,
89
wherein, in the final annealing process,
the annealing separator includes MgO of 60 mass% or more, and
a forsterite film formed on a surface is removed by grinding or pickling the
surface of the final annealed steel sheet after final annealing.
5
8. The producing method for the grain oriented electrical steel sheet according to
any one of claims 5 to 7,
wherein, in the decarburization annealing process,
when S1 is an average heating rate in units of C/second in a temperature range
of 500C or more and less than 60010 C during raising a temperature of the cold rolled
steel sheet and when S2 is an average heating rate in units of C/second in a temperature
range of 600C or more and 700C or less during raising the temperature of the cold
rolled steel sheet,
the S1 and the S2 satisfy 300 ≤ S1 ≤ 1000, 1000 ≤ S2 ≤ 3000, and 1.0 < S2 / S1
15 ≤ 10.0.
9. The producing method for the grain oriented electrical steel sheet according to
any one of claims 5 to 8,
wherein, in the hot rolling process,
20 the steel piece includes, as the chemical composition, by mass%, at least one
selected from a group consisting of
0.0005 to 0.03% of Bi,
0.0005 to 0.03% of Te, and
0.0005 to 0.03% of Pb.