[0001]The present invention relates to a grain-oriented electrical steel sheet that has a
low iron loss and is excellent in terms of the adhesion of an insulation coating and a
method for manufacturing the same.
10 Priority is claimed on Japanese Patent Application No. 2019-5199, filed January
16, 2019, and Japanese Patent Application No. 2019-4873, filed January 16, 2019, the
contents of which are incorporated herein by reference.
[Background Art]
[0002]
15 Grain-oriented electrical steel sheets are used as iron core materials of
transformers and the like and are required to have magnetic properties represented by a
high magnetic flux density and a low iron loss.
[0003]
In order to ensure magnetic properties in grain-oriented electrical steel sheets,
20 crystal orientations in base steel sheets are controlled to, for example, an orientation
(Goss orientation) in which a {110} plane is aligned parallel to the sheet surface and a
<100> axis is aligned to a rolling direction. In order to increase the accumulation of the
Goss orientation, secondary recrystallization processes in which AlN, MnS, or the like is
used as an inhibitor are being widely used.
25 [0004]
2
In order to reduce the iron losses of grain-oriented electrical steel sheets, a
coating is formed on a surface of a base steel sheet. This coating is formed to apply
tension to the base steel sheet to reduce the iron loss of the steel sheet as a single sheet
and also to ensure an electrical insulating property between grain-oriented electrical steel
sheets at the time of using a 5 laminate of the grain-oriented electrical steel sheets and
thereby reduce iron losses as iron cores.
[0005]
As a grain-oriented electrical steel sheet having a coating formed on a surface of
a base steel sheet, for example, there is a grain-oriented electrical steel sheet in which a
10 final-annealed film mainly containing forsterite (Mg2SiO4) is formed on a surface of a
base steel sheet and an insulation coating is formed on the surface of the final-annealed
film. These coatings (final-annealed film and insulation coating) each have a function
of imparting an insulating property and a function of applying tension to the base steel
sheet.
15 [0006]
The final-annealed film is formed by, for example, a reaction between an
annealing separator mainly containing magnesium (MgO) and the base steel sheet
occurring during a heat treatment in which the annealing separator and the base steel
sheet are held within a temperature range of 600ºC to 1200ºC for 30 hours or longer in
20 final annealing for causing secondary recrystallization in the base steel sheet. In
addition, the insulation coating is formed by, for example, applying a coating solution
containing phosphoric acid or a phosphate, colloidal silica, and chromic anhydride or a
chromate to the final-annealed base steel sheet and baking and drying the coating
solution within a temperature range of 300ºC to 950ºC for 10 seconds or longer.
25 [0007]
3
In order for coatings to exhibit desired tension and a desired insulating property,
these coatings need to remain stuck to the base steel sheet and to have strong adhesion to
the base steel sheet.
[0008]
The adhesion between coatings a 5 nd steel sheets is ensured mainly by an
anchoring effect attributed to unevenness in the interface between a base steel sheet and a
final-annealed film. However, this unevenness in the interface also serves as an
obstacle to domain wall motion occurring during the magnetization of grain-oriented
electrical steel sheets and thus also serves as a cause for hindering the iron loss reduction
10 action. Therefore, in order to reduce the iron losses of grain-oriented electrical steel
sheets in the absence of final-annealed film, techniques as described below, which are
intended to ensure the adhesion of insulation coatings in a state in which the abovedescribed
interface is smoothed, have been performed.
[0009]
15 For example, in order to enhance the adhesion of an insulation coating to a
smoothed surface of a base steel sheet, the formation of an intermediate layer (base
coating) between the base steel sheet and the insulation coating is proposed. Patent
Document 1 discloses a method for forming an intermediate layer by applying an
aqueous solution of a phosphate or an alkaline metal silicate. Patent Documents 2 to 4
20 disclose methods for forming an external oxidation-type silicon oxide film as an
intermediate layer by performing a heat treatment on a base steel sheet at an
appropriately controlled temperature in an appropriately controlled atmosphere for
several tens of seconds to several minutes.
[0010]
25 These external oxidation-type silicon oxide films exhibit a certain degree of
4
effect on the improvement of the adhesion of the insulation coatings and the reduction of
iron losses by the smoothing of unevenness in the interface between the base steel sheet
and the coating. However, the effect was not sufficient in terms of practical use
regarding, particularly, the adhesion of insulation coatings, and thus additional technical
5 developments have been underway.
[0011]
For example, Patent Document 5 discloses a grain-oriented silicon steel sheet in
which a base steel sheet is manufactured by intentionally preventing the generation of an
inorganic mineral coating of forsterite and then a tension-applying insulation coating is
10 formed. In this grain-oriented silicon steel sheet, a film-like externally oxidized film
mainly containing silica having an average film thickness of 2 nm or more and 500 nm or
less is provided in the interface between the tension-applying insulation coating and the
steel sheet. Additionally, Patent Document 5 discloses a grain-oriented silicon steel
sheet that is excellent in terms of the coating adhesion of a tension-applying insulation
15 coating and has an externally oxidized granular oxide mainly containing silica that is
generated in a form of penetrating the film thickness of the film-like externally oxidized
film, is present in a form of intruding into the tension-applying insulation coating, and
has a cross-sectional area rate of 2% or more of the film-like externally oxidized film.
[Citation List]
20 [Patent Document]
[0012]
[Patent Document 1]
Japanese Unexamined Patent Application, First Publication No. H05-279747
[Patent Document 2]
25 Japanese Unexamined Patent Application, First Publication No. H06-184762
5
[Patent Document 3]
Japanese Unexamined Patent Application, First Publication No. H09-078252
[Patent Document 4]
Japanese Unexamined Patent Application, First Publication No. H07-278833
5 [Patent Document 5]
Japanese Patent No. 3930696
[Summary of the Invention]
[Problems to be Solved by the Invention]
[0013]
10 In the case of directly forming an insulation coating on metallic Fe, which is a
main component of a base steel sheet, it is rarely possible to obtain the adhesion of the
insulation coating. Therefore, the coating structures of grain-oriented electrical steel
sheets that are widely used practically at the moment include a three-layer structure “base
steel sheet 1/final-annealed film 2A/insulation coating 3” shown in Fig. 2 as a basic
15 structure. The insulation coating 3 is ordinarily made up of a plurality of compounds
containing one or more of P, O, and S.
[0014]
In contrast, the coating structures of grain-oriented electrical steel sheets in
which the interface form between a base steel sheet and an insulation coating is smoothed
20 using an intermediate layer include a three-layer structure “base steel sheet
1/intermediate layer 2B/insulation coating 3” shown in Fig. 1 as a basic structure.
[0015]
In the above-described grain-oriented electrical steel sheets having an
intermediate layer mainly containing silicon oxide (for example, silicon dioxide (SiO2) or
25 the like) described in Patent Documents 1 to 5, the iron losses were reduced (that is, the
6
surfaces of the base steel sheets were smoothed), but it was not possible to say that the
adhesion of the insulation coatings was sufficient compared with grain-oriented electrical
steel sheets having a final-annealed film.
[0016]
The present invention ha 5 s been made in consideration of the above-described
circumstances. An objective of the present invention is to provide a grain-oriented
electrical steel sheet that has a low iron loss and is excellent in terms of the adhesion of
an insulation coating and a method for manufacturing the same.
[Means for Solving the Problem]
10 [0017]
The gist of the present invention is as described below.
(1) A grain-oriented electrical steel sheet according to an aspect of the present
invention is a grain-oriented electrical steel sheet having a base steel sheet in which a
final-annealed film is substantially not present on a surface,
15 an intermediate layer that is disposed on a surface of the base steel sheet and
mainly contains silicon oxide, and
an insulation coating disposed on a surface of the intermediate layer,
in which, in the intermediate layer, a value obtained by dividing a standard
deviation σ of a thickness of the intermediate layer by an average value T of the thickness
20 of the intermediate layer is 0.500 or less.
(2) A method for manufacturing a grain-oriented electrical steel sheet according
to another aspect of the present invention is a method for manufacturing the grainoriented
electrical steel sheet according to (1), including
a hot rolling process of heating a slab containing Si and then performing hot
25 rolling to obtain a hot-rolled steel sheet,
7
a hot-band annealing process of performing hot band annealing on the hot-rolled
steel sheet to obtain an annealed steel sheet,
a cold rolling process of performing cold rolling on the annealed steel sheet once
or twice or more with intermediate annealing performed therebetween to obtain a cold-
5 rolled steel sheet,
a decarburization annealing process of performing decarburization annealing on
the cold-rolled steel sheet to obtain a decarburization-annealed steel sheet,
a final annealing process of heating the decarburization-annealed steel sheet
with an annealing separator having a MgO content of 10 mass% to 50 mass% applied to
10 a surface of the decarburization-annealed steel sheet and then removing the annealing
separator to obtain a final-annealed steel sheet,
an intermediate layer forming process of performing thermal oxidation
annealing on the final-annealed steel sheet to form an intermediate layer on a surface of
the final-annealed steel sheet, and
15 an insulation coating forming process of forming an insulation coating on the
final-annealed steel sheet having the intermediate layer formed thereon,
in which, in a cooling procedure of the final annealing process,
T1 is set to 1100ºC in a case where a final annealing temperature is 1100ºC or
higher and T1 is set to the final annealing temperature in a case where the final annealing
20 temperature is lower than 1100ºC, and
the decarburization-annealed steel sheet is cooled within a temperature range of
T1 to 500ºC in an atmosphere having an oxidation degree (PH2O/PH2) of 0.3 to 100000,
during the thermal oxidation annealing in the intermediate layer forming
process,
25 in a heating procedure,
8
an average heating rate within a temperature range of 300ºC to 750ºC is
set to 20 ºC/second to 200 ºC/second, an oxidation degree (PH2O/PH2) within the
temperature range is set to 0.0005 to 0.1, the final-annealed steel sheet is heated up to a
temperature range of 750ºC to 1150ºC, and,
5 within the temperature range of 750ºC to 1150ºC,
the final-annealed steel sheet is held in an atmosphere having an
oxidation degree (PH2O/PH2) of 0.0005 to 0.2 for 10 seconds to 90 seconds.
[Effects of the Invention]
[0018]
10 According to the aspects of the present invention, it is possible to provide a
grain-oriented electrical steel sheet that has a low iron loss and is excellent in terms of
the adhesion of an insulation coating and a method for manufacturing the same.
[Brief Description of Drawings]
[0019]
15 Fig. 1 is a view schematically showing a coating structure of a grain-oriented
electrical steel sheet according to a first embodiment.
Fig. 2 is a view schematically showing a coating structure of a grain-oriented
electrical steel sheet having a final-annealed film and an insulation coating, which
corresponds to the related art.
20 Fig. 3 is a view schematically showing a coating structure of a grain-oriented
electrical steel sheet according to a second embodiment.
Fig. 4 is a graph showing a relationship of lengths of metallic Fe phases with
frequencies and cumulative relative frequencies of metallic Fe phases in the grainoriented
electrical steel sheet according to the second embodiment.
25 Fig. 5 is a schematic view of a final-annealed steel sheet in a process of forming
9
an intermediate layer in a method for manufacturing the grain-oriented electrical steel
sheet according to the second embodiment.
Fig. 6 is a graph showing a relationship among lengths, frequencies, and
cumulative relative frequencies of metallic Fe phases in a grain-oriented electrical steel
5 sheet corresponding to the related art.
[Embodiments for implementing the Invention]
[0020]
In the present embodiments, among grain-oriented electrical steel sheets having
a base steel sheet, an intermediate layer disposed on a surface of the base steel sheet, and
10 an insulation coating disposed on the surface of the intermediate layer, particularly, a
grain-oriented electrical steel sheet having a characteristic in the thickness of the
intermediate layer is referred to as a grain-oriented electrical steel sheet according to a
first embodiment. In addition, in the present embodiments, among grain-oriented
electrical steel sheets having a base steel sheet, an intermediate layer disposed on a
15 surface of the base steel sheet, and an insulation coating disposed on the surface of the
intermediate layer, a grain-oriented electrical steel sheet having a characteristic
particularly in metallic Fe phases present in the interface between the intermediate layer
and the insulation coating is referred to as a grain-oriented electrical steel sheet according
to a second embodiment.
20 Hereinafter, the grain-oriented electrical steel sheet according to the first
embodiment and the grain-oriented electrical steel sheet according to the second
embodiment will be described.
[0021]
[Grain-oriented electrical steel sheet according to first embodiment]
25 First, the grain-oriented electrical steel sheet according to the first embodiment
10
and a method for manufacturing the same will be described in detail.
[0022]
The grain-oriented electrical steel sheet according to the first embodiment is a
grain-oriented electrical steel sheet having a base steel sheet in which a final-annealed
film is substantially 5 not present on a surface, an intermediate layer that is disposed on a
surface of the base steel sheet and mainly contains silicon oxide, and an insulation
coating disposed on a surface of the intermediate layer. A value (σ/T) obtained by
dividing the standard deviation σ of the thickness of the intermediate layer by the average
value T of the thickness of the intermediate layer is 0.500 or less.
10 [0023]
Here, the intention of “final-annealed film is substantially not present” will be
described.
In ordinary grain-oriented electrical steel sheets, a final-annealed film made
from an oxide of forsterite (Mg2SiO4), spinel (MgAl2O4), cordierite (Mg2Al4Si5O16),
15 and/or the like is interposed between a base steel sheet and an insulation coating, and
adhesion between oxide films (final-annealed film and insulation coating) and the base
steel sheet is ensured by an anchoring effect of complicated interfacial unevenness.
When there is, even locally, a portion in which this final-annealed film is not present, it is
not possible to ensure the adhesion between the base steel sheet and the insulation
20 coating in that portion. Therefore, in ordinary grain-oriented electrical steel sheets, the
final-annealed film is formed in a state of fully covering the surface of the base steel
sheet.
[0024]
In contrast, in the grain-oriented electrical steel sheet according to the first
25 embodiment, the final-annealed film is not required to ensure the adhesion of the
11
insulation coating. In the grain-oriented electrical steel sheet according to the first
embodiment, it is possible to ensure the adhesion of the insulation coating even in a case
where the final-annealed film is completely not present, surely, in a case where the finalannealed
film is locally deficient. In addition, the complicated interfacial unevenness
attributed to the final-annealed 5 film is not a preferable condition in terms of the magnetic
properties of grain-oriented electrical steel sheets. Therefore, from the viewpoint of the
magnetic properties, there is no merit of leaving the final-annealed film, and it is
preferable that the final-annealed film is completely not present.
[0025]
10 However, in a procedure for manufacturing the grain-oriented electrical steel
sheet according to the first embodiment, it is possible to consider a status in which the
oxide of forsterite, spinel, cordierite, or the like is formed in a non-film-shaped form or,
in a procedure of removing a once-formed final-annealed film, a part of the finalannealed
film slightly remains. The present embodiment does not exclude the presence
15 of such an oxide. That is, the “final-annealed film is substantially not present” is
specified in consideration of such a form. Specifically, in the cross-sectional
observation of the grain-oriented electrical steel sheet, the area of the oxide of forsterite,
spinel, cordierite, or the like observed is equal to or smaller than the area of the
intermediate layer observed, furthermore, 1/2 or smaller, and furthermore, 1/10 or
20 smaller. It is needless to say that the best form is that the area of the oxide of forsterite,
spinel, cordierite, or the like observed is zero.
[0026]
A grain-oriented electrical steel sheet A having an intermediate layer 2B mainly
containing silicon oxide on a surface of a base steel sheet 1 in which a final-annealed
25 film is substantially not present has a coating structure as schematically shown in Fig. 1.
12
The grain-oriented electrical steel sheet A has a three-layer structure “base steel sheet
1/intermediate layer 2B/insulation coating 3” shown in Fig. 1 as a basic structure.
[0027]
In the grain-oriented electrical steel sheet having the intermediate layer 2B
mainly containing 5 silicon oxide on the surface of the base steel sheet 1, the iron loss is
reduced by smoothing the surface of the base steel sheet. However, in the related art,
there have been no studies to improve the adhesion of insulation coatings by paying
attention to the shape of the intermediate layer 2B.
[0028]
10 As described above, in grain-oriented electrical steel sheets having a finalannealed
film, which correspond to the related art, interfacial unevenness between the
final-annealed film 2A and the base steel sheet 1, that is, unevenness on the surface of the
final-annealed film 2A leads to an anchoring effect. Therefore, the present inventors
conduct studies regarding the adhesion of the insulation coating 3 by paying attention to
15 the thickness of the intermediate layer 2B with an expectation that the adhesion of the
insulation coating 3 is enhanced when the thickness of the intermediate layer 2B is
nonuniform. As a result, the present inventors found that, unlike the expectation, when
the thickness of the intermediate layer 2B is made uniform, the adhesion of the insulation
coating 3 improves.
20 [0029]
The reason for the adhesion of the insulation coating 3 being improved by
uniforming the thickness of the intermediate layer 2B is not clear, but the present
inventors consider as described below. Unlike the final-annealed film 2A, in the
intermediate layer 2B having a smoothed surface, even when the thickness is made
25 nonuniform, the anchoring effect is not strong as much. When the thickness is made
13
nonuniform, since a demerit of stress concentrating at a specific site is greater than a
merit of obtaining the anchoring effect, the adhesion of the insulation coating 3 degrades.
Therefore, when the thickness of the intermediate layer 2B is made uniform as in the
grain-oriented electrical steel sheet according to the first embodiment, stress does not
concentrate at a specific 5 site, and the adhesion of the insulation coating 3 improves.
[0030]
Hereinafter, the three-layer structure of the grain-oriented electrical steel sheet
according to the first embodiment will be described. In the following description,
reference signs in the drawings will be shown only in a case where the drawings are
10 described.
[0031]
Intermediate layer
The intermediate layer is formed on a surface of the base steel sheet and mainly
contains silicon oxide. The intermediate layer has a function of adhering the base steel
15 sheet and the insulation coating. In the grain-oriented electrical steel sheet according to
the first embodiment, the intermediate layer refers to a layer present between a base steel
sheet described below and an insulation coating described below. The expression
“mainly containing silicon oxide” means that the Fe content is less than 30 atom%, the P
content is less than 5 atom%, the Si content is 20 atom% or more, the O content is 50
20 atom% or more, and the Mg content is 10 atom% or less. Silicon oxide, which is the
main component of the intermediate layer, is preferably SiOx (x=1.0 to 2.0) and more
preferably SiOx (x=1.5 to 2.0). This is because silicon oxide is more stable. When a
heat treatment for forming silicon oxide on the surface of the base steel sheet is
sufficiently performed, it is possible to form silica (SiO2).
25 [0032]
14
In the grain-oriented electrical steel sheet according to the first embodiment, in
the intermediate layer, the value obtained by dividing the standard deviation σ of the
thickness of the intermediate layer by the average value T of the thickness of the
intermediate layer is 0.500 or less. That is, the intermediate layer satisfies an expression
(standard deviation σ of thickness of intermediate 5 layer/average value T of thickness of
intermediate layer ≤ 0.500). Ordinarily, a value obtained by dividing the standard
deviation σ by the average value T is referred to as the coefficient of variation. With
this coefficient of variation, it is possible to relatively evaluate the relationship between
the average value of data and the variation of the data.
10 Hereinafter, “the value obtained by dividing the standard deviation σ of the
thickness of the intermediate layer by the average value T of the thickness of the
intermediate layer” will be simply referred to as “the coefficient of variation of the
thickness of the intermediate layer” in some cases.
[0033]
15 In the grain-oriented electrical steel sheet according to the first embodiment, the
coefficient of variation of the thickness of the intermediate layer is set to 0.500 or less to
make the thickness of the intermediate layer uniform, whereby it is possible to suppress
stress concentrating at a part of the interface between the intermediate layer and the
insulation coating. Therefore, it becomes possible to improve the adhesion of the
20 insulation coating. In order to further improve the adhesion of the insulation coating,
the coefficient of variation of the thickness of the intermediate layer is preferably set to
0.400 or less, more preferably set to 0.350 or less, and still more preferably set to 0.300
or less. The coefficient of variation of the thickness of the intermediate layer is
preferably as small as possible, but may be set to 0.050 or more or 0.100 or more.
25 [0034]
15
When the thickness of the intermediate layer is too thin, there is a case where a
region in which the intermediate layer is inevitably and partially not coated is formed on
the surface of the base steel sheet and it is not possible to ensure the adhesion of the
insulation coating. Therefore, the thickness of the intermediate layer is preferably 2 nm
5 or more and more preferably 5 nm or more.
On the other hand, when the thickness of the intermediate layer is too thick,
there is a case where it is not possible to control the thickness of the intermediate layer
uniformly or a case where a defect such as a void or a crack is generated in the
intermediate layer. Therefore, the thickness of the intermediate layer is preferably 400
10 nm or less and more preferably 300 nm or less. In addition, the intermediate layer is
made as thin as possible as long as it is possible to ensure the adhesion of the insulation
coating, whereby it is possible to contribute to the enhancement of productivity by
shortening the formation time and to suppress a decrease in the space factor at the time of
using the grain-oriented electrical steel sheet as an iron core. Therefore, the thickness
15 of the intermediate layer is preferably set to 200 nm or less and more preferably 100 nm
or less.
[0035]
The thickness of the intermediate layer can be obtained by, for example,
observing a specimen cross section with a scanning transmission electron microscope
20 (STEM) as described below and measuring the thickness. From measurement values
obtained as described above, the average value T and standard deviation σ of the
thickness of the intermediate layer are obtained.
[0036]
Specifically, a test piece is cut out by focused ion beam (FIB) machining such
25 that the cut surface becomes parallel to the sheet thickness direction and perpendicular to
16
a rolling direction, and the cross-sectional structure of this cut surface is observed with a
STEM at a magnification at which each layer is included in an observation visual field
(light field image). In a case where each layer is not included in the observation visual
field, the cross-sectional structure is observed in a plurality of visual fields that are
5 continuous with each other.
[0037]
In order to specify each layer in the cross-sectional structure, a line analysis is
performed along the sheet thickness direction from the surface of the grain-oriented
electrical steel sheet using STEM-energy dispersive X-ray spectroscopy (STEM-EDS),
10 and a quantitative analysis is performed on the chemical composition of each layer. On
the observation cross section of the specimen, the line analysis is performed at 100 sites
at intervals of 0.1 μm in a direction parallel to the surface of the base steel sheet. As the
line analysis, a quantitative analysis is performed at intervals of 1 nm in the sheet
thickness direction by energy dispersive X-ray spectroscopy (EDS) in which the diameter
15 of an electron beam is set to 10 nm.
Elements to be quantitatively analyzed are five elements of Fe, P, Si, O, and Mg.
[0038]
From the light field image observation results with the STEM and the
quantitative analysis results of STEM-EDS, the kind of each layer is specified, and the
20 thickness of each layer is measured. Specifically, the kind of each layer is specified
according to criteria described below, and the average value of the thicknesses of each
layer measured at the 100 sites is calculated to obtain the thickness of each layer. The
obtained thickness of the intermediate layer (the average value of the thicknesses of the
intermediate layer measured at the 100 sites) is defined as the average value T of the
25 thickness of the intermediate layer. In addition, a standard deviation is calculated from
17
the thicknesses of the intermediate layer at the 100 sites, thereby obtaining the standard
deviation σ of the thickness of the intermediate layer. The obtained standard deviation
σ of the thickness of the intermediate layer is divided by the average value T, thereby
obtaining the coefficient of variation (σ/T) of the thickness of the intermediate layer.
The specification of each 5 layer and the measurement of the thickness described
below are all performed on the same scanning line.
[0039]
A region in which the Fe content is 80 atom% or more is determined as the base
steel sheet.
10 A region in which the Fe content is less than 45 atom%, the P content is 5
atom% or more, the Si content is less than 20 atom%, the O content is 50 atom% or
more, and the Mg content is 10 atom% or less is determined as the insulation coating.
A region satisfying a Fe content of less than 30 atom%, a P content of less than 5
atom%, a Si content of 20 atom% or more, an O content of 50 atom% or more, and a Mg
15 content of 10 atom% or less is determined as the intermediate layer.
[0040]
When each layer is determined by the chemical composition as described above,
there is a case where a region that does not correspond to any compositions in the
analysis (blank region) is generated. However, in the grain-oriented electrical steel
20 sheet according to the first embodiment, each layer is specified so as to be included in the
three-layer structure of the base steel sheet, the intermediate layer, and the insulation
coating. Determination criteria therefor are as described below.
[0041]
Regarding a blank region between the base steel sheet and the intermediate
25 layer, the center of the blank region (the center in the thickness direction, which shall
18
apply below) is considered as a boundary, the base steel sheet side is regarded as the base
steel sheet, and the intermediate layer side is regarded as the intermediate layer.
Regarding a blank region between the insulation coating and the intermediate layer, the
center of the blank region is considered as a boundary, the insulation coating side is
regarded as the insulation c 5 oating, and the intermediate layer side is regarded as the
intermediate layer.
[0042]
When the intermediate layer is not present, regarding a blank region between the
base steel sheet and the insulation coating, the center of the blank region is regarded as a
10 boundary, the base steel sheet side is regarded as the base steel sheet, and the insulation
coating side is regarded as the insulation coating. A blank region, the base steel sheet,
and the insulation coating that are present between the intermediate layer and the
intermediate layer are regarded as the intermediate layer. A blank region and the
insulation coating that are present between the base steel sheet and the base steel sheet is
15 regarded as the base steel sheet. A blank region between the insulation coating and the
insulation coating is regarded as the insulation coating.
With this system, it is possible to separate the base steel sheet, the insulation
coating, and the intermediate layer.
[0043]
20 Insulation coating
The insulation coating 3 is formed on the surface of the intermediate layer 2B as
shown in Fig. 1 and has a function of reducing the iron loss of the grain-oriented
electrical steel sheet A as a single sheet by applying tension to the base steel sheet 1 and a
function of ensuring an electrical insulating property between the grain-oriented
25 electrical steel sheets A at the time of using a laminate of the grain-oriented electrical
19
steel sheets A.
[0044]
The insulation coating is not particularly limited, can be appropriately selected
and used from well-known insulating coatings depending on uses or the like, and may be
any of an organic coating or an inorganic 5 coating. Examples of the organic coating
include a polyamine-based resin, an acrylic resin, an acrylic styrene resin, an alkyd resin,
a polyester resin, a silicone resin, a fluororesin, a polyolefin resin, a styrene resin, a vinyl
acetate resin, an epoxy resin, a phenolic resin, an urethane resin, a melamine resin, and
the like. Examples of the inorganic coating include a phosphate-based coating,
10 furthermore, an organic-inorganic complex-based coating containing the above-described
resin, and the like. More specifically, the insulation coating may be an insulating
coating obtained by baking an insulating coating having colloidal silica particles
dispersed in a matrix as shown in Fig. 1. Here, the “matrix” refers to a substrate of the
insulation coating and is made from, for example, a non-crystalline phosphate.
15 Examples of the non-crystalline phosphate that configures the matrix include aluminum
phosphate, magnesium phosphate, and the like. The baked insulation coating is made
up of a plurality of compounds containing one or more of P, O, and Si.
[0045]
When the thickness of the insulation coating becomes thin, tension that is
20 applied to the base steel sheet becomes small, and the insulating property also degrades.
Therefore, the thickness of the insulation coating is preferably 0.1 μm or more and more
preferably 0.5 μm or more. On the other hand, when the thickness of the insulation
coating exceeds 10 μm, there is a case where a crack is generated in the insulation
coating in an insulation coating forming stage. Therefore, the thickness of the
25 insulation coating is preferably 10 μm or less and more preferably 5 μm or less.
20
[0046]
On the insulation coating, a magnetic domain refining treatment for forming a
local fine strain region or groove may be performed with a laser or plasma or by a
mechanical method, etching, and/or other methods.
5 [0047]
Base steel sheet
The chemical composition and configuration such as the structure of the base
steel sheet in the grain-oriented electrical steel sheet according to the first embodiment do
not have any direct relationship with the coating structure of the grain-oriented electrical
10 steel sheet except that Si is contained as an essential component. Therefore, the base
steel sheet in the grain-oriented electrical steel sheet according to the first embodiment is
not particularly limited as long as the action and effect of the grain-oriented electrical
steel sheet according to the first embodiment can be obtained, and it is possible to use,
for example, a base steel sheet in an ordinary grain-oriented electrical steel sheet.
15 Hereinafter, the base steel sheet in the grain-oriented electrical steel sheet
according to the first embodiment will be described.
[0048]
Chemical composition of base steel sheet
As the chemical composition of the base steel sheet, it is possible to use the
20 chemical composition of a base steel sheet in an ordinary grain-oriented electrical steel
sheet. In the following description, the unit of the amount of each component in the
chemical composition of the base steel sheet is “mass%”. Numerical limitation ranges
expressed using “to” in the middle include the lower limit value and the upper limit value
in the ranges.
25 [0049]
21
The base steel sheet of the grain-oriented electrical steel sheet according to the
first embodiment contains, for example, Si: 0.50% to 7.00%, C: 0.005% or less, and N:
0.0050% or less, and the remainder is made up of Fe and an impurity. Hereinafter,
regarding a typical example of the chemical composition of the base steel sheet of the
grain-oriented electrical steel shee 5 t according to the present embodiment, reasons for
limiting the chemical composition will be described.
[0050]
Si: 0.50% to 7.00%
Silicon (Si) increases the electrical resistance of the grain-oriented electrical
10 steel sheet to decrease the iron loss. When the Si content is less than 0.50%, this effect
cannot be sufficiently obtained. Therefore, the Si content is preferably 0.50% or more.
The Si content is more preferably 1.50% or more and still more preferably 2.50% or
more.
On the other hand, when the Si content exceeds 7.00%, the saturation magnetic
15 flux density of the base steel sheet decreases, and the iron loss of the grain-oriented
electrical steel sheet deteriorates. Therefore, the Si content is preferably 7.00% or less.
The Si content is more preferably 5.50% or less and still more preferably 4.50% or less.
[0051]
C: 0.005% or less
20 Carbon (C) forms a compound in the base steel sheet and deteriorates the iron
loss of the grain-oriented electrical steel sheet. Therefore, the C content is preferably
0.005% or less. The C content is more preferably 0.004% or less and still more
preferably 0.003% or less.
On the other hand, the C content is preferably as small as possible and thus may
25 be 0%, but there is a case where C is contained in steel as an impurity. Therefore, the C
22
content may be more than 0%.
[0052]
N: 0.0050% or less
Nitrogen (N) forms a compound in the base steel sheet and deteriorates the iron
loss of the grain-oriented electrical steel shee 5 t. Therefore, the N content is preferably
0.0050% or less. The N content is more preferably 0.0040% or less and still more
preferably 0.0030% or less.
On the other hand, the N content is preferably as small as possible and thus may
be 0%, but there is a case where N is contained in steel as an impurity. Therefore, the N
10 content may be more than 0%.
[0053]
The remainder of the chemical composition of the base steel sheet is made up of
Fe and an impurity. The “impurity” mentioned herein refers to an element that comes
from a component contained in a raw material or a component being mixed in a
15 manufacturing procedure at the time of industrially manufacturing the base steel sheet
and has no substantial influence on an effect that is obtained by the grain-oriented
electrical steel sheet according to the present embodiment.
[0054]
[Optional elements]
20 Basically, the chemical composition of the base steel sheet contains the abovedescribed
elements with the remainder made up of Fe and an impurity, but may contain
one or more optional elements instead of some of Fe for the purpose of improving the
magnetic properties or solving problems relating to manufacturing. Examples of the
optional elements that are contained instead of some of Fe include the following
25 elements. Since these elements may not be contained, the lower limits are 0%. On the
23
other hand, when the amounts of these elements are too large, a precipitate is generated,
thereby deteriorating the iron loss of the grain-oriented electrical steel sheet or ferrite
transformation is suppressed to prevent the sufficient obtainment of a Goss orientation or
to decrease the saturation magnetic flux density, thereby deteriorating the iron loss of the
grain-oriented electrical steel sheet. 5 Therefore, even in a case where these elements are
contained, the contents are preferably set within the following ranges.
Acid-soluble Al: 0.0065% or less,
Mn: 1.00% or less,
S and Se: 0.001% or less in total,
10 Bi: 0.010% or less,
B: 0.0080% or less,
Ti: 0.015% or less,
Nb: 0.020% or less,
V: 0.015% or less,
15 Sn: 0.50% or less,
Sb: 0.50% or less,
Cr: 0.30% or less,
Cu: 0.40% or less,
P: 0.50% or less,
20 Ni: 1.00% or less, and
Mo: 0.10% or less.
“S and Se: 0.001% or less in total” means that the base steel sheet may contain
any one of S or Se alone and the amount of any one of S or Se may be 0.001% or less or
the base steel sheet may contain both S and Se and the amount of S and Se may be
25 0.001% or less in total.
24
[0055]
The above-described chemical composition of the base steel sheet of the grainoriented
electrical steel sheet according to the present embodiment is obtained by
adopting a method for manufacturing the grain-oriented electrical steel sheet according to
the present embodiment using a 5 slab having a chemical composition described below.
[0056]
The chemical composition of the base steel sheet of the grain-oriented electrical
steel sheet according to the present embodiment is preferably measured using spark
optical emission spectrometry (Spark-OES). In addition, in the case of a small content,
10 the content may be measured using inductively coupled plasma-mass spectrometry (ICPMS).
Acid-soluble Al may be measured by ICP-MS using a filtrate obtained by
hydrolyzing a specimen with an acid. In addition, C and S may be measured using an
infrared absorption method after combustion, and N may be measured using an inert gas
fusion thermal conductivity method.
15 [0057]
Surface roughness (Ra)
Ordinarily, the surface roughness (Ra) of the base steel sheet is controlled from
the viewpoint of enhancing the adhesion of the insulation coating by increasing the
surface roughness and the viewpoint of avoiding adverse influences on the iron loss by
20 decreasing the surface roughness. In a case where the surface roughness is large, it is
possible to ensure the adhesion of the insulation coating regardless of variations in the
coefficient of variation of the thickness of the intermediate layer. In other words, the
control of the coefficient of variation of the thickness of the intermediate layer for the
purpose of ensuring the adhesion of the insulation coating becomes important in base
25 steel sheets having a small surface roughness. Originally, the grain-oriented electrical
25
steel sheet according to the first embodiment is about a grain-oriented electrical steel
sheet in which the interface between a base steel sheet and an insulation coating is
smoothed using an intermediate layer.
[0058]
The surface roughness of the base 5 steel sheet in the grain-oriented electrical steel
sheet according to the first embodiment is preferably set to 1.0 μm or less in terms of Ra
(arithmetic average roughness) so as to prevent the formation of unevenness in the
interface between the insulation coating and the base steel sheet and to prevent the iron
loss reduction effect from being hindered. The surface roughness is more preferably 0.8
10 μm or less or 0.6 μm or less. In addition, from the viewpoint of reducing the iron loss
of the grain-oriented electrical steel sheet by applying large tension to the base steel
sheet, the surface roughness is still more preferably 0.5 μm or less or 0.3 μm or less in
terms of Ra. The surface roughness is preferably as small as possible, but may be set to
0.01 μm or more in terms of Ra.
15 [0059]
The surface roughness (Ra: arithmetic surface roughness) of the base steel sheet
can be obtained by, for example, observing the reflected electron image of a cross section
of the base steel sheet perpendicular to a rolling direction with a scanning electron
microscope (SEM). Specifically, a reflected electron image obtained with an SEM is
20 converted to a monochromatic image with 256 levels of grayscale and converted to a
binarized image using a 30% grayscale level from the white side as a threshold value,
and a white region is defined as the base steel sheet. The positional coordinates of the
surface of the base steel sheet in the sheet thickness direction in this binarized image are
measured with a precision of 0.01 μm or more, and Ra is calculated. The positional
25 coordinates are measured in a continuous 2 mm range at 0.1 μm pitches in a direction
26
parallel to the surface of the base steel sheet (20000 points in total), and this
measurement is performed in at least five places. In addition, the average value of the
calculated Ra values in each place is calculated, thereby obtaining the surface roughness
(Ra) of the base steel sheet.
5 [0060]
Method for manufacturing grain-oriented electrical steel sheet according to first
embodiment
Next, a method for manufacturing the grain-oriented electrical steel sheet
according to the first embodiment will be described.
10 [0061]
The method for manufacturing the grain-oriented electrical steel sheet described
below is a method for manufacturing the grain-oriented electrical steel sheet described in
the section of “the grain-oriented electrical steel sheet according to the first
embodiment”.
15 The method for manufacturing the grain-oriented electrical steel sheet according
to the first embodiment, in which the intermediate layer and the insulation coating are
formed in separate processes, includes
a hot rolling process of heating a slab and then performing hot rolling to obtain a
hot-rolled steel sheet,
20 a hot-band annealing process of performing hot band annealing on the hot-rolled
steel sheet to obtain an annealed steel sheet, and
a cold rolling process of performing cold rolling on the annealed steel sheet once
or twice or more with intermediate annealing performed therebetween to obtain a coldrolled
steel sheet.
25 [0062]
27
In addition, the method for manufacturing the grain-oriented electrical steel
sheet according to the first embodiment includes
a decarburization annealing process of performing decarburization annealing on
the cold-rolled steel sheet to obtain a decarburization-annealed steel sheet and
a final annealing process of heating 5 the decarburization-annealed steel sheet
with an annealing separator having a MgO content of 10 mass% to 50 mass% applied to
a surface of the decarburization-annealed steel sheet to a temperature range of 1000ºC or
higher to perform final annealing and then removing the annealing separator to obtain a
final-annealed steel sheet.
10 In a cooling procedure after heating the decarburization-annealed steel sheet to a
temperature range of 1000ºC or higher, T1 is set to 1100ºC in a case where the final
annealing temperature is 1100ºC or higher and T1 is set to the final annealing
temperature in a case where the final annealing temperature is lower than 1100ºC, and the
decarburization-annealed steel sheet is cooled within a temperature range of T1 to 500ºC
15 in an atmosphere having an oxidation degree (PH2O/PH2) of 0.3 to 100000.
[0063]
Furthermore, the method for manufacturing the grain-oriented electrical steel
sheet according to the first embodiment includes
an intermediate layer forming process of performing thermal oxidation
20 annealing, in which the final-annealed steel sheet is heated to a temperature range of
750ºC to 1150ºC and held within the temperature range of 750ºC to 1150ºC in an
atmosphere having an oxidation degree (PH2O/PH2) of 0.0005 to 0.2 for 10 seconds to 90
seconds, to form an intermediate layer mainly containing silicon oxide on the surface of
the final-annealed steel sheet and
25 an insulation coating forming process of applying a coating solution to the
28
surface of the intermediate layer and baking the coating solution to form an insulation
coating.
In the thermal oxidation annealing in the intermediate layer forming process, in
a heating procedure, the final-annealed steel sheet is heated within a temperature range of
300ºC to 750ºC at an 5 average heating rate of 20 ºC/second to 200 ºC/second in an
atmosphere having an oxidation degree (PH2O/PH2) of 0.0005 to 0.1.
[0064]
The method for manufacturing the grain-oriented electrical steel sheet according
to the first embodiment is characterized particularly in that the hindrance of the iron loss
10 reduction action of the insulation coating due to interfacial unevenness between the finalannealed
film and the base steel sheet is avoided and the intermediate layer mainly
containing silicon oxide is formed on the surface of the base steel sheet in order to ensure
the adhesion between the insulation coating and the base steel sheet attributed to the
intermediate layer. Therefore, in the method for manufacturing the grain-oriented
15 electrical steel sheet according to the first embodiment, particularly characteristic
processes are the final annealing process and the intermediate layer forming process.
[0065]
First, the chemical composition of the slab in the method for manufacturing the
grain-oriented electrical steel sheet according to the first embodiment will be described.
20 The slab is prepared according to a well-known technique, and a typical example
of the chemical composition is as described below.
The chemical composition contains, by mass%,
Si: 0.80% to 7.00%,
C: 0.085% or less,
25 acid-soluble Al: 0.010% to 0.065%,
29
N: 0.004% to 0.012%,
Mn: 0.05% to 1.00%, and
S and Se: 0.003% to 0.015% in total
with a remainder being made up of Fe and an impurity.
Hereinafter, reasons fo 5 r limiting the typical example of the chemical
composition will be described. “%” used to express the amount of each element in the
chemical composition of the slab indicates “mass%” unless particularly otherwise
described. Numerical limitation ranges expressed using “to” in the middle include the
lower limit value and the upper limit value in the ranges.
10 [0066]
Si: 0.80% to 7.00%
Si is an essential component and increases the electrical resistance to reduce the
iron loss of the grain-oriented electrical steel sheet. In addition, when Si is contained in
a high concentration, a strong chemical affinity is developed between the intermediate
15 layer mainly containing silicon oxide and the base steel sheet, and the intermediate layer
and the base steel sheet adhere to each other more strongly. However, when the Si
content exceeds 7.00%, cold rolling becomes extremely difficult, and a crack is likely to
be generated during cold rolling. Therefore, the Si content is preferably set to 7.00% or
less. The Si content is more preferably 4.50% or less and still more preferably 4.00% or
20 less. On the other hand, when Si content is less than 0.80%, γ transformation occurs
during final annealing, and the crystal orientation of the grain-oriented electrical steel
sheet is impaired. Therefore, the Si content is preferably set to 0.80% or more. The Si
content is more preferably 2.00% or more and still more preferably 2.50% or more.
[0067]
25 C: 0.085% or less
30
C is an effective element for controlling primary recrystallization structures, but
adversely affects the magnetic properties of the grain-oriented electrical steel sheet.
Therefore, in the method for manufacturing the grain-oriented electrical steel sheet
according to the first embodiment, decarburization annealing is performed before final
annealing. When the C content e 5 xceeds 0.085%, the decarburization annealing time
becomes long, and the productivity in industrial production is impaired. Therefore, the
C content is preferably set to 0.085% or less. The lower limit of the C content is not
particularly limited, but the C content is more preferably 0.020% or more and still more
preferably 0.050% or more.
10 C is purified in the decarburization annealing process and the final annealing
process, which will be described below, and the C content reaches 0.005% or less after
the final annealing process. Depending on the conditions of the decarburization
annealing process and final annealing, there is a case where the final-annealed steel sheet
contains no C.
15 [0068]
Acid-soluble Al: 0.010% to 0.065%
Acid-soluble Al bonds with N to be precipitated as (Al, Si)N. This precipitate
functions as an inhibitor. In a case where the acid-soluble Al content is 0.010% to
0.065%, secondary recrystallization is stabilized. Therefore, the acid-soluble Al content
20 is preferably set to 0.010% to 0.065%. The acid-soluble Al content is more preferably
0.020% or more and still more preferably 0.025% or more. In addition, from the
viewpoint of the stability of secondary recrystallization, the acid-soluble Al content is
more preferably 0.040% or less and still more preferably 0.030% or less.
Since acid-soluble Al is purified in the final annealing process, depending on the
25 conditions of final annealing, there is a case where the final-annealed steel sheet contains
31
no acid-soluble Al.
[0069]
N: 0.004% to 0.012%
N bonds with Al to function as an inhibitor. When the N content is less than
0.004%, it is not possible 5 to obtain a sufficient amount of an inhibitor. Therefore, the N
content is preferably set to 0.004% or more. The N content is more preferably 0.006%
or more and still more preferably 0.007% or more. On the other hand, when the N
content is more than 0.012%, a defect called a blister is likely to be generated in the steel
sheet. Therefore, the N content is preferably set to 0.012% or less. The N content is
10 more preferably 0.010% or less and still more preferably 0.009% or less. Since N is
purified in the final annealing process, depending on the conditions of final annealing,
there is a case where the final-annealed steel sheet contains no N.
[0070]
Mn: 0.05% to 1.00%
15 S and Se: 0.003% to 0.015% in total
Mn generates MnS and MnSe together with S and Se. These composite
compounds function as an inhibitor. In a case where the Mn content is 0.05% to 1.00%,
secondary recrystallization is stabilized. Therefore, the Mn content is preferably set to
0.05% to 1.00%. The Mn content is more preferably 0.08% or more and still more
20 preferably 0.09% or more. In addition, the Mn content is more preferably 0.50% or less
and still more preferably 0.20% or less.
[0071]
In a case where the amount of S and Se is 0.003% to 0.015% in total, secondary
recrystallization is stabilized. Therefore, the amount of S and Se is preferably set to
25 0.003% to 0.015% in total.
32
[0072]
Here, “the amount of S and Se is 0.003% to 0.015% in total” means that the slab
may contain any one of S or Se alone and the amount of any one of S or Se may be
0.003% to 0.015% or the slab may contain both S and Se and the amount of S and Se
5 may be 0.003% to 0.015% in total.
[0073]
Remainder
The remainder is made up of Fe and an impurity. The “impurity” refers to an
element that comes from a component contained in a raw material or a component being
10 mixed in a manufacturing procedure at the time of industrially manufacturing the slab.
[0074]
Optional elements
In consideration of the strengthening of the inhibitor function or the influence on
the magnetic properties attributed to the formation of a compound, it is possible to
15 contain a variety of kinds of optional elements instead of some of Fe that is the remainder
according to well-known documents. Examples of the optional elements that are
contained instead of some of Fe include the following elements. These elements are
optional elements and may not be contained, and thus the lower limits thereof are 0%.
Bi: 0.010% or less,
20 B: 0.080% or less,
Ti: 0.015% or less,
Nb: 0.20% or less,
V: 0.15% or less,
Sn: 0.10% or less,
25 Sb: 0.10% or less,
33
Cr: 0.30% or less,
Cu: 0.40% or less,
P: 0.50% or less,
Ni: 1.00% or less, and
5 Mo: 0.10% or less.
[0075]
Hereinafter, each process of the method for manufacturing the grain-oriented
electrical steel sheet according to the first embodiment will be described. Hereinafter,
as the conditions of processes other than the above-described particularly characteristic
10 processes (final annealing process and intermediate layer forming process), ordinary
conditions will be described as an example. Therefore, even when the ordinary
conditions are not satisfied, it is possible to obtain the effect of the grain-oriented
electrical steel sheet according to the first embodiment.
[0076]
15 Hot rolling process
In the hot rolling process, ordinarily, the slab is heated within a temperature
range of 800ºC to 1300ºC and then hot-rolled, thereby obtaining a hot-rolled steel sheet.
Examples of the chemical composition of the slab include the above-described chemical
composition of the slab.
20 [0077]
The slab is obtained by, for example, melting steel having the above-described
chemical composition in a converter, an electric furnace, or the like, performing a
vacuum degassing treatment as necessary, and then performing continuous casting or
ingot casting and blooming. The thickness of the slab is not particularly limited, but is,
25 for example, preferably 150 mm to 350 mm and more preferably 220 mm to 280 mm.
34
In addition, the slab may have a thickness of approximately 10 mm to 70 mm (so-called
“thin slab”). In the case of using a thin slab, it is possible to skip rough rolling before
final rolling in the hot rolling process.
[0078]
The heating temperature 5 of the slab is preferably set to 1200ºC or lower since it
is possible to avoid, for example, a variety of problems generated in the case of heating
the slab at, for example, a temperature higher than 1200ºC (a necessity of a designated
heating furnace, a large amount of molten scale, and the like).
In a case where the heating temperature of the slab is too low, there is a case
10 where hot rolling becomes difficult and the productivity degrades. Therefore, the
heating temperature of the slab is preferably set to 950°C or higher. In addition, it is
also possible to skip the slab heating process and begin hot rolling until the temperature
of the slab lowers after casting.
The heating time of the slab may be set to 40 minutes to 120 minutes.
15 [0079]
In the hot rolling process, rough rolling is performed on the heated slab, and
final rolling is further performed thereon, thereby producing a hot-rolled steel sheet
having a predetermined thickness. After the completion of final rolling, the hot-rolled
steel sheet is coiled at a predetermined temperature.
20 In addition, the sheet thickness of the hot-rolled steel sheet is not particularly
limited, but is preferably set to, for example, 3.5 mm or less.
[0080]
Hot-band annealing process
In the hot-band annealing process, hot band annealing is performed on the hot25
rolled steel sheet, thereby obtaining an annealed steel sheet. As hot band annealing
35
conditions, ordinary conditions may be adopted, and it is preferable to set, for example,
the annealing temperature (the furnace temperature of a hot band annealing furnace) to
750ºC to 1200ºC and the annealing time (the dwell time in the hot band annealing
furnace) to 30 seconds to 600 seconds as the conditions. The hot-rolled steel sheet may
be quenched a 5 fter being held under the above-described conditions.
[0081]
Cold rolling process
In the cold rolling process, cold rolling is performed on the annealed steel sheet
once or twice or more with intermediate annealing performed therebetween to obtain a
10 cold-rolled steel sheet. A pickling treatment may be performed on the annealed steel
sheet before cold rolling on the annealed steel sheet.
[0082]
In the case of performing the cold rolling process a plurality of times without
performing an intermediate annealing process, there is a case where it is difficult to
15 obtain uniform characteristics in the manufactured grain-oriented electrical steel sheet.
On the other hand, in the case of performing the cold rolling process a plurality of times
with an intermediate annealing process performed therebetween, there is a case where the
magnetic flux density decreases in the manufactured grain-oriented electrical steel sheet.
Therefore, the number of times of the cold rolling process and the presence or absence of
20 the intermediate annealing process are determined depending on characteristics
demanded for the finally manufactured grain-oriented electrical steel sheet and the
manufacturing costs.
[0083]
The cold rolling reduction in the final cold rolling (final cold rolling reduction)
25 in cold rolling performed once or a plurality of times is not particularly limited, but is
36
preferably set to 80% or larger and more preferably 90% or larger from the viewpoint of
crystal orientation control.
[0084]
The cold-rolled steel sheet obtained by the cold rolling process is wound in a
coil shape. The sheet t 5 hickness of the cold-rolled steel sheet is not particularly limited,
but is preferably set to 0.35 mm or less and more preferably set to 0.30 mm or less in
order to further reduce the iron loss of the grain-oriented electrical steel sheet.
[0085]
Decarburization annealing process
10 In the decarburization annealing process, it is preferable to perform
decarburization annealing on the cold-rolled steel sheet to obtain a decarburizationannealed
steel sheet. Specifically, decarburization annealing is performed, thereby
causing primary recrystallization in the cold-rolled steel sheet and removing C contained
in the cold-rolled steel sheet. Decarburization annealing is preferably performed in a
15 wet atmosphere containing hydrogen and nitrogen in order to remove C. As
decarburization annealing conditions, it is preferable to set, for example, the
decarburization annealing temperature (the temperature of a furnace in which
decarburization annealing is performed) to 800ºC to 950ºC and the decarburization
annealing time to 30 seconds to 180 seconds.
20 [0086]
Final annealing process
In the final annealing process, final annealing is performed by heating the
decarburization-annealed steel sheet with an annealing separator applied thereto. With
the final annealing, secondary recrystallization is caused in the decarburization-annealed
25 steel sheet.
37
[0087]
In ordinary methods for manufacturing grain-oriented electrical steel sheets, a
final annealing process is performed by, ordinarily, applying an annealing separator
having a high magnesium concentration (for example, MgO ≥ 90%) to the surface of the
decarburization-annealed 5 steel sheet in order to form a final-annealed film mainly
containing forsterite (Mg2SiO4). Ordinarily, the annealing separator is applied not only
to prevent seizure between final-annealed steel sheets but also to form a final-annealed
film made from forsterite (Mg2SiO4).
[0088]
10 In contrast, in the final annealing process of the method for manufacturing the
grain-oriented electrical steel sheet according to the first embodiment, the final annealing
is performed by heating the decarburization-annealed steel sheet with an annealing
separator having a low magnesium concentration and containing aluminum oxide (for
example, MgO: 10 mass% to 50 mass%, Al2O3: 50 mass% to 90 mass%) applied to the
15 surface of the decarburization-annealed steel sheet. After that, the annealing separator
is removed to obtain a final-annealed steel sheet. As a result, it is possible to form an
intermediate layer without substantially forming a final-annealed film made from
forsterite (Mg2SiO4). The MgO content in the annealing separator is preferably 15
mass% or more and more preferably 20 mass% or more. In addition, the MgO content
20 in the annealing separator is preferably 45 mass% or less and more preferably 40 mass%
or less.
[0089]
As the heating conditions in final annealing, ordinary conditions may be
adopted, and, for example, the heating rate to the final annealing temperature is set to 5
25 ºC/h to 100 ºC/h, the final annealing temperature (the temperature of a furnace in which
38
final annealing is performed) is set to 1000ºC to 1300ºC, and the final annealing time (the
holding time at the final annealing temperature) is set to 10 hours to 50 hours.
[0090]
In order to obtain an intermediate layer having a thickness that varies only to a
small extent in the intermediate 5 layer forming process described below, the oxidation
degree (PH2O/PH2) of the atmosphere within a predetermined temperature range is
controlled to 0.3 to 100000 in a cooling procedure after holding the decarburizationannealed
steel sheet at the final annealing temperature of 1000ºC to 1300ºC for 10 hours
to 50 hours. When T1 is set to 1100ºC in a case where the final annealing temperature
10 is 1100ºC or higher and T1 is set to the final annealing temperature in a case where the
final annealing temperature is lower than 1100ºC, the temperature range within which the
oxidation degree of the atmosphere is controlled is set to a temperature range of T1 to
500ºC.
[0091]
15 In the final-annealed steel sheet from which the annealing separator has been
removed after the cooling of the decarburization-annealed steel sheet under the abovedescribed
conditions, Fe-based oxides are appropriately formed on the surface, and it is
considered that these oxides affect the formation of the intermediate layer and thereby the
film thickness of the intermediate layer becomes uniform.
20 [0092]
In a case where the oxidation degree of the atmosphere within the temperature
range of T1 to 500ºC is less than 0.3, since no Fe-based oxides are formed, the film
thickness of the intermediate layer becomes nonuniform. In a case where the oxidation
degree (PH2O/PH2) of the atmosphere within the temperature range of T1 to 500ºC exceeds
25 100000, since a large amount of an oxide is formed, and the oxide remains even after the
39
intermediate layer forming process, the adhesion of the insulation coating degrades.
[0093]
The time taken to cool the decarburization-annealed steel sheet under the abovedescribed
conditions (time taken to cool the decarburization-annealed steel sheet from
T1ºC to 500ºC) is not particularly 5 limited, but is preferably set to 5 hours to 30 hours.
The method for removing the annealing separator is also not particularly limited, and
examples thereof include rubbing the surface of the final-annealed steel sheet with a
brush and the like.
[0094]
10 Intermediate layer forming process
In the intermediate layer forming process, thermal oxidation annealing is
performed by heating the final-annealed steel sheet to a temperature range of 750ºC to
1150ºC and holding the final-annealed steel sheet within the temperature range in an
atmosphere having an oxidation degree (PH2O/PH2) of 0.0005 to 0.2 for 10 seconds to 60
15 seconds, whereby an intermediate layer mainly containing silicon oxide is formed on the
surface of the final-annealed steel sheet.
[0095]
In the heating procedure of thermal oxidation annealing, the final-annealed steel
sheet is heated within a temperature range of 300ºC to 750ºC at an average heating rate
20 of 20 ºC/second to 200 ºC/second in an atmosphere having an oxidation degree
(PH2O/PH2) of 0.0005 to 0.1. The average heating rate mentioned herein refers to a value
obtained by dividing the temperature rise width from 300ºC to 750ºC by the time taken
for the temperature to reach 750ºC from 300ºC.
In the case of raising the temperature under such conditions, it is considered that
25 an oxide formed on the surface of the final-annealed steel sheet is reduced from a low
40
temperature range in which a reaction is slow to form the intermediate layer and thus the
thickness of the intermediate layer become uniform.
The intermediate layer is preferably formed in a thickness of 2 nm to 400 nm.
[0096]
In the intermediate layer forming process, t 5 he surface of the final-annealed steel
sheet is thermally oxidized by a heat treatment, thereby forming an intermediate layer on
the surface of the final-annealed steel sheet.
From the viewpoint of the reaction rate, the temperature at which the finalannealed
steel sheet is held for 10 seconds to 60 seconds during thermal oxidation
10 annealing is preferably 750ºC or higher. However, when the holding temperature
becomes higher than 1150ºC, it becomes difficult to maintain the intermediate layer
forming reaction uniform, unevenness in the interface between the intermediate layer and
the base steel sheet becomes large, and there are a case where the iron loss of the grainoriented
electrical steel sheet deteriorates and a case where the strength of the grain15
oriented electrical steel sheet decreases, treatments in continuous annealing furnaces
become difficult, and the productivity degrades.
[0097]
The holding time within the temperature range of 750ºC to 1150ºC is preferably
set to 10 seconds or longer from the viewpoint of preferably forming the intermediate
20 layer. In addition, from the viewpoint of the productivity and the viewpoint of avoiding
a decrease in the space factor caused by the thickening of the thickness of the
intermediate layer, the holding time is preferably set to 60 seconds or shorter.
[0098]
From the viewpoint of forming the intermediate layer in a thickness of 2 nm to
25 400 nm, the final-annealed steel sheet is preferably held within the temperature range of
41
750ºC to 1000ºC for 15 seconds to 60 seconds and more preferably held with the
temperature range of 750ºC to 900ºC for 25 seconds to 60 seconds.
[0099]
Insulation coating forming process
In the insulation coating 5 forming process, well-known conditions may be
applied. For example, a coating solution is applied to the surface of the intermediate
layer and then baked within a temperature range of 350ºC to 1150ºC for 5 to 300 seconds
in an atmosphere containing hydrogen, water vapor, and nitrogen and having an
oxidation degree (PH2O/PH2) of 0.001 to 1.0 to form the coating solution to the
10 intermediate layer.
The insulation coating is preferably formed in a thickness of 0.1 μm to 10 μm.
[0100]
The coating solution is also not particularly limited, and it is possible to
distinctively use a coating solution containing colloidal silica and a coating solution
15 containing no colloidal silica. In the case of forming an insulation coating using a
coating solution containing colloidal silica, it is possible to form an insulation coating
containing Si. In addition, in the case of forming an insulation coating using a coating
solution containing no colloidal silica, it is possible to form an insulation coating
containing no Si.
20 [0101]
The coating solution is also not particularly limited, and a well-known coating
solution may be appropriately used. For example, it is possible to use a coating solution
mainly containing a phosphate and colloidal silica.
Examples of the coating solution containing no colloidal silica include coating
25 solutions containing boric acid and alumina sol.
42
In addition, examples of the coating solution containing colloidal silica include
coating solutions containing phosphoric acid or a phosphate, colloidal silica, and chromic
anhydride or a chromate. Examples of the phosphate include phosphates of Ca, Al, Mg,
Sr, and the like. Examples of the chromate include chromates of Na, K, Ca, Sr, and the
like. The colloidal silica is not particularly 5 limited, and any appropriate particle size
thereof can be used.
[0102]
A variety of elements or compounds may be further added to the coating
solution in order to improve a variety of characteristics as long as the effects of the grain10
oriented electrical steel sheet according to the first embodiment are not lost.
[0103]
In a cooling procedure of the insulation coating forming process, it is preferable
to perform cooling under the following conditions within a temperature range of 600ºC to
1150ºC in order to prevent the insulation coating and the intermediate layer from
15 changing (decomposing or the like) after baking.
Oxidation degree (PH2O/PH2) of atmosphere: 0.001 to 1.0
Dwell time: 10 seconds to 30 seconds
[0104]
In the cooling procedure of the insulation coating forming process, when the
20 oxidation degree (PH2O/PH2) within the temperature range of 600ºC to 1150ºC is less than
0.001, there is a case where the insulation coating decomposes. In addition, when the
oxidation degree (PH2O/PH2) of the atmosphere within the above-described temperature
range exceeds 1.0, there is a case where the base steel sheet is significantly oxidized and
the iron loss of the grain-oriented electrical steel sheet deteriorates. The oxidation
25 degree (PH2O/PH2) of the atmosphere within the above-described temperature range is
43
preferably 0.002 to 0.05 and more preferably 0.003 to 0.03.
[0105]
The gas in the atmosphere may be a gas that is ordinarily used, and it is possible
to use, for example, a gas made up of hydrogen and nitrogen with an impurity.
After the end of such 5 a heat treatment, cooling is performed.
[0106]
The temperature at which the cooling is controlled is preferably 600ºC to
1050ºC and more preferably 650ºC to 950ºC.
[0107]
10 When the dwell time within the temperature range of 600ºC to 1150ºC is shorter
than 10 seconds, there is a case where the steel sheet shape becomes poor due to cooling
unevenness. When the dwell time within the above-described temperature range
exceeds 30 seconds, there is a case where the steel sheet is oxidized and the iron loss of
the grain-oriented electrical steel sheet deteriorates. The dwell time within the above15
described temperature range is preferably 10 seconds to 25 seconds and more preferably
10 seconds to 20 seconds.
[0108]
Other processes
The method for manufacturing the grain-oriented electrical steel sheet according
20 to the first embodiment may further have a process that is ordinarily performed in
methods for manufacturing grain-oriented electrical steel sheets. The manufacturing
method may further have a nitriding treatment process of performing a nitriding
treatment that increases the N content of the decarburization-annealed steel sheet
between the beginning of the decarburization annealing and the initiation of secondary
25 recrystallization in the final annealing. This is because it is possible to stably improve
44
the magnetic flux density by increasing an inhibitor such as AlN. The nitriding
treatment may be an ordinary nitriding treatment, and examples thereof include a
treatment of annealing the decarburization-annealed steel sheet in an atmosphere
containing a gas having a nitriding capability such as ammonia, a treatment of finalannealing
the decarburization-annealed steel she 5 et to which an annealing separator
containing powder having a nitriding capability such as MnN is applied, and the like.
[0109]
Grain-oriented electrical steel sheet according to second embodiment
Next, a grain-oriented electrical steel sheet according to a second embodiment
10 will be described. The grain-oriented electrical steel sheet according to the second
embodiment is a grain-oriented electrical steel sheet having a base steel sheet in which a
final-annealed film is substantially not present on a surface, an intermediate layer that is
disposed on a surface of the base steel sheet and mainly contains silicon oxide, and an
insulation coating disposed on a surface of the intermediate layer. Metallic Fe phases
15 are present in the interface between the intermediate layer and the insulation coating, and,
in a cross section perpendicular to a rolling direction, the percentage of the total of the
lengths of the metallic Fe phases with respect to the length of the interface is 5% to 50%.
[0110]
In the grain-oriented electrical steel sheet according to the second embodiment,
20 in a cross section perpendicular to the rolling direction, the length of the metallic Fe
phase when the cumulative relative frequency is 0.95 in the cumulative frequency
distribution of the lengths of the metallic Fe phases present in the interface may be 500
nm or less.
[0111]
25 In the grain-oriented electrical steel sheet according to the second embodiment,
45
the number of Fe-based oxides having a thickness of more than 2 nm may be zero in the
interface between the base steel sheet and the intermediate layer. The thickness of the
Fe-based oxide refers to the length in a direction perpendicular to the surface of the base
steel sheet (the interface between the base steel sheet and the intermediate layer). In
addition, the Fe-based oxides refer to Fe2O3, F 5 e3O4, FeO, and Fe2SiO4.
Hereinafter, the grain-oriented electrical steel sheet according to the second
embodiment will be described in detail.
[0112]
As a result of studying a grain-oriented electrical steel sheet that has a low iron
10 loss and is excellent in terms of the adhesion of an insulation coating and a method for
manufacturing the same, the present inventors found that the adhesion of the insulation
coating can be improved by controlling the cooling condition of a cooling procedure of a
final annealing process and the annealing condition of a process of forming the
intermediate layer.
15 [0113]
The present inventors found that, in a final-annealed steel sheet obtained by
preferably controlling the cooling condition of the cooling procedure of the final
annealing process, an appropriate amount of a Fe-based oxide coating is formed on the
surface of the final-annealed steel sheet. In addition, the present inventors found that, in
20 the process of forming the intermediate layer, Fe in the Fe-based oxide coating is reduced
and thereby an intermediate layer mainly containing silicon oxide is formed, after a
process of forming the insulation coating, metallic Fe phases are generated in the
interface between the intermediate layer and the insulation coating, and, particularly in a
case where these metallic Fe phases are fine, the adhesion of the insulation coating
25 further improves.
46
[0114]
Fig. 3 is a view schematically showing a coating structure when a cross section
perpendicular to a rolling direction is seen regarding a grain-oriented electrical steel sheet
A2 according to the second embodiment. The grain-oriented electrical steel sheet A2
according to the second e 5 mbodiment has an intermediate layer 2B2 mainly containing
silicon oxide and an insulation coating 32 on a surface of a base steel sheet 12.
[0115]
Metallic Fe phases 42 are present in the interface between the intermediate layer
2B2 and the insulation coating 32 in the grain-oriented electrical steel sheet A2 according
10 to the second embodiment. As shown in Fig. 3, when a cross section of the grainoriented
electrical steel sheet A2 according to the second embodiment perpendicular to
the rolling direction is observed, the fragment-like metallic Fe phases 42 are observed to
be continuously present along the interface between the intermediate layer 2B2 and the
insulation coating 32.
15 [0116]
In a method for manufacturing the grain-oriented electrical steel sheet A2
according to the second embodiment, an appropriate amount of the Fe-based oxides are
formed on the surface of a final-annealed steel sheet in a final annealing process. After
that, in the process of forming the intermediate layer (intermediate layer forming process
20 or intermediate layer and insulation coating forming process), Fe in the Fe-based oxides
is reduced and replaced by Si, whereby the intermediate layer 2B2 mainly containing
silicon oxide is formed. Therefore, the intermediate layer 2B2 having excellent
adhesion to the base steel sheet 12 is formed.
[0117]
25 When the Fe-based oxides are excessively formed on the surface of the final47
annealed steel sheet, in the end, coarse metallic Fe phases 42 are formed in the interface
between the intermediate layer 2B2 and the insulation coating 32, and it is not possible to
improve the adhesion of the insulation coating 32. When the Fe-based oxides are more
excessively formed on the surface of the final-annealed steel sheet, it is not possible for
all of the Fe-based oxides to be 5 replaced by the intermediate layer 2B2, and there is a
case where Fe-based oxides 52 remain in the interface between the intermediate layer
2B2 and the base steel sheet 12. The Fe-based oxides 52 that remain as described above
significantly deteriorate the adhesion of the insulation coating 32.
[0118]
10 Therefore, during the final annealing process in the middle of manufacturing, it
is necessary for an appropriate amount of Fe-based oxides, specifically, Fe-based oxides
having a thickness of 10 to 100 nm, to be formed on the surface of the final-annealed
steel sheet.
That is, the final-annealed steel sheet in the middle of the manufacturing of the
15 grain-oriented electrical steel sheet A2 according to the second embodiment needs to
include a base steel sheet and a Fe-based oxide coating disposed on the surface of the
base steel sheet, and the thickness of the Fe-based oxide coating needs to be 10 nm to
100 nm.
[0119]
20 The thickness mentioned herein refers to the length in a direction perpendicular
to the surface of the final-annealed steel sheet. When the thicknesses of the Fe-based
oxides are less than 10 nm, there is a case where it is not possible to form the
intermediate layer 2B2. When the thicknesses of the Fe-based oxides are more than 100
nm, as mentioned above, there are cases where the coarse metallic Fe phases 42 are
25 formed in the interface between the intermediate layer 2B2 and the insulation coating 32
48
and where the Fe-based oxides 52 remain in the interface between the intermediate layer
2B2 and the base steel sheet 12. Therefore, the final-annealed steel sheet preferably has
Fe-based oxides having a thickness of 10 to 100 nm on the surface.
[0120]
In the grain-oriented electrical st 5 eel sheet A2 obtained by forming the
intermediate layer 2B2 and the insulation coating 32 on the final-annealed steel sheet, it
is preferable that the Fe-based oxides 52 are not substantially present in the interface
between the base steel sheet 12 and the intermediate layer 2B2 in order to further
improve the adhesion of the insulation coating 32. When the number of the Fe-based
10 oxides 52 having a thickness of more than 2 nm is zero, it is possible to regard the Febased
oxides 52 as not substantially present. Therefore, in the grain-oriented electrical
steel sheet A2, the number of the Fe-based oxides 52 having a thickness of more than 2
nm is preferably set to zero in the interface between the base steel sheet 12 and the
intermediate layer 2B2.
15 [0121]
The presence or absence of the Fe-based oxides 52 having a thickness of more
than 2 nm in the interface between the base steel sheet 12 and the intermediate layer 2B2
can be confirmed by identifying Fe-based oxides using electron beam diffraction with a
TEM. In a cross section of the grain-oriented electrical steel sheet A2 perpendicular to
20 the rolling direction, the diameter of the electron beam is set to 10 nm, an electron beam
diffraction image oriented in a direction perpendicular to the surface of the grain-oriented
electrical steel sheet 2A from the inside of the base steel sheet 12 is acquired, and the
presence or absence of the Fe-based oxides 52 having a thickness of more than 2 nm is
confirmed. In a case where the Fe-based oxides 52 are present in the interface between
25 the base steel sheet 12 and the intermediate layer 2B2, regions in which an electron beam
49
diffraction image of the Fe-based oxide 52 is obtained are continuously present in a
region in which an electron beam diffraction image of the base steel sheet 12 is obtained.
In a case where the Fe-based oxides 52 are not present in the interface, a region in which
an electron beam diffraction pattern unique to amorphous substances, from which no
clear dot-like electron beam diffraction pa 5 ttern can be obtained and which is ordinarily
called a halo pattern, is obtained appears in a region in which an electron beam
diffraction image of the base steel sheet 12 is obtained. The distance from a point at
which the electron beam diffraction image of the Fe-based oxide 52 appears to a point at
which the electron beam diffraction pattern disappears (the length in a direction
10 perpendicular to the surface of the base steel sheet 12 (the interface between the base
steel sheet 12 and the intermediate layer 2B2)) is defined as the thickness of the Fe-based
oxide 52. Fe2O3, Fe3O4, FeO, and Fe2SiO4 are determined as the Fe-based oxides 52.
The presence or absence of the Fe-based oxides having a thickness of more than 2 nm is
confirmed by the above-described method at 10 to 50 sites.
15 [0122]
Hereinafter, the three-layer structure of the grain-oriented electrical steel sheet
according to the second embodiment and the metallic Fe phases that are observed in the
interface between the intermediate layer and the insulation coating will be described. In
the following description, reference signs in the drawings will be shown only in a case
20 where the drawings are described.
[0123]
Intermediate layer
The intermediate layer is formed on a surface of the base steel sheet and mainly
contains silicon oxide. The intermediate layer has a function of adhering the base steel
25 sheet and the insulation coating.
50
[0124]
In the grain-oriented electrical steel sheet according to the second embodiment,
the intermediate layer refers to a layer present between a base steel sheet described below
and an insulation coating described below.
Silicon o 5 xide, which is the main component of the intermediate layer, is
preferably SiOx (x=1.0 to 2.0) and more preferably SiOx (x=1.5 to 2.0). This is
because silicon oxide is more stable. When a heat treatment for forming silicon oxide
on the surface of the base steel sheet is sufficiently performed, it is possible to form silica
(SiO2).
10 [0125]
The expression “mainly containing silicon oxide” means that, as the
composition of the intermediate layer, a Fe content of less than 30 atom%, a P content of
less than 5 atom%, a Si content of 20 atom% or more, an O content of 50 atom% or
more, and a Mg content of 10 atom% or less are satisfied.
15 [0126]
When the thickness of the intermediate layer is too thin, a thermal stress
relaxation effect is not sufficiently developed, and it is not possible to ensure the
adhesion of the insulation coating. Therefore, the thickness of the intermediate layer is
preferably 2 nm or more and more preferably 5 nm or more. On the other hand, when
20 the thickness of the intermediate layer is too thick, since the thickness becomes
nonuniform and a defect such as a void or a crack is generated in the intermediate layer,
the thickness of the intermediate layer is preferably 400 nm or less and more preferably
300 nm or less. In addition, the intermediate layer is made as thin as possible as long as
it is possible to ensure the adhesion of the insulation coating, whereby it is possible to
25 contribute to the enhancement of productivity by shortening the formation time and to
51
suppress a decrease in the space factor at the time of using the grain-oriented electrical
steel sheet as an iron core. Therefore, the thickness of the intermediate layer is more
preferably 100 nm or less or 50 nm or less.
[0127]
The thickness or position of the 5 intermediate layer can be obtained by observing
a cross section of the intermediate layer as described below with a scanning transmission
electron microscope (STEM) in which the diameter of an electron beam is set to 10 nm
and measuring the thickness or position.
Specifically, a test piece is cut out by focused ion beam (FIB) machining such
10 that the cut surface becomes parallel to the sheet thickness direction and perpendicular to
a rolling direction, and the cross-sectional structure of this cut surface is observed with a
Scanning-TEM at a magnification at which each layer is included in an observation
visual field (light field image). In a case where each layer is not included in the
observation visual field, the cross-sectional structure is observed in a plurality of visual
15 fields that are continuous with each other.
[0128]
In order to specify each layer in the cross-sectional structure, a line analysis is
performed along the sheet thickness direction from the surface of the grain-oriented
electrical steel sheet using scanning TEM-energy dispersive X-ray spectroscopy (STEM20
EDS), and a quantitative analysis is performed on the chemical composition of each
layer. On the observation cross section of the specimen, the line analysis is performed
at 100 sites at intervals of 0.1 μm in a direction parallel to the surface of the base steel
sheet. As the line analysis, a quantitative analysis is performed at intervals of 1 nm in
the sheet thickness direction by energy dispersive X-ray spectroscopy (EDS) in which the
25 diameter of an electron beam is set to 10 nm.
52
Elements to be quantitatively analyzed are five elements of Fe, P, Si, O, and Mg.
[0129]
From the light field image observation with the STEM and the quantitative
analysis results of STEM-EDS, the kind of each layer is specified, and the thickness of
each layer is measured. Specifically, the kind of 5 each layer is specified according to
criteria described below, and the average value of the thicknesses of each layer measured
at the 100 sites is calculated to obtain the thickness of each layer. The specification of
each layer and the measurement of the thickness described below are all performed on
the same scanning line of the same specimen.
10 [0130]
A region in which the Fe content is 80 atom% or more is determined as the base
steel sheet.
A region in which the Fe content is less than 45 atom%, the P content is 5
atom% or more, the Si content is less than 20 atom%, the O content is 50 atom% or
15 more, and the Mg content is 10 atom% or less is determined as the insulation coating.
A region satisfying a Fe content of less than 30 atom%, a P content of less than 5
atom%, a Si content of 20 atom% or more, an O content of 50 atom% or more, and a Mg
content of 10 atom% or less is determined as the intermediate layer.
[0131]
20 When each layer is determined by the chemical composition as described above,
there is a case where a region that does not correspond to any compositions in the
analysis (blank region) is generated. However, in the grain-oriented electrical steel
sheet according to the second embodiment, each layer is specified so as to be included in
the three-layer structure of the base steel sheet, the intermediate layer, and the insulation
25 coating. Determination criteria therefor are as described below.
53
[0132]
Regarding a blank region between the base steel sheet and the intermediate
layer, the center of the blank region (the center in the thickness direction, which shall
apply below) is considered as a boundary, the base steel sheet side is regarded as the base
steel sheet, and the intermediate layer side 5 is regarded as the intermediate layer.
Regarding a blank region between the insulation coating and the intermediate layer, the
center of the blank region is considered as a boundary, the insulation coating side is
regarded as the insulation coating, and the intermediate layer side is regarded as the
intermediate layer.
10 [0133]
When the intermediate layer is not present, regarding a blank region between the
base steel sheet and the insulation coating, the center of the blank region is regarded as a
boundary, the base steel sheet side is regarded as the base steel sheet, and the insulation
coating side is regarded as the insulation coating. A blank region, the base steel sheet,
15 and the insulation coating that are present between the intermediate layer and the
intermediate layer are regarded as the intermediate layer. A blank region and the
insulation coating that are present between the base steel sheet and the base steel sheet is
regarded as the base steel sheet. A blank region between the insulation coating and the
insulation coating is regarded as the insulation coating.
20 With this procedure, it is possible to separate the base steel sheet, the insulation
coating, and the intermediate layer.
[0134]
Insulation coating
The insulation coating is formed on the surface of the intermediate layer 2B2 as
25 shown in Fig. 3 and has a function of reducing the iron loss of the grain-oriented
54
electrical steel sheet A2 as a single sheet by applying tension to the base steel sheet 12
and a function of ensuring an electrical insulating property between the grain-oriented
electrical steel sheets A2 at the time of using a laminate of the grain-oriented electrical
steel sheets A2.
5 [0135]
The insulation coating is not particularly limited, can be appropriately selected
and used from well-known insulating coatings depending on uses or the like, and may be
any of an organic coating or an inorganic coating.
Examples of the organic coating include a polyamine-based resin, an acrylic
10 resin, an acrylic styrene resin, an alkyd resin, a polyester resin, a silicone resin, a
fluororesin, a polyolefin resin, a styrene resin, a vinyl acetate resin, an epoxy resin, a
phenolic resin, an urethane resin, a melamine resin, and the like. In addition, examples
of the inorganic coating include a phosphate-based coating, an aluminum phosphatebased
coating, furthermore, an organic-inorganic complex-based coating containing the
15 above-described resin, or the like. More specifically, the insulation coating may be an
insulating coating obtained by baking an insulating coating having colloidal silica
particles dispersed in a matrix as shown in Fig. 3. Here, the “matrix” refers to a
substrate of the insulation coating and is made from, for example, a non-crystalline
phosphate. Examples of the non-crystalline phosphate that configures the matrix
20 include aluminum phosphate, magnesium phosphate, and the like. The baked insulation
coating is made up of a plurality of compounds containing one or more of P, O, and S.
[0136]
When the thickness of the insulation coating is too thin, tension that is applied to
the base steel sheet becomes small, and the insulating property also degrades.
25 Therefore, the thickness of the insulation coating is preferably 0.1 μm or more and more
55
preferably 0.5 μm or more. On the other hand, when the thickness of the insulation
coating exceeds 10 μm, there is a case where a crack is generated in the insulation
coating in an insulation coating forming stage. Therefore, the thickness of the
insulation coating is preferably 10 μm or less and more preferably 5 μm or less.
5 [0137]
On the insulation coating, a magnetic domain refining treatment for forming a
local fine strain region or groove may be performed with a laser or plasma or by a
mechanical method, etching, or other methods.
[0138]
10 Base steel sheet
The chemical composition and configuration such as the structure of the base
steel sheet in the grain-oriented electrical steel sheet according to the second embodiment
do not have any direct relationship with the coating structure of the grain-oriented
electrical steel sheet except that Si and one or more of Sn and Sb are contained as
15 essential components. Therefore, the base steel sheet in the grain-oriented electrical
steel sheet according to the second embodiment is not particularly limited as long as the
action and effect of the grain-oriented electrical steel sheet according to the second
embodiment can be obtained, and it is possible to use, for example, a base steel sheet in
an ordinary grain-oriented electrical steel sheet. Hereinafter, the base steel sheet in the
20 grain-oriented electrical steel sheet according to the second embodiment will be
described.
[0139]
Chemical composition of base steel sheet
As the chemical composition of the base steel sheet, it is possible to use the
25 chemical composition of a base steel sheet in an ordinary grain-oriented electrical steel
56
sheet except that one or more of Sn and Sb and Si are contained as essential components.
Since the function of Si in the grain-oriented electrical steel sheet is the same as in
ordinary grain-oriented electrical steel sheets, the Si content may be determined within an
ordinary range depending on characteristics required for a target grain-oriented electrical
steel shee 5 t. In the following description, the unit of the amount of each component in
the chemical composition of the base steel sheet is “mass%”.
[0140]
The base steel sheet of the grain-oriented electrical steel sheet according to the
second embodiment contains, for example, Si: 0.50% to 7.00%, Sn and Sb: 0.005% to
10 1.00% in total, C: 0.005% or less, and N: 0.0050% or less, and the remainder is made up
of Fe and an impurity. Hereinafter, regarding a typical example of the chemical
composition of the base steel sheet of the grain-oriented electrical steel sheet according to
the present embodiment, reasons for limiting the chemical composition will be described.
[0141]
15 Si: 0.50% to 7.00%
Silicon (Si) increases the electrical resistance of the grain-oriented electrical
steel sheet to decrease the iron loss. When the Si content is less than 0.50%, this effect
cannot be sufficiently obtained. Therefore, the Si content is preferably 0.50% or more.
The Si content is more preferably 1.50% or more and still more preferably 2.50% or
20 more.
On the other hand, when the Si content exceeds 7.00%, the saturation magnetic
flux density of the base steel sheet decreases, and the iron loss of the grain-oriented
electrical steel sheet deteriorates. Therefore, the Si content is preferably 7.00% or less.
The Si content is more preferably 5.50% or less and still more preferably 4.50% or less.
25 [0142]
57
Sn and Sb: 0.005% to 1.00% in total
Sn or Sb is an essential component and an effective component for preferably
controlling the forms of the metallic Fe phases. The reason for the forms of the metallic
Fe phases being preferably controlled by containing Sn or Sb is not clear, but Sn and Sb
are a component having 5 an influence on surface oxidation behaviors through surface
segregation. Therefore, it is considered that the forms of the metallic Fe phases can be
preferably controlled indirectly by changing the forms of the Fe-based oxides that serve
as the origin of the metallic Fe phases. When the total amount of Sn and Sb is 0.005%
or less, an effect of preferably controlling the forms of the metallic Fe phases is not
10 obtained. Therefore, the total amount of Sn and Sb is set to 0.005% or more. The total
amount of Sn and Sb is preferably 0.10% or more and more preferably 0.30% or more.
On the other hand, when the total amount of Sn and Sb exceeds 1.00%, no metallic Fe
phases are formed. Therefore, the total amount of Sn and Sb is set to 1.00% or less.
The total amount of Sn and Sb is preferably 0.80% or less and more preferably 0.70% or
15 less.
[0143]
Here, “the amount of Sn and Sb is 0.005% to 1.00% in total” means that the
base steel sheet may contain any one of Sn or Sb alone and the amount of any one of Sn
or Sb may be 0.005% to 1.00% or the base steel sheet may contain both Sn and Sb and
20 the amount of Sn and Sb may be 0.005% to 1.00% in total.
[0144]
C: 0.005% or less
Carbon (C) forms a compound in the base steel sheet and deteriorates the iron
loss of the grain-oriented electrical steel sheet. Therefore, the C content is preferably
25 0.005% or less. The C content is more preferably 0.004% or less and still more
58
preferably 0.003% or less.
On the other hand, the C content is preferably as small as possible and thus may
be 0%, but there is a case where C is contained in steel as an impurity. Therefore, the C
content may be more than 0%.
5 [0145]
N: 0.0050% or less
Nitrogen (N) forms a compound in the base steel sheet and deteriorates the iron
loss of the grain-oriented electrical steel sheet. Therefore, the N content is preferably
0.0050% or less. The N content is more preferably 0.0040% or less and still more
10 preferably 0.0030% or less.
On the other hand, the N content is preferably as small as possible and thus may
be 0%, but there is a case where N is contained in steel as an impurity. Therefore, the N
content may be more than 0%.
The remainder of the chemical composition of the base steel sheet is made up of
15 Fe and an impurity. The “impurity” mentioned herein refers to an element that comes
from a component contained in a raw material or a component being mixed in a
manufacturing procedure at the time of industrially manufacturing the base steel sheet
and has no substantial influence on an effect that is obtained by the grain-oriented
electrical steel sheet according to the present embodiment.
20 [0146]
[Optional elements]
Basically, the chemical composition of the base steel sheet contains the abovedescribed
elements with the remainder made up of Fe and an impurity, but may contain
one or more optional elements instead of some of Fe for the purpose of improving the
25 magnetic properties or solving problems relating to manufacturing. Examples of the
59
optional elements that are contained instead of some of Fe include the following
elements. Since these elements may not be contained, the lower limits are 0%. On the
other hand, when the amounts of these elements are too large, a precipitate is generated,
thereby deteriorating the iron loss of the grain-oriented electrical steel sheet or ferrite
transformation is suppre 5 ssed to prevent the sufficient obtainment of a Goss orientation or
to decrease the saturation magnetic flux density, thereby deteriorating the iron loss of the
grain-oriented electrical steel sheet. Therefore, even in a case where these elements are
contained, the contents are preferably set within the following ranges.
Acid-soluble Al: 0.0065% or less,
10 Mn: 1.00% or less,
S and Se: 0.001% or less in total,
Bi: 0.010% or less,
B: 0.0080% or less,
Ti: 0.015% or less,
15 Nb: 0.020% or less,
V: 0.015% or less,
Cr: 0.30% or less,
Cu: 0.40% or less,
P: 0.50% or less,
20 Ni: 1.00% or less, and
Mo: 0.10% or less.
“S and Se: 0.001% or less in total” means that the base steel sheet may contain
any one of S or Se alone and the amount of any one of S or Se may be 0.001% or less or
the base steel sheet may contain both S and Se and the amount of S and Se may be
25 0.001% or less in total.
60
[0147]
The above-described chemical composition of the base steel sheet of the grainoriented
electrical steel sheet according to the present embodiment is obtained by
adopting a method for manufacturing the grain-oriented electrical steel sheet according to
the present embodiment using a 5 slab having a chemical composition described below.
[0148]
The chemical composition of the base steel sheet of the grain-oriented electrical
steel sheet according to the present embodiment is preferably measured using spark
optical emission spectrometry (Spark-OES). In addition, in the case of a small content,
10 the content may be measured using inductively coupled plasma-atomic emission
spectrometry (ICP-AES). Acid-soluble Al may be measured by ICP-MS using a filtrate
obtained by hydrolyzing a specimen with an acid. In addition, C and S may be
measured using an infrared absorption method after combustion, and N may be measured
using an inert gas fusion thermal conductivity method.
15 [0149]
Metallic Fe phases present in interface between intermediate layer and insulation
coating
Regarding the metallic Fe phases present in the interface between the
intermediate layer and the insulation coating, the present inventors found that the
20 adhesion of the insulation coating improves in a case where the percentage of the total of
the lengths of the metallic Fe phases with respect to the length of the interface is 5% to
50% in a cross section perpendicular to the rolling direction of the grain-oriented
electrical steel sheet. The percentage of the total of the lengths of the metallic Fe phases
with respect to the length of the interface can also be expressed as the linear fraction of
25 the metallic Fe phases (=“total of lengths of metallic Fe phases”/“length of interface
61
between intermediate layer and insulation coating”x100).
The length mentioned herein refers to the maximum length in a direction parallel
to the interface between the base steel sheet and the intermediate layer.
[0150]
The linear fraction of the 5 metallic Fe phases present in the interface between the
intermediate layer and the insulation coating is the degree of the interface between the
intermediate layer and the insulation coating occupied by the metallic Fe phases that is
expressed using a cross-sectional profile perpendicular to the rolling direction. As the
value of the linear fraction of the metallic Fe phases increases, the occupancy of the
10 metallic Fe phases in the interface between the intermediate layer and the insulation
coating increases, and the adhesion of the insulation coating is more likely to deteriorate.
Therefore, the linear fraction of the metallic Fe phases is preferably set to be small in
order to improve the adhesion of the insulation coating. Therefore, in the grain-oriented
electrical steel sheet according to the second embodiment, the linear fraction of the
15 metallic Fe phases is set to 50% or less. The linear fraction of the metallic Fe phases is
preferably 40% or less, more preferably 35% or less, and still more preferably 25% or
less.
[0151]
In the grain-oriented electrical steel sheet according to the second embodiment,
20 in the case of forming the intermediate layer and the insulation coating on a finalannealed
steel sheet in which the Fe-based oxides are present, the metallic Fe phases are
inevitably formed in a linear fraction of 5% or more. Therefore, in the grain-oriented
electrical steel sheet according to the second embodiment, the linear fraction of the
metallic Fe phases is set to 5% or more.
25 [0152]
62
Method for measuring linear fraction of metallic Fe phases
First, on a cross section perpendicular to the rolling direction, the lengths of a
region that is 1000 μm or longer in the sheet width direction and 10 or more metallic Fe
phases are measured with a SEM. The metallic Fe phases can be determined using a
reflected electron image that is obtained b 5 y observing a cross section of the grainoriented
electrical steel sheet perpendicular to the rolling direction with a SEM. The
reflected electron image is converted to a monochromatic image with 256 levels of
grayscale, and regions having ±20% grayscale levels of the average grayscale level of the
base steel sheet are determined as metallic Fe. Among the regions determined as
10 metallic Fe, regions that are not continuous with the base steel sheet are defined as the
metallic Fe phases. This is because the measurement target is the metallic Fe phases
present in the interface between the intermediate layer and the insulation coating. The
monochromatic image is converted to a binarized image using a 30% grayscale level
from the white side as a threshold value, and a white region is defined as the base steel
15 sheet.
The total of the obtained lengths of the metallic Fe phases is calculated, thereby
obtaining the total of the lengths of the metallic Fe phases present in the interface
between the intermediate layer and the insulation coating. The obtained total of the
lengths of the metallic Fe phases is divided by the length of the observation region in the
20 sheet width direction, thereby obtaining the percentage of the total of the lengths of the
metallic Fe phases with respect to the length of the interface between the intermediate
layer and the insulation coating in the cross section perpendicular to the rolling direction.
[0153]
Length of metallic Fe phase when cumulative relative frequency is 0.95
25 The present inventors found that a parameter having a correlation with the
63
adhesion of the insulation coating is not the average value and/or central value of the
lengths of the metallic Fe phases but the length of the metallic Fe phase when the
cumulative relative frequency is 0.95 in the cumulative frequency distribution of the
lengths of the metallic Fe phases. The present inventors found that it is possible to
enhance the adhesion of the insulation c 5 oating by controlling the length of the metallic Fe
phase when the cumulative relative frequency is 0.95 to 500 nm or less in a cross section
perpendicular to the rolling direction.
[0154]
That is, in a cross section of the grain-oriented electrical steel sheet according to
10 the second embodiment perpendicular to the rolling direction, the length of the metallic
Fe phase when the cumulative relative frequency is 0.95 in the cumulative frequency
distribution of the lengths of the metallic Fe phases present in the interface between the
intermediate layer and the insulation coating is preferably 500 nm or less. The length of
the metallic Fe phase when the cumulative relative frequency is 0.95 is preferably as
15 small as possible, but may be set to 50 nm or more.
Frequencies of metallic Fe phases are obtained every 25 nm in length, and the
cumulative frequency distribution of the lengths of the metallic Fe phases is obtained.
[0155]
The length of the metallic Fe phase when the cumulative relative frequency is
20 0.95 being 500 nm or less can also be said in a different manner as described below.
A distribution showing the number of metallic Fe phases every 25 nm in length
is obtained for the metallic Fe phases present in the interface between the intermediate
layer and the insulation coating in a cross section perpendicular to the rolling direction,
the numbers of the metallic Fe phases are sequentially added from the short length side
25 based on this distribution, and the cumulative frequency distribution is specified. In the
64
obtained cumulative frequency distribution, the length at which the number of the
metallic Fe phases reaches 95% of the total number is 500 nm or less.
[0156]
In a case where metallic Fe phases having a long length in the sheet thickness
direction are included in the interface 5 between the intermediate layer and the insulation
coating, adverse influences on the adhesion of the insulation coating are significant. In
the grain-oriented electrical steel sheet according to the second embodiment, the length
of the metallic Fe phase when the cumulative relative frequency is 0.95 is set to 500 nm
or less, whereby no large metallic Fe phases are present in the interface between the
10 intermediate layer and the insulation coating or, even when present, the number of large
metallic Fe phases is small, and thus it is possible to further improve the adhesion of the
insulation coating.
[0157]
Fig. 4 and Fig. 6 show examples of the relationship of the lengths of the metallic
15 Fe phases with frequencies and cumulative relative frequencies of the metallic Fe phases
present in the interface between the intermediate layer and the insulation coating of the
grain-oriented electrical steel sheet. The lengths (lengths in a direction parallel to the
interface) of the metallic Fe phases present in the interface between the intermediate
layer and the insulation coating can be measured using a reflected electron image that is
20 obtained by observing a cross section of the grain-oriented electrical steel sheet
perpendicular to the rolling direction with a scanning electron microscope (SEM). The
reflected electron image is converted to a monochromatic image with 256 levels of
grayscale, and regions having ±20% grayscale levels of the average grayscale level of the
base steel sheet are determined as metallic Fe. Among the regions determined as
25 metallic Fe, regions that are not continuous with the base steel sheet are defined as the
65
metallic Fe phases. This is because the measurement target is the metallic Fe phases
present in the interface between the intermediate layer and the insulation coating.
The monochromatic image is converted to a binarized image using a 30%
grayscale level from the white side as a threshold value, and a white region is defined as
5 the base steel sheet.
[0158]
The length of the metallic Fe phase is defined as the maximum length in a
direction parallel to the interface between the base steel sheet and the intermediate layer.
In addition, from the measurement values of the lengths of the metallic Fe phases, it is
10 possible to obtain a graph (cumulative frequency distribution) showing the relationship
of the lengths of the metallic Fe phases with frequencies and cumulative relative
frequencies of the metallic Fe phases present in the interface between the intermediate
layer and the insulation coating as shown in Fig. 4 and Fig. 6.
[0159]
15 In the method for measuring the lengths of the metallic Fe phases for preparing
the cumulative frequency distribution, the lengths of a region that is 1000 μm or longer in
the sheet width direction and 10 or more metallic Fe phases are measured with a SEM in
a cross section perpendicular to the rolling direction.
[0160]
20 Fig. 4 is a graph (cumulative frequency distribution) showing a relationship
among the lengths of the metallic Fe phases in the grain-oriented electrical steel sheet
according to the second embodiment, the frequencies and cumulative relative frequencies
of the lengths of the metallic Fe phases. In contrast, Fig. 6 is a graph (cumulative
frequency distribution) showing a relationship among the lengths of the metallic Fe
25 phases in a grain-oriented electrical steel sheet corresponding to the related art, the
66
frequencies and cumulative relative frequencies of the lengths of the metallic Fe phases.
[0161]
Fig. 6 and Fig. 4 are rarely different from each other in terms of the average
value and central value of the lengths of the metallic Fe phases. However, while the
length of the metallic Fe phase 5 when the cumulative relative frequency is 0.95 is 500 nm
or less in Fig. 4, the length of the metallic Fe phase when the cumulative relative
frequency is 0.95 exceeds 500 nm in Fig. 6.
[0162]
Method for manufacturing grain-oriented electrical steel sheet according to second
10 embodiment
Next, a method for manufacturing the grain-oriented electrical steel sheet
according to the second embodiment will be described.
[0163]
The method for manufacturing the grain-oriented electrical steel sheet described
15 below is a method for manufacturing the grain-oriented electrical steel sheet described in
the section of “the grain-oriented electrical steel sheet according to the second
embodiment”.
The method for manufacturing the grain-oriented electrical steel sheet according
to the second embodiment is classified into a manufacturing method according to a first
20 example in which the intermediate layer and the insulation coating are formed in separate
processes and a manufacturing method according to a second example in which the
intermediate layer and the insulation coating are formed in one process.
[0164]
The manufacturing method according to the first example, in which the
25 intermediate layer and the insulation coating are formed in separate processes, includes
67
a hot rolling process of heating a slab and then performing hot rolling to obtain a
hot-rolled steel sheet,
a hot-band annealing process of performing hot band annealing on the hot-rolled
steel sheet to obtain an annealed steel sheet, and
a cold rolling process of performing 5 cold rolling on the annealed steel sheet once
or twice or more with intermediate annealing performed therebetween to obtain a coldrolled
steel sheet.
[0165]
In addition, the manufacturing method according to the first example includes
10 a decarburization annealing process of performing decarburization annealing on
the cold-rolled steel sheet to obtain a decarburization-annealed steel sheet and
a final annealing process of heating the decarburization-annealed steel sheet
with an annealing separator having a MgO content of 10 mass% to 50 mass% applied to
a surface of the decarburization-annealed steel sheet to a temperature range of 1000ºC or
15 higher to perform final annealing and then removing the annealing separator to obtain a
final-annealed steel sheet.

WE CLAIMS

1. A grain-oriented electrical steel sheet comprising:
a base steel sheet in which a final-annealed film is substantially not present on a
5 surface;
an intermediate layer that is disposed on a surface of the base steel sheet and
mainly contains silicon oxide; and
an insulation coating disposed on a surface of the intermediate layer,
wherein, in the intermediate layer, a value obtained by dividing a standard
10 deviation σ of a thickness of the intermediate layer by an average value T of the thickness
of the intermediate layer is 0.500 or less.
2. A method for manufacturing the grain-oriented electrical steel sheet according to
claim 1, the method comprising:
15 heating a slab containing Si and then performing hot rolling to obtain a hotrolled
steel sheet,
performing hot band annealing on the hot-rolled steel sheet to obtain an
annealed steel sheet,
performing cold rolling on the annealed steel sheet once or twice or more with
20 intermediate annealing performed therebetween to obtain a cold-rolled steel sheet,
performing decarburization annealing on the cold-rolled steel sheet to obtain a
decarburization-annealed steel sheet,
heating the decarburization-annealed steel sheet with an annealing separator
having a MgO content of 10 mass% to 50 mass% applied to a surface of the
25 decarburization-annealed steel sheet and then removing the annealing separator to obtain
118
a final-annealed steel sheet,
performing thermal oxidation annealing on the final-annealed steel sheet to form
an intermediate layer on a surface of the final-annealed steel sheet, and
forming an insulation coating on the final-annealed steel sheet having the
5 intermediate layer formed thereon,
wherein, during cooling for final annealing,
T1 is set to 1100ºC in a case where a final annealing temperature is 1100ºC or
higher and T1 is set to the final annealing temperature in a case where the final annealing
temperature is lower than 1100ºC, and
10 the decarburization-annealed steel sheet is cooled within a temperature range of
T1 to 500ºC in an atmosphere having an oxidation degree (PH2O/PH2) of 0.3 to 100000,
in the thermal oxidation annealing for the formation of the intermediate layer,
during heating,
an average heating rate within a temperature range of 300ºC to 750ºC is
15 set to 20 ºC/second to 200 ºC/second, an oxidation degree (PH2O/PH2) within the
temperature range is set to 0.0005 to 0.1, the final-annealed steel sheet is heated up to a
temperature range of 750ºC to 1150ºC and
held within the temperature range of 750ºC to 1150ºC
in an atmosphere having an oxidation degree (PH2O/PH2) of 0.0005 to
20 0.2 for 10 seconds to 90 seconds.