[0001]The present invention relates to a grain-oriented electrical steel sheet, an
intermediate steel sheet for a grain-oriented electrical steel sheet, and methods for
10 manufacturing the same.
Priority is claimed on Japanese Patent Application No. 2019-5200, filed in Japan
on January 16, 2019, the content of which is incorporated herein by reference.
[Background Art]
[0002]
15 Grain-oriented electrical steel sheets are used as iron core materials of
transformers and the like. Grain-oriented electrical steel sheets are required to have
magnetic properties such as a low iron loss.
[0003]
Ordinarily, a coating is formed on the surface of a grain-oriented electrical steel
20 sheet in order to reduce the iron loss. This coating applies tension to the grain-oriented
electrical steel sheet and thereby reduces the iron loss of the steel sheet as a single sheet.
This coating also ensures an electrical insulating property between the grain-oriented
electrical steel sheets at the time of using a laminate of the steel sheets as an iron core
and thereby reduces the iron loss as the iron core.
25 [0004]
2
As a grain-oriented electrical steel sheet on which a coating is formed, there is a
grain-oriented electrical steel sheet in which a final-annealed film mainly containing
forsterite (Mg2SiO4) is formed on a surface of a base steel sheet and, furthermore, an
insulation coating is formed on the surface of the final-annealed film. That is, in this
case, the coating on the base 5 steel sheet includes the final-annealed film and the
insulation coating. The final-annealed film and the insulation coating each have both
functions of imparting an insulating property and of applying tension to the base steel
sheet.
[0005]
10 The final-annealed film mainly containing forsterite (Mg2SiO4) is formed by a
reaction between an annealing separator mainly containing magnesia (MgO) and the base
steel sheet occurring during a heat treatment in which the annealing separator and the
base steel sheet are held at 600ºC to 1200ºC for 30 hours or longer in final annealing that
causes secondary recrystallization in the steel sheet.
15 [0006]
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 steel sheet and baking and drying the coating solution at
300ºC to 950ºC for 10 seconds or longer.
20 [0007]
In order for the insulation coating to exhibit the functions of imparting an
insulating property and of applying tension to the base steel sheet, there is a demand for
high adhesion between these coatings (the final-annealed film and the insulation coating)
and the base steel sheet.
25 [0008]
3
In the related art, the adhesion has been ensured mainly by an anchoring effect
attributed to unevenness in the interface between the base steel sheet and the finalannealed
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. Therefore, this unevenness in the interface 5 also serves as a cause for hindering
the reduction of the iron loss of grain-oriented electrical steel sheets.
[0009]
Since the formation of a final-annealed film such as a forsterite film causes
unevenness in the interface between the base steel sheet and the final-annealed film, in
10 order to reduce the iron loss, it is effective to suppress the formation of the final-annealed
film and thereby smooth the surface of the base steel sheet.
[0010]
For example, Patent Document 1 and Patent Document 2 propose techniques for
smoothing the surface of the base steel sheet in the absence of a final-annealed film
15 mainly containing forsterite in order to accelerate the reduction of the iron loss.
[0011]
Specifically, Patent Document 1 discloses a method for manufacturing a grainoriented
electrical steel sheet in which a final-annealed film is removed by pickling or the
like and the surface of a base steel sheet is smoothed by chemical polishing or electric
20 field polishing. In addition, Patent Document 2 discloses a method for manufacturing a
grain-oriented electrical steel sheet in which the formation of a final-annealed film is
suppressed using an annealing separator containing alumina (Al2O3) during final
annealing to smooth the surface of a base steel sheet.
[0012]
25 However, in the case of forming an insulation coating in contact with the smooth
4
surface of a base steel sheet (directly on the surface of the base steel sheet) on which a
final-annealed film is not formed as obtained by the technique of Patent Document 1 or
Patent Document 2, there has been a problem in that it is difficult to make the insulation
coating adhere to the surface of the base steel sheet (sufficient adhesion cannot be
5 obtained).
[0013]
Regarding such a problem, for example, Patent Document 3, Patent Document 4,
Patent Document 5, and Patent Document 6 propose techniques for forming an
intermediate layer (base coating) between the base steel sheet and the insulation coating
10 in order to enhance the adhesion of the insulation coating to the smoothed surface of the
base steel sheet.
[0014]
Patent Document 3 discloses a method for forming an intermediate layer on the
surface of a base steel sheet by applying an aqueous solution of a phosphate or an
15 alkaline metal silicate to the surface of the base steel sheet. In addition, Patent
Document 4 to Patent Document 6 disclose methods for forming an external oxidationtype
silicon oxide film as an intermediate layer on a base steel sheet by performing a heat
treatment at an appropriately controlled temperature in an appropriately controlled
atmosphere for several tens of seconds to several minutes.
20 [0015]
According to the intermediate layers proposed by Patent Document 3 to Patent
Document 6, a certain degree of effect can be obtained in terms of the improvement of
the adhesion of the insulation coating to the base steel sheet and the suppression of the
reduction of the iron loss by smoothing unevenness in the interface between the base
25 steel sheet and the coating. However, in recent years, there has been a demand for
5
additional improvement in coating adhesion. Regarding such a demand, new techniques
as described in Patent Document 7, Patent Document 8, Patent Document 9, Patent
Document 10, Patent Document 11, and Patent Document 12 have been proposed.
[0016]
Patent Document 7 d 5 iscloses a technique for forming an externally oxidized
granular oxide on the surface of a base steel sheet in addition to an externally oxidized
film mainly containing silicon oxide. In addition, Patent Document 8 discloses a
technique for controlling cavities in an externally oxidized layer mainly containing
silicon oxide.
10 [0017]
Patent Document 9 to Patent Document 11 disclose techniques for modifying an
externally oxidized film mainly containing silicon oxide by containing metallic iron or a
metallic oxide (for example, a Si-Mn-Cr oxide, a Si-Mn-Ca-Ti oxide, a Fe oxide, or the
like) in the externally oxidized film.
15 [0018]
Patent Document 12 discloses a grain-oriented electrical steel sheet having a
multilayered intermediate layer including an oxide film mainly containing silicon oxide
generated by an oxidation reaction and a coating layer mainly containing silicon oxide
formed by application and baking.
20 [0019]
As described above, grain-oriented electrical steel sheets in which an externally
oxidized film mainly containing silicon oxide is used as an intermediate layer, thereby
ensuring the adhesion of an insulation coating to a base steel sheet and having excellent
magnetic properties even when the surface of the base steel sheet is smoothed have been
25 proposed.
6
[0020]
Meanwhile, in a case where a grain-oriented electrical steel sheet is used for a
toroidal core, an EI core, or the like as an iron core of a transformer, the grain-oriented
electrical steel sheet is worked (bent) to a desired shape. In addition, in the case of
using a grain-oriented electrical st 5 eel sheet having an intermediate layer worked to a
desired shape in a transformer, there is a case where an insulation coating peels off due to
a reaction with moisture in the air, moisture in an oil in which the iron core is immersed,
or the like. Therefore, for grain-oriented electrical steel sheets that are used for a
toroidal core, an EI core, or the like as an iron core of a transformer, not only the
10 adhesion of an insulation coating to a base steel sheet, but also water resistance are
required.
However, among the techniques of the above-described grain-oriented electrical
steel sheet having an intermediate layer mainly containing silicon oxide described in the
patent documents, no documents mention the peeling of the insulation coating attributed
15 to water.
[Citation List]
[Patent Document]
[0021]
[Patent Document 1]
20 Japanese Unexamined Patent Application, First Publication No. S49-096920
[Patent Document 2]
International Publication WO 2002/088403
[Patent Document 3]
Japanese Unexamined Patent Application, First Publication No. H05-279747
25 [Patent Document 4]
7
Japanese Unexamined Patent Application, First Publication No. H06-184762
[Patent Document 5]
Japanese Unexamined Patent Application, First Publication No. H09-078252
[Patent Document 6]
Japanese Unexamined P 5 atent Application, First Publication No. H07-278833
[Patent Document 7]
Japanese Unexamined Patent Application, First Publication No. 2002-322566
[Patent Document 8]
Japanese Unexamined Patent Application, First Publication No. 2002-363763
10 [Patent Document 9]
Japanese Unexamined Patent Application, First Publication No. 2003-313644
[Patent Document 10]
Japanese Unexamined Patent Application, First Publication No. 2003-171773
[Patent Document 11]
15 Japanese Unexamined Patent Application, First Publication No. 2002-348643
[Patent Document 12]
Japanese Unexamined Patent Application, First Publication No. 2004-342679
[Summary of the Invention]
[Problems to be Solved by the Invention]
20 [0022]
The present invention has been made in consideration of the above-described
problems. An object of the present invention is to provide a grain-oriented electrical
steel sheet having an intermediate layer mainly containing silicon oxide that has achieved
the improvement of the adhesion of an insulation coating and the improvement of water
25 resistance, which has not been recognized as a problem in the related art, an intermediate
8
steel sheet for the grain-oriented electrical steel sheet, and methods for manufacturing the
same.
The expression “water resistance is excellent” means that, when water is
attached to the surface of the grain-oriented electrical steel sheet, it is possible to
suppress the progress of peeling 5 of the insulation coating attributed to corrosion.
[Means for Solving the Problem]
[0023]
The gist of the present invention is as described below.
(1) A grain-oriented electrical steel sheet including a base steel sheet, an
10 intermediate layer that is formed on a surface of the base steel sheet and mainly contains
silicon oxide, and an insulation coating that is formed on a surface of the intermediate
layer, in which a number density of oxide particles in a region from the surface of the
base steel sheet to a depth of 10 μm toward an inside of the base steel sheet is 0.020
oxide particles/μm2 or less, and an area rate of an intermediate layer-remaining region in
15 which the intermediate layer does not peel off but remains in a region in which the
insulation coating peels off after a bend test performed using a mandrel according to JIS
K 5600-5-1 (1999) is 20% or more.
[0024]
(2) A method for manufacturing a grain-oriented electrical steel sheet including a
20 hot rolling process of heating a slab at 1280ºC or lower and then performing hot rolling
to manufacture a hot-rolled steel sheet, a hot-band annealing process of performing hot
band annealing on the hot-rolled steel sheet to manufacture an annealed steel sheet, a
cold rolling process of performing cold rolling on the annealed steel sheet to manufacture
a cold-rolled steel sheet, a decarburization annealing process of performing
25 decarburization annealing on the cold-rolled steel sheet to manufacture a base steel sheet,
9
an annealing separator applying process of applying an annealing separator having a
composition containing 50 mass% or more of alumina (Al2O3) and, as a remainder, 0 to
50 mass% of magnesia (MgO) to the base steel sheet, a final annealing process of
performing final annealing on the base steel sheet after the annealing separator applying
process, a cooling process of cooling the base 5 steel sheet after the final annealing process
in an atmosphere having an oxidation degree PH2O/PH2, which is a ratio of a water vapor
partial pressure to a hydrogen partial pressure, within a temperature range of 1100ºC to
500ºC set to 0.30 to 100000, an intermediate layer forming process of performing a heat
treatment on the base steel sheet after the cooling process to form an intermediate layer
10 mainly containing silicon oxide on a surface of the base steel sheet, and an insulation
coating forming process of forming an insulation coating on a surface of the intermediate
layer after the intermediate layer forming process.
[0025]
(3) An intermediate steel sheet for a grain-oriented electrical steel sheet
15 including a base steel sheet and a film-shaped oxide formed on a surface of the base steel
sheet, in which the film-shaped oxide is present so as to cover the surface of the base
steel sheet in a film shape, and a number density of the oxide particles in a region from
an outermost surface of the base steel sheet to a depth of 10 μm toward an inside of the
base steel sheet is 0.020 oxide particles/μm2 or less.
20 [0026]
(4) A method for manufacturing an intermediate steel sheet for a grain-oriented
electrical steel sheet including a hot rolling process of heating a slab at 1280ºC or lower
and then performing hot rolling to manufacture a hot-rolled steel sheet, a hot-band
annealing process of performing hot band annealing on the hot-rolled steel sheet to
25 manufacture an annealed steel sheet, a cold rolling process of performing cold rolling on
10
the annealed steel sheet to manufacture a cold-rolled steel sheet, a decarburization
annealing process of performing decarburization annealing on the cold-rolled steel sheet
to manufacture a base steel sheet, an annealing separator applying process of applying an
annealing separator having a composition containing 50 mass% or more of alumina
(Al2O3) and, as a remainder, 0 to 50 m 5 ass% of magnesia (MgO) to the base steel sheet, a
final annealing process of performing final annealing on the base steel sheet after the
annealing separator applying process, and a cooling process of cooling the base steel
sheet after the final annealing process in an atmosphere having an oxidation degree
PH2O/PH2, which is a ratio of a water vapor partial pressure to a hydrogen partial pressure,
10 within a temperature range of 1100ºC to 500ºC set to 0.30 to 100000.
[Effects of the Invention]
[0027]
According to the present invention, it is possible to provide a grain-oriented
electrical steel sheet having an intermediate layer mainly containing silicon oxide in
15 which the adhesion of an insulation coating and the water resistance are favorable. In
addition, it is possible to provide an intermediate steel sheet for a grain-oriented electrical
steel sheet and a method for manufacturing the same.
[Embodiment for implementing the Invention]
[0028]
20 The present inventors performed studies regarding a method for solving the
above-described problems.
[0029]
In the beginning, the present inventors observed regions in which an insulation
coating peeled off due to moisture in the air, moisture in an oil in which an iron core was
25 to be immersed, or the like (hereinafter, referred to as insulation coating-peeling region).
11
As a result, the present inventors noticed the fact that the structure of an insulation
coating-peeling portion due to water and the structure of an insulation coating-peeling
portion due to bending deformation have a correlation with each other.
[0030]
Specifically, the 5 correlation is as described below.
In the beginning, the present inventors performed the bend test regulated by JIS
K 5600-5-1 (1999) on grain-oriented electrical steel sheets having an intermediate layer
and an insulation coating. On the surfaces (the inner side surfaces of bent portions) of
test pieces after the bend test, regions from which the insulation coating peeled off were
10 observed using a scanning electron microscope (SEM). The observation results showed
that, in the region from which the insulation coating peeled off (insulation coatingpeeling
region), there were a region in which the insulation coating peeled off but the
intermediate layer remained (intermediate layer-remaining region) and a region in which
the intermediate layer also peeled off together with the insulation coating and the surface
15 of the base steel sheet (base metal) was exposed (base steel sheet-exposed region).
[0031]
Both the intermediate layer-remaining region and the base steel sheet-exposed
region as described above also appeared in grain-oriented electrical steel sheets in which
the insulation coating peeled off due to water. In addition, in a case where the
20 insulation coating peeled off due to water, the total area of the base steel sheet-exposed
region was larger than the total area of the intermediate layer-remaining region in the
region in which the insulation coating peeled off.
[0032]
Based on the above-described finding, the present inventors considered the
25 peeling property of an insulation coating attributed to water in grain-oriented electrical
12
steel sheets having an intermediate layer mainly containing silicon oxide as described
below. In a case where a part of the insulation coating peels off due to bending or the
like, as the proportion of the total area of the base steel sheet-exposed region in the
insulation coating-peeling region increases, the progress rate of the peeling of the
insulation coating due to water increases. 5 That is, the peeling of the insulation coating
due to water is further accelerated. The reason therefor is not clear, but is considered to
be that, in the base steel sheet-exposed region, corrosion occurs due to the contact with
water, and thus the peeling of the insulation coating is accelerated due to this corrosion.
On the other hand, as the proportion of the total area of the intermediate layer-remaining
10 region in the insulation coating-peeling region increases, the progress rate of the peeling
of the insulation coating due to water decreases. In addition, the degree of peeling of
the insulation coating due to water has a correlation with the proportion of the
intermediate layer-remaining region in the insulation coating-peeling region at the time
of performing the bend test regulated by JIS K 5600-5-1 (1999).
15 [0033]
Furthermore, the present inventors performed studies regarding a method for
increasing the area rate of the intermediate layer-remaining region in the insulation
coating-peeling region after the bend test. At this time, the studies were performed with
attention paid to a change in the adhesion between the base steel sheet and the
20 intermediate layer by the control of the surface state of the base steel sheet on which the
intermediate layer was still to be formed.
[0034]
As a result, the present inventors found that, when an appropriate annealing
separator is selected, furthermore, the atmosphere in a cooling procedure for final
25 annealing is controlled, and the oxidation state of the surface of the base steel sheet is
13
made to be appropriate at a point in time where the final annealing ends, the adhesion of
the intermediate layer that is to be formed afterwards improves.
[0035]
Specifically, the magnesia (MgO) content rate of the annealing separator is set to
50 mass% or less, whereby 5 the presence of an internal oxidation-type oxide in the
vicinity of the surface layer of the base steel sheet is prevented at least at a point in time
where secondary recrystallization ends. The point in time where secondary
recrystallization ends means a point in time where cooling for the final annealing begins.
[0036]
10 Here, the internal oxidation type means a state in which an oxide does not
penetrate the base steel sheet up to the surface of the base steel sheet and is present
surrounded by the base steel sheet when observed on a cross section of the steel sheet.
Examples of the internal oxidation-type oxide (hereinafter, also referred to as the internal
oxide) include forsterite (Mg2SiO4), silica (Si-O), mullite (Al-Si-O), and the like. When
15 the internal oxidation-type oxide is formed in the base steel sheet, the iron loss of the
grain-oriented electrical steel sheet deteriorates.
[0037]
Furthermore, regarding the atmosphere within a temperature range of 1100ºC to
500ºC in the cooling process of the final annealing, the oxidation degree (PH2O/PH2)
20 represented by the ratio of the water vapor partial pressure to the hydrogen partial
pressure is set within a range of 0.30 to 100000, and an external oxidation-type oxide is
formed on the surface of the base steel sheet.
[0038]
Here, the external oxidation-type does not mean a form of an oxide that intrudes
25 into the inside of the base steel sheet, which is the internal oxidation type, but means a
14
shape of an oxide that almost uniformly covers the surface of the base steel sheet, that is,
a state in which an oxide covers the surface of the base steel sheet in a film shape.
Therefore, hereinafter, there will be a case where the external oxidation-type oxide is also
referred to as the film-shaped oxide. The external oxidation-type oxide is a compound
of an element of the base steel shee 5 t and oxygen. In the present embodiment, examples
thereof include oxides such as iron oxides (FeO and Fe2O3) and fayalite (Fe-Si-O) having
a laminar structure.
[0039]
Technically, “internal oxidation” and “external oxidation” are not classified by
10 the above-described forms, but classified by the oxidation mechanisms. However, in
the invention, such classification is complicated, and it is also difficult to confirm the
mechanisms after oxidation. Therefore, in the description of the present embodiment,
the forms of oxides as a result of the above-described oxidation will be used for
classification.
15 [0040]
The reason for the area rate of the intermediate layer-remaining region in the
insulation coating-peeling region after the bend test being increased by the control of the
oxide on the surface of the final-annealed base steel sheet is not clear, but is considered
as described below.
20 Ordinarily, the intermediate layer that is formed in an intermediate layer forming
process is considered to be formed in a procedure in which the base steel sheet containing
Si is oxidized. However, in a case where an oxide is already present on the surface of
the final-annealed base steel sheet, there is a need to consider an influence of the
reduction of the oxide on the intermediate layer. External oxidation-type oxides that are
25 relatively slowly formed as the temperature lowers within a broad temperature range of
15
1100ºC to 500ºC after final annealing are considered to have a film shape and highly
maintain continuousness between the base steel sheet and the oxides in terms of a
concentration change of an element in the sheet thickness direction, the structural change,
and the like. It is considered that the formation of the intermediate layer during the
reduction of such an oxide makes the bondin 5 g structures of atoms between the surface of
the base steel sheet and the intermediate layer stronger and improves the adhesion.
[0041]
In a case where an oxide has a tendency of intruding into the base steel sheet,
this oxide is not reduced during the formation of the intermediate layer, and an uneven
10 shape remains in the interface between the base steel sheet and the intermediate layer.
This uneven shape serves as an obstacle to domain wall motion when electrical steel
sheets have been magnetized. Therefore, it is considered that the formation of an
internal oxidation-type oxide needs to be avoided as much as possible.
[0042]
15 A grain-oriented electrical steel sheet according to an embodiment of the present
invention (grain-oriented electrical steel sheet according to the present embodiment), an
intermediate steel sheet for a grain-oriented electrical steel sheet according to the present
embodiment, and methods for manufacturing the same, which have been completed
based on the above-described findings, will be described.
20 The grain-oriented electrical steel sheet according to the present embodiment
includes a base steel sheet, an intermediate layer that is formed on a surface of the base
steel sheet and mainly contains silicon oxide, and an insulation coating that is formed on
the surface of the intermediate layer. The number density of oxide particles in a region
from the surface of the base steel sheet to a depth of 10 μm toward the inside of the base
25 steel sheet (a region from the surface of the base steel sheet as the starting point through a
16
depth position of 10 μm in the depth direction (thickness direction) toward the inside as
the ending point) is 0.020 oxide particles/μm2 or less. In addition, the area rate of an
intermediate layer-remaining region in which the intermediate layer does not peel off but
remains in a region in which the insulation coating peels off after a bend test performed
using a mandrel a 5 ccording to JIS K 5600-5-1 (1999) is 20% or more.
[0043]
[Grain-oriented electrical steel sheet]
The grain-oriented electrical steel sheet according to the present embodiment is
a steel sheet obtained by forming an intermediate layer and an insulation coating on an
10 intermediate steel sheet for a grain-oriented electrical steel sheet.
In other words, the grain-oriented electrical steel sheet according to the present
embodiment includes a base steel sheet and a coating that is formed in contact with a
surface of the base steel sheet. This coating includes an intermediate layer that is
formed in contact with the surface of the base steel sheet and an insulation coating that is
15 formed in contact with the surface of the intermediate layer.
[0044]
[Base steel sheet]
The grain-oriented electrical steel sheet according to the present embodiment
has characteristics in the number density of oxide particles in the surface layer portion of
20 the base steel sheet and the configuration of the coating (intermediate layer and insulation
coating) that is formed on the surface of the base steel sheet.
Specifically, the number density of an oxide in a region from the surface of the
base steel sheet to a depth of 10 μm toward the inside of the base steel sheet is 0.020
oxide particles/μm2 or less. In the present embodiment, a state in which the number
25 density of oxide particles is 0.020 oxide particles/μm2 or less is expressed as “an internal
17
oxide is substantially not present”. That is, an internal oxide, which is a state in which
the oxide has intruded into the inside of the base steel sheet, is substantially not present
in the surface layer portion (the region from the surface of the base steel sheet to a depth
of 10 μm toward the inside of the base steel sheet) of the base steel sheet provided in the
grain-oriented electrical steel shee 5 t according to the present embodiment. When the
number density of oxide particles in the region from the surface of the base steel sheet to
a depth of 10 μm toward the inside of the base steel sheet is more than 0.020 oxide
particles/μm2, the iron loss of the grain-oriented electrical steel sheet deteriorates.
[0045]
10 The number density of oxide (internal oxide) particles in the above-described
region can be obtained by the following method. That is, the number density can be
obtained by observing a cross section of the steel sheet perpendicular to a rolling
direction with a scanning electron microscope (SEM) at a magnification of 5000 times or
more and measuring the number density of oxide particles having a circle-equivalent
15 diameter of 0.1 μm or more in the region that is 100 μm long in a direction parallel to the
surface of the steel sheet and is 10 μm deep from the surface (outermost surface) of the
base steel sheet toward the inside of the base steel sheet.
[0046]
Furthermore, in the grain-oriented electrical steel sheet according to the present
20 embodiment, the area rate of an intermediate layer-remaining region in which the
intermediate layer does not peel off but remains in a region in which the insulation
coating peels off after a bend test performed using a mandrel according to JIS K 5600-5-
1 (1999) is 20% or more. The diameter of the mandrel is, for example, 10 to 16 mm.
[0047]
25 When the base steel sheet is exposed, it is considered that the base steel sheet
18
corrodes due to the contact with water and the peeling of the insulation coating further
progresses. On the other hand, when the adhesion between the base steel sheet and the
intermediate layer is favorable, the intermediate layer does not peel off but remains even
in a region in which the insulation coating peeled off. That is, it is considered that, even
when the insulation coating has p 5 eeled off, as long as the intermediate layer remains, it is
possible to suppress the corrosion of the base steel sheet and to suppress the additional
peeling of the insulation coating. Therefore, in the grain-oriented electrical steel sheet
according to the present embodiment, the adhesion between the base steel sheet and the
intermediate layer is enhanced.
10 [0048]
Since the base steel sheet provided in the grain-oriented electrical steel sheet
according to the present embodiment is controlled to a state in which the area rate of the
intermediate layer-remaining region in which the intermediate layer does not peel off but
remains in the region in which the insulation coating peels off after the bend test
15 (hereinafter, expressed as intermediate layer residual rate in some cases) reaches 20% or
more, the water resistance is excellent. When the area rate of the above-described
intermediate layer-remaining region is less than 20%, the water resistance degrades.
The intermediate layer residual rate may be 100%.
[0049]
20 As long as the base steel sheet of the grain-oriented electrical steel sheet
according to the present embodiment satisfies the number density of the internal oxide
particles and the area rate of the intermediate layer-remaining region, the chemical
composition and the structure are not particularly limited. For example, the base steel
sheet of the present embodiment may be a base steel sheet in an ordinary grain-oriented
25 electrical steel sheet. Hereinafter, an example of the base steel sheet of the grain19
oriented electrical steel sheet according to the present embodiment will be described.
[0050]
[Chemical composition of base steel sheet]
As the chemical composition of the base steel sheet of the grain-oriented
electrical steel sheet 5 according to the present embodiment, it is possible to use the
chemical composition of a base steel sheet in an ordinary grain-oriented electrical steel
sheet. The chemical composition of the base steel sheet contains, for example, the
following elements. “%” used to express the amount of each element in the chemical
composition of the base steel sheet indicates “mass%” unless particularly otherwise
10 described. Numerical limitation ranges expressed using “to” in the middle include the
lower limit value and the upper limit value in the ranges.
[0051]
The base steel sheet of the grain-oriented electrical steel sheet according to the
present embodiment contains, for example, Si: 0.50% to 7.00%, C: 0.005% or less, and
15 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.
[0052]
20 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
25 more.
20
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.
5 [0053]
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
0.005% or less. The C content is more preferably 0.004% or less and still more
10 preferably 0.003% or less.
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%.
[0054]
15 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
preferably 0.0030% or less.
20 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%.
[0055]
The remainder of the chemical composition of the base steel sheet is made up of
25 Fe and an impurity. The “impurity” mentioned herein refers to an element that comes
21
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.
5 [0056]
[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
10 magnetic characteristics or solving problems relating to manufacturing. Examples of
the 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
15 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. 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,
20 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,
25 Nb: 0.020% or less,
22
V: 0.015% or less,
Sn: 0.50% or less,
Sb: 0.50% or less,
Cr: 0.30% or less,
5 Cu: 0.40% or less,
P: 0.50% or less,
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
10 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
0.001% or less in total.
[0057]
The above-described chemical composition of the base steel sheet of the grain15
oriented 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 slab having a chemical composition described below.
[0058]
The chemical composition of the base steel sheet of the grain-oriented electrical
20 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,
the content may be measured using inductively coupled plasma-mass spectrometry (ICPMS)
as necessary. 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
25 measured using an infrared absorption method after combustion, and N may be measured
23
using an inert gas fusion thermal conductivity method.
[0059]
[Roughness of surface of base steel sheet]
The roughness of the surface of the base steel sheet is not particularly limited.
However, when unevenness i 5 s formed on the surface of the base steel sheet, there is a
case where an iron loss reduction action is hindered. In order to avoid such hindrance
of the iron loss reduction action, for example, the roughness of the surface of the base
steel sheet is preferably 1.0 μm or less in terms of the arithmetic average roughness (Ra).
A more preferable upper limit of the arithmetic average roughness Ra of the surface of
10 the base steel sheet is 0.8 μm, and a still more preferable upper limit is 0.6 μm. The
lower limit of the arithmetic average roughness Ra of the surface of the base steel sheet
may be set to 0.001 μm.
[0060]
The arithmetic average roughness Ra of the surface of the base steel sheet is
15 measured by the following method.
A sample is collected in a manner that a cross section of the grain-oriented
electrical steel sheet perpendicular to a rolling direction is used as an observation surface.
The roughness of the surface of the base steel sheet is measured on the obtained
observation surface. Specifically, the positional coordinates of the surface of the base
20 steel sheet in the sheet thickness direction are measured with a precision of 0.01 μm or
more in the interface between the base steel sheet and the intermediate layer on the
observation surface (cross section) in a case where a coating such as a final-annealed film
or the intermediate layer is formed on the surface of the base steel sheet or on the
observation surface (cross section) in a case where no coating is formed and the surface
25 of the base steel sheet is exposed, and the arithmetic average roughness Ra is calculated
24
according to JIS B 0601 (2001). The positional coordinates are measured in a
continuous 2 mm range at 0.1 μm pitches in a direction parallel to the surface of the base
steel sheet (20000 points in total), and the arithmetic average roughness Ra is obtained
with a standard length set to 2 mm. The arithmetic average roughness Ra is obtained by
the above-described method in at least five a 5 rbitrary places on the surface of the base
steel sheet, and the average value of the Ra values obtained in the respective places is
defined as the arithmetic average roughness Ra of the surface of the base steel sheet.
This observation can be performed with a SEM, and it is practical to apply image
processing for the measurement of the positional coordinates.
10 [0061]
[Intermediate layer]
The intermediate layer is formed in contact with the surface of the base steel
sheet on which the internal oxide is substantially not present. The intermediate layer is
an externally oxidized film mainly containing silicon oxide. Here, the expression
15 “mainly containing silicon oxide” means that, as the composition of the intermediate
layer, a Fe content of less than 30% by atom, a P content of less than 5% by atom, a Si
content of less than 50% by atom and 20% by atom or more, an O content of less than
80% by atom and 50% by atom or more, and a Mg content of 10% by atom or less are
satisfied.
20 [0062]
The intermediate layer is a layer that is disposed between the base steel sheet
and the insulation coating and is effective for making the base steel sheet and the
insulation coating adhere to each other. The intermediate layer is formed by, for
example, as described in manufacturing processes described below, reducing a film25
shaped oxide formed by performing a specific cooling process in a final annealing
25
process.
[0063]
Silicon oxide that 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 5 heat treatment for forming silicon oxide on the surface of
the base steel sheet is sufficiently performed, it is possible to form silica (SiO2).
[0064]
In the intermediate layer formed by performing a heat treatment on the base steel
sheet under conditions in which the base steel sheet is held within a temperature range of
10 600ºC to 1150ºC for 10 to 600 seconds in an atmosphere containing 20 to 50 volume% of
hydrogen with a remainder made up of nitrogen and an impurity and having a dew point
of -20ºC to 2ºC, silicon oxide is present in an amorphous state. The intermediate layer
mainly containing amorphous silicon oxide formed under these heat treatment conditions
is an intermediate layer that has a high strength enough to withstand thermal stress and is
15 made of a dense material that has a relatively small elastic modulus to be capable of
easily relaxing thermal stress, which is preferable.
[0065]
The base steel sheet of the grain-oriented electrical steel sheet contains Si in a
high concentration (for example, Si: 0.50 to 7.00 mass%). Therefore, a strong chemical
20 affinity is developed between the intermediate 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.
[0066]
The thickness of the intermediate layer is not particularly limited. When the
25 thickness is 2 nm or more, since the adhesion of the insulation coating to the base steel
26
sheet is effectively enhanced, the thickness of the intermediate layer is preferably 2 nm or
more and more preferably 5 nm or more. When the thickness of the intermediate layer
is 400 nm or less, a defect such as a void or a crack in the intermediate layer is
effectively suppressed. Therefore, the thickness of the intermediate layer is preferably
400 nm or less and more preferably 5 300 nm or less. The intermediate layer is made as
thin as possible as long as it is possible to ensure the coating adhesion, 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 of the intermediate layer
10 is still more preferably 100 nm or less and far still more preferably 50 nm or less.
[0067]
The method for measuring the thickness of the intermediate layer is as described
below.
The thickness is measured by observing a cross section of the intermediate layer
15 with a transmission electron microscope (TEM) in which the diameter of an electron
beam is set to 10 nm. Specifically, for example, a specimen is cut out for TEM
observation so as to have an observation cross section parallel to the sheet thickness
direction, in the observation cross section of the specimen, five or more measurement
positions that are 2 μm or more apart from each other in the width direction are selected
20 from a measurement region that is 10 μm or more wide in a direction parallel to the
surface of the base steel sheet and includes the intermediate layer, the above-described
base steel sheet, and the insulation coating described below, and the thicknesses of the
intermediate layer are measured with a TEM. The average of the measured values is
regarded as the thickness of the intermediate layer. In the case of measuring the
25 thickness of the intermediate layer at each measurement position in the measurement
27
region with a TEM, a layer that is present between the base steel sheet and the insulation
coating is measured as the intermediate layer.
[0068]
[Insulation coating]
The insulation coating 5 is formed on the surface of the intermediate layer. As
the insulation coating, it is possible to use a well-known insulation coating. As an
example, the insulation coating is made of a compound mainly containing P, O, and Si
and may contain Cr. The insulation coating applies tension to the base steel sheet to
reduce the iron loss of the steel sheet as a single sheet. Furthermore, the insulation
10 coating ensures an electrical insulating property between the grain-oriented electrical
steel sheets at the time of using a laminate of the grain-oriented electrical steel sheets.
[0069]
When the insulation coating becomes thin, since tension that is applied to the
base steel sheet becomes small, and the insulating property also degrades, the thickness
15 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,
since there is a concern that a crack may be generated in the insulation coating in an
insulation coating-forming stage, the thickness of the insulation coating is preferably 10
μm or less and more preferably 5 μm or less.
20 The thickness of the insulation coating can be measured by observing a cross
section of the insulation coating (or grain-oriented electrical steel sheet) with a
transmission electron microscope (TEM). As a specific measurement method, the same
method as the method for measuring the thickness of the intermediate layer may be used.
[0070]
25 On the insulation coating, a magnetic domain refining treatment for forming a
28
local fine strain region or groove may be performed with a laser or plasma or by a
mechanical method, etching, or other methods as necessary.
[0071]
[Characteristics of coating structure of grain-oriented electrical steel sheet]
In the grain-oriented electrical st 5 eel sheet according to the present embodiment,
the area rate of the intermediate layer-remaining region in which the intermediate layer
does not peel off but remains in the region in which the insulation coating peels off after
a bend test performed using a mandrel according to JIS K 5600-5-1 (1999) is controlled
to be 20% or more. Therefore, in the case of performing a bend test according to JIS K
10 5600-5-1 (1999), the area rate of the intermediate layer-remaining region in which the
intermediate layer does not peel off but remains in the region in which the insulation
coating peels off reaches 20% or more. The above-described area rate of the
intermediate layer-remaining region is preferably 30% or more and more preferably 40%
or more. The intermediate layer residual rate may be 100%.
15 [0072]
The area rate of the intermediate layer-remaining region is obtained by the
following method.
A rectangular sample that is 10 mm long in a direction perpendicular to a rolling
direction of the grain-oriented electrical steel sheet and 150 mm long in a direction
20 parallel to the rolling direction is collected. In a test piece, the observation surface of
the 10 mm × 150 mm sample is regarded as a surface including the coating. A bend test
is performed on the collected sample according to JIS K 5600-5-1 (1999). Specifically,
the collected sample is coiled around a round bar (mandrel) having a diameter of 10 to 16
mm and bent 180°. The bent test piece is bent back.
25 [0073]
29
The observation surface after the bend test (the inner side surface of the bent
portion) is observed with a COMPO image of a SEM, and a region in which the
insulation coating peeled off (insulation coating-peeling region) in the observation
surface is specified. Specifically, the COMPO image of the observation surface is
converted to a monochromatic imag 5 e with 256 levels of grayscale, and a region having a
grayscale level of 50% or less from the white side is determined as the region in which
the insulation coating peels off. The total area of the specified insulation coatingpeeling
region is obtained.
[0074]
10 The evaluation area of insulation coating peeling in the bend test is defined by
the following expression. In a case where the insulation coating peeling area is less
than 5% of the evaluation area, the insulation coating peeling area is re-evaluated by
decreasing the bending diameter (using a mandrel having a small diameter). As a result
of the re-evaluation, in a case where the insulation coating peeling area is 5% or more of
15 the evaluation area, the area rate of the intermediate layer-remaining region is obtained.
(Evaluation area of insulation coating peeling)=(diameter of mandrel)×(ratio of
circumference to diameter)÷2
[0075]
Furthermore, the insulation coating-peeling region in the observation surface is
20 mapped using an energy dispersive X-ray spectroscope (SEM-EDS), and a Si
concentration distribution by atom% is obtained. In the obtained Si concentration
distribution, the maximum value of the Si concentration and the minimum value of the Si
concentration are specified. A region that satisfies the following expression is defined
as the intermediate layer-remaining region.
25 (Si concentration of region)>{(maximum value of Si concentration)+(minimum
30
value of Si concentration)}/2
In a case where the maximum value of the Si concentration and the minimum
value of the Si concentration satisfy the following expression, the area rate of the
intermediate layer-remaining region is regarded as 0%.
(Maximum value of Si 5 concentration)-(minimum value of Si concentration)<5
atom%
[0076]
The proportion of the total area of the intermediate layer-remaining region in the
observation surface in the EDS mapping total area of the insulation coating-peeling
10 region (coating peeling portion) is defined as the area rate (%) of the intermediate layerremaining
region. That is, the area rate of the intermediate layer-remaining region is
defined by the following expression.
Area rate of intermediate layer-remaining region=(total area of intermediate
layer-remaining region)/(EDS mapping total area)×100
15 Here, the EDS mapping total area is set to 15 mm2 or more. In a case where
the area of the coating peeling portion is not sufficient in one test piece, the area rate of
the intermediate layer-remaining region may be calculated as the average value obtained
using a plurality of test pieces.
[0077]
20 When the area rate of the intermediate layer-remaining region in which the
intermediate layer does not peel off but remains in the region in which the insulation
coating peels off after a bend test performed using a mandrel according to JIS K 5600-5-
1 (1999) is 20% or more, the adhesion of the intermediate layer to the base steel sheet is
sufficiently high. Therefore, in this case, since the base steel sheet is covered with the
25 intermediate layer even in a state in which a part of the insulation coating peeled off, it is
31
possible to suppress the progress of the peeling of the insulation coating attributed to
corrosion occurring when water is attached to the surface of the steel sheet. That is, it is
possible to enhance the water resistance of the grain-oriented electrical steel sheet.
[0078]
[Regarding intermediate steel shee 5 t for grain-oriented electrical steel sheet]
An intermediate steel sheet for a grain-oriented electrical steel sheet according to
the present embodiment includes a base steel sheet and a film-shaped oxide formed on a
surface of the base steel sheet. The film-shaped oxide is present so as to cover the
surface of the base steel sheet in a film shape. In addition, in the base steel sheet, the
10 number density of oxide (internal oxide) particles present in the base steel sheet in a
region from the surface of the base steel sheet to a depth of 10 μm toward the inside of
the base steel sheet is 0.020 oxide particles/μm2 or less.
This intermediate steel sheet is a steel sheet that is used to manufacture the
grain-oriented electrical steel sheet according to the present embodiment and is a final15
annealed steel sheet (more specifically, a steel sheet after a cooling process and before an
intermediate layer forming process described below). With respect to this intermediate
steel sheet, the intermediate layer mainly containing silicon oxide is formed on the
surface of the base steel sheet, and furthermore, the insulation coating is formed on the
surface of the intermediate layer, whereby the grain-oriented electrical steel sheet
20 according to the present embodiment is obtained.
[0079]
In the intermediate steel sheet for a grain-oriented electrical steel sheet
according to the present embodiment, an internal oxide, which is a state in which the
oxide has intruded into the inside of the base steel sheet, is substantially not present on
25 the surface of the base steel sheet. In a case where an internal oxide is present after
32
final annealing, the internal oxide is not reduced during the formation of the intermediate
layer, and the internal oxide remains on the surface of the base steel sheet. This internal
oxide serves as an obstacle to domain wall motion when the grain-oriented electrical steel
sheet has been magnetized, and the iron loss of the grain-oriented electrical steel sheet
5 deteriorates.
On the other hand, a film-shaped oxide formed by external oxidation, which
covers the surface of the base steel sheet in a film shape, is present on the surface of the
base steel sheet.
[0080]
10 The expression “the internal oxide is substantially not present” specifically
indicates that the number density of oxide particles in a region from the surface
(outermost surface) of the base steel sheet to a depth of 10 μm in the sheet thickness
direction toward the inside of the base steel sheet (a region from the surface of the base
steel sheet as the starting point through a depth position of 10 μm in the depth direction
15 (thickness direction) toward the inside as the ending point) is 0.020 oxide particles/μm2
or less. The number density of oxide particles in this region can be obtained by
observing a cross section of the steel sheet with a scanning electron microscope (SEM) at
a magnification of 5000 times or more and measuring the number density of oxide
particles having a circle-equivalent diameter of 0.1 μm or more in the region that is 100
20 μm long in a direction parallel to the surface of the steel sheet and is 10 μm deep from
the surface of the base steel sheet toward the inside of the base steel sheet.
This number density of the internal oxide particles does not change even when
the intermediate layer and the insulation coating are formed.
[0081]
25 The oxide is configured in a film shape that covers the entire surface of the base
33
steel sheet by adjusting the conditions of a cooling process after final annealing.
Specifically, the base steel sheet is cooled in the cooling process after final annealing,
and the oxide is obtained by cooling the base steel sheet in an atmosphere in which the
oxidation degree (PH2O/PH2) represented by the ratio of the water vapor partial pressure to
the hydrogen pa 5 rtial pressure is set to 0.30 to 100000 within a temperature range in
which the base steel sheet reaches 1100ºC to 500ºC. When the oxidation degree is 0.30
to 100000, the film-shaped oxide has a hierarchical structure and uniformly covers the
surface of the base steel sheet. As a result, an intermediate layer having a strong bond
with the base steel sheet is formed in the next process, and it is considered that the
10 adhesion of the insulation coating is enhanced.
[0082]
The film-shaped oxide after final annealing is mainly iron oxides (FeO and
Fe2O3) and fayalite (Fe-Si-O). Therefore, it is considered that, in an atmosphere in the
next process in which the intermediate layer is mainly formed, Fe in the iron oxides is
15 reduced, and this film-shaped oxide turns into an intermediate layer mainly containing
external oxidation-type silicon oxide.
[0083]
Next, a method for manufacturing a grain-oriented electrical steel sheet
according to the present embodiment and a method for manufacturing an intermediate
20 steel sheet for a grain-oriented electrical steel sheet according to the present embodiment
will be described.
The coatings (intermediate layer and insulation coating) having the abovedescribed
characteristics can be manufactured by, for example, manufacturing methods
described below.
25 [0084]
34
The intermediate steel sheet for a grain-oriented electrical steel sheet according
to the present embodiment is obtained by a manufacturing method including the
following processes (S0) to (S62).
(S0) Preparation process
5 (S1) Hot rolling process
(S2) Hot-band annealing process
(S3) Cold rolling process
(S4) Decarburization annealing process
(S5) Annealing separator applying process
10 (S61) Final annealing process
(S62) Cooling process
[0085]
The grain-oriented electrical steel sheet according to the present embodiment is
obtained by a manufacturing method including the processes (S0) to (S62) and,
15 furthermore, processes (S7) and (S8).
(S7) Intermediate layer forming process
(S8) Insulation coating forming process
[0086]
Hereinafter, each process will be described.
20 [0087]
[S0: Preparation process]
In the preparation process, a slab is prepared. The method for manufacturing
the slab is not particularly limited, and the following method is an exemplary example.
Molten steel is manufactured (smelting). The slab is manufactured using the
25 molten steel. The slab may be manufactured by the continuous casting method. The
35
slab may be manufactured by manufacturing an ingot using molten steel and blooming
the ingot. The slab may be manufactured by a different method. The thickness of the
slab is not particularly limited. The thickness of the slab is, for example, 150 to 350
mm. The thickness of the slab is preferably 220 to 280 mm. As the slab, a so-called
thin slab having a thickness of 10 to 70 mm m 5 ay be used. In the case of using a thin
slab, it is possible to skip rough rolling before final rolling in the hot rolling process.
[0088]
[Chemical composition of slab]
In order to obtain the chemical composition of the base steel sheet in an ordinary
10 grain-oriented electrical steel sheet, the chemical composition of the slab can be set to,
for example, the following ranges in consideration of the contents or the like that change
in the middle of manufacturing from the slab to the grain-oriented electrical steel sheet.
“%” used to express the amount of each element in the chemical composition of the slab
indicates “mass%” unless particularly otherwise described. Numerical limitation ranges
15 expressed using “to” in the middle include the lower limit value and the upper limit value
in the ranges.
Si: 0.80% to 7.00%,
C: 0.085% or less,
Acid-soluble Al: 0.010% to 0.065%,
20 N: 0.0040% to 0.0120%,
Mn: 0.05% to 1.00%,
S and Se: 0.003% to 0.015% in total, and
Remainder: Fe and impurity.
Hereinafter, each element will be described.
25 [0089]
36
Si: 0.80 to 7.00%
Silicon (Si) increases the electrical resistance of the grain-oriented electrical
steel sheet to decrease the iron loss. When Si content is less than 0.80%, γ
transformation occurs during final annealing, and the crystal orientation of the grainoriented
e 5 lectrical steel sheet is impaired.
On the other hand, when the Si content exceeds 7.00%, cold workability
degrades, and a crack is likely to be generated during cold rolling. Therefore, a
preferable Si content is 0.80% to 7.00%. The Si content is more preferably 2.00% or
more and still more preferably 2.50% or more. In addition, the Si content is more
10 preferably 4.50% or less and still more preferably 4.00% or less.
[0090]
C: 0.085% or less
Carbon (C) is inevitably contained. C is an effective element for controlling
primary recrystallization structures, but adversely affects the magnetic characteristics.
15 Therefore, the C content is preferably 0.085% or less. The C content is preferably as
small as possible.
However, in the case of taking the productivity in industrial production into
account, the C content is preferably 0.020% or more and more preferably 0.040% or
more.
20 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.
[0091]
Acid-soluble Al: 0.010% to 0.065%
25 Acid-soluble aluminum (Al) bonds to N to be precipitated as (Al, Si)N and
37
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
is preferably 0.010% to 0.065%. The acid-soluble Al content is more preferably
0.015% or more and still more preferably 0.020% or more. From the viewpoint of the
stability of secondary recrystallization, the a 5 cid-soluble Al content is more preferably
0.045% or less and still more preferably 0.035% or less.
When remaining after final annealing, acid-soluble Al forms a compound and
deteriorates the iron loss of the grain-oriented electrical steel sheet. Therefore, it is
preferable to decrease the amount of acid-soluble Al that is contained in the final10
annealed steel sheet as much as possible by purification during final annealing.
Depending on the conditions of final annealing, there is a case where the final-annealed
steel sheet contains no acid-soluble Al.
[0092]
N: 0.0040% to 0.0120%
15 Nitrogen (N) bonds to Al to function as an inhibitor. When the N content is
less than 0.0040%, a sufficient amount of an inhibitor is not generated. The N content
is more preferably 0.0050% or more and still more preferably 0.0060% or more.
On the other hand, when the N content exceeds 0.0120%, a blister, which is one
kind of defect, is likely to be generated in the steel sheet. Therefore, a preferable N
20 content is 0.0040% to 0.0120%. The N content is more preferably 0.0110% or less and
still more preferably 0.0100% or less.
N is purified in the final annealing process, and the N content reaches 0.0050%
or less after the final annealing process.
[0093]
25 Mn: 0.05% to 1.00%
38
Manganese (Mn) bonds to S or Se to generate MnS or MnSe and functions as an
inhibitor. In a case where the Mn content is within a range of 0.05% to 1.00%,
secondary recrystallization is stabilized. Therefore, a preferable Mn content is 0.05% to
1.00%. The Mn content is preferably 0.06% or more and more preferably 0.07% or
5 more.
In addition, the Mn content is more preferably 0.50% or less and still more
preferably 0.20% or less.
Depending on the conditions of final annealing, there is a case where the finalannealed
steel sheet contains no Mn.
10 [0094]
S and Se: 0.003% to 0.015% in total
Sulfur (S) and selenium (Se) bond to Mn to generate MnS or MnSe and function
as an inhibitor. When the amount of S and Se is 0.003% to 0.015% in total, secondary
recrystallization is stabilized. Therefore, a preferable amount of S and Se is 0.003% to
15 0.015% in total.
When remaining after final annealing, S and Se form a compound and
deteriorate the iron loss of the grain-oriented electrical steel sheet. Therefore, it is
preferable to decrease the amount of S and Se that are contained in the final-annealed
steel sheet as much as possible by purification during final annealing. Depending on the
20 conditions of final annealing, there is a case where the final-annealed steel sheet contains
no S and Se.
[0095]
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
25 0.003% to 0.015% or the slab may contain both S and Se and the amount of S and Se
39
may be 0.003% to 0.015% in total.
[0096]
The remainder in the chemical composition of the slab that is used to
manufacture the grain-oriented electrical steel sheet according to the present embodiment
is made up of Fe and an impurity. 5 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 of the grain-oriented electrical steel sheet according to the present
embodiment and has no substantial adverse influence on an effect that is obtained by the
10 grain-oriented electrical steel sheet according to the present embodiment.
[0097]
[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, the chemical
15 composition of the slab may contain one or more optional elements instead of some of
Fe. 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: 0.50% or less,
25 Sb: 0.50% or less,
40
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.
[0098]
[S1: Hot rolling process]
In the hot rolling process, hot rolling is performed on the prepared slab using a
hot rolling mill to manufacture a steel sheet (hot-rolled steel sheet).
10 Specifically, first, the slab is heated. During heating, for example, the slab is
charged into a well-known heating furnace or a well-known soaking furnace and heated.
A preferable heating temperature of the slab is 1280ºC or lower. The heating
temperature of the slab is set to 1280ºC or lower, whereby it is possible to avoid a variety
of problems generated in the case of heating the slab at, for example, a temperature
15 higher than 1280ºC (a necessity of a designated heating furnace, a large amount of
molten scale, and the like). A preferable upper limit of the heating temperature of the
slab is 1250ºC. The heating time of the slab may be set to 40 to 120 minutes.
[0099]
The lower limit value of the heating temperature of the slab is not particularly
20 limited. However, in a case where the heating temperature is too low, there is a case
where hot rolling becomes difficult and the productivity degrades. Therefore, the
heating temperature may be set within a range of 1280ºC or lower in consideration of the
productivity. A preferable lower limit of the heating temperature of the slab is 1100ºC.
[0100]
25 It is also possible to begin hot rolling before the temperature of the slab lowers
41
after casting without performing the slab heating process.
[0101]
Hot rolling is performed on the heated slab using a hot rolling mill to
manufacture a hot-rolled steel sheet. The hot rolling mill includes, for example, a rough
rolling mill and a final rolling 5 mill disposed downstream of the rough rolling mill. The
rough rolling mill includes rough rolling stands arranged in a row. Each rough rolling
stand includes a plurality of rolls disposed vertically. The final rolling mill also,
similarly, includes final rolling stands arranged in a row. Each final rolling stand
includes a plurality of rolls disposed vertically. Heated steel is rolled with the rough
10 rolling mill and then further rolled with the final rolling mill, thereby manufacturing a
hot-rolled steel sheet.
[0102]
The thickness of the hot-rolled steel sheet that is manufactured by hot rolling is
not particularly limited. The thickness of the hot-rolled steel sheet is, for example, 3.5
15 mm or less.
The final temperature in the hot rolling process (the temperature of the steel
sheet on the outlet side of the final rolling stand that rolls the steel sheet at the end in the
final rolling mill) is, for example, 900ºC to 1000ºC.
The hot-rolled steel sheet is manufactured by the above-described hot rolling
20 process.
[0103]
[S2: Hot-band annealing process]
In the hot-band annealing process, hot band annealing is performed on the hotrolled
steel sheet obtained by the hot rolling process to obtain an annealed steel sheet.
25 [0104]
42
As the conditions of the hot band annealing, well-known conditions may be
used. For example, the annealing temperature (the furnace temperature in a hot band
annealing furnace) in the hot band annealing is 750ºC to 1200ºC. The holding time at
the annealing temperature is, for example, 30 to 600 seconds.
5 [0105]
[S3: Cold rolling process]
In the cold rolling process, cold rolling is performed on the annealed steel sheet
after the hot band annealing.
[0106]
10 In the cold rolling process, cold rolling may be performed only once or may be
performed a plurality of times. In the case of performing the cold rolling a plurality of
times, it is also possible to perform cold rolling, then, perform intermediate annealing for
the purpose of softening, and then perform cold rolling again. As the intermediate
annealing conditions, a well-known method may be used.
15 A pickling treatment may be performed on the annealed steel sheet before cold
rolling is performed on the annealed steel sheet.
[0107]
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
20 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
25 the intermediate annealing process are determined depending on characteristics
43
demanded for the finally manufactured grain-oriented electrical steel sheet and the
manufacturing costs.
[0108]
In the cold rolling performed once or a plurality of times, the cumulative cold
rolling reduction (cumulative 5 rolling reduction) is preferably 80% or larger and more
preferably 90% or larger. A preferable upper limit of the cumulative cold rolling
reduction is 95%. Here, the cumulative cold rolling reduction (%) is defined as
described below.
Cumulative cold rolling reduction (%)=(1-sheet thickness of cold-rolled steel
10 sheet after final cold rolling/sheet thickness of annealed steel sheet before beginning of
initial cold rolling)×100
[0109]
The cold-rolled steel sheet obtained by the cold rolling process is wound in a
coil shape. The sheet thickness of the cold-rolled steel sheet is not particularly limited,
15 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.
[0110]
[S4: Decarburization annealing process]
In the decarburization annealing process, decarburization annealing is performed
20 on the cold-rolled steel sheet obtained by the cold rolling process.
The decarburization annealing is performed by, for example, the following
method. The cold-rolled steel sheet is charged into a heat treatment furnace. The
temperature of the heat treatment furnace (decarburization annealing temperature) is held
at, for example, 800ºC to 950ºC for 30 to 180 seconds, and the atmosphere of the heat
25 treatment furnace is set to a wet atmosphere containing hydrogen and nitrogen.
44
Decarburization annealing is performed under the above-described conditions,
thereby developing primary recrystallization and removing carbon in the steel sheet from
the steel sheet.
[0111]
[5 S5: Annealing separator applying process]
In the annealing separator applying process, an annealing separator is applied to
the surface of the decarburization-annealed base steel sheet. In ordinary methods for
manufacturing a grain-oriented electrical steel sheet, an annealing separator containing
90 mass% or more of MgO is used. However, in this case, a glass film having an
10 uneven shape is formed on the surface of the steel sheet. The formation of a glass film
having an uneven shape deteriorates iron losses. Therefore, in the method for
manufacturing a grain-oriented electrical steel sheet according to the present
embodiment, an annealing separator having a composition containing 50 mass% or more
of alumina (Al2O3) with a remainder of 0 to 50 mass% of magnesia (MgO) is used as the
15 annealing separator. When the MgO content is 50 mass% or less, it is possible to
suppress the formation of an internal oxide that serves as a cause for an uneven shape in
the interface with the steel sheet while forming the film-shaped oxide. A preferable
upper limit of MgO in the annealing separator is 45 mass% and a more preferable upper
limit is 40 mass%.
20 [0112]
A preferable lower limit of MgO is 10 mass% and a more preferable lower limit
is 15 mass%. When the MgO content is 10 mass% or more, it is possible to suppress
the formation of mullite (Al-Si-O), which is a kind of internal oxide. Therefore, it is
possible to suppress the deterioration of iron losses due to internal oxides.
25 Al2O3 may be set to 100 mass%. In addition, Al2O3 may be set to 90 mass% or
45
less or 85 mass% or less. Furthermore, Al2O3 may be set to 55 mass% or more or 60
mass%.
[0113]
[S61: Final annealing process]
In the final annealing process, fina 5 l annealing is performed on the base steel
sheet (coil) after the annealing separator applying process. Therefore, the annealing
separator is baked, and secondary recrystallization is caused in the base steel sheet.
[0114]
When the final annealing is performed, the surface of the base steel sheet is
10 oxidized, and a film-shaped oxide is formed on the surface of the base steel sheet.
For example, in the case of applying an annealing separator mainly containing
Al2O3, a film-shaped oxide mainly containing an oxide of Fe and Si, which are the main
components of the steel sheet, is formed.
[0115]
15 The final annealing conditions are, for example, as described below. The
atmosphere in a furnace in the final annealing is not particularly limited and may be a
well-known atmosphere.
[0116]
Final annealing temperature: 1100°C to 1300°C
20 Holding time at final annealing temperature: 20 to 24 hours
When the final annealing temperature is 1100ºC to 1300ºC, sufficient secondary
recrystallization is developed, and the magnetic properties of the grain-oriented electrical
steel sheet are enhanced. Furthermore, the film-shaped oxide is formed on the surface
of the base steel sheet.
25 When the final annealing temperature is lower than 1100ºC, there is a case
46
where sufficient secondary recrystallization is not developed. In addition, when the
final annealing temperature is higher than 1300ºC, there is a case where the coil strength
at high temperatures decreases and the coil deforms. In addition, when the holding time
is shorter than 20 hours, there is a case where the base steel sheet is poorly purified. On
the other hand, when the holding 5 time is longer than 24 hours, the productivity degrades,
which is not preferable.
[0117]
[S62: Cooling process]
After the final annealing process, a cooling process of cooling the base steel
10 sheet is performed. At this time, the cooling is performed in a gas atmosphere in which
the oxidation degree (PH2O/PH2) is 0.30 to 100000 within a temperature range in which
the base steel sheet reaches 1100ºC to 500ºC. The temperature range of 1100ºC to
500ºC is a temperature range in which the base steel sheet can be oxidized. Therefore,
it is possible to form a preferable film-shaped oxide by controlling the oxidation over this
15 broad temperature range.
[0118]
When the oxidation degree within the temperature range of 1100ºC to 500ºC is
less than 0.30, no oxide is formed. In this case, the adhesion of the intermediate layer
that is to be formed in the intermediate layer forming process, which is the next process,
20 to the base steel sheet degrades. As a result, in the manufactured grain-oriented
electrical steel sheet, the area rate of the intermediate layer-remaining region in which the
intermediate layer does not peel off but remains in the region in which the insulation
coating peels off after a bend test performed using a mandrel according to JIS K 5600-5-
1 (1999) reaches less than 20%. Consequently, the resistance of the insulation coating
25 to peeling due to water (water resistance) degrades. On the other hand, when the
47
oxidation degree within the above-described temperature range exceeds 100000, an
internal oxide is formed. In this case, since the internal oxide is not reduced but
remains even after the formation of the intermediate layer, the iron loss of the grainoriented
electrical steel sheet deteriorates.
Therefore, the oxidation degr 5 ee of the atmosphere within a temperature range in
which the base steel sheet reaches 1100ºC to 500ºC is 0.30 to 100000.
[0119]
The cooling method within the temperature range in which the base steel sheet
reaches 1100ºC to 500ºC is not particularly limited. Examples of the cooling method
10 include a method in which a heater is cut in batch annealing and the base steel sheet is
cooled as it is.
[0120]
With the above-described processes, the base steel sheet in which an internal
oxide is substantially not present and the film-shaped oxide is formed, that is, the
15 intermediate steel sheet for a grain-oriented electrical steel sheet according to the present
embodiment is manufactured. The intermediate steel sheet for a grain-oriented
electrical steel sheet according to the present embodiment substantially does not contain
an internal oxide. Therefore, the surface of the base steel sheet after the final annealing
process is a smooth surface, and unevenness is suppressed. For example, the arithmetic
20 average roughness Ra of the surface of the base steel sheet is 1.0 μm or less. Therefore,
grain-oriented electrical steel sheets that are obtained using this intermediate steel sheet
are capable of realizing a low iron loss.
[0121]
The final annealing also serves as purification annealing. With the purification
25 annealing, the above-described inhibitor components such as Al, N, Mn, S, and Se are
48
removed from steel.
[0122]
[S7: Intermediate layer forming process]
In the intermediate layer forming process, a heat treatment is performed on the
intermediate steel sheet for a grain-oriented electrical st 5 eel sheet according to the present
embodiment. Therefore, an intermediate layer mainly containing silicon oxide is
formed in contact with the surface of the base steel sheet.
[0123]
The conditions of the heat treatment at the time of forming the intermediate
10 layer are not particularly limited. In the case of forming the intermediate layer in a
thickness of 2 to 400 nm, the base steel sheet is preferably held within a temperature
range of 300ºC to 1150ºC for five to 120 seconds and more preferably held within a
temperature range of 600ºC to 1150ºC for 10 to 60 seconds.
Furthermore, from the viewpoint of preventing the oxidization of the inside of
15 the base steel sheet, the atmosphere in which the base steel sheet is heated up to a
temperature range in which the temperature is held and the temperature is held is
preferably set to a reducing atmosphere and more preferably set to a hydrogen-mixed
nitrogen atmosphere. Examples of the hydrogen-mixed nitrogen atmosphere include an
atmosphere containing 5 to 50 vol% of hydrogen with a remainder made up of nitrogen
20 and an impurity and having a dew point of -20ºC to 2ºC. Particularly, an atmosphere
containing 10 to 35 vol% of hydrogen and a remainder made up of nitrogen and an
impurity and having a dew point of -10ºC to 0ºC is preferable.
[0124]
In the intermediate layer forming process, the film-shaped oxide is reduced, and
25 the above-described intermediate layer mainly containing silicon oxide is formed.
49
Therefore, the adhesion of the intermediate layer to the base steel sheet is enhanced. As
a result, in the manufactured grain-oriented electrical steel sheet, the area rate of the
intermediate layer-remaining region in which the intermediate layer does not peel off but
remains in the region in which the insulation coating peels off after a bend test performed
using a mandrel according 5 to JIS K 5600-5-1 (1999) reaches 20% or more.
[0125]
As the heat treatment in the intermediate layer forming process, a separate heat
treatment intended only for the formation of the intermediate layer may be performed.
The heat treatment may be performed at the same time as or continuously with a heat
10 treatment intended for the formation of the insulation coating. In the case of performing
the separate heat treatment intended only for the formation of the intermediate layer, the
heat treatment intended for the formation of the insulation coating is separately
performed afterwards.
[0126]
15 [S8: Insulation coating forming process]
In the insulation coating forming process, an insulation coating made from a
compound containing P, O, and Si is formed on the surface of the intermediate layer.
The insulation coating may further contain Cr.
[0127]
20 In the insulation coating forming process, a coating solution containing
phosphoric acid or a phosphate, colloidal silica, and, as necessary, chromic anhydride or
a chromate is applied to the surface of the intermediate layer. The coating fluid is
applied and then baked, thereby forming an insulation coating in contact with the surface
of the intermediate layer.
25 [0128]
50
Examples of the phosphate include phosphates of Ca, Al, Mg, Sr, and the like.
The colloidal silica is not particularly limited, and the particle sizes thereof can also be
appropriately used. Furthermore, a variety of elements or compounds may be further
added to the coating solution in order to improve a variety of characteristics.
5 [0129]
The baking conditions are not particularly limited. As the baking conditions,
for example, the coating solution is held in an atmosphere containing hydrogen, water
vapor, and nitrogen and having an oxidation degree (PH2O/PH2) of the atmosphere of
0.0001 to 1.0 within a temperature range of 300ºC to 1150ºC for five to 300 seconds.
10 [0130]
In the insulation coating forming process, it is preferable to apply the coating
solution to the surface of the intermediate layer and hold and bake the coating solution in
an atmosphere having an oxidation degree (PH2O/PH2) of the atmosphere of 0.001 to 0.1
within a temperature range of 300ºC to 900ºC for 10 seconds or longer. When the
15 oxidation degree of the atmosphere is 0.001 or more, the phosphate, which is a main
configuration phase of the insulation coating, does not easily decompose, and the water
resistance is further enhanced. In addition, when the oxidation degree of the
atmosphere is 0.1 or less, it is possible to further decrease iron losses.
[0131]
20 In the insulation coating forming process, the steel sheet is preferably cooled in
an atmosphere in which the oxidation degree of the gas is held at a lower value such that
the insulation coating and the intermediate layer do not change after the baking. The
cooling conditions may be ordinary conditions, and, for example, an atmosphere
containing hydrogen, nitrogen, water vapor, and an impurity and having an oxidation
25 degree (PH2O/PH2) of the atmosphere of less than 0.01 is used.
51
[0132]
The method for manufacturing the grain-oriented electrical steel sheet according
to the present embodiment may further include a process that is ordinarily performed in
methods for manufacturing grain-oriented electrical steel sheets. For example, the
method for manufacturing a grain-oriented electrical st 5 eel sheet according to the present
embodiment may further include a nitriding treatment process of performing a nitriding
treatment that increases the N content of the base steel sheet after the decarburization
annealing process and before the annealing separator applying process. This is because
it is possible to stably improve the magnetic flux density while a temperature gradient to
10 be imparted to the steel sheet in the boundary portion between a primary recrystallization
region and a secondary recrystallization region is small. The nitriding treatment may be
an ordinary nitriding treatment. 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 final-annealing the decarburization-annealed
15 steel sheet to which an annealing separator containing powder having a nitriding
capability such as MnN is applied, and the like.
[0133]
The present invention is not limited to the above-described embodiments. The
above-described embodiments are exemplary examples, and any grain-oriented electrical
20 steel sheets and methods for manufacturing the same are included in the technical scope
of the present invention as long as the grain-oriented electrical steel sheets and the
manufacturing methods have substantially the same configuration and exhibit the same
action and effect as the technical concept described in the claims of the present invention.
[Examples]
25 [0134]
52
Hereinafter, the present invention will be specifically described by proposing
examples. Hereinafter, conditions in the examples are simply examples of conditions
adopted to confirm the feasibility and effect of the present invention. The present
invention is not limited to these examples of the conditions. The present invention is
capable of adopting a 5 variety of conditions within the scope of the gist of the present
invention as long as the object of the present invention is achieved.
[0135]
Slabs having a chemical composition containing Si: 3.30%, C: 0.050%, acidsoluble
Al: 0.030%, N: 0.0080%, Mn: 0.10%, and S and Se: 0.005% in total with a
10 remainder made up of Fe and an impurity were prepared.
The slabs were heated for soaking at 1150ºC for 60 minutes, and hot rolling was
performed on the heated slabs, thereby manufacturing hot-rolled steel sheets having a
sheet thickness of 2.6 mm. Hot band annealing was performed on the manufactured
hot-rolled steel sheets, thereby manufacturing annealed steel sheets. As the conditions
15 of the hot band annealing, the hot-rolled steel sheets were held at an annealing
temperature of 900ºC for 120 seconds. Cold rolling was performed on the obtained
annealed steel sheets, thereby manufacturing cold-rolled steel sheets having a final sheet
thickness of 0.23 mm.
[0136]
20 Decarburization annealing was performed on the obtained cold-rolled steel
sheets. As the conditions of the decarburization annealing, the cold-rolled steel sheets
were held in a wet atmosphere containing 75 vol% of hydrogen with a remainder made
up of nitrogen and an impurity at 850ºC for 90 seconds.
[0137]
25 An annealing separator containing MgO was applied to the surface of each of
53
the obtained steel sheets at a proportion shown in Table 1. In the annealing separator,
the remainder other than MgO was Al2O3.
[0138]
Final annealing was performed on the steel sheets to which the annealing
separator had been applied and dr 5 ied, and cooling was performed, thereby obtaining base
steel sheets. As the conditions of the final annealing, the steel sheets were heated up to
1200ºC at a temperature rise rate of 15 ºC/hour in a hydrogen-nitrogen mixed atmosphere
and then held at 1200ºC for 20 hours in a hydrogen atmosphere. The heater in batch
annealing was stopped, and the final-annealed base steel sheets were cooled as they were.
10 The oxidation degrees (PH2O/PH2) represented by the ratio of the water vapor partial
pressure to the hydrogen partial pressure within a temperature range in which the base
steel sheets reached 1100ºC to 500ºC were as shown in Table 1.
In addition, all of the chemical compositions of the final-annealed base steel
sheets contained Si: 3.30%, C: 0.002% or less, acid-soluble Al: 0.0030% or less, N:
15 0.0020% or less, Mn: 0.10%, and S and Se: 0.0005% or less in total, and the remainder
was made up of Fe and an impurity.
54
[0139]
[Table 1]
Test No.
MgO content in
annealing
separator
(mass%)
Oxidation
degree in
cooling process
(PH2O/PH2)
Number
density of
internal oxide
particles
(oxide
particles
/μm2)
Bending
diameter
(mm)
Evaluation
area
(mm2)
Insulation
coating
peeling area
(mm2)
Intermediate layer residual
rate of insulation coatingpeeling
portion
(%)
Insulation coating
peeling area after
water immersion
(mm2)
Peeling
area due
to water
(mm2)
Iron
loss
(W/kg)
Note
1 30 0.20 0.003 16 25.1 12.5 10 21.5 9.0 0.82 Comparative Example
2 30 0.30 0.006 16 25.1 3.4 30 4.0 0.6 0.85 Invention Example
3 30 0.10 0.019 16 25.1 6.7 8 15.9 9.2 0.83 Comparative Example
4 30 10000 0.010 16 25.1 2.9 54 3.6 0.7 0.87 Invention Example
5 40 0.0001 0.012 16 25.1 10.1 12 18.1 8.0 0.81 Comparative Example
6 40 0.0001 0.012 10 15.7 15.0 3 15.7 0.7 0.81 Comparative Example
7 40 50000 0.004 16 25.1 1.8 66 1.9 0.1 0.81 Invention Example
8 40 50000 0.004 10 15.7 7.1 38 8.3 1.2 0.81 Invention Example
9 40 200000 0.512 16 25.1 7.1 15 19.3 12.2 1.02 Comparative Example
10 95 0.30 0.048 16 25.1 6.6 30 8.9 2.3 1.00 Comparative Example
11 40 0.01 0.012 16 25.1 13.5 3 25.1 11.6 0.81 Comparative Example
12 40 100 0.004 16 25.1 2.5 45 7.4 4.9 0.81 Invention Example
13 40 0.001 0.001 16 25.1 9.2 10 18.9 9.7 0.79 Comparative Example
14 40 100 0.008 16 25.1 3.1 46 4.2 1.1 0.80 Invention Example
15 40 5000 0.006 10 15.7 4.1 61 5.5 1.4 0.83 Invention Example
16 40 150000 0.497 16 25.1 5.6 17 16.1 10.5 1.12 Comparative Example
17 40 0.25 0.002 16 25.1 4.2 14 17.1 12.9 0.87 Comparative Example
55
[0140]
In Test No. 1 to Test No. 12, a heat treatment for forming an intermediate layer
and an insulation coating at the same time was performed on the final-annealed base steel
sheet.
The conditions of an intermediate 5 layer and insulation coating forming process
were as described below.
A coating solution was applied to the surface of the steel sheet. The
composition of the coating solution was, by mass%, a phosphate: 50%, colloidal silica:
45%, and chromic anhydride: 5% in Test No. 1 to Test No. 10. The composition of the
10 coating solution in Test No. 11 and Test No. 12 was, by mass%, a phosphate: 55% and
colloidal silica: 45%. The steel sheet to which the coating solution had been applied
was heated up to 850ºC and held for 30 seconds in an atmosphere containing hydrogen,
nitrogen, water vapor, and an impurity and having an oxidation degree (PH2O/PH2) of 0.1.
[0141]
15 In Test No. 13 to Test No. 17, an intermediate layer forming process and an
insulation coating forming process were separately performed. A heat treatment was
performed on the final-annealed base steel sheet, thereby forming an intermediate layer.
The conditions of the intermediate layer forming process were as described below. The
final-annealed steel sheet was heated up to 850ºC and held for 30 seconds in an
20 atmosphere having an oxidation degree (PH2O/PH2) of 0.01.
In addition, an insulation coating was formed on the base steel sheet on which
the intermediate layer had been formed. In the insulation coating forming process, a
coating solution was applied to the surface of the intermediate layer. The composition
of the coating solution was a phosphate: 60% and colloidal silica: 40%. The steel sheet
25 to which the coating solution had been applied was heated up to 850ºC and held for 30
56
seconds in an atmosphere containing 75 vol% of hydrogen with a remainder made up of
nitrogen and an impurity to form an insulation coating and was cooled to room
temperature.
[0142]
5 [Cross section observation]
A test piece having a cross section perpendicular to a rolling direction was
collected from the grain-oriented electrical steel sheet of each test number, and the cross
section was observed with a scanning electron microscope (SEM). A region at a depth
of 10 μm from the surface of the steel sheet was observed at a magnification of 10000
10 times in a range of 100 μm in a direction parallel to the surface of the steel sheet. In
Test No. 1 to Test No. 8, Test No. 11 to Test No. 15, and Test No. 17, an internal oxide
was rarely formed. That is, the number density of oxide particles having a circleequivalent
diameter of 0.1 μm or more in a region from the surface of the base steel sheet
to a depth of 10 μm toward the inside of the base steel sheet was 0.020 oxide
15 particles/μm2 or less.
On the other hand, in Test No. 9 and Test No. 16, a large amount of an internal
oxide mainly containing silicon oxide that was to form unevenness on the surface of the
base steel sheet was formed. That is, the number density of oxide particles having a
circle-equivalent diameter of 0.1 μm or more in a region from the surface of the base
20 steel sheet to a depth of 10 μm toward the inside of the base steel sheet was more than
0.020 oxide particles/μm2. In Test No. 10, a large amount of an internal oxide mainly
containing forsterite that was to form unevenness on the surface of the base steel sheet
and having a circle-equivalent diameter of 0.1 μm or more was formed.
[0143]
25 Regarding the grain-oriented electrical steel sheet of each test number, it was
57
also confirmed from an electron beam diffraction pattern and an energy dispersive X-ray
analysis (EDX) in the cross section observation with a transmission electron microscope
(TEM) that the composition of the intermediate layer was a Fe content of less than 30
atom%, a P content of less than 5 atom%, a Si content of less than 50 atom% and 20
atom% 5 or more, an O content of less than 80 atom% and 50 atom% or more, and a Mg
content of 10 atom% or less.
[0144]
[Adhesion test]
An adhesion test was performed according to the bend resistance test of JIS K
10 5600-5-1 (1999). A test piece that was 80 mm long in the rolling direction and 40 mm
long in a direction perpendicular to the rolling direction was collected from the grainoriented
electrical steel sheet of each of Test No. 1 to Test No. 17. The collected test
piece was coiled around a mandrel having a diameter of 10 mm or 16 mm. In the
adhesion test, the test piece was bent 180° using a type 1 testing device described in the
15 bend resistance test of JIS K 5600-5-1 (1999). The total area of portions in which the
insulation coating peeled off on the inner side surface of the bent test piece (insulation
coating-peeling area) was measured.
After that, the area rate of the intermediate layer-remaining region was obtained
by the above-described method. The results are shown in Table 1. The bending
20 diameter in Table 1 indicates the diameter of the mandrel.
In a case where the diameter of the coiled mandrel was 10 mm, the adhesion was
determined as excellent when the insulation coating-peeling area was 7.5 mm2 or less.
In addition, in a case where the diameter of the coiled mandrel was 16 mm, the adhesion
was determined as excellent when the insulation coating-peeling area was 5.0 mm2 or
25 less.
58
[0145]
The evaluation area of insulation coating peeling in the bend test was defined by
the following expression. In a case where the insulation coating peeling area was less
than 5% of the evaluation area, the insulation coating peeling area was re-evaluated by
decreasing the bending diameter 5 (the diameter of the mandrel). As a result of the reevaluation,
in a case where the insulation coating peeling area was 5% or more of the
evaluation area, the area rate of the intermediate layer-remaining region was obtained.
(Evaluation area)=(bending diameter)×(ratio of circumference to diameter)÷2
[0146]
10 Regarding the area rate of the intermediate layer-remaining region, a specified
insulation coating-peeling region was mapped using an energy dispersive X-ray
spectroscope (SEM-EDS), a Si concentration distribution was obtained, in the obtained
Si concentration distribution, the maximum value of the Si concentration and the
minimum value of the Si concentration were specified, and a region that satisfied the
15 following expression was defined as the intermediate layer-remaining region.
(Si concentration of region)>{(maximum value of Si concentration)+(minimum
value of Si concentration)}/2
In addition, the proportion of the total area of the defined intermediate layerremaining
region in the EDS mapping total area of the coating peeling portion was
20 defined as the area rate (%) of the intermediate layer-remaining region. In a case where
the area rate of the intermediate layer-remaining region was 20% or more, the adhesion
was regarded as satisfying the requirement regulated by the present invention and
determined as pass. On the other hand, in a case where the area rate of the intermediate
layer-remaining region was less than 20%, the adhesion was regarded as not satisfying
25 the requirement regulated by the present invention and determined as fail.
59
In a case where the maximum value of the Si concentration and the minimum
value of the Si concentration satisfied the following expression, the area rate of the
intermediate layer-remaining region was regarded as 0%.
(Maximum value of Si concentration)-(minimum value of Si concentration)<5
5 atom%
[0147]
[Water resistance test]
A bend test was performed on the test pieces of Test No. 1 to Test No. 17 under
the same conditions as in the adhesion test. While the bent portions (bending regions)
10 of the test piece remained bent, the entire bending regions were immersed in pure water
for one minute. After one minute elapsed, the test pieces were lifted. After that, the
test pieces were dried. The test pieces were bent back, and the insulation coating
peeling areas after the water immersion were calculated by image analysis. The peeling
areas due to water were calculated by the following expression. The results are shown
15 in Table 1.
(Peeling area due to water)=(insulation coating peeling area after water
immersion)-(insulation coating peeling area)
When the peeling area due to water was 5.0 mm2 or less, the water resistance
was determined as excellent. On the other hand, when the peeling area due to water
20 was more than 5.0 mm2, the water resistance was determined as poor.
[0148]
[Measurement of iron losses]
Regarding iron losses, the iron loss W17/50 (W/kg) at an excited magnetic flux
density of 1.7 T and a frequency of 50 Hz was measured by the Epstein test based on JIS
25 C 2550-1. In a case where the iron loss W17/50 was less than 1.00, the iron loss was
60
determined as favorable. On the other hand, in a case where the iron loss W17/50 was
1.00 or more, the iron loss was determined as poor.
[0149]
With reference to Table 1, in Test No. 2, Test No. 4, Test No. 7, Test No. 8, Test
No. 12, Test No. 14, and Test No. 15, the insulation c 5 oating peeling areas were small, in
addition, the area rates of the intermediate layer-remaining regions reached 20% or more,
and the adhesion and the water resistance were excellent. Particularly, in Test No. 2,
Test No. 4, Test No. 7, Test No. 8, Test No. 14, and Test No. 15, the peeling areas due to
water became smaller than the insulation coating peeling areas, and the water resistance
10 was superior. Furthermore, in these invention examples, the number densities of the
internal oxide particles having a circle-equivalent diameter of 0.1 μm or more were 0.020
oxide particles/μm2 or less, and the iron losses were favorable. In addition, in these
invention examples, the arithmetic average roughness Ra of the surfaces of the base steel
sheets was 1.0 μm or less, and the thicknesses of the intermediate layers were 2 to 400
15 nm. The arithmetic average roughness Ra and the thicknesses of the intermediate layers
were measured by the above-described method.
[0150]
On the other hand, in Test No. 1, Test No. 3, Test No. 5, Test No. 6, Test No. 11,
and Test Nos. 13 and 17, the oxidation degrees in the cooling process were less than 0.30.
20 Therefore, the area rates of the intermediate layer-remaining regions were less than 20%,
and the adhesion was poor. In Test No. 1, Test No. 3, Test No. 5, Test No. 11, Test No.
13, and Test No. 17, the peeling areas due to water were more than 5.0 mm2, and the
water resistance was poor.
[0151]
25 In Test No. 9 and Test No. 16, the oxidation degrees in the cooling process after
61
the final annealing exceeded 100000. Therefore, an internal oxide mainly containing
silicon oxide was formed, and the number densities of the internal oxide particles
exceeded 0.020 oxide particles/μm2. Therefore, it was not possible to obtain a low iron
loss, which is necessary for grain-oriented electrical steel sheets.
5 [0152]
In Test No. 10, the MgO content in the annealing separator was high.
Therefore, an internal oxide mainly containing forsterite was formed, and the number
densities of the internal oxide particles having a circle-equivalent diameter of 0.1 μm or
more exceeded 0.020 oxide particles/μm2. Therefore, it was not possible to obtain a low
10 iron loss, which is necessary for grain-oriented electrical steel sheets.
In Test No. 1, Test No. 3, Test No. 5, Test No. 6, Test No. 9, Test No. 10, Test
No. 11, Test No. 13, and Test No. 16, the peeling areas of the insulation coatings were
also large.
[0153]
15 Hitherto, the embodiment of the present invention has been described.
However, the above-described embodiment is simply an exemplary example for
performing the present invention. Therefore, the present invention is not limited to the
above-described embodiment, and the above-described embodiment can be appropriately
modified and performed within the scope of the gist of the present invention.
20 [Industrial Applicability]
[0154]
According to the present invention, it is possible to provide a grain-oriented
electrical steel sheet having an intermediate layer mainly containing silicon oxide in
which the adhesion of an insulation coating and the water resistance are favorable. In
25 addition, it is possible to provide an intermediate steel sheet for a grain-oriented electrical
62
steel sheet and a method for manufacturing the same.

WE CLAIMS

1. A grain-oriented electrical steel sheet comprising:
a base steel sheet;
an intermediate 5 layer that is formed on a surface of the base steel sheet and
mainly contains silicon oxide; and
an insulation coating that is formed on a surface of the intermediate layer,
wherein a number density of oxide particles in a region from the surface of the
base steel sheet to a depth of 10 μm toward an inside of the base steel sheet is 0.020
10 oxide particles/μm2 or less, and
an area rate of an intermediate layer-remaining region in which the intermediate
layer does not peel off but remains in a region in which the insulation coating peels off
after a bend test performed using a mandrel according to JIS K 5600-5-1 (1999) is 20%
or more.
15
2. A method for manufacturing a grain-oriented electrical steel sheet comprising:
a hot rolling process of heating a slab at 1280ºC or lower and then performing
hot rolling to manufacture a hot-rolled steel sheet;
a hot-band annealing process of performing hot band annealing on the hot-rolled
20 steel sheet to manufacture an annealed steel sheet;
a cold rolling process of performing cold rolling on the annealed steel sheet to
manufacture a cold-rolled steel sheet;
a decarburization annealing process of performing decarburization annealing on
the cold-rolled steel sheet to manufacture a base steel sheet;
25 an annealing separator applying process of applying an annealing separator
64
having a composition containing 50 mass% or more of alumina and, as a remainder, 0 to
50 mass% of magnesia to the base steel sheet;
a final annealing process of performing final annealing on the base steel sheet
after the annealing separator applying process;
a cooling process of cooling the base 5 steel sheet after the final annealing process
in an atmosphere having an oxidation degree PH2O/PH2, which is a ratio of a water vapor
partial pressure to a hydrogen partial pressure, within a temperature range of 1100ºC to
500ºC set to 0.30 to 100000;
an intermediate layer forming process of performing a heat treatment on the base
10 steel sheet after the cooling process to form an intermediate layer mainly containing
silicon oxide on a surface of the base steel sheet; and
an insulation coating forming process of forming an insulation coating on a
surface of the intermediate layer after the intermediate layer forming process.
15 3. An intermediate steel sheet for a grain-oriented electrical steel sheet comprising:
a base steel sheet; and
a film-shaped oxide formed on a surface of the base steel sheet,
wherein the film-shaped oxide is present so as to cover the surface of the base
steel sheet in a film shape, and
20 a number density of the oxide particles in a region from the surface of the base
steel sheet to a depth of 10 μm toward an inside of the base steel sheet is 0.020 oxide
particles/μm2 or less.
4. A method for manufacturing an intermediate steel sheet for a grain-oriented
25 electrical steel sheet comprising:
65
a hot rolling process of heating a slab at 1280ºC or lower and then performing
hot rolling to manufacture a hot-rolled steel sheet;
a hot-band annealing process of performing hot band annealing on the hot-rolled
steel sheet to manufacture an annealed steel sheet;
a cold rolling process of performing 5 cold rolling on the annealed steel sheet to
manufacture a cold-rolled steel sheet;
a decarburization annealing process of performing decarburization annealing on
the cold-rolled steel sheet to manufacture a base steel sheet;
an annealing separator applying process of applying an annealing separator
10 having a composition containing 50 mass% or more of alumina and, as a remainder, 0 to
50 mass% of magnesia to the base steel sheet;
a final annealing process of performing final annealing on the base steel sheet
after the annealing separator applying process; and
a cooling process of cooling the base steel sheet after the final annealing process
15 in an atmosphere having an oxidation degree PH2O/PH2, which is a ratio of a water vapor
partial pressure to a hydrogen partial pressure, within a temperature range of 1100ºC to
500ºC set to 0.30 to 100000.