[0001]The present invention relates to a grain-oriented electrical steel sheet that has an
intermediate layer mainly composed of silicon oxide on a surface of a finally-annealed
grain-oriented silicon steel sheet, which is manufactured under conditions that inhibit
10 formation of a forsterite coating, or is produced by removing a forsterite coating by
means such as grinding or pickling, or by flattening the surface until it exhibits a mirror
gloss, and has an insulation coating mainly composed of phosphate and colloidal silica
on the intermediate layer. In particular, the present invention relates to a grain-oriented
electrical steel sheet having excellent strongly bending workability and excellent
15 manufacturability of a wound iron core. Priority is claimed on Japanese Patent
Application No. 2019-005395, filed January 16, 2019, the content of which is
incorporated herein by reference.
[Background Art]
[0002]
20 A grain-oriented electrical steel sheet is a soft magnetic material and is used for
an iron core of electrical equipment such as a transformer. A grain-oriented electrical
steel sheet contains about 7% by mass or less of Si, and the crystal grains are strongly
aligned in the {110}<001> direction in Miller indices.
[0003]
25 One of characteristics required by a grain-oriented electrical steel sheet is that an
2
energy loss when excited by alternating current, that is, the iron loss, be small. Further,
when a grain-oriented electrical steel sheet is used for an iron core material of a
transformer, it is essential to secure insulation characteristics for the steel sheet, and thus
an insulation coating is formed on a surface of the steel sheet. For example, a method
disclosed in Patent Document 1 in which a 5 coating agent mainly composed of colloidal
silica and phosphate is applied to a surface of a steel sheet and baked to form an
insulation coating is effective in ensuring insulation. In this way, it is a general grainoriented
electrical steel sheet and a manufacturing method thereof to form an insulation
coating mainly composed of colloidal silica and phosphate on a forsterite (Mg2SiO4)-
10 based coating (may be hereinafter simply referred to as a “glass film” or a “forsterite
coating”) generated in a final annealing process.
[0004]
Under such circumstances, in recent years, efficiency regulations for a
transformer using grain-oriented electrical steel sheets has been implemented due to
15 growing awareness of global environmental problems such as global warming.
Conventionally, strict efficiency regulations have been implemented in applications that
have been using low grade grain-oriented electrical steel sheets, especially in a wound
iron core transformer, and the movement to using higher-grade grain-oriented electrical
steel sheets is spreading. For this reason, there is an increasing demand for further
20 reduction in iron loss of a grain-oriented electrical steel sheet.
[0005]
For the above reason, characteristics required for a grain-oriented electrical steel
sheet used for a wound iron core are that (A) the iron loss be low, and (B) the insulation
coating does not peel off at a strongly bent processing part. Since a wound iron core is
25 manufactured by winding an elongated steel sheet into a coil shape, there is a problem
3
that a radius of curvature of a steel sheet on an inner circumferential side thereof
becomes small, which causes a strongly bent processing, and thus the insulation coating
may peel off.
[0006]
Regarding 5 the above (A), in order to further reduce the iron loss with respect to
a general grain-oriented electrical steel sheet, it is important to eliminate a pinning effect
due to unevenness of an interface of a glass film on a surface of the steel sheet that
hinders control of orientation of crystal grains and movement of magnetic domains
(hereinafter, may be referred to as “mirror finishing” and “smoothing”).
10 [0007]
First, an abnormal grain growth phenomenon called secondary recrystallization
is used to control the orientation of crystal grains. In order to accurately control the
secondary recrystallization, it is important to accurately form a structure (a primary
recrystallization structure) obtained by primary recrystallization before the secondary
15 recrystallization, and appropriately precipitate fine precipitates or intergranular
segregation elements called inhibitors.
[0008]
In the secondary recrystallization, since the inhibitor has a function of inhibiting
growth of crystal grains other than the {110}<001> orientation in the primary
20 recrystallization structure and preferentially growing the crystal grains in the
{110}<001> orientation, adjustment of a type and an amount of the inhibitor is of
particular importance.
[0009]
Many research results have been disclosed regarding inhibitors. Among them,
25 one of distinctive techniques is a technique that utilizes B as an inhibitor. Patent
4
Documents 2 and 3 disclose that solid solution B functions as an inhibitor and is effective
in developing the {110}<001> orientation.
[0010]
Patent Documents 4 and 5 disclose that fine BN formed by nitriding a material
to which B is added after cold roll 5 ing functions as an inhibitor and is effective in
developing the {110}<001> orientation.
[0011]
Patent Document 6 discloses that extremely fine BN obtained by inhibiting
precipitation of BN as much as possible in hot rolling to precipitate in a subsequent
10 heating process for annealing has a function as an inhibitor. Patent Documents 6 and 7
disclose a method of controlling a precipitation form of B in a hot rolling process to exert
a function as an inhibitor.
[0012]
Next, in order to eliminate a pinning effect due to unevenness of an interface of
15 a glass film on a surface of a steel sheet that hinders movement of magnetic domains, for
example, Patent Documents 7 to 9 disclose that a dew point of decarburization annealing
is controlled and Fe-based oxides (Fe2SiO4, FeO, etc.) are not formed in an oxide layer
formed during decarburization annealing, and that a substance such as alumina that does
not react with silica is used as an annealing separator to achieve surface smoothing after
20 final annealing.
[0013]
Regarding the above (B), since a general grain-oriented electrical steel sheet
having an insulation coating on a glass film generated in a final annealing process has
good insulation coating adhesion, the insulation coating adhesion does not become an
25 issue. However, in a case in which a glass film is removed, or a glass film is not formed
5
in a final annealing process intentionally, it is difficult to obtain good insulation coating
adhesion, and thus improvement of insulation coating adhesion is an issue.
[0014]
Therefore, as a technique for ensuring insulation coating adhesion in a grainoriented
electrical steel shee 5 t that does not have a glass film, a method of forming an
oxide layer on a surface of a final-annealed grain-oriented silicon steel sheet before
forming an insulation coating has been proposed, for example, in Patent Documents 10 to
13.
[0015]
10 For example, the technique disclosed in Patent Document 11 is a method in
which a final-annealed grain-oriented silicon steel sheet produced by mirror finishing or
produced in a state close to having a mirror surface is annealed at a specific atmosphere
at each of temperatures to form an externally oxidized layer on a surface of a steel sheet,
and the adhesion between the insulation coating and the steel sheet is secured due to the
15 oxide layer.
[0016]
The technique disclosed in Patent Document 12 is a technique in which in the
case of a crystalline insulation coating, an amorphous oxide base coating is formed on a
surface of a final-annealed grain-oriented silicon steel sheet that does not have an
20 inorganic mineral coating to prevent the steel sheet from being oxidized when the
crystalline insulation coating is formed.
[0017]
The technique disclosed in Patent Document 13 is a method for further
developing the technique disclosed in Patent Document 11, in which a layer structure of a
25 metal oxide layer containing Al, Mn, Ti, Cr, and Si is controlled at an interface between
6
an insulation coating and a steel sheet to improve the adhesion of the insulation coating.
[0018]
However, the grain-oriented electrical steel sheets that do not have a forsterite
coating proposed in Patent Documents 10 to 13 are also based on Al-based inhibitors and
do not mention improvement of 5 the insulation coating adhesion in the grain-oriented
electrical steel sheets to which B is added disclosed in Patent Documents 2 to 6.
Although a grain-oriented electrical steel sheet without a forsterite coating to which B is
added has a low iron loss, there still remains a problem in the insulation coating adhesion
required for a wound iron core.
10 [Citation List]
[Patent Document]
[0019]
[Patent Document 1]
Japanese Unexamined Patent Application, First Publication No. S48-039338
15 [Patent Document 2]
Specification of U.S. Patent No. 3905842
[Patent Document 3]
Specification of U.S. Patent No. 3905843
[Patent Document 4]
20 Japanese Unexamined Patent Application, First Publication No. H01-230721
[Patent Document 5]
Japanese Unexamined Patent Application, First Publication No. H01-283324
[Patent Document 6]
Japanese Unexamined Patent Application, First Publication No. H10-140243
25 [Patent Document 7]
7
Japanese Unexamined Patent Application, First Publication No. H07-278670
[Patent Document 8]
Japanese Unexamined Patent Application, First Publication No. H11-106827
[Patent Document 9]
Japanese Unexamined P 5 atent Application, First Publication No. 2002-173715
[Patent Document 10]
Japanese Unexamined Patent Application, First Publication No. S60-131976
[Patent Document 11]
Japanese Unexamined Patent Application, First Publication No. H06-184762
10 [Patent Document 12]
Japanese Unexamined Patent Application, First Publication No. H07-278833
[Patent Document 13]
Japanese Unexamined Patent Application, First Publication No. 2002-348643
[Summary of the Invention]
15 [Problems to be Solved by the Invention]
[0020]
A grain-oriented electrical steel sheet having a low iron loss without a forsterite
coating has been obtained as a material for an iron core using the above-mentioned
conventional techniques, but when a transformer, particularly a wound iron core
20 transformer is manufactured, there is a problem that the insulation coating peels off at a
strongly bent processing part on an inner circumferential side of the steel sheet, and this
problem has not been solved yet. While high-efficiency transformers are required, the
above-mentioned problem awaits resolution in order to industrially manufacture highefficiency
transformers.
25 [0021]
8
The present invention has been made in view of the current state of the
conventional techniques, a technical problem thereof being to inhibit peeling off of an
insulation coating generated at a strongly bent processing part of a steel sheet serving as
an inner circumferential side of an iron core in an grain-oriented electrical steel sheet
having a low iron loss that uses BN as an inhibitor a 5 nd does not have a forsterite coating,
which is used as an iron core material for a transformer, especially a wound iron core
transformer, and an object thereof is to provide a grain-oriented electrical steel sheet
which has excellent insulation coating adhesion and has a low iron loss, which solves the
above problem.
10 [Means for Solving the Problem]
[0022]
In a grain-oriented electrical steel sheet having a low iron loss that uses BN as
an inhibitor and does not have a forsterite coating, in order to improve the insulation
coating adhesion, it is important to strongly align crystal grains in the {110}<001>
15 orientation in secondary recrystallization to increase the magnetic flux density and
control a precipitation form of B in a steel sheet.
[0023]
In the case of using BN as an inhibitor, when BN after final annealing is
precipitated over the entire thickness of the steel sheet, a hysteresis loss increases to
20 make it difficult to obtain a grain-oriented electrical steel sheet having a low iron loss,
and the insulation coating adhesion also becomes inferior.
[0024]
Based on these facts, the present inventors have diligently studied a method for
solving the above problems. As a result, in a grain-oriented electrical steel sheet that
25 does not have a forsterite coating, it has been found that the above problems can be
9
solved by precipitating B as fine spherical BN on a surface layer of a steel sheet
containing an oxide layer mainly composed of silicon oxide.
The present invention has been made based on the above finding, and the gist
thereof is as follows.
5 [0025]
(1) A grain-oriented electrical steel sheet including a base steel sheet, an
intermediate layer which is disposed in contact with the base steel sheet and mainly
composed of silicon oxide, and an insulation coating which is disposed in contact with
the intermediate layer and mainly composed of phosphate and colloidal silica, in which
10 the base steel sheet has, as a chemical composition, by mass%:C: 0.085% or less, Si: 0.80
to 7.00%, Mn: 0.05 to 1.00%, acid-soluble Al: 0.010 to 0.065%, N: 0.0040% or less, S:
0.0100% or less, B: 0.0005 to 0.0080%, and a remainder of Fe and impurities, BN having
an average particle size of 50 to 300 nm is present on a surface layer of the intermediate
layer, when a total thickness of the base steel sheet and the intermediate layer is defined
15 as d, a time until a sputtering depth reaches a position of d/100 from an outermost surface
of the intermediate layer when an emission intensity of B is measured using glow
discharge emission spectrometry (GDS) is defined as t(d/100), and a time until the
sputtering depth reaches a position of d/10 from the outermost surface of the intermediate
layer is defined as t(d/10), an emission intensity IB_t(d/100) of B at t(d/100) and an emission
20 intensity IB_t(d/10) of B at t(d/10) satisfy the following Equation (1), and a ratio of a major
axis to a minor axis of BN is 1.5 or less.
IB_t(d/100)>IB_t(d/10) ∙∙∙ Equation (1)
[0026]
(2) The grain-oriented electrical steel sheet according to the above (1), in which
25 a number density of BN on the surface layer of the intermediate layer is 2×106
10
pieces/mm2 or more.
[Effects of the Invention]
[0027]
According to the present invention, in a grain-oriented electrical steel sheet
using BN as an inhibitor, it is possible to inhibit peeling 5 off of an insulation coating
generated at a strongly bent processing part of a steel sheet serving as an inner
circumferential side of an iron core, and it is possible to stably provide a grain-oriented
electrical steel sheet having excellent insulation coating adhesion, a low iron loss, and
excellent manufacturability of a wound steel core.
10 [Embodiments for implementing the Invention]
[0028]
A grain-oriented electrical steel sheet having excellent insulation coating
adhesion without a forsterite coating of the present invention (may be hereinafter simply
referred to as an “electrical steel sheet of the present invention”) includes a base steel
15 sheet, an intermediate layer which is disposed in contact with the base steel sheet and
mainly composed of silicon oxide, and an insulation coating which is disposed in contact
with the intermediate layer and mainly composed of phosphate and colloidal silica, in
which the base steel sheet contains, as a chemical composition, by mass%: C: 0.085% or
less, Si: 0.80 to 7.00%, Mn: 0.05 to 1.00%, acid-soluble Al: 0.010 to 0.065%, N:
20 0.0040% or less, S: 0.0100% or less, B: 0.0005 to 0.0080%, and a remainder of Fe and
impurities, BN having an average particle size of 50 to 300 nm is present on a surface
layer of the intermediate layer, when a total thickness of the base steel sheet and the
intermediate layer is defined as d, a time until a sputtering depth reaches a position of
d/100 from an outermost surface of the intermediate layer when an emission intensity of
25 B is measured using glow discharge emission spectrometry (GDS) is defined as t(d/100),
11
and a time until the sputtering depth reaches a position of d/10 from the outermost
surface of the intermediate layer is defined as t(d/10), an emission intensity IB_t(d/100) of B
at t(d/100) and an emission intensity IB_t(d/10) of B at t(d/10) satisfy the following
Equation (1), and a ratio of a major axis to a minor axis of BN in the surface layer of the
5 intermediate layer is 1.5 or less.
IB_t(d/100)>IB_t(d/10) ∙∙∙ Equation (1)
[0029]
Also, the grain-oriented electrical steel sheet of the present invention is
characterized in that the number density of BN on the surface layer of the intermediate
10 layer is 2×106 pieces/mm2 or more.
[0030]
First, in the electrical steel sheet of the present invention, the reason for limiting
the chemical composition of the base steel sheet will be described. Hereinafter, “%”
means “mass%” unless otherwise specified.
15 [0031]

C: 0.085% or less
C is an element that is effective in controlling a primary recrystallization
structure, but since it adversely affects magnetic characteristics, it is an element that is
20 removed by decarburization annealing before final annealing. If it exceeds 0.085% in a
final product, age precipitation will occur and a hysteresis loss will increase, and thus C
is set to 0.085% or less. C is preferably 0.070% or less, and more preferably 0.050% or
less.
[0032]
25 A lower limit thereof includes 0%, but if C is reduced to less than 0.0001%,
12
manufacturing costs will increase significantly, and thus 0.0001% is an actual lower limit
for a practical steel sheet. Also, in the grain-oriented electrical steel sheet, C is usually
reduced to about 0.001% or less by decarburization annealing.
[0033]
5 Si: 0.80 to 7.00%
Si is an element that increases electrical resistance of the electrical steel sheet
and improves iron loss characteristics. If it is less than 0.80%, γ transformation occurs
during final annealing and the crystal orientation of the steel sheet is impaired, and thus
Si is set to 0.80% or more. Si is preferably 1.50% or more, and more preferably 2.50%
10 or more.
[0034]
On the other hand, if Si exceeds 7.00%, workability deteriorates and cracks
occur during rolling, and thus Si is set to 7.00% or less. It is preferably 5.50% or less,
and more preferably 4.50% or less.
15 [0035]
Mn: 0.05 to 1.00%
Mn is an element that prevents cracks during hot rolling and is combined with S
to form MnS that functions as an inhibitor. If Mn is less than 0.05%, the addition effect
is not sufficiently exhibited, and thus Mn is set to 0.05% or more. It is preferably
20 0.07% or more, and more preferably 0.09% or more.
[0036]
On the other hand, if Mn exceeds 1.00%, the precipitation and dispersion of
MnS become non-uniform, a required secondary recrystallization structure cannot be
obtained, and the magnetic flux density decreases, and thus Mn is set to 1.00% or less.
25 Mn is preferably 0.80% or less, and more preferably 0.60% or less.
13
[0037]
Acid-soluble Al: 0.010 to 0.065%
Acid-soluble Al is an element that is combined with N to produce (Al, Si) N that
functions as an inhibitor. If the acid-soluble Al is less than 0.010%, the addition effect
is not sufficiently exhibited, and the secondary 5 recrystallization does not proceed
sufficiently, and thus the acid-soluble Al is set to 0.010% or more. The acid-soluble Al
is preferably 0.015% or more, and more preferably 0.020% or more.
[0038]
On the other hand, if the acid-soluble Al exceeds 0.065%, the precipitation and
10 dispersion of (Al, Si) N become non-uniform, the required secondary recrystallization
structure cannot be obtained, and the magnetic flux density decreases, and thus the acidsoluble
Al is set to 0.065% or less. The acid-soluble Al is preferably 0.050% or less,
and more preferably 0.040% or less.
[0039]
15 N: 0.0040% or less
N is an element that is combined with Al to form AlN that functions as an
inhibitor, but if it is 0.0040% or more in a final product, it is precipitated as AlN in the
steel sheet and deteriorates the hysteresis loss, and thus it is set to 0.0040% or less. A
lower limit thereof includes 0%, but if N is reduced to less than 0.0001%, the
20 manufacturing costs will increase significantly, and thus 0.0001% is a substantial lower
limit for a practical steel sheet. Also, in the grain-oriented electrical steel sheet, N is
usually reduced to about 0.0001% or less by final annealing.
[0040]
S: 0.0100% or less
25 S is combined with Mn and functions as an inhibitor, but if S is more than
14
0.0100% in a final product, it is precipitated as MnS in the steel sheet and increases the
hysteresis loss, and thus it is set to 0.0100% or less. A lower limit thereof includes 0%,
but if S is reduced to less than 0.0001%, the manufacturing costs will increase
significantly, and thus 0.0001% is a substantial lower limit for a practical steel sheet.
Also, in the grain-oriented electrical st 5 eel sheet, S is usually reduced to about 0.005% or
less by final annealing.
[0041]
B: 0.0005 to 0.0080%
B is an element that is combined with N and is complex-precipitated with MnS
10 to form BN that functions as an inhibitor.
[0042]
If it is less than 0.0005%, the addition effect is not sufficiently exhibited, and
thus B is set to 0.0005% or more. B is preferably 0.0010% or more, and more
preferably 0.0015% or more. On the other hand, if it exceeds 0.0080%, the
15 precipitation and dispersion of BN become non-uniform, the required secondary
recrystallization structure cannot be obtained, and the magnetic flux density decreases,
and thus B is set to 0.0080% or less. It is preferably 0.0060% or less, and more
preferably 0.0040% or less.
[0043]
20 In the components of the base steel sheet, the remainder excluding the above
elements is Fe and impurities. The impurities include elements that are inevitably
mixed from a steel raw material and/or in a steelmaking process and are permissible
elements as long as they do not impair the characteristics of the electrical steel sheet of
the present invention.
25 [0044]
15
Further, instead of some of Fe, the base steel sheet may contain at least one
selected from the group consisting of Cr: 0.30% or less, Cu: 0.40% or less, P: 0.50% or
less, Ni: 1.00% or less, Sn: 0.30% or less, Sb: 0.30% or less, and Bi: 0.01% or less,
within a range in which it does not impair the magnetic characteristics and can enhance
5 other characteristics.
[0045]
The chemical composition of the base steel sheet described above may be
measured using a general analysis method for steel. For example, the chemical
composition may be measured using inductively coupled plasma-atomic emission
10 spectrometry (ICP-AES). Also, the acid-soluble Al may be measured by ICP-AES
using a filtrate obtained by heat-decomposing a sample with an acid. Further, C and S
may be measured using a combustion-infrared absorption method, and N may be
measured using an inert gas melting-thermal conductivity method.
[0046]
15
The electrical steel sheet of the present invention includes the intermediate layer
mainly composed of silicon oxide which formed in contact with the base steel sheet. In
the electrical steel sheet of the present invention, the intermediate layer has a function of
bringing the base steel sheet and the insulation coating into adhesion with each other.
20 [0047]
The silicon oxide that forms the main component of the intermediate layer is
preferably SiOα (α=1.0 to 2.0). When α = 1.5 to 2.0, silicon oxide is more stable, which
is more preferable. If sufficient oxidation annealing is performed to form silicon oxide
on the surface of the steel sheet, SiO2 having α≈2.0 can be formed.
25 [0048]
16
A thickness of the intermediate layer (a length in a sheet thickness direction) is
not particularly limited, and can be, for example, 1 nm or more and 1 μm or less. The
thickness of the intermediate layer is preferably 10 nm or more and 500 nm or less.
[0049]
The surface layer of the intermediate 5 layer (in the vicinity of an interface
between the intermediate layer and the insulation coating) indicates a range from an
outermost surface of the intermediate layer to A×1/4 nm when the thickness of the
intermediate layer is A nm.
[0050]
10
The electrical steel sheet of the present invention is formed in contact with the
intermediate layer and includes the insulation coating mainly including phosphate and
colloidal silica. The electrical steel sheet of the present invention includes the
insulation coating, so that high surface tension can be applied to the electrical steel sheet
15 of the present invention.
[0051]

The average particle size of BN present in the surface layer of the intermediate
layer (may be hereinafter simply referred to as an intermediate layer surface layer): 50
20 nm or more and 300 nm or less.
If BN having an average particle size (a length of the major axis) of 50 nm or
more and 300 nm or less is present in the intermediate layer surface layer (in the vicinity
of the interface between the intermediate layer and the insulation coating), the insulation
coating adhesion (adhesion between the base steel sheet and the insulation coating) is
25 improved. The reason for this is not clear, but it is believed that BN having the above
17
average particle size is present in the oxide layer (intermediate layer) present after final
annealing or the oxide layer (intermediate layer) formed through an intermediate layer
formation heat treatment, whereby it functions as an anchor for the oxide layer and
improves the insulation coating adhesion.
5 [0052]
Since BN is a reprecipitate after solid solution, it often has a spherical shape in
order to reduce surface energy. Therefore, the shape of BN is preferably spherical.
Also, in the present embodiment, the “spherical BN” represents a BN having (a major
axis) / (minor axis) ratio 1.5 or less.
10 [0053]
The average particle size of BN is 50 nm or more and 300 nm or less. If the
average particle size of BN is less than 50 nm when the average particle size is defined
by the major axis of the BN precipitates, the precipitation frequency of BN increases and
the iron loss increases, and thus the average particle size of BN is 50 nm or more. The
15 average particle size of BN is preferably 80 nm or more.
[0054]
If the average particle size of BN exceeds 300 nm, the precipitation frequency of
BN decreases and the effect of improving the insulation coating adhesion cannot be
sufficiently obtained, and thus the average particle size of BN is 300 nm or less. The
20 average particle size of BN is preferably 280 nm or less.
[0055]
The average particle size is obtained by visually observing 10 visual fields of 4
μm in a sheet width direction×2 μm in the sheet thickness direction using an energy
dispersive X-ray spectroscope (EDS) attached to a scanning electron microscope (SEM)
25 or a transmission electron microscope (TEM), measuring lengths of major axes of
18
precipitates in observed visual fields identified as BN using EDS, and setting an average
value thereof to the average particle size.
[0056]
Number density of BN: 2×106 pieces/mm2 or more
The number density 5 of BN having an average particle size of 50 nm or more and
300 nm or less is preferably 2×106 pieces/mm2 or more. If the number density of BN is
less than 2×106 pieces/mm2, the dispersion of BN functioning as an anchor becomes
insufficient, and the effect of improving the insulation coating adhesion cannot be
sufficiently obtained. For that reason, the number density of BN is preferably 2×106
10 pieces/mm2 or more. The number density of BN is more preferably 3×106 pieces/mm2
or more. Since the number density of BN varies depending on an amount of B in the
steel sheet, no particular upper limit is set.
[0057]
The number density of BN is measured by washing the grain-oriented electrical
15 steel sheet (product) with sodium hydroxide, removing the insulation coating on the
surface of the steel sheet, and observing the surface of the steel sheet (that is, the
intermediate layer surface layer) using a field emission scanning electron microscope
(FE-SEM). The number density of the intermediate layer surface layer can be measured
in a cross-section thereof perpendicular to a rolling direction of the steel sheet by visually
20 imaging 10 visual fields of 4 μm in the sheet width direction×2 μm in the sheet thickness
direction using the EDS attached to the FE-SEM, and counting the number of BNs
identified by the EDS.
[0058]
In a distribution of B in a thickness direction of the steel sheet, in a case in
25 which a concentration (strength) of B in a surface layer of the steel sheet including the
19
oxide layer (intermediate layer) present in contact with and on the base steel sheet of the
steel sheet after final annealing or the oxide layer (intermediate layer) formed by thermal
oxidation is lower than a concentration (strength) of B of a base iron (base steel sheet)
inside the steel sheet, BN is not precipitated on the surface layer of the steel sheet, or
even if it is precipitated, t 5 he amount is small, and the insulation coating adhesion
becomes inferior. Also, the surface layer of the steel sheet indicates a part ranging from
the outermost surface of the intermediate layer to a position from an interface between a
surface of the base iron and the intermediate layer to a position of 1/100 of a thickness of
the base iron. Therefore, the surface layer of the steel sheet includes the intermediate
10 layer and a part of the base steel sheet.
[0059]
IB_t(d/100)>IB_t(d/10)
In the grain-oriented electrical steel sheet according to the present embodiment,
when the sheet thickness excluding the insulation coating is defined as d, the
15 measurement is performed using glow discharge emission spectrometry (GDS), the time
until the sputtering depth reaches the position of d/100 from the outermost surface layer
of the steel sheet (the outermost surface of the intermediate layer) excluding the
insulation coating is defined as t(d/100), and the time until the sputtering depth reaches
the position of d/10 from the outermost surface of the intermediate layer is defined as
20 t(d/10), the emission intensity IB of B satisfies the following Equation (1). The position
of d/100 from the outermost surface of the intermediate layer is located on the surface
layer of the steel sheet, and the position of d/10 from the outermost surface of the
intermediate layer is located on a base steel sheet side with respect to the surface layer of
the steel sheet. Therefore, if the emission intensity IB of B satisfies the following
25 Equation (1), a sufficient amount of BN is precipitated on the surface layer of the steel
20
sheet, and thus the iron loss does not deteriorate and the insulation coating adhesion is
further improved.
[0060]
IB_t(d/100)>IB_t(d/10) ∙∙∙ Equation (1)
IB_5 t(d/100): Emission intensity of B at t(d/100)
IB_t(d/10): Emission intensity of B at t(d/10)
[0061]
Also, as described above, in order to accurately control the particle size, the
precipitation frequency, and the presence position of BN, it is necessary to appropriately
10 control a temperature lowering rate after final annealing.
[0062]

In order to identify each layer in a cross-sectional structure of the present
electrical steel sheet, line analysis is performed in the sheet thickness direction using
15 EDS attached to SEM or TEM, and quantitative analysis of the chemical composition of
each layer is performed. The elements to be quantitatively analyzed are 6 elements of
Fe, P, Si, O, Mg and Al.
[0063]
A layered region present at the deepest position in the sheet thickness direction
20 and a region in which Fe content is 80 atomic% or more and O content is less than 30
atomic% excluding measurement noise is determined to be the base steel sheet.
[0064]
Regarding regions excluding the base steel sheet identified above, a region in
which Fe content is less than 80 atomic%, P content is 5 atomic% or more, and O content
25 is 30 atomic% or more excluding measurement noise is determined to be the insulation
21
coating.
[0065]
A region excluding the silicon steel sheet and the insulation coating identified
above is determined to be the intermediate layer. The intermediate layer preferably
satisfies that, on average as a 5 whole, Fe content is less than 80 atomic% on average, P
content is less than 5 atomic% on average, Si content is 20 atomic% or more on average,
and O content is 30 atomic% or more on average. Further, in the present embodiment,
since the intermediate layer is not a forsterite coating but an oxide layer mainly including
silicon oxide, Mg content of the intermediate layer is preferably less than 20 atomic% on
10 average.
[0066]
A manufacturing method for manufacturing the electrical steel sheet of the
present invention will be described.
[0067]
15
A silicon steel slab that is a material of the electrical steel sheet of the present
invention contains, as a chemical composition, by mass%: C: 0.085% or less, Si: 0.80 to
7.00%, Mn: 0.05 to 1.00%. , acid-soluble Al: 0.010 to 0.065%, N: 0.0040 to 0.0120%, S:
0.0100% or less, and B: 0.0005 to 0.0080%.
20 [0068]
C: 0.085% or less
C is an element that is effective in controlling the primary recrystallization
structure, but it adversely affects the magnetic characteristics, and thus it is an element
that is removed by decarburization annealing before final annealing. If it exceeds
25 0.085%, a time of decarburization annealing becomes longer and the productivity
22
decreases, and thus C is set to 0.085% or less. C is preferably 0.070% or less, and more
preferably 0.050% or less.
[0069]
A lower limit thereof includes 0%, but if C is reduced to less than 0.0001%, the
manufacturing costs will increase significantly, 5 and thus 0.0001% is an actual lower limit
for a practical steel sheet. Also, in the grain-oriented electrical steel sheet, C is usually
reduced to about 0.001% or less by decarburization annealing.
[0070]
Si: 0.80 to 7.00%
10 Si is an element that increases electrical resistance of the steel sheet and
improves iron loss characteristics. If it is less than 0.80%, γ transformation occurs
during final annealing and the crystal orientation of the steel sheet is impaired, and thus
Si is set to 0.80% or more. Si is preferably 1.50% or more, and more preferably 2.50%
or more.
15 [0071]
On the other hand, if it exceeds 7.00%, workability deteriorates and cracks occur
during rolling, and thus Si is set to 7.00% or less. Si is preferably 5.50% or less, and
more preferably 4.50% or less.
[0072]
20 Mn: 0.05 to 1.00%
Mn is an element that prevents cracks during hot rolling and is combined with S
and/or Se to form MnS that functions as an inhibitor. If it is less than 0.05%, the
addition effect is not sufficiently exhibited, and thus Mn is set to 0.05% or more. Mn is
preferably 0.07% or more, and more preferably 0.09% or more.
25 [0073]
23
On the other hand, if it exceeds 1.00%, the precipitation and dispersion of MnS
become non-uniform, the required secondary recrystallization structure cannot be
obtained, and the magnetic flux density decreases, and thus Mn is set to 1.00% or less.
Mn is preferably 0.80% or less, and more preferably 0.60% or less.
5 [0074]
Acid-soluble Al: 0.010 to 0.065%
Acid-soluble Al is an element that is combined with N to produce (Al, Si) N that
functions as an inhibitor. If it is less than 0.010%, the addition effect is not sufficiently
exhibited and the secondary recrystallization does not proceed sufficiently, and thus the
10 acid-soluble Al is set to 0.010% or more. The acid-soluble Al is preferably 0.015% or
more, and more preferably 0.020% or more.
[0075]
On the other hand, if it exceeds 0.065%, the precipitation and dispersion of (Al,
Si) N become non-uniform, the required secondary recrystallization structure cannot be
15 obtained, and the magnetic flux density decreases, and thus the acid-soluble Al is 0.065%
or less. The acid-soluble Al is preferably 0.050% or less, and more preferably 0.040%
or less.
[0076]
N: 0.0040 to 0.0120%
20 N is an element that is combined with Al to form AlN that functions as an
inhibitor, but on the other hand, it is also an element that forms blisters (voids) in the
steel sheet during cold rolling. If it is less than 0.004%, the formation of AlN is
insufficient, and thus N is set to 0.004% or more. N is preferably 0.006% or more, and
more preferably 0.007% or more.
25 [0077]
24
On the other hand, if it exceeds 0.012%, there is a concern that blisters (voids)
may be formed in the steel sheet during cold rolling, and thus N is set to 0.012% or less.
N is preferably 0.010% or less, and more preferably 0.009% or less.
[0078]
5 S: 0.0100% or less
S is an element that is combined with Mn to form MnS that functions as an
inhibitor.
[0079]
If S is 0.0100% or more, the precipitation dispersion of MnS becomes non10
uniform after purification, and the desired secondary recrystallization structure cannot be
obtained, and thus the magnetic flux density decreases, the hysteresis loss increases, MnS
remains after purification, and the hysteresis loss increases.
There is no particular lower limit, but it is preferably 0.0030% or more. More
preferably, it is 0.0070% or more.
15 [0080]
B: 0.0005 to 0.0080%
B is an element that is combined with N and is complex-precipitated with MnS
to form BN that functions as an inhibitor.
[0081]
20 If it is less than 0.0005%, the addition effect is not sufficiently exhibited, and
thus B is set to 0.0005% or more. B is preferably 0.0010% or more, and more
preferably 0.0015% or more. On the other hand, if it exceeds 0.0080%, the
precipitation and dispersion of BN become non-uniform, the required secondary
recrystallization structure cannot be obtained, and the magnetic flux density decreases,
25 and thus B is set to 0.0080% or less. B is preferably 0.0060% or less, and more
25
preferably 0.0040% or less.
[0082]
In the silicon steel slab, the remainder excluding the above elements is Fe and
impurities. The impurities include elements that are inevitably mixed from the steel raw
material and/or in the steelmaking process and 5 are permissible elements within the range
in which they do not impair the characteristics of the electrical steel sheet of the present
invention.
[0083]
Further, instead of some of Fe, the silicon steel slab may contain at least one
10 selected from the group consisting of Cr: 0.30% or less, Cu: 0.40% or less, P: 0.50% or
less, Ni: 1.00% or less, Sn: 0.30% or less, Sb: 0.30% or less, and Bi: 0.01% or less within
the range in which the magnetic characteristics of the electrical steel sheet of the present
invention are not impaired and other characteristics can be enhanced.
[0084]
15
The silicon steel slab is obtained by continuously casting or ingot casting and
slabbing molten steel having a required composition that has been melted in a converter
or an electric furnace and, if necessary, vacuum degassed. The silicon steel slab is
usually a slab having a thickness of 150 to 350 mm, preferably 220 to 280 mm, but may
20 be a thin slab of 30 to 70 mm. In the case of a thin slab, there is an advantage that
roughening into an intermediate thickness is not required at the time of manufacturing a
hot-band.
[0085]

25 The silicon steel slab is preferably heated to 1250°C or lower and subjected to
26
hot rolling. If the heating temperature exceeds 1250°C, an amount of molten scale
increases, and MnS and/or MnSe is completely solid-solved and finely precipitated in the
subsequent processes, and thus it is necessary to set the decarburization annealing
temperature to 900°C or higher to obtain a desired primary recrystallization particle size.
For that reason, the heating temperature 5 is preferably 1250°C or lower. The heating
temperature is more preferably 1200°C or lower.
[0086]
A lower limit of the heating temperature is not particularly limited, but the
heating temperature is preferably 1100°C or higher from the viewpoint of ensuring the
10 workability of the silicon steel slab.
[0087]

The silicon steel slab heated to 1250°C or lower is subjected to hot rolling to
form a hot-band. In the hot-band annealing, the hot-band is heated to 1000 to 1150°C (a
15 first stage temperature) to recrystallize, and then heated to 850 to 1100°C (a second stage
temperature), which is lower than the first stage temperature, and annealed to
homogenize a non-uniform structure generated during hot rolling. The hot-band
annealing is preferably performed once or more in order to homogenize the history of the
hot-band in the hot rolling before it is subjected to final cold rolling.
20 [0088]
In the hot-band annealing, the first stage temperature greatly affects the
precipitation of the inhibitor in the subsequent processes. If the first stage temperature
exceeds 1150°C, the inhibitor is finely precipitated in the subsequent processes, and the
decarburization annealing temperature for obtaining the desired primary recrystallization
25 particle size needs to be 900°C or higher. For that reason, the first stage temperature is
27
preferably 1150°C or lower. The first stage temperature is more preferably 1120°C or
lower.
[0089]
On the other hand, if the first stage temperature is lower than 1000°C,
recrystallization is insufficient a 5 nd homogenization of the hot-band structure is not
achieved, and thus the first stage temperature is preferably 1000°C or higher. The first
stage temperature is more preferably 1030°C or higher.
[0090]
If the second stage temperature exceeds 1100°C, the inhibitor is finely
10 precipitated in the subsequent processes as in the case of the first stage temperature, and
thus the second stage temperature is preferably 1100°C or lower. The second stage
temperature is more preferably 1070°C or lower. On the other hand, if the second stage
temperature is lower than 850°C, the γ phase is not generated and homogenization of the
hot-band structure is not achieved, and thus the second stage temperature is preferably
15 850°C or higher. The second stage temperature is more preferably 880°C or higher.
[0091]

The steel sheet that has been subjected to hot-band annealing is subjected to cold
rolling once or to cold rolling twice or more with intermediate annealing interposed
20 between to obtain the steel sheet having a final thickness. The cold rolling may be
performed at room temperature (10 to 30°C), or the steel sheet may be heated to a
temperature higher than the room temperature, for example, about 200°C for warm
rolling.
[0092]
25
28
For the purpose of removing C in the steel sheet and controlling a primary
recrystallization grain size to a desired grain size on the steel sheet having the final
thickness, the decarburization annealing is performed in a moist atmosphere with an
oxidation degree of less than 0.15. For example, it is preferable to perform the
decarburization annealing 5 at a temperature of 770 to 950°C for a time during which the
primary recrystallization particle size is 15 μm or more. Here, the oxidation degree is
obtained by dividing a partial pressure (PH2O) of H2O gas in the atmospheric gas by a
partial pressure (PH2) of H2 gas, that is, PH2O/PH2.
[0093]
10 If the decarburization annealing temperature is less than 770°C, the desired
crystal grain size cannot be obtained, and thus the decarburization annealing temperature
is preferably 770°C or higher. The decarburization annealing temperature is more
preferably 800°C or higher. On the other hand, if the decarburization annealing
temperature exceeds 950°C, the crystal grain size exceeds the desired crystal grain size,
15 and thus the decarburization annealing temperature is preferably 950°C or lower. The
decarburization annealing temperature is more preferably 920°C or lower.
[0094]

Before final annealing, the decarburization-annealed steel sheet is subjected to
20 nitriding treatment so that N content of the steel sheet is 40 to 1000 ppm. The nitriding
treatment method is not particularly limited, and for example, a steel sheet that has been
decarburization-annealed can be nitriding-treated with ammonia gas. If the N content of
the steel sheet after the nitriding treatment is less than 40 ppm, AlN does not sufficiently
precipitate and AlN does not function as an inhibitor, and thus the N content of the steel
25 sheet after the nitriding treatment is preferably 40 ppm or more. The N content of the
29
steel sheet after the nitriding treatment is more preferably 80 ppm or more.
[0095]
On the other hand, if the N content of the steel sheet exceeds 1000 ppm, AlN is
excessively present even after the completion of the secondary recrystallization in the
next final annealing, 5 and the iron loss increases, and thus the N content is preferably
1000 ppm or less. The N content of the steel sheet after the nitriding treatment is more
preferably 970 ppm or less.
[0096]

10 Subsequently, an annealing separator containing magnesia as a main component
is applied to the nitriding-treated steel sheet and subjected to final annealing. A glass
film made of forsterite is formed on the surface of the steel sheet by final annealing, and
the coating is removed by means such as pickling and grinding. After removing the
glass film, the surface of the steel sheet is preferably smoothed by chemical polishing or
15 electric field polishing.
[0097]
Alternatively, an annealing separator containing alumina as the main component
can be used instead of magnesia as the annealing separator, and the nitriding-treated steel
sheet is applied with this, dried, coiled into a coil after drying, and subjected to final
20 annealing (secondary recrystallization and/or purification annealing). Due to the final
annealing, the formation of a coating made of an inorganic mineral substance such as
forsterite can be inhibited to produce the grain-oriented electrical steel sheet. After
production, the surface of the steel sheet is preferably smoothed by chemical polishing or
electric field polishing.
25 [0098]
30

[Secondary recrystallization annealing]
In the secondary recrystallization annealing of the final annealing, the crystal
grains in the {110}<001> orientation grow preferentially due to the inhibitor function of
BN. The secondary recrystallization annealing 5 is a process of annealing a steel sheet
coated with an annealing separator at a heating rate of 15 °C/hour or less in a temperature
range of 1000 to 1100°C in the heating process up to a purification annealing
temperature. The heating rate in the temperature range of 1000 to 1100°C is more
preferably 10 °C/hour or less. In the secondary recrystallization annealing, instead of
10 controlling the heating rate, the steel sheet coated with the annealing separator may be
held in a temperature range of 1000 to 1100°C for 10 hours or more.
[0099]
[Purification annealing]
The steel sheet that has been subjected to the secondary recrystallization
15 annealing may be subjected to purification annealing following the secondary
recrystallization annealing. When the steel sheet after the completion of the secondary
recrystallization is subjected to the purification annealing, the precipitates used as the
inhibitor are detoxified and the hysteresis loss in the final magnetic characteristics is
reduced. The purification annealing is preferably carried out by retaining at 1200°C for
20 10 to 30 hours in a hydrogen atmosphere, for example.
[0100]
In order to control the average particle size of BN to 50 to 300 nm, a
temperature lowering rate in the temperature range of 1200 to 1000°C is less than
50 °C/hour. Further, the temperature lowering rate in the temperature range of 1000 to
25 600°C is less than 30 °C/hour.
31
[0101]
The reason for setting such a temperature lowering rate is as follows.
BN becomes solid solution B and solid solution N in a high temperature range,
and N that cannot be solid-solved is released into the atmosphere during lowering the
temperature, but during 5 lowering the temperature, B that cannot be solid-solved is not
released into the atmosphere and is precipitated as B compounds, for example, BN, Fe2B,
and Fe3B, on the surface layer of the steel sheet including the intermediate layer mainly
composed of silicon oxide or inside the steel sheet. If the solid solution N is not
sufficiently present inside the steel sheet, BN does not precipitate and Fe2B or Fe3B
10 precipitates.
[0102]
During lowering the temperature from the high temperature range, if the
temperature lowering rate is appropriate, the solid solution N is released to the outside of
the system, Fe2B or Fe3B is precipitated inside the steel sheet, and the precipitated Fe2B
15 or Fe3B is Ostwald-grown and becomes coarse. The solid solution B on the surface
layer of the steel sheet is combined with N in the atmosphere and precipitates as a fine
BN in the oxide layer present on the surface layer or the outermost layer of the steel
sheet.
[0103]
20 If the temperature lowering rate is high, the solid solution N is not released to
the outside of the system, and BN is finely precipitated inside the steel sheet, or Fe2B or
Fe3B is finely precipitated without Ostwald-growth. The BN finely precipitated inside
the steel sheet increases the hysteresis loss and causes an increase in the iron loss of the
final product.
25 [0104]
32
A lower limit of the temperature lowering rate is not particularly limited, but if
the temperature lowering rate is less than 10 °C/hour, it greatly affects the productivity,
and thus the temperature lowering rate is preferably 10 °C/hour or more. Therefore, the
temperature lowering rate in the temperature range of 1200 to 1000°C is preferably 10 to
50 °C/hour, and the temperature 5 lowering rate in the temperature range of 1000 to 600°C
is preferably 10 to 30 °C/hour.
[0105]

The grain-oriented electrical steel sheet from which a coating of an inorganic
10 mineral substance such as forsterite (forsterite film) has been removed or the grainoriented
electrical steel sheet in which formation of a coating of an inorganic mineral
substance such as forsterite is inhibited is annealed to form the intermediate layer mainly
composed of silicon oxide on the surface of the base steel sheet.
[0106]
15 The annealing atmosphere is preferably a reducing atmosphere so that the inside
of the steel sheet is not oxidized, and particularly preferably a nitrogen atmosphere mixed
with hydrogen. For example, an atmosphere in which hydrogen: nitrogen is 75% by
volume: 25% by volume and the dew point is −20 to 0°C is preferable.
[0107]
20 The intermediate layer formation heat treatment process may be omitted for the
grain-oriented electrical steel sheet from which the coating of the inorganic mineral
substance such as forsterite has been removed or the grain-oriented electrical steel sheet
in which formation of the coating of the inorganic mineral substance such as forsterite is
inhibited.
25 [0108]
33

After applying an aqueous coating solution (insulation coating forming solution)
mainly composed of phosphate and colloidal silica to the intermediate layer mainly
composed of silicon oxide on the steel sheet having the intermediate layer, the insulation
coating 5 formation solution is baked to form the insulation coating.
As the phosphate, for example, a phosphate of Ca, Al, Sr, or the like is
preferable, and among them, an aluminum phosphate is more preferable. A type of
colloidal silica is not particularly limited, and its particle size (average particle size) can
be appropriately selected, but if it exceeds 200 nm, it may settle in a treatment agent, and
10 thus the particle size (average particle size based on the number) of the colloidal silica is
preferably 200 nm or less. The particle size of colloidal silica is more preferably 170
nm.
[0109]
Even if the particle size of the colloidal silica is less than 100 nm, there is no
15 problem in dispersion, but the manufacturing costs increase, and thus 100 nm or more is
preferable from the economical point of view. The particle size of the colloidal silica is
more preferably 150 nm or more.
[0110]
The coating method of the insulation coating formation solution is not
20 particularly limited, and for example, a wet coating method using a roll coater or the like
can be used.
[0111]
The baking atmosphere can be formed by, for example, baking in air at 800 to
900°C for 10 to 60 seconds, but the baking atmosphere is not particularly limited.
25 [0112]
34

Magnetic domain control is performed to the grain-oriented electrical steel sheet
on which the insulation coating is formed in order to reduce the iron loss. The magnetic
domain control method is not limited to a specific method, but the magnetic domain
control can be performed using, for 5 example, laser irradiation, electron beam irradiation,
etching, or a groove forming method using gears. As a result, a grain-oriented electrical
steel sheet having a lower iron loss can be obtained. The magnetic domain control
processing may be performed for the steel sheet after cold rolling.
[Examples]
10 [0113]

Steel slabs A1 to A15 having the composition shown in Table 1-1 were heated to
1150°C and subjected to hot rolling to obtain hot-rolled steel sheets having a sheet
thickness of 2.6 mm, the hot-rolled steel sheets were subjected to hot-rolled sheet
15 annealing in which annealing is performed at 1100°C and subsequently at 900°C, and
then cold-rolled once or cold-rolled a plurality of times with intermediate annealing
interposed therebetween at 30°C to obtain cold-rolled steel sheets having a final sheet
thickness of 0.22 mm.
Steel slabs a1 to a13 having the composition shown in Table 1-1 were heated to
20 1150°C and subjected to hot rolling to obtain hot-rolled steel sheets having a sheet
thickness of 2.6 mm, the hot-rolled steel sheets were subjected to hot-rolled sheet
annealing in which annealing is performed at 1100°C and subsequently at 900°C, and
then cold-rolled once or cold-rolled a plurality of times with intermediate annealing
interposed therebetween at 30°C to obtain cold-rolled steel sheets having a final sheet
25 thickness of 0.22 mm.
35
[0114]
[Table 1-1]
Slab No. Steel slab chemical components (mass%) (remainder is Fe and impurities)
C Si Mn Al N S B
A1 0.085 3.45 0.10 0.028 0.0040 0.008 0.0015
A2 0.031 1.21 0.10 0.029 0.0100 0.009 0.0020
A3 0.033 6.52 0.10 0.029 0.0100 0.007 0.0018
A4 0.041 3.45 0.08 0.028 0.0070 0.005 0.0019
A5 0.044 3.33 0.80 0.029 0.0060 0.004 0.0021
A6 0.052 4.52 0.12 0.020 0.0050 0.003 0.0016
A7 0.055 3.12 0.09 0.055 0.0017 0.001 0.0017
A8 0.061 2.81 0.09 0.030 0.0120 0.009 0.0018
A9 0.062 3.12 0.11 0.030 0.0040 0.001 0.0019
A10 0.071 2.92 0.13 0.030 0.0050 0.001 0.0021
A11 0.078 3.45 0.12 0.028 0.0110 0.010 0.0022
A12 0.055 3.44 0.10 0.027 0.0090 0.007 0.0006
A13 0.085 4.21 0.10 0.027 0.0080 0.006 0.0078
A14 0.082 3.45 0.11 0.031 0.0100 0.008 0.0025
A15 0.045 3.35 0.12 0.030 0.0060 0.009 0.0017
a1 0.092 3.45 0.12 0.029 0.0019 0.007 0.0002
a2 0.076 0.50 0.08 0.028 0.0028 0.007 0.0004
a3 0.065 8.00 0.09 0.028 0.0031 0.007 0.0004
a4 0.045 3.45 0.04 0.029 0.0021 0.009 0.0002
a5 0.061 3.35 1.21 0.029 0.0035 0.009 0.0006
a6 0.032 3.25 0.08 0.005 0.0038 0.006 0.0007
a7 0.012 3.12 0.07 0.082 0.0032 0.006 0.0009
a8 0.072 3.23 0.08 0.030 0.0051 0.009 0.0061
a9 0.043 3.45 0.10 0.027 0.0152 0.009 0.0003
a10 0.033 3.55 0.09 0.026 0.0012 0.012 0.0055
a11 0.039 3.15 0.08 0.026 0.0022 0.030 0.0002
a12 0.058 3.28 0.10 0.027 0.0019 0.007 0.0003
a13 0.021 3.19 0.13 0.028 0.0036 0.007 0.0152
[0115]
36
The grain-oriented electrical steel sheets of Nos. B1 to B15 shown in Table 2
were manufactured as follows. Cold-rolled steel sheets having a final sheet thickness of
0.22 mm were subjected to decarburization annealing in which uniform heat treatment is
performed at 860°C in a moist atmosphere with the oxidation degree of 0.10, and then
nitriding treatment (annealing 5 that increases an amount of nitrogen in the steel sheets) is
performed with ammonia gas. Subsequently, an annealing separator containing alumina
as a main component was applied to the nitriding-treated steel sheets, and final annealing
was performed at a temperature of 1200°C for 20 hours in a hydrogen gas atmosphere.
When the temperature was raised in the final annealing, the heating rate in the range of
10 1000 to 1100°C. was set to 5 °C/hour. Further, after holding at 1200°C for 20 hours, the
temperature lowering rate in the range of 1200 to 1000°C was set to 45 °C/hour, and the
temperature lowering rate in the range of 1000 to 600°C was set to 25 °C/hour. After
the final annealing, excess alumina was removed from the steel sheets, and intermediate
layer formation heat treatment was performed on the steel sheets from which excess
15 alumina had been removed in an atmosphere of hydrogen: nitrogen of 75% by volume:
25% by volume and a dew point of −5°C. An aqueous coating solution mainly
including colloidal silica and phosphate is applied onto the steel sheets after the
intermediate layer formation heat treatment, and insulation coatings were formed by
baking at a temperature of −5°C for 30 seconds in an atmosphere of 75% by volume of
20 hydrogen: 25% by volume of nitrogen to obtain products. The average particle size
based on the number of the colloidal silica in the aqueous coating solution used was 100
nm.
Table 1-2 shows chemical compositions contained in the base steel sheets in the
products. The compositions of the base steel sheets were measured using ICP-AES.
25 Acid-soluble Al was measured by ICP-AES using a filtrate obtained by heat37
decomposing samples with an acid. Further, C and S were measured using a
combustion-infrared absorption method, and N was measured using an inert gas meltingthermal
conductivity method.
[0116]
The grain-oriented electrical st 5 eel sheets of Nos. b1 to b13 shown in Table 1-2
were manufactured as follows. Cold-rolled steel sheets having a final sheet thickness of
0.22 mm were subjected to decarburization annealing in which uniform heat treatment is
performed at 860°C in a moist atmosphere with an oxidation degree of 0.10, and then
nitriding treatment (annealing to increase an amount of nitrogen in the steel sheets) was
10 performed with ammonia gas. Subsequently, an annealing separator containing alumina
as a main component was applied to the steel sheets after nitriding treatment, and final
annealing was performed at a temperature of 1200°C for 20 hours in a hydrogen gas
atmosphere. When the temperature was raised in the final annealing, the heating rate in
the range of 1000 to 1100°C was set to 5 °C/hour. Further, after holding at 1200°C for
15 20 hours, the temperature lowering rate in the range of 1200 to 1000°C was set to
100 °C/hour, and the temperature lowering rate in the range of 1000 to 600°C was
100 °C/hour. After the final annealing, excess alumina was removed from the steel
sheets, and intermediate layer formation heat treatment was performed on the steel sheets
from which the excess alumina have been removed in an atmosphere of hydrogen:
20 nitrogen of 75% by volume: 25% by volume and a dew point of −5°C. An aqueous
coating solution mainly including colloidal silica and phosphate is applied onto the steel
sheets after the intermediate layer formation heat treatment, and insulation coatings were
formed by baking at a temperature of −5°C for 30 seconds in an atmosphere of 75% by
volume of hydrogen: 25% by volume of nitrogen to obtain products. The average
25 particle size based on the number of the colloidal silica in the aqueous coating solution
38
used was 100 nm.
Table 1-2 shows chemical compositions contained in the base steel sheets in the
products. The compositions of the base steel sheets were measured using the same
method as for steel Nos. B1 to B15.
5 [0117]
The grain-oriented electrical steel sheet of steel No. b14 shown in Table 1-2 was
manufactured as follows. A cold-rolled steel sheet having a final sheet thickness of 0.22
mm was subjected to decarburization annealing in which uniform heat treatment is
performed at 850°C in a moist atmosphere with an oxidation degree of 0.10, and then
10 nitriding treatment (annealing to increase an amount of nitrogen in the steel sheet) was
performed with ammonia gas. Subsequently, an annealing separator containing alumina
as a main component was applied to the steel sheet after nitriding treatment, and final
annealing was performed at a temperature of 1200°C for 20 hours in a hydrogen gas
atmosphere. When the temperature was raised in the final annealing, the heating rate in
15 the range of 1000 to 1100°C was set to 5 °C/hour. Further, after holding at 1200°C for
20 hours, the temperature lowering rate in the range of 1200 to 1000°C was set to
200 °C/hour, and the temperature lowering rate in the range of 1000 to 600°C was set to
100 °C/hour. After the final annealing, excess alumina was removed from the steel
sheet, and the intermediate layer formation heat treatment was performed on the steel
20 sheet from which the excess alumina has been removed in an atmosphere in which
hydrogen: nitrogen was 75% by volume: 25% by volume and a dew point was −5°C.
An aqueous coating solution mainly composed of colloidal silica and phosphate was
applied onto the steel sheet after the intermediate layer formation heat treatment, and an
insulation coating was formed by baking at a temperature of 800°C for 30 seconds in an
25 atmosphere of 75% by volume of hydrogen: 25% by volume of nitrogen to obtain a
39
product. The average particle size based on the number of the colloidal silica in the
aqueous coating solution used was 100 nm.
[0118]
The grain-oriented electrical steel sheet of steel No. b15 shown in Table 1-2 was
manufactured as follows. A 5 cold-rolled steel sheet having a final sheet thickness of 0.22
mm was subjected to decarburization annealing in which uniform heat treatment is
performed at 860°C in a moist atmosphere with an oxidation degree of 0.10, and then
nitriding treatment (annealing to increase an amount of nitrogen in the steel sheet) was
performed with ammonia gas. Subsequently, an annealing separator containing alumina
10 as a main component was applied to the steel sheet after nitriding treatment, and final
annealing was performed at a temperature of 1200°C for 20 hours in a hydrogen gas
atmosphere. When the temperature was raised in the final annealing, the heating rate in
the range of 1000 to 1100°C was set to 5 °C/hour. Further, after holding at 1200°C for
20 hours, the temperature lowering rate in the range of 1200 to 1000°C was set to
15 30 °C/hour, and the temperature was kept at 1000°C for 1 hour or more, and the
temperature lowering rate in the range of 1000 to 600°C was set to 50 °C/hour. After
the final annealing, excess alumina was removed from the steel sheet, and intermediate
layer formation heat treatment was performed on the steel sheet from which the excess
alumina has been removed in an atmosphere of 75% by volume of hydrogen: 25% by
20 volume of nitrogen and a dew point of −5°C. An aqueous coating solution mainly
composed of colloidal silica and phosphate was applied onto the steel sheet after the
intermediate layer formation heat treatment, and an insulation coating was formed by
baking at a temperature of 800°C for 30 seconds in an atmosphere of 75% by volume of
hydrogen: 25% by volume of nitrogen to obtain a product. The average particle size
25 based on the number of the colloidal silica in the aqueous coating solution used was 100
40
nm.
[0119]
[Table 1-2]
Steel
No.
Slab
No.
Chemical components (mass%) (remainder is Fe and
impurities)
C Si Mn Al N S B
Examples B1 A1 0.080 3.45 0.10 0.028 0.0021 0.0021 0.0015
B2 A2 0.031 1.21 0.10 0.029 0.0031 0.0032 0.0020
B3 A3 0.001 6.52 0.10 0.029 0.0012 0.0012 0.0018
B4 A4 0.003 3.45 0.08 0.028 0.0010 0.0007 0.0019
B5 A5 0.005 3.33 0.80 0.029 0.0021 0.0005 0.0021
B6 A6 0.001 4.52 0.12 0.020 0.0019 0.0007 0.0016
B7 A7 0.002 3.12 0.09 0.055 0.0017 0.0008 0.0017
B8 A8 0.003 2.81 0.09 0.030 0.0006 0.0009 0.0018
B9 A9 0.007 3.12 0.11 0.030 0.0039 0.0051 0.0019
B10 A10 0.006 2.92 0.13 0.030 0.0022 0.0004 0.0021
B11 A11 0.012 3.45 0.12 0.028 0.0018 0.0092 0.0022
B12 A12 0.011 3.44 0.10 0.027 0.0019 0.0007 0.0006
B13 A13 0.002 4.21 0.10 0.027 0.0010 0.0081 0.0078
B14 A14 0.003 3.45 0.11 0.031 0.0009 0.0005 0.0025
B15 A15 0.001 3.35 0.12 0.030 0.0008 0.0005 0.0017
Comparative
examples
b1 a1 0.090 3.45 0.12 0.029 0.0008 0.0012 0.0002
b2 a2 0.008 0.50 0.08 0.028 0.0010 0.0014 0.0004
b3 a3 0.001 8.00 0.09 0.028 0.0009 0.0018 0.0004
b4 a4 0.002 3.45 0.04 0.029 0.0011 0.0022 0.0002
b5 a5 0.001 3.35 1.21 0.029 0.0019 0.0009 0.0006
b6 a6 0.012 3.25 0.08 0.005 0.0018 0.0010 0.0007
b7 a7 0.011 3.12 0.07 0.082 0.0018 0.0022 0.0009
b8 a8 0.001 3.23 0.08 0.030 0.0018 0.0018 0.0061
b9 a9 0.002 3.45 0.10 0.027 0.0018 0.0011 0.0003
b10 a10 0.001 3.55 0.09 0.026 0.0009 0.0025 0.0055
b11 a11 0.020 3.15 0.08 0.026 0.0018 0.0021 0.0002
b12 a12 0.010 3.28 0.10 0.027 0.0007 0.0012 0.0003
41
b13 a13 0.002 3.19 0.13 0.028 0.0018 0.0011 0.0152
b14 a14 0.002 3.28 0.12 0.028 0.0019 0.0012 0.0029
b15 a15 0.001 3.32 0.11 0.019 0.0009 0.0018 0.0112
[0120]

The magnetic domain control was performed on the product on which the
insulation coating was formed using a mechanical method, a laser, or an electron beam.
For some products, the cold-rolled sheets we 5 re grooved by etching or laser irradiation to
control the magnetic domain.
[0121]

Regarding the precipitates, the B compound observed up to 5 μm from the
10 outermost surface of the intermediate layer perpendicular to the rolling direction of the
steel sheet was analyzed using SEM-EDS to identify the particle size and the
composition of BN. In addition, in the item of “presence or absence of BN
precipitation” in Table 2, ○ represents that one or more spherical BNs (BNs having a
ratio of the major axis to the minor axis of 1.5 or less) were present in an observed visual
15 field, and x represents that there were no spherical BN in the observed visual field.
[0122]

The emission intensity IB of B was measured using glow discharge emission
spectrometry (GDS). IB_t(d/100) that is the emission intensity of B at t(d/100), and IB_t(d/10)
20 that is the emission intensity of B at t(d/10) were obtained when a sputtering time during
which the sputtering depth reached the position of d/100 from the outermost surface of
the steel sheet excluding the insulation coating was defined as t(d/100), and a sputtering
time during which the sputtering depth reached the position of d/10 from the outermost
42
surface of the steel sheet excluding the insulation coating was defined as t (d/10), and
IB_t(d/100)/IB_t(d/10) that is the ratio of them was written in the table.
[0123]

1. A grain-oriented electrical steel sheet comprising:
a base steel sheet;
an intermediate 5 layer which is disposed in contact with the base steel sheet and
mainly includes silicon oxide; and
an insulation coating which is disposed in contact with the intermediate layer
and mainly includes phosphate and colloidal silica,
wherein the base steel sheet contains, as a chemical compositions, by mass%:
10 C: 0.085% or less;
Si: 0.80 to 7.00%;
Mn: 0.05 to 1.00%;
acid-soluble Al: 0.010 to 0.065%;
N: 0.0040% or less;
15 S: 0.0100% or less;
B: 0.0005 to 0.0080%; and
a remainder of Fe and impurities,
BN having an average particle size of 50 to 300 nm is present on a surface layer
of the intermediate layer,
20 when a total thickness of the base steel sheet and the intermediate layer is
defined as d, a time until a sputtering depth reaches a position of d/100 from an
outermost surface of the intermediate layer when an emission intensity of B is measured
using glow discharge emission spectrometry (GDS) is defined as t(d/100), and a time
until the sputtering depth reaches a position of d/10 from the outermost surface of the
25 intermediate layer is defined as t(d/10),
52
an emission intensity IB_t(d/100) of B at t(d/100) and an emission intensity IB_t(d/10)
of B at t(d/10) satisfy the following Equation (1), and
a ratio of a major axis to a minor axis of BN is 1.5 or less,
IB_t(d/100)>IB_t(d/10) ∙∙∙ Equation (1).
5
2. The grain-oriented electrical steel sheet according to claim 1, wherein a number
density of BN on the surface layer of the intermediate layer is 2×106 pieces/mm2 or more.