[0001]The present invention relates to a grain-oriented electrical steel sheet and a
method for manufacturing the same.
Priority is claimed on Japanese Patent Application No. 2019-5239, filed January
10 16, 2019, the content of which is incorporated herein by reference.
[Background Art]
[0002]
Generally, grain-oriented electrical steel sheets are utilized as iron cores for
transformers or the like and the magnetic characteristics of the grain-oriented electrical
15 steel sheets have a significant influence on the performance of transformers. Thus,
various research and development has been conducted to improve the magnetic
characteristics. As a means for reducing the iron loss of grain-oriented electrical steel
sheets, for example, Patent Document 1 below describes a technique for forming a
tension application coating by application a solution containing colloidal silica and
20 phosphate as main components to a surface of steel sheet which has been subjected to
final annealing and firing these to reduce the iron loss. Furthermore, Patent Document
2 below describes a technique for irradiating a surface of a material which has been
subjected to final annealing with a laser beam to apply local strain to a steel sheet to
subdivide magnetic domains and reduce iron loss. With these techniques, the iron loss
25 of grain-oriented electrical steel sheets has become extremely good.
1
[0003]
Incidentally, in recent years, there has been an increasing demand for reducing
the size and increasing the performance of transformers. In addition, in order to reduce
the size of transformers, grain-oriented electrical steel sheets are required to be excellent
5 in terms of having a high magnetic field iron loss so that excellent iron loss is provided
even when a high magnetic flux density is provided. As a means for improving this
high magnetic field iron loss, research regarding eliminating an inorganic coating
existing on an ordinary grain-oriented electrical steel sheet to apply more tension has
been conducted. Since the tension application coating is formed later, the inorganic
10 coating may be referred to as a "primary coating" and a tension application coating may
be referred to as a "secondary coating" is some cases.
[0004]
Inorganic coatings containing forsterite (Mg2Si04) as a main component are
generated on surfaces of grain-oriented electrical steel sheets by reacting oxide layers
15 containing silica (Si02) generated using a decarburization annealing process as a main
component with magnesium oxides applied to a surface to prevent baking during final
annealing. Inorganic coatings have a slight tension effect and have the effect of
improving the iron loss of grain-oriented electrical steel sheets. However, as a result of
the research so far, it has become clear since the inorganic coatings are non-magnetic
20 layers, they adversely affect the magnetic characteristics (particularly, high magnetic
field iron loss characteristics). Therefore, research regarding techniques for
manufacturing grain-oriented electrical steel sheets in which inorganic coatings are not
provided or techniques for making the surfaces of steel sheets have mirror surfaces
(techniques for magnetically smoothing surfaces of steel sheets) by removing the
25 inorganic coatings using mechanical means such as polishing or chemical means such as
2
pickling or preventing the formation of inorganic coatings during high-temperature final
annealing is being conducted.
[0005]
As techniques for preventing the formation of such inorganic coatings or
5 smoothing the surfaces of the steel sheets, for example, Patent Document 3 below
describes a technique for subjecting a surface of a steel sheet to ordinary final annealing,
pickling to remove surface formations and then making the surface of the steel sheet have
a mirror surface through chemical polishing or electrolytic polishing. In recent years,
for example, a technique or the like as described in Patent Document 4 below for
10 preventing the formation of an inorganic coating by incorporating bismuth (Bi) or a
bismuth compound in an annealing separator used at the time of final annealing has been
disclosed. It has been found that a superior iron loss improving effect can be obtained
by forming tension application coatings on the surfaces of the grain-oriented electrical
steel sheets which are obtained through these known methods, and in which inorganic
15 coatings are not provided or which have excellent magnetic smoothness.
[0006]
However, the inorganic coatings need to have the effect of exhibiting insulating
properties, serve as intermediate layers configured to secure adhesion when tensioninsulation
coatings are applied, and serve as intermediate layers of inorganic coatings
20 when tension-application secondary coatings are formed on grain-oriented electrical steel
sheets in which inorganic coatings are not provided.
[0007]
That is to say, although an inorganic coating is formed on a surface of a steel
sheet which has been subjected to final annealing when a grain-oriented electrical steel
25 sheet is manufactured through an ordinary manufacturing process, such an inorganic
3
coating is formed in a state of deeply entering the steel sheet. Thus, the inorganic
coating has good adhesion to the steel sheet made of a metal. For this reason, it is
possible to form a tension-insulation coating containing colloidal silica, phosphate, and
the like as a main component on a surface of an inorganic coating. Incidentally, in
5 general, a metal does not easily bond to oxides. Thus, when there is no inorganic
coating, sufficient adhesion is not easily secured between a tension-insulation coating
and a surface of an electrical steel sheet.
[0008]
As a method for improving the adhesion between a steel sheet and a tension-
1 0 insulation coating as described above, for example, Patent Document 5 below describes a
technique for forming an iron-based oxide by annealing a grain-oriented electrical steel
sheet which does not include an inorganic coating in an acidic atmosphere, forming a
Si02 coating on a surface of a steel sheet by further annealing the grain-oriented
electrical steel sheet in a weakly reducing atmosphere, and then forming a tension-
IS insulation coating.
[0009]
Also, as a method for improving iron loss in a grain-oriented electrical steel
sheet which does not have an inorganic coating, for example, Patent Document 6 below
describes a technique for forming a nitride/oxide layer which contains Si as an under-
20 coating of a tension-insulation coating by attaching Si in an active state to a surface of
the grain-oriented electrical steel sheet which does not have an inorganic coating and
then forming the tension-insulation coating.
[Citation List]
[Patent Document]
25 [0010]
4
[Patent Document 1]
Japanese Unexamined Patent Application, First Publication No. S48-39338
[Patent Document 2]
Japanese Examined Patent Application, Second Publication No. S58-26405
5 [Patent Document 3]
10
Japanese Unexamined Patent Application, First Publication No. S49-96920
[Patent Document 4]
Japanese Unexamined Patent Application, First Publication No. H7-54155
[Patent Document 5]
Japanese Patent No. 4041289
[Patent Document 6]
Japanese Patent No. 4300604
[Summary of the Invention]
[Problems to be Solved by the Invention]
15 [0011]
20
However, even when the techniques disclosed in Patent Document 5 and Patent
Document 6 above are used, there is a room for improvement in adhesion and iron loss in
a grain-oriented electrical steel sheet which does not have an inorganic coating.
[0012]
Therefore, the present invention has been made in view of the above problems,
and an object of the present invention is to provide a grain-oriented electrical steel sheet
for which adhesion of a tension-insulation coating can be improved in a stable manner
and excellent magnetic characteristics can be realized even in the case of a grain-oriented
electrical steel sheet having no inorganic coating, and a method for manufacturing the
25 same.
5
[Means for Solving the Problem]
[0013]
In order to achieve the above object, the inventors conducted extensive studies,
and as a result, found that, after a pickling treatment using a specific acid and a heat
5 treatment are performed on a grain-oriented electrical steel sheet having no inorganic
coating containing forsterite as a main component, a tension-insulation coating is formed
under specific conditions, and thus an iron-based oxide layer and a silicon-containing
oxide layer in a specific state are formed between the tension-insulation coating and a
base steel sheet, and it is possible to stably improve the adhesion of the tension-insulation
10 coating and realize excellent magnetic characteristics.
The scope of the present invention completed based on the above findings is as
follows.
[0014]
[1] A grain-oriented electrical steel sheet according to an aspect of the present invention
15 is a grain-oriented electrical steel sheet which does not have an inorganic coating
20
containing forsterite as a main component, including:
a base steel sheet;
a silicon-containing oxide layer provided on the base steel sheet;
an iron-based oxide layer provided on the silicon-containing oxide layer; and
a tension-insulation coating provided on the iron-based oxide layer, having a
thickness of 1 to 3 ~m and containing phosphate and colloidal silica as main components;
wherein the base steel sheet contains, as chemical components, in terms of, 2.5
to 4.5% of Si, 0.05 to 1.00% of Mn, 0% or more and less than 0.05% of Al, 0% or more
and less than 0.1% of C, 0% or more and less than 0.05% of N, 0% or more and less than
25 0.1% of S, 0% or more and less than 0.05% of Se and 0% or more and less than 0.01% of
6
5
Bi, and the remainder: Fe and impurities,
wherein, when elemental analysis is performed from a surface of the tensioninsulation
coating in a sheet thickness direction by glow discharge optical emission
spectrometry,
(a) in a profile of a Si light emission intensity, there are four or more inflection
points;
(b) in the sheet thickness direction, the inflection point of the Si light emission
intensity present closest to the base steel sheet side is present within a range of 0.3 to 1.5
~m toward the side of the surface of the tension-insulation coating from a saturation
10 point at which an Fe light emission intensity is a maximum, and
15
(c) a peak of the Si light emission intensity present closest to the base steel sheet
side has a light emission intensity that is 1.3 times or more and 2.0 times or less the Si
light emission intensity in the base steel sheet.
[2] The grain-oriented electrical steel sheet according to [1],
wherein the silicon-containing oxide layer may contain silica and fayalite as
main components, and
wherein the tension-insulation coating may contain 25 to 45 mass% of colloidal
silica, with a remainder that contains one or more selected from the group consisting of
aluminum phosphate, magnesium phosphate, zinc phosphate, manganese phosphate,
20 cobalt phosphate, and iron phosphate as main components.
25
[3] The grain-oriented electrical steel sheet according to [1] or [2],
wherein the iron-based oxide layer may contain magnetite, hematite and fayalite
as main components.
[4] The grain-oriented electrical steel sheet according to any one of [1] to [3],
wherein a thickness of the base steel sheet may be 0.27 mm or less.
7
[5] A method for manufacturing a grain-oriented electrical steel sheet according to
another aspect of the present invention is a method for manufacturing a grain-oriented
electrical steel sheet which includes a base steel sheet and a tension-insulation coating
and does not have an inorganic coating containing forsterite as a main component,
5 including:
a washing process of cleaning a surface of the grain-oriented electrical steel
sheet;
a surface treatment process of treating the surface of the grain -oriented electrical
steel sheet which has been subjected to the washing process using a surface treatment
10 liquid which contains one or more of sulfuric acid, phosphoric acid and nitric acid and
having a total acid concentration of 2 to 20% and a liquid temperature of 70 to 90°C;
a heating treatment process of heating the grain-oriented electrical steel sheet
which has been subjected to the surface treatment process at a temperature of 700 to
900°C for 10 to 60 seconds in an atmosphere having an oxygen concentration of 1 to 21
15 volume% and a dew point of -20 to 30°C; and
a tension-insulation coating forming process of forming a tension-insulation
coating which has a thickness of 1 to 3 ~m by applying a treatment solution for forming a
tension-insulation coating containing phosphate and colloidal silica as main components
to the surface of the grain-oriented electrical steel sheet after the heating treatment
20 process, and heating is performed at an average heating rate of 20 to 100 °C/s within 1.0
to 20 seconds after the application, and baking is performed at a temperature of 850 to
950°C for 10 to 60 seconds.
25
[6] The method for manufacturing an insulation coating of a grain-oriented electrical
steel sheet according to [5], may further include:
before the washing process,
8
5
a hot rolling process of subjecting a steel piece which contains, as chemical
components, in terms of mass%, 2.5 to 4.5% of Si, 0.05 to 1.00% of Mn, less than 0.05%
of Al, less than 0.1% of C, less than 0.05% of N, less than 0.1% of S, less than 0.05% of
Se and less than 0.01% of Bi with the remainder being Fe and impurities to hot rolling;
an optional annealing process;
a cold rolling process of performing one cold rolling or two or more cold
rollings having intermediate annealing performed between the cold rollings;
a decarburization annealing process; and
a final annealing process of applying an annealing separator obtained by
10 incorporating bismuth chloride into a mixture of MgO and Ah03 or an annealing
separator obtained by incorporating a bismuth compound and a metallic chloride
compound into a mixture of MgO and Ah03, drying the annealing separator, and then
performing final annealing.
[Effects of the Invention]
15 [0015]
As described above, according to the present invention, even in a grain-oriented
electrical steel sheet having no inorganic coating containing forsterite as a main
component, it is possible to stably improve the adhesion of the tension-insulation coating
and realize excellent magnetic characteristics.
20 [Brief Description of Drawings]
[0016]
25
Fig. 1 is an explanatory diagram schematically showing an example of a
structure of a grain-oriented electrical steel sheet according to an embodiment of the
present invention.
Fig. 2 is an explanatory diagram for explaining the grain-oriented electrical steel
9
5
sheet according to the same embodiment.
Fig. 3A is a graph diagram showing an example of analysis results of the grainoriented
electrical steel sheet according to the same embodiment obtained by a glow
discharge optical emission spectrometry.
Fig. 3B is a graph diagram showing an example of analysis results of the grainoriented
electrical steel sheet having poor adhesion of a tension-insulation coating
obtained by a glow discharge optical emission spectrometry.
Fig. 4 is a flowchart showing an example of a flow of a method of producing a
grain-oriented electrical steel sheet according to the same embodiment.
10 [Embodiment(s) for implementing the Invention]
[0017]
Preferable embodiments of the present invention will be described below in
detail with reference to the attached figures. Here, in this specification and drawings,
components having substantially the same functional configuration will be denoted with
15 the same reference numerals and redundant descriptions thereof will be omitted.
[0018]
(Regarding grain-oriented electrical steel sheet)
First, a grain -oriented electrical steel sheet according to an embodiment of the
present invention will be described in detail with reference to Fig. 1 and Fig. 2. Fig. 1 is
20 an explanatory diagram schematically showing an example of a structure of the grainoriented
electrical steel sheet according to the present embodiment. Fig. 2 is an
explanatory diagram for explaining the grain-oriented electrical steel sheet according to
the present embodiment.
[0019]
25 The inventors found that, ( 1) for example, for a high magnetic field iron loss
10
such as at 1.7 T to 1.9 T, when an inorganic coating containing forsterite (Mg2Si04) or
the like is removed, the iron loss is significantly reduced, and (2) in order to form a
tension-insulation coating that exhibits a high tension of 1.0 kgf/mm2 or more on the
surface of a steel sheet having no inorganic coating with favorable adhesion, it is
5 necessary to form a silicon-containing oxide layer and an iron-based oxide layer on the
surface of the steel sheet in this order, and when the silicon-containing oxide layer and
the iron-based oxide layer are formed, the adhesion of the tension-insulation coating and
the high magnetic field iron loss are improved. Based on the above findings, the
inventors completed the grain-oriented electrical steel sheet according to the present
10 embodiment.
15
[0020]
A grain-oriented electrical steel sheet 1 according to the present embodiment is a
grain-oriented electrical steel sheet which does not have an inorganic coating containing
forsterite as a main component, and as schematically shown in Fig. 1, includes
a base steel sheet ll;
a silicon-containing oxide layer 17 provided on the base steel sheet;
an iron-based oxide layer 15 provided on the silicon-containing oxide layer; and
a tension-insulation coating 13 provided on the iron-based oxide layer, having a
thickness of 1 to 3 ~m and containing phosphate and colloidal silica as main components.
20 As schematically shown in Fig. 1, the silicon-containing oxide layer 17, the iron-based
oxide layer 15 and the tension-insulation coating 13 are provided on both surfaces of the
base steel sheet 11. Here, although Fig. 1 shows a case in which the silicon-containing
oxide layer 17, the iron-based oxide layer 15 and the tension-insulation coating 13 are
provided on both surfaces of the base steel sheet 11, the silicon-containing oxide layer
25 17, the iron-based oxide layer 15 and the tension-insulation coating 13 may be provided
11
only on one surface of the base steel sheet 11.
[0021]
Hereinafter, the base steel sheet 11, the tension-insulation coating 13 (hereinafter
simply abbreviated as "insulation coating" in some cases), the iron-based oxide layer 15
5 and the silicon-containing oxide layer 17 of the grain-oriented electrical steel sheet 1
according to the present embodiment will be described in detail.
[0022]
< Regarding base steel sheet 11 >
Generally, a grain-oriented electrical steel sheet contains silicon (Si) as a
10 chemical component, but silicon is very easily oxidized, an oxidized coating containing
silicon (more specifically, an oxidized coating containing silica as a main component) is
formed on the surface of a steel sheet after decarburization annealing. An annealing
separator is applied to the surface of the steel sheet after decarburization annealing, and
the steel sheet is then wound into a coil, and final annealing is performed. In a general
15 method of producing a grain-oriented electrical steel sheet, when an annealing separator
containing MgO as a main component is used, MgO reacts with the oxidized coating on
the surface of the steel sheet during final annealing and an inorganic coating containing
forsterite (Mg2Si04) as a main component is formed. However, in the grain-oriented
electrical steel sheet 1 according to the present embodiment, a grain -oriented electrical
20 steel sheet having no inorganic coating containing forsterite as a main component on its
surface is used as the base steel sheet 11 instead of the above grain-oriented electrical
steel sheet having an inorganic coating containing forsterite as a main component on its
surface.
[0023]
25 Here, a method for manufacturing a grain-oriented electrical steel sheet having
12
no inorganic coating containing forsterite as a main component on its surface will be
described below again.
[0024]
In the grain -oriented electrical steel sheet 1 according to the present
5 embodiment, the grain-oriented electrical steel sheet used as the base steel sheet 11 is not
particular! y limited, and a grain -oriented electrical steel sheet containing known chemical
components can be used. Examples of such a grain-oriented electrical steel sheet
include a grain-oriented electrical steel sheet containing, as chemical components, by
mass%, 2.5 to 4.5% of Si, 0.05 to 1.00% of Mn, 0% or more and less than 0.05% of Al,
10 0% or more and less than 0.1% ofC, 0% or more and less than 0.05% ofN, 0% or more
and less than 0.1% of S, 0% or more and less than 0.05% of Se, and 0% or more and less
than 0.01% of Bi with the remainder being Fe and impurities.
[0025]
When the Si content in the base steel sheet is 2.5 mass% or more, desired
15 magnetic characteristics can be obtained. On the other hand, when the Si content in the
base steel sheet is more than 4.5 mass%, since the steel sheet becomes brittle, production
becomes difficult. Therefore, the Si content in the base steel sheet is 4.5 mass% or less.
[0026]
When the Mn content in the base steel sheet is 0.05 mass% or more, it is
20 possible to secure the absolute amount of MnS, which is an inhibitor required for causing
secondary recrystallization. On the other hand, when the Mn content in the base steel
sheet exceeds 1.00 mass%, steel undergoes phase transformation during secondary
recrystallization annealing, secondary recrystallization does not proceed sufficient! y, and
it is not possible to obtain favorable magnetic flux density and iron loss characteristics.
25 Therefore, the Mn content in the base steel sheet is 1.00 mass% or less.
13
5
[0027]
The base steel sheet may contain, as chemical components, less than 0.005
mass% of each of Al, C, N, S, Se and Bi in addition to Si and Mn. Since these elements
do not have to be contained, the lower limit value is 0 mass%.
When the Al content in the base steel sheet is more than 0 mass% and less than
0.05 mass%, it is possible to minimize embrittlement of the steel sheet and improve iron
loss characteristics.
When the C content in the base steel sheet is more than 0 mass% and less than
0.1 mass%, it is possible to realize favorable magnetic flux density and iron loss
10 characteristics.
15
When the N content in the base steel sheet is more than 0 mass% and less than
0.05 mass%, it is possible to minimize the decrease in passability during production.
When the S content in the base steel sheet is more than 0 mass% and 0.1 mass%
or less, it is possible to minimize embrittlement of the steel sheet.
When theSe content in the base steel sheet is 0 mass% or more and 0.05 mass%
or less, it is possible to realize a magnetic improvement effect.
When the Bi content in the base steel sheet is 0 mass% or more and 0.01 mass%
or less, it is possible to realize favorable magnetic flux density and iron loss
characteristics.
20 [0028]
As schematically shown in Fig. 2, a microstructure 21 also called an etch pit is
provided on the surface of the base steel sheet 11 according to the present embodiment.
In a method of producing a grain-oriented electrical steel sheet according to the present
embodiment to be described below in detail, the microstructure 21 is formed when a
25 surface treatment liquid using a specific acid is applied to the surface of a grain -oriented
14
electrical steel sheet having no inorganic coating and subjected to final annealing.
When the microstructure 21 schematically shown in Fig. 2 is provided on the surface of
the base steel sheet 11, the silicon-containing oxide layer 17 and the iron-based oxide
layer 15 formed on the surface of the base steel sheet 11 further improve adhesion to the
5 base steel sheet 11 due to a so-called anchor effect.
[0029]

The tension-insulation coating 13 is provided on the surface of the grainoriented
electrical steel sheet 1 according to the present embodiment. The tension-
1 0 insulation coating 13 imparts electrical insulation to the grain -oriented electrical steel
sheet, and thus an eddy current loss is reduced, and the iron loss of the grain-oriented
electrical steel sheet is reduced. In addition, the tension-insulation coating 13 exhibits
various characteristics such as corrosion resistance, heat resistance, and slipperiness in
addition to the above electrical insulation.
15 [0030]
In addition, the tension-insulation coating 13 has a function of application a
tension to the grain-oriented electrical steel sheet. The tension-insulation coating
applies a tension to the grain-oriented electrical steel sheet, facilitates domain wall
motion in the grain-oriented electrical steel sheet, and thus can reduce the iron loss of the
20 grain-oriented electrical steel sheet.
[0031]
The tension-insulation coating 13 is a tension-insulation coating of a phosphate
silica mixed system containing phosphate and colloidal silica as main components. The
tension-insulation coating of such a phosphate silica mixed system contains, for example,
25 25 to 45 mass% of colloidal silica, with the remainder that preferably contains one or
15
5
more selected from the group consisting of aluminum phosphate, magnesium phosphate,
zinc phosphate, manganese phosphate, cobalt phosphate, and iron phosphate as main
components.
[0032]
The thickness of the tension-insulation coating 13 (thickness d1 in Fig. 1) of the
phosphate silica mixed system is in a range of 1 to 3 ~m. When the thickness of the
tension-insulation coating 13 is less than 1 ~m, it is not possible to sufficiently improve
various characteristics such as electrical insulation, corrosion resistance, heat resistance,
slipperiness, and tension application properties as described above. On the other hand,
10 when the thickness of the tension-insulation coating 13 exceeds 3 ~m, this is not
preferable because the space factor of the base steel sheet 11 decreases. When the
thickness of the tension-insulation coating 13 is within a range of 1 to 3 ~m, it is possible
to realize a high tension of 1.0 kgf/mm2 or more. The thickness d1 of the tensioninsulation
coating 13 is preferably within a range of 2.5 to 3.0 ~m.
15 [0033]

The iron-based oxide layer 15 functions as an intermediate layer between the
base steel sheet 11 and the tension-insulation coating 13 together with the siliconcontaining
oxide layer 17 to be described below in the grain-oriented electrical steel sheet
20 1 according to the present embodiment. The iron-based oxide layer 15 contains, for
example, an iron-based oxide such as magnetite (Fe304), hematite (Fe203), or fayalite
(Fe2Si04) as a main component.
[0034]
Since the iron-based oxide, which is the main component of the iron-based oxide
25 layer 15, is formed when the surface of the base steel sheet 11 reacts with oxygen, the
16
adhesion between the iron-based oxide layer 15 and the base steel sheet 11 is favorable.
In addition, as described above, as schematically shown in Fig. 2, the microstructure 21
also called an etch pit is provided on the surface of the base steel sheet 11. Therefore,
the iron-based oxide layer 15 formed on the microstructure 21 can further improve the
5 adhesion to the base steel sheet 11 due to a so-called anchor effect together with the
silicon -containing oxide layer 17 to be described below.
[0035]
Generally, it is often difficult to improve the adhesion between a metal and a
ceramic. On the other hand, in the grain-oriented electrical steel sheet 1 according to
10 the present embodiment, since the iron-based oxide layer 15 is provided between the base
steel sheet 11 and the tension-insulation coating 13 which is a type of ceramic, it is
possible to improve the adhesion of the tension-insulation coating 13 even if the
inorganic coating is not formed on the surface of the base steel sheet 11.
15
[0036]
In the grain -oriented electrical steel sheet 1 according to the present
embodiment, the thickness (thickness d2 in Fig. 1) of the iron-based oxide layer 15 is
preferably within a range of 100 to 500 nm. When the thickness d2 of the iron-based
oxide layer 15 is less than 100 nm, the iron-based oxide layer 15 and the siliconcontaining
oxide layer 17 may be dissolved due to an acidic treatment solution used
20 when the tension-insulation coating 13 is formed, and there is a high possibility of
sufficient adhesion not being obtained. On the other hand, when the thickness d2 of the
iron-based oxide layer 15 exceeds 500 nm, the iron-based oxide layer 15 becomes too
thick, and a possibility of partial peeling increases. In the grain-oriented electrical steel
sheet 1 according to the present embodiment, the thickness d2 of the iron-based oxide
25 layer 15 is preferably in a range of 150 to 400 nm, and more preferably in a range of 170
17
to 250 nm.
[0037]
The thickness d2 of the iron-based oxide layer 15 can be determined by
observing a distribution of iron-oxygen bonds on the cross section of the grain-oriented
5 electrical steel sheet 1 according to the present embodiment, using, for example, using Xray
photoelectron spectroscopy (XPS). That is, in XPS, focusing on the intensity of Fe-
0 peaks appearing at 712 e V and the intensity of metal Fe peaks appearing at 708 e V,
sputtering is performed from the side of the surface of the grain-oriented electrical steel
sheet 1 from which the tension-insulation coating 13 is removed toward the base steel
10 sheet 11, a distance from the outermost layer where the measurement starts to the
position in the depth direction at which the intensity of Fe-0 peaks appearing at 712 e V
and the intensity of metal Fe peaks appearing at 708 e V are interchanged can be used as
the thickness of the iron-based oxide layer 15.
15
[0038]
The main component of the iron-based oxide layer 15 can be determined by
performing an X-ray crystal structure analysis method or XPS analysis. Based on the
measurement results so far, the inventors found that the iron-based oxide layer 15 mainly
contains an iron-based oxide as a main component and a small amount of silica.
[0039]
20
The silicon-containing oxide layer 17 is a layer functioning as an intermediate
layer between the base steel sheet 11 and the tension-insulation coating 13 together with
the above iron-based oxide layer 15 in the grain-oriented electrical steel sheet 1
according to the present embodiment. The silicon-containing oxide layer 17 contains
25 silica and fayalite (Fe2Si04) as main components.
18
[0040]
As will be described below, when the surface of the grain-oriented electrical
steel sheet having no inorganic coating is treated using a treatment solution containing at
least one of sulfuric acid, nitric acid and phosphoric acid, the microstructure 21 also
5 called an etch pit as shown in Fig. 2 is formed on the surface of the base steel sheet 11,
and the adhesion of the tension-insulation coating 13 is secured. Here, the inventors
conducted verification in more detail on the adhesion of the tension-insulation coating in
the grain-oriented electrical steel sheet in which the microstructure is formed on the
surface of the base steel sheet, and found that there are some parts with favorable
10 adhesion and some parts with poor adhesion under certain production conditions.
[0041]
As a result of verifying the above phenomenon, it is found that, in parts with
favorable adhesion, a silicon-containing oxide layer containing silica derived from Si
diffused from the base steel sheet and fayalite (Fe2Si04) as main components is formed
15 on the side of a layer (the side of the base steel sheet) below the iron-based oxide layer,
but there is no iron-based oxide layer or silicon-containing oxide layer in parts with poor
adhesion. One reason for a part in which there is no iron-based oxide layer or siliconcontaining
oxide layer is generated is considered to be that the abundance of the ironbased
oxide layer and the silicon-containing oxide layer is small (in other words, the
20 thickness is thin). It is speculated that, since the treatment solution used for forming a
tension-insulation coating is acidic, the thin iron-based oxide layer and the siliconcontaining
oxide layer are dissolved when the tension-insulation coating is formed, and
an adhesion improving effect is reduced. In addition, as another possibility, a
possibility of the iron-based oxide layer being excessively formed is considered. It is
25 speculated that, when the iron-based oxide layer is excessively formed, since the iron-
19
5
based oxide (smudge) released from the surface is generated, a treatment solution used
for forming the tension-insulation coating does not adhere to the surface of the steel
sheet.
[0042]
Based on the above findings, it became clear that it is important to form the ironbased
oxide layer and the silicon -containing oxide layer in an appropriate state in order to
realize excellent adhesion of the tension-insulation coating.
[0043]
Based on the above findings, it became clear that, when the grain-oriented
10 electrical steel sheet with favorable adhesion is analyzed by glow discharge optical
emission spectrometry (GDS), characteristic peak is observed in the obtained GDS chart.
Fig. 3A shows an example of results obtained by analyzing the grain-oriented electrical
steel sheet with favorable adhesion by GDS, and Fig. 3B shows an example of results
obtained by analyzing the grain -oriented electrical steel sheet with poor adhesion by
15 GDS. For each grain-oriented electrical steel sheet, a tension-insulation coating is
formed using a treatment solution containing colloidal silica and aluminum phosphate.
In Fig. 3A and Fig. 3B, the horizontal axis represents the elapsed time [seconds] from
when the analysis started, and the vertical axis represents the GDS relative intensity [a.
u.]. Since GDS is a method of analyzing the surface of a sample toward a deeper part in
20 the thickness direction while sputtering, a longer elapsed time indicates that a deeper part
of the sample is analyzed. In addition, in Fig. 3A and Fig. 3B, for elements other than
Fe, the obtained results are enlarged three times, and displayed in the figures.
[0044]
With reference to Fig. 3A and Fig. 3B, a light emission peak derived from Al
25 and a light emission peak derived from Si are observed in an area in which the elapsed
20
time is about 0 seconds to 50 seconds. In addition, it can be seen that the GDS relative
intensity derived from P also slightly increases near 5 seconds and then gradually
decreases, and there is a gently and broadly distributed light emission peak derived from
P. Since these peaks contain Al, Si, and P, they are derived from the tension-insulation
5 coating 13. In addition, it can be understood that, since the number of light emission
peaks derived from Fe increases as the elapsed time is longer, the iron-based oxide layer
is formed.
[0045]
Focusing on the GDS analysis results of the grain-oriented electrical steel sheet
10 with excellent adhesion shown in Fig. 3A, it can be understood that the light emission
peak derived from Aland the light emission peak derived from P decrease monotonically,
but the second light emission peak derived from Si is observed in the area A surrounded
by the dashed line in Fig. 3A, and there are a total of four inflection points in the profile
regarding the Si light emission intensity. These four inflection points are observed in all
15 of the grain-oriented electrical steel sheets with favorable adhesion although the elapsed
times at which the inflection points are present are different. Therefore, it can be
understood that the second Si light emission peak present between the third inflection
point and the fourth inflection point located on the side of the base steel sheet is derived
from a silicon-containing oxide layer containing silica and fayalite (Fe2Si04) as a main
20 component.
[0046]
In particular, focusing on the position of the inflection point (hereinafter referred
to as an inflection point B in some cases) positioned closest to the base steel sheet side, it
became clear that, in any of the grain-oriented electrical steel sheets with favorable
25 adhesion, the position of the inflection point B is present within a range of 0.3 to 1.5 ~m
21
toward the surface of the grain-oriented electrical steel sheet (that is, the side of the
tension-insulation coating) with respect to the point at which the Fe light emission peak
intensity is a maximum (in Fig. 3A, the position at which the elapsed time is about 80
seconds; hereinafter, will be referred to as a saturation point in some case). The
5 distance in the sheet thickness direction from the saturation point of the Fe light emission
intensity to the inflection point (inflection point B) positioned closest to the base steel
sheet side corresponds to the distanceD in Fig. 3A, and is D=0.8 ~min Fig. 3A
In addition, it became clear that, in any of the grain-oriented electrical steel
sheets with favorable adhesion, the light emission intensity of the Si light emission peak
10 (hereinafter referred to as a peak B in some cases) positioned closest to the base steel
sheet side is 1.3 times or more and 2.0 times or less the Si light emission intensity in the
base steel sheet (that is, the light emission intensity of a part in which sputtering proceeds
to the part of the base steel sheet and the intensity of the light emission peak derived from
Si becomes steady). In Fig. 3A, the Si light emission intensity of the peak B is 1.8
15 times the Si light emission intensity in the base steel sheet. On the other hand, it
became clear that, when the position of the inflection point B is not present within a
range of 0.3 to 1.5 ~m with respect to the saturation point or when the Si light emission
intensity of the peak B is less than 1.5 times or more than 3.5 times the Si light emission
intensity in the base steel sheet, the tension-insulation coating has poor adhesion.
20 [0047]
Here, the position of the inflection point in the profile of the Si light emission
intensity described above can be determined by generating a profile obtained by secondorder
differentiating a Si light emission intensity profile by any known numerical
calculation application and specifying the position at which the intensity becomes zero in
25 the second derivative profile.
22
[0048]
In this manner, it became clear that, when a part in which the Si element is
segregated at a certain depth position of the grain-oriented electrical steel sheet is the
silicon -containing oxide layer 17 in the present embodiment, and the Si element in the
5 part (the area A in Fig. 3A) corresponding to the silicon-containing oxide layer 17 has a
specific concentration (1.3 times or more and 2.0 times or less the Si light emission
intensity in steel), favorable adhesion is exhibited. Since the Si element segregated part
is derived from Si diffused from the base steel sheet, the Si element segregated part is
present at a position close to the base steel sheet.
10 [0049]
On the other hand, as shown in Fig. 3B, in the GDS analysis results of the grainoriented
electrical steel sheets with poor adhesion, although the second peak derived
from Si as described above is slightly observed, the position (distanceD in Fig. 3B) of
the inflection point positioned closest to the base steel sheet side is 0.4 ~m, which is
15 outside the above range, and the Si light emission intensity is 1.2 times the Si light
emission intensity in the steel, which is outside the above range. In addition, it became
clear that, when other grain-oriented electrical steel sheets with poor adhesion are
analyzed by GDS, the second peak derived from Si is not observed, and as a result, four
inflection points are not present.
20 [0050]
Here, since GDS is a method of analyzing an area with a diameter of about 5
mm while sputtering, it can be considered that, in the GDS analysis results as shown in
Fig. 3A, an average behavior of each element is observed in an area having a diameter of
about 5 mm in the sample. Therefore, it is considered that, in a coil in which the grain-
25 oriented electrical steel sheet is wound, when the GDS analysis result of an optional area
23
at a position an optional distance away from the head of the coil shows the behavior as
shown in Fig. 3A, parts having the same distance from the head of the coil show the
same GDS analysis results as shown in Fig. 3A. In addition, it can be considered that, if
the GDS analysis results show the behavior as shown in Fig. 3A at both the head and the
5 tail of the coil, the GDS analysis results show the behavior as shown in Fig. 3A in the
entire coil.
[0051]
As described above, in the grain -oriented electrical steel sheet 1 according to the
present embodiment, when elemental analysis is performed from the surface of the grain-
1 0 oriented electrical steel sheet 1 in the sheet thickness direction of the grain -oriented
electrical steel sheet 1 by glow discharge optical emission spectrometry (GDS), the
silicon-containing oxide layer 17 that satisfies all of the following conditions (a) to (c) is
present.
[0052]
15 (a) In a profile of a Si light emission intensity, there are four or more inflection points.
(b) In the sheet thickness direction, the inflection point of the Si light emission intensity
present closest to the base steel sheet side is present within a range of 0.3 to 1.5 ~m
toward the side of the surface of the tension-insulation coating from the saturation point
at which the Fe light emission intensity is a maximum.
20 (c) A peak of the Si light emission intensity present closest to the base steel sheet side has
a light emission intensity that is 1.3 times or more and 2.0 times or less the Si light
emission intensity in the base steel sheet.
[0053]
In the above condition (a), the reason why the number of inflection points in the
25 profile of the Si light emission intensity is four or more is as follows. When the grain-
24
oriented electrical steel sheet is analyzed by GDS, depending on the state of the tensioninsulation
coating, shoulders (overlapping peaks) occur at the Si light emission peak
derived from the tension-insulation coating, and in Fig. 3A, two or more light emission
peaks that are visible as one peak may be observed. In addition, in the grain-oriented
5 electrical steel sheet, in order to apply a stronger tension, the tension-insulation coating
may be formed a plurality of time while changing the Si concentration of the treatment
solution. In this case, at the left end of the GDS analysis results as shown in Fig. 3A
(short elapsed time=side of surface layer of grain-oriented electrical steel sheet), a
plurality of light emission peaks derived from the tension-insulation coating are
10 observed. As a result, in the profile of the Si light emission intensity, four or more
inflection points may be observed. However, when the number of inflection points of
the Si light emission intensity is five or more, since the Si segregated part to be focused
on is derived from Si diffused from the base steel sheet, the inflection point B present
closest to the base steel sheet side may be focused among the plurality of observed
15 inflection points.
[0054]
In the above condition (b), the position of the inflection point B of the Si light
emission intensity present closest to the base steel sheet side can be calculated using a
time difference between the saturation point and the inflection point B and the sputtering
20 speed in the GDS.
[0055]
The silicon-containing oxide layer 17 is formed when a pickling treatment for
forming the microstructure 21 on the surface of the base steel sheet 11 is performed using
a surface treatment liquid and a heat treatment is then performed at a predetermined
25 temperature.
25
[0056]
The conditions for performing depth direction analysis by GDS from the surface
of the grain-oriented electrical steel sheet are as follows. When depth direction analysis
is performed by GDS under the following conditions, in the grain-oriented electrical steel
5 sheet with excellent adhesion, the GDS analysis results as shown in Fig. 3A can be
obtained. That is, in a high frequency mode of a general glow-discharge optical
emission spectrometer (for example, GDA 750 commercially available from Rigaku
Corporation), measurement is performed under output: 30 W, Ar pressure: 3 hPa,
measurement area: 4 mm
In the grain -oriented electrical steel sheet 1 according to the present
embodiment, the thickness (thickness din Fig. 1) of the base steel sheet 11 is not
particularly limited, and can be, for example, 0.27 mm or less. Generally, in the grain-
25 oriented electrical steel sheet, as the thickness of the steel sheet is thinner, the adhesion of
26
the tension-insulation coating decreases in many cases. However, in the grain-oriented
electrical steel sheet 1 according to the present embodiment, when the iron-based oxide
layer 15 and the silicon-containing oxide layer 17 are provided, excellent adhesion of the
tension-insulation coating 13 can be obtained even if the thickness dis 0.27 mm or less.
5 [0060]
In the present embodiment, even if the thickness d of the base steel sheet 11 is as
thin as 0.23 mm or less, excellent adhesion of the tension-insulation coating 13 can be
obtained. In the grain -oriented electrical steel sheet 1 according to the present
embodiment, the thickness d of the base steel sheet 11 is more preferably in a range of
10 0.17 to 0.23 mm. Here, in the grain-oriented electrical steel sheet 1 according to the
present embodiment, the thickness d of the base steel sheet 11 is not limited to the above
range.
[0061]
The grain -oriented electrical steel sheet according to the present embodiment
15 does not have an inorganic coating containing forsterite as a main component. The state
in which "an inorganic coating containing forsterite as a main component is not formed"
is determined by the following analysis.
[0062]
In order to specify each layer in the cross-sectional structure, using energy
20 dispersive X-ray spectroscopy (EDS) attached to a scanning electron microscope (SEM)
or a transmission electron microscope (TEM), line analysis is performed in the sheet
thickness direction, and quantitative analysis is performed on chemical components of
each layer. The elements to be quantitatively analyzed are 6 elements: Fe, P, Si, 0, Mg,
andAl.
25 [0063]
27
A layered area which is present at the deepest position in the sheet thickness
direction, which is an area in which the Fe content is 80 atom% or more and the 0
content is less than 30 atom% excluding measurement noises, is determined as the base
steel sheet.
5 [0064]
Regarding the area excluding the base steel sheet determined above, an area in
which the Fe content is less than 80 atom%, the P content is 5 atom% or more, and the 0
content is 30 atom% or more excluding measurement noises is determined as the tensioninsulation
coating.
10 [0065]
An area excluding the base steel sheet and the tension-insulation coating
determined above is determined as an intermediate layer composed of a siliconcontaining
oxide layer and an iron-based oxide layer. The intermediate layer may
satisfy, as an overall average, an Fe content of less than 80 atom% on average, a P
15 content of less than 5 atom% on average, a Si content of 20 atom% or more on average,
and an 0 content of 30 atom% or more on average. In addition, in the present
embodiment, since the intermediate layer is not a forsterite coating, the intermediate
layer may satisfy a Mg content of less than 20 atom% on average. The Mg content of
the intermediate layer is preferably 10 atom% or less, more preferably 5 atom% or less,
20 and still more preferably 3 atom% or less.
[0066]
As described above, when the grain-oriented electrical steel sheet according to
the present embodiment includes the iron-based oxide layer 15 and the silicon-containing
oxide layer 17 which are provided between the base steel sheet 11 and the tension-
25 insulation coating 13, it is possible to further improve the adhesion of the tension-
28
insulation coating 13, and it is possible to extremely reduce the high magnetic field iron
loss, for example, at 1.7 T to 1.9 T.
[0067]
Various magnetic characteristics of the grain -oriented electrical steel sheet
5 according to the present embodiment such as a magnetic flux density and iron loss can be
measured according to the Epstein's method defined in JIS C 2550 and the single sheet
magnetic characteristic measurement method (Single Sheet Tester: SST) defined in JIS C
2556.
10
[0068]
The grain -oriented electrical steel sheet according to the present embodiment
has been described above in detail.
[0069]
(Regarding method for manufacturing a grain-oriented electrical steel sheet)
Subsequently, with reference to Fig. 4, a method for manufacturing a grain-
15 oriented electrical steel sheet according to the present embodiment will be described in
detail. Fig. 4 is a flowchart showing an example of a flow of a method of producing a
grain-oriented electrical steel sheet according to the present embodiment.
[0070]
In the method for manufacturing a grain-oriented electrical steel sheet according
20 to the present embodiment, as described above, a grain-oriented electrical steel sheet
having no inorganic coating containing forsterite as a main component on its surface
(more specifically, a finally annealed grain-oriented electrical steel sheet that does not
have an inorganic coating containing forsterite as a main component on its surface) is
used as the base steel sheet 11.
25 [0071]
29
A method for obtaining a grain-oriented electrical steel sheet having no
inorganic coating is not particularly limited. For example, a method including a hot
rolling process in which a steel piece containing, as chemical components, by mass%, 2.5
to 4.5% of Si, 0.05 to 1.00% of Mn, less than 0.05% of Al, less than 0.1% of C, less than
5 0.05% of N, less than 0.1% of S, less than 0.05% of Se and less than 0.01% of Bi with
the remainder being Fe and impurities is hot-rolled, an optional annealing process, a cold
rolling process in which one instance of cold rolling or two or more instances of cold
rolling with intermediate annealing therebetween are performed, a decarburization
annealing process, and a final annealing process may be exemplified.
10 Here, in order to prevent formation of an inorganic coating, for example, a
method in which an annealing separator that does not form an inorganic coating is
applied and final annealing is performed and a method in which final annealing is
performed using a generally used annealing separator and the generated inorganic coating
is then removed by a known method such as grinding or pickling may be exemplified.
15 [0072]
Among the above methods, the method in which final annealing is performed
using an annealing separator that does not form an inorganic coating is preferable
because it is easy to control and the surface state of the steel sheet is also favorable. As
such an annealing separator, for example, it is preferable to use an annealing separator
20 incorporating bismuth chloride into a mixture of MgO and Ah03 or an annealing
separator incorporating a bismuth compound and a metallic chloride compound into a
mixture of MgO and Ah03.
[0073]
Examples of bismuth chlorides include bismuth oxychloride (BiOCl) and
25 bismuth trichloride (BiCb). Examples of bismuth compounds include bismuth oxide,
30
bismuth hydroxide, bismuth sulfide, bismuth sulfate, bismuth phosphate, bismuth
carbonate, bismuth nitrate, organic acid bismuth, and bismuth halide. Examples of
metal chloride compounds include iron chloride, cobalt chloride, and nickel chloride.
The amount of the bismuth chloride or the bismuth compound and the metallic
5 chlorinated product is not particular! y limited, but is preferably about 3 to 15 parts by
mass with respect to 100 parts by mass of the mixture of MgO and Ah03.
[0074]
Generally, when a grain-oriented electrical steel sheet is produced, after final
annealing, the excess adhered annealing separator is removed by cleaning, and flattening
10 annealing is then performed.
On the other hand, as shown in Fig. 4, in a method for manufacturing a grainoriented
electrical steel sheet according to the present embodiment, using the finally
annealed grain -oriented electrical steel sheet having no inorganic coating, an excess
annealing separator is removed by cleaning (Step S101, washing process), and an acid
15 with a specific concentration (surface treatment liquid) is then applied to the surface of
the steel sheet to perform a surface treatment (Step S103, surface treatment process), a
heating treatment is performed at a specific temperature in an oxidizing atmosphere (Step
S105, heating treatment process), and the tension-insulation coating is formed with
favorable adhesion under specific conditions (Step S107, tension-insulation coating
20 forming process). Thereby, on the surface of the finally annealed grain-oriented
electrical steel sheet having no inorganic coating, it is possible to form an intermediate
layer mainly composed of the iron-based oxide layer and the silicon-containing oxide
layer described above, and it is possible to improve the adhesion of the tension-insulation
coating.
25 [0075]
31

The surface treatment liquid used in the surface treatment process of Step S 103
contains one or two or more of sulfuric acid, nitric acid, and phosphoric acid, and has a
total acid concentration of 2 to 20 mass% and a liquid temperature of 70 to 90°C. When
5 the surface of the steel sheet is etched using the surface treatment liquid, etch pits are
formed on the surface of the steel sheet, and additionally it is possible to form an active
surface state that cannot generally be obtained. The etch pits formed on the surface of
the steel sheet are schematically shown as the microstructure 21 in Fig. 2.
10
[0076]
When the liquid temperature of the surface treatment liquid is lower than 70°C,
the solubility of the surface treatment liquid decreases, not only the possibility of a
precipitate being formed can increase, but also effective etch pits cannot be obtained.
On the other hand, when the liquid temperature of the surface treatment liquid is higher
than 90°C, this is not preferable because the reactivity of the surface treatment liquid
15 becomes too high, and the surface of the steel sheet is excessively etched during the
20
surface treatment process.
The liquid temperature of the surface treatment liquid is preferably in a range of
75 to 87°C and more preferably in a range of 80 to 85°C.
[0077]
When the total acid concentration of the surface treatment liquid is less than 2
mass%, this is industrially disadvantageous because etch pits cannot be appropriately
formed on the surface of the steel sheet and the treatment time becomes long. When the
total acid concentration of the surface treatment liquid exceeds 20 mass%, this is not
preferable because the surface of the steel sheet is excessively etched during the surface
25 treatment process.
32
The total acid concentration of the surface treatment liquid is preferably in a
range of 2 to 17 mass% and more and more preferably in a range of 2 to 10 mass%.
[0078]
The treatment time for the surface treatment process is not particularly limited.
5 The surface treatment process is performed by continuously immersing steel sheets in a
treatment bath in which the surface treatment liquid is retained in many cases. When
this method is used, the time for the steel sheet to pass through the treatment bath is the
treatment time for the surface treatment process. When steel sheets are immersed in the
treatment bath and caused to pass therethrough at a general sheet passing speed, it is
10 possible to realize the active surface state described above.
[0079]
< Regarding heating treatment process>
In order to form the iron-based oxide layer and the silicon-containing oxide
layer on the grain-oriented electrical steel sheet after the surface treatment process,
15 heating is performed in an atmosphere having an oxygen concentration of 1 to 21
volume% and a dew point of -20 to 30°C, for 10 to 60 seconds so that the steel sheet
temperature becomes 700 to 900°C (heating treatment process).
[0080]
When the oxygen concentration in the atmosphere is less than 1 volume%, it
20 takes too much time for the iron-based oxide layer to be formed, and the productivity is
lowered. On the other hand, when the oxygen concentration in the atmosphere exceeds
21 volume%, this is not preferable because the formed iron-based oxide layer tends to be
non-uniform. The concentration of oxygen in the atmosphere is preferably in a range of
2 to 21 volume% and more preferably in a range of 15 to 21 volume%.
25 [0081]
33
When the dew point in the atmosphere is lower than -20°C, it takes too much
time for the iron-based oxide layer to be formed, and the productivity is lowered. On
the other hand, when the dew point in the atmosphere is higher than 30°C, this is not
preferable because the formed iron-based oxide layer tends to be non-uniform. The dew
5 point in the atmosphere is preferably in a range of -10 to 25°C, and more preferably in a
range of -10 to 20°C.
[0082]
When the heating temperature of the steel sheet in the heating treatment process
is lower than 700°C, this is not preferable because it is difficult to form the iron-based
10 oxide layer and the silicon-containing oxide layer in an appropriate state even if the
heating time is 60 seconds. On the other hand, when the heating temperature of the
steel sheet is higher than 900°C, this is not preferable because the iron-based oxide layer
tends to be non-uniform and the silicon-containing oxide layer in a desired state cannot
be formed.
15 The heating temperature of the steel sheet in the heating treatment process is
preferably in a range of 750 to 800°C.
[0083]
When the heating time is shorter than 10 seconds, this is not preferable because
the produced iron-based oxide layer and silicon-containing oxide layer tend to be non-
20 uniform. On the other hand, when the heating time is longer than 60 seconds, this is not
preferable because high cost is industrially required. The heating time is preferably in a
range of 20 to 30 seconds.
[0084]
When the heating treatment process is performed after the surface treatment
25 process, the activated surface of the grain-oriented electrical steel sheet having no
34
inorganic coating is oxidized, an iron-based oxide layer having a coefficient of thermal
expansion that is between those of the metal and the insulation coating is formed, and a
silicon -containing oxide layer is formed with Si diffused from the base steel sheet. Etch
pits are formed on the surface of the grain-oriented electrical steel sheet, and an iron-
5 based oxide layer having a preferable coefficient of thermal expansion and a siliconcontaining
oxide layer in a preferable segregation state are formed to alleviate strain, and
thus further improvement of the adhesion of the tension-insulation coating can be
realized, and an effect of improving a high magnetic field iron loss can be exhibited.
[0085]
10
In the method for manufacturing a grain-oriented electrical steel sheet according
to the present embodiment, in the tension-insulation coating forming process, using the
following treatment solution for forming a tension-insulation coating of the phosphate
silica mixed system, the treatment solution is applied and dried under the following
15 conditions. When a tension-insulation coating is formed on the surface of the steel
sheet, it is possible to further improve the magnetic characteristics of the grain-oriented
electrical steel sheet.
[0086]
Before the treatment solution for forming a tension-insulation coating is applied,
20 the surface of the steel sheet on which the tension-insulation coating is formed may be
subjected to an optional pretreatment such as a degreasing treatment with an alkali or the
like, or the surface may remain without such a pretreatment.
[0087]
The tension-insulation coating formed on the surface of the steel sheet is not
25 particular! y limited as long as it is used as the tension-insulation coating of the phosphate
35
silica mixed system of the grain-oriented electrical steel sheet, and it is possible to use a
tension-insulation coating of a known phosphate silica mixed system. Examples of
such a tension-insulation coating include a coating containing phosphate and colloidal
silica as main components. As another example, a composite insulation coating which
5 contains phosphate and colloidal silica as main components and in which fine organic
resin particles are diffused may be exemplified.
In the method for manufacturing a grain-oriented electrical steel sheet according
to the present embodiment, a treatment solution for forming a tension-insulation coating
is applied to the surface of the grain-oriented electrical steel sheet after the heating
10 treatment process, and within 1.0 to 20 seconds after the application, the grain-oriented
electrical steel sheet after application is heated at an average heating rate of 20 to 100
°C/s, and baked at a steel sheet temperature of 850 to 950°C for 10 to 60 seconds.
[0088]
In an actual operation, since it is often difficult to set the time until heating starts
15 after the treatment solution for forming a tension-insulation coating is applied to shorter
than 1.0 seconds, the time until heating starts is 1.0 seconds or longer after application.
On the other hand, when the time until heating starts is longer than 20 seconds, the
reaction between the surface of the grain-oriented electrical steel sheet subjected to the
heat treatment process and the treatment solution for forming a tension-insulation coating
20 has progressed too much, and the iron-based oxide layer and the silicon-containing oxide
layer formed in the heat treatment process are highly likely to dissolve. Therefore, the
time until heating starts after the treatment solution is applied is 1.0 seconds or longer
and 20 seconds or shorter. Here, a shorter time until heating starts is better.
[0089]
25 When the average heating rate is less than 20 oc/s, the reaction between the
36
surface of the grain-oriented electrical steel sheet subjected to the heat treatment process
and the treatment solution for forming a tension-insulation coating has progressed too
much, and the iron-based oxide layer and the silicon-containing oxide layer formed in the
heat treatment process are highly likely to dissolve. On the other hand, when the
5 average heating rate exceeds 100 °C/s, this is not preferable because the desired steel
sheet temperature during baking is highly likely to be overshot. Therefore, in the
present embodiment, the average heating rate is in a range of 20 to 100 °C/s. The
average heating rate is preferably in a range of 25 to 50 °C/s.
10
[0090]
In the tension-insulation coating forming process, the treatment solution is
baked at a steel sheet temperature of 850 to 950°C for 10 to 60 seconds. When the steel
sheet temperature is lower than 850°C, even if the retention time is 60 seconds, the
formed tension-insulation coating cannot achieve desired characteristics. On the other
hand, when the steel sheet temperature is higher than 950°C, even if the retention time is
15 10 seconds, the tension-insulation coating is excessively baked, and the formed tensioninsulation
coating cannot achieve desired characteristics. In addition, when the
retention time is shorter than 10 seconds, the treatment solution for forming a tensioninsulation
coating cannot be sufficiently dried, and when the retention time is longer than
60 seconds, the formed tension-insulation coating cannot achieve desired characteristics.
20 The steel sheet temperature is preferably in a range of 870 to 900°C, and the retention
time is preferably in a range of 25 to 45 seconds.
[0091]
Thereby, the tension-insulation coating with a thickness of 1 to 3 ~m is formed
on the surface of the iron-based oxide layer.
25 [0092]
37
The time between the surface treatment process and the heat treatment process is
preferably as short as possible, and for example, preferably within several minutes.
[0093]
Following the tension-insulation coating forming process, flattening annealing
5 for shape correction may be performed. When flattening annealing is performed on the
steel sheet, it is possible to further reduce the iron loss.
[0094]
The method of producing a grain -oriented electrical steel sheet according to the
present embodiment has been described above in detail.
10 [Examples]
[0095]
A grain-oriented electrical steel sheet and a method of producing a grainoriented
electrical steel sheet according to the present invention will be described below
in detail with reference to examples and comparative examples. Here, the following
15 examples are only examples of the grain-oriented electrical steel sheet and the method of
producing a grain-oriented electrical steel sheet according to the present invention. The
grain-oriented electrical steel sheet and the method of producing a grain-oriented
electrical steel sheet according to the present invention are not limited to the following
examples.
20 [0096]
(Experimental example)
A steel piece (silicon steel slab) containing, by mass%, C: 0.08%, Si: 3.24%,
Mn: 0.08%, Al: 0.028%, N: 0.008%, S: 0.03%, Se: 0.01 %, and Bi: 0.004% with the
remainder being Fe and impurities was cast, and the obtained steel piece was heated and
25 then hot-rolled to obtain a hot band with a sheet thickness of 2.2 mm. After annealing
38
at a steel sheet temperature of 1,1 oooc for 60 seconds, cold rolling was performed until
the sheet thickness became 0.22 mm, and decarburization annealing was performed at a
steel sheet temperature of 830°C. Then, an annealing separator containing MgO and
Ah03 as main components and 10 mass% ofBiOCl which is bismuth chloride was
5 applied and dried, and final annealing was performed at a steel sheet temperature of
1,200°C for 20 hours (the final annealing under such conditions is also called
"purification annealing"). When the excess annealing separator was removed by
cleaning with water after final annealing, no inorganic coating was formed on the surface
of the steel sheet. In addition, in the results of such final annealing, the Al content was
10 0% or more and less than 0.05%, the C content was 0% or more and less than 0.1 %, the
N content was 0% or more and less than 0.05%, the S content was 0% or more and less
than 0.1 %, the Se content was 0% or more and less than 0.05%, and the Bi content was
0% or more and less than 0.01 %.
15
[0097]
An aqueous solution containing aluminum phosphate and colloidal silica as
main components shown in Table 1 was prepared. Here, for various phosphates shown
in Table 1, a commercially available general special grade reagent was used, and for
colloidal silica, a commercially available general special grade reagent was used. Here,
the average particle sizes of colloidal silica shown in Table 1 are all catalog values.
20 [0098]
After the surface treatment process and the heat treatment process were
performed on the steel sheet after final annealing under conditions shown in Table 2-1, an
aqueous solution containing aluminum phosphate and colloidal silica as main
components shown in Table 1 was applied and baked, and a tension-insulation coating
25 with a thickness of 2.5 ~m was formed on the surface of the steel sheet.
39
[0099]
For the grain-oriented electrical steel sheets produced in this manner, using XPS
(PHI 5600 commercially available from ULVAC-PHI, Inc.), the thickness d2 of the ironbased
oxide layer was measured according to the above method, and the main component
5 of the iron-based oxide layer was determined by the X-ray crystal structure analysis
method. In addition, the obtained grain -oriented electrical steel sheet was analyzed by a
GDS (glow-discharge optical emission spectrometer GDA 750 commercially available
from Rigaku Corporation) according to the following analysis conditions.
[0100]
10 XPS measurement conditions
15
20
X-ray source: MgKa
Analysis area: about 800 ~m

The adhesion of the tension-insulation coating was evaluated as follows. First,
20 a sample with a width of 30 mm and a length of 300 mm was collected from each grainoriented
electrical steel sheet, and subjected to strain-removing annealing at 800°C in a
nitrogen flow for 2 hours, a bending adhesion test was then performed using a 10 mm

In addition, the coating tension of the tension-insulation coating was calculated
by back calculation from the bending status when one side of the tension-insulation
10 coating was peeled off. That is, the coating tension cr was calculated using the
following Formula (1).
15
20
[0106]
[0107]
cr~{E/(1-1-1) }x(T2/3t)x(2 H/L2) ... Formula (1)
Here, in Formula (1 ),
cr: coating tension [Pa]
E: Young's modulus [Pa]
1-1: Poisson's ratio [-]
T: thickness [ m] of sample
t: thickness [ m] of steel sheet
H: bending [ m] of sample
L: length [ m] of sample.
Then, the obtained coating tension was evaluated according to the following
evaluation criteria. Evaluation criteria were as follows, and the score A to score C were
25 satisfactory.
42
Score A: 8 MPa or more
B: 7 MPa or more and less than 8 MPa
C: 6 MPa or more and less than 7 MPa
D: 5 MPa or more and less than 6 MPa
5 E: less than 5 MPa
[0108]
43
[Table 1]
No. Phosphate Solid content Colloidal silica Solid content
concentration (mass%) concentration
(mass%)
1 Aluminum phosphate 65 Average particle size 15 nm, alkaline type 35
2 Aluminum 60 Average particle size 8 nm, aluminum 40
phosphate+ magnesium coated type
phosphate
3 Aluminum phosphate+zinc 70 Average particle size 30 nm, alkaline type 30
phosphate
4 Aluminum phosphate 58 Average particle size 8 nm, alkaline type 42
5 Manganese phosphate 34 Average particle size 15 nm, acid type 66
6 Cobalt phosphate 72 Average particle size 15 nm, alkaline type 28
7 Aluminum phosphate+zinc 72 Average particle size 15 nm, alkaline type 28
phosphate+iron phosphate
[0109]
[Table 2-1]
No. Surface treatment process Heating treatment process Tension-insulation coating forming process
Acid Liquid Treatment Atmosphere Dew Steel sheet Treatment Treatment Time Heating Steel sheet Retention
temperature time (volume%) point temperature time solution before rate temperature time
(oC) (seconds) (oC) (oC) (seconds) heating (°C/s) (oC) (seconds)
(seconds)
1 10% sulfuric 80 10 20%02 28 800 10 1 4 50 900 30
acid
2 5% sulfuric 80 12 20%02 -18 800 20 2 8 50 900 30
acid
3 5% sulfuric 80 12 1%02 28 850 10 3 8 25 860 60
acid
4 7% nitric acid 70 20 20%02 20 800 10 4 16 85 950 12
44
5 15% 85 14 20%02 5 800 10 5 16 50 900 20
phosphoric
acid
6 5% sulfuric 80 12 20%02 -18 850 10 6 4 50 900 20
acid
7 5% sulfuric 80 12 20%02 -18 850 10 7 4 50 900 20
acid
8 25% sulfuric 60 10 20%02 5 850 10 1 4 25 830 55
acid
9 1% sulfuric 80 60 20%02 0 800 10 1 4 50 900 20
acid
10 10% sulfuric 60 10 20%02 0 800 30 2 8 50 900 20
acid
11 5% sulfuric 95 10 20%02 0 800 10 2 8 50 900 20
acid
12 10% sulfuric 75 10 20%02 5 600 30 3 8 50 900 20
acid
13 15% 80 14 20%02 0 1,000 10 3 4 50 900 20
phosphoric
acid
14 10% sulfuric 80 10 3%02 25 800 1 1 8 50 900 20
acid
15 10% sulfuric 80 10 20%02 -15 800 80 1 4 50 900 20
acid
16 10% sulfuric 80 10 20%02 25 750 10 2 0.5 50 900 20
acid
17 10% sulfuric 80 10 20%02 5 880 30 2 30 50 900 20
acid
18 10% sulfuric 80 10 20%02 25 800 10 3 4 u 830 60
acid
19 10% sulfuric 80 10 20%02 5 800 30 3 4 160 950 12
acid
20 10% sulfuric 80 15 20%02 25 800 10 1 8 50 800 60
acid
21 10% sulfuric 80 12 20%02 5 800 30 2 8 85 980 12
acid
45
22 10% sulfuric 80 12 20%02 25 800 10 3 8 85 950 Q
acid
23 10% sulfuric 80 12 20%02 5 800 30 4 8 25 830 90
acid
24 10% sulfuric 80 12 No heat treatment 4 4 160 830 Q
acid
[0110]
[Table 2-2]
No. Iron-based GDS · Si light emission intensity Adhesion Coating High magnetic field iron loss Note
oxide layer tension (W/kg)
Thickness Number of Distance from Si ratio in W17/50 W19/50
(nm) inflection saturation point steel
points (Jlm)
1 240 4 1.5 1.4 A A 0.64 1.01 Example
2 140 4 1.2 1.8 A A 0.62 0.93 Example
3 140 4 0.6 1.8 B c 0.68 1.03 Example
4 340 4 1.0 1.7 B A 0.65 0.97 Example
5 260 4 1.0 1.6 A A 0.61 0.89 Example
6 120 4 0.7 1.8 A A 0.61 0.87 Example
7 120 4 0.9 1.6 B A 0.66 0.99 Example
8 220 4 1.5 2.3 B B 0.71 1.21 Comparative
example
9 40 ~ -- -- D A 0.68 1.18 Comparative
example
10 420 4 0.2 11 D B 0.67 1.08 Comparative
example
11 80 4 0.4 11 D A 0.65 1.10 Comparative
example
12 60 ~ -- -- E B 0.69 1.17 Comparative
example
13 560 4 1.5 u c A 0.73 1.21 Comparative
example
14 80 4 0.3 0.8 E A 0.71 1.15 Comparative
46
example
15 460 4 2.J. 3.3 B B 0.70 1.18 Comparative
example
16 100 ~ -- -- c B 0.66 1.14 Comparative
example
17 300 4 0.4 0.4 D A 0.69 1.13 Comparative
example
18 140 4 0.3 0.8 D B 0.69 1.08 Comparative
example
19 240 4 0.4 0.5 B D 0.66 1.08 Comparative
example
20 140 4 0.5 0.7 B E 0.71 1.17 Comparative
example
21 220 4 il 1.9 c B 0.72 1.17 Comparative
example
22 160 4 2.3 1.5 c D 0.69 1.09 Comparative
example
23 240 4 2.4 2.J. B E 0.68 1.09 Comparative
example
24 160 4 0.6 0.9 D D 0.70 1.09 Comparative
example
47
[0111]
Based on the results of analysis by the X-ray crystal structure analysis method,
in the samples corresponding to the examples of the present invention, the iron-based
oxide layer contained magnetite, hematite, and fayalite as main components, and the
5 silicon-containing oxide layer contained silica and fayalite as main components. On the
other hand, in comparative examples outside the scope of the present invention, the ironbased
oxide layer containing magnetite, hematite, and fayalite as main components was
formed, but the silicon-containing oxide layer having a predetermined number of
inflection points and distance from the saturation point and exhibiting a predetermined Si
10 light emission intensity was not formed.
[0112]
As can be clearly seen in Table 2-2, it can be understood that the samples
corresponding to the examples of the present invention had very excellent adhesion and
the high magnetic field iron loss was improved. On the other hand, it can be understood
15 that the samples corresponding to the comparative examples of the present invention
were inferior in at least either the adhesion or the high magnetic field iron loss.
[0113]
While preferable embodiments of the present invention have been described
above in detail with reference to the appended drawings, the present invention is not
20 limited to these examples. It can be clearly understood that those skilled in the art can
implement various alternations or modifications within the technical ideas described in
the scope of claims and of course these also belong to the technical scope of the present
invention.
[Brief Description of the Reference Symbols]
25 [0114]
48
5
1 Grain-oriented electrical steel sheet
11 Base steel sheet
13 Tension-insulation coating
15 Iron-based oxide layer
17 Silicon-containing oxide layer
21 Microstructure (etch pit)

WE CLAIMS

1. A grain-oriented electrical steel sheet which does not have an inorganic coating
containing forsterite as a main component, comprising:
a base steel sheet;
a silicon-containing oxide layer provided on the base steel sheet;
an iron-based oxide layer provided on the silicon-containing oxide layer; and
a tension-insulation coating provided on the iron-based oxide layer, having a
thickness of 1 to 3 ~m, and containing phosphate and colloidal silica as main
10 components;
wherein the base steel sheet contains, as chemical components, in terms of
mass%, 2.5 to 4.5% of Si, 0.05 to 1.00% of Mn, 0% or more and less than 0.05% of Al,
0% or more and less than 0.1% ofC, 0% or more and less than 0.05% ofN, 0% or more
and less than 0.1% of S, 0% or more and less than 0.05% of Se and 0% or more and less
15 than 0.01% of Bi, and the remainder: Fe and impurities,
wherein, when elemental analysis is performed from a surface of the tensioninsulation
coating in a sheet thickness direction by glow discharge optical emission
spectrometry,
(a) in a profile of a Si light emission intensity, there are four or more inflection
20 points;
25
(b) in the sheet thickness direction, the inflection point of the Si light emission
intensity present closest to the base steel sheet side is present within a range of 0.3 to 1.5
~m toward the side of the surface of the tension-insulation coating from a saturation
point at which an Fe light emission intensity is a maximum, and
(c) a peak of the Si light emission intensity present closest to the base steel sheet
50
side has a light emission intensity that is 1.3 times or more and 2.0 times or less the Si
light emission intensity in the base steel sheet.
2. The grain-oriented electrical steel sheet according to claim 1,
5 wherein the silicon-containing oxide layer contains silica and fayalite as main
components, and
wherein the tension-insulation coating contains 25 to 45 mass% of colloidal
silica, with a remainder that contains one or more selected from the group consisting of
aluminum phosphate, magnesium phosphate, zinc phosphate, manganese phosphate,
10 cobalt phosphate, and iron phosphate as main components.
15
3. The grain-oriented electrical steel sheet according to claim 1 or 2,
wherein the iron-based oxide layer contains magnetite, hematite and fayalite as
main components.
4. The grain-oriented electrical steel sheet according to any one of claims 1 to 3,
wherein a thickness of the base steel sheet is 0.27 mm or less.
5. A method for manufacturing a grain-oriented electrical steel sheet which includes a
20 base steel sheet and a tension-insulation coating and does not have an inorganic coating
containing forsterite as a main component, comprising:
a washing process of cleaning a surface of the grain-oriented electrical steel
sheet;
a surface treatment process of treating the surface of the grain -oriented electrical
25 steel sheet which has been subjected to the washing process using a surface treatment
51
liquid which contains one or more of sulfuric acid, phosphoric acid and nitric acid and
having a total acid concentration of 2 to 20% and a liquid temperature of 70 to 90°C;
a heating treatment process of heating the grain-oriented electrical steel sheet
which has been subjected to the surface treatment process at a temperature of 700 to
5 900°C for 10 to 60 seconds in an atmosphere having an oxygen concentration of 1 to 21
volume% and a dew point of -20 to 30°C; and
a tension-insulation coating forming process of forming a tension-insulation
coating which has a thickness of 1 to 3 ~m by applying a treatment solution for forming
a tension-insulation coating containing phosphate and colloidal silica as main
10 components to the surface of the grain -oriented electrical steel sheet after the heating
treatment process, and heating is performed at an average heating rate of 20 to 100 °C/s
within 1.0 to 20 seconds after the application, and baking is performed at a temperature
of 850 to 950°C for 10 to 60 seconds.
15 6. The method for manufacturing a grain-oriented electrical steel sheet according to
claim 5, further comprising:
before the washing process,
a hot rolling process of subjecting a steel piece which contains, as chemical
components, in terms of mass%, 2.5 to 4.5% of Si, 0.05 to 1.00% of Mn, less than 0.05%
20 of Al, less than 0.1% of C, less than 0.05% of N, less than 0.1% of S, less than 0.05% of
25
Se and less than 0.01% of Bi with the remainder being Fe and impurities to hot rolling;
an optional annealing process;
a cold rolling process of performing one cold rolling or two or more cold
rollings having intermediate annealing performed between the cold rollings ;
a decarburization annealing process; and
52
a final annealing process of applying an annealing separator obtained by
incorporating bismuth chloride into a mixture of MgO and Ah03 or an annealing
separator obtained by incorporating a bismuth compound and a metallic chloride
compound into a mixture of MgO and Ah03, drying the annealing separator, and then
5 performing final annealing.