[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. 2019-5238, 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 applying 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.
2
[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
in terms of having a high magnetic field iron loss so that excellent 5 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” in some cases.
[0004]
Inorganic coatings containing forsterite (Mg2SiO4) as a main component are
generated on surfaces of grain-oriented electrical steel sheets by causing oxide layers
15 containing silica (SiO2) generated using a decarburization annealing process as a main
component and magnesium oxides applied to a surface to prevent firing to react 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
3
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
smoothing the surfaces of the steel sheets, for example, 5 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
4
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
general, a metal does not easily bond to oxides. Thus, when 5 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 tension10
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
SiO2 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 tension15
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 under20
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]
5
[Patent Document 1]
Japanese Unexamined Patent Application, First Publication No. S48-39338
[Patent Document 2]
Japanese Unexamined Patent Application, Second Publication No. S58-26405
5 [Patent Document 3]
Japanese Unexamined Patent Application, First Publication No. S49-96920
[Patent Document 4]
Japanese Unexamined Patent Application, First Publication No. H7-54155
[Patent Document 5]
10 Japanese Patent No. 4041289
[Patent Document 6]
Japanese Patent No. 4300604
[Summary of the Invention]
[Problems to be Solved by the Invention]
15 [0011]
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]
20 Therefore, the present invention was made in view of the above problems, and
an object of the present invention is to provide a grain-oriented electrical steel sheet and a
method for manufacturing the same in which the adhesion of a tension-insulation coating
is stably improved and excellent magnetic characteristics can be realized even when the
grain-oriented electrical steel sheet does not have an inorganic coating.
25 [Means for Solving the Problem]
6
[0013]
In order to achieve the above object, as a result of diligent research by the
inventors of the present invention, it was found that the adhesion of a tension-insulation
coating is stably improved and excellent magnetic characteristics can be realized by
subjecting a grain-oriented electrical steel sheet which does not have 5 an inorganic coating
to a pickling treatment using a specific acid and a heating treatment and then further
subjecting the grain-oriented electrical steel sheet to a pickling treatment to form an ironbased
oxide layer and a silicon-containing oxide layer in a specific state between the
tension-insulation coating and a base steel sheet.
10 The gist of the present invention completed on the basis of the above findings is
as follows.
[0014]
[1] A grain-oriented electrical steel sheet according to an aspect of the present
invention is a grain-oriented electrical steel sheet which does not have an inorganic
15 coating 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
20 thickness of 1 to 3 μm, and containing phosphate and colloidal silica as main
components,
wherein the base steel sheet contains, 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%
of C, 0% or more and less than 0.05% of N, 0% or more and less than 0.1% of S, 0% or
25 more and less than 0.05% of Se, 0% or more and less than 0.01% of Bi, and the
7
remainder: Fe and impurities as chemical components, and
when the tension-insulation coating undergoes elemental analysis using a glow
discharge optical emission spectrometry in a sheet thickness direction from a surface of
the tension-insulation coating,
(a) there 5 are two or more peaks of a Si emission intensity;
(b) a peak A which is a peak of the Si emission intensity existing furthest to the
base steel sheet side in the sheet thickness direction exists between an inflection point at
which a rate of increase in an Fe emission intensity in the sheet thickness direction from
the surface of the tension-insulation coating changes and a saturation point at which the
10 Fe emission intensity become saturated; and
(c) when a length of a perpendicular line when a perpendicular line is drawn
from the top portion of a peak to a baseline connecting valley portions closest to the peak
is defined as a peak height, a peak height of the peak A is 0.30 times or more and 2.5
times or less the Si emission intensity in the base steel sheet.
15 [2] In the grain-oriented electrical steel sheet according to [1], the siliconcontaining
oxide layer may contain silica and fayalite as main components, and
the tension-insulation coating may contain 25 to 45 mass% of colloidal silica
and the remainder may be one or more selected from the group consisting of aluminum
phosphate, magnesium phosphate, zinc phosphate, manganese phosphate, cobalt
20 phosphate, and iron phosphate.
[3] In the grain-oriented electrical steel sheet according to [1] or [2], the ironbased
oxide layer may contain magnetite, hematite, and fayalite as main components.
[4] In the grain-oriented electrical steel sheet according to any one of [1] to [3],
a thickness of the base steel sheet may be 0.27 mm or less.
25 [5] A method for manufacturing a grain-oriented electrical steel sheet according
8
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,
including:
a washing process of cleaning a surface 5 of the grain-oriented electrical steel
sheet;
a first surface treatment process of treating the surface of the grain-oriented
electrical steel sheet which has been subjected to the washing process using a first
treatment liquid which contains one or more of sulfuric acid, phosphoric acid, and nitric
10 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 first 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
15 21% by volume and a dew point of -20 to 30°C;
a second surface treatment process of treating the surface of the grain-oriented
electrical steel sheet which has been subjected to the heating treatment process for 1 to 10
seconds using a second treatment liquid which contains one or more of sulfuric acid,
phosphoric acid, and nitric acid and having a total acid concentration of 1 to 10%; and
20 a tension-insulation coating forming process of forming a tension-insulation
coating which has a thickness of 1 to 3 μm and contains phosphate and colloidal silica as
main components on the surface of the grain-oriented electrical steel sheet which has
been subjected to the second surface treatment process.
[6] In the method for manufacturing a grain-oriented electrical steel sheet
25 according to [5], the method for manufacturing a grain-oriented electrical steel sheet may
9
further include, before the washing process,
a hot rolling process of subjecting a steel piece which contains, in terms of
mass%, 2.5 to 4.5% of Si, 0.05 to 1.00% of Mn, 0.05% or less of Al, 0.1% or less of C,
0.05% or less of N, 0.1% or less of S, 0.05% or less of Se, 0.01% or less of Bi, and the
remainder: Fe and im 5 purities as chemical components 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
10 a final annealing process of applying an annealing separator obtained by
incorporating bismuth chloride into a mixture of MgO and Al2O3 or an annealing
separator obtained by incorporating a bismuth compound and a metallic chlorine
compound into a mixture of MgO and Al2O3, drying the annealing separator, and then
performing final annealing.
15 [Effects of the Invention]
[0015]
As described above, according to the present invention, it is possible to stably
improve the adhesion of a tension-insulation coating and realize excellent magnetic
characteristics even when a grain-oriented electrical steel sheet does not have an
20 inorganic coating.
[Brief Description of Drawings]
[0016]
Fig. 1 is a schematic explanatory diagram of an example of a structure of a
grain-oriented electrical steel sheet according to an embodiment of the present invention.
25 Fig. 2 is an explanatory diagram for explaining the grain-oriented electrical steel
10
sheet according to the embodiment.
Fig. 3A is a graph diagram illustrating an example of an analysis result using a
glow discharge optical emission spectrometry of the grain-oriented electrical steel sheet
according to the embodiment.
Fig. 3B is a graph diagram illustrating an example 5 of an analysis result using a
glow discharge optical emission spectrometry of the grain-oriented electrical steel sheet
having a poor adhesion of a tension-insulation coating.
Fig. 4 is a flowchart for describing an example of a flow of a method for
manufacturing a grain-oriented electrical steel sheet according to the embodiment.
10 [Embodiments for implementing the Invention]
[0017]
Preferred embodiments of the present invention will be described in detail below
with reference to the accompanying drawings. In this specification and the drawings,
constituent elements having substantially the same functional constitution will be
15 denoted by the same reference numerals and duplicate description thereof will be
omitted.
[0018]
(Regarding grain-oriented electrical steel sheet)
First, a grain-oriented electrical steel sheet according to an embodiment of the
20 present will be described in detail with reference to Figs. 1 and 2. Fig. 1 is a schematic
explanatory diagram of an example of a structure of the grain-oriented electrical steel
sheet according to this embodiment. Fig. 2 is an explanatory diagram for explaining the
grain-oriented electrical steel sheet according to this embodiment.
[0019]
25 The inventors of the present invention have found that (1) for example, for a
11
high magnetic field iron loss such as 1.7 T to 1.9 T, iron loss is significantly reduced
when an inorganic coating such as forsterite (Mg2SiO4) is removed, and that (2), in order
to form a tension-insulation coating in which a high tension of 1.0 kgf/mm2 or more is
exhibited and which has a good adhesion on a surface of a steel sheet which does not
have an inorganic coating, forming of a silicon-containing oxide 5 layer and an iron-based
oxide layer in order on the surface of the steel sheet is required and a good adhesion and
high magnetic field iron loss of the tension-insulation coating is provided by forming
such a silicon-containing oxide layer and an iron-based oxide layer. Based on the above
findings, the inventors of the present invention have come up with the grain-oriented
10 electrical steel sheet according to this embodiment.
[0020]
A grain-oriented electrical steel sheet 1 according to this embodiment is a grainoriented
electrical steel sheet which does not have an inorganic coating containing
forsterite as a main component, and as schematically illustrated in Fig. 1, includes:
15 a base steel sheet 11;
a silicon-containing oxide layer 17 which is provided on the base steel sheet;
an iron-based oxide layer 15 which is provided on the silicon-containing oxide
layer; and
a tension-insulation coating 13 which is provided on the iron-based oxide layer,
20 has a thickness of 1 to 3 μm, and contains phosphate and colloidal silica as main
components.
As schematically illustrated 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. Although Fig. 1 illustrates a case in which the
25 silicon-containing oxide layer 17, the iron-based oxide layer 15, and the tension12
insulation coating 13 are provided on both surfaces of the base steel sheet 11, the siliconcontaining
oxide layer 17, the iron-based oxide layer 15, and the tension-insulation
coating 13 may be provided only on one surface of the base steel sheet 11 in some cases.
[0021]
The base steel sheet 11, the tension-insulation coating 5 13 (hereinafter, may be
simply abbreviated as an “insulation coating” in some cases), the iron-based oxide layer
15, and the silicon-containing oxide layer 17 included in the grain-oriented electrical
steel sheet 1 according to this embodiment will be described in detail below.
[0022]
10
Generally, although a grain-oriented electrical steel sheet contains silicon (Si) as
a chemical component, silicon is extremely easily oxidized. Thus, a silicon-containing
oxide coating (more specifically, an oxide coating containing silica as a main component)
is formed on a surface of a steel sheet which has been subjected to decarburization
15 annealing. After an annealing separator is applied to the surface of the steel sheet which
has been subjected to decarburization annealing, the steel sheet is wound to have a coil
shape and subjected to final annealing. In an ordinary method for manufacturing a
grain-oriented electrical steel sheet, an inorganic coating containing forsterite (Mg2SiO4)
as a main component is formed by causing MgO and an oxide coating of the surface of
20 the steel sheet to react with each other during final annealing using an annealing
separator containing MgO as a main component. However, the grain-oriented electrical
steel sheet 1 according to this embodiment is not a grain-oriented electrical steel sheet
which has an inorganic coating containing forsterite as a main component as described
above formed on a surface thereof and a grain-oriented electrical steel sheet which does
25 not have an inorganic coating containing forsterite as a main component formed on a
13
surface thereof is used as the base steel sheet 11.
[0023]
A method for manufacturing a grain-oriented electrical steel sheet which does
not have an inorganic coating containing forsterite as a main component on a surface will
5 be described again below.
[0024]
In the grain-oriented electrical steel sheet 1 according to this embodiment, the
grain-oriented electrical steel sheet used as the base steel sheet 11 is not particularly
limited and a grain-oriented electrical steel sheet containing known chemical components
10 can be utilized. Examples of such a grain-oriented electrical steel sheet include a grainoriented
electrical steel sheet containing, 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% of
C, 0% or more less than 0.05% of N, 0% or more and less than 0.1% of S, 0% or more
and less than 0.05% of Se, 0% or more and less than 0.01% of Bi, and the remainder: Fe
15 and impurities as chemical components.
[0025]
When the Si content in the base steel sheet is 2.5 mass% or more, it is possible
to obtain desired magnetic characteristics. On the other hand, when the Si content in the
base steel sheet is more than 4.5 mass%, a brittle steel sheet is provided, which makes
20 manufacturing difficult. For this reason, 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
possible to secure an absolute amount of MnS which is an inhibitor required for causing
25 secondary recrystallization. On the other hand, when the Mn content in the base steel
14
sheet is more than 1.00 mass%, in secondary recrystallization annealing, steel undergoes
phase transformation, sufficient secondary recrystallization does not proceed, and good
magnetic flux density and iron loss characteristics may not be able to be obtained. For
this reason, the Mn content in the base steel sheet is 1.00 mass% or less.
5 [0027]
In addition to Si and Mn, the base steel sheet may contain less than 0.05 mass%
of Al, less than 0.1 mass% of C, less than 0.05 mass% of N, less than 0.1 mass% of S,
less than 0.05 mass% of Se, and less than 0.01 mass% of Bi as chemical components.
Since these elements do not need to be contained, a lower limit is 0 mass%.
10 When the Al content in the base steel sheet is more than 0 mass% and less than
0.05 mass%, it is possible to improve the iron loss characteristics while minimizing the
embrittlement of the steel sheet.
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 good magnetic flux density and iron loss
15 characteristics.
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 a decrease in passability at the time of
manufacturing.
When the S content in the base steel sheet is more than 0 mass% and less than
20 0.1 mass%, it is possible to minimize the embrittlement of the steel sheet.
When the Se content in the base steel sheet is 0 mass% or more and less than
0.05 mass%, it is possible to realize the magnetic improvement effect.
When the Bi content in the base steel sheet is 0 mass% or more and less than
0.01 mass%, it is possible to realize good magnetic flux density and iron loss
25 characteristics.
15
[0028]
A microstructure 21 as schematically illustrated in Fig. 2 which is also called an
etch pit is provided on a surface of the base steel sheet 11 according to this embodiment.
In the method for manufacturing a grain-oriented electrical steel sheet according to this
embodiment which will be describe later, the microstructure 5 21 is formed by causing a
first treatment liquid containing a specific acid to act on the surface of the grain-oriented
electrical steel sheet which does not have an inorganic coating and has been subjected to
final annealing to react. When the microstructure 21 as schematically illustrated in Fig.
2 is provided on the surface of the base steel sheet 11, the adhesion between the silicon10
containing oxide layer 17 and the iron-based oxide layer 15 formed on the surface of the
base steel sheet 11 and the base steel sheet 11 are further improved due to a so-called
anchor effect.
[0029]

15 The tension-insulation coating 13 is provided on the surface of the grainoriented
electrical steel sheet 1 according to this embodiment. The tension-insulation
coating 13 reduces the eddy current loss by imparting electrical insulating properties to
the grain-oriented electrical steel sheet and reduces the iron loss of the grain-oriented
electrical steel sheet. Furthermore, the tension-insulation coating 13 exhibits various
20 characteristics such as corrosion resistance, heat resistance, and slipperiness in addition
to the above-described electrical insulating properties.
[0030]
Also, the tension-insulation coating 13 has a function of applying tension to the
grain-oriented electrical steel sheet. The tension-insulation coating 13 can reduce the
25 iron loss of the grain-oriented electrical steel sheet by applying tension to the grain16
oriented electrical steel sheet to facilitate a domain wall motion in the 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 si 5 lica as a main component. It
is desirable that such a tension-insulation coating of the phosphate silica mixed system
contain, for example, 25 to 45 mass% of colloidal silica and the remainder be mainly
composed of one or more selected from the group consisting of aluminum phosphate,
magnesium phosphate, zinc phosphate, manganese phosphate, cobalt phosphate, and iron
10 phosphate.
[0032]
A thickness (a thickness d1 in Fig. 1) of the tension-insulation coating 13 of the
phosphate silica mixed system is within the range of 1 to 3 μm. When the thickness of
the tension-insulation coating 13 is less than 1 μm, it is not possible to sufficiently
15 improve various characteristics such as electrical insulating properties, corrosion
resistance, heat resistance, slipperiness, and tension-application properties as described
above. On the other hand, when the thickness of the tension-insulation coating 13 is
more than 3 μm, a space factor of the base steel sheet 11 decreases, which is not
preferable. When the thickness of the tension-insulation coating 13 is within the range
20 of 1 to 3 μm, it is possible to realize a high tension of 1.0 kgf/mm2 or more. The
thickness d1 of the tension-insulation coating 13 is preferably within the range of 2.5 to
3.0 μm.
[0033]

25 In the grain-oriented electrical steel sheet 1 according to this embodiment, the
17
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 silicon-containing oxide layer
17 which will be described later. The iron-based oxide layer 15 contains, for example,
an iron-based oxide such as magnetite (Fe3O4), hematite (Fe2O3), and fayalite (Fe2SiO4)
5 as a main component.
[0034]
Since the iron-based oxide which is a main component of the iron-based oxide
layer 15 is formed through the surface of the base steel sheet 11 and oxygen reacting each
other, a good adhesion between the iron-based oxide layer 15 and the base steel sheet 11
10 is provided. Furthermore, as described above, the microstructure 21 also called an etch
pit schematically illustrated in Fig. 2 is provided on the surface of the base steel sheet 11.
For this reason, the iron-based oxide layer 15 formed in the microstructure 21 can further
improve the adhesion between the iron-based oxide layer 15 and the base steel sheet 11
due to a so-called anchor effect together with the silicon-containing oxide layer 17 which
15 will be described later.
[0035]
Generally, improving the adhesion between a metal and ceramics may not be
easy in many cases. On the other hand, when 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
20 ceramics in the grain-oriented electrical steel sheet 1 according to this embodiment, even
though the inorganic coating is not formed on the surface of the base steel sheet 11, it is
possible to improve the adhesion of the tension-insulation coating 13.
[0036]
Also, in the method for manufacturing a grain-oriented electrical steel sheet
25 according to this embodiment, the surface of the iron-based oxide layer 15 has the
18
microstructure as illustrated in Fig. 2 formed through a pickling treatment using a second
treatment liquid. For this reason, it is possible to further improve the adhesion between
the iron-based oxide layer 15 and the tension-insulation coating 13.
[0037]
In the grain-oriented electrical steel sheet 1 5 according to this embodiment, a
thickness (a thickness d2 in Fig. 1) of the iron-based oxide layer 15 is preferably within
the 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 silicon-containing oxide layer 17
will be dissolved due to an acidic treatment liquid used when the tension-insulation
10 coating 13 is formed, which is not likely to obtain a sufficient adhesion. On the other
hand, when the thickness d2 of the iron-based oxide layer 15 is more than 500 nm, the
iron-based oxide layer 15 is too thick, which is highly likely to increase partial peeling.
In the grain-oriented electrical steel sheet 1 according to this embodiment, the thickness
d2 of the iron-based oxide layer 15 is preferably within the range of 150 to 400 nm, and
15 more preferably within the range of 170 to 250 nm.
[0038]
The thickness d2 of the iron-based oxide layer 15 can be specifically identified,
for example, by observing a distribution of iron-oxygen bonds with respect to a cross
section of the grain-oriented electrical steel sheet 1 according to this embodiment using
20 an X-ray photoelectron spectroscopy (XPS). That is to say, sputtering is performed
from the surface of the grain-oriented electrical steel sheet 1 from which the tensioninsulation
coating 13 has been removed toward the base steel sheet 11 side while paying
attention to an intensity of Fe-O peaks appearing at 712 eV and an intensity of metal Fe
peaks appearing at 708 eV using an XPS and a distance from the outermost layer in
25 which the measurement starts to a position in a depth direction in which the intensity of
19
Fe-O peaks appearing at 712 eV and the intensity of metal Fe peaks appearing at 708 eV
are interchanged can be defined as the thickness of the iron-based oxide layer 15.
[0039]
A main component of the iron-based oxide layer 15 can be specifically identified
by performing analysis using an X-ray crystal structure 5 analysis method or an XPS. It
has been found from the measurement results so far by the inventors of the present
invention that the iron-based oxide layer 15 mainly contains an iron oxide as a main
component and contains a small amount of silica.
[0040]
10
In the grain-oriented electrical steel sheet 1 according to this embodiment, the
silicon-containing oxide layer 17 is a layer configured to function as an intermediate
layer between the base steel sheet 11 and the tension-insulation coating 13 together with
the iron-based oxide layer 15 described above. The silicon-containing oxide layer 17
15 contains silica and fayalite (Fe2SiO4) as main components.
[0041]
As will be described in detail later, the microstructure 21 also called an etch pit
as illustrated in Fig. 2 is formed on the surface of the base steel sheet 11 by treating the
surface of the grain-oriented electrical steel sheet which does not have an inorganic
20 coating using a treatment liquid containing at least one of sulfuric acid, nitric acid, and
phosphoric acid so that the adhesion of the tension-insulation coating 13 is secured.
Here, the inventors of the present invention have found that, when the adhesion of the
tension-insulation coating in the grain-oriented electrical steel sheet in which the
microstructure has been formed on the surface of the base steel sheet has been subjected
25 to further detailed verification, there are parts with good adhesion and parts with poor
20
adhesion under the certain manufacturing conditions.
[0042]
As a result of verifying the above phenomenon, it has been found that, in the
parts with good adhesion, a silicon-containing oxide layer mainly composed of silica
derived from Si which has diffused from the base steel sheet 5 and fayalite (Fe2SiO4) is
formed on an underlayer side (the base steel sheet side) of the iron-based oxide layer, and
in the parts with poor adhesion, there is no iron-based oxide layer or silicon-containing
oxide layer. The fact that small amounts of the iron-based oxide layer and the siliconcontaining
oxide layer to exist are provided (in other words, thin thicknesses are
10 provided) is conceivable as one of the reasons why the iron-based oxide layer and the
silicon-containing oxide layer do not exist. It is presumed that, since an acidic
treatment liquid is utilized for forming a tension-insulation coating, the effect of adhesion
improvement is reduced by dissolving the thin iron-based oxide layer and siliconcontaining
oxide layer at the time of forming the tension-insulation coating.
15 Furthermore, the fact that an excessive amount of iron-based oxide layer is likely to be
generated is conceivable as another possible reason. It is presumed that, when an
excessive amount of iron-based oxide layer is generated, an iron oxide (smudge) isolated
from a surface is generated, and thus the treatment liquid used for forming the tensioninsulation
coating does not adhere to the surface of the steel sheet.
20 [0043]
It is clear from the above findings that forming the iron-based oxide layer and
the silicon-containing oxide layer in an appropriate state is important to realize good
adhesion of the tension-insulation coating.
[0044]
25 It is clear based on the above findings that, when the grain-oriented electrical
21
steel sheet with good adhesion is analyzed using a glow discharge optical emission
spectrometry (a glow discharge spectrometry: GDS), characteristic peaks are observed in
the obtained GDS chart.
[0045]
Fig. 3A illustrates an example of the 5 analysis result using a GDS of the grainoriented
electrical steel sheet with good adhesion and Fig. 3B illustrates an example of
the analysis result using a GDS of the grain-oriented electrical steel sheet with poor
adhesion. For each grain-oriented electrical steel sheet, a tension-insulation coating is
formed using a treatment liquid containing colloidal silica and aluminum phosphate. In
10 Figs. 3A and 3B, the horizontal axis indicates an elapsed time [second] from the start of
analysis and the vertical axis indicates a GDS relative intensity [a.u.]. Since a GDS is a
method for analyzing a surface of a sample toward a deeper part in a thickness direction
while performing sputtering, when an elapsed time increases, it means that a deeper part
of a sample is analyzed. Furthermore, in Figs. 3A and 3B, for elements other than Fe,
15 the three-times-enlarged obtained results are illustrated in the drawings.
[0046]
Referring to Figs. 3A and 3B, light emission peaks derived from Al and light
emission peaks derived from Si are acknowledged in a region in which an elapsed time is
about 0 seconds to 40 seconds. Furthermore, it seems that a GDS relative intensity
20 derived from P also slightly increases in the vicinity of 5 seconds and then gradually
decays, and there are gentle and broadly distributed light emission peaks derived from P.
Since theses peaks contain Al, Si, and P, they are derived from the tension-insulation
coating 13. In addition, since the light emission peaks derived from Fe increase when
an elapsed time increases, it can be seen that the iron-based oxide layer is formed.
25 [0047]
22
When attention is paid to the GDS analysis result of the grain-oriented electrical
steel sheet with good adhesion illustrated in Fig. 3A, it can be seen that the light emission
peaks derived from Al and the light emission peaks derived from P decrease
monotonically, whereas a second light emission peak derived from Si (hereinafter, may
be referred to as a “peak A”) is obse 5 rved in the region A surrounded by the broken line in
Fig. 3A. The second light emission peak (the peak A) exists between an inflection point
at which a rate of increase in light emission peak intensity derived from Fe changes (in
the case of Fig. 3A, a point in which an elapsed time is about 40 seconds) and a point at
which the light emission peak intensity derived from Fe saturates (in the case of Fig. 3A,
10 a position in which an elapsed time is about 70 seconds; hereinafter may be referred to as
a “saturation point”). Although a second light emission peak (a peak A) derived from Si
has a different elapsed time at which peaks are observed, the second light emission peak
(a peak A) derived from Si is observed in all of the grain-oriented electrical steel sheets
with good adhesion. Therefore, it can be seen that the second light emission peak (the
15 peak A) is derived from the silicon-containing oxide layer containing silica and fayalite
(Fe2SiO4) as main components.
[0048]
Also, as illustrated in the enlarged part of Fig. 3A, when a line segment
connecting valley portions close to a second Si-derived peak (a peak A) is defined as a
20 baseline, a length of a perpendicular line drawn from a peak top portion of the second Siderived
peak (the peak A) to the baseline is defined as a peak height of the peak A. It is
clarified that the peak height of the peak A is 0.30 times or more and 2.5 times or less of
a Si emission intensity in the steel (that is, a light emission intensity of a portion in which
the sputtering proceeds to a portion of the base steel sheet and an intensity of the light
25 emission peaks derived from Si becomes a steady state) in all of the grain-oriented
23
electrical steel sheets with good adhesion. On the other hand, it is clarified that, when
the peak height of the peak A is less than 0.30 times or more than 2,5 times the Si
emission intensity in the base steel sheet, the tension-insulation coating has inferior
adhesion.
5 [0049]
As described above, it is clarified that good adhesion is provided when a portion
in which a Si element is segregated at a certain depth position of the grain-oriented
electrical steel sheet is the silicon-containing oxide layer 17 in this embodiment and a Si
element in a portion corresponding to the silicon-containing oxide layer 17 (the region A
10 in Fig. 3A) has a specific concentration (0.30 times or less of the Si emission intensity in
the steel). Since the segregated portion of the Si element is derived from the inside of
Si diffusing from the base steel sheet, the segregated portion of the Si element exists at a
position close to the base steel sheet.
[0050]
15 On the other hand, it can be seen that, although the second peaks derived from Si
as described above is slightly observed in the GDS analysis result of the grain-oriented
electrical steel sheet with poor adhesion illustrated in Fig. 3B, the height of such peaks
are not 0.30 times or more and 2.5 times or less the Si emission intensity in the steel. It
is also clarified that, when the other grain-oriented electrical steel sheets with poor
20 adhesion are analyzed using a GDS, the second peaks derived from Si may not be
observed.
[0051]
Since a GDS is a method for performing analyzing while sputtering a region
having a diameter of about 5 mm, it can be conceivable that, in the GDS analysis result
25 as illustrated in Fig. 3A, an average behavior of each element in a region having a
24
diameter of about 5 mm of a sample is observed. Therefore, in a coil in which the
grain-oriented electrical steel sheet is wound, when the GDS analysis result of an
optional region at a position away from a head portion of the coil by an optional distance
shows the behavior as illustrated in Fig. 3A, a portion of the coil having the same
distance from the head portion thereof is c 5 onsidered to show the same GDS analysis
result that is shown in Fig. 3A. Furthermore, if the GDS analysis result shows the
behavior as shown in Fig. 3A at both the head portion and a tail portion of the coil, it can
be conceivable that the GDS analysis result shows the behavior as illustrated in Fig. 3A
in the entire coil.
10 [0052]
As described above, in the grain-oriented electrical steel sheet 1 according to
this embodiment, when the grain-oriented electrical steel sheet 1 undergoes elemental
analysis using a glow discharge optical emission spectrometry (GDS) in a sheet thickness
direction from the surface of the grain-oriented electrical steel sheet 1, there is the
15 silicon-containing oxide layer 17 in which all of the following conditions (a) to (c) are
satisfied.
[0053]
(a) There are two or more peaks of a Si emission intensity.
(b) A peak A which is a peak of the Si emission intensity existing furthest to the
20 base steel sheet side in the sheet thickness direction exists between an inflection point at
which a rate of increase in Fe emission intensity in the sheet thickness direction from the
surface of the tension-insulation coating changes and a saturation point at which the Fe
emission intensity saturates.
(c) When a length of a perpendicular line when the perpendicular line is drawn
25 from the top portion of a peak to a baseline connecting valley portions close to the peak
25
is defined as a peak height, a peak height of a peak A is 0.30 times or more and 2.5 times
or less a Si emission intensity in the base steel sheet.
[0054]
The reason why the number of peaks of the Si emission intensity is two or more
in the above condition (1) is as follows. When 5 the grain-oriented electrical steel sheet is
analyzed using a GDS, shoulders (overlapping of peaks) may occur in the Si light
emission peak derived from the tension-insulation coating in accordance with a state of
the tension-insulation coating, and in Fig. 3A, there may be a case in which light
emission peaks which are viewed as one peak appear as two or more peaks.
10 Furthermore, in the grain-oriented electrical steel sheet, in order to apply stronger
tension, a tension-insulation coating may be formed multiple times while changing a Si
concentration of a treatment liquid in some cases. In this case, a plurality of light
emission peaks derived from the tension-insulation coating are observed at a left end
portion of the GDS analysis result as illustrated in Fig. 3A (a short elapsed time=a
15 surface layer side of the grain-oriented electrical steel sheet). However, even when the
number of peaks of the Si emission intensity is 3 or more, the segregated portion of Si to
which attention is to be paid is derived from Si diffusing from the inside of the base steel
sheet. Thus, attention may be paid to a peak (the peak A) which exists furthest to the
base steel sheet side among the plurality of observed peaks.
20 [0055]
The silicon-containing oxide layer 17 is formed when the surface of the base
steel sheet 11 is subjected to a pickling treatment used for forming the microstructure 21
using the first treatment liquid and then a heating treatment is performed at a
predetermined temperature.
25 [0056]
26
The conditions when a depth direction analysis using a GDS is performed from
the surface of the grain-oriented electrical steel sheet are as follows. When the depth
direction analysis using a GDS is performed under the following conditions, it is possible
to obtain the GDS analysis result as illustrated in Fig. 3A in the grain-oriented electrical
steel sheet with good adhesion. That is to say, in a 5 high frequency mode of a general
glow discharge optical emission spectroscopic analyzer (for example, GDA 750
manufactured by Rigaku Co., Ltd.), when measurement is performed under the
conditions such as an output: 30 W; an Ar pressure: 3 hPa; a measurement area: 4 mmφ;
and a measurement time: 100 seconds, it is possible to obtain the GDS analysis result as
10 illustrated in Fig. 3A.
[0057]
A thickness of the silicon-containing oxide layer 17 (a thickness d3 in Fig. 1)
may be 100 nm or less and may be often about 20 to 30 nm in some cases. The
thickness of the silicon-containing oxide layer 17 can be calculated from a sputtering rate
15 in a GDS and an elapsed time width in which the second peak derived from Si is
observed as illustrated in the region A of Fig. 3A.
[0058]
A main component of the silicon-containing oxide layer 17 can be specifically
identified through analysis using an X-ray crystal structure analysis method or an XPS.
20 [0059]

In the grain-oriented electrical steel sheet 1 according to this embodiment, a
thickness of the base steel sheet 11 (the thickness d in Fig. 1) is not particularly limited
and may be, for example, 0.27 mm or less. Generally, in the grain-oriented electrical
25 steel sheet, when a thin thickness of the steel sheet is provided, poor adhesion of the
27
tension-insulation coating may be provided in many cases. However, in the grainoriented
electrical steel sheet 1 according to this embodiment, when the iron-based oxide
layer 15 and the silicon-containing oxide layer 17 are provided, even when the thickness
d is 0.27 mm or less, it is possible to obtain good adhesion of the tension-insulation
5 coating 13.
[0060]
In this embodiment, even when the thickness d of the base steel sheet 11 is as
thin as 0.23 mm or less, the tension-insulation coating 13 can obtain good adhesion. In
the grain-oriented electrical steel sheet 1 according to this embodiment, the thickness d of
10 the base steel sheet 11 is more preferably within the range of 0.17 to 0.23 mm. The
thickness d of the base steel sheet 11 in the grain-oriented electrical steel sheet 1
according to this embodiment is not limited to the above-described range.
[0061]
The grain-oriented electrical steel sheet according to this embodiment does not
15 have an inorganic coating containing forsterite as a main component. The fact that “an
inorganic coating containing forsterite as a main component is not formed” is determined
using an analysis which will be illustrated later.
[0062]
In order to specifically identify each layer in a cross-sectional structure, line
20 analysis is performed in the sheet thickness direction and quantitative analysis of
chemical components of each layer is performed using an energy dispersive X-ray
spectroscopy (EDS) attached to a scanning electron microscope (SEM) or a transmission
electron microscope (TEM). The elements to be subjected to quantitative analysis are 6
elements such as Fe,P, Si, O, Mg, and Al.
25 [0063]
28
It is determined that a layered region existing at the deepest position in the sheet
thickness direction which is a region in which measurement noise is removed, the Fe
content is 80 atom% or more, and the O content is less than 30 atom% is a base steel
sheet.
5 [0064]
With regard to the region excluding the base steel sheet which has been
specifically identified described above, it is determined that a region in which
measurement noise is removed, the Fe content is less than 80 atom%, the P content is 5
atom% or more, and the O content is 30 atom% or more is a tension-insulation coating.
10 [0065]
It is determined that the region excluding the base steel sheet and the tensioninsulation
coating which has been specifically identified described above is an
intermediate layer composed of the silicon-containing oxide layer and the iron-based
oxide layer. An intermediate layer may be adopted as long as, in the intermediate layer,
15 the average Fe content is less than 80 atom%, the average P content is less than 5 atom%,
the average Si content is 20 atom% or more, and the average O content is 30 atom% or
more as an overall average. Furthermore, since the intermediate layer is not a forsterite
coating in this embodiment, in the intermediate layer, the average Mg content may be
satisfied to be less 20 atom%. The Mg content of the intermediate layer is preferably 10
20 atom% or less, more preferably 5 atom% or less, and still more preferably 3 atom% or
less.
[0066]
As described above, in the grain-oriented electrical steel sheet according to this
embodiment, it is possible to further improve the adhesion of the tension-insulation
25 coating 13 by providing the iron-based oxide layer 15 and the silicon-containing oxide
29
layer 17 between the base steel sheet 11 and the tension-insulation coating 13 and, for
example, it is possible to significantly reduce high magnetic field iron loss such as 1.7T
to 1.9T.
[0067]
Various magnetic characteristics 5 such as magnetic flux density and iron loss of
the grain-oriented electrical steel sheet according to this embodiment can be measured in
accordance with an Epstein method stipulated in JIS C2550 or a single sheet magnetic
characteristic measurement method (a single sheet tester: SST) stipulated in JIS C2556.
[0068]
10 The grain-oriented electrical steel sheet according to this embodiment has been
described in detail above.
[0069]
(Regarding method for manufacturing grain-oriented electrical steel sheet)
Subsequently, a method for manufacturing a grain-oriented electrical steel sheet
15 according to this embodiment will be described in detail with reference to Fig. 4. Fig. 4
is a flowchart for describing an example of a flow of the method for manufacturing a
grain-oriented electrical steel sheet according to this embodiment.
[0070]
In the method for manufacturing a grain-oriented electrical steel sheet according
20 to this embodiment, as described above, a grain-oriented electrical steel sheet which
contains forsterite as a main component and does not have an inorganic coating on a
surface thereof (more specifically, a grain-oriented electrical steel sheet which has been
subjected to final annealing and which contains forsterite as a main component and does
not have an inorganic coating on a surface thereof) is used as the base steel sheet 11.
25 [0071]
30
A method for obtaining a grain-oriented electrical steel sheet which does not
have an inorganic coating is not particularly limited. For example, a method including:
a hot rolling process of subjecting a steel piece containing, in terms of mass%, 2.5 to
4.5% of Si, 0.05 to 1.00% of Mn, 0.05% or less of Al, 0.1% or less of C, 0.05% or less of
N, 0.1% or less of S, 0.05% or less of S 5 e, 0.01% or less of Bi, and the remainder: Fe and
impurities as chemical components to hot rolling; an arbitrarily annealing process; a cold
rolling process of performing one cold rolling or two or more cold rolling having an
intermediate annealing performed between the two or more cold rolling; a
decarburization annealing process; and a final annealing process is exemplified.
10 Here, in order not to form an inorganic coating, for example, a method for
applying an annealing separator which does not form an inorganic coating and
performing final annealing, a method for performing final annealing using a commonly
utilized annealing separator and then performing removing the generated inorganic
coating using a known method such as grinding or pickling, and the like are exemplified.
15 [0072]
Among the above methods, the method for performing final annealing using an
annealing separator which does not form an inorganic coating is preferable because
controlling is easier and a good surface of the steel sheet is also provided. As such an
annealing separator, for example, it is desirable to utilize an annealing separator in which
20 bismuth chloride is provided in a mixture of MgO and Al2O3 or an annealing separator in
which a bismuth compound and a metallic chlorine compound are provided in a mixture
of MgO and Al2O3.
[0073]
Examples of the above-described bismuth chloride include bismuth oxychloride
25 (BiOCl), bismuth trichloride (BiCl3), and the like. Examples of the above-described
31
bismuth compound include bismuth oxides, bismuth hydroxides, bismuth sulfides,
bismuth sulfates, bismuth phosphates, bismuth carbonates, bismuth nitrates, organic acid
bismuth, bismuth halide, and the like. In addition, examples of the metallic chlorine
compound include iron chloride, cobalt chloride, nickel chloride, and the like.
The amount 5 of bismuth chloride or a chlorinated product of a bismuth
compound and a metal is not particularly limited, but is preferably about 3 to 15 parts by
mass with respect to 100 parts by mass of a mixture of MgO and Al2O3.
[0074]
Usually, when a grain-oriented electrical steel sheet is manufactured, after final
10 annealing, an excessive annealing separator which has been attached is removed through
cleaning and then flattening and annealing is performed.
On the other hand, as illustrated in Fig.4, the method for manufacturing a grainoriented
electrical steel sheet according to this embodiment includes: removing an
excessive annealing separator through cleaning using a grain-oriented electrical steel
15 sheet which has been subjected to final annealing and does not have an inorganic coating
(Step S101; a washing process); then performing a surface treatment by causing the
surface of the steel sheet and a specific concentration of acid (a first treatment liquid) to
react (Step S103; a first surface treatment process); performing a heating treatment at a
specific temperature in an oxidizing atmosphere (Step S105; a heating treatment
20 process); and performing a surface treatment by causing the surface of the steel sheet
which has been subjected to a heating treatment and a specific concentration of acid (a
second treatment liquid) to react (Step S107; a second surface treatment process). Thus,
an intermediate layer mainly composed of the iron-based oxide layer and the siliconcontaining
oxide layer as described above is formed on the surface of the grain-oriented
25 electrical steel sheet which has been subjected to final annealing and does not have an
32
inorganic coating. After that, a tension-insulation coating is formed with good adhesion
to the grain-oriented electrical steel sheet having the iron-based oxide layer and the
silicon-containing oxide layer formed thereon (Step S109; a tension-insulation coating
forming process).
5 [0075]

A first treatment liquid used in the first surface treatment process of Process
S103 contains one 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℃. When
10 the surface of the steel sheet is etched using the first treatment liquid, etch pits are formed
in the surface of the steel sheet and it is possible to generate an active surface state which
cannot normally be obtained. The microstructure 21 illustrated in Fig. 2 schematically
represents the etch pits formed in the surface of the steel sheet.
[0076]
15 When a liquid temperature of the first treatment liquid is lower than 70℃, the
solubility of the first treatment liquid decreases, a precipitate is highly likely to be
generated, and an effective etch pit cannot be obtained. On the other hand, when the
liquid temperature of the first treatment liquid exceeds 90℃, the reactivity of the first
treatment liquid is too high, which is not desirable because the surface of the steel sheet
20 is excessively etched during the first surface treatment process.
The liquid temperature of the first treatment liquid is preferably within the range
of 75 to 87℃, and more preferably within the range of 80 to 85℃.
[0077]
When a total acid concentration of the first treatment liquid is less than 2
25 mass%, etch pits cannot be appropriately formed in the surface of the steel sheet and a
33
treatment time is long, which is industrially disadvantageous. When the total acid
concentration of the first treatment liquid exceeds 20 mass%, the surface of the steel
sheet is excessively etched during the first surface treatment process, which is not
preferable.
The total acid concentration 5 of the first treatment liquid is preferably within the
range of 2 to 17 mass%, and more preferably within the range of 2 to 10 mass%.
[0078]
The treatment time of the first surface treatment process is not particularly
limited. The first surface treatment process may be carried out by continuously
10 immersing the steel sheet in a treatment bath having the first treatment liquid held therein
in many cases. When this method is adopted, a time at which the steel sheet passes
through the treatment bath is a treatment time for the first surface treatment process.
When the steel sheet is immersed in and caused to pass through the treatment bath at a
general sheet-passing rate, it is possible to realize the above-described active surface
15 state.
[0079]

In order to form the iron-based oxide layer and the silicon-containing oxide
layer on the grain-oriented electrical steel sheet which has undergone the first surface
20 treatment process, in an atmosphere in which an oxygen concentration is 1 to 21% by
volume and a dew point is −20 to 30℃, heating is performed for 10 to 60 seconds so that
a temperature of the steel sheet reaches 700 to 900℃ (the heating treatment process).
[0080]
When the oxygen concentration in the atmosphere is less than 1% by volume, it
25 takes too much time for the iron-based oxide layer to be formed, which deteriorates the
34
productivity. On the other hand, when the oxygen concentration in the atmosphere
exceeds 21% by volume, the iron-based oxide layer to be formed is easily non-uniform,
which is not desirable. The oxygen concentration in the atmosphere is preferably within
the range of 2 to 21% by volume, and more preferably within the range of 15 to 21% by
5 volume.
[0081]
When the dew point in the atmosphere is less than −20℃, it takes too much time
for the iron-based oxide layer to be formed, which the productivity deteriorates. On the
other hand, when the dew point in the atmosphere exceeds 30℃, the iron-based oxide
10 layer to be formed is easily non-uniform, which is not desirable. The dew point in the
atmosphere is preferably within the range of −10 to 25℃, and more preferably within the
range of −10 to 20℃.
[0082]
When a heating temperature of the steel sheet in the heating treatment process is
15 less than 700℃, even if a heating time is 60 seconds, it is difficult to form the iron-based
oxide layer and the silicon-containing oxide layer in an appropriate state, which is not
preferable. On the other hand, when the heating temperature of the steel sheet exceeds
900℃, the iron-based oxide layer is easily non-uniform and the silicon-containing oxide
layer in a desired state cannot be formed, which is not preferable. The heating
20 temperature of the steel sheet in the heating treatment process is preferably within the
range of 750 to 800℃.
[0083]
When the heating time is less than 10 seconds, the iron-based oxide layer and
the silicon-containing oxide layer to be generated are easily non-uniform, which is not
25 preferable. On the other hand, when the heating time exceeds 60 seconds, the
35
manufacturing costs industrially increase, which is not preferable. The heating time is
preferably within the range of 20 to 30 seconds.
[0084]
When the heating treatment process is performed after the first surface treatment
process, the activated surface of the grain-5 oriented electrical steel sheet which does not
have an inorganic coating is oxidized to form an iron-based oxide layer whose thermal
expansion coefficient is positioned between those of the meal and the insulation coating
and a silicon-containing oxide layer is formed of Si diffusing from the inside of the base
steel sheet. When etch pits are formed in the surface of the grain-oriented electrical
10 steel sheet and an iron-based oxide layer having a preferable thermal expansion
coefficient and a silicon-containing oxide layer in a preferable segregation state are
formed to alleviate strain, it is possible to realize further improvement of the adhesion of
the tension-insulation coating and the effect of improving high magnetic field iron loss.
[0085]
15
The second treatment liquid used in the second surface treatment process of Step
S107 contains one or more of sulfuric acid, nitric acid, and phosphoric acid and has a
total acid concentration of 1 to 10 mass%. When the surface of the iron-based oxide
layer is lightly etched using the second treatment liquid, etch pits are formed in the
20 surface of the iron-based oxide layer and it is possible to generate an active surface state
which cannot normally be obtained.
[0086]
The liquid temperature of the second treatment liquid is preferably 50℃ or
higher and 90℃ or lower. When the liquid temperature of the second treatment liquid is
25 lower than 50℃, the solubility of the second treatment liquid decreases, in which a
36
precipitate is highly likely to be generated and effective etch pits cannot be obtained.
On the other hand, when the liquid temperature of the second treatment liquid exceeds
90℃, the reactivity of the second treatment liquid is too high and the iron-based oxide
layer and the silicon-containing oxide layer are highly likely to dissolve. The liquid
temperature of the second treatment l 5 iquid is preferably within the range of 70 to 85℃,
and more preferably within the range of 80 to 85℃.
[0087]
When the total acid concentration of the second treatment liquid is less than 1
mass%, etch pits cannot be appropriately formed in the surface of the iron-based oxide
10 layer and the treatment time increases, which is industrially disadvantageous. When the
total acid concentration of the second treatment liquid exceeds 10 mass%, the surface of
the steel sheet is excessively etched during the second surface treatment process, which is
not preferable.
The total acid concentration of the second treatment liquid is preferably within
15 the range of 1 to 5 mass%, and more preferably within the range of 1 to 3 mass%.
[0088]
The treatment time of the second surface treatment process is 1 second or more
and 10 seconds or less. When the treatment time is less than 1 second, etch pits cannot
appropriately formed in the surface of the iron-based oxide layer. On the other hand,
20 when the treatment time exceeds 10 seconds, the surface of the steel sheet is excessively
etched during the second surface treatment process, which is not preferable.
The treatment time of the second surface treatment process is preferably within
the range of 2 to 8 seconds, and more preferably within the range of 2 to 5 seconds.
[0089]
25
37
In the method for manufacturing a grain-oriented electrical steel sheet according
to this embodiment, the process of forming a tension-insulation coating is not particularly
limited and the insulation coating treatment liquid may be applied and dried through a
known method using an insulation coating treatment liquid for the phosphate silica mixed
system as will be described later. When 5 the 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.
[0090]
The surface of the steel sheet having the tension-insulation coating formed
10 thereon may be subjected to any pretreatment such as a degreasing treatment using an
alkali or the like before the insulation coating treatment liquid is applied or may be a
surface without these pretreatments.
[0091]
The tension-insulation coating formed on the surface of the steel sheet is not
15 particularly limited as long as it is used as the tension-insulation coating for the
phosphate silica mixed system of the grain-oriented electrical steel sheet and it is possible
to utilize a known tension-insulation coating for a 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
20 coating containing phosphate and colloidal silica as main components and having fine
organic resin particles dispersed therein can be exemplified.
[0092]
When the tension-insulation coating is formed, first, the insulation coating
treatment liquid in which colloidal silica is contained in an amount of 25 to 45 mass%
25 with respect to the total solid content and the remainder solid content contains one or
38
more types selected from the group consisting of aluminum phosphate, magnesium
phosphate, zinc phosphate, manganese phosphate, cobalt phosphate, and iron phosphate
as a main component is adjusted.
[0093]
It is desirable that the pH of the insulation c 5 oating treatment liquid be adjusted
within the range of 1.2 to 3.4. When the pH of the treatment liquid is within the above
range, it is possible to form a tension-insulation coating in a more suitable state.
[0094]
The adjusted insulation coating treatment liquid is applied to the surface of the
10 grain-oriented electrical steel sheet which has been subjected to the second surface
treatment process through a known method so that the thickness after drying is 1 to 3 μm,
dried, and fired.
[0095]
Times between the first surface treatment process and the heating treatment
15 process and between the second surface treatment process and the tension-insulation
coating forming process are preferably as short as possible, for example, within several
minutes.
[0096]
Subsequent to the tension-insulation coating forming process, flattening and
20 annealing for shape correction may be performed. When the flattening and annealing
are performed on the steel sheet, it is possible to further reduce the iron loss.
[0097]
The method for manufacturing a grain-oriented electrical steel sheet according
to this embodiment has been described in detail above.
25 [Example]
39
[0098]
The grain-oriented electrical steel sheet and the method for manufacturing a
grain-oriented electrical steel sheet according to the present invention will be described
in detail below with reference to examples and comparative examples. The examples
which will be illustrated later are merely examples of 5 the grain-oriented electrical steel
sheet and the method for manufacturing a grain-oriented electrical steel sheet according
to the present invention and the grain-oriented electrical steel sheet and the method for
manufacturing a grain-oriented electrical steel sheet according to the present invention is
not limited to the following examples.
10 [0099]
(Experimental example)
A hot band with a sheet thickness of 2.2 mm was obtained by casting a steel
piece (a silicon steel slab) which contains, in terms of mass%; C: 0.08%; Si: 3.24%; Mn:
0.08%; Al: 0.028%; N: 0.008%; S: 0.03%; Se: 0.01%; Bi: 0.004%, and the remainder: Fe
15 and impurities and heating the obtained steel piece and then subjecting the steel piece to
hot rolling. The steel piece was subjected to annealing at a temperature of the steel
sheet of 1100℃ for 60 seconds, subjected to cold rolling to have a sheet thickness of 0.22
mm, and subjected to decarburization annealing at a temperature of the steel sheet of
830℃. After that, an annealing separator which contains MgO and Al2O3 as main
20 components and contains 10 mass% of BiOCl which is bismuth chloride is applied and
dried and final annealing at a temperature of the steel sheet of 1200℃ for 20 hours (final
annealing under such conditions is also referred to as “purification annealing”) was
performed. When the excessive annealing separator was removed through washing
with water after final annealing, an inorganic coating was not formed on the surface of
25 the steel sheet. Furthermore, as a result of such final annealing, the Al content was less
40
than 0.05%, the C content was less than 0.1%, the N content was less than 0.05%, the S
content was less than 0.1%, the Se content was less than 0.05%, and the Bi content was
less than 0.01%.
[0100]
The steel sheet which has been subj 5 ected to final annealing was subjected to the
first surface treatment process under the conditions illustrated in Table 1, subjected to the
heating treatment process under the conditions illustrated in Table 1, and then subjected
to the second surface treatment process under the conditions illustrated in Table 1.
After that, an insulation coating treatment liquid which contains aluminum phosphate
10 (content: 60 mass% with respect to the total solid content) and silica (colloidal silica;
average particle size of 20 nm (a catalog value); content: 40 mass% with respect to the
total solid content) as main components was applied and fired to form a tensioninsulation
coating with a thickness of 2.5 μm.
[0101]
15 Chemicals used for the first treatment liquid and the second treatment liquid
were both commercially available general special grade reagents and commercially
available general special grade reagents were used for aluminum phosphate and colloidal
silica.
[0102]
20 For each of the grain-oriented electrical steel sheets manufactured in this way, a
thickness d2 of the iron-based oxide layer was measured in accordance with the above
method using an XPS (PHI5600 manufactured by ULVAC-PHI) and the main
components of the iron-based oxide layer were specifically identified using an X-ray
crystal structure analysis method. Furthermore, the obtained grain-oriented electrical
25 steel sheets were analyzed in accordance with the following analysis conditions using a
41
GDS (glow discharge emission analyzer GDA750 manufactured by Rigaku).
[0103]
XPS measurement condition
X-ray source: MgKα
5 Analytical area: about 800 μmφ
Depth direction analysis (sputtering yield: 2 nm/min in terms of SiO2)
Measurement elements: C, O, Al, Si, and Fe
Measurement surface: outmost surface, after sputtering for 0.1, 0.5, 1, 2, 5, 10,
20, 30, 40, 50, 60, 70, 80, 90, and 100 minutes
10 [0104]
GDS measurement condition
High frequency mode
Output: 30W
Ar pressure: 3hPa
15 Measurement area: 4 mmφ
Measurement time: 100 seconds
Measurement elements: O, Al, Si, P, and Fe
[0105]
Also, high magnetic field iron loss after irradiation with a laser beam was
20 performed and magnetic domain subdivision processing was performed (iron loss at a
frequency of 50 Hz when a maximum magnetic flux density was 1.7T or 1.9T) was
measured using a single sheet magnetic characteristic measurement method (a single
sheet tester: SST) according to JIS C2556. Furthermore, the adhesion of the tensioninsulation
coating was evaluated in accordance with the following evaluation method.
25 The obtained results are summarized in Table 1.
42
[0106]
In Table 1, the column of a “peak position” in a “GDS/Si emission intensity”
indicates whether the peak of the Si emission intensity existing on a portion closest to the
base steel sheet side exists between a position of an inflection point in which a rate of
increase of an Fe emission intensity in the sheet t 5 hickness direction from the surface of
the grain-oriented electrical steel sheet changes and a saturation point in which the Fe
emission intensity saturates. The score “A” indicates that the peak of the Si emission
intensity existing on a portion closest to the base steel sheet side exists between the
position of the inflection point and the saturation point and the score “B” indicates that
10 the peak of the Si emission intensity existing on a portion closest to the base steel sheet
side does not exist between the position of the inflection point and the saturation point.
[0107]

The adhesion of the tension-insulation coating was evaluated as follows. First,
15 a sample with width of 30 mm×length 300 mm was taken from each of the grain-oriented
electrical steel sheets, subjected to strain removal and annealing in a nitrogen stream at
800℃ for 2 hours, subjected to a bending adhesion test using a cylindrical column of 10
mmφ, and subjected to evaluation in accordance with a degree of peeling of the tensioninsulation
coating. Evaluation criteria are as follows and the scores A and B were
20 accepted.
Score A: no peeling
Score B: almost no peeling
Score C: a few mm of peeling is seen
Score D: 1/3 to 1/2 peeling is seen
25 Score E: full peeling
43
[0108]
[Table 1]
No First surface treatment process Heating treatment process Second surface treatment
process
Iron-based
oxide
layer
GDS Si emission intensity Adhesion High magnetic
field iron loss
(W/kg)
Remarks
Acid Liquid
temperature
(°C)
Treatment
time
(second)
Atmosphere (%
by volume)
Dew
point
(°C)
Steel sheet
temperature
(°C)
Treatment
time
(second)
Acid Liquid
tempe
rature
(°C)
Treatment
time
(second)
Thickness
(nm)
Number
of peaks
Peak
position
Si ratio
in steel
W17/5
0
W19/50
1 5%
Sulfuric
acid
80 10 20% O2 25 850 30 1%
Sulfur
ic
acid
60 10 360 2 A 0.50 B 0.65 0.96 Example
2 2%
Sulfuric
acid
85 10 20% O2 −18 800 40 5%
Sulfur
ic
acid
70 5 200 2 A 0.36 A 0.66 0.99 Example
3 10%
Sulfuric
acid
70 2 20% O2 15 880 10 5%
Sulfur
ic
acid
80 5 160 2 A 1.20 A 0.67 1.00 Example
4 5%
Nitric
acid
70 10 20% O2 28 750 55 1%
Nitric
acid
55 3 180 2 A 0.70 B 0.63 1.04 Example
5 20%
Phosph
oric
acid
80 20 2% O2 −10 850 30 7%
Phosp
horic
acid
70 3 200 2 A 2.20 B 0.62 0.91 Example
6 25%
Sulfuric
acid
60 10 20% O2 15 850 30 5%
Sulfur
ic
acid
60 10 180 2 A 0.21 C 0.66 1.01 Comparative
example
7 0.5%
Sulfuric
acid
80 60 20% O2 15 850 30 1%
Sulfur
ic
acid
80 60 80 0 − − E 0.68 1.07 Comparative
example
8 10%
Sulfuric
acid
60 10 20% O2 15 850 30 5%
Sulfur
ic
acid
60 10 410 0 − − E 0.71 1.08 Comparative
example
9 5%
Sulfuric
acid
95 10 20% O2 15 850 30 5%
Sulfur
ic
acid
95 10 80 2 A 0.26 D 0.67 1.15 Comparative
example
10 10%
Sulfuric
acid
75 10 20% O2 20 600 30 5%
Sulfur
ic
acid
75 10 40 0 − − E 0.72 1.09 Comparative
example
11 15%
Phosph
oric
75 10 20% O2 20 1000 10 7%
Phosp
horic
80 14 440 2 A 2.80 C 0.69 1.13 Comparative
example
44
acid acid
12 5%
Sulfuric
acid
85 10 20% O2 10 800 4 5%
Sulfur
ic
acid
80 10 120 2 A 0.12 E 0.74 1.10 Comparative
example
13 5%
Sulfuric
acid
85 10 20% O2 −8 850 80 1%
Sulfur
ic
acid
80 10 320 2 A 0.08 D 0.64 1.18 Comparative
example
14 5%
Sulfuric
acid
85 10 20% O2 15 800 30 0.5%
Sulfur
ic
acid
80 10 240 2 A 0.21 E 0.67 1.03 Comparative
example
15 5%
Sulfuric
acid
85 15 20% O2 25 750 30 15%
Sulfur
ic
acid
80 10 60 0 − − E 0.65 1.12 Comparative
example
16 5%
Sulfuric
acid
85 15 2% O2 25 850 30 5%
Sulfur
ic
acid
80 0.5 160 2 A 0.22 E 0.63 1.08 Comparative
example
17 5%
Sulfuric
acid
85 15 20% O2 20 850 15 5%
Sulfur
ic
acid
80 12 120 0 − − E 0.63 0.99 Comparative
example
18 5%
Sulfuric
acid
80 10 No heating treatment 1%
Sulfur
ic
acid
60 10 100 1 A 0.25 E 0.72 1.21 Comparative
example
19 5%
Sulfuric
acid
80 10 20% O2 15 850 15 7%
Phosp
horic
acid
80 5 200 2 A 0.6 B 0.64 0.97 Example
45
[0109]
As a result of the analysis using the X-ray crystal structure analysis method
described above, the iron-based oxide layers of the samples corresponding to the
examples of the present invention contained magnetite, hematite, and fayalite as main
components and the silicon-containing oxide layers c 5 ontained silica and fayalite as main
components. On the other hand, although the iron-based oxide layers contained
magnetite, hematite, and fayalite as main components were formed in the comparative
examples outside of the scope of the present invention, the silicon-containing oxide
layers showing a prescribed number of peaks and prescribed peak heights were not
10 formed.
Samples were prepared from the grain-oriented electrical steel sheets according
to the examples and analyzed using a SEM-EDS. As a result, in the intermediate layers
in the grain-oriented electrical steel sheets according to the examples, the Mg content in
each case was 20 atom% or less and an inorganic coating containing forsterite as a main
15 component was not formed.
[0110]
As is clear from Table 1 above, it can be seen that the samples corresponding to
the examples of the present invention have extremely excellent adhesion and the high
magnetic field iron loss is improved. On the other hand, it can be seen that the samples
20 corresponding to the comparative examples of the present invention are inferior in at
least either adhesion or high magnetic field iron loss.
[0111]
Although the preferred embodiments of the present invention have been
described in detail above with reference to the accompanying drawings, the present
25 invention is not limited to such examples. It is clear that a person having ordinary
46
knowledge in the field of technology to which the present invention belongs can come up
with various changed examples or modified examples within the scope of the technical
ideas described in the claims and it is naturally understood that these also belong to the
technical scope of the present invention.
5 [Reference Signs List]
[0112]
1 Grain-oriented electrical steel sheet
11 Base steel sheet
13 Tension-insulation coating
10 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 5 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 μm, and containing phosphate and colloidal silica as main
components,
10 wherein the base steel sheet contains, 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%
of C, 0% or more and less than 0.05% of N, 0% or more and less than 0.1% of S, 0% or
more and less than 0.05% of Se, 0% or more and less than 0.01% of Bi, and the
remainder: Fe and impurities as chemical components, and
15 when the tension-insulation coating undergoes elemental analysis using a glow
discharge optical emission spectrometry in a sheet thickness direction from a surface of
the tension-insulation coating,
(a) there are two or more peaks of a Si emission intensity;
(b) a peak A which is a peak of the Si emission intensity existing furthest to the
20 base steel sheet side in the sheet thickness direction exists between an inflection point at
which a rate of increase in an Fe emission intensity in the sheet thickness direction from
the surface of the tension-insulation coating changes and a saturation point at which the
Fe emission intensity become saturated; and
(c) when a length of a perpendicular line when a perpendicular line is drawn
25 from the top portion of a peak to a baseline connecting valley portions closest to the peak
48
is defined as a peak height, a peak height of the peak A is 0.30 times or more and 2.5
times or less the Si emission intensity in the base steel sheet.
2. The grain-oriented electrical steel sheet according to claim 1, wherein the siliconcontaining
oxide layer contains 5 silica and fayalite as main components, and
the tension-insulation coating contains 25 to 45 mass% of colloidal silica and the
remainder is one or more selected from the group consisting of aluminum phosphate,
magnesium phosphate, zinc phosphate, manganese phosphate, cobalt phosphate, and iron
phosphate.
10
3. The grain-oriented electrical steel sheet according to claim 1 or 2, wherein the ironbased
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,
15 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
base steel sheet and a tension-insulation coating and does not have an inorganic coating
containing forsterite as a main component, comprising:
20 a washing process of cleaning a surface of the grain-oriented electrical steel
sheet;
a first surface treatment process of treating the surface of the grain-oriented
electrical steel sheet which has been subjected to the washing process using a first
treatment liquid which contains one or more of sulfuric acid, phosphoric acid, and nitric
25 acid and having a total acid concentration of 2 to 20% and a liquid temperature of 70 to
49
90°C;
a heating treatment process of heating the grain-oriented electrical steel sheet
which has been subjected to the first 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
5 21% by volume and a dew point of -20 to 30°C;
a second surface treatment process of treating the surface of the grain-oriented
electrical steel sheet which has been subjected to the heating treatment process for 1 to 10
seconds using a second treatment liquid which contains one or more of sulfuric acid,
phosphoric acid, and nitric acid and having a total acid concentration of 1 to 10%; and
10 a tension-insulation coating forming process of forming a tension-insulation
coating which has a thickness of 1 to 3 μm and contains phosphate and colloidal silica as
main components on the surface of the grain-oriented electrical steel sheet which has
been subjected to the second surface treatment process.
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, 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, less than 0.01% of
20 Bi, and the remainder: Fe and impurities as chemical components 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
25 a final annealing process of applying an annealing separator obtained by
50
incorporating bismuth chloride into a mixture of MgO and Al2O3 or an annealing
separator obtained by incorporating a bismuth compound and a metallic chlorine
compound into a mixture of MgO and Al2O3, drying the annealing separator, and then
performing final annealing.