[0001]The present invention relates to a method for manufacturing a grain-oriented
electrical steel sheet having excellent coating adhesion. Particular! y, the present
invention relates to a method for manufacturing a grain-oriented electrical steel sheet
10 having excellent coating adhesion of an insulation coating even without having a
forsterite film.
Priority is claimed on Japanese Patent Application No. 2019-005059, filed
January 16, 2019, the content of which is incorporated herein by reference.
[Background Art]
15 [0002]
Grain-oriented electrical steel sheets are soft magnetic materials and are mainly
used as iron core materials for transformers. Therefore, magnetic characteristics such as
high magnetization characteristics and low iron loss are required. The magnetization
characteristics are a magnetic flux density induced when the iron core is excited. As the
20 magnetic flux density becomes higher, the iron core can be smaller, and thus it is
advantageous in terms of an equipment composition of the transformer and also in terms
of manufacturing cost of the transformer.
[0003]
In order to improve the magnetization characteristics, it is necessary to align
25 { 110} surfaces parallel to steel sheet surfaces, and also to control a crystal grain texture
1
so that as many crystal grains as possible in a crystal orientation (a Goss orientation) in
which <100> axes are aligned in a rolling direction are formed. In order to accumulate
crystal orientations in the Goss orientation, it is usual practice to finely precipitate
inhibitors such as AlN, MnS, and MnSe in the steel to control a secondary
5 recrystallization.
[0004]
The iron loss is a power loss consumed as heat energy when the iron core is
excited by an alternating magnetic field. From the viewpoint of energy saving, the iron
loss is required to be as low as possible. Magnetic susceptibility, sheet thickness, film
10 tension, amount of impurities, electrical resistivity, crystal grain size, magnetic domain
size, and the like affect a level of the iron loss. Even now that various technologies for
electrical steel sheets are being developed, research and development to reduce the iron
loss is being continued to improve energy efficiency.
15
[0005]
Other characteristics required for grain-oriented electrical steel sheets are
characteristics of a coating formed on a surface of a base steel sheet. Generally, in
grain-oriented electrical steel sheets, as shown in FIG. 1, a forsterite film 2 mainly
composed of Mg2Si04 (forsterite) is formed on the base steel sheet 1, and an insulation
coating 3 is formed on the forsterite film 2. The forsterite film and the insulation
20 coating have a function of electrically insulating the surface of the base steel sheet and
25
applying tension to the base steel sheet to reduce the iron loss. The forsterite film also
contains a small amount of the impurities and additives contained in the base steel sheet
and an annealing separator, and reaction products thereof, in addition to Mg2Si04.
[0006]
In order for the insulation coating to exhibit insulation characteristics and
2
required tension, the insulation coating should not peel from the electrical steel sheet.
Therefore, the insulation coating is required to have high coating adhesion. However, it
is not easy to increase both the tension applied to the base steel sheet and the coating
adhesion at the same time. Even now, research and development to enhance both of
5 them at the same time is continuing.
[0007]
Grain-oriented electrical steel sheets are usually manufactured by the following
procedure. A silicon steel slab containing 2.0 to 7.0 mass% of Si is hot-rolled, the steel
sheet after the hot-rolling is annealed as necessary, and then the annealed steel sheet is
10 cold-rolled once or twice or more with intermediate annealing interposed therebetween to
finish the steel sheet with a final thickness. Then, the steel sheet having the final
thickness is decarburization-annealed in a wet hydrogen atmosphere to promote primary
recrystallization in addition to decarburization and to form an oxide layer on the surface
of the steel sheet.
15 [0008]
An annealing separator containing MgO (magnesia) as a main component is
applied to the steel sheet having an oxide layer, dried, and after drying, the steel sheet is
coiled in a coil shape. Next, the coiled steel sheet is final-annealed to promote
secondary recrystallization, and the crystal orientations of the crystal grains are
20 accumulated in the Goss orientation. Further, MgO in the annealing separator is reacted
with Si02 (silica) in the oxide layer to form an inorganic forsterite film mainly composed
of Mg2Si04 on the surface of the base steel sheet.
[0009]
Next, the steel sheet having the forsterite film is purification-annealed to diffuse
25 the impurities in the base steel sheet to the outside and to remove them. Further, after
3
the steel sheet is flattening-annealed, a solution mainly composed of, for example, a
phosphate and colloidal silica is applied to the surface of the steel sheet having the
forsterite film and is baked to form an insulation coating. At this time, tension due to a
difference in a coefficient of thermal expansion is applied between the crystalline base
5 steel sheet and the substantially amorphous insulation coating. Therefore, the insulation
coating may be referred to as a tension coating.
[0010]
An interface between the forsterite film mainly composed of Mg2Si04 ("2" in
FIG. 1) and the steel sheet ("1" in FIG. 1) usually has a non-uniform uneven shape (refer
10 to FIG. 1). The uneven interface slightly diminishes the effect of reducing the iron loss
due to tension. Since the iron loss is reduced when the interface is smoothed, the
following developments have been carried out to date.
[0011]
Patent Document 1 discloses a manufacturing method in which the forsterite
15 film is removed by a method such as pickling and the surface of the steel sheet is
smoothed by chemical polishing or electrolytic polishing. However, in the
manufacturing method of Patent Document 1, it may be difficult for the insulation
coating to adhere to the surface of the base steel sheet.
20
[0012]
Therefore, in order to improve the coating adhesion of the insulation coating to
the smoothed surface of the steel sheet, as shown in FIG. 2, it has been proposed to form
an intermediate layer 4 (or a base film) between the base steel sheet and the insulation
coating. A base film disclosed in Patent Document 2 and formed by applying an
aqueous solution of a phosphate or alkali metal silicate is also effective in the coating
25 adhesion. As a more effective method, Patent Document 3 discloses a method in which
4
5
10
a steel sheet is annealed in a specific atmosphere before an insulation coating is formed
and an externally oxidized silica layer is formed as an intermediate layer on the surface
of the steel sheet.
[0013]
The coating adhesion can be improved by forming such an intermediate layer,
but since large-scale equipment such as electrolytic treatment equipment and dry coating
equipment is additionally required, it may be difficult to secure a site therefor, and the
manufacturing cost may increase.
[0014]
Patent Documents 4 to 6 disclose techniques in which, when an insulation
coating containing an acidic organic resin as a main component which does not
substantially contain chromium is formed on a steel sheet, a phosphorus compound layer
(a layer composed of FeP04, Fe3(P04)2, FeHP04, Fe(H2P04)2, Zn2Fe(P04)2, Zn3(P04)2,
and hydrates thereof, or a layer composed of a phosphate of Mg, Ca, and Al having a
15 thickness of 10 to 200 nm) is formed between the steel sheet and the insulation coating to
improve the exterior and adhesion of the insulation coating.
[0015]
On the other hand, a magnetic domain control method (which refines a 180°
magnetic domain) in which a width of a 180° magnetic domain is narrowed by forming
20 stress strain parts and groove parts extending in a direction intersecting the rolling
direction at predetermined intervals in the rolling direction is known as a method for
reducing abnormal eddy current loss which is a part of iron loss. In a method of
forming stress strain, a 180° magnetic domain refining effect of a closure magnetic
domain generated in the strain part (a strain region) is used. A representative method is
25 a method which utilizes shock waves or rapid heating by radiating a laser beam. In this
5
method, the surface shape of the irradiated portion hardly changes, and a stress strain part
is formed on the base steel sheet. Further, a method of forming a groove utilizes a
demagnetizing field effect due to a magnetic pole generated on a side wall of the groove.
That is, the magnetic domain control is classified as of a strain applying type and a
5 groove forming type.
[0016]
For example, Patent Document 7 discloses that an oxide on the surface of the
final-annealed steel sheet is removed, the surface is smoothed, then a film is formed on
the surface, and also the magnetic domain is refined by irradiation with a laser beam, an
10 electron beam, or a plasma flame.
[Citation List]
15
[Patent Document]
[0017]
[Patent Document 1]
Japanese Unexamined Patent Application, First Publication No. S49-096920
[Patent Document 2]
Japanese Unexamined Patent Application, First Publication No. H05-279747
[Patent Document 3]
Japanese Unexamined Patent Application, First Publication No. H06-184762
20 [Patent Document 4]
25
Japanese Unexamined Patent Application, First Publication No. 2001-220683
[Patent Document 5]
Japanese Unexamined Patent Application, First Publication No. 2003-193251
[Patent Document 6]
Japanese Unexamined Patent Application, First Publication No. 2003-193252
6
[Patent Document 7]
Japanese Unexamined Patent Application, First Publication No. H11-012755
[Summary of the Invention]
[Problems to be Solved by the Invention]
5 [0018]
In a grain -oriented electrical steel sheet having a three-layer structure of "base
steel sheet-intermediate layer mainly composed of silicon oxide-insulation coating" as
exemplified above and not having a forsterite film, there is a problem that the width of
the magnetic domain is wider than that of a grain -oriented electrical steel sheet having
10 the forsterite film as shown in FIG. 1. As a result of examining various magnetic
domain controls for grain -oriented electrical steel sheets not having a forsterite film, the
present inventors have focused on the fact that the magnetic domain is preferably refined
when an energy density of the laser beam or electron beam radiated to the grain-oriented
electrical steel sheet is increased.
15 [0019]
However, according to the studies by the present inventors, it has been found
that when the energy density of the laser beam or the electron beam is increased, the
refinement of the magnetic domain is promoted and at the same time, the insulation
coating is affected. Specifically, a problem that, when a laser beam or an electron beam
20 having a high energy density is radiated, a structure of the insulation coating is changed
due to an influence of radiation heat, and the adhesion of the insulation coating is
reduced has been found.
[0020]
The present invention has been made in view of the above problems, and an
25 object thereof is to provide a method for manufacturing a grain-oriented electrical steel
7
sheet capable of ensuring good adhesion of an insulation coating and obtaining a good
iron loss reduction effect in grain-oriented electrical steel sheets which do not have a
forsterite film and have strain regions formed on the base steel sheet.
[Means for Solving the Problem]
5 [0021]
( 1) A method for manufacturing a grain -oriented electrical steel sheet according
to one aspect of the present invention includes a strain region forming process of
irradiating a grain-oriented electrical steel sheet having a base steel sheet, an intermediate
layer disposed to be in contact with the base steel sheet, and an insulation coating
10 disposed to be in contact with the intermediate layer with an electron beam and forming a
strain region which extends in a direction intersecting a rolling direction of the base steel
sheet on a surface of the base steel sheet, wherein, in the strain region forming process, a
temperature of a central portion of the strain region in the rolling direction of the base
steel sheet and an extension direction of the strain region is heated to 800°C or higher
15 and 2000°C or lower.
[0022]
(2) In the method for manufacturing a grain-oriented electrical steel sheet
described in (1), in the strain region forming process, the temperature of the central
portion of the strain region in the rolling direction of the base steel sheet and the
20 extension direction of the strain region may be heated to 800°C or higher and 1500°C or
lower.
(3) In the method for manufacturing a grain-oriented electrical steel sheet
described in (1) or (2), in the strain region forming process, radiation conditions of an
electron beam may be acceleration voltage: 50 kV or more and 350kV or less, beam
25 current: 0.3 rnA or more and 50 rnA or less, beam radiation diameter: 10 ~m or more and
8
500 ~m or less, radiation interval: 3 mm or more and 20 mm or less, and scanning speed:
5 m/sec or more, 80 m/sec or less.
(4) The method for manufacturing a grain-oriented electrical steel sheet
described in any one of (1) to (3) may further include an intermediate layer forming
5 process of forming the intermediate layer on the base steel sheet, and in the intermediate
layer forming process, the base steel sheet may be heat-treated to form an intermediate
layer under annealing conditions adjusted to annealing temperature: 500°C or higher and
1500°C or lower, holding time: 10 seconds or more and 600 seconds or less, and dew
point: -20°C or higher and soc or lower.
10 (5) The method for manufacturing a grain-oriented electrical steel sheet
described in any one of (1) to (4) may further include an insulation coating forming
process of forming the insulation coating on the base steel sheet on which the
intermediate layer is formed, and in an insulation coating forming process, an insulation
coating forming solution may be applied to a surface of the base steel sheet at a coating
15 amount of 2 g/m2 to 10 g/m2
, a base steel sheet to which the insulation coating forming
solution is applied may be left for 3 seconds to 300 seconds, a base steel sheet to which
the insulation coating forming solution is applied may be heated at a heating rate of
5 °C/sec or more and 30 °C/sec or less in an atmospheric gas containing hydrogen and
nitrogen and having an oxidation degree of PH20IPH2 adjusted to 0.001 or more and 0.3
20 or less, the heated base steel sheet may be soaked in a temperature range of 300°C or
higher and 950°C or lower for 10 seconds or more and 300 seconds or less in an
atmospheric gas containing hydrogen and nitrogen and having an oxidation degree of
PH20IPH2 adjusted to 0.001 or more and 0.3 or less, and the soaked base steel sheet may
be cooled to 500°C at a cooling rate of 5 °C/sec or more and 50 °C/sec or less in an
25 atmospheric gas containing hydrogen and nitrogen and having an oxidation degree of
9
PH20/PH2 controlled to 0.001 or more and 0.05 or less.
[Effects of the Invention]
[0023]
According to the present invention, it is possible to provide a method for
5 manufacturing a grain-oriented electrical steel sheet capable of ensuring good adhesion
of an insulation coating and obtaining a good iron loss reduction effect in grain-oriented
electrical steel sheets which do not have a forsterite film and have strain regions formed
on the base steel sheet.
[Brief Description of Drawings]
10 [0024]
15
FIG. 1 is a schematic cross-sectional view showing a coating structure of a
conventional grain-oriented electrical steel sheet.
FIG. 2 is a schematic cross-sectional view showing another coating structure of
the conventional grain-oriented electrical steel sheet.
FIG. 3 is a schematic cross-sectional view for explaining a strain region obtained
by a method for manufacturing a grain-oriented electrical steel sheet according to an
embodiment of the present invention.
FIG. 4 is a schematic enlarged cross-sectional view of a portion A of FIG. 3.
FIG. 5 is a diagram for explaining a definition of a line segment ratio of voids in
20 the grain-oriented electrical steel sheet according to the embodiment.
[Embodiments for implementing the Invention]
[0025]
The present inventors have found that, for a grain-oriented electrical steel sheet
having no forsterite film, there is a difference in adhesion of an insulation coating
25 between a case in which a laser beam is radiated and a case in which an electron beam is
10
radiated, and have studied magnetic domain control by the electron beam.
[0026]
The present inventors have found that a width of a magnetic domain can be
narrowed and adhesion of an insulation coating can be ensured under specific radiation
5 conditions, as a result of diligent studies on grain-oriented electrical steel sheets which do
not have a forsterite film by changing the radiation conditions of an electron beam.
Further, the present inventors have also found that, when the above specific
radiation conditions are not satisfied, even though the width of the magnetic domain can
be narrowly controlled, voids are generated in the insulation coating and the adhesion of
10 the insulation coating deteriorates.
[0027]
Further, the present inventors have also found that no change is observed in the
insulation coating after irradiation under the conventional radiation conditions, but when
a strain region is formed under the specific radiation conditions as described above, a
15 unique structure containing M2P4013 can be seen in a central portion of the strain region
and the vicinity thereof.
[0028]
Hereinafter, preferred embodiments of the present invention will be described.
However, it is obvious that the present invention is not limited to configurations
20 disclosed in the embodiments, and various modifications can be made without departing
from the purpose of the present invention. It is also obvious that elements of the
following embodiments can be combined with each other within the scope of the present
invention.
Further, in the following embodiments, a numerical limitation range represented
25 by using "to" means a range including numerical values before and after "to" as a lower
11
5
limit value and an upper limit value. Numerical values indicated by "greater than" or
"less than" are not included in the numerical range thereof.
[0029]
[Method for manufacturing grain -oriented electrical steel sheet]
Hereinafter, a method for manufacturing a grain-oriented electrical steel sheet
according to the present invention will be described. A method for manufacturing a
grain-oriented electrical steel sheet according to the present embodiment is not limited to
the following method. The following manufacturing method is an example for
manufacturing the grain -oriented electrical steel sheet according to the present
10 embodiment.
The grain -oriented electrical steel sheet according to the present embodiment
may be manufactured by forming the intermediate layer on the base steel sheet, from
which the formation of the forsterite film is curbed during the final annealing or the
forsterite film is removed after the final annealing, as a starting material, forming the
15 insulation coating and then forming the strain region.
[0030]
The method for manufacturing a grain-oriented electrical steel sheet according
to the present embodiment includes a strain region forming process of irradiating the
grain-oriented electrical steel sheet having a base steel sheet, an intermediate layer
20 disposed to be in contact with the base steel sheet, and an insulation coating disposed to
be in contact with the intermediate layer with an electron beam and forming a strain
region which extends in a direction intersecting a rolling direction on a surface of the
base steel sheet.
In the strain region forming process of the method for manufacturing a grain-
25 oriented electrical steel sheet according to the present embodiment, a temperature of a
12
central portion of the strain region in the rolling direction and an extension direction of
the strain region is heated to 800°C or higher and 2000°C or lower.
[0031]
In the method for manufacturing a grain-oriented electrical steel sheet according
5 to the present embodiment,
(a) a base steel sheet from which a film of an inorganic mineral substance such
as a forsterite generated by final-annealing is removed by pickling, grinding, or the like is
annealed, or
(b) a base steel sheet in which formation of the above-described film of the
10 inorganic mineral substance is curbed at final-annealing is annealed,
(c) an intermediate layer is formed on a surface of the base steel sheet by
thermal oxidation annealing, that is, annealing in an atmosphere with a controlled dew
point, and
(d) an insulation coating forming solution mainly composed of a phosphate and
15 colloidal silica is applied onto the intermediate layer and is baked.
The grain -oriented electrical steel sheet having the base steel sheet, the
intermediate layer disposed to be in contact with the base steel sheet, and the insulation
coating disposed to be in contact with the intermediate layer as the outermost surface can
be manufactured by the above-described manufacturing method.
20 [0032]
The base steel sheet is produced, for example, as follows.
A silicon steel piece containing 0.8 to 7.0 mass% of Si, preferably a silicon steel
piece containing 2.0 to 7.0 mass% of Si is hot-rolled, the steel sheet after hot-rolling is
annealed as necessary, and then the annealed steel sheet is cold-rolled once or twice or
25 more with intermediate annealing interposed between them to finish the steel sheet with a
13
5
final thickness. Next, in addition to decarburization, primary recrystallization is
promoted by subjecting the steel sheet having the final thickness to decarburization
annealing, and an oxide layer is formed on the surface of the steel sheet.
[0033]
Next, an annealing separator containing magnesia as a main component is
applied to the surface of the steel sheet having the oxide layer and is dried, and after the
drying, the steel sheet is coiled in a coil shape. Then, the coiled steel sheet is subjected
to final annealing (secondary recrystallization). A forsterite film mainly composed of a
forsterite (Mg2Si04) is formed on the surface of the steel sheet by final annealing. This
10 forsterite film is removed by pickling, grinding, or the like. After the removal, the
surface of the steel sheet is preferably smoothed by chemical polishing or electrolytic
polishing.
[0034]
On the other hand, as the above-described annealing separator, an annealing
15 separator containing alumina instead of magnesia as a main component can be used.
The annealing separator containing alumina as a main component is applied to the
surface of the steel sheet having an oxide layer and is dried, and after the drying, the steel
sheet is coiled in a coil shape. Then, the coiled steel sheet is subjected to final
annealing (secondary recrystallization). When the annealing separator containing
20 alumina as a main component is used, even when final annealing is performed, the
formation of the film of the inorganic mineral substance such as a forsterite on the
surface of the steel sheet is curbed. After final-annealing, the surface of the steel sheet
is preferably smoothed by chemical polishing or electrolytic polishing.
[0035]
25 The base steel sheet from which the film of inorganic mineral substances such as
14
a forsterite is removed, or the base steel sheet in which the formation of the film of the
inorganic mineral substance such as a forsterite is curbed is subjected to thermal
oxidation annealing under the following annealing conditions, and the intermediate layer
is formed on the surface of the base steel sheet. In some cases, the annealing may not
5 be performed after the final annealing, and the insulation coating may be formed on the
surface of the base steel sheet after the final annealing.
[0036]
The annealing atmosphere when the intermediate layer is formed is preferably a
reducing atmosphere so that the inside of the steel sheet is not oxidized, and particular! y
10 preferably a nitrogen atmosphere mixed with hydrogen. For example, an atmosphere in
which hydrogen:nitrogen is 80 to 20%: 20 to 80% (100% in total) is preferable.
[0037]
Further, when the intermediate layer is formed, it is preferable to adjust the
annealing conditions so that an annealing temperature is 500°C or higher and 1500°C or
15 lower, a holding time is 10 seconds or more and 600 seconds or less, and a dew point is-
20°C or higher and 10°C or lower. The dew point is more preferably soc or lower.
20
The intermediate layer is formed on the surface of the base steel sheet by heat-treatment
of the base steel sheet under such annealing conditions.
[0038]
The thickness of the intermediate layer is controlled by appropriately adjusting
one or more of the annealing temperature, the holding time, and the dew point of the
annealing atmosphere. The thickness of the intermediate layer is preferably 2 to 400 nm
on average from the viewpoint of ensuring the coating adhesion of the insulation coating.
More preferably, it is 5 nm to 300 nm.
25 [0039]
15
Next, the insulation coating is formed on the intermediate layer. A preferred
method for forming the insulation coating is as follows. Of course, the method of
forming the insulation coating is not limited to the following method. First, an
insulation coating forming solution mainly composed of a phosphate and colloidal silica
5 is applied and baked.
10
Next, the insulation coating forming solution is applied to the surface of the base
steel sheet at a coating amount of 2 g/m2 to 10 g/m2
, and the base steel sheet to which the
insulation coating forming solution is applied is left for 3 seconds to 300 seconds.
[0040]
Next, the base steel sheet to which the insulation coating forming solution is
applied is heated at a heating rate of 5 °C/sec or more and 30 °C/sec or less in an
atmospheric gas containing hydrogen and nitrogen and having an oxidation degree of
PH20/PH2 adjusted to 0.001 or more and 0.3 or less. The base steel sheet heated under
these conditions is soaked in a temperature range of 300°C or higher and 950°C or lower
15 for 10 seconds or more and 300 seconds or less in an atmospheric gas containing
hydrogen and nitrogen and having an oxidation degree of PH20/PH2 adjusted to 0.001 or
more and 0.3 or less.
The base steel sheet soaked under these conditions is cooled to 500°C at a
cooling rate of 5 °C/sec or more and 50 °C/sec or less in an atmospheric gas containing
20 hydrogen and nitrogen and having an oxidation degree of PH20/PH2 controlled to 0.001
or more and 0.05 or less.
When the oxidation degree of the atmosphere during heating to cooling is less
than the lower limit value shown above, the intermediate layer may become thin.
Further, when the upper limit value shown above is exceeded, the intermediate layer may
25 become thick.
16
5
Further, when the cooling rate at the time of cooling is less than 5 °C/sec,
productivity may decrease. Further, when the cooling rate exceeds 50 °C/sec, many
voids may be generated in the insulation coating.
[0041]
Next, the grain-oriented electrical steel sheet obtained in the above-described
process is irradiated with an electron beam to form a strain region which extends in a
direction intersecting the rolling direction on the surface of the base steel sheet. Here, a
temperature of the central portion of the strain region in the rolling direction and the
extension direction of the strain region is heated to 800°C or higher and 2000°C or lower
10 by irradiating the grain-oriented electrical steel sheet with an electron beam. Thus, the
strain region which extends in the direction intersecting the rolling direction is formed on
the surface of the base steel sheet. Here, the central portion of the strain region in the
rolling direction is a region which includes a center of the strain region (details will be
described later, but the center between end portions of the strain region in the rolling
15 direction when the strain region is crosssectioned on a plane parallel to the rolling
direction and the sheet thickness direction) and has a width of 10 ~m in the rolling
direction. The central portion of the strain region in the extension direction of the strain
region is a region which includes a midpoint (that is, a center) of a line segment
connecting the end portions in the extension direction of the strain region in a continuous
20 strain region, and means a region having a width of 10 ~m in the extension direction of
the strain region from the midpoint (the center).
25
Therefore, the regions corresponding to both the central portion of the strain
region in the rolling direction and the central portion of the strain region in the extension
direction of the strain region are heated to 800°C or higher and 2000°C or lower.
Here, in order to heat the temperature of the central portion of the strain region
17
in the rolling direction and the extension direction of the strain region to 800°C or higher
and 2000°C or lower, in the strain region forming process, preferably, the electron beam
is radiated under conditions of an acceleration voltage of 50 kV or more and 350 kV or
less, a beam current of 0.3mA or more and 50mA or less, a beam radiation diameter of 10
5 ~m or more and 500 ~m or less, a radiation interval of 3 mm or more and 20 mm or less,
and a scanning speed of 5 m/sec or more and 80 m/sec or less. It is preferable to use an
electron beam because it has features such as an effect of curbing coating damage due to
a high acceleration voltage, and a high-speed beam control.
In the strain region forming process, the temperature of the central portion of the
10 strain region in the rolling direction and the extension direction of the strain region may
be heated to 800°C or higher and 1500°C or lower.
[0042]
The radiation of the electron beam is preferably performed while the beam is
scanned from one width end portion to the other width end portion of the steel sheet
15 using one or more radiation devices (for example, an electron gun). A scanning
direction of the electron beam preferably has an angle of 45 to 135° in the clockwise or
counterclockwise direction parallel to the surface of the grain -oriented electrical steel
sheet with respect to the rolling direction, and is more preferable goo, that is, parallel to
the surface of the grain -oriented electrical steel sheet and perpendicular with respect to
20 the rolling direction. When deviation from goo becomes large, a volume of the strain
region increases excessively, and thus hysteresis loss tends to increase.
[0043]
The acceleration voltage is preferably 50 kV or more and 350 kV or less.
Preferably, the acceleration voltage of the electron beam is high. As the
25 acceleration voltage of the electron beam becomes higher, material penetration of the
18
electron beam increases, and the electron beam easily pass through the insulation coating.
Therefore, damage to the insulation coating is curbed. Further, when the acceleration
voltage is high, there is an advantage that the beam diameter can be easily reduced. In
order to obtain the above-described effects, preferably, the acceleration voltage is 50 kV
5 or more. The acceleration voltage is preferably 70 kV or more, and more preferably
100 kV or more.
On the other hand, from the viewpoint of curbing equipment costs, the
acceleration voltage is preferably 350 kV or less. The acceleration voltage is preferably
300 kV or less, and more preferably 250 kV or less.
10 [0044]
The beam current is preferably 0.3 rnA or more and 50 rnA or less.
The beam current is preferably small from the viewpoint of reducing the beam
diameter. When the beam current is too large, it may be difficult to converge the beam.
Therefore, the beam current is preferably 50 rnA or less. The beam current is more
15 preferably 30 rnA or less. When the beam current is too small, it may not be possible to
form the strain required to obtain a sufficient magnetic domain refining effect. Thus,
preferably, the beam current is 0.3 rnA or more, The beam current is more preferably 0.5
rnA or more, and further preferably 1 rnA or more.
20
[0045]
The beam radiation diameter is preferably 10 ~m or more and 500 ~m or less.
As the beam radiation diameter in a direction orthogonal to the scanning
direction of the beam becomes smaller, it is advantageous to improve single sheet iron
loss. The beam radiation diameter in the direction orthogonal to the scanning direction
of the electron beam is preferably 500 ~m or less. Here, in the present embodiment, the
25 beam radiation diameter is defined as a half width of a beam profile measured by a slit
19
method (using a slit having a width of 0.03 mm). The beam radiation diameter in the
direction orthogonal to the scanning direction is preferably 400 ~m or less, and more
preferably 300 ~m or less.
A lower limit of the beam radiation diameter in the direction orthogonal to the
5 scanning direction is not particularly limited, but is preferably 10 ~m or more. When
the beam radiation diameter in the direction orthogonal to the scanning direction of the
electron beam is 10 ~m or more, it is possible to irradiate a wide range with one electron
beam source. The beam radiation diameter in the direction orthogonal to the scanning
direction is preferably 30 ~m or more, and more preferably 100 ~m or more.
10 [0046]
The radiation interval is preferably 3 mm or more and 20 mm or less.
Further, when the radiation interval is 3 mm or more and 20 mm or less, an
effect of reducing the iron loss by balancing reduction of eddy current loss due to the
refinement of the magnetic domain and suppression of an increase in the hysteresis loss
15 can be obtained. The radiation interval is a distance to radiate the electron beam in the
rolling direction of the base steel sheet, and is an interval between the strain regions in
the rolling direction.
20
[0047]
The scanning speed is preferably 5 m/sec or more and 80 m/sec or less.
Further, when the scanning speed is 5 m/sec or more and 80 m/sec or less, both
the magnetic domain refining effect and the productivity improvement can be achieved.
The scanning speed of the beam is preferably 5 m/sec or more. Here, the
scanning speed is a scanning speed obtained by dividing a distance from a radiation start
point to a radiation end point of the electron beam when each of the strain regions is
25 formed by a time required for scanning between the points, that is, an average scanning
20
speed. For example, when the radiation start point and the radiation end point of the
electron beam are both end portions of the steel sheet in a width direction, the scanning
speed is an average scanning speed during irradiation while the beam is scanned from
one width end portion to the other width end portion of the steel sheet (a speed obtained
5 by dividing a distance between the width end portions of the steel sheet by a time
required for scanning between the width end portions). When the scanning speed is less
than 5 m/sec, a processing time becomes long, and the productivity may decrease. The
scanning speed is more preferably 45 m/sec or more.
10
[0048]
Next, an example of a grain-oriented electrical steel sheet obtained by the
method for manufacturing a grain-oriented electrical steel sheet according to the abovedescribed
embodiment will be described. However, it is obvious that the grain-oriented
electrical steel sheet obtained by the method for manufacturing a grain-oriented electrical
steel sheet of the present invention is not limited to the following embodiment.
15 [0049]
20
[Grain-oriented electrical steel sheet]
A grain-oriented electrical steel sheet according to the present embodiment has a
base steel sheet, an intermediate layer disposed to be in contact with the base steel sheet,
and an insulation coating disposed to be in contact with the intermediate layer.
The grain -oriented electrical steel sheet according to the present embodiment
has a strain region which extends in a direction intersecting a rolling direction on a
surface of the base steel sheet, and M2P 4Q13 is present in the insulation coating on the
strain region in a cross-sectional view of a plane parallel to the rolling direction and a
sheet thickness direction. M means at least one or both of Fe and Cr.
25 [0050]
21
5
10
In the grain -oriented electrical steel sheet according to the present embodiment,
there are a base steel sheet, an intermediate layer disposed to be in contact with the base
steel sheet, and an insulation coating disposed to be in contact with the intermediate
layer, and there is no forsterite film.
Here, the grain-oriented electrical steel sheet without a forsterite film is a grainoriented
electrical steel sheet manufactured by removing the forsterite film after
production, or a grain-oriented electrical steel sheet manufactured by curbing formation
of a forsterite film.
[0051]
In the present embodiment, the rolling direction of the base steel sheet is a
rolling direction in hot rolling or cold rolling when the base steel sheet is manufactured
by a manufacturing method which will be described later. The rolling direction may
also be referred to as a sheet passing direction, a conveying direction, or the like of a
steel sheet. The rolling direction is a longitudinal direction of the base steel sheet.
15 The rolling direction can also be identified using a device for observing a magnetic
domain structure or a device for measuring a crystal orientation such as an X-ray Laue
method.
In the present embodiment, the direction intersecting the rolling direction means
a direction in a range of inclination within 45° in a clockwise or counterclockwise
20 direction from a direction parallel to the surface of the base steel sheet and perpendicular
with respect to the rolling direction (hereinafter, it is also simply referred to as a
"direction perpendicular to the rolling direction"). Since the strain region is formed on
the surface of the base steel sheet, the strain region extends to a direction of inclination
within 45 o on the plate surface of the base steel sheet from a direction perpendicular to
25 the rolling direction and the sheet thickness direction on the surface of the base steel
22
sheet.
[0052]
The plane parallel to the rolling direction and the sheet thickness direction
means a plane parallel to both the above-described rolling direction and sheet thickness
5 direction of the base steel sheet.
[0053]
The insulation coating on the strain region means a portion of the insulation
coating disposed on the base steel sheet which is located above the strain region in the
sheet thickness direction in a cross-sectional view of a plane parallel to the rolling
10 direction and the sheet thickness direction.
[0054]
Hereinafter, each of constituent components of the grain-oriented electrical steel
sheet according to the present embodiment will be described. The grain-oriented
electrical steel sheet according to the present embodiment can be manufactured by the
15 above-described method for manufacturing a grain-oriented electrical steel sheet.
[0055]
(Base steel sheet)
The base steel sheet which is a base material has a crystal grain texture in which
a crystal orientation is controlled such that it becomes a Goss orientation on the surface
20 of the base steel sheet. A surface roughness of the base steel sheet is not particularly
limited, but an arithmetic mean roughness (Ra) thereof is preferably 0.5 ~m or less, and
more preferably 0.3 ~m or less to apply a large tension to the base steel sheet to reduce
iron loss. A lower limit of the arithmetic mean roughness (Ra) of the base steel sheet is
not particularly limited, but when it is 0.1 ~m or less, an iron loss improving effect
25 becomes saturated, and thus the lower limit may be 0.1 ~m.
23
[0056]
A sheet thickness of the base steel sheet is also not particular! y limited, but an
average sheet thickness thereof is preferably 0.35 mm or less, and more preferably 0.30
mm or less to further reduce the iron loss. A lower limit of the sheet thickness of the
5 base steel sheet is not particularly limited, but may be 0.10 mm from the viewpoint of
manufacturing equipment and cost. A method for measuring the sheet thickness of the
base steel sheet is not particularly limited, but it can be measured using, for example, a
micrometer or the like.
10
[0057]
A chemical composition of the base steel sheet is not particular! y limited, but
preferably, it includes, for example, a high concentration of Si (for example, 0.8 to 7.0
mass%). In this case, a strong chemical affinity develops between the base steel sheet
and the intermediate layer mainly composed of a silicon oxide, and the intermediate layer
and the base steel sheet are firmly adhered to each other.
15 [0058]
(Intermediate layer)
The intermediate layer is disposed to be in contact with the base steel sheet (that
is, formed on the surface of the base steel sheet), and has a function of bringing the base
steel sheet and the insulation coating into close contact with each other. The
20 intermediate layer extends continuous! y on the surface of the base steel sheet. The
adhesion between the base steel sheet and the insulation coating is improved and stress is
applied to the base steel sheet by forming the intermediate layer between the base steel
sheet and the insulation coating.
[0059]
25 The intermediate layer can be formed by heat-treatment of a base steel sheet in
24
5
which the formation of the forsterite film is curbed during final annealing, or a base steel
sheet from which the forsterite film is removed after the final annealing in an
atmospheric gas adjusted to a predetermined oxidation degree.
[0060]
The silicon oxide which is a main component of the intermediate layer is
preferably SiOx (x=l.O to 2.0). When the silicon oxide is SiOx (x=1.5 to 2.0), the
silicon oxide is more stable, which is more preferable. When the intermediate layer is
formed on the surface of the base steel sheet, if thermal oxidation annealing is
sufficiently performed (that is, to satisfy the conditions of the above-described
10 embodiment), SiOx (x;::::;2.0) can be formed on the intermediate layer.
[0061]
When the thermal oxidation annealing is performed under the conditions of the
above-described embodiment, the silicon oxide is in an amorphous state. Therefore, the
intermediate layer made of a dense material which has high strength to withstand thermal
15 stress and has increased elasticity and can easily relieve the thermal stress can be formed
on the surface of the base steel sheet.
[0062]
When a thickness of the intermediate layer is thin, a thermal stress relaxation
effect may not be sufficiently exhibited. Therefore, the thickness of the intermediate
20 layer is preferably 2 nm or more on average. The thickness of the intermediate layer is
more preferably 5 nm or more. On the other hand, when the thickness of the
intermediate layer is thick, the thickness becomes non-uniform, and defects such as voids
and cracks may occur in a layer. Therefore, the thickness of the intermediate layer is
preferably 400 nm or less on average, and more preferably 300 nm or less. A method
25 for measuring the thickness of the intermediate layer will be described later.
25
[0063]
The intermediate layer may be an external oxide film formed by external
oxidation. The external oxide film is an oxide film formed in an atmospheric gas
having a low oxidation degree and means an oxide formed in a film shape on the surface
5 of the steel sheet after an alloying element (Si) in the steel sheet is diffused to the surface
of the steel sheet.
[0064]
As described above, the intermediate layer contains silica (a silicon oxide) as a
main component. In addition to the silicon oxide, the intermediate layer may contain an
10 oxide of an alloying element contained in the base steel sheet. That is, it may contain
any oxide of Fe, Mn, Cr, Cu, Sn, Sb, Ni, V, Nb, Mo, Ti, Bi, and Al, or a composite oxide
thereof. The intermediate layer may also contain metal grains of Fe or the like.
Further, the intermediate layer may contain impurities as long as the effect is not
impaired.
15 [0065]
In the grain -oriented electrical steel sheet according to the present embodiment,
more preferably, an average thickness of the intermediate layer in a central portion
thereof is 0.5 times or more and 2 times or less an average thickness of the intermediate
layer other than the strain region in the cross-sectional view of the plane parallel to the
20 rolling direction and the sheet thickness direction. Here, the central portion is a central
portion of the strain region which will be described later.
25
With such a configuration, good adhesion of the insulation coating can be
maintained even in the strain region.
[0066]
Usually, in the rolling direction a plurality of strain regions are formed
26
substantially continuously (for example, continuously except for joints of the strain
regions). Thus, a region between the Nth strain region counted in the rolling direction
and, for example, theN+ lth strain region (or the N-lth strain region) adjacent to the Nth
strain region in the rolling direction can be referred to as a region other than the strain
5 reg1on.
[0067]
An average thickness of the intermediate layer other than the strain region can
be measured with a scanning electron microscope (SEM) or a transmission electron
microscope (TEM) by a method which will be described later. Further, an average
10 thickness of the intermediate layer in the strain region can also be measured by the same
method.
Specifically, the average thickness of the intermediate layer in the strain region
and the average thickness of the intermediate layer other than the strain region can be
measured by the method described below.
15 [0068]
First, a test piece is cut out so that a cutting direction is parallel to the sheet
thickness direction (specifically, the test piece is cut out so that a cut surface is parallel to
the sheet thickness direction and perpendicular to the rolling direction), and a crosssectional
structure of the cut surface is observed by the SEM at a magnification at which
20 each of layers (that is, the base steel sheet, the intermediate layer, and the insulation
coating) is included in an observation field of view. It is possible to infer how many
layers the cross-sectional structure includes by observing with a backscattered electron
composition image (a COMPO image).
[0069]
25 In order to identify each of layers in the cross-sectional structure, a line analysis
27
in the sheet thickness direction is performed using an energy dispersive X-ray
spectroscopy (SEM-EDS), and a quantitative analysis of the chemical composition of
each of layers is performed.
Elements to be quantitatively analyzed are five elements of Fe, Cr, P, Si, and 0.
5 "Atomic%" described below is not an absolute value of atomic%, but a relative value
calculated based on an X-ray intensity corresponding to the five elements.
[0070]
In the following, it is assumed that the relative value measured by the SEM-EDS
is a specific numerical value obtained by performing a line analysis with a scanning
10 electron microscope (NB5000) manufactured by Hitachi High-Technologies Corporation
and an EDS analyzer (XFlash (r) 6130) manufactured by Bruker AXS GmbH. and
inputting the results thereof to EDS data software (ESPRIT 1.9) manufactured by Bruker
AXS GmbH. for calculation.
Further, the relative value measured by TEM-EDS shall be a specific numerical
15 value obtained by performing a line analysis with a transmission electron microscope
(JEM-2100F) manufactured by JEOL Ltd. and an energy dispersive X-ray analyzer (JED-
2300T) manufactured by JEOL Ltd. and inputting the results thereof to the EDS data
software (an analysis station) manufactured by JEOL Ltd. for calculation. Of course,
the measurement with SEM-EDS and TEM-EDS is not limited to examples shown
20 below.
[0071]
First, the base steel sheet, the intermediate layer, and the insulation coating are
identified as follows based on the observation results of the COMPO image and the
quantitative analysis results of the SEM-EDS. That is, when there is a region in which a
25 Fe content is 80 atomic% or more and an 0 content is less than 30 atomic% excluding
28
the measurement noise, and also a line segment (a thickness) on a scanning line of the
line analysis corresponding to this region is 300 nm or more, this region is determined as
the base steel sheet, and the regions excluding the base steel sheet are determined as the
intermediate layer and the insulation coating.
5 [0072]
As a result of observing the region excluding the base steel sheet identified
above, when there is a region in which a P content is 5 atomic% or more and the 0
content is 30 atomic% or more excluding the measurement noise, and also the line
segment (the thickness) on the scanning line of the line analysis corresponding to this
10 region is 300 nm or more, this region is determined as the insulation coating.
[0073]
When the above-described region which is the insulation coating is identified,
precipitates or inclusions contained in the film are not included in targets for
determination, and a region which satisfies the above-described quantitative analysis
15 results as a matrix phase is determined as the insulation coating. For example, when it
is confirmed from the COMPO image or the line analysis results that the precipitates or
inclusions are present on the scanning line of the line analysis, determination is made
based on the quantitative analysis results as the matrix phase without this region being
included in the targets. The precipitates or inclusions can be distinguished from the
20 matrix phase by a contrast in the COMPO image, and can be distinguished from the
matrix phase by an amount of constituent elements present in the quantitative analysis
results.
[0074]
When there is the region excluding the base steel sheet and the insulation
25 coating identified above, and the line segment (the thickness) on the scanning line of the
29
line analysis corresponding to this region is 300 nm or more, this region is determined as
the intermediate layer. The intermediate layer may satisfy an average Si content of 20
atomic% or more and an average 0 content of 30 atomic% or more as an overall average
(for example, the arithmetic mean of the atomic% of each of the elements measured at
5 each of measurement points on the scanning line). The quantitative analysis results of
the intermediate layer are quantitative analysis results as the matrix phase, which do not
include analysis results of the precipitates or inclusions contained in the intermediate
layer.
10
[0075]
Further, in the region determined as the insulation coating above, a region in
which a total amounts of Fe, Cr, P and 0 is 70 atomic% or more and the Si content is less
than 10 atomic% excluding the measurement noise is determined as the precipitate.
[0076]
As will be described later, a crystal structure of the above-described precipitate
15 can be identified from a pattern of electron beam diffraction.
[0077]
Although M2P207 may be present in the conventional insulation coating, the
crystal structure of M2P207 (M is at least one or both of Fe and Cr) can be identified and
discriminated from the pattern of the electron beam diffraction.
20 [0078]
The identification of each of the layers and the measurement of the thickness by
the above-described COMPO image observation and SEM-EDS quantitative analysis are
performed at five or more locations with different observation fields of view. An
arithmetic mean value is obtained from values excluding a maximum value and a
25 minimum value among the thicknesses of the layers obtained at five or more locations in
30
total, and this average value is used as the thickness of each of the layers. However, the
thickness of the oxide film which is the intermediate layer is measured at a location at
which it can be determined that it is an external oxidation region and not an internal
oxidation region while a texture form is observed, and an average value thereof is
5 obtained. The thickness (the average thickness) of the insulation coating and the
intermediate layer can be measured by such a method.
[0079]
When there is a layer in which the line segment (the thickness) on the scanning
line of the line analysis is less than 300 nm in at least one of the above-described five or
10 more observation fields of view, preferably, a corresponding layer is observed in detail
with the TEM, and the identification of the corresponding layer and the measurement of
the thickness are performed by the TEM.
[0080]
More specifically, a test piece including a layer to be observed in detail using the
15 TEM is cut out by focused ion beam (FIB) processing so that a cutting direction is
parallel to the sheet thickness direction (specifically, the test piece is cut out so that a cut
surface is parallel to the sheet thickness direction and perpendicular to the rolling
direction), and the cross-sectional structure of this cut surface (a bright field image) is
observed by scanning-TEM (STEM) at a magnification at which the corresponding layer
20 is included in the observation field of view. When each of the layers is not included in
the observation field of view, the cross-sectional structure is observed in a plurality of
continuous fields of view.
[0081]
In order to identify each of the layers in the cross-sectional structure, the line
25 analysis is performed in the sheet thickness direction using the TEM-EDS, and the
31
quantitative analysis of the chemical composition of each of the layers is performed.
The elements to be quantitatively analyzed are five elements, Fe, Cr, P, Si, and 0.
[0082]
Each of the layers is identified and the thickness of each of the layers is
5 measured based on the bright field image observation results by the TEM and the
quantitative analysis results of the TEM-EDS described above. The method for
identifying each of the layers and the method for measuring the thickness of each of the
layers using the TEM may be performed according to the above-described method using
the SEM.
10 [0083]
When the thickness of each of the layers identified by the TEM is 5 nm or less,
it is preferable to use a TEM having a spherical aberration correction function from the
viewpoint of a spatial resolution. Further, when the thickness of each of the layers is 5
nm or less, a point analysis may be performed in the sheet thickness direction at intervals
15 of, for example, 2 nm or less, the line segment (the thickness) of each of the layers may
be measured, and this line segment may be adopted as the thickness of each of the layers.
For example, when the TEM having the spherical aberration correction function is used,
EDS analysis can be performed with the spatial resolution of about 0.2 nm.
20
[0084]
In the above-described method for identifying each of the layers, first, since the
base steel sheet in the entire region is identified, then the insulation coating in a
remainder is identified, and finally the remainder is determined as the intermediate layer,
and also the precipitate is identified, in the case of a grain-oriented electrical steel sheet
which satisfies the configuration of the present embodiment, there is no unidentified
25 region other than each of the above-described layers in the entire region.
32
[0085]
(Insulation coating)
The insulation coating is a vitreous insulation coating formed by applying a
solution mainly composed of a phosphate and colloidal silica (Si02) to the surface of the
5 intermediate layer and baking it. Alternatively, a solution mainly composed of alumina
sol and boric acid may be applied and baked to form the insulation coating.
This insulation coating can provide high surface tension to the base steel sheet.
The insulation coating constitutes, for example, the outermost surface of the grainoriented
electrical steel sheet.
10 [0086]
The average thickness of the insulation coating is preferably 0.1 to 10 ~m.
When the average thickness of the insulation coating is less than 0.1 ~m, the coating
adhesion of the insulation coating may not be improved, and it may be difficult to apply
the required surface tension to the steel sheet. Therefore, the average thickness is
15 preferably 0.1 ~m or more, and more preferably 0.5 ~m or more on average.
[0087]
When the average thickness of the insulation coating is more than 10 ~m, cracks
may occur in the insulation coating at the stage of forming the insulation coating.
Therefore, the average thickness is preferably 10 ~m or less, and more preferably 5 ~m
20 or less on average.
[0088]
In consideration of recent environmental problems, an average Cr concentration
in the insulation coating is preferably limited to less than 0.10 atomic%, and more
preferably limited to less than 0.05 atomic% as the chemical composition.
25 [0089]
33
(Strain region)
The strain region formed on the base steel sheet will be described with reference
to FIGS. 3 and 4.
FIG. 3 is a schematic view showing a cross section of a plane parallel to the
5 rolling direction and the sheet thickness direction, and is a view including a strain region
D formed on a surface of the base steel sheet 1. As shown in FIG. 3, an intermediate
layer 4 is disposed to be in contact with the base steel sheet 1, an insulation coating 3 is
disposed to be in contact with the intermediate layer 4, and the strain region D is formed
on the surface of the base steel sheet 1. Since the intermediate layer 4 has a smaller
10 thickness than those of the other layers, the intermediate layer 4 is represented by a line
in FIG. 3.
[0090]
Here, a center of the strain region means a center between end portions of the
strain region in the rolling direction when a plane parallel to the rolling direction and the
15 sheet thickness direction is seen in cross section, and for example, when a distance
between the end portions of the strain regions in the rolling direction is 40 ~m, the center
of the strain regions is located at a distance of 20 ~m from each of the end portions. In
the cross-sectional view of FIG. 3, a center c of the strain region is indicated by a point
located at an equal distance from an end portion e and an end portion e' of the strain
20 region D.
[0091]
In the example shown in FIG. 3, the insulation coating on the strain region D
formed on the base steel sheet is a region of the insulation coating 3 interposed between
the end portion e and the end portion e'.
25 [0092]
34
The end portion e or the end portion e' of the strain region D shown in FIG. 3
can be determined, for example, by a confidential index (CI) value map of electron
backscatter diffraction (EBSD). That is, since crystal lattices are strained in a region in
which the strain is accumulated by the radiation of the electron beam, a CI value is
5 different from that in a non-irradiation region. Therefore, for example, the CI value
map of the EBSD in the region including both the irradiation region and the nonirradiation
region is acquired, and the region in the map is divided into a region in which
the CI value is equal to or higher than a critical value and a region in which the CI value
is less than the critical value with an arithmetic mean value of the upper limit value and
10 the lower limit value (excluding measurement noise) of the CI value in the map as the
critical value. Then, one of the regions is defined as the strain region (the irradiation
region), and the other region is defined as a region (the non-irradiation region) other than
the strain region. Thus, the strain region can be identified.
15
20
[0093]
FIG. 4 is a schematic view showing the cross section of the plane parallel to the
rolling direction and the sheet thickness direction, and is an enlarged view of a range A
surrounded by a broken line in FIG. 3. FIG. 4 shows a range including a central portion
C of the strain region D.
[0094]
The central portion of the strain region is a region including the center of the
strain region and having a width of 10 ~m in the rolling direction. In FIG. 4, the central
portion C of the strain region D is shown surrounded by a straight line m and a straight
line m'. The straight line m and the straight line m' are straight lines perpendicular to
the rolling direction of the base steel sheet 1 and parallel to each other, and have an
25 interval of 10 ~m. In the example of FIG. 4, distances from the straight line m and the
35
5
10
straight line m' to the center c of the strain region D are equal.
More preferably, positions of the center of the strain region and the center of the
central portion of the strain region coincide with each other in the rolling direction.
[0095]
A width of the strain region D which is the distance between the end portion e
and the end portion e' is preferably 10 ~m or more, and more preferably 20 ~m or more.
The width of the strain region D is preferably 500 ~m or less, and more preferably 100
~m or less.
[0096]
In the grain -oriented electrical steel sheet according to the present embodiment,
it is more preferable that M2P 4013 is present in the insulation coating at the central
portion of the strain region. M means at least one or both of Fe and Cr.
In the example shown in FIG. 4, a precipitate of M2P4013 is present in the
insulation coating 3 of the central portion C of the strain region D. In FIG. 4, the
15 precipitate is referred to as a region 5. Further, a region 6 containing a precipitate of an
20
amorphous phosphorus oxide is present around the region 5 of FIG. 4. In the insulation
coating 3, regions other than the region 5 and the region 6 include a matrix phase 7 or
voids 8 of the insulation coating.
[0097]
The region 5 may be composed of only the precipitate of M2P4013, or may be a
region containing the precipitate of M2P 4013 and other precipitates. Further, the region
6 may be composed of only the precipitate of the amorphous phosphorus oxide, or may
be a region containing the precipitate of the amorphous phosphorus oxide and other
precipitates.
25 [0098]
36
M2P 4013 is a phosphorus oxide, for example, Fe2P 4013 or Cr2P 4013, or (Fe, Cr)
The region 6 may be formed in the vicinity of the surface of the insulation
coating 3.
5 [0099]
The matrix phase 7 of the insulation coating contains P, Si, and 0 as a
composition.
[0100]
The precipitate of M2P4013, the precipitate of the amorphous phosphorus oxide,
10 and the like can be discriminated by a method for analyzing the pattern of the electron
beam diffraction.
This identification may be performed using a power diffraction file (PDF) of the
international centre for diffraction data (ICDD). Specifically, when the precipitate is
M2P4013, a diffraction pattern of PDF:01-084-1956 appears, and when the precipitate is
15 M2P207 which is present in the conventional insulation coating, a diffraction pattern of
PDF:00-048-0598 appears. When the precipitate is the amorphous phosphorus oxide,
the diffraction pattern is a halo pattern.
[0101]
In the grain -oriented electrical steel sheet according to the present embodiment,
20 due to the presence of M2P 4013 in the insulation coating of the central portion in the
strain region, good adhesion of the insulation coating can be ensured even when the
strain region is formed with an energy density at which a good iron loss reduction effect
can be obtained.
[0102]
25 In the grain -oriented electrical steel sheet according to the present embodiment,
37
as shown in FIG. 5, in the cross-sectional view of the strain region in the plane parallel to
the rolling direction and the sheet thickness direction, when an entire length of the
observation field of view in a direction orthogonal to the sheet thickness direction is Lz,
and a total of void lengths Lct (L1 to L4 in the example of FIG. 5) in the direction
5 orthogonal to the sheet thickness direction is LLct, and a line segment ratio X of a void
region in which the voids are present is defined by the following Equation 1, more
preferably, the line segment ratio X is 20% or less.
10
[0103]
X=(LLct/Lz)x100 (Equation 1)
With such a configuration, peeling of the insulation coating starting from the
void is curbed, and an effect of improving the adhesion of the insulation coating can be
obtained.
[0104]
The void length Lct can be identified by the following method. The insulation
15 coating identified by the above-described method is observed by the TEM (the bright
field image). In the bright field image, a white region is a void. Whether or not the
white region is the void can be clearly discriminated by the above-described TEM-EDS.
On the observation field of view (the entire length Lz), a region which is the void and a
region which is not the void in the insulation coating are binarized, and the void length Lct
20 in the direction orthogonal to the sheet thickness direction can be obtained by an image
analysis.
Here, in the example of FIG. 5, the total LLct of the lengths Lct of the voids 8 are
LLct=Ll +L2+L3+L4. As shown in FIG. 5, when the voids 8 overlap in the sheet
thickness direction, a value obtained by subtracting a length of an overlapping portion
25 from a length of the overlapping voids Lct is defined as the void length. In FIG. 5, a
38
length of the two voids 8 which overlap when seen in the sheet thickness direction is L4
which is obtained by subtracting the overlapping length.
[0105]
The line segment ratio X is more preferably 10% or less from the viewpoint of
5 improving the adhesion of the insulation coating. The lower limit of the line segment
ratio X is not particular! y limited and may be 0%.
In binarization of an image for performing the image analysis, the image may be
binarized by manually coloring voids in a structure photograph based on the abovedescribed
void discrimination result.
10 [0106]
15
The observation field of view may be the above-described central portion of the
strain region. That is, the entire length Lz of the observation field of view may be set to
101-1m.
[0107]
For the line segment ratio X of the void, the line segment ratio of the void is
measured at three points in the strain region with an interval of 50 mm or more in the
direction perpendicular to the rolling direction and the sheet thickness direction of the
base steel sheet, and an arithmetic mean value of the line segment ratios is set as the line
segment ratio X.
20 [0108]
In the grain -oriented electrical steel sheet according to the present embodiment,
more preferably, the strain region Dis continuously or discontinuously provided when
seen in a direction perpendicular to the plate surface of the base steel sheet 1. The fact
that the strain region Dis continuously provided means that the strain region Dis formed
25 by 5 mm or more in the direction intersecting the rolling direction of the base steel sheet
39
1. The fact that the strain region D is discontinuous! y provided means that a pointshaped
strain region D or an intermittent linear strain region D of 5 mm or less is formed
in the direction intersecting the rolling direction of the base steel sheet 1.
With such a configuration, an effect in which the magnetic domain refining
5 effect can be stably obtained can be obtained.
[0109]
In the grain -oriented electrical steel sheet according to the present embodiment,
more preferably, a ratio ofM2P4013 in the insulation coating of the central portion is 10%
or more and 60% or less in terms of an area ratio in the cross-sectional view of the plane
10 parallel to the rolling direction and the sheet thickness direction.
The area ratio is preferably 20% or more, and more preferably 30% or more.
The area ratio is preferably 50% or less, and more preferably 40% or less. With such a
configuration, the effect of improving the adhesion of the insulation coating can be
obtained.
15 [0110]
The area ratio of M2P 4013 in the insulation coating of the central portion can be
calculated by identifying the precipitate with the above-described method and then
identifying the precipitate of M2P4013 according to the analysis of the beam diffraction
pattern. The area ratio of M2P 4013 in the insulation coating of the central portion is a
20 ratio of a total cross-sectional area of M2P 4013 in the same cross section to the entire
cross-sectional area of the insulation coating of the central portion including the
precipitates or the voids. The cross-sectional areas may be calculated by image analysis
or may be calculated from cross-sectional photographs.
[0111]
25 In the grain -oriented electrical steel sheet according to the present embodiment,
40
5
more preferably, the area ratio of the amorphous phosphorus oxide region in the
insulation coating of the central portion is 1% or more and 60% or less in the crosssectional
view of the plane parallel to the rolling direction and the sheet thickness
direction.
When the area ratio of the amorphous phosphorus oxide region is 1% or more,
local stress in the insulation coating is relaxed. Further, when the area ratio of the
amorphous phosphorus oxide region is 60% or less, an effect in which the tension of the
insulation coating is not lowered can be obtained.
The area ratio of the amorphous phosphorus oxide region is more preferably 5%
10 or more, and the area ratio of the amorphous phosphorus oxide region is more preferably
15
20
40% or less. The area ratio of the amorphous phosphorus oxide region in the insulation
coating of the central portion can be measured by the same method as that in the area
ratio of M2P 4Q13 in the insulation coating of the central portion.
[0112]
In the above-described cross-sectional view, as described above, the strain
region Din the base steel sheet 1 of the grain-oriented electrical steel sheet according to
the present embodiment can be discriminated by the confidential index (CI) value map of
the electron backscatter diffraction (EBSD).
[0113]
Regarding the grain -oriented electrical steel sheet according to the present
embodiment, a component composition of the base steel sheet is not particularly limited.
However, since the grain-oriented electrical steel sheet is manufactured through various
processes, there are component compositions of material steel pieces (slabs) and base
steel sheets which are preferable for manufacturing the grain-oriented electrical steel
25 sheet according to the present embodiment. Such component compositions will be
41
described below.
Hereinafter, % relating to the component composition of the material steel piece
and the base steel sheet means mass% with respect to a total mass of the material steel
piece or the base steel sheet.
5 [0114]
(Component composition of base steel sheet)
The base steel sheet of the grain -oriented electrical steel sheet according to the
present embodiment contains, for example, Si: 0.8 to 7.0%, and is limited to C: 0.005%
or less, N: 0.005% or less, a total amount of S and Se: 0.005% or less, and acid-soluble
10 Al: 0.005% or less, and a remainder thereof is composed of Fe and impurities.
[0115]
Si: 0.8% or more and 7.0% or less
Silicon (Si) increases electrical resistance of the grain-oriented electrical steel
sheet and reduces the iron loss. The lower limit of the Si content is preferably 0.8% or
15 more, and more preferably 2.0% or more. On the other hand, when the Si content
exceeds 7.0%, the saturation magnetic flux density of the base steel sheet decreases, and
thus it may be difficult to reduce a size of an iron core. Therefore, the upper limit of the
Si content is preferably 7.0% or less.
20
[0116]
C: 0.005% or less
Since carbon (C) forms a compound in the base steel sheet and deteriorates the
iron loss, it is preferable to reduce an amount thereof. The C content is preferably
limited to 0.005% or less. The upper limit of the C content is preferably 0.004% or less,
and more preferably 0.003% or less. Since it is more preferable to reduce the amount of
25 C, the lower limit includes 0%. However, when the amount of Cis reduced to less than
42
5
0.0001%, the manufacturing cost will increase significantly. Thus, 0.0001% is a
practical lower limit in manufacturing.
[0117]
N: 0.005% or less
Since nitrogen (N) forms a compound in the base steel sheet and deteriorates the
iron loss, it is preferable to reduce an amount thereof. TheN content is preferably
limited to 0.005% or less. The upper limit of the N content is preferably 0.004% or
less, and more preferably 0.003% or less. Since it is more preferable to reduce the
amount of N, the lower limit may be 0%.
10 [0118]
Total amount of S and Se: 0.005% or less
Since sulfur (S) and selenium (Se) form a compound in the base steel sheet and
deteriorate the iron loss, it is preferable to reduce an amount thereof. The total of one or
both of Sand Se is preferably limited to 0.005% or less. The total amount of Sand Se
15 is preferably 0.004% or less, and more preferably 0.003% or less. Since it is more
preferable to reduce the amounts of S or Se, the lower limit may be 0%.
[0119]
Acid-soluble Al: 0.005% or less
Since acid-soluble Al (acid-soluble aluminum) forms a compound in the base
20 steel sheet and deteriorates the iron loss, it is preferable to reduce an amount thereof.
25
The acid-soluble Al is preferably 0.005% or less. The acid-soluble Al is preferably
0.004% or less, and more preferably 0.003% or less. Since it is more preferable to
reduce the amount of acid-soluble Al, the lower limit may be 0%.
[0120]
The remainder in the component composition of the base steel sheet is
43
5
composed of Fe and impurities. The "impurities" refer to those mixed in from ore,
scrap, manufacturing environment, and the like as raw materials when steel is
manufactured industrially.
[0121]
Further, the base steel sheet of the grain-oriented electrical steel sheet according
to the present embodiment may contain at least one selected from, for example, Mn
(manganese), Bi (bismus), B (boron), Ti (titanium), Nb (niobium), V (vanadium), Sn
(tin), Sb (antimony), Cr (chromium), Cu (copper), P (phosphorus), Ni (nickel), and Mo
(molybdenum) as a selective element in place of part of Fe which is the remainder in an
10 extent in which characteristics thereof are not impaired.
[0122]
An amount of the above-described selective element may be, for example, as
follows. The lower limit of the selected element is not particularly limited, and the
lower limit may be 0%. Further, even when the selective element is contained as
15 impurities, the effect of the grain-oriented electrical steel sheet according to the present
20
25
embodiment is not impaired.
Mn: 0% or more and 1.00% or less,
Bi: 0% or more and 0.010% or less,
B: 0% or more and 0.008% or less,
Ti: 0% or more and 0.015% or less,
Nb: 0% or more and 0.20% or less,
V: 0% or more and 0.15% or less,
Sn: 0% or more and 0.30% or less,
Sb: 0% or more and 0.30% or less,
Cr: 0% or more and 0.30% or less,
44
5 [0123]
Cu: 0% or more and 0.40% or less,
P: 0% or more and 0.50% or less,
Ni: 0% or more and 1.00% or less, and
Mo: 0% or more and 0.10% or less.
The above-described chemical composition of the base steel sheet may be
measured by a general analysis method. For example, a steel component may be
measured using an inductively coupled plasma-atomic emission spectrometry (ICPAES).
C and S may be measured using a combustion-infrared absorption method, N
10 may be measured using an inert gas melting-thermal conductivity method, and 0 may be
measured using an inert gas melting-non-dispersive infrared absorption method.
[0124]
The base steel sheet of the grain -oriented electrical steel sheet according to the
present embodiment preferably has a crystal grain texture developed in an { 110} <00 1 >
15 orientation. The { 110} <00 1 > orientation means a crystal orientation (a Goss
orientation) in which a { 110} surface is aligned parallel to the surface of the steel sheet
and an <100> axis is aligned in the rolling direction. In the grain-oriented electrical
steel sheet, the magnetic characteristics are preferably improved by controlling the
crystal orientation of the base steel sheet to the Goss orientation.
20 The texture of the base steel sheet may be measured by a general analysis
method. For example, it may be measured by an X-ray diffraction method (a Laue
method). The Laue method is a method in which a steel sheet is vertically irradiated
with an X-ray beam and transmitted or reflected diffraction spots are analyzed. The
crystal orientation of a place to which the X-ray beam is radiated can be identified by
25 analyzing the diffraction spots. When the diffraction spots are analyzed at a plurality of
45
5
locations by changing an irradiation position, the crystal orientation distribution at each
of the irradiation positions can be measured. The Laue method is a method suitable for
measuring the crystal orientation of a crystal structure having coarse crystal grains.
[0125]
Each of the layers of the grain-oriented electrical steel sheet according to the
present embodiment is observed and measured as follows.
[0126]
A test piece is cut out from the grain-oriented electrical steel sheet, and a coating
structure of the test piece is observed with a scanning electron microscope or a
10 transmission electron microscope.
[0127]
Specifically, first, the test piece is cut out so that a cutting direction is parallel to
the sheet thickness direction (in detail, the test piece is cut out so that a cut surface is
parallel to the sheet thickness direction and perpendicular to the rolling direction), and a
15 cross-sectional structure of the cut surface is observed by the SEM at a magnification at
which each of the layers is included in the observation field of view. It is possible to
infer how many layers the cross-sectional structure includes by observing with a
backscattered electron composition image (the COMPO image).
20
[0128]
In order to identify each of the layers in the cross-sectional structure, a line
analysis in the sheet thickness direction is performed, and a quantitative analysis of the
chemical composition of each of the layers is performed using an energy dispersive Xray
spectroscopy (SEM-EDS).
The elements to be quantitatively analyzed are five elements, Fe, Cr, P, Si, and
25 0. The "atomic%" described below is not an absolute value of atomic%, but a relative
46
5
value calculated based on the X-ray intensity corresponding to the five elements. In the
following, specific numerical values when the relative values are calculated using the
above-described device or the like are shown.
[0129]
First, the base steel sheet, the intermediate layer, and the insulation coating are
identified as follows based on the observation results of the COMPO image and the
quantitative analysis results of the SEM-EDS. That is, when there is a region in which
the Fe content is 80 atomic% or more and a 0 content is less than 30 atomic% excluding
the measurement noise, and a line segment (a thickness) on the scanning line of the line
10 analysis corresponding to this region is 300 nm or more, this region is determined as the
base steel sheet, and the regions excluding the base steel sheet are determined as the
intermediate layer and the insulation coating.
[0130]
As a result of observing the region excluding the base steel sheet identified
15 above, when there is a region in which a P content is 5 atomic% or more and the 0
content is 30 atomic% or more excluding the measurement noise, and also the line
segment (the thickness) on the scanning line of the line analysis corresponding to this
region is 300 nm, this region is determined as the insulation coating.
20
[0131]
When the region that is the above-described insulation coating is identified,
precipitates or inclusions contained in the film are not included in targets for
determination, and the region which satisfies the above quantitative analysis result as the
matrix phase is determined to be the insulation coating. For example, when it is
confirmed from the COMPO image or the line analysis result that precipitates or
25 inclusions are present on the scanning line of the line analysis, determination is made
47
based on the quantitative analysis results as the matrix phase without this region being
included in the targets. The precipitates or inclusions can be distinguished from the
matrix phase by a contrast in the COMPO image, and can be distinguished from the
matrix phase by an amount of constituent elements present in the quantitative analysis
5 results.
[0132]
When there is the region excluding the base steel sheet and the insulation
coating identified above, and the line segment (the thickness) on the scanning line of the
line analysis corresponding to this region is 300 nm or more, this region is determined as
10 the intermediate layer. The intermediate layer may satisfy an average Si content of 20
atomic% or more and an average 0 content of 30 atomic% or more as an overall average
(for example, the arithmetic mean of the atomic% of each of the elements measured at
each of measurement points on the scanning line). The quantitative analysis results of
the intermediate layer are quantitative analysis results as the matrix phase, which do not
15 include analysis results of the precipitates or inclusions contained in the intermediate
layer.
[0133]
Further, in the region determined as the insulation coating above, a region in
which the total amounts of Fe, Cr, P and 0 is 70 atomic% or more and the Si content is
20 less than 10 atomic% excluding the measurement noise is determined as the precipitate.
25
[0134]
As described above, the crystal structure of the above-described precipitate can
be identified from a pattern of electron beam diffraction.
[0135]
Although M2P207 may be present in the conventional insulation coating, the
48
crystal structure of M2P207 (M is at least one or both of Fe and Cr) can be identified and
discriminated from the pattern of the electron beam diffraction.
[0136]
The identification of each of the layers and the measurement of the thickness by
5 the above-described COMPO image observation and SEM-EDS quantitative analysis are
performed at five or more locations with different observation fields of view. An
arithmetic mean value is obtained from values excluding a maximum value and a
minimum value among the thicknesses of the layers obtained at five or more locations in
total, and this average value is used as the thickness of each of the layers. However,
10 preferably, the thickness of the oxide film which is the intermediate layer is measured at
a location at which it can be determined that it is an external oxidation region and not an
internal oxidation region while a texture form is observed, and an average value thereof
is obtained.
Also, in the strain region, the average thickness of the intermediate layer and the
15 average thickness of the insulation coating can be calculated by the same method.
[0137]
When there is a layer in which the line segment (the thickness) on the scanning
line of the line analysis is less than 300 nm in at least one of the above-described five or
more observation fields of view, a corresponding layer is observed in detail with the
20 TEM, and the identification of the corresponding layer and the measurement of the
thickness are performed by the TEM.
[0138]
More specifically, a test piece including a layer to be observed in detail using the
TEM is cut out by focused ion beam (FIB) processing so that a cutting direction is
25 parallel to the sheet thickness direction (specifically, the test piece is cut out so that a cut
49
surface is parallel to the sheet thickness direction and perpendicular to the rolling
direction), and the cross-sectional structure of this cut surface (a bright field image) is
observed by scanning-TEM (STEM) at a magnification at which the corresponding layer
is included in the observation field of view. When each of the layers is not included in
5 the observation field of view, the cross-sectional structure is observed in a plurality of
continuous fields of view.
[0139]
In order to identify each of the layers in the cross-sectional structure, the line
analysis is performed in the sheet thickness direction using the TEM-EDS, and the
10 quantitative analysis of the chemical composition of each of the layers is performed.
The elements to be quantitatively analyzed are five elements, Fe, Cr, P, Si, and 0.
[0140]
Each of the layers is identified and the thickness of each of the layers is
measured based on the bright field image observation results by the TEM and the
15 quantitative analysis results of the TEM-EDS described above. The method for
identifying each of the layers and the method for measuring the thickness of each of the
layers using the TEM may be performed according to the above-described method using
the SEM.
20
25
[0141]
Specifically, the region in which the Fe content is 80 atomic% or more and the 0
content is less than 30 atomic% excluding the measurement noise is determined as the
base steel sheet, and the regions excluding the base steel sheet are determined as the
intermediate layer and the insulation coating.
[0142]
In the region excluding the base steel sheet identified above, the region in which
50
the P content is 5 atomic% or more and the 0 content is 30 atomic% or more excluding
the measurement noise is determined as the insulation coating. When the abovedescribed
region which is the insulation coating is determined, the precipitates or
inclusions contained in the insulation coating are not included in targets for
5 determination, and the region which satisfies the above quantitative analysis result as the
matrix phase is determined as the insulation coating.
[0143]
The region excluding the base steel sheet and the insulation coating identified
above is determined as the intermediate layer. The intermediate layer may satisfy an
10 average Si content of 20 atomic% or more and an average 0 content of 30 atomic% or
more as an average of the entire intermediate layer. The above-described quantitative
analysis results of the intermediate layer do not include the analysis results of the
precipitates or inclusions contained in the intermediate layer and are the quantitative
analysis results as the matrix phase.
15 [0144]
Further, in the region determined as the insulation coating above, a region in
which the total amounts of Fe, Cr, P and 0 is 70 atomic% or more and the Si content is
less than 10 atomic% excluding the measurement noise is determined as the precipitate.
As described above, a crystal structure of the precipitate can be identified from the
20 pattern of beam diffraction.
[0145]
For the intermediate layer and the insulation coating identified above, the line
segment (the thickness) is measured on the scanning line of the above-described line
analysis. When the thickness of each of the layers is 5 nm or less, it is preferable to use
25 a TEM having a spherical aberration correction function from the viewpoint of spatial
51
resolution. Further, when the thickness of each of the layers is 5 nm or less, a point
analysis may be performed in the sheet thickness direction at intervals of, for example, 2
nm, the line segment (the thickness) of each of the layers may be measured, and this line
segment may be adopted as the thickness of each of the layers. For example, when the
5 TEM having the spherical aberration correction function is used, an EDS analysis can be
performed with a spatial resolution of about 0.2 nm.
[0146]
The observation and measurement with the TEM was carried out at five or more
locations with different observation fields of view, and an arithmetic mean value is
10 calculated from values obtained by excluding the maximum and minimum values from
the measurement results obtained at five or more locations in total, and the average value
is adopted as the average thickness of the corresponding layer. Also, in the strain
region, the average thickness of the intermediate layer and the average thickness of the
insulation coating can be calculated by the same method.
15 [0147]
In the grain -oriented electrical steel sheet according to the above-described
embodiment, since the intermediate layer is present to be in contact with the base steel
sheet and the insulation coating is present to be in contact with the intermediate layer,
when each of the layers is identified by the above-described determination standards,
20 there is no layer other than the base steel sheet, the intermediate layer, and the insulation
coating. However, the above-described M2P 4013 region or amorphous phosphorus
oxide region may be present in a layer shape.
[0148]
Further, the above-described contents of Fe, P, Si, 0, Cr, and the like contained
25 in the base steel sheet are the determination standards for identifying the base steel sheet,
52
the intermediate layer, and the insulation coating and obtaining the thickness thereof.
[0149]
When the coating adhesion of the insulation coating of the grain-oriented
electrical steel sheet according to the above-described embodiment is measured, it can be
5 evaluated by performing a bending adhesion test. Specifically, a flat sheet-shaped test
piece of 80 mmx80 mm is wound around a round bar having a diameter of 20 mm and is
then stretched flat. Then, an area of the insulation coating which is not peeled off from
the electrical steel sheet is measured, and a value obtained by dividing the area which is
not peeled off by an area of the steel sheet is defined as a coating residual area ratio(%)
10 to evaluate the coating adhesion of the insulation coating. For example, it may be
calculated by placing a transparent film with a 1 mm grid scale on the test piece and
measuring the area of the insulation coating which is not peeled off.
[0150]
The iron loss (W 17 ;so) of the grain -oriented electrical steel sheet is measured
15 under conditions of an AC frequency of 50 hertz and an induced magnetic flux density of
1.7 tesla.
[Examples]
[0151]
Next, although the effect of one aspect of the present invention will be described
20 in more detail by examples, the conditions in the examples are one condition example
adopted for confirming feasibility and effect of the present invention, and the present
invention is not limited to this one condition example.
In the present invention, various conditions can be adopted as long as the gist of
the present invention is not deviated and the object of the present invention is achieved.
25 [0152]
53
(Experimental example 1)
The material steel pieces having the component composition shown in Table 1
were soaked at 1150°C for 60 minutes and then subjected to hot rolling to obtain a hotrolled
steel sheet having a thickness of 2.3 mm. Next, the hot-rolled steel sheet was
5 subjected to hot-band annealing in which it is held at 1120°C for 200 seconds,
immediately cooled, held at 900°C for 120 seconds, and then rapidly cooled. The hotband
annealed steel sheet was pickled and then subjected to cold rolling to obtain a coldrolled
steel sheet having a final sheet thickness of 0.23 mm.
10
[0153]
[Table 1]
Material Component composition (mass%)
Steel piece Si c Al Mn s N
A 3.25 0.052 0.029 0.110 0.007 0.008
[0154]
This cold-rolled steel sheet (hereinafter, referred to as a "steel sheet") was
subjected to decarburization annealing in which it is held in an atmosphere of
15 hydrogen:nitrogen of75%:25% at 850°C for 180 seconds. The steel sheet after the
decarburization annealing was subjected to nitriding annealing in which it is held in a
mixed atmosphere of hydrogen, nitrogen and ammonia at 750°C for 30 seconds to adjust
a nitrogen content of the steel sheet to 230 ppm.
20
[0155]
An annealing separator containing alumina as a main component is applied to
the steel sheet after the nitriding annealing, and then the steel sheet is heated to 1200°C at
a heating rate of 10 °Cihour in a mixed atmosphere of hydrogen and nitrogen for final
54
5
annealing. Then, the steel sheet was subjected to purification annealing in which it is
held at 1200°C for 20 hours in a hydrogen atmosphere. Then, the steel sheet was freely
cooled to prepare a base steel sheet having a smooth surface.
[0156]
The intermediate layer was formed on the produced base steel sheet under the
conditions shown in Table 2.
A solution mainly composed of a phosphate and colloidal silica was applied to
the surface of the base steel sheet on which the intermediate layer was formed under the
conditions shown in Table 2, and the insulation coating was formed under the conditions
10 shown in Table 2.
55
[0157]
[Table 2]
Formation of intermediate layer Applying condition
Formation of insulation coating
Heating Soaking Cooling
Annealing Holding Dew Applying Leaving
Oxidation
Heating
Temperature Oxidation
Holding
Oxidation
Cooling
temperature time point amount time rate time rate
(oC) (sec) (oC) (g/m2) (sec)
degree
(°C/sec)
(oC) degree
(sec)
degree
(°C/sec)
Example 1 800 30 -10 4.8 30 0.110 15 850 0.110 120 0.030 20
Example 2 890 30 -5 5.0 20 0.100 20 910 0.090 90 0.040 15
Example 3 1050 15 2 4.3 20 0.200 10 730 0.220 100 0.025 30
Example 4 950 30 -12 5.3 30 0.160 16 890 0.150 130 0.020 40
Example 5 1100 10 0 6.8 35 0.130 20 780 0.150 110 0.030 20
Example 6 930 20 -10 5.5 40 0.220 18 810 0.090 80 0.005 18
Example 7 1000 20 -3 3.8 25 0.008 25 700 0.220 150 0.010 16
Example 8 880 30 -9 6.3 30 0.140 10 930 0.150 70 0.040 20
Example 9 850 60 6 4.6 70 0.210 20 870 0.190 160 0.030 30
Example 10 900 7 -5 5.6 40 0.150 16 790 0.130 90 0.020 20
Example 11 1050 35 -4 4.1 320 0.110 20 860 0.090 120 0.060 45
Example 12 880 60 -12 3.9 60 0.130 40 800 0.080 200 0.020 30
Example 13 700 150 -16 6.2 45 0.200 15 1000 0.160 50 0.030 20
Example 14 800 60 10 4.2 20 0.330 20 880 0.280 80 0.040 40
Example 15 750 8 -10 5.0 50 0.150 45 920 0.230 100 0.020 30
Example 16 1000 30 -10 5.3 30 0.1 15 850 0.11 150 0.03 15
Example 17 1100 30 -5 6.3 20 0.2 20 900 0.15 100 0.02 30
Comparative 950 20 -12 4.8 40 0.110 23 860 0.170 120 0.030 36
example 1
Comparative 1050 50 -14 5.6 55 0.160 18 890 0.210 90 0.020 30
example 2
Comparative 850 7 6 4.8 120 0.320 35 850 0.140 100 0.060 25
example 3
56
[0158]
Next, under the conditions shown in Table 3, the strain region was formed by
radiating an electron beam, and the grain -oriented electrical steel sheets according to
5 each of experimental examples were obtained. In Table 3, the "temperature at central
portion of the strain region" means a temperature at the central portion of the strain
region in the rolling direction of the base steel sheet and the extension direction of the
strained region.
[0159]
10 [Table 3]
Formation of strain region
Temperature at Acceleration Beam
Beam
Radiation Scanning
radiation
central portion voltage current
diameter
interval speed
of strain region ( kV) (rnA)
()lm)
(mm) (m/sec)
Example 1 900 60 15.00 250 4 20
Example 2 1030 120 2.50 200 5 15
Example 3 1100 160 2.60 150 5 15
Example 4 1330 200 3.20 180 5 20
Example 5 1450 250 1.20 200 5 15
Example 6 1000 40 10.00 160 5 10
Example 7 1150 260 0.28 120 6 12
Example 8 1260 150 2.50 520 4 7
Example 9 980 100 2.00 180 6 9
Example 10 1100 150 5.00 210 6 18
Example 11 1020 50 6.50 220 5 11
Example 12 1170 130 7.50 190 7 19
Example 13 1420 90 16.00 180 6 25
Example 14 1130 70 11.00 200 5 23
Example 15 1390 120 8.00 190 5 20
Example 16 1500 160 8.00 180 5 23
Example 17 2000 200 8.00 160 6 26
Comparative
780 60 5.20 230 6 30
example 1
Comparative
790 130 1.20 200 6 15
example 2
Comparative
750 100 1.50 520 7 11
example 3
[0160]
A test piece was cut out from each of the grain-oriented electrical steel sheets,
57
the coating structure of each of test pieces was observed with a scanning electron
microscope (SEM) or a transmission electron microscope (TEM), and the identification
of the strain region and the central portion of the strain region, the measurement of the
thickness of the intermediate layer, and the measurement of the thickness of the
5 insulation coating were performed based on the observation and measurement method
according to the above-described embodiment. In addition, the precipitate was
identified. The specific method thereof is as described above.
[0161]
Table 4 shows the results of the presence or absence of M2P 4013 in the insulation
10 coating on the strain region. As can be seen from Table 4, in the grain-oriented
electrical steel sheet produced by the manufacturing method of the present embodiment,
M2P 4013 is present in the insulation coating on the strain region.
[0162]
[Table 4]
Presence or absence of Iron loss
phosphorus oxide Adhesion Wn/Wso
(M2P4013) (W/kg)
Example 1 Presence Excellent 0.74
Example 2 Presence Excellent 0.75
Example 3 Presence Excellent 0.73
Example 4 Presence Excellent 0.72
Example 5 Presence Excellent 0.74
Example 6 Presence Excellent 0.78
Example 7 Presence Excellent 0.78
Example 8 Presence Excellent 0.77
Example 9 Presence Excellent 0.75
Example 10 Presence Excellent 0.77
Example 11 Presence Excellent 0.74
Example 12 Presence Excellent 0.73
Example 13 Presence Excellent 0.76
Example 14 Presence Excellent 0.74
Example 15 Presence Excellent 0.76
Example 16 Presence Excellent 0.75
Example 17 Presence Excellent 0.74
58
Comparative
Absence Poor 0.83
example 1
Comparative
Absence Poor 0.84
example 2
Comparative
Absence Poor 0.83
example 3
[0163]
Next, a test piece of 80 mmx80 mm was cut out from the grain-oriented
electrical steel sheet on which the insulation coating was formed, wound around a round
5 bar having a diameter of 20 mm, and then stretched flat. Then, the area of the insulation
coating which is not peeled from the electrical steel sheet was measured, and the coating
residual area ratio(%) was calculated. The results thereof are shown in Table 4 as the
adhesion of the film. The adhesion of the insulation coating was evaluated in two
stages. "(Excellent)" means that the coating residual area ratio is 90% or more.
10 "Poor" means that the coating residual area ratio is less than 90%.
As can be seen from Table 4, the grain-oriented electrical steel sheets produced
by the manufacturing method of the present invention have excellent adhesion.
[0164]
In addition, the iron loss of the grain-oriented electrical steel sheet of each of the
15 experimental examples was measured. The results are shown in Table 4.
As can be seen from Table 4, in the grain-oriented electrical steel sheet produced
by the manufacturing method of the present invention, the iron loss was reduced.
[Industrial Applicability]
[0165]
20 According to the present invention, it is possible to provide a method for
manufacturing a grain-oriented electrical steel sheet capable of ensuring good adhesion
of an insulation coating and obtaining a good iron loss reduction effect in grain-oriented
59
5
10
electrical steel sheets which do not have a forsterite film and have strain regions formed
on the base steel sheet. Therefore, it has high industrial applicability.
[Brief Description of the Reference Symbols]
[0166]
1 Base steel sheet
2 Forsterite film
3 Insulation coating
4 Intermediate layer
5 Region containing precipitate of M2P 4Q13
6 Region containing precipitate of amorphous phosphorus oxide
7 Matrix phase of insulation coating
8 Void

WE CLAIMS

1. A method for manufacturing a grain-oriented electrical steel sheet, comprising:
a strain region forming process of irradiating a grain-oriented electrical steel
5 sheet having a base steel sheet, an intermediate layer disposed to be in contact with the
base steel sheet, and an insulation coating disposed to be in contact with the intermediate
layer with an electron beam and forming a strain region which extends in a direction
intersecting a rolling direction of the base steel sheet on a surface of the base steel sheet,
wherein, in the strain region forming process, a temperature of a central portion
10 of the strain region in the rolling direction of the base steel sheet and an extension
direction of the strain region is heated to 800°C or higher and 2000°C or lower.
2. The method for manufacturing a grain-oriented electrical steel sheet according to
claim 1, wherein, in the strain region forming process, the temperature of the central
15 portion of the strain region in the rolling direction of the base steel sheet and the
extension direction of the strain region is heated to 800°C or higher and 1500°C or lower.
3. The method for manufacturing a grain-oriented electrical steel sheet according to
claim 1 or 2, wherein, in the strain region forming process, radiation conditions of an
20 electron beam are,
25
acceleration voltage: 50 kV or more and 350 kV or less,
beam current: 0.3 rnA or more and 50 rnA or less,
beam radiation diameter: 10 ~m or more and 500 ~m or less,
radiation interval: 3 mm or more and 20 mm or less, and
scanning speed: 5 m/sec or more, 80 m/sec or less.
61
5
10
4. The method for manufacturing a grain-oriented electrical steel sheet according to any
one of claims 1 to 3, further comprising an intermediate layer forming process of forming
the intermediate layer on the base steel sheet,
wherein, in the intermediate layer forming process, the base steel sheet is heattreated
to form an intermediate layer under annealing conditions adjusted to,
annealing temperature: 500°C or higher and 1500°C or lower,
holding time: 10 seconds or more and 600 seconds or less, and
dew point: -20°C or higher and soc or lower.
5. The method for manufacturing a grain-oriented electrical steel sheet according to any
one of claims 1 to 4, further comprising an insulation coating forming process of forming
the insulation coating on the base steel sheet on which the intermediate layer is formed,
wherein, in an insulation coating forming process,
15 an insulation coating forming solution is applied to a surface of the base steel
sheet at a coating amount of 2 g/m2 to 10 g!m2
,
a base steel sheet to which the insulation coating forming solution is applied is
left for 3 seconds to 300 seconds,
a base steel sheet to which the insulation coating forming solution is applied is
20 heated at a heating rate of 5 °C/sec or more and 30 °Csec or less in an atmospheric gas
containing hydrogen and nitrogen and having an oxidation degree of PH20/PH2 adjusted
to 0.001 or more and 0.3 or less,
the heated base steel sheet is soaked in a temperature range of 300°C or higher
and 950°C or lower for 10 seconds or more and 300 seconds or less in an atmospheric
25 gas containing hydrogen and nitrogen and having an oxidation degree of PH20/PH2
62
5
adjusted to 0.001 or more and 0.3 or less, and
the soaked base steel sheet is cooled to 500°C at a cooling rate of 5 °C/sec or
more and 50 °Csec or less in an atmospheric gas containing hydrogen and nitrogen and
having an oxidation degree of PH20/PH2 controlled to 0.001 or more and 0.05 or less.