【DESCRIPTION】
【Invention Title】
GRAIN-ORIENTED ELECTRICAL STEEL SHEET AND METHOD OF
MANUFACTURING THE SAME
【Technical Field】
The present invention relates to a grain-oriented electrical steel sheet and a
method of manufacturing the same.
【Background Art】
A grain-oriented electrical steel sheet is used as a material for an iron core of
an electrical device such as an electric transformer, and a steel sheet, which has
magnetic characteristics with low core loss and high magnetic flux density, is
required to reduce a loss of electric power of the electrical device and improve
efficiency.
In general, the grain-oriented electrical steel sheet refers to a material having
a texture (so-called "Goss texture") oriented in a rolling direction, a {110}<001>
direction through hot rolling, cold rolling, and annealing processes.
In the case of the grain-oriented electrical steel sheet, the more greatly the
{110}<001> direction is oriented in an easy magnetization axis direction of iron, the
better the magnetic characteristics is achieved.
In general, the grain-oriented electrical steel sheet is manufactured by
allowing a slab, which is manufactured by a continuous casting process, to be
subjected to hot rolling, hot rolled plate annealing, cold rolling, decarburizing
annealing, high temperature annealing, planarization annealing, insulation coating,
and laser treatment processes in sequence.
To form uniform grooves 20 in a surface of an electrical steel sheet 10, it is
necessary to radiate continuous high power laser to the surface of the high-speed
electrical steel sheet 10, and form the grooves 20 with accompanying melting of a
base portion caused by the radiation of the laser.
A method of refining magnetic domains is used to improve magnetic
characteristics of the grain-oriented electrical steel sheet, and the magnetic domain
refinement method may be classified into a temporary magnetic domain refinement
method and a permanent magnetic domain refinement method in accordance with
whether an effect of improving magnetic domain refinement is maintained even after
stress removing annealing.
The temporary magnetic domain refinement method is a magnetic domain
refinement technology that refines the magnetic domain by forming a 90° magnetic
domain in order to minimize magnetic elastic energy generated by exerting local
compressive stress on the surface using thermal energy or mechanical energy.
The temporary magnetic domain refinement technology is classified into a
laser magnetic domain refinement method, a ball scratch method, and a magnetic
domain refinement method using plasma or ultrasonic wave in accordance with an
energy source for refining the magnetic domain.
The permanent magnetic domain refinement method, which may maintain an
effect of improving a core loss even after heat treatment, may be classified into an
etching method, a roll method, and a laser method.
The etching method forms a groove in a surface of the steel sheet by an
electrochemical corrosion reaction caused by an acid solution in a solution, and as a
result, the etching method has drawbacks in that it is difficult to control a shape of
the groove, it is difficult to ensure core loss characteristics of a final product because
the groove is formed during an intermediate process (before decarburizing annealing
and high temperature annealing) for producing the steel sheet, and this method is
not environmentally friendly because the acid solution is used.
The permanent magnetic domain refinement method using a roll is a
magnetic domain refinement technology that forms a groove having predetermined
width and depth in the surface of the steel sheet by processing a protrusion shape
on the roll and using a pressing method, and generates recrystallization at a lower
portion of the groove by annealing the steel sheet after forming the groove, but has
drawbacks in that reliability is low such that it is difficult to ensure machining stability
and stable core loss according to a thickness, and processes are complicated.
The permanent magnetic domain refinement method using Q-Switch or pulse
laser forms a groove by evaporation of a material at an irradiated portion at the time
of irradiation, but has drawbacks in that it is difficult to ensure a core loss
improvement rate immediately after forming the groove and before heat treatment,
only a magnetic domain refinement effect caused by the simple groove is maintained
even after the heat treatment, and a conveying speed of the steel sheet cannot be
increased to a high speed.
The permanent magnetic domain refinement method using continuous wave
laser forms a resolidification layer only on a sidewall of the groove at the time of
forming the groove, or cannot uniformly form the resolidification layer on the entire
surface of the groove, such that excessive deformation is maintained at a lower base
portion of the groove, and as a result, this method has drawbacks in that this method
is difficult to be applied to a process before primary recrystallization, and is applied
only to an iron core for a wound core electric transformer which is required to be
subjected to heat treatment.
FIG. 1 illustrates a cross-sectional shape of a groove at the time of forming
an excessively melted portion and a non-uniform resolidification layer. A
technology, which forms an excessively melted portion (a) at a lower side in the
groove and a central portion (b) of the resolidification layer, forms the groove in the
steel sheet at a relatively low speed, and as a result, this technology has drawbacks
in that it is difficult to form a groove in a surface of a grain-oriented electrical steel
sheet surface which moves at a high speed of 0.9 m/s or higher, this technology
cannot be applied to a material for the grain-oriented electrical steel sheet before
primary recrystallization, and the resolidification layer may hinder a growth of the
Goss texture at the time of annealing.
【DISCLOSURE】
【Technical Problem】
An exemplary embodiment of the present invention has been made in an
effort to provide a grain-oriented electrical steel sheet which has a surface formed
with grooves to refine a magnetic domain.
Another exemplary embodiment of the present invention provides a method
of manufacturing a grain-oriented electrical steel sheet, which has a surface formed
with grooves to refine a magnetic domain.
【Technical Solution】
The present invention has also been made in an effort to provide a method of
manufacturing a grain-oriented electrical steel sheet which has a surface formed with
grooves to refine a magnetic domain. An exemplary embodiment of the present
invention provides a grain-oriented electrical steel sheet, which has a surface which
is formed with grooves for a magnetic domain refinement treatment, in which a
scattering alloy layer in the groove is eroded in a Goss texture during a
recrystallization annealing process.
When a thickness of the scattering alloy layer on a bottom surface of the
groove is defined as TB, and a thickness of the scattering alloy layer at a point that is
one-half the distance between any one end of the groove and the bottom surface of
the groove is defined as TL, TB/TL may be 0.2 to 0.8.
A thickness of the scattering alloy layer may be 4% to 12% of a depth of the
groove.
The depth of the groove may be 4% to 11% of a thickness of the electrical
steel sheet.
The groove may be formed diagonally with respect to a width direction of the
electrical steel sheet.
The groove may be formed at an angle greater than 0° and equal to or
smaller than 5° with respect to the width direction of the electrical steel sheet.
Three to six grooves may be intermittently formed in the width direction of the
electrical steel sheet.
Another exemplary embodiment of the present invention provides a method
of manufacturing a grain-oriented electrical steel sheet, the method including:
providing an electrical steel sheet before forming primary recrystallization or after
forming the primary recrystallization; and forming a groove in a surface of the
electrical steel sheet by radiating laser and simultaneously spraying gas onto the
electrical steel sheet, in which energy density Ed and a laser scanning speed Vs of
the radiated laser satisfy the following conditions,
1.0 J/mm2 ≤ Ed ≤ 5.0 J/mm2,
0.0518 mm/μsec ≤ Vs ≤ 0.2 mm/μsec.
Pressure of the sprayed gas may be 0.2 kg/cm2 to 5.0 kg/cm2.
An angle formed between the spray direction of the gas and the laser
radiation direction may be 0° to 50°.
In the radiating of the laser, a laser beam may be radiated on the surface of
the electrical steel sheet at an angle greater than 0° and equal to or smaller than 5°
with respect to a width direction of the electrical steel sheet.
In the radiating of the laser, a movement speed VL of the electrical steel
sheet may be at least 0.9 m/s.
In the radiating of the laser, when a beam length in the width direction of the
electrical steel sheet is dt, and a beam length in a rolling direction of the electrical
steel sheet is L, a light collecting shape of the laser may satisfy the following
condition,
0.20≤ L/dt ≤ 1.0.
The dt may be 50 μm or smaller.
In the radiating of the laser, a scattering alloy layer in which a melted portion
of the electrical steel sheet by the radiation of the laser scatters and is resolidified
may be generated, and when a thickness of the scattering alloy layer on a bottom
surface of the groove is defined as TB, and a thickness of the scattering alloy layer
at a point that is one-half the a distance between any one end of the groove and the
bottom surface of the groove is defined as TL, TB/TL may be 0.2 to 0.8.
A thickness of the scattering alloy layer may be 4% to 12% of a depth of the
groove.
In the radiating of the laser, the laser may be radiated diagonally with respect
to a width direction of the electrical steel sheet.
In the radiating of the laser, the laser may be radiated at an angle greater
than 0° and equal to or smaller than 5° with respect to the width direction of the
electrical steel sheet.
In the radiating of the laser, three to six grooves may be intermittently formed
in the width direction of the electrical steel sheet.
【Advantageous Effects】
According to the method of manufacturing the grain-oriented electrical steel
sheet according to the exemplary embodiment of the present invention, the groove is
formed by radiating a high-speed laser beam, and as a result, it is possible to form a
groove in the steel sheet on which rolling is performed at a high speed of 0.9 m/sec
or higher.
In addition, according to the method of manufacturing the grain-oriented
electrical steel sheet according to the exemplary embodiment of the present
invention, a layer melted by the radiation of the laser and resolidified is uniformly
formed, thereby improving magnetism of a final product.
In addition, according to the method of manufacturing the grain-oriented
electrical steel sheet according to the exemplary embodiment of the present
invention, magnetic domain refinement by the radiation of the laser may be
performed on the electrical steel sheet before primary recrystallization or after the
primary recrystallization.
In addition, according to the method of manufacturing the grain-oriented
electrical steel sheet according to the exemplary embodiment of the present
invention, even though magnetic domain refinement by the radiation of the laser is
performed on the electrical steel sheet before primary recrystallization, an effect of
improving a core loss is maintained even after a subsequent heat treatment process.
【Description of the Drawings】
FIG. 1 is a view illustrating a groove formed in a surface of a steel sheet by a
magnetic domain refinement method according to the related art.
FIG. 2 is a view illustrating shapes of grooves on an XY plane which are
formed in a surface of a steel sheet when laser is radiated on the surface of the steel
sheet.
FIG. 3 is a view illustrating a cross section (YZ plane) of a part 30 of the
continuous groove illustrated in FIG. 2.
【Mode for Invention】
Advantages and features of the present invention and methods of achieving
the advantages and features will be clear with reference to exemplary embodiments
described in detail below together with the accompanying drawings. However, the
present invention is not limited to the exemplary embodiments set forth below, and
may be embodied in various other forms. The present exemplary embodiments are
for rendering the disclosure of the present invention complete and are set forth to
provide a complete understanding of the scope of the invention to a person with
ordinary skill in the technical field to which the present invention pertains, and the
present invention will only be defined by the scope of the claims. Like reference
numerals indicate like elements throughout the specification.
Therefore, in some exemplary embodiments, well-known technologies will
not be specifically described in order to avoid obscuring the present invention.
Unless there are other definitions, all terms used in the present specification
(including technical and scientific terms) have the meanings that those having
ordinary skill in the technical field to which the present invention pertains typically
understand. Unless explicitly described to the contrary, the word "comprise" and
variations such as "comprises" or "comprising", will be understood to imply the
inclusion of stated elements but not the exclusion of any other elements. In addition,
singular expressions used herein may include plural expressions unless they have
definitely opposite meanings.
A scattering alloy layer in which a melted portion, which has been melted
from an electrical steel sheet by the laser, is resolidified on the steel sheet exists in a
groove formed by magnetic domain refinement by radiation of laser.
The scattering alloy layer is a texture having high energy, and in a case in
which the scattering alloy layer is non-uniformly distributed, the scattering alloy layer
may act as an obstruction factor to a growth a Goss texture at the time of
recrystallization annealing. In addition, in a case in which the scattering alloy layer
is non-uniformly distributed, the scattering alloy layer is not eroded in the Goss
texture at the time of recrystallization annealing, and remains as random texturing
instead of the Goss texture, thereby adversely affecting magnetism of the electrical
steel sheet.
According to a method of manufacturing a grain-oriented electrical steel
sheet according to an exemplary embodiment of the present invention, the scattering
alloy layer, which is a layer formed when a melted portion melted from the electrical
steel sheet by the radiation of the laser is resolidified on the steel sheet, is uniformly
distributed in the groove, and as a result, the scattering alloy layer is eroded in the
Goss texture at the time of recrystallization annealing, such that a fraction of the
Goss texture is improved, thereby providing a grain-oriented electrical steel sheet
having excellent magnetism.
In general, a manufacturing process of the grain-oriented electrical steel
sheet is performed by allowing a slab to be subjected to hot rolling, hot rolled plate
annealing, cold rolling, decarburizing annealing (primary recrystallization annealing),
high temperature annealing (secondary recrystallization annealing), planarization
annealing, insulation coating in sequence.
The magnetic domain refinement treatment in the related art is performed
after the insulation coating, but according to the method of manufacturing the grainoriented
electrical steel sheet according to the exemplary embodiment of the present
invention, after cold rolling, before primary recrystallization or after the primary
recrystallization, the magnetic domain refinement may be performed by radiating the
laser to the electrical steel sheet.
In addition, even though the magnetic domain refinement is performed by
radiating the laser to the electrical steel sheet before the primary recrystallization, an
effect of improving a core loss is maintained even after a subsequent heat treatment
process.
To provide the aforementioned method of manufacturing the grain-oriented
electrical steel sheet, the following method of manufacturing the grain-oriented
electrical steel sheet may be provided.
The method of manufacturing the grain-oriented electrical steel sheet
according to the exemplary embodiment of the present invention includes: providing
an electrical steel sheet before forming primary recrystallization or after forming the
primary recrystallization; and forming a groove in a surface of the electrical steel
sheet by radiating laser and simultaneously spraying gas onto the electrical steel
sheet.
Energy density Ed of the radiated laser may be 1.0 J/mm2 to 5.0 J/mm2. In a
case in which the laser energy density exceeds 5.0 J/mm2, the melted portion is
excessively formed, and as a result, in a final product, the scattering alloy layer is not
eroded in the Goss texture, and forms random texturing. In the case of a value of
the laser energy density which is less than 1.0 J/mm2, a sufficient groove depth
cannot be ensured, and as a result, an effect of improving a core loss cannot be
ensured after the heat treatment.
A scanning speed Vs of the radiated laser may be 0.0518 mm/μsec to 0.2
mm/μsec. In a case in which a value of the scanning speed of the laser exceeds
0.2 mm/μsec, the scattering alloy layer is not formed, and as a result, an effect of
improving a core loss cannot be ensured. In addition, in a case in which the
scanning speed of the laser is lower than 0.0518 mm/μsec, the melted portion is
excessively formed, and as a result, in a final product, the scattering alloy layer is not
eroded in the Goss texture, and forms random texturing.
The sprayed gas may be air, inert gas, or any type of gas which does not
cause oxidation of the electrical steel sheet.
Pressure Pa of the sprayed gas may be 0.2 kg/cm2 to 5.0 kg/cm2. In a case
in which the pressure of the sprayed gas is lower than 0.20 kg/cm2, the scattering
alloy layer is not formed, and as a result, an effect of improving a core loss cannot be
ensured. In addition, in a case in which the pressure of the sprayed gas exceeds
5.0 kg/cm2, the melted portion is excessively formed, and as a result, in a final
product, the scattering alloy layer is not eroded in the Goss texture, and forms
random texturing.
An angle formed between the spray direction of the gas and the laser
radiation direction may be 0° to 50° (in this case, a state in which the angle formed
between the spray direction of the gas and the laser radiation direction is 0° means
that the spray direction of the gas and the laser radiation direction are parallel to
each other). The angle formed between the spray direction of the gas and the laser
radiation direction affects a shape of the scattering alloy layer formed. The smaller
the angle formed between the spray direction of the gas and the laser radiation
direction, the smaller the thickness of the scattering alloy layer on the bottom surface
of the groove, and the greater the thickness of the scattering alloy layer at an end of
the groove.
Here, the bottom surface of the groove means the deepest portion in the
groove formed in the electrical steel sheet.
In addition, a light collecting shape of the laser may be 0.20 ≤ L/dt ≤ 1.0,
in which dt is a beam length in a width direction(x-axis) of the electrical steel sheet,
and L is a beam length in a rolling direction (y-axis). In addition, the dt may be 50
μm or smaller.
In a case in which the L/dt value exceeds 1.0, a heat-affected zone in the
rolling direction is increased, thereby adversely affecting a growth of the Goss
texture, and in a case in which the L/dt is below 0.20, a width of the groove in the
rolling direction is narrow, and the melted portion does not scatter, such that it is
impossible to ensure a sufficient groove depth.
Under the above condition, a movement speed VL of the electrical steel sheet
10 may be 0.9 m/s or higher.
In addition, the groove may be intermittently formed by being divided into
three to six grooves.
In addition, the laser may be radiated diagonally with respect to the width
direction (x-axis) of the electrical steel sheet. In addition, an angle with respect to
the width direction (x-axis) may be greater than 0° and equal to or smaller than 5°.
Since the laser is diagonally radiated, it is possible to improve magnetism by
decreasing a demagnetizing field.
The depth of the groove formed as described above may be equal to or
greater than 4% of the thickness of the electrical steel sheet in order to ensure a
core loss improvement rate. Alternatively, the depth of the groove may be 4% to
11% of the thickness of the electrical steel sheet.
In addition, an average thickness of the scattering alloy layer may be 4% to
12% of the depth of the groove. In a case in which the average thickness of the
scattering alloy layer is below 4% of the depth of the groove, an appropriate groove
for improving a core loss is not formed, and in a case in which the average thickness
of the scattering alloy layer exceeds 12% of the depth of the groove, the heataffected
zone is increased, which may have an adverse effect on a growth of the
Goss texture.
In addition, when a thickness of the scattering alloy layer on the bottom
surface of the groove is defined as TB, and a thickness of the scattering alloy layer at
a point that is one-half the distance between any one end of the groove and the
bottom surface of the groove is defined as TL, TB/TL may be 0.2 to 1.5. Alternatively,
the TB/TL may be 0.2 to 0.8, or 1.0 to 1.5. In a case in which a value of the TB/TL is
below 0.2, or exceeds 1.5, non-uniformity of the scattering alloy layer is increased,
which has an adverse effect on magnetism.
In the case of the electrical steel sheet on which the recrystallization
annealing has been performed under the aforementioned magnetic domain
refinement condition, the scattering alloy layer may be eroded in the Goss texture
during the recrystallization annealing process. In general, at the time of the
magnetic domain refinement treatment of the grain-oriented electrical steel sheet, a
heat-affected zone is included in the groove, and the heat-affected zone is not
eroded in the Goss texture when the Goss texture grows during a high temperature
annealing process, and remains in a shape recrystallized along the groove. The
texture has an adverse effect on magnetism.
However, the grain-oriented electrical steel sheet according to the exemplary
embodiment of the present invention allows the scattering alloy layer to be uniformly
distributed, such that a thermal effect is minimized, and as a result, the recrystallized
texture does not remain in the groove.
Hereinafter, the present invention will be described in detail with reference to
Examples. However, the following Examples are intended for the purpose of
illustration of the present invention, and the contents of the present invention are not
limited by the following Examples.
Example 1
The magnetism was measured by radiating continuous wave laser on the
grain-oriented electrical steel sheet having a thickness of 0.23 mm under the
condition as disclosed in Table 1. A radiation line is illustrated as a line divided into
three to six sections in the width direction as illustrated in FIG. 2. A laser radiation
interval was 2.50 mm, and the beam length dt in the width direction of the electrical
steel sheet at the time of radiating the laser was 50 μm and had a spherical shape.
In this case, the movement speed of the electrical steel sheet was 0.9 m/s.
Table 1
Ed
J/m
m2
DH
μm TL/TB
Average
thickness of
scattering
alloy layer
μm
Pa
Kgf
/cm
2
Vs
m/s
Before
radiating
laser
W17/50
Before
heat
treatment
W17/50
Before
heat
treatme
nt
W17/50
Comparison
1.0
10.0 0.3 1.2 0.2 51.8 0.82 0.78 0.78 Example
11.0 0.4 1.1 5.0 51.8 0.82 0.75 0.74 Example
6.4 0.2 0.768 5.0 200 0.82 0.79 0.79 Example
5.0
21.0 0.7 1.26 0.2 51.8 0.82 0.70 0.69 Example
22.2 0.8 0.9 5.0 51.8 0.82 0.71 0.71 Example
15.3 0.5 1.224 5.0 200 0.82 0.69 0.69 Example
1.2
15 0.5 0.6 61.
0 51.8 0.83 0.68 0.68 Example
20 0.6 1.6 51.8 0.82 0.67 0.67 Example
25 0.7 3 200 0.83 0.68 0.67 Example
5.3 25.5 0.85
1.5 5.0 51.8 0.82 0.86 0.82 Comparative
Example
1.8 5.0 51.8 0.82 0.87 0.83 Comparative
Example
0.5 5.0 200 0.82 0.85 0.83 Comparative
Example
In the laser radiation condition range according to the present invention, it is
possible to provide the grain-oriented electrical steel sheet, which may obtain stable
core loss characteristics even at a high movement speed of the steel sheet.
Example 2
The magnetism was measured by setting the energy density to 1.2 J/mm2
and the depth of the groove to 15 μm, and by radiating continuous wave laser on the
grain-oriented electrical steel sheet having a thickness of 0.23 mm while changing
the angle with respect to the width direction of the electrical steel sheet. A laser
radiation interval was 2.50 mm, and the beam length dt in the width direction of the
electrical steel sheet at the time of radiating the laser was 50 μm and had a spherical
shape. In this case, the movement speed of the electrical steel sheet was 0.9 m/s.
In addition, pressure of the sprayed gas was 4.5 kg/cm2, and the scanning speed
was 53 m/s.
Table 2
Radiation
Angle
Not treated by laser
core loss
(W17/50)/magnetic
flux density B8
Before heat treatment
core loss
(W17/50)/magnetic flux
density B8
After heat treatment
core loss
(W17/50)/magnetic flux
density B8
Comparison
0 0.82/1.92 0.67/1.89 0.67/1.90 Example
3 0.83/1.92 0.68/1.905 0.68/1.910 Example
5 0.82/1.92 0.67/1.907 0.67/1.915 Example
7 1.07/1.34 0.88/1.330 0.88/1.330 Comparative
Example
9 1.16/1.34 0.92/1.320 0.92/1.320 Comparative
Example
As can be seen from Table 2, magnetism is excellent when the laser is
radiated at an angle greater than 0° and equal to or smaller than 5° with respect to
the width direction of the electrical steel sheet.
The exemplary embodiment of the present invention has been described with
reference to the accompanying drawings, but those skilled in the art will understand
that the present invention may be implemented in any other specific form without
changing the technical spirit or an essential feature thereof.
Thus, it should be appreciated that the exemplary embodiments described
above are intended to be illustrative in every sense, and not restrictive. The scope
of the present invention is represented by the claims to be described below rather
than the detailed description, and it should be interpreted that all the changes or
modified forms, which are derived from the meaning and the scope of the claims,
and the equivalents thereto, are included in the scope of the present invention.

10: Electrical steel sheet
20: Groove
30: Part of continuous groove
40: Scattering alloy layer

【CLAIMS】
【Claim 1】
A grain-oriented electrical steel sheet, which has a surface which is formed
with grooves for a magnetic domain refinement treatment,
wherein a scattering alloy layer in the groove is eroded in a Goss texture
during a recrystallization annealing process.
【Claim 2】
The grain-oriented electrical steel sheet of claim 1, wherein:
when a thickness of the scattering alloy layer on a bottom surface of the
groove is defined as TB, and a thickness of the scattering alloy layer at a point that is
one-half the distance between any one end of the groove and the bottom surface of
the groove is defined as TL, TB/TL is 0.2 to 0.8.
【Claim 3】
The grain-oriented electrical steel sheet of claim 2, wherein:
a thickness of the scattering alloy layer is 4% to 12% of a depth of the groove.
【Claim 4】
The grain-oriented electrical steel sheet of claim 3, wherein:
the depth of the groove is 4% to 11% of a thickness of the electrical steel
sheet.
【Claim 5】
The grain-oriented electrical steel sheet of claim 4, wherein:
the groove is formed diagonally with respect to a width direction of the
electrical steel sheet.
【Claim 6】
The grain-oriented electrical steel sheet of claim 5, wherein:
the groove is formed at an angle greater than 0° and equal to or smaller than
5° with respect to the width direction of the electrical steel sheet.
【Claim 7】
The grain-oriented electrical steel sheet of claim 6, wherein:
three to six grooves are intermittently formed in the width direction of the
electrical steel sheet.
【Claim 8】
A method of manufacturing a grain-oriented electrical steel sheet, the method
comprising:
providing electrical steel sheet before forming primary recrystallization or
after forming the primary recrystallization; and
forming a groove in a surface of the electrical steel sheet by radiating laser
and simultaneously spraying gas onto the electrical steel sheet,
wherein energy density Ed and a laser scanning speed Vs of the radiated
laser satisfy the following conditions,
1.0 J/mm2≤ Ed ≤ 5.0 J/mm2,
0.0518 mm/μsec≤ Vs ≤ 0.2 mm/μsec
【Claim 9】
The method of claim 8, wherein:
pressure of the sprayed gas is 0.2 kg/cm2 to 5.0 kg/cm2.
【Claim 10】
The method of claim 9, wherein:
an angle formed between the spray direction of the gas and the laser
radiation direction is 0° to 50° (here, a state in which the angle formed between
the spray direction of the gas and the laser radiation direction is 0° means that the
spray direction of the gas and the laser radiation direction are parallel to each other).
【Claim 11】
The method of claim 10, wherein:
in the radiating of the laser, a laser beam is radiated on the surface of the
electrical steel sheet at an angle greater than 0° and equal to or smaller than 5°
with respect to a width direction of the electrical steel sheet.
【Claim 12】
The method of claim 11, wherein:
in the radiating of the laser, a movement speed VL of the electrical steel sheet
is at least 0.9 m/s.
【Claim 13】
The method of claim 12, wherein:
in the radiating of the laser,
when a beam length in the width direction of the electrical steel sheet is dt,
and a beam length in a rolling direction of the electrical steel sheet is L, a light
collecting shape of the laser satisfies the following condition,
0.20≤ L/dt ≤ 1.0
【Claim 14】
The method of claim 13, wherein:
dt is 50 μm or smaller.
【Claim 15】
The method of claim 14, wherein:
in the radiating of the laser,
a scattering alloy layer in which a melted portion of the electrical steel sheet
by the radiation of the laser scatters and is resolidified is generated, and when a
thickness of the scattering alloy layer on a bottom surface of the groove is defined as
TB, and a thickness of the scattering alloy layer at a point that is one-half the
distance between any one end of the groove and the bottom surface of the groove is
defined as TL, TB/TL is 0.2 to 0.8.
【Claim 16】
The method of claim 15, wherein:
a thickness of the scattering alloy layer is 4% to 12% of a depth of the groove.
【Claim 17】
The method of claim 16, wherein:
in the radiating of the laser,
the laser is radiated diagonally with respect to a width direction of the
electrical steel sheet.
【Claim 18】
The method of claim 17, wherein:
in the radiating of the laser,
the laser is radiated at an angle greater than 0° and equal to or smaller
than 5° with respect to the width direction of the electrical steel sheet.
【Claim 19】
The method of claim 18, wherein:
in the radiating of the laser,
three to six grooves are intermittently formed in the width direction of the
electrical steel sheet.