The present invention relates to a laser processing apparatus which i1Tadiatcs
laser beams on a grain-oriented electromagnetic steel sheet used for the core of a
transfonner or the like thereby refining magnetic domains.
[Related Att]
[0002]
A grain-oriented electromagnetic steel sheet is e-asily magnetized in the rolling
direction during the production of the steel sheet. Therefore, the grain-oriented
electromagnetic steel sheet is also called a unidirectional electromagnetic steel sheet
The grain-oriented electromagnetic steel sheet is used as a material for fanning the
core of an electrical device such as a transfonner or a rotary machine.
When the grain-oriented eledromagnetic steel sheet is magnetized, energy
loss such as core loss is generated. In recent years, due to the progress of global
wanning, energy-saving electrical devices have been required worldwide. Therefore,
a technology for further reducing the core loss in a grain-oriented electromagnetic steel
sheet is necessary.
[0003]
Core loss is classified into eddy-current loss and hysteresis loss. Eddycurrent
loss is classified into classical eddy-current loss and anomalous eddy-cutrcnt
loss. In order to reduce classical eddy-current loss, a grain-oriented electromagnetic
steel sheet which has an insulating coatingfilm formed at the surface and has a small
sheet thickness is known. For example, Patent Document I mentioned below
- I -
discloses a grain-oriented electromagnetic steel sheet which includes a glass coating
film formed on the surface of a steel sheet base steel material, and an insulating coating
!lim formed on the surface of the glass coating !lim.
[0004]
For example, Patent Documents 2 and 3 mentioned below disclose a laser
magnetic domain control method capable oflimiting anomalous eddy-current loss. In
the laser magnetic domain control method, the surface of a grain-oriented
electromagnetic steel sheet in which an insulating coating film is formed is in·adiated
with a laser beam and the laser beam is scanned substantially along a width direction
of the grain-oriented electromagnetic steel sheet (that is, a direction substantially
perpendicular to the rolling direction of the grain-oriented electromagnetic steel sheet).
As a result, a number of residual strains are periodically formed along the rolling
direction on the surface of the grain-oriented electromagnetic steel sheet (that is, the
surface of the base steel material) such that magnetic domains of the grain-oriented
electromagnetic steel sheet are refined.
According to the laser magnetic domain control method, a thermal history
having a steep temperature gradient along the thickness direction is generated in the
outermost surface of the grain-oriented electromagnetic steel sheet through the
scanning with the laser beam. Since the thermal histmy is given, residual strains are
generated on the surface of the base steel material of the grain-oriented
electromagnetic steel sheet, and circulating cutTent magnetic domains are fonned due
to the residual strains. Intervals between 180° domain walls are refined by the
circulating current magnetic domains, and as a result, anomalous eddy-current loss in
the grain~oriented electromagnetic steel sheet is reduced.
[0005]
- 2 -
As described above, intervals between 180° domain walls are refined by the
circulating current magnetic domains formed on the surface of the base steel material,
and as a result, anomalous eddy-current loss is reduced. However, the circulating
current magnetic domains fom1ed on the surface of the base steel material cause an
increase in hysteresis loss. Therefore, in order to minimize core loss including eddycurrent
Joss and hysteresis loss, it is cflectiw to reduce the width of the circulating
current magnetic domains. For example, Patent Document 3 discloses a method in
which strong strains are fanned in a narrow region by using a TEMoo mode laser beam,
which enables a very small beam spot size by its excellent focusing characteristics,
such that circulating current magnetic domains which are narrow and have sufficient
strength are obtained.
[Prior Art Document]
(Patent Document]
[0006]
[Patent Document I] Japanese Unexamined Patent Application, First
Publication No. 2007-119821
[Patent Document 2] Japanese Unexamined Patent Application, First
Publication No. S59-33802
[Patent Document 3] PCT Jntemational Publication No. W02004/083465
[Patent Document 4] Japanese Unexamined Patent Application, First
Publication No. S58-29592
[Patent Document 5] Japanese Unexamined Patent Application, First
Publication No. H2-52192
[Disclosure of the Invention]
[Problems to be Solved by the Invention]
- 3 -
[0007]
In the laser magnetic domain control method in the related art, in order to
perform scanning with the laser beam rapidly and etlicicntly, an optical system which
linearly scans a single laser beam fi-om a position at a predetermined height fi·om the
surf.~ce of a grain-oriented electromagnetic steel sheet onto the grain-oriented
electromagnetic steel sheet along a width direction thereof is used.
In a case where this optical system is used, the laser beam is incident
perpendicular to the surface of the grain-oriented electromagnetic steel sheet at a center
portion of the laser scanning width. That is, in a case where the incident position of
the laser beam is coincident with the center portion of the laser scanning width, the
angle between the direction perpendicular (nonnal direction) to the surface of the
grain-oriented electromagnetic steel sheet and the propagation direction of the laser
beam (an incident angle~ of the laser beam) becomes 0°. On the other hand, as the
incident position of the laser beam approaches an end pmiion of the laser scanning
width, the incident angle of the laser beam increases.
In such an optical system, as the incident position of the laser beam
approaches the end portion apart fi·om the center pmiion of the laser scanning width (as
the incident angle ~ of the laser beam increases), the beam diameter of the laser beam
increases, and the power density of the laser beam decreases.
As a result, a temperatme gradient along the thickness direction given to the
end portion of the laser scanning width becomes smaller than a temperature gradient
along the thickness direction given to the center portion of the laser scanning width,
and it becomes difficult to appropriately refine magnetic domains at the end portion of
the laser scanning width.
As described above, in the laser magnetic domain control method in the
- 4 -
'l "~
related art, there is a problem that an effect of controlling magnetic domains over the
entire laser scanning width (core loss reduction etlect) is insutliciently obtained.
(0008]
In order to solve this problem, increasing the absorptance of the laser beam at
the end portion of the laser scanning width may be considered. I' or example, Patent
Documents 4 and 5 mentioned above disclose a technology in which the incident angle
of a laser beam (linearly polarized light) is fixed to an angle close to the Brewster's
angle (for example, an angle of 45° or higher, referring to Claim 3 in Patent Document
4 and Claim I in Patent Document 5) such that the surface of a processing object is ·
inadiated with the laser beam in a state in which the absorptance of the laser beam is
always maximized.
However, although the technology disclosed in Patent Documents 4 and 5 is
effective in a system in which the incident angle of the laser beam can be fixed, it is
difficult to apply the technology to a system in which a laser beam is scanned onto a
processing object over a predetennined laser scanning width as in the system used for
the laser magnetic domain control method in the related art described above (in other
words, a system in which the incident angle of a laser beam varies).
[0009]
The present invention has been made taking the foregoing circumstances into
consideration, and an object thereof is to provide a laser processing apparatus capable
of reducing core loss of a grain-oriented electromagnetic steel sheet over the entire
laser scanning width of a laser beam.
[Means for Solving the Problem]
[0010]
In order to achieve the object by solving the problems, the present invention
- 5 -
'I b
R
employs the following measures.
(I) An aspect of the present invention provides a laser processing apparatus
lor refining magnetic domains of a grain-oriented electromagnetic steel sheet by
setting a laser beam to be focused on the grain-oriented electromagnetic steel sheet and
scanned in a scanning direction, in which the laser beam focused on the grain-oriented
electromagnetic steel sheet is linearly polarized light, and an angle between a linear
polarization direction and the scanning direction is equal to or higher than oo and lower
than45°.
(0011)
(2) In the laser processing apparatns described in (I), a maximum incident
angle
A grain-oriented electromagnetic steel sheet is an electromagnetic steel sheet
in which the easy magnetization axis of grains of the steel sheet (<001> direction of a
body-centered cubic crystal) is substantially aligned with the rolling direction in a
production process. In the grain-oriented electromagnetic steel sheet described above,
a number of magnetic domains of which the magnetization direction aligns with the
rolling direction are an·anged and these magnetic domains are separated by domain
- 8 -
walls. The grain-oriented electromagnetic steel sheet is easily magnetized in the
rolling direction and is thus appropriate as the core material of a transformer in which
the directions of lines of magnetic forces arc substantially constant.
A core lor a transformer is roughly classi!lcd into a wound core and a stacked
core. In a production process of a wound core, a steel sheet is assembled into the
shape of the core while winding deformation is given thereto, and thcreatler annealing
is perfonned on the resultant in order to remove strains introduced due to the
mechanical deformation. However, in the annealing process, as described above,
strains introduced due to laser in·adiation are also removed, and thus the effect of
refining the magnetic domains is lost. On the other hand, in a production process of a
stacked core, an annealing process for strain removal described above is unnecessary.
Therefore, the grain-oriented electromagnetic steel sheet according to this embodiment
is particularly appropriate as the material of stacked cores.
[0020]
FIG. I is a sectional view of a grain-oriented electromagnetic steel sheet 10
according to this embodiment. As shown in FIG. I, the grain-oriented
electromagnetic steel sheet I 0 includes a steel sheet body (base steel material) 12, glass
coating films 14 fonned on both surfaces of the steel sheet body 12, and insulating
coating films 16 fanned on the glass coating films 14.
[0021]
The steel sheet body 12 is formed of an iron alloy containing Si. The
composition of the steel sheet body 12 includes, as an example, Si: 2.5 mass% or more
and 4.0 mass% or less, C: 0.02 mass% or more and 0.10 mass% or less, Mu: 0.05
mass% or more and 0.20 mass% or less, acid-soluble AI: 0.020 mass% or more and
0.040 mass% or less, N: 0.002 mass% or more and 0.012 mass% or less, S: 0.001
- 9 -
mass% or more and 0.010 mass% or less, 1': 0.01 mass% or more and 0.04 mass% or
less, and Fe and unavoidable impurities as the remainder. For example, the thickness
of the steel sheet body 12 is 0.1 nun or greater and 0.4 mm or smaller.
[0022]
For example, the glass coating film 14 is fonned of complex oxides such as
forsteritc (MgzSi04), spinel (MgAb04), and cordierite (Mg2AI4Si50 16). For example,
the thickness of the glass coating film 14 is I ftm.
[0023]
For example, the insulating coating film 16 is fonned of a coating liquid
primarily containing colloidal silica and phosphate (magnesium phosphate, aluminum
phosphate, or the like), or a coating liquid in which alumina sol and boric acid are
mixed together. For example, the thickness of the insulating coating film 16 is 2 Jlm
or greater and 3 fllll or smaller.
[0024]
In the grain-oriented electromagnetic steel sheet I 0 having the abovedescribed
configuration, a laser beam is emitted toward the upper side of the insulating
coating film 16 such that residual strains are given to line-shaped regions substantially
perpendicular to the rolling direction. The line-shaped regions to which the residual
strains are given arc fanned at predetermined periods in the rolling direction. In
regions which exist between two line-shaped regions and arc magnetized in the rolling
direction, magnetic domain widths in a direction substantially perpendicular to the
rolling direction are refined.
[0025]

A production method of the grain-oriented electromagnetic steel sheet 1 0
- 10 -
according to this embodiment will be described with reference to FIG. 2. FIG. 2 is a
tlowchart showing an example of a production process of the grain-oriented
electromagnetic steel sheet I 0 according to this embodiment.
[0026]
As shown in FIG. 2, the production process of the grain-oriented
electromagnetic steel sheet 10 includes a casting process S2, a hot rolling process S4,
an annealing process S6, a cold rolling process S8, a decarburization annealing process
SlO, an annealing separating agent applying process Sl2, a final finishing annealing
process S 14, an insulating coating film fonning process S 16, and a laser in-adiation
process SJ8.
[0027]
In the casting process 82, molten steel which is adjusted to have a
predetem1ined composition is supplied to a continuous casting machine to
continuously form an ingot. In the hot rolling process 84, hot rolling is perfonned by
heating the ingot to a predetennined temperature (for example, 1150°C to 1400°C).
Accordingly, a hot rolled material having a predetem1ined thickness (for example, 1.8
to 3.5 mm) is formed.
[0028]
In the annealing process S6, a heat treatment is perfonned on the hot rolled
material, for example, under the condition of a heating temperature of750°C to
1200°C and a heating time of30 seconds to 10 minutes. In the cold rolling process
S8, the surface of the hot rolled material is pickled, and thereafter cold rolling is
performed thereon. Accordingly, a cold rolled material having a predetermined
thickness (for example, 0.1 to 0.4 mm) is fonned.
(0029]
- ll -
In the dccarburization annealing process S I 0, a heat treatment is performed on
the cold rolled material, for example, under the condition of a heating temperature of
700°C to
- 13 -
,,
~
An example of the configuration of a laser processing apparatus I 00 which
inadiatcs the grain-oriented electromagnetic steel sheet I 0 with a laser beam to
generate residual strains will be described with reference to FIGS. 3 and 4. FIG. 3 is a
schematic view showing the example of the configuration of the laser processing
apparatus I 00 according to this embodiment. FIG. 4 is a schematic view showing an
example ofthe conliguration of a single laser irradiation device I 06.
[0035]
The laser processing apparatus I 00 emits the laser beam toward the upper side
of the insulating coating t11m 16 of the grain-oriented electromagnetic steel sheet 10,
which is transported in the rolling direction at a predetem1ined speed, in order to
generate line-shaped strains substantially perpendicular to the rolling direction. As
shown in FIG. 3, the laser processing apparatus I 00 includes a number of laser
oscillators 102, a number of transmission fibers 104, and a number of the laser
irradiation devices I 06. In FIG. 3, three laser oscillators 102, three transmission
fibers 104, and three laser inadiation devices I 06 are shown, and the configurations of
the three are the same.
[0036]
For example, the laser oscillator I 02 emits a laser beam with an output of I 00
W or more. For example, the laser oscillator I 02 emits a laser beam at a wavelength
of0.15 Jlm or higher and 7 ltm or lower. The transmission fiber I 04 is an optical
fiber which transmits the laser beam emitted from the laser oscillator 102 to the laser
irradiation device I 06.
[0037]
As the type of the laser oscillator I 02, a fiber laser or a disk laser is preferable
because il allows a very small beam spot size by its excellent focusing characteristics
- 14 -
and enables to form narrow circulating current magnetic domains. A fiber laser or
disk laser has a wavelength in a region tl"om the near-ultraviolet region to the ncarinfrared
region (for example, 1 run band) and thus can be transmitted through an
optical fiber. Since the laser beam can be transmitted through an optical fiber, the
laser processing apparatus I 00 which is relatively compact can be realized. The laser
oscillator I 02 may be either a continuous wave laser or a pulsed laser.
[0038]
The laser irradiation device I 06 allows the laser beam transmitted from the
laser oscillator I 02 to the transmission fiber I 04 to be focused on the grain-oriented
electromagnetic steel sheet I 0 such that the laser beam is scanned on the grain-oriented
electromagnetic steel sheet I 0 along a direction substantially perpendicular to the
rolling direction. A width which is scanned with the laser beam by a single laser
irradiation device 106 may be smaller than the sheet width of the grain-oriented
electromagnetic steel sheet 10. However, as shown in I'! G. 3, by a!Tanging a number
of laser irradiation devices 106 in the sheet width direction, the region of the overall
sheet width of the grain-oriented electromagnetic steel sheet I 0 can be scanned with
the laser beams.
[0039]
As shown in FIG. 4, the laser irradiation device I 06 includes a collimator lens
122, a polarizing beam splitter 124 as an example of a polarizer, a IJ2 plate 125, a
metallic minor 126, a polygon mirror 128, and a parabolic min-or 130.
[0040]
The collimator lens 122 conve11s the laser beam transmitted from the
transmission fiber I 04 into collimated light. The laser beam as the collimated light is
an unpolarized beam in the description and is incident on the polarizing beam splitter
- 15 -
i-i
fl
124.
[0041]
The polarizing beam split1er 124 converts the incident unpolarized beam into
linearly polarized light. When the /J2 plate 125 is provided behind the polarizing
beam splitter 124, the linear polarization direction can be adjusted by changing the
rotational angle of the /J2 plate 125. In addition, by ananging the polarizing beam
splitter 124 to rotate around the center axis of the laser beam, the linear polarization
direction can be adjusted without the /J2 plate 125. As an element for changing the
polarization direction, a Faraday rotator or the like may be us.ed instead of the /J2 plate
125. The reason that the laser beam is linearly polarized will be described later. In a
case where the laser oscillator I 02 which originally oscillates a linearly polarized laser
beam (for example, a disk laser, a polari7.ation-maintaining fiber laser, a slab C02 laser,
or lasers provided with a polarized light regulation element in a resonator) is used, for
example, an optical element for converting polarization into linearly polarized light,
such as the polarizing beam spli!1er 124 shown in FIG. 4, may be omitted.
Furthermore, in a case where the linear polarization direction on the steel sheet follows
a predetennined direction, which will be described later, the IJ2 plate 125 may be
omitted.
A laser light having an electric field component (linearly polarized
component) that oscillates only in one direction is ideal for the linearly polarized laser
in the present invention. Strictly speaking, an electric field component that is
perpendicular to the linearly polarized component (orthogonal component) exists very
slightly. The ratio between the power of the linearly polarized component and the
power of the orthogonal component is dependent on the perfotmance of the polarizing
beam splitter 124 described above and the performance of the laser oscillator 102.
- 16 -
'I ,,
R
When the power oft he linearly polarized component is given by PWI, the power of
the orthogonal component is given by PW2, and (I'W 1/(PW 1 +PW2)) is defined as a
degree of polarization, the linearly polarized light in the present invention has a degree
of polarization of 0.9 or higher and lower than 1.0. That is, in a case where a linearly
polarized laser having a degree of polarization of 0. 9 or higher and lower than 1.0
(90% or higher and lower than I 00%) was used, the results of Examples, which will be
described later, were obtained. In addition, by splitting the linearly polarized light
using an orthogonal prism or the like, the proportions of the linearly polarized
components can be analyzed.
[0042]
The metallic mirror 126 is a mirror that squeezes and adjusts the beam
diameter of the incident laser beam in the sheet width direction (see FIG. 5) of the
grain-oriented electromagnetic steel sheet I 0. As the metallic mirror 126, for
example, a cylindrical mirror or a parabolic mitTor having a curvature in a uniaxial
direction may be used. The laser beam reflected by the metallic mirror 126 is
incident on the polygon mirror 128 that rotates at a prcdetennincd rotational speed.
[0043]
The polygon mirror 128 is a rotatable polyhedron and scans the laser beam on
the grain-oriented electromagnetic steel sheet 1 0 along the sheet width direction
thereof as the polygon mirror 128 rotates. While the laser beam is incident on one
side of the polyhedron of the polygon mirror 128, a single line-shaped region on the
grain-oriented electromagnetic steel sheet 1 0 along the sheet width direction is scanned
with the laser beam as the side rotates such that a residual strain is generated to the
line-shaped region. As the polygon mil1'or rotates, scanning of the laser beam is
repeatedly perfonned, and the grain-oriented electromagnetic steel sheet I 0 is
- 17 -
simultaneously transported in the rolling direction. As a result, a region having a
line-shaped residual strain is periodically lonned on the grain-oriented electromagnetic
steel sheet 10 in the rolling direction. The period of the line-shaped regions along the
rolling direction is adjusted by the transpm1ation speed of the grain-oriented
electromagnetic steel sheet 10 and the rotational speed of the polygon mirror 128.
[0044]
The parabolic mirror 130 is a mirror that squeezes and adjusts the beam
diameter ofthe laser beam reflected by the polygon mirror 128 in the rolling direction.
The laser beam reflected by the parabolic mitTor 130 is focused on the surface of the
grain-oriented electromagnetic steel sheet I 0.
[0045]
FIG. 5 is a view showing the shape of the laser beam focused on the grainoriented
electromagnetic steel sheet 10. In this embodiment, the shape of the focused
laser beam is an ellipse as shown in FlG. 5. The major axis direction of the ellipse is
parallel to the scanning direction of the laser beam, and the minor axis direction of the
ellipse is pe1pendicular to the scanning direction. In other words, the minor axis
direction of the ellipse is parallel to the rolling direction. By setting the shape of the
focused laser beam to be the ellipse, the time for inadiating one point on the grainoriented
electromagnetic steel sheet I 0 with the laser beam increases. As a result, the
temperature of the grain-oriented electromagnetic steel sheet 10 can be increased
toward a deep position of the inside thereof, which is effective in reducing core loss.
Since the beam diameter in the sheet width direction (scanning direction) is squeezed
by the metallic mirror 126 and the beam diameter in the rolling direction is squeezed
by the parabolic mirror 130, the shape of the focused laser beam becomes an ellipse.
In addition, when the shape of the focused laser beam is the ellipse, the area of the
- 18 -
focused laser beam increases compared to a case where the tocused shape is a true
circle, resulting in a reduction in power density. As a result, a temperature gradient
along the thickness direction in the vicinity of the surface of the grain-oriented
electromagnetic steel sheet 10 is prevented from becoming steep, which is effective in
suppressing the generation of defects in the glass coating film 14.
[0046]
In the above description, a case where the shape of the laser beam focused on
the grain-oriented electromagnetic steel sheet I 0 is an ellipse is an example, but the
present invention is not limited thereto. For example, the shape of the focused laser
beam may also be a true circle.
[0047]
In this embodiment, it is preferable that the intensity distribution of the laser
beam be set such that the beam diameter (a width including 86% of the integrated
intensity) in the rolling direction becomes 200 ~tm or smaller. Accordingly, narrower
circulating current magnetic domains are fom1ed while further limiting the expansion
of thetmal conduction in the rolling direction, thereby significantly reducing core loss.
Fm1hennore, in order to reliably reduce core loss, it is more preferable that the beam
diameter be set to 120 fUll or smaller.
[0048]

When the laser inadiation device 106 scans the surface of the grain-oriented
electromagnetic steel sheet l 0 with the laser beam over a predetermined laser scanning
width, the states of the laser beam incident on the surface of the grain-oriented
electromagnetic steel sheet 10 at the center pmiion and the end portion of the laser
scanning width are different from each other.
- 19 -
[0049]
FIG. 6 is a schematic view showing the state of the laser beam incident on the
grain-oriented electromagnetic steel sheet l 0. When the laser irradiation device I 06
scans the laser beam over a predetermined laser scanning width L in the scanning
direction, as shown in FIG. 6, the state of the laser beam incident on a center portion PI
or the laser scanning width Lis di!lerent !rom the state ofthe laser beam incident on
end portions P2 and P3 of the laser scanning width L. Specifically, the laser beam
rctlectcd by the parabolic mirror 130 of the laser irradiation device 1 06 is incident
perpendicular to the surface (insulating coating film 16) of the grain-oriented
electromagnetic steel sheet I 0 at the center portion PI of the laser scanning width L.
On the other hand, the laser beam is obliquely incident on the surface of the grainoriented
electromagnetic steel sheet I 0 (incident at an incident angle 4> with respect to
the direction nom1al to the surface) at both the end portions P2 and 1'3 of the laser
scanning width L.
That is, in a case where the incident position of the laser beam is coincident
with the center portion PI of the laser scanning width L, the angle between the
direction perpendicular to (direction nonnal to) the surface of the grain-oriented
electromagnetic steel sheet 10 and the propagation direction of the laser beam (the
incident angle~ of the laser beam) becomes 0°. On the other hand, as the incident
position of the laser beam approaches the end p01iion P2 or P3 of the laser scanning
width L, the incident angle~ of the laser beam increases.
[0050]
FIG. 7 is a schematic view showing beam diameters of the laser beam on the
grain-oriented electromagnetic steel sheet 10. In FIG. 7, reference numeral LBI
denotes a laser beam focused on the center portion PI of the laser scanning width L.
- 20 -
Reference numeral LB2 denotes a laser beam focused on one end portion P2 of the
laser scanning width L. Reference numeral LB3 denotes a laser beam lt1cused on the
other end portion P3 of the laser scanning width L. Since the laser beams are
obliquely incident on the end portions P2 and P3 of the laser scanning width L, the
beam diameters oft he laser beams LB2 and LB3 in the scanning direction (the length
of !he major axis of an elliptical beam in the scanning direction) arc greater than the
beam diameter of the laser beam LBI of the center portion Pl. In addition, since the
laser beams arc obliquely incident on the end portions P2 and P3 of the laser scanning
width L, the distance from the parabolic min·or 130 to an irradiation point on the steel
sheet increases. As a result, the beam diameters of the laser beams LB2 and LB3 in
the rolling direction (the length of the minor axis of the elliptical beam along the
rolling direction) are greater than the beam diameter of the laser beam LBI of the
center portion PI.
[0051]
As described above, as the beam diameter increases, the area irradiated with
the laser beam increases, and thus the power density of the laser beam decreases. As
a result, the temperature gradient along the thickness direction at the end portions P2
and P3 of the laser scanning width L becomes smaller than the temperature gradient at
the center portion PI, and thus magnetic domains at the end portions P2 and P3 cannot
be appropriately refined.
[0052]
In this embodiment, in order to solve this problem, the laser beam focused on
the surface (the insulating coating film 16) of the grain-oriented electromagnetic steel
sheet I 0 is set to be linearly polarized light, and as shown in fiG. 8, and the angle 0
between the linear polarization direction and the scanning direction of the laser beam is
- 21 -
set to be equal to or higher than 0° and lower than 45°. FIG. 8 is a schematic view
showing the relationship between the linear polarization direction and the scanning
direction of the laser beam in a case where the incident angle of the laser beam is oo.
As far as the angle 0 between the scanning direction of the laser beam and I he linear
polarization direction is equal to or higher than 0° and lower than 45°, the relationship
between the linear polarization direction and the scanning direction of the laser beam
may have a reflectional symmetry with respect to FIG. 8.
[0053]
As in this embodiment, in a case where the angle 0 is set to be equal to or
higher than 0° and lower than 45°, as described later, the absorptance of the laser beam
at the end portions P2 and P3 of the laser scanning width L can be increased.
Therefore, even when the beam diameter of the laser beam at the end portions P2 and
P3 increases, a reduction in the power density absorbed by the steel sheet can be
limited. Accordingly, a reduction in the temperature gradient along the thickness
direction at the end portions P2 and P3 of the laser scanning width L can be limited,
and the difference in temperature gradient from the center portion PI can be reduced.
As a result, core loss can be unifonnly reduced over the entire laser scanning width L.
[0054]

Here, the principle that the absorptance of the laser beam is increased,
depending on the angle e between the linear polarization direction and the scanning
direction of the laser beam, is described.
[0055]
A portion of the laser beam incident on the grain-oriented electromagnetic
steel sheet 10 is reflected by the insulaiing coating film 16, and lhe remainder is
- 22 -
incident on the insulating coating film 16. A portion oft he laser beam incident on the
insulating coating lilm 16 is absorbed inside the insulating coating film 16 and the
remainder reaches the upper surface of the glass coating film 14 such that a portion
thereof is reflected and the remainder thereof is incident on the glass coating 111m 14.
A portion of the laser beam incident on the glass coating film 14 is absorbed inside the
glass coating tilm 14 and the remainder reaches the upper surface orthe steel sheet
body (hereinafter, also called base steel material) 12 such that a portion thereof is
reflected and the remainder thereof is absorbed by the surface of the steel sheet body
12. In addition, the power of the laser beam transmitted to the grain-oriented
electromagnetic steel sheet l 0 is dependent on the absorptance of the laser beam
absorbed by the insulating cuating film 16 and the like as described above. When the
absorptance of the laser beam at the insulating coating film 16 and the like is high, the
power of the laser beam transmitted to the grain-oriented electromagnetic steel sheet
I 0 increases.
[0056]
Line increases, the absorptance of the laser beam decreases.
[0060]
In this embodiment, for increasing the absorptance of the laser beam at the
end portions P2 and P3 of the laser scanning width L of the laser irradiation device 106,
the angle 9 between the linear polarization direction and the scanning direction ofthe
laser beam is set to be equal to or higher than 0° and lower than 45°. Accordingly,
the power of the laser beam transmitted to the insulating coating film 16 and the like at
the end portions P2 and P3 of the laser scanning width L can be increased. Therefore,
even though the beam diameter at the end portions 1'2 and P3 of the laser scanning
width L increases, a reduction in the power density of the laser beam at the end
portions P2 and P3 can be limited, As a result, a reduction in the temperature
gradient along the thickness direction at the end portions P2 and P3 of the laser
scanning width L can be limited, and thus the difference in temperature gradient from
the center pm1ion PI can be reduced.
[0061]
Particularly, in a case where the angle 9 between the linear polarization
- 25 -
direction and the scanning direction of the laser beam is set to 0° or higher and 20° or
lower, a reduction in the power density of the laser beam at the end portions 1'2 and 1'3
of the laser scanning width L can be fm1her limited, and thus the temperature gradient
along the thickness direction over the entire laser scanning width L can be unifonnizcd.
[0062)
In addition, in this embodiment, a laser beam having a wavelength of0.15}Llll
or higher and 7 !llll or lower is particularly effective. In a case where the wavelength
of the laser beam is 0.15 }Lm or higher and 7 }Lm or lower, the insulating coating film
16 and the glass coating film I 4 are transparent to the laser beam, and the laser beam is
less likely to be absorbed inside the insulating coating film 16 and the glass coating
film 14. In this case, the power of the laser beam transmilted to the grain-oriented
electromagnetic steel sheet 1 0 is determined depending on the absmvtance of the laser
beam on the upper surface of the insulating coating film 16, the absorptance of the
laser beam on the upper surface of the glass coating film 14, and the absorptance of the
laser beam on the upper surface of the base steel material 12. That is, the product of
the absorptance of the laser beam on the upper surface of the insulating coating film 16,
the absorptance of the laser beam on the upper surface of the glass coating film 14, and
the absorptance of the laser beam on the upper surface of the base steel material 12 is
important. Regarding any of the three absorptances, as shown in FIG. 10, as the angle
9 increases, the absmptancc of the P-polarized light increases. Due to the
multiplicative ell'ect, by setting the angle 9 to be equal to or higher than 0° and lower
than 45°, absmption of the laser beam by the insulating coating film 16 at the end
portions P2 and P3 of the laser scaw1ing width L can be further promoted. As a result,
a reduction in the temperature gradient at the end portions P2 and P3 of the laser
scanning width L can be limited, and thus the effectiveness of this embodiment can be
- 26 -
'I
~
further reliably exhibited.
[0063]
In addition, the inventors discovere-d that when the magnification of a beam
diameter respect to a beam diameter (hereinafter, called a reference beam diameter) in
a case where the incident angle cp of the laser beam is 0° is higher than 24%, as
described above, even when the angle 8 between the linear polarization direction and
the scanning direction is set to be equal to or higher than 0° and lower than 45°, a
reduction in the power density of the laser beam at the end portions P2 and P3 of the
laser scanning width L cannot be sufficiently limited (in other words, a core loss
improvement ratio at the end portions P2 and P3 of the laser scanning width L
decreases).
It is thought that this is because when the magnification of the beam diameter
with respect to the reference beam diameter is higher than 24%, the amount of a
reduction in the power density caused by an increase in the beam diameter cannot be
covered by the amount of an increase in the absorptance of the laser beam (linearly
polarized light).
Therefore, in order to uniformly and reliably reduce core loss over the entire
laser scanning width L, it is preferable that the maximum incident angle MAX of the
laser beam be set on the basis of the following conditional expression (I).
1/coscpMAX :'0 1.24 ... (J)
(0064]
In the conditional expression (I), the left side represents the magnification of
the beam diameter (the beam diameter at the maximum incident angle .PMAx) with
respect to the reference beam diameter. Therefore, using the conditional expression
(1 ), the maximum incident angle $MAX at which the magnification with respect to the
- 27 -
reference beam diameter is not higher than 24% can be obtained. According to the
conditional expression ( l ), it can be seen that it is preferable that the maximum
incident angle
As described above, the grain-oriented electromagnetic steel sheet 10 in
which a magnetic field is applied in the rolling direction has a stmcture in which a
number of magnetic domains having a magnetization direction that substantially aligns
with the rolling direction are stmctured. Here, in order to achieve a further reduction
in the core loss ofthe grain-oriented electromagnetic steel sheet I 0, it is effective to
refine the magnetic domains (reduce the magnetic domains in width) through laser
- 29 -
beam in·adiation. Particularly, it is effective to obtain circulating current magnetic
domains which arc narrow and have sutlicient strength by generating a signitlcant
temperature gradient along the thickness direction in a very narrow region that is
present in the vicinity of the uppermost layer of the grain-oriented electromagnetic
steel sheet I 0 along the rolling direction.
[0068]
On the other hand, when the temperature gradient along the thickness
direction is increased, the temperature of the surface of the grain-oriented
electromagnetic steel sheet 10 increases. Due to the temperature increase, there may
be cases where defects are generated in the insulating coating film 16 or the glass
coating film 14. Here, defects mean film damage such as defective peeling, swelling,
alteration, and discoloration of the insulating coating film 16 and the glass coating film
14. In a case where defects are generated in the glass coating film 14, the steel sheet
body 12 is exposed to the outside, and there is conccm that rust may be generated.
Therefore, in a case where defects are generated in the glass coating film 14, the
insulating coating film 16 needs to be applied again, which causes an addition of a
process and an increase in production costs.
[0069]
During the production process of the grain-oriented electromagnetic steel
sheet I 0, many heat treatments are performed, and the interface stmcturc and thickness
of the glass coating film 14 or the insulating coating film 16 may vary in the rolling
direction and width direction of the steel sheet body 12. Therefore, it was difficult to
reliably limit the generation of defects in the glass coating film 14 over the entire steel
sheet body 12 even when laser conditions arc adjusted. Therefore, preventing the
generation of defects in the glass coating film 14 while reducing the core loss of the
- 30 -
grain-oriented electromagnetic steel sheet l 0 is required.
[0070]
According to this embodiment, not only the core loss can be reduced over the
entire laser scanning width L, hut also an effect of suppressing the generation of
defects can be obtained. That is, in a laser magnetic domain control method in which
an unpolarized laser bemn is used in the related ari, as described above, a temperature
gradient in a laser scanning width decreases as the beam diameter at the end portions
P2 and P3 of the laser scanning width L increases, and thus a reduction in core loss
cannot be sufficiently obtained. In order to compensate for this, the power of the
laser beam may be increased. In this case, while the core loss at the end portions P2
and P3 can be further reduced, the power of the laser beam absorbed by the center
portion PI of the laser scanning width L becomes excessive, and there is a problem
that defects are easily generated. On the other hand, in this embodiment, as described
above, in order to increase the absorptance of the laser beam at the end portions P2 and
P3 of the laser scanning width Las described above, the grain-oriented electromagnetic
steel sheet I 0 is scanned with the linearly polarized light including !he !'-polarized
light of which the absorptance increases as the incident angle increases. Here, at
the center portion PI of the laser scanning width L, since the linearly polarized light is
incident perpendicular to the surface of the grain-oriented electromagnetic steel sheet
I 0 (the incident angle shown in FIGS. 6, 9A, and 98 is small), the absorptances of
the P-polarized light and the S-polarized light at the center pmiion PI are substantially
the same (see FIG. I 0). Since there is no difference in absorptance between the Ppolarized
light and the S-polarized light forming an unpolarized state, an increase in
absorptance, which is caused by employing the P-polarized light, rarely occurs.
Therefore, in the laser processing apparatus I 00 of this embodiment, without an
- 31 -
excessive increase in the power of the laser beam transmitted to the grain-oriented
electromagnetic steel sheet I 0 at the center portion PI of the laser scanning width L,
the power of the laser beam absorbed at the end portions 1'2 and P3 can be increased.
Accordingly, a reduction in core loss and a suppression of the generation of defects can
be realized over the entire laser scanning width L.
[0071]
In the above-described embodiment, as shown in FIG. I, an example in which
the grain-oriented electromagnetic steel sheet I 0 constituted by a three-layer structure
including the base steel material 12, the glass coating film 14, and the insulating
coating film 16 irradiated with the laser beam has been described. However, even for
a steel sheet having two layers including the base steel material 12 and the insulating
coating film 16 as the basic structure without the glass coating film 14, the laser
processing apparatus I 00 of this embodiment exhibits an effect of core loss over the
laser scanning width L. This is because even when the glass coating film 14 is absent,
by employing the linearly polarized light as the laser beam and setting the angle 0 to be
in the above-described mnge, the absorptance of the laser beam absorbed by the upper
surfaces of the insulating coating film 16 and the base steelmaterial12 at the end
portions P2 and P3 of the laser scanning width L can be increased. As a grainoriented
electromagnetic steel sheet without the glass coating film 14, a grain-oriented
electromagnetic steel sheet in which the surface of a base steel material has small
roughness and is close to a mirror surface and thus exhibits ultra-low core loss
characteristics arc provided is known. In the grain-oriented electromagnetic steel
sheet having such ultra-low core loss characteristics, in order to prevent the generation
of rust caused by the exposure of the base steel material 12, it is important that defects
are not generated in the insulating coating film 16 during laser beam irradiation. As
- 32 -
described above, in the laser processing apparatus I 00 of this embodiment, a reduction
in core loss over the entire laser scanning width Land the suppression of the
generation of defects in the insulating coating ftlm 16 are realized.
[0072]

In order to cmitinn the etlectiveness of Examples according to the
embodiment described above, a confinnation test example according to Examples and
Comparative Examples will be described.
[0073]
First, a slab having a composition including Si: 3.0 mass%, C: 0.05 mass%,
Mn: 0.1 mass%, acid-soluble AI: 0.02 mass%, N: 0.01 mass%, S: O.Oimass%, P: 0.02
mass%, and Fe and unavoidable impurities as the remainder was prepared. Hot
rolling was performed on the slab at 1280°C, thereby producing a hot rolled material
having a thickness of23 mm. Next, a heat treatment was perfonned on the hot rolled
material under the condition of I 000°C x l minute. A pickling treatment was
performed on the resultant after the heat treatment, and cold rolling was perfonned on
the resultant, thereby producing a cold rolled material having a thickness of 0.23 mm.
Decarburization annealing was performed on the cold rolled material under the
condition of 800°C x 2 minutes. Next, an annealing separating agent primarily
containing magnesia was applied to both surfaces of the cold rolled material after the
decarburization annealing. In addition, the cold rolled material to which the
annealing separating agent was applied was put in a batch type fumace in a state of
being wound in a coil shape, and finishing annealing was perfonncd thereon under the
condition of 1200°C x 20 hours. Accordingly, a steel sheet base steel material (steel
sheet body) having glass coating films fonned on the surfaces was produced. Next,
- 33 -
.,
"R
an insulating material formed of aluminum phosphate was applied onto the glass
coaling films and was baked (850°C x I minute), thereby tMAX was 24°.
[0076]
- 34 -
A portion of the laser-processed steel sheet and a portion in the steel sheet
ti'Om the same coil, which was not subjected to laser processing, were subjected to a
single sheet tester (SST), and the core loss at W 171SO (W /kg) was evaluated. W 171SO is
the core loss at a ti·equcncy of 50 Hz and a maximum magnetic t1ux density of I. 7 T.
As a test piece for the SST measurement, a rectangular piece which was cut into a size
or l 00 m111 in length in the width direction ofthe steel sheet and 500 nun in length in
the rolling direction of the steel sheet was used. Cutting positions in the width
direction were 100 111111 for each of the center portion and the end portion with respect
to 500 mm of the laser scanning width. The core loss improvement ratio(%) of the
laser-processed steel sheet was defined with respect to the core loss of the potiion in
the steel sheet from the same coil, which was not subjected to laser processing, as the
reference.
[0077]
TI1e test results are shown in the following Table I. In Comparative
Example 1 in which the unpolarized laser beam was used, the core loss of the end
portion was deteriorated compared to that of the center portion. On the other hand, in
Examples I to 4, since the linearly polarized laser beam was used and the angle 9 was
set to be lower than 45°, an e!Tect of improving the core loss of the end portion was
obtained (improvement margin is meaningful because it is higher than about 0.5%,
which is typically an error in evaluation of the core loss improvement ratio).
Particularly, in a case where the angle 9 was 20° or lower, the degree of deterioration
of the core loss was lower than 0.5%, which means that there was actually no
deterioration. On the other hand, in Comparative Example 2 in which the angle() was
45°, there was no substantial difference in the core loss improvement ratio from that of
Comparative Example 1 with the unpolarized light. This is because in a case where
- 35 -
the angle 0 is 45°, P-polarizcd light and S-polarizcd light are incident on an incident
surtacc in an even ratio and an etTect of increasing the absorptance of the laser beam at
the end pm1ion of the laser scanning width cannot be obtained. In Comparative
Example 3 in which the angle 0 is 60°, the core loss improvement ratio was lower than
that of Comparative Example I with the unpolarizcd light. This is because the
absorptancc of the laser beam at the end portion oft he laser scanning width was
conversely decreased.
- 36 -
[0078]
[Table I]
Core loss Core loss
Type of
Angle e C)
improvement improvement
polarization ratio of center ratio of end
portion(%) pmtion (%)
Example I
Linearly
polarized light 0 13.4 13.2
Example2
Linearly
polarized light 10 13.0 12.8
Example 3 Linearly
polarized light 20 13.1 12.8
Example4
Linearly
polarized light 30 13.5 12.4
Comparative Unpolarized - 13.2 11.2 Example I light
Comparative Linearly 45 13.2 11.3 Example2 I polarized light
Comparative Linearly
Example3 I polarized light 60 13.3 10.2
[0079]
From the above-described test results, it can be seen that by setting the angle 0
in a range where the effect of the P-polarized light out of the P-polarized light and Spolarized
light becomes dominant, that is, by setting the angle 0 to be equal to or
higher than oo and lower than 45°, the absorptance of the laser beam at the end portion
of the laser scanning width can be increased compared to a case of unpolarizcd light,
and as a result, the core loss improvement ratio at the end portion of the laser scanning
width can be increased.
[0080)
In addition, in a case where the angle 9 between the linear polarization
direction and the scanning direction is fixed to 0° and the maximum incident angle
MAX of the laser beam was changed in a range of24° to 45°, a change in the core loss
improvement ratio al the end portion of the laser scanning width L was checked. The
- 37 -
results arc shown in Table 2.
[0081)
[Table 2]
Maximum Core loss
incident angle 1/cos.PMAX reduction ratio
cJ!MAX (") ··-·- (%)
24 1.09 13.2
30 1.15 12.9
33 1.19 12.5
36 1.24 12
40 1.31 11.4
45 1.41 10.5
[0082]
As shown in Table 2, it could be seen that when the maximum incident angle
MAX of the laser beam was higher than 36°, the core loss improvement ratio of the end
portion of the laser scanning width L was rapidly deteriorated. In a case where the
maximum incident angle MAX is 40° or higher, the core loss improvement ratio at the
end portion of the laser scanning width L was equal to or lower than that of
Comparative Example I (in a case ofunpolarized light) shown in Table 1. It is
thought that this is because when the maximum incident angle MAX is higher than 36°,
the magnification of a beam diameter with respect to the reference beam diameter
becomes higher than 24%. That is, it was confinned by the experiment that in order
to unifom1ly and reliably reduce core loss over the entire laser scanning width L, it is
preferable that the maximum incident angle MAX of the laser beam be set on the basis
of the above-described conditional expression (1 ).
[0083]

As descried above, in the laser processing apparatus I 00 according to this
embodiment, the angle 0 between the linear polarization direction of the light scanned
- 38 -
on the grain-oriented electromagnetic steel sheet 10 and the scanning direction is set to
be equal to or higher than 0° and lower than 45°.
[0084]
Accordingly, the power of the laser beam transmi!ted to the steel sheet body
12 or the glass coating tllm 14 at the end portions P2 and P3 of the laser scanning
width Lofthe laser in·adiation device 106 can be increased. Therefore, even when
the beam diameter at the end portions P2 and P3 increases, a reduction in the power
density of the laser beam at the end portions P2 and P3 can be limited. As a result, a
reduction in the temperature gradient along the thickness direction at the end portions
P2 and P3 of the laser scanning width Lean be limited, and the difference in
temperature gradient between the center portion PI and the end portions P2 and P3 of
the laser scanning width L can be reduced. Furthem1ore, as described above, since
the power of the laser beam absorbed at the center portion PI is not increased, the
generation of defects in the center portion Pl can be suppressed. That is, reducing
core loss and preventing the generation of defects in the glass coating film 14 can be
simultaneously realized over the entire laser scanning width L.
[0085]
In the laser processing apparatus 100 according to this embodiment, since a
reduction in core loss and the limitation of defects in the glass coating film 14
described above can be achieved, the grain-oriented electromagnetic steel sheet I 0
which has lower core loss than that in the related ati along the whole width direction of
the grain-oriented electromagnetic steel sheet I 0 can be produced. As a result, the
grain-oriented electromagnetic steel sheet 10 with ultra-low core loss can be supplied
at a lower cost. Furthennore, from the viewpoint of realizing a reduction in energy
consumption through the distribution of the grain-oriented electromagnetic steel sheet
- 39 -
I 0 with ultra-low core loss worldwide, a great economic e!Tect is exhibited.
[0086]
While the preferred embodiment of the present invention has been Jescribcd
in detail with reference to the accompanying drawings, the present invention is not
limited to the examples. It should be noted by those skilled in the technical field to
which the present invention belongs that various changes and modifications can be
made without depat1ing from the technical spirit described in the claims, and it should
be understood that these changes and modifications naturally belong to the technical
scope oft he present invention.
[Brief Description of the Reference Symbols]
[0087]
10: GRAIN-ORIENTED ELECTROMAGNETIC STEEL SHEET
12: STEEL SHEET BODY
I4: GLASS COATING FILM
16: INSULATING COATING FILM
100: LASER PROCESSING APPARATUS
102: LASER OSCILLATOR
104: TRANSMISSION FIBER
106: LASER IRRADIATION DEVICE
122: COLLIMATOR LENS
124: l'OLARIZING BEAM SPLITTER
125: ')J2PLATE
126: METALLIC MIRROR
128: POLYGON MIRROR
130: PARABOLIC MIRROR

(Document Type] CLAIMS
1. A laser processing apparatus for refining magnetic domains of a grainoriented
electromagnetic steel sheet by setting a laser beam to be focused on the grainoriented
electromagnetic steel sheet and scanned in a scanning direction,
wherein the laser beam focused on the grain-oriented electromagnetic steel
sheet is linearly polarized light, and
an angle between a linear polarization direction and the scanning direction is
equal to or higher than 0° and lower than 45°.
2. The laser processing apparatus according to claim I,
wherein a maximum incident angle cl>MAX of the laser beam incident on the
grain-oriented electromagnetic steel sheet satisfies the following conditional
expression (! ).
1/coscl>MAX::; 1.24 ... (1)
3. 1l1e laser processing apparatus according to claim I or 2,
wherein a wavelength of the laser beam focused on the grain-oriented
electromagnetic steel sheet is 0.1 5 pm or higher and 7 ~tm or lower.
4. The laser processing apparatus according to any one of claims I to 3,
further comprising:
a laser oscillator which emits the laser beam; and
a polarizer which converts the laser beam emitted by the laser oscillator into
the linearly polarized light.
- 41 -
5. The laser processing apparatus according to claim 4,
wherein the laser oscillator is a fiber laser or a disk laser.
6. The laser processing apparatus according to any one of claims 1 to 5,
wherein a shape of the laser beam focused on the grain-oriented
electromagnetic steel sheet is an ellipse, and
a minqr axis direction of the ellipse is perpendicular to the scanning direction.