DESCRIPTION
TITLE OF INVENTION: GRAIN-ORIENTED ELECTRICAL STEEL
SHEET AND MANUFACTURING METHOD THEREOF
TECHNICAL FIELD
[0001] The present invention relates to a grainoriented
electrical steel sheet suitable for an iron
core of a transformer and the like and a
manufacturing method thereof.
BACKGROUND ART
[0002] A grain-oriented electrical steel sheet
contains Si, and axes of easy magnetization <001>) of
crystal grains in the steel sheet are substantially
parallel to a rolling direction in a manufacturing
process of the steel sheet. The grain-oriented
electrical steel sheet is excellent as a material of
iron core of a transformer and the like.
Particularly important properties among magnetic
properties of the grain-oriented electrical steel
sheet are a magnetic flux density and an iron loss.
[0003] There is a tendency that a magnetic flux
density of the grain-oriented electrical steel sheet
when a predetermined magnetizing force is applied is
larger, as the degree in which the axes of easy
magnetization of crystal grain are parallel to the
rolling direction (which is also referred to as L
direction) of the steel sheet is higher, namely, as
the matching degree of crystal orientation is higher.
- 1 -
As an index for representing the magnetic flux
density, a magnetic flux density Be is generally used.
The magnetic flux density Bs is a magnetic flux
density generated in the grain-oriented electrical
steel sheet when a magnetizing force of 800 A/m is
applied in the L direction. Specifically, it can be
said that the grain-oriented electrical steel sheet
with a large value of the magnetic flux density Bg is
more suitable for a transformer having small size and
excellent efficiency, since it has a large magnetic
flux density generated by a certain magnetizing
force.
[0004] Further, as an index for representing the
iron loss, an iron loss W17/50 is generally used. The
iron loss W17/50 is an iron loss obtained when the
grain-oriented electrical steel sheet is subjected to
AC excitation under conditions where the maximum
magnetic flux density is 1.7 T, and a frequency is 50
Hz. It can be said that the grain-oriented
electrical steel sheet with a small value of the iron
loss W17/50 is more suitable for a transformer, since
it has a small energy loss. Further, there is a
tendency that the larger the value of the magnetic
flux density Bg, the smaller the value of the iron
loss W17/50. Therefore, it is effective to improve the
orientation of crystal grains also for reducing the
iron loss W17/50.
[0005] Generally, the grain-oriented electrical
steel sheet is manufactured in the following manner.
- 2 -
A material of silicon steel sheet containing a
predetermined amount of Si is subjected to hotrolling,
annealing, and cold-rolling, so as to obtain
a silicon steel sheet with a desired thickness.
Then, the cold-rolled silicon steel sheet is
annealed. Through this annealing, a primary
recrystallization occurs, resulting in that crystal
grains in a so-called Goss orientation in which axes
of easy magnetization are parallel to the rolling
direction (Goss-oriented grains, crystal grain size:
20 \im. to 30 iim) are formed. This annealing is
performed also as a decarburization annealing.
Thereafter, an annealing separating agent containing
MgO as its major constituent is coated on a surface
of the silicon steel sheet after the occurrence of
primary recrystallization. Subsequently, the silicon
steel sheet coated with the annealing separating
agent is coiled to produce a steel sheet coil, and
the steel sheet coil is subjected to an annealing
through batch processing. Through this annealing, a
secondary recrystallization occurs, and a glass film
is formed on the surface of the silicon steel sheet.
When the secondary recrystallization occurs, due to
an influence of inhibitor included in the silicon
steel sheet, the crystal grains in the Goss
orientation preferentially grow, and a large crystal
grain has a crystal grain size of 100 mm or more.
Then, an annealing is performed for flattening the
silicon steel sheet after the occurrence of secondary
- 3 -
recrystallization, a formation of insulating film and
the like, while uncoiling the steel sheet coil.
[0006] Almost all of the orientations of respective
crystal grains of the grain-oriented electrical steel
sheet manufactured through such a method are
determined when the secondary recrystallization
occurs. Fig. lA is a diagram illustrating
orientations of crystal grains obtained through the
secondary recrystallization. As described above,
when the secondary recrystallization occurs, crystal
grains 14 in the Goss orientation, in which a
direction 12 of the axis of easy magnetization
matches a rolling direction 13, preferentially grow.
At this time, if the silicon steel sheet is not flat
and is coiled, a tangential direction of a periphery
of the steel sheet coil matches the rolling direction
13. Meanwhile, the crystal grains 14 do not grow in
accordance with curvature of the coiled steel sheet
surface but grow while maintaining a linearity of the
crystal orientation in the crystal grains 14, as
illustrated in Fig. lA. For this reason, when the
steel sheet coil is uncoiled and flattened after the
occurrence of secondary recrystallization, a part in
which the direction 12 of the axis of easy
magnetization is not parallel to the surface of the
grain-oriented electrical steel sheet is generated in
a large number of crystal grains 14. In short, an
angle deviation p between the axis of easy
magnetization direction <001>) of each crystal grain
- 4 -
14 and the rolling direction is increased. When the
angle deviation (3 is increased, the matching degree
of crystal orientation is decreased, and the magnetic
flux density Be is decreased.
[0007] Further, the larger the crystal grain size,
the more significant the increase in the angle
deviation p. In recent years, because of
strengthening of inhibitors and the like, it is
possible to facilitate a selective growth of crystal
grains in the Goss orientation, and in a crystal
grain having a large size in the rolling direction in
particular, the decrease in the magnetic flux density
Bs is significant.
[0008] Further, various techniques have been
conventionally proposed for the purpose of improving
the magnetic flux density, reducing the iron loss or
the like. However, with the conventional techniques,
it is difficult to achieve the improvement in the
magnetic flux density and the reduction in the iron
loss, while maintaining high productivity.
CITATION LIST
PATENT LITERATURE
[0009] Patent Literature 1: Japanese Laid-open
Patent Publication No. 07-268474
Patent Literature 2: Japanese Laid-open Patent
Publication No. 60-114519
Patent Literature 3: Japanese Examined Patent
Application Publication No. 06-19112
Patent Literature 4: Japanese Laid-open Patent
- 5 -
Publication No. 61-75506
Patent Literature 5: Japanese Laid-open Patent
Publication No. 10-183312
Patent Literature 6: Japanese Laid-open Patent
Publication No. 2006-144058
NON-PATENT LITERATURE
[0010] Non-Patent Literature 1: T. Nozawa, et al.,
IEEE Transaction on Magnetics, Vol. MAG-14 (1978)
P252-257
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0011] The present invention has an object to
provide a grain-oriented electrical steel sheet and a
manufacturing method thereof capable of improving a
magnetic flux density and reducing an iron loss,
while maintaining high productivity.
SOLUTION TO PROBLEM
[0012] As a result of earnest studies, the present
inventors have devised various aspects described
below.
[0013] (1) A manufacturing method of a grainoriented
electrical steel sheet, including:
cold-rolling a silicon steel sheet containing Si;
next, performing a decarburization annealing of
the silicon steel sheet so as to cause a primary
recrystallization;
next, coiling the silicon steel sheet so as to
obtain a steel sheet coil;
- 6 -
next, performing an annealing of the steel sheet
coil through batch processing so as to cause a
secondary recrystallization; and
next, uncoiling and flattening the steel sheet
coil, wherein
the manufacturing method further comprising,
between the cold-rolling the silicon steel sheet
containing Si and the coiling the silicon steel sheet
so as to obtain the steel sheet coil, irradiating a
laser beam a plurality of times at a predetermined
interval in a rolling direction on a surface of the
silicon steel sheet from one end to the other end of
the silicon steel sheet along a sheet width
direction, and
while the secondary recrystallization is caused,
grain boundaries passing from a front surface to a
rear surface of the silicon steel sheet are generated
along paths of the laser beams.
[0014] (2) The manufacturing method of a grainoriented
electrical steel sheet according to (1),
wherein a part of the surface of the silicon steel
sheet to which the laser beam has been irradiated is
flat .
[0015] (3) The manufacturing method of a grainoriented
electrical steel sheet according to (1) or
(2), wherein the predetermined interval is set based
on a radius of curvature of the silicon steel sheet
in the steel sheet coil.
[0016] (4) The manufacturing method of a grain-
- 7 -
oriented electrical steel sheet according to any one
of (1) to (3), wherein, when a radius of curvature at
an arbitrary position in the silicon steel sheet in
the steel sheet coil is R (mm) and the predetermined
interval at the position is PL (mm), the following
relation is satisfied,
PL^O . 13xR.
[0017] (5) The manufacturing method of a grainoriented
electrical steel sheet according to (4),
wherein the predetermined interval is fixed.
[0018] (6) The manufacturing method of a grainoriented
electrical steel sheet according to (4),
wherein the predetermined interval is wider as the
position approaches from an inner surface toward an
outer surface of the steel sheet coil.
[0019] (7) The manufacturing method of a grainoriented
electrical steel sheet according to any one
of (1) to (6), wherein the predetermined interval is
2 mm or more.
[0020] (8) The manufacturing method of a grainoriented
electrical steel sheet according to any one
of (1) to (7), wherein, when
an average intensity of the laser beam is P (W),
a size in the rolling direction of a focused beam
spot of the laser beam is Dl (mm),
a scanning rate in the sheet width direction of
the laser beam is Vc (mm/s), and
an irradiation energy density of the laser beam
is Up = 4/nxp/(DlxVc) ,
the following relation is satisfied.
0. 5J/mm^^Up^20J/ mm
[0021] (9) The manufacturing method of the grainoriented
electrical steel sheet according to any one
of (1) to (8), wherein, when
an average intensity of the laser beam is P (W) ,
a size in the rolling direction and a size in the
sheet width direction of a focused beam spot of the
laser beam are Dl (mm) and Dc (mm), respectively, and
a local power density of the laser beam is
Ip = 4/nxp/(DlxDc) ,
the following relation is satisfied,
Ip^lOOkW/mm^.
[0022] (10) A grain-oriented electrical steel sheet,
including
grain boundaries passing from a front surface to
a rear surface of the grain-oriented electrical steel
sheet along paths of laser beams scanned from one end
to the other end of the grain-oriented electrical
steel sheet along a sheet width direction,
wherein, when a sheet thickness direction
component of an angle made by a rolling direction of
the grain-oriented electrical steel sheet and a
direction of an axis of easy magnetization direction
<001> of each crystal grain is P(°), a value of (3 at
a position separated by 1 mm from the grain boundary
is 7.3° or less.
[0023] (11) The grain-oriented electrical steel
sheet according to (10), wherein a surface of a base
9 -
material along the grain boundary is flat.
ADVANTAGEOUS EFFECTS OF INVENTION
[0024] According to the present invention, an angle
deviation can be lowered by grain boundaries which
are created along paths of laser beams and which pass
from a front surface to a rear surface of a silicon
steel sheet, so that it is possible to improve a
magnetic flux density and to reduce an iron loss
while maintaining high productivity.
BRIEF DESCRIPTION OF DRAWINGS
[0025] [Fig. lA] Fig. lA is a diagram illustrating
orientations of crystal grains obtained through a
secondary recrystallization;
[Fig, IB] Fig. IB is a diagram illustrating
crystal grains after flattening;
[Fig. 2A] Fig. 2A is a diagram illustrating a
manufacturing method of a grain-oriented electrical
steel sheet according to an embodiment of the present
invention;
[Fig. 2B] Fig. 2B is a diagram illustrating a
modified example of the embodiment;
[Fig. 3A] Fig. 3A is a diagram illustrating an
example of a method of scanning laser beams;
[Fig. 3B] Fig. SB is a diagram illustrating
another example of the method of scanning laser
beams;
[Fig. 4A] Fig. 4A is a plan view illustrating a
- 10 -
laser beam spot;
[Fig. 4B] Fig. 4B is a sectional view
illustrating the laser beam spot;
[Fig. 5A] Fig. 5A is a plan view illustrating
grain boundaries generated in the embodiment of the
present invention;
[Fig. 5B] Fig. 5B is a sectional view
illustrating the grain boundaries generated in the
embodiment of the present invention;
[Fig. 6A] Fig. 6A is a diagram illustrating a
picture of a surface of a silicon steel sheet
obtained when an irradiation of laser beam is
performed;
[Fig. 6B] Fig. 6B is a diagram illustrating a
picture of a surface of a silicon steel sheet
obtained when the irradiation of laser beam is
omitted;
[Fig. 7] Fig. 7 is a diagram illustrating a
picture of cross section of the silicon steel sheet
obtained when the irradiation of laser beam is
performed;
[Fig. 8] Fig. 8 is a diagram illustrating a
relation between a grain boundary and an angle
deviation (3;
[Fig. 9A] Fig. 9A is a diagram illustrating a
relation among a radius of curvature R, an inner
radius Rl and an outer radius R2;
[Fig. 9B] Fig. 9B is a diagram illustrating
intervals of irradiation of laser beams with respect
- 11 -
to a coil No. CI;
[Fig. 9C] Fig. 9C is a diagram illustrating
intervals of irradiation of laser beams with respect
to a coil No. C2; and
[Fig. 9D] Fig. 9D is a diagram illustrating
intervals of irradiation of laser beams with respect
to a coil No. C3.
DESCRIPTION OF EMBODIMENTS
[0026] Hereinafter, an embodiment of the present
invention will be described while referring to the
accompanying drawings. Fig. 2A is a diagram
illustrating a manufacturing method of a grainoriented
electrical steel sheet according to an
embodiment of the present invention.
[0027] In the present embodiment, cold-rolling of a
silicon steel sheet 1 containing Si of, for example,
2 mass% to 4 mass% is performed, as illustrated in
Fig. 2A. This silicon steel sheet 1 may be produced
through continuous casting of molten steel, hotrolling
of a slab obtained through the continuous
casting, an annealing of a hot-rolled steel sheet
obtained through the hot-rolling, and so on. A
temperature at the time of the annealing is about
1100°C, for example. Further, a thickness of the
silicon steel sheet 1 after the cold-rolling may be
set to about 0.20 mm to 0.3 mm, for example, and the
silicon steel sheet 1 after the cold-rolling is
coiled so as to be formed as a cold-rolled coil, for
- 12 -
example.
[0028] Then, the coil-shaped silicon steel sheet 1
is supplied to a decarburization annealing furnace 3
while being uncoiled, and is subjected to an
annealing in the annealing furnace 3. A temperature
at the time of the annealing is set to 700°C to
900°C, for example. During the annealing, a
decarburization occurs, and a primary
recrystallization occurs resulting in that crystal
grains in a Goss orientation, in which axes of easy
magnetization are parallel to the rolling direction,
are formed. Thereafter, the silicon steel sheet 1
discharged from the decarburization annealing furnace
3 is cooled with a cooling apparatus 4.
Subsequently, a coating 5 of an annealing separating
agent containing MgO as its major constituent is
performed on a surface of the silicon steel sheet 1.
Further, the silicon steel sheet 1 coated with the
annealing separating agent is coiled with a
predetermined inner radius Rl to be formed as a steel
sheet coil 31.
[0029] Further, in the present embodiment, between
the uncoiling the coil-shaped silicon steel sheet 1
and the supplying it to the decarburization annealing
furnace 3, a laser beam is irradiated a plurality of
times at predetermined intervals in the rolling
direction on a surface of the silicon steel sheet 1
from one end to the other end of the silicon steel
sheet 1 along a sheet width direction with a laser
- 13 -
beam irradiation apparatus 2. Incidentally, as
illustrated in Fig. 2B, the laser beam irradiation
apparatus 2 may be disposed on a downstream side in a
transferring direction of the cooling apparatus 4,
and the laser beams may be irradiated to the surface
of the silicon steel sheet 1 between the cooling with
the cooling apparatus 4 and the coating 5 of the
annealing separating agent. Further, the laser beam
irradiation apparatus 2 may be disposed on both of an
upstream side in the transferring direction of the
annealing furnace 3 and a downstream side in the
transferring direction of the cooling apparatus 4,
and the laser beams may be irradiated with both of
the apparatuses. Furthermore, the irradiation of
laser beam may be conducted between the annealing
furnace 3 and the cooling apparatus 4, and the
irradiation may be conducted in the annealing furnace
3 or in the cooling apparatus 4.
[0030] Incidentally, the irradiation of laser beam
may be performed by a scanner 10 when it scans a
laser beam 9 radiated from a light source (laser) at
a predetermined interval PL in the sheet width
direction (hereafter called also C direction)
substantially perpendicular to the rolling direction
(hereafter called also L direction) of the silicon
steel sheet 1, as illustrated in Fig. 3A, for
example. As a result of this, paths 23 of the laser
beams 9 remain on the surface of the silicon steel
sheet 1, regardless of whether they can be visually
- 14 -
recognized or not. The rolling direction
substantially matches the transferring direction.
[0031] Further, the scanning of laser beams over the
entire width of the silicon steel sheet 1 may be
performed with one scanner 10, or with a plurality of
scanners 20 as illustrated in Fig. 3B. When the
plurality of scanners 20 are used, only one light
source (laser) of laser beams 19, which are incident
on the respective scanners 20, may be provided, or
one light source may be provided for each scanner 20.
When the number of light source is one, a laser beam
radiated from the light source may be split to form
the laser beams 19. If the scanners 20 are used, it
is possible to divide an irradiation region into a
plurality of regions in the sheet width direction, so
that it is possible to reduce a period of time of
scanning and irradiation required per one laser beam.
Therefore, using the scanners 20 is particularly
suitable for a high-speed transferring facility.
[0032] The laser beam 9 or 19 is focused by a lens
in the scanner 10 or 20. As illustrated in Fig. 4A
and Fig. 4B, a shape of a laser beam spot 24 of the
laser beam 9 or 19 on the surface of the silicon
steel sheet 1 may have a circular shape or an
elliptical shape with a diameter in the sheet width
direction (C direction) of Dc and a diameter in the
rolling direction (L direction) of Dl. Further, the
scanning of laser beam 9 or 19 may be performed at a
rate Vc with a polygon mirror in the scanner 10 or
- 15 -
20, for example. The diameter in the sheet width
direction (diameter in the C direction) Dc may be set
to 5 mm, the diameter in the rolling direction
(diameter in the L direction) Dl may be set to 0.1
mm, and the scanning rate Vc may be set to about 1000
mm/s, for example.
[0033] Incidentally, as the light source (laser
device), a CO2 laser may be used, for example.
Further, a high-power laser which is generally used
for industrial purposes such as a YAG laser, a
semiconductor laser, and a fiber laser may be used.
[0034] Further, a temperature of the silicon steel
sheet 1 during irradiating the laser beam is not
particularly limited, and the irradiation of laser
beam may be performed on the silicon steel sheet 1 at
about room temperature, for example. Further, the
direction in which the laser beam is scanned does not
have to coincide with the sheet width direction (C
direction), but, from the viewpoint of working
efficiency and the like and from a point in which a
magnetic domain is refined into long strip shapes
along the rolling direction, a deviation of the
direction from the sheet width direction (C
direction) is preferably within 45°, more preferably
within 20°, and even more preferably within 10°.
[0035] Details of the irradiation interval PL of
laser beam will be described later.
[0036] After the coating 5 of the annealing
separating agent and the coiling, the steel sheet
- 16 -
coil 31 is conveyed into an annealing furnace 6, and
is placed with a center axis of the steel sheet coil
31 set substantially in a vertical direction, as
illustrated in Fig. 2A. Then, an annealing (finish
annealing) of the steel sheet coil 31 is performed
through batch processing. The maximum attained
temperature and a period of time at the time of this
annealing are set to about 1200°C and about 20 hours,
respectively, for example. During this annealing, a
secondary recrystallization occurs, and a glass film
is formed on the surface of the silicon steel sheet
1. Thereafter, the steel sheet coil 31 is taken out
from the annealing furnace 6.
[0037] Subsequently, the steel sheet coil 31 is
supplied, while being uncoiled, to an annealing
furnace 7, and is subjected to an annealing in the
annealing furnace 7. During this annealing, a curl,
distortion and deformation occurred during the finish
annealing are eliminated, resulting in that the
silicon steel sheet 1 becomes flat. Then, a
formation 8 of a film on the surface of the silicon
steel sheet 1 is performed. As the film, one capable
of securing insulation performance and imposing a
tension for reducing the iron loss may be formed, for
example. Through these series of processing, a
grain-oriented electrical steel sheet 32 is
manufactured. After the formation 8 of the film, the
grain-oriented electrical steel sheet 32 may be
coiled for the convenience of storage, conveyance and
- 17 -
the like, for example.
[0038] When the grain-oriented electrical steel
sheet 32 is manufactured through such a method,
during the secondary recrystallization, grain
boundaries 41 are created which pass from a front
surface to a rear surface of the silicon steel sheet
1 beneath the paths 23 of laser beams, as illustrated
in Fig. 5A and Fig. 5B.
[0039] It may be considered that the reason why such
a grain boundary 41 is generated is because internal
stress and distortion are introduced by the rapid
heating and cooling caused due to the irradiation of
laser beam. Further, it may also be considered that
due to the irradiation of laser beam the size of
crystal grains obtained through the primary
recrystallization differs from that of surrounding
crystal grains, resulting in that the grain growth
rate during the secondary recrystallization differs,
and the like.
[0040] Actually, when a grain-oriented electrical
steel sheet was manufactured based on the abovedescribed
embodiment, grain boundaries illustrated in
Fig. 6A and Fig. 7 were observed. These grain
boundaries included grain boundaries 61 formed along
paths of laser beams. Further, when a grain-oriented
electrical steel sheet was manufactured based on the
above-described embodiment except that the
irradiation of laser beam was omitted, a grain
boundary illustrated in Fig. 6B was observed.
- 18
[0041] Fig. 6A and Fig. 6B are pictures photographed
after a glass film and the like were removed from
surfaces of the grain-oriented electrical steel
sheets to expose the base material of steel, and then
a pickling of the surfaces was followed. In these
pictures, crystal grains and grain boundaries
obtained through the secondary recrystallization
appear. Further, regarding the manufacture of the
grain-oriented electrical steel sheets set as targets
of photographing of the pictures, an inner radius and
an outer radius of each of steel sheet coils were set
to 300 mm and 1000 mm, respectively. Further, the
irradiation interval PL of laser beam was set to
about 30 mm. Further, Fig. 7 illustrates a cross
section perpendicular to the sheet width direction (C
direction).
[0042] When the grain-oriented electrical steel
sheet illustrated in Fig. 6A and Fig. 7 was observed
in detail, a length in the rolling direction (L
direction) of crystal grain was about 30 mm, at
maximum, which corresponds to the irradiation
interval PL. Further, change in shape such as a
groove was rarely confirmed on a part to which the
laser beam was irradiated, and a surface of base
material of the grain-oriented electrical steel sheet
was substantially flat. Moreover, in both cases
where the irradiation of laser beam was conducted
before the annealing with the annealing furnace 3,
and the irradiation was conducted after the
19 -
annealing, similar grain boundaries were observed.
[0043] The present inventors conducted detailed
examination regarding an angle deviation p of the
grain-oriented electrical steel sheet manufactured
along the aforementioned embodiment. In this
examination, crystal orientation angles of various
crystal grains were measured by an X-ray Laue method.
A spatial resolution of the X-ray Laue method,
namely, a size of X-ray spot on the grain-oriented
electrical steel sheet was about 1 mm. This
examination showed that any of the angle deviations (3
at various measurement positions in the crystal
grains divided by grain boundaries extending along
paths of laser beams was within a range of 0° to 6°.
This means that a very high matching degree of
crystal orientation was obtained.
[0044] Meanwhile, the grain-oriented electrical
steel sheet manufactured by omitting the irradiation
of laser beam included a large number of crystal
grains each having a size in the rolling direction (L
direction) larger than that obtained when performing
the irradiation of laser beam. Further, when the
examination of angle deviation p was performed on
such large crystal grains, through the X-ray Laue
method, the angle deviation p exceeded 6° on the
whole, and further, the maximum value of the angle
deviation p exceeded 10° in a large number of crystal
grains .
[0045] Here, explanation will be made on the
- 20 -
irradiation interval PL of laser beam.
[0046] The relation between the magnetic flux
density Be and the magnitude of the angle deviation p
is according to Non-Patent Literature 1, for example.
The present inventors experimentally obtained
measurement data similar to the relation according to
Non-Patent Literature 1, and obtained, from the
measurement data, a relation between the magnetic
flux density Bs (T) and (B (°) represented by an
expression (1) through the least-squares method.
B8 = -0. 026xp + 2 . 090 ... (1)
[0047] Meanwhile, as illustrated in Fig. 5A, Fig. 5B
and Fig. 8, there exists at least one crystal grain
42 between two grain boundaries 41 along paths of
laser beams. Here, attention is focused on one
crystal grain 42, in which an angle deviation at each
position in the crystal grain 42 is defined as 3', by
setting a crystal orientation in an end portion on
one side of the two grain boundaries 41 of the
crystal grain 42 as a reference. At this time, as
illustrated in Fig. 8, the angle deviation P' at the
end portion on the one side is 0°. Further, at the
end portion on the other side, the maximum angle
deviation in the crystal grain 42 is generated.
Here, this angle deviation is expressed as the
maximum angle deviation pm (P'=pm). In this case,
the maximum angle deviation pm is represented as an
expression (2) with an interval PL between the grain
boundaries 41, namely, a length Lg in the rolling
- 21 -
direction of the crystal grain 42, and a radius of
curvature R of the silicon steel sheet at the
position in the steel sheet coil in the finish
annealing. Incidentally, a thickness of the silicon
steel sheet is thin so that it is negligible compared
to the inner radius and the outer radius of the steel
sheet coil. For this reason, there is no difference,
almost at all, between the radius of curvature of the
surface on the inside of the steel sheet coil and the
radius of curvature of the surface on the outside of
the steel sheet coil, and thus there is no influence,
almost at all, on the maximum angle deviation pm,
even if either value is used as the radius of
curvature R.
pm=(180/n) X (Lg/R) ... (2)
[0048] When attention is focused on the expression
(1), it can be understood that when the angle
deviation p is 7.3° or less, the magnetic flux
density Bg of 1.90 T or more can be obtained.
Conversely, it can be said that it is important to
set the angle deviation p to 7.3° or less for
obtaining the magnetic flux density Ba of 1.90 T or
more. Further, when attention is focused on the
expression (2), it can be said that, in order to set
the maximum angle deviation pm to 7.3° or less,
namely, in order to obtain the magnetic flux density
Be of 1.90 T or more, it is important to satisfy the
following expression (3).
Lg^0.13xR ... (3)
- 22 -
[0049] From these relations, it can be said that
regarding a part of the silicon steel sheet in which
the radius of curvature in the steel sheet coil is
"R", when the length Lg in the rolling direction of
the crystal grain grown in that part satisfies the
expression (3), the maximum angle deviation pm
becomes 7.3° or less, and the magnetic flux density Bg
of 1.90 T or more can be obtained. Further, the
length Lg corresponds to the irradiation interval PL
of laser beam. Therefore, it can be said that by
setting, at an arbitrary position in the silicon
steel sheet, the irradiation interval PL of laser
beam to satisfy an expression (4) in accordance with
the radius of curvature R, it is possible to obtain a
high magnetic flux density Be-
PL^0.13xR ... (4)
[0050] Further, even before the steel sheet coil is
obtained, the radius of curvature R in the steel
sheet coil of each part of the silicon steel sheet
can be easily calculated from information regarding
the length in the rolling direction of the silicon
steel sheet, the set value of the inner radius of the
steel sheet coil, a position Ps of the part by
setting a front edge or a rear edge of the silicon
steel sheet as a reference, and the like.
[0051] Further, when attention is focused on the
expression (1) and the expression (2), it is
important to set the angle deviation (3 to 5.4° or
less for obtaining the magnetic flux density Bs of
- 23 -
•
1.95 T or more, and to realize that, it is important
to set the irradiation interval PL of laser beam to
satisfy an expression (5).
PL^0.094xR ... (5)
[0052] Here, explanation will be made on an example
of method of adjusting the irradiation interval PL in
accordance with the radius of curvature R.
Specifically, in this method, the irradiation
interval PL is not fixed, and is adjusted to suitable
one in accordance with the radius of curvature R. As
described above, the inner radius Rl when coiling the
silicon steel sheet 1 after the coating 5 of the
annealing separating agent is performed, namely, the
inner radius Rl of the steel sheet coil 31 is
predetermined. The outer radius R2 and a coiling
number N of the steel sheet coil 31 can be easily
calculated from a size A of gap existed between
silicon steel sheets 1 within the steel sheet coil
31, a thickness t of the silicon steel sheet 1, a
length LO in the rolling direction of the silicon
steel sheet 1, and the inner radius Rl. Further,
from values of these, it is possible to calculate the
radius of curvature R in the steel sheet coil 31 of
each part of the silicon steel sheet 1 as a function
of a distance LI from the front edge in the
transferring direction. Incidentally, as the size A
of gap, an experientially obtained value, a value
based on the way of coiling or the like may be used,
and a value of 0 or a value other than 0 may be used.
- 24 -
Further, the radius of curvature R may be calculated
by empirically or experimentally obtaining the outer
radius R2 and the coiling number N when the length
LO, the coil inner radius Rl, and the thickness t are
already known.
[0053] Further, based on the radius of curvature R
as a function of the distance LI, the irradiation of
laser beam is conducted in the following manner.
(a) The laser beam irradiation apparatus 2 is
placed on the upstream side and/or the downstream
side of the annealing furnace 3.
(b) A transferring speed and a passage distance
(which corresponds to the distance Ll from the front
edge in the transferring direction) of the silicon
steel sheet 1 at a point at which the laser beam is
irradiated, are measured by a line speed monitoring
apparatus and an irradiation position monitoring
apparatus.
(c) Based on the sheet transfer speed of the
silicon steel sheet 1, the distance Ll from the front
edge, and the scanning rate Vc of laser beam, setting
is conducted so that the irradiation interval PL on
the surface of the silicon steel sheet 1 satisfies
the expression (4), preferably the expression (5).
Further, the irradiation energy density, and the
local power density and the like of laser beam are
also set.
(d) The irradiation of laser beam is performed.
[0054] As described above, the irradiation interval
- 25 -
PL can be adjusted in accordance with the radius of
curvature R. Incidentally, the irradiation interval
PL may be fixed within a range of satisfying the
expression (4), preferably the expression (5). When
the adjustment as described above is conducted, as a
point in the steel sheet coil 31 approaches the outer
periphery of the coil, the irradiation interval PL at
that point is increased, so that when compared to a
case where the irradiation interval PL is fixed, it
is possible to reduce an average power of irradiation
of laser.
[0055] Next, explanation will be made on conditions
of the irradiation of laser beam. From an experiment
described below, the present inventors found out that
when the irradiation energy density Up of laser beam
defined by an expression (6) satisfies an expression
(7), a grain boundary along a path of laser beam is
particularly properly formed.
Up = 4/nxp/(DlxVc) ... (6)
0 . 5 J/mm^^Up^20 J/mm^ (7)
Here, P represents an intensity (W) of laser
beam, Dl represents a size (mm) in the rolling
direction of focused beam spot of laser beam, and Vc
represents a scanning rate (mm/sec) of laser beam.
[0056] In this experiment, hot-rolling was first
performed on a steel material for a grain-oriented
electrical steel containing Si of 2 mass% to 4 mass%,
so as to obtain a silicon steel sheet after the hotrolling
(hot-rolled steel sheet). Then, the silicon
- 26 -
steel sheet was annealed at about 1100°C.
Thereafter, cold-rolling was performed to set a
thickness of the silicon steel sheet to 0.23 mm, and
the resultant was coiled to have a cold-rolled coil.
Subsequently, from the cold-rolled coil, single-plate
samples each having a width in the C direction of 100
mm and a length in the rolling direction (L
direction) of 500 mm were cut out. Then, on a
surface of each of the single-plate samples, laser
beams were irradiated while being scanned in the
sheet width direction. Conditions for them are
presented in Table 1. Thereafter, a decarburization
annealing was conducted at 700°C to 900°C to cause a
primary recrystallization. Subsequently, the singleplate
samples were cooled to about room temperature,
and thereafter, an annealing separating agent
containing MgO as its major constituent was coated on
the surfaces of each of the single-plate samples.
Then, a finish annealing at about 1200°C for about 20
hours was conducted so as to cause a secondary
recrystallization.
[0057] Further, an evaluation regarding the
presence/absence of grain boundaries along paths of
laser beams, and the presence/absence of melting and
deformation of the surface of each of the singleplate
samples being a base material, were conducted.
Incidentally, in the evaluation regarding the
presence/absence of the grain boundaries along the
paths of laser beams, an observation of picture of a
- 27 -
cross section of each of the single-plate samples
orthogonal to the sheet width direction was
conducted. Further, regarding the presence/absence
of the melting and deformation of the surface, an
observation of the surface of each of the singleplate
samples after the removal of glass film formed
during the finish annealing and the performance of
pickling, was conducted. Results of these are also
presented in Table 1.
[0058]
[Table 1]
- 28 -
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TABLE 1
SAMPLE
No.
1
2
3
4
5
6
7
8
9
P
(W)
500
500
500
500
500
500
500
2000
500
Vc
(mm/s)
15000
10000
5000
2000
1000
500
300
400
400
Dl
(mm)
0 .1
0 .1
0.1
0.1
0.1
0.1
0.1
1
0.05
DC
(mm)
5
5
5
5
5
5
5
10
10
Up
(J/min )
0.4
0.5
1.3
3.2
6.4
12.7
21.2
6.4
12.7
GRAIN
BOUNDARIES
ALONG PATHS
ABSENT
PRESENT
PRESENT
PRESENT
PRESENT
PRESENT
PRESENT
PRESENT
PRESENT
MELTING,
DEFORMATION
AT SURFACE
ABSENT
ABSENT
ABSENT
ABSENT
ABSENT
ABSENT
PRESENT
ABSENT
ABSENT
^"ymmrns^smm mi*}M*i>»wvMmmm9M'm'mmmmmmf'm
than 0.5 J/mm^, the grain boundaries along the paths
of laser beams were not formed. It can be considered
that this is because, since a sufficient heat
quantity was not provided, a variation in local
distortion strength and a variation in a size of
crystal grain obtained through the primary
recrystallization did not occur almost at all.
Further, in a sample No. 7, in which the irradiation
energy density Up exceeded 20 J/mm^, although the
grain boundaries along the paths of laser beams were
formed, the deformation and/or a trace of melting
caused by the irradiation of laser beams existed on
the surface of the single-plate sample (the base
material of steel). When the grain-oriented
electrical steel sheets are stacked to be used, the
deformation and/or the trace of melting as above
reduce(s) a space factor and generate(s) stress and
deformation, which leads to the reduction in the
magnetic properties.
[0060] Meanwhile, in samples No. 2 to No. 6 and
samples No. 8 and No. 9, in which the expression (7)
was satisfied, the grain boundaries along the paths
of laser beams were properly formed, regardless of
the shape of focused beam spot of laser beam, the
scanning rate, and the intensity of laser beam.
Further, no deformation and trace of melting caused
by the irradiation of laser beam existed.
[0061] From such an experiment, it can be said that
the irradiation energy density Up of laser beam
- 30 -
defined by the expression (6) preferably satisfies
the expression (7).
[0062] Incidentally, a similar result was obtained
also when the irradiation of laser beam was performed
between the decarburization annealing and the finish
annealing. Therefore, also in this case, it is
preferable that the irradiation energy density Up
satisfies the expression (7). Further, also when the
irradiation of laser beam is conducted before and
after the decarburization annealing, the irradiation
energy density Up preferably satisfies the expression
(7) .
[0063] Further, in order to prevent the occurrence
of deformation and melting of the silicon steel sheet
(the base material of steel) caused by the
irradiation of laser beam, it is preferable that the
local power density Ip of laser defined by an
expression (8) satisfies an expression (9).
Ip = 4/nxp/(DlxDc) ... (8)
Ip^lOOkW/mm^ ... (9)
Here, Dc represents the size (mm) in the sheet
width direction of the focused beam spot of laser
beam.
[0064] The larger the local power density Ip, the
higher the chance of occurrence of melting,
scattering, and vaporization of the silicon steel
sheet, and when the local power density Ip exceeds
100 kW/mm^, a hole, a groove or the like is likely to
be formed on the surface of the silicon steel sheet.
- 31 -
Further, when comparing a pulse laser and a
continuous wave laser, a groove or the like is likely
to be formed when the pulse laser is used, even if
the same local power density Ip is employed. This is
because, when a pulse laser is used, a sudden change
in temperature easily occurs at a region to which the
laser beam is irradiated. Therefore, it is
preferable to use a continuous wave laser.
[0065] The same applies to a case where the
irradiation of laser beam is conducted between the
decarburization annealing and the finish annealing,
and a case where the irradiation of laser beam is
conducted before and after the decarburization
annealing.
[0066] As described above, when the steel sheet coil
of the silicon steel sheet after the occurrence of
primary recrystallization is annealed to cause the
secondary recrystallization, a part is generated in
the crystal grain obtained through the secondary
recrystallization, in which the axis of easy
magnetization is deviated from the rolling direction
due to the influence of curvature, as illustrated in
Fig. lA and Fig. IB. Further, the larger the size of
the crystal grains in the rolling direction and the
smaller the radius of curvature, the more noticeable
the degree of the deviation. Further, since the size
in the rolling direction as above is not particularly
controlled in the conventional technique, there is a
case where the angle deviation p being one of indexes
- 32
for representing the degree of deviation described
above reaches 10° or more. On the contrary,
according to the embodiment described above, the
proper irradiation of laser beam is conducted, and
the grain boundaries passing from the front surface
to the rear surface of the silicon steel sheet
beneath the paths of laser beams are generated during
the secondary recrystallization, so that the size of
each crystal grain in the rolling direction is
preferable. Therefore, when compared to a case where
the irradiation of laser beam is not conducted, it is
possible to reduce the angle deviation (3 and improve
the orientation of crystal orientation to obtain a
high magnetic flux density Eg and a low iron loss
Wl7/50 •
[0067] Further, the irradiation of laser beam may be
performed at high speed, and the laser beam can be
focused into a very small space to obtain a high
energy density, so that an influence on a production
time due to the laser processing is small, when
compared to a case where the irradiation of laser
beam is not conducted. In other words, the
transferring speed in the processing of performing
the decarburization annealing while uncoiling the
cold-rolled coil and the like, does not have to be
changed almost at all, regardless of the
presence/absence of the irradiation of laser beam.
Further, since the temperature at the time of
performing the irradiation of laser beam is not
- 33 -
particularly limited, a heat insulating apparatus or
the like for the laser irradiation apparatus is not
required. Therefore, it is possible to simplify the
structure of the facility, when compared to a case
where a processing in a high-temperature furnace is
required.
[0068] Incidentally, an irradiation of laser beam
may be performed for the purpose of refining a
magnetic domain after the formation of the insulating
film.
EXAMPLE
[0069] (First Experiment)
In a first experiment, a steel material for a
grain-oriented electrical steel containing Si of 3
mass% was hot-rolled, so as to obtain a silicon steel
sheet after the hot-rolling (hot-rolled steel sheet).
Then, the silicon steel sheet was annealed at about
1100°C. Thereafter, cold-rolling was conducted so as
to make a thickness of the silicon steel sheet 0.23
mm, and the resultant was coiled to have a coldrolled
coil. Incidentally, the number of produced
cold-rolled coils was four. Subsequently, an
irradiation of laser beam was performed on three
cold-rolled coils (coils Nos. CI to C3), and after
that, a decarburization annealing was conducted to
cause a primary recrystallization. Regarding the
remaining one cold-rolled coil (coil No. C4), no
irradiation of laser beam was conducted, and after
- 34 -
that, the decarburization annealing was conducted to
cause the primary recrystallization.
[0070] After the decarburization annealing, a
coating of an annealing separating agent, and a
finish annealing under the same condition were
performed on these silicon steel sheets.
[0071] Here, explanation will be made on the
irradiation interval PL of laser beam in the coils
Nos. CI to C3, while referring to Fig. 9A to Fig. 9D.
After the coating of the annealing separating agent,
the silicon steel sheet was coiled to have a steel
sheet coil 51 as illustrated in Fig. 9A, and the
finish annealing was conducted under this state. In
advance of making the steel sheet coil 51, an inner
radius Rl of the steel sheet coil 51 was set to 310
mm. Further, a length LO in the rolling direction of
the silicon steel sheet in the steel sheet coil 51
was equivalent to a length in the rolling direction
of the silicon steel sheet after the cold-rolling,
and was about 12000 m. Therefore, an outer radius R2
of the steel sheet coil 51 could be calculated from
these, and was 1000 mm.
[0072] Further, in the irradiation of laser beam
with respect to the coil No, CI, the irradiation
interval PL was set to 40 mm, as illustrated in Fig.
9B. Specifically, the irradiation of laser beam was
conducted with the same interval from a part
corresponding to an inside edge 52 to a part
corresponding to an outside edge 53 of the steel
- 35
sheet coil 51, to leave paths 54 on a surface of a
silicon steel sheet 55. Incidentally, the value of
the irradiation interval PL (40 mm) in this
processing is equivalent to the maximum value within
a range which satisfies the expression (4) in
relation to the inner radius Rl (310 mm) of the steel
sheet coil 51. Therefore, the expression (4) is
satisfied at each position of the silicon steel sheet
55.
[0073] Further, in the irradiation of laser beam
with respect to the coil No. C2, the irradiation
interval PL was changed in accordance with a local
radius of curvature R in the steel sheet coil 51, as
illustrated in Fig. 9C. In other words, the
irradiation of laser beam was conducted from a part
corresponding to the inside edge 52 to a part
corresponding to the outside edge 53 of the steel
sheet coil 51 while gradually enlarging the
irradiation interval PL, which was set equal to
0.13xR, to leave the paths 54 on the surface of the
silicon steel sheet 55.
[0074] Further, in the irradiation of laser beam
with respect to the coil No. C3, the irradiation
interval PL was set to 150 mm, as illustrated in Fig.
9D. In other words, the irradiation of laser beam
was conducted with the same interval from a part
corresponding to the inside edge 52 to a part
corresponding to the outside edge 53 of the steel
sheet coil 51, to leave the paths 54 on the surface
- 36 -
of the silicon steel sheet 55. Incidentally, the
value of the irradiation interval PL (150 mm) in this
processing is larger than the maximum value (130 mm)
within a range of satisfying the expression (4) in
relation to the outer radius R2 (1000 mm) of the
steel sheet coil 51. Therefore, the expression (4)
is not satisfied at any position of the silicon steel
sheet 55.
[0075] Further, in the irradiation of laser beam
with respect to the coils Nos. CI to C3, the
condition in which the irradiation energy density Up
and the local power density Ip satisfy the expression
(7) and the eicpression (9), was selected. As
described above, no irradiation of laser beam was
performed on the coil No. C4.
[0076] After the finish annealing, an annealing was
performed for eliminating a curl, distortion and
deformation occurred during the finish annealing, so
as to flatten the silicon steel sheets 55. Further,
an insulating film was formed on the surface of each
of the silicon steel sheets 55. Thus, the four types
of grain-oriented electrical steel sheets were
manufactured.
[0077] Then, from each of the grain-oriented
electrical steel sheets, ten samples were cut out at
each of six positions indicated in Table 2 along the
rolling direction by setting the inside edge 52 of
the steel sheet coil 51 as a starting point. The
magnetic flux density Bs, the iron loss W17/50, and the
- 37 -
maximum value of the angle deviation (3 of each sample
were measured. The magnetic flux density Be and the
iron loss W17/50 were measured by a well-known
measuring method with respect to electrical steel
sheets. In the measurement of the maximum value of
the angle deviation (3, the X-ray Laue method was
employed. Incidentally, the size of X-ray spot on
the sample, namely, the spatial resolution in the Xray
Laue method was 1 mm. Results of these are also
presented in Table 2. Note that each numerical value
presented in Table 2 is an average value of the ten
samples.
[0078]
[Table 2]
- 38 -
TABLE 2
POSITION
IN ROLLING
DIRECTION (m)
10
2000
4000
6000
8000
12000
PL
(mm)
40
40
40
40
40
40
COIL
( °)
7 .2
6 .0
4 . 6
3 .4
2 . 5
2 . 3
No. CI
BB
(T)
1.904
1 . 9 33
1 . 9 36
1 . 9 40
1 . 9 42
1 . 9 50
Wl7/50
(W/kg)
0 . 77
0 . 7 6
0 . 76
0 . 75
0 . 7 5
0 . 7 5
COIL
PL
(mm)
41
64
81
95
107
128
("}
7 . 1
7 .0
6 .9
6 .7
6 .9
7 .0
No. C2
Be
(T)
1 . 9 10
1 . 9 08
1 . 9 13
1 . 9 20
1 . 9 16
1 . 9 10
Wn/50
(W/kg)
0 . 77
0 . 76
0 . 7 5
0 . 75
0 . 76
0 . 75
COIL
PL
(mm)
150
150
150
150
150
150
1 3 . 0
1 1 .2
1 0 . 5
9 .8
9 .6
8 .6
No. C3
Be
(T)
1 . 8 50
1 . 8 60
1 . 8 70
1 . 8 60
1 . 8 60
1 . 8 70
Wl7/50
(W/kg)
0 . 85
0 . 8 5
0 . 8 6
0 . 84
0 . 83
0 . 84
COIL No.
P
(°)
1 3 . 5
1 4 .2
1 5 . 1
1 6 .2
1 7 .0
1 8 . 9
Ba
(T)
1.840
1 . 8 30
1 . 8 29
1 . 8 35
1 . 8 45
1.830
C4
Wn/50
(W/kg)
0 . 86
0 . 86
0 . 88
0 . 8 9
0 . 90
0 . 89
mmmmwrnftttmi
[0079] As presented in Table 2, in the coils Nos. CI
and C2, in which the expression (4) was satisfied,
the maximum value of the angle deviation p was less
than 7.3° at each position. For this reason, the
magnetic flux density Bs was significantly large and
the iron loss W17/50 was extremely low, when compared
to the coil No. C4 (comparative example), in which no
irradiation of laser beam was conducted. In short,
the magnetic flux density BB of 1.90 T or more and the
iron loss W17/50 of 0.77 W/kg or less were stably
obtained. Moreover, in the coil No. C2, the
irradiation interval PL was adjusted in accordance
with the radius of curvature R, so that more uniform
magnetic properties were obtained.
[0080] Further, in the coil No. C3, in which the
expression (4) was not satisfied, the magnetic flux
density Eg was large and the iron loss W17/50 was low
when compared to the coil No. C4 (comparative
example), but the magnetic flux density Eg was small
and the iron loss W17/50 was high when compared to the
coils Nos. Cl and C2.
[0081] Further, regarding each sample cut out from
the coils No, 1 to No. 3, a distribution of angle
deviation p in a crystal grain was measured through
the X-ray Laue method. As a result, it was confirmed
that in a crystal grain between two grain boundaries
formed along the paths of laser beams, the angle
deviation p is large in a region closer to either of
the grain boundaries. Generally, a position
40 -
resolution in the measurement with the X-ray Laue
method is 1 mm, and a position resolution in this
measurement was also 1 mm.
[0082] From the first experiment as described above,
it was proved that when the angle deviation (3 at the
position separated by 1 mm from the grain boundary
formed along the path of laser beam is 7.3° or less,
it is possible to improve the matching degree of
crystal orientation to obtain the magnetic flux
density Be of 1.90 T or more.
[0083] (Second Experiment)
In a second experiment, cold-rolled coils were
first produced in a similar manner to the first
experiment. Incidentally, the number of produced
cold-rolled coils was five. Subsequently, regarding
four cold-rolled coils, the irradiation of laser beam
was conducted by differentiating the irradiation
intervals PL as presented in Table 3, and after that,
the decarburization annealing was conducted to cause
the primary recrystallization. Regarding the
remaining one cold-rolled coil, no irradiation of
laser beam was conducted, and after that, the
decarburization annealing was conducted to cause the
primary recrystallization.
[0084] After the decarburization annealing, the
coating of the annealing separating agent, and the
finish annealing under the same condition were
performed on these silicon steel sheets. Further, an
annealing was performed for eliminating a curl.
- 41 -
distortion and deformation occurred during the finish
annealing, so as to flatten the silicon steel sheets.
Further, an insulating film was formed on the surface
of each of the silicon steel sheets. Thus, the five
types of grain-oriented electrical steel sheets were
manufactured.
[0085] Then, a sample was cut out from a part
corresponding to the inside edge of the steel sheet
coil (Rl=310mm) of each grain-oriented electrical
steel sheet, and the magnetic flux density Bs and the
iron loss W17/50 of each sample were measured. Results
thereof are also presented in Table 3.
[0086] [Table 3]
TABLE 3
SAMPLE
No.
10
11
12
13
14
GRAIN
BOUNDARIES
ALONG PATHS
ABSENT
PRESENT
PRESENT
PRESENT
PRESENT
PL
(mm)
-
1
2
5
10
Be
(T)
1.880
1.890
1 . 9 15
1 . 9 35
1.940
W17/50
(W/]cg)
0 . 8 30
0 . 8 25
0 . 7 60
0 . 7 50
0 . 7 30
[0087] As presented in Table 3, in samples No. 10
and No. 11, in which the irradiation interval PL was
less than 2 mm, the magnetic flux density Be was low
to be less than 1.90 T, and the iron loss W17/50 was
42 -
high to be 0.8 W/kg or more. In short, the magnetic
properties were deteriorated, when compared to
samples No. 12 to No. 14, in which the irradiation
interval PL was 2 mm or more. It can be estimated
that this is because when the irradiation interval PL
is extremely small, a size in the rolling direction
of crystal grain between two grain boundaries is too
small so that an influence of very small distortion
occurred by the irradiation of laser beam becomes
relatively large. In other words, it can be
estimated that this is because, although the angle
deviation (3 becomes small, a hysteresis loss of the
silicon steel sheet is increased and the magnetic
properties become difficult to be improved.
Therefore, it is preferable to set a lower limit
value of the range of the irradiation interval PL to
2 mm, regardless of the radius of curvature R.
INDUSTRIAL APPLICABILITY
[0088] The present invention may be utilized in an
industry of manufacturing electrical steel sheets and
an industry of utilizing electrical steel sheets, for
example.
- 43 -

CLAIMS
[Claim 1] A manufacturing method of a grain-oriented
electrical steel sheet, comprising:
cold-rolling a silicon steel sheet containing Si;
next, performing a decarburization annealing of
the silicon steel sheet so as to cause a primary
recrystallization;
next, coiling the silicon steel sheet so as to
obtain a steel sheet coil;
next, performing an annealing of the steel sheet
coil through batch processing so as to cause a
secondary recrystallization; and
next, uncoiling and flattening the steel sheet
coil, wherein
the manufacturing method further comprising,
between the cold-rolling the silicon steel sheet
containing Si and the coiling the silicon steel sheet
so as to obtain the steel sheet coil, irradiating a
laser beam a plurality of times at a predetermined
interval in a rolling direction on a surface of the
silicon steel sheet from one end to the other end of
the silicon steel sheet along a sheet width
direction, and
while the secondary recrystallization is caused,
grain boundaries passing from a front surface to a
rear surface of the silicon steel sheet are generated
along paths of the laser beams.
[Claim 2] The manufacturing method of a grainoriented
electrical steel sheet according to claim 1,
- 44 -
wherein a part of the surface of the silicon steel
sheet to which the laser beam has been irradiated is
flat.
[Claim 3] The manufacturing method of a grainoriented
electrical steel sheet according to claim 1,
wherein the predetermined interval is set based on a
radius of curvature of the silicon steel sheet in the
steel sheet coil.
[Claim 4] The manufacturing method of a grainoriented
electrical steel sheet according to claim 1,
wherein, when a radius of curvature at an arbitraryposition
in the silicon steel sheet in the steel
sheet coil is R (mm) and the predetermined interval
at the position is PL (mm), the following relation is
satisfied,
PL^O . 13xR.
[Claim 5] The manufacturing method of a grainoriented
electrical steel sheet according to claim 4,
wherein the predetermined interval is fixed.
[Claim 6] The manufacturing method of a grainoriented
electrical steel sheet according to claim 4,
wherein the predetermined interval is wider as the
position approaches from an inner surface toward an
outer surface of the steel sheet coil.
[Claim 7] The manufacturing method of a grainoriented
electrical steel sheet according to claim 1,
wherein the predetermined interval is 2 mm or more.
[Claim 8] The manufacturing method of a grainoriented
electrical steel sheet according to claim 1,
- 45 -
•
wherein, when
an average intensity of the laser beam is P (W),
a size in the rolling direction of a focused beam
spot of the laser beam is Dl (mm) ,
a scanning rate in the sheet width direction of
the laser beam is Vc (mm/s), and
an irradiation energy density of the laser beam
is Up = 4/nxp/(DlxVc) ,
the following relation is satisfied,
0 . 5J/mm^^Up^20J/mm^.
[Claim 9] The manufacturing method of a grainoriented
electrical steel sheet according to claim 1,
wherein, when
an average intensity of the laser beam is P (W) ,
a size in the rolling direction and a size in the
sheet width direction of a focused beam spot of the
laser beam are Dl (mm) and Dc (mm), respectively, and
a local power density of the laser beam is
Ip=4/nxp/(DlxDc),
the following relation is satisfied,
Ip^lOOkW/mm^.
[Claim 10] A grain-oriented electrical steel sheet,
comprising
grain boundaries passing from a front surface to
a rear surface of the grain-oriented electrical steel
sheet along paths of laser beams scanned from one end
to the other end of the grain-oriented electrical
steel sheet along a sheet width direction,
wherein, when a sheet thickness direction of an
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#
angle made by a rolling direction of the grainoriented
electrical steel sheet and a direction of an
axis of easy magnetization direction (100)<001> of
each crystal grain is |3 ( °) , a value of p at a
position separated by 1 mm from the grain boundary is
7.3° or less.
[Claim 11] The grain-oriented electrical steel sheet
according to claim 10, wherein a surface of a base
material along the grain boundary is flat.