The present invention relates to a grain-oriented electrical steel sheet that is
10 suitable for an iron core or the like ofa transformer, and a method of manufacturing the
grain-oriented electrical steel sheet. Priority is claimed on Japanese Patent Application
No. 2010-202394 filed on September 9,2010, the contents of which are incorporated
herein by reference.
Background Art
[0002]
As a technique for reducing iron loss of a grain-oriented electrical steel sheet,
there is a technique of subdividing a magnetic domain by introducing a strain into the
surface of a ferrite (patent Document 3). However, in a wound iron core, since strain
relief annealing is performed in the manufacturing process thereof, at the time of
20 annealing, the introduced strain is relaxed, and thus the subdivision ofthe magnetic
domain does not become sufficient.
[0003]
As a method of supplementing this shortcoming, there is a technique of forming
a groove in the surface of a ferrite (patent Documents 1, 2, 4, and 5). In addition, there
25 is a technique of forming a groove in the surface of a ferrite and also forming a crystal
2
grain boundary ranging from a bottom portion ofthe groove to the rear surface ofthe
I
ferrite in a sheet thickness direction (patent Document 6).
[0004]
A method offorming a groove and a grain boundary has a high improvement
5 effect for iron loss. However, in the technique stated in Patent Document 6,
productivity is significantly reduced. This is because the width ofthe groove is set to
be in a range of 30 to 300 Jlm in order to obtain a desired effect and then, attachment of
Sn or the like to the groove and annealing, addition of a strain to the groove, or radiation
of laser light, plasma, or the like for heat treatment to the groove, is required for further
10 formation of a crystal grain boundary. That is, it is because it is difficult to perform
treatment such as the attachment of Sn, the addition of a strain, or the radiation of laser
light in exact conformity with a narrow groove and it is necessary to slow a sheet passing
speed extremely, in order to realize them. In Patent Document 6, a method of
performing electrolytic etching is given as the method of forming a groove. However,
15 in order to perform the electrolytic etching, it is necessary to perform application of a
resist, corrosion treatment using an etching solution, removal ofthe resist, and cleaning.
For this reason, the number of processes and the treating time significantly increase.
Citation List
Patent Documents
20
25
[0005]
[Patent Document 1] Japanese Examined Patent Application, Second
Publication No. S62-53579
[Patent Document 2] Japanese Examined Patent Application, Second
Publication No. S62-54873
[Patent Document 3] Japanese Unexamined Patent Application, First
• 3
Publication No. S56-51528
[patent Document 4] Japanese Unexamined Patent Application, First
Publication No. H6-57335
[Patent Document 5] Japanese Unexamined Patent Application, First
5 Publication No. 2003-129135
[patent Document 6] Japanese Unexamined Patent Application, First
Publication No. H7-268474
[patent Document 7] Japanese Unexamined Patent Application, First
Publication No. 2000-109961
10 [Patent Document 8] Japanese Unexamined Patent Application, First
Publication No. H9-49024
[patent Document 9] Japanese Unexamined Patent Application, First
Publication No. H9-268322
15 Summary of Invention
Technical Problem
[0006]
The present invention has an obj ect of providing amethod of manufacturing a
grain-oriented electrical steel sheet, in which it is possible to industrially mass-produce a
20 grain-oriented electrical steel sheet having low iron loss, and a grain-oriented electrical
steel sheet having low iron loss.
Solution to Problem
[0007]
In order to solve the above problem, thereby achieving such an object, the
25 present invention adopts the following measures.
4
[0008]
(1) That is, according to an aspect ofthe present invention, there is provided a
method ofmanufacturing a grain-oriented electrical steel sheet including: a cold rolling _
process of performing a cold rolling while moving a silicon steel sheet containing Si-
S along a sheet passing direction; a first continuous annealing process ofcausing a
decarburization and a primary recrystallization of the silicon steel sheet; a winding
process of winding the silicon steel sheet, thereby obtaining a steel sheet coil; a groove
formation process of irradiating a surface of the silicon steel sheet with a laser beam
multiple times at predetermined intervals in the sheet passing direction, over an area from
10 one end edge to the other end edge, in a sheet width direction ofthe silicon steel sheet,
thereby forming a groove along a locus ofthe laser beam, during the period from the cold
rolling process to the winding process; a batch annealing process ofcausing secondary
recrystallization in the steel sheet coil; a second continuous annealing process of
unwinding and planarizing the steel sheet coil; and a continuous coating process of
15 imparting tension and electrical insulation properties to the surface ofthe silicon steel
sheet, wherein in the batch annealing process, a crystal grain boundary penetrating the
silicon steel sheet from a front surface to back surface along the groove is generated, and
when an average intensity ofthe laser beam is set to be P (W), a focusing diameter in the
sheet passing direction ofa focused spot of the laser beam is set to be DI (mm), a
20 focusing diameter in the sheet width direction is set to be Dc (mm), a scanning speed in
the sheet width direction ofthe laser beam is set to be Vc (mm/s), an irradiation energy
density Up ofthe laser beam is represented by the following Formula 1, and an
instantaneous power density Ip of the laser beam is represented by following Formula 2,
following Formulae 3 and 4 are satisfied.
25 Up = (4/n)xP/(DlxVc) (Formula 1)
(Formula 4)
5
Ip= (4/1t)xP/(DlxDc) (Formula 2)
1 ~ Up ~ 10 (J/mm2) (Formula 3)
100 (kW/mm2
) ~ Ip ~ 2000 (kW/mm2
)
[0009]
5 (2) In the aspect stated in the above (1), in the groove formation process, gas
may be blown onto a portion ofthe silicon steel sheet that is irradiated with the laser
beam, at a flow rate of greater than or equal to 10 L/minute and less than or equal to 500
L/minute.
[0010]
10 (3) According to another aspect ofthe present invention, there is provided a
grain-oriented electrical steel sheet including: a groove formed from a locus of a laser
beam that performed scanning over an area from one end edge to the other end edge in a
sheet width direction; and a crystal grain boundary extending along the groove and
penetrating the grain-oriented electrical steel sheet from a front surface to back surface.
15 [0011]
(4) In the aspect stated in the above (3), the grain-oriented electrical steel sheet
may further include a crystal grain in which a grain diameter thereof in the sheet width
direction ofthe grain-oriented electrical steel sheet is greater than or equal to 10 mm and
less than or equal to a sheet width and a grain diameter thereof in a longitudinal direction
20 ofthe grain-oriented electrical steel sheet exceeds 0 mm and is 10 mm or less, wherein
the crystal grain may be present to range from the groove to the back surface ofthe
grain-oriented electrical steel sheet.
[0012]
(5) In the aspect stated in the above (3) or (4), a glass coating may be formed in
25 the groove, and a X-ray intensity ratio Ir of a characteristic X-ray intensity ofMg at a
25
6
portion ofthe groove in a case where an average value ofthe characteristic X-ray
intensity ofMg of portions other than the portion of the groove ofthe surface ofthe
grain-oriented electrical steel sheet is set to be 1, in the glass coating, may be in a range
ofO::s;Ir::S;0.9.
5 Advantageous Effects of Invention
[0013]
According to the above aspects of the present invention, it is possible to obtain a
grain-oriented electrical steel sheet having low iron loss by a method-in which it is
possible to industrially mass-produce the grain-oriented electrical steel sheet.
10
Brief Description of Drawings
[0014]
FIG. 1 is a diagram showing a method of manufacturing a grain-oriented
electrical steel sheet related to an embodiment of the present invention.
15 FIG. 2 is a diagram showing a modified example ofthe embodiment ofthe
present invention.
FIG. 3A is a diagram showing another example of a scanning method of a laser
beam in the embodiment ofthe present invention.
FIG. 3B is a diagram showing another example of a scanning method of a laser
20 beam in the embodiment ofthe present invention.
FIG. 4A is a diagram showing a focused spot ofa laser beam in the embodiment
of the present invention.
FIG. 4B is a diagram showing the focused spot ofthe laser beam in the
embodiment ofthe present invention.
FIG. 5 is a diagram showing a groove and crystal grains which are formed in the
7
embodiment ofthe present invention.
FIG. 6A is a diagram showing crystal grain boundaries which are formed in the
embodiment ofthe present invention.
FIG. 6B is a diagram showing the crystal grain boundaries which are formed in
5 the embodiment of the present invention.
FIG. 7A is a diagram showing a photograph ofthe surface of a silicon steel sheet
in the embodiment of the present invention.
FIG. 7B is a diagram showing a photograph ofthe surface of a silicon steel sheet
in an embodiment of a comparative example.
10 FIG. 8A is a diagram showing another example ofthe crystal grain boundary in
the embodiment of the present invention.
FIG. 8B is a diagram showing another example ofthe crystal grain boundary in
the embodiment of the present invention.
15 Description of Embodiments
[0015]
Hereinafter, an embodiment of the present invention will be described with
reference to the accompanying drawings. FIG. 1 is a diagram showing a method of
manufacturing a grain-oriented electrical steel sheet related to the embodiment of the
20 present invention.
[0016]
In this embodiment, as shown in FIG. 1, cold rolling is performed on a silicon
steel sheet 1 that contains, for example, 2% to 4% of Si, by mass%. The silicon steel
sheet 1 is produced, for example, through continuous casting of molten steel, hot rolling
25 of a slab obtained by the continuous casting, annealing of a hot-rolled steel sheet
5
8
obtained by the hot rolling, and the like. The temperature of the annealing is about
1100°c, for example. The thickness ofthe silicon steel sheet 1 after the cold rolling is
in a range of 0.2 mm to 0.3 mm, for example, and for example, after the cold rolling, the
silicon steel sheet 1 is wound in the form of a coil and kept as a cold-rolled coil.
[0017]
Subsequently, the coiled silicon steel sheet 1 is unwound and supplied to a
decarburization annealing furnace 3 and fIrst continuous annealing, so-called
decarburization annealing is performed in the annealing furnace 3. The temperature of
this annealing is in a range of 700°C to 900°C, for example. At the time ofthis
10 annealing, decarburization and primary recrystallization is caused. As a result, a crystal
grain having a Goss orientation, in which an easy magnetization axis is aligned in a
rolling direction, is formed with a certain degree ofprobability. Thereafter, the silicon
steel sheet 1 discharged from the decarburization annealing furnace 3 is cooled by using
a cooling device 4. Subsequently, application 5 of an annealing separating agent,
15 containing MgO as its main constituent, to the surface of the silicon steel sheet 1 is
performed. Then, the silicon steel sheet 1 with the annealing separating agent applied
thereto is wound in the form of a coil, thereby being turned into a steel sheet coil 31.
[0018]
In this embodiment, during the period after the coiled silicon steel sheet 1 is
20 unwound until the silicon steel sheet 1 is supplied to the decarburization annealing
furnace 3, a groove is formed in the surface ofthe silicon steel sheet 1 by using a laser
beam irradiation device 2. At this time, the irradiation of a laser beam from one end
edge toward the other end edge, in a sheet width direction ofthe silicon steel sheet 1, is
performed multiple times at predetermined intervals with respect to a sheet passing
25 direction, at predetermined focusing power density Ip and predetermined focusing energy
,
9
density Up. As shown in FIG. 2, a configuration is also possible in which the laser
beam irradiation device 2 is disposed further to the downstream side in the sheet passing
direction than the cooling device 4 and the surface ofthe silicon steel sheet 1 is irradiated
with a laser beam during the period after cooling by the cooling device 4 is performed
5 until the application 5 ofthe annealing separating agent is performed. Aconfiguration
is also possible in which the laser beam irradiation devices 2 are disposed both further to
the upstream side in the sheet passing direction than the annealing furnace 3 and further
to the downstream side in the sheet passing direction than the cooling device 4 and the
irradiation of a laser beam is performed at the both places. The irradiation of a laser
10 beam may also be performed between the annealing furnace 3 and the cooling device 4,
and may also be performed in the annealing furnace 3 or in the cooling device 4. In the
formation ofthe groove by the laser beam, unlike a formation of the groove in machining,
a melt layer that will be described later is produced. Since the melt layer does not
disappear in decarburization annealing or the like, even if laser irradiation is performed at
15 any process before secondary recrystallization, the effect thereof is obtained.
[0019]
For example, as shown in FIG. 3A, a scanning device 10 performs scanning ofa
laser beam 9 emitted from a laser device that is a light source, at predetermined intervals
PL in a C direction that is the sheet width direction almost perpendicular to an L direction
20 that is the rolling direction ofthe silicon steel sheet 1, whereby the irradiation ofthe laser
beam is performed. At this time, assist gas 25 such as air or inert gas is blown onto a
part that is irradiated with the laser beam 9, o.fthe silicon steel sheet 1. As a result, a
groove 23 is formed in a portion irradiated with the laser beam 9, ofthe surface ofthe
silicon steel sheet 1. The rolling direction corresponds with the sheet passing direction.
25 [0020]
10
The scanning ofthe laser beam over the entire width ofthe silicon steel sheet 1
may also be performed by a single scanning device 10 and may also be performed by a
plurality of scanning devices 20, as shown in FIG 3B. In a case in which the plurality
of scanning devices 20 is used, only one laser device that is a light source of a laser beam
5 19 which is incident on each scanning device 20 may also be provided and one may also
be provided for each scanning device 20. In a case where there is one light source, it is
preferable if a laser beam emitted from the light source is divided into the laser beams 19.
Since it becomes possible to divide an irradiated area into a plurality of areas in the sheet
width direction by using the plurality of scanning devices 20, the times of scanning and
10 irradiation required per laser beam are shortened. Therefore, it is particularly suitable
for high-speed sheet passing equipment.
[0021]
The laser beam 9 or 19 is focused by a lens in the scanning device 10 or 20. As
shown in FIGS. 4A and 4B, the shape of a laser beam focused spot 24 ofthe laser beam 9
15 or 19 on the surface ofthe silicon steel sheet 1 is, for example, a circular shape or an
elliptical shape in which a diameter in the C direction that is the sheet width direction is
Dc and a diameter in the L direction that is the rolling direction is Dl. The scanning of
the laser beam 9 or 19 is performed at a speed Vc by using, for example, a polygon
mirror or the like in the scanning device 10 or 20. For example, the diameter Dc in the
20 C direction that is the sheet width direction may be set to be 0.4 mm and the diameter DI
in the L direction that is the rolling direction may be set to be 0.05 mm.
[0022]
As the laser device that is the light source, for example, a CO2 laser can be used.
A high-power laser that is generally used for industrial purposes, such as a YAG laser, a
25 semiconductor laser, or a fiber laser, may also be used. The laser that is used may also
20
11
be any of a pulsed laser and a continuous-wave laser, provided that the groove 23 and a
crystal grain 26 are stably fonned.
[0023]
The temperature ofthe silicon steel sheet I when perfonning the irradiation of
5 the laser beam is not particularly limited. For example, the irradiation ofthe laser beam
can be perfonned with respect to the silicon steel sheet 1 under about room temperature.
A scanning direction of the laser beam need not correspond with the C direction that is
the sheet width direction. However, from the viewpoint of work efficiency or the like
and subdivision of a magnetic domain into strip shapes long in the rolling direction, it is
10 preferable that the angle between the scanning direction and the C direction that is the
sheet width direction be within 45°. It is more preferable that the angle is within 20°
and it is even more preferable that the angle be within 10°.
[0024]
Instantaneous power density Ip and irradiation energy density Up ofthe laser
15 beam which are suitable for the fonnation of the groove 23 will be described. In this
embodiment, for the reason described below, it is preferable that the peak power density,
that is, the instantaneous power density Ip of the laser beam that is defmed by Fonnula 2
satisfies Fonnula 4, and it is preferable that the irradiation energy density Up ofthe laser
beam that is defined by Fonnula 1 satisfy Fonnula 3.
Up = (4/1t)xP/(DlxVc) (Fonnula 1)
Ip = (4/1t)xP/(DlxDc) (Fonnula 2)
1 ::; Up::; 10 J/mm2 (Fonnula 3)
100 kW/mm2
::; Ip::; 2000 kW/mm2 (Fonnula 4)
Here, P represents the average intensity, that is, the power (W) ofthe laser beam,
5
12
DI represents the diameter (mm) in the rolling direction ofthe focused spot ofthe laser
beam, Dc represents the diameter (mm) in the sheet width direction ofthe focused spot of
the laser beam, and Vc represents a scanning speed (mm/s) in the sheet width direction of
the laser beam.
[0025]
If the silicon steel sheet 1 is irradiated with the laser beam 9, an irradiated
portion is melted and a portion thereof scatters or evaporates. As a result, the groove 23
is formed. A portion ofthe melted portion that did not scatter or evaporate remains as it
is, and is solidified after the ending of irradiation ofthe laser beam 9. At the time ofthe
10 solidification, as shown in FIG. 5, a columnar crystal extending long toward the inside of
the silicon steel sheet from the bottom ofthe groove, and/or a crystal grain having a large
grain diameter compared to a laser non-irradiated portion, that is, the crystal grain 26
having a different shape from a crystal grain 27 obtained by primary recrystallization are
formed. The crystal grain 26 becomes the starting point of crystal grain boundary
15 growth at the time of secondary recrystallization.
[0026]
Ifthe instantaneous power density Ip described above is less than 100 kW/mm2
,
it becomes difficult to sufficiently cause the melting and the scattering or the evaporation
ofthe silicon steel sheet 1. That is, it becomes difficult to form the groove 23. On the
20 . other hand, if the instantaneous power density Ip exceeds 2000 kW/mm2
, most of the
molted steel scatters or evaporates, and thus the crystal grain 26 is not easily formed. If
the irradiation energy density Up exceeds 10 J/mm2
, a melting portion of the silicon steel
sheet 1 is increased, and thus the silicon steel sheet 1 is easily deformed. On the other
hand, if the irradiation energy density is less than 1 J/mm2
, the improvement in magnetic
25 characteristics does not appear. For these reasons, it is preferable that Formulae 3 and 4
13
described above are satisfied.
[0027]
At the time ofthe irradiation of the laser beam, the assist gas 25is blown in
order to remove components scattered or evaporated from the silicon steel sheet 1, from
5 an irradiation path of the laser beam 9. Since the laser beam 9 stably reaches the silicon
steel sheet 1 due to the blowing, the groove 23 is stably formed. Further, the assist gas
25 is blown, whereby reattachment ofthe components to the silicon steel sheet 1 can be
suppressed. In order to sufficiently obtain these effects, it is preferable that the flow
rate of the assist gas 25 be greater than or equal to 10 L (liter)/minute. On the other
10 hand, if the flow rate exceeds 500 L/minute, the effect is saturated and the cost also
increases. For this reason, it is preferable that the upper limit is set to be 500 L/minute.
[0028]
The preferable conditions described above are also the same in a case where the
irradiation of the laser beam is performed between decarburization annealing and fmish
15 annealing and a case where the irradiation ofthe laser beam is performed before and after
decarburization annealing.
[0029]
Returning to the description using FIG. 1, after the application 5 ofthe annealing
separating agent and the winding, as shown in FIG. 1, the steel sheet coil 31 is
20 transported into an annealing furnace 6 and placed with the central axis ofthe steel sheet
coil 31 being almost in the vertical direction. Thereafter, batch annealing, that is, finish
annealing ofthe steel sheet coil 31 is performed in a batch treatment. The highest
temperature of the batch annealing to be achieved is set to be about 1200°C, for example,
and a retention time is set to be about 20 hours, for example. At the time of the batch
25 annealing, secondary recrystallization is caused and also a glass coating is formed on the
t
14
surface ofthe silicon steel sheet 1. Thereafter, the steel sheet coil 31 is taken out ofthe
annealing furnace 6.
In the glass coating obtained by the above-described aspect, it is desirable that
an X-ray intensity ratio Ir ofthe characteristic X-ray intensity ofMg of a groove portion,
5 in a case where the average value ofthe characteristic X-ray intensity ofMg of portions
other than the groove portion of the surface of a grain-oriented electrical steel sheet is set
to be 1, is in a range of 0~Ir~0.9. If it is in the range, a favorable iron loss characteristic
is obtained.
The X-ray intensity ratio is obtained by measurement using an EPMA (Electron
10 Probe MicroAnalyser) or the like.
[0030]
Subsequently, the steel sheet coil 31 is unwound and supplied to an annealing
furnace 7 and second continuous annealing, so-called planarization annealing, is
performed in the annealing furnace 7. At the time ofthe second continuous annealing,
15 curling and strain deformation generated at the time ofthe finish annealing are eliminated,
and thus the silicon steel sheet 1 becomes flat. As the annealing conditions, for example,
retention of greater than or equal to 10 seconds and less than or equal to 120 seconds can
be performed at temperature greater than or equal to 700°C and less than or equal to
900°C. Subsequently, coating 8 on the surface ofthe silicon steel sheet 1 is performed.
20 In the coating 8, a material, in which securing of electrical insulation properties and the
action of tension to reduce iron loss are possible, is coated. A grain-oriented electrical
steel sheet 32 is produced through a series ofthese processes. After a coating is formed
by the coating 8, for the convenience' of, for example, storage, transport, and the like, the
grain-oriented electrical steel sheet 32 is wound in the form of a coil.
25 [0031]
15
If the grain-oriented electrical steel sheet 32 is produced by the above-described
method, at the time ofthe secondary recrystallization, as shown in FIGS. 6A and 6B, a
crystal grain boundary 41 penetrating the silicon steel sheet 1from front surface to back
surface along the groove 23 is formed. This is caused by the fact that the crystal grain
5 26 remains until the terminal phase ofthe secondary recrystallization because the crystal
grain 26 is not easily eroded in a crystal grain having a Goss orientation and that
although the crystal grain 26 is eventually absorbed into the crystal grain having a Goss
orientation, at that time, crystal grains greatly growing from both sides of the groove 23
cannot erode each other.
10 [0032]
In the grain-oriented electrical steel sheet produced according to the
above-described embodiment, crystal grain boundaries shown in FIG. 7A were observed.
In the crystal grain boundaries, the crystal grain boundary 41 formed along the groove
was included. Further, in a grain-oriented electrical steel sheet produced according to
15 the above-described embodiment except that the irradiation of the laser beam is omitted,
crystal grain boundaries shown in FIG. 7B were observed.
[0033]
FIGS. 7A and 7B are photographs taken with pickling ofthe surface of the
grain-oriented electrical steel sheet performed after the glass coating or the like is
20 removed fromthe surface ofthe grain-oriented electrical steel sheet, and ferrite is
exposed. In these photographs, the crystal grains and the crystal grain boundaries
obtained by the secondary recrystallization appear.
[0034]
In the grain-oriented electrical steel sheet produced by the above-described
25 method, the effect of magnetic domain subdivision is obtained by the grooves 23 formed
5
16
in the surface ofthe ferrite. Further, the effect of magnetic domain subdivision is also
obtained by the crystal grain boundaries 41 penetrating the silicon steel sheet 1 from the
front surface to the back surface along the grooves 23. Iron loss can be further reduced
due to the synergistic effect thereof.
[0035]
25
Since the groove 23 is formed by the irradiation of a predetermined laser beam,
the formation ofthe crystal grain boundary 41 is very easy. That is, after the formation
of the groove 23, it is not necessary to perform alignment or the like based on the
position ofthe groove 23 for the formation of the crystal grain boundary 41. Therefore,
lOa significant decrease in sheet passing speed or the like is not necessary, and thus it is
possible to industrially mass-produce a grain-oriented electrical steel sheet.
[0036]
It is possible to perform the irradiation ofthe laser beam at high speed, and
high-energy density is obtained by light-focusing into a minute space. Therefore, even
15 compared with a case where the irradiation of a laser beam is not performed, an increase
in time required for treatment is small. That is, regardless ofthe presence or absence of
the irradiation of a laser beam, it is almost not necessary to change a sheet passing speed
in treatment performing decarburization annealing or the like while unwinding a
cold-rolled coil. In addition, since the temperature at which the irradiation of a laser
20 beam is performed is not limited, a heat-insulating mechanism or the like of a laser
irradiation device is unnecessary. Therefore, compared to a case where treatment in a
high-temperature furnace is necessary, the configuration of an apparatus can be
simplified.
[0037]
The depth ofthe groove 23 is not particularly limited. However, it is preferable
17
that the depth is greater than or equal to 1 /lm and less than or equal to 30 /lm. Ifthe
depth ofthe groove 23 is less than 1 /lm, subdivision of a magnetic domain sometimes
does not become sufficient. Ifthe depth ofthe groove 23 exceeds 30 /lm, the amount of
a silicon steel sheet that is a magnetic material, that is, the amount of a ferrite is reduced
5 and magnetic flux density is reduced. More preferably, the depth ofthe groove 23 is
greater than or equal to 10 Jlm and less than or equal to 20 /lm. The groove 23 may also
be formed in only one surface of a silicon steel sheet and may also be formed in both
surfaces.
[0038]
10 The interval PL between the grooves 23 is not particularly limited. However, it
is preferable that the interval PL is greater than or equal to 2 mm and less than or equal to
10 mm. If the interval PL is less than 2 mm, inhibition of the formation of a magnetic
flux by the groove becomes noticeable and it becomes difficult for the sufficiently high
magnetic flux density required for a transformer to be formed. On the other hand, if the
15 interval PL exceeds 10 mm, the effect of improving a magnetic characteristic by a groove
and a grain boundary is greatly reduced.
[0039]
In the embodiment described above, one crystal grain boundary 41 is formed
along one groove 23. However, for example, in a case where the width ofthe groove 23
20 is wide and the crystal grains 26 are formed over a wide range in the rolling direction, at
the time ofthe secondary recrystallization, some ofthe crystal grains 26 sometimes grow
earlier than other crystal grains 26. In this case, as shown in FIGS. 8A and 8B, a
plurality of crystal grains 53 each having a certain degree ofwidth and along the groove
23 is formed below the grooves 23 in a sheet thickness direction. It is acceptable if a
,
18
grain diameter Wcl in the rolling direction of the crystal grain 53 exceeds 0 mm, and the
grain diameter WeI becomes greater than or equal to, for example, 1 mm. However, the
grain diameter Wcl tends to become less than or equal to 10 mm. The reason that the
grain diameter Wc1 tends to become less than or equal to 10 mm is because a crystal
5 grain growing with the highest priority at the time ofthe secondary recrystallization is a
crystal grain 54 having a Goss orientation and growth is hindered by the crystal grain 54.
A crystal grain boundary 51 approximately parallel to the groove 23 is present between
the crystal grain 53 and the crystal grain 54. A crystal grain boundary 52 is present
between adjacent crystal grains 53. A grain diameter Wcc in the sheet width direction
10 ofthe crystal grain 53 tends to become greater than or equal to, for example, 10 mm.
The crystal grain 53 may also be present as a single crystal grain in the width direction
over the entire sheet width, and in this case, the crystal grain boundary 52 need not be
present. With respect to the grain diameter, for example, it can be measured by the
following method. After the glass coating is removed and pickling is performed so as to
15 expose the ferrite, a field of view of 300 mm in the rolling direction and 100 mm in the
sheet width direction is observed, dimensions in the rolling direction and the sheet width
direction ofthe crystal grain are measured by viewing and by image processing, and the
average value thereof is obtained.
[0040]
20 The crystal grain 53 extending along the groove 23 is not necessarily a crystal
grain having a Goss orientation. However, since the size thereof is limited, an influence
on a magnetic characteristic is very small.
[0041]
In Patent Documents 1 to 9, a feature that a groove is formed by the irradiation
25 of a laser beam is not stated and further, a crystal grain boundary extending along the
5
,
19
groove is created at the time of secondary recrystallization, as in the above-described
embodiment. That is, even if the irradiation ofa laser beam is stated, sin~e timing or
the like ofthe irradiation is not appropriate, it is not possible to obtain the effects that are
obtained in the above-described embodiment.
[Examples]
[0042]
(First Experiment)
In a fIrst experiment, hot rolling, annealing, and cold rolling of a steel material
for oriented electrical steel were performed, the thickness ofthe silicon steel sheet was
10 set to be 0.23 mm, and the silicon steel sheet was wound, thereby being turned into a
cold-rolled coil. Five cold-rolled coils were produced. Subsequently, with respect to
three cold-rolled coils related to Example Nos. 1,2, and 3, the formation ofthe groove by
the irradiation ofthe laser beam was performed and thereafter, the decarburization
annealing was performed, thereby causing the primary recrystallization. The irradiation
15 ofthe laser beam was performed by using a fIber laser. In all the examples, the power P
was 2000 W, and with respect to a focused shape, in Example Nos. 1 and 2, the diameter
Dl in the L direction was 0.05 mm and the diameter Dc in the C direction was 0.4 mm.
With respect to Example No.3, the diameter Dl in the L direction was 0.04 mm and the
diameter Dc in the C direction was 0.04 mm. The scanning speed Vc was set to be 10
20 mls in Example Nos. 1 and 3 and 50 mls in Example No.2. Therefore, the
instantaneous power density Ip was 127 kW/mm2 in Example Nos. 1 and 2 and 1600
kW/mm2 in Example No.3. The irradiation energy density Up was 5.1 J/mm2 in
Example No.1, 1.0 J/mm2 in Example No.2, and 6.4 J/mm2 in Example No.3. The
irradiation pitch PL was set to be 4 mm, and air was blown at a flow rate of 15 L/minute
25 as the assist gas. As a result, the width of the formed groove was about 0.06 mm, that is,
20
60 ~m in Example Nos. 1 and 3 and 0.05 mm, that is, 50 /lm in Example No.2. The
depth ofthe groove was about 0.02 mm, that is, 20 ~m in Example No.1, 3 ~m in
Example No.2, and 30 /lm in Example No.3. Variation in the width was within ±5 ~m,
and variation in the depth was within ±2 ~m.
5 [0043]
With respect to another cold-rolled coil related to Comparative Example No.1,
the formation of a groove by etching was performed and thereafter, decarburization
annealing was performed, thereby causing primary recrystallization. The shape ofthis
groove was made to be the same as the shape ofthe groove in Example No.1 formed by
10 the irradiation of the laser beam described above. With respect to the remaining one
cold-rolled coil related to Comparative Example No.2, the formation of a groove was not
performed and thereafter, decarburization annealing was performed, thereby causing
primary recrystallization.
15
[0044]
In all of Example Nos. 1 to 3 and Comparative Example Nos. 1 and 2, after the
decarburization annealing, application of an annealing separating agent, fmish annealing,
planarization annealing, and coating were performed on the silicon steel sheets. In this
way, five kinds of grain-oriented electrical steel sheets were produced.
[0045]
20 When the structures of these grain-oriented electrical steel sheets were observed,
in all ofExample Nos. 1 to 3 and Comparative Example Nos. 1 and 2, secondary
recrystallized grains formed by secondary recrystallization were present. In Example
Nos. 1 to 3, similarly to the crystal grain boundary 41 shown in FIG 6A or 6B, the crystal
grain boundary along the groove was present. However, in Comparative Example Nos.
25
21
1 and 2, such a crystal grain boundary was not present.
[0046]
Thirty single sheets each having a length in the rolling direction of 300 mm and
a length in the sheet width direction of 60 mm were sampled from each ofthe
5 grain-oriented electrical steel sheets respectively, and the average value ofthe magnetic
characteristics was measured by a single sheet magnetometric method (SST: Single Sheet
Test). The measurement method was carried out in conformity with IEC60404-3:1982.
As the magnetic characteristics, magnetic flux density B8 (T) and iron loss W17/S0 (W/kg)
were measured. The magnetic flux density B8 is magnetic flux density that is generated
lOin a grain-oriented electrical steel sheet at a magnetizing force of 800 Aim. Since the
larger the value ofthe magnetic flux density B8 ofa grain-oriented electrical steel sheet,
the larger the magnetic flux density that is generated at a certain magnetizing force, the
grain-oriented electrical steel sheet in which the value of the magnetic flux density B8 is
large is suitable for a small and efficient transformer. The iron loss W17/S0 is iron loss
15 when a grain-oriented electrical steel sheet is subjected to alternating-current
energization under conditions in which the maximum magnetic flux density is 1.7 T and
a frequency is 50 Hz. The smaller the value of the iron loss W17/S0 ofa grain-oriented
electrical steel sheet, the lower the energy loss, and thus the grain-oriented electrical steel
sheet in which the value ofthe iron loss W17/S0 is small is suitable for a transformer.
20 The average value of each of the magnetic flux density B8 (T) and the iron loss W17/S0
(W/kg) is shown in Table 1 below. Further, with respect to the single sheet samples
described above, the measurement ofthe X-ray intensity ratio Ir was performed by using
the EPMA. Each average value is shown together in Table 1 below.
[0047]
[Table 1]
22
Average value ofBs Average value of Average value ofIr
(T) W17I50
(W/kg)
Example No.1 1.89 0.74 0.5
Example No.2 1.90 0.76 0.9
Example No.3 1.87 0.75 0.1
Comparative 1.88 0.77 1.0
Example No.1
Comparative 1.91 0.83 1.0
Example No.2
[0048]
As shown in Table 1, in Example Nos. 1 to 3, compared with Comparative
Example No.2, the magnetic flux density Bs was low with the formation ofthe groove.
5 However, since the groove and the crystal grain boundary along the groove were present:
the iron loss was significantly low. In Example Nos. 1 to 3, even compared with
Comparative Example No.1, since the crystal grain boundary along the groove was
present, the iron loss was low.
10
15
[0049]
(Second Experiment)
In a second experiment, verification regarding the irradiation conditions ofthe
laser beam was performed. Here, the irradiation of the laser beam was performed in
four types of conditions described below.
[0050]
In a first condition among the four type conditions, a continuous-wave fiber
23
laser was used. The power P was set to be 2000 W, the diameter Dl in the L direction
was set to be 0.05 mm, the diameter Dc in the C direction was set to be 0.4 mm, and the
scanning speed Vc was set to be 5 m/s. Therefore, the instantaneous power density Ip
was 127 kW/mm2 and the irradiation energy density Up was 10.2 J/mm2
• That is,
5 compared to the conditions ofthe first experiment, the scanning speed was reduced by
half, and thus the irradiation energy density Up was doubled. Therefore, the first
condition does not satisfy Formula 3. As a result, warp deformation of the steel sheet
was generated with an irradiated portion as the starting point. Since a warp angle
reached a range of 30 to 100
, winding into the form of a coil was difficult.
10 [0051]
Also in a second condition, a continuous-wave fiber laser was used. Further,
the power P was set to be 2000 W, the diameter Dl in the L direction was set to be 0.10
mm, the diameter Dc in the C direction was set to be 0.3 mm, and the scanning speed Vc
was set to be 10 mls. Therefore, the instantaneous power density Ip was 85 kW/mm2
15 and the irradiation energy density Up was 2.5 J/mm2
• That is, compared to the
conditions ofthe first experiment, the diameter Dl in the L direction and the diameter Dc
in the C direction are changed, and thus the instantaneous power density Ip was set to be
small. The second condition does not satisfy Formula 4. As a result, it was difficult to
form a grain boundary that could penetrate.
20 [0052]
Also in a third condition, a continuous-wave fiber laser was used. The power P
was set to be 2000 W, the diameter DI in the L direction was set to be 0.03 mm, the
diameter Dc in the Cdirection was set to be 0.03 mm, and the scanning speed Vc was set
to be 10 mls. Therefore, the instantaneous power density Ip was 2800 kW/mm2 and the
25 irradiation energy density Up was 8.5 J/mm2
• That is, the diameter DI in the L direction
5
24
was set to be smaller than in the condition of the first experiment, and thus the
instantaneous power density Ip was set to be large. Therefore, the third condition does
not also satisfy Formula 4. As a result, it was difficult to sufficiently form a crystal
grain boundary along the groove.
[0053]
15
Also in a fourth condition, a continuous-wave fiber laser was used. The power
P was set to be 2000 W, the diameter DI in the L direction was set to be 0.05 mm, the
diameter Dc in the C direction was set to be 0.4 rom, and the scanning speed Vc was set
to be 60 mls. Therefore, the instantaneous power density Ip was 127 kW/mm2 and the
10 irradiation energy density Up was 0.8 J/mm2
. That is, the scanning speed was set to be
larger than the condition ofthe first experiment, and thus the irradiation energy density
Up was set to be small. The fourth condition does not satisfy Formula 3. As a result,
in the fourth condition, it was difficult to form a groove having a depth of greater than or
equal to Illm.
[0054]
(Third Experiment)
In a third experiment, the irradiation ofthe laser beam was performed under two
sets of conditions, a condition in which the flow rate ofthe assist gas was set to be less
than 10 Llminute and a condition in which the assist gas is not supplied. As a result, it
20 was difficult to stabilize the depth ofthe groove, variation in the width ofthe groove was
25
greater than or equal to range of±10 Ilm, and variation in the depth was greater than or
equal to range of ±5 Ilm. For this reason, variation in magnetic characteristics was large,
compared with the examples.
Industrial Applicability
[0055]
5
10
15
25
According to an aspect ofthe present invention, a grain-oriented electrical steel
sheet having low iron loss can be obtained by a method in which it is possible to
industrially mass-produce the grain-oriented electrical steel sheet.
Reference Signs List
[0056]
1: silicon steel sheet
2: laser beam irradiation device
3, 6, 7: annealing furnace
31: steel sheet coil
32: grain-oriented electrical steel sheet
9, 19: laser beam
10, 20: scanning device
23: groove
24: laser beam focused spot
25: assist gas
26, 27, 53, 54: crystal grain
41,51,52: crystal grain boundary

•
5
26
CLAIMS
1. A method of manufacturing a grain-oriented electrical steel sheet, the
method comprising:
a cold rolling process ofperforming a cold rolling while moving a silicon steel
sheet containing Si along a sheet passing direction;
a first continuous annealing process of causing a decarburization and a primary
recrystallization of the silicon steel sheet;
a winding process ofwinding the silicon steel sheet, thereby obtaining a steel
10 sheet coil;
a groove formation process of irradiating a surface ofthe silicon steel sheet with
a laser beam multiple times at predetermined intervals in the sheet passing direction, over
an area from one end edge to the other end edge, in a sheet width direction ofthe silicon
steel sheet, thereby forming a groove along a locus ofthe laser beam, during the period
15 from the cold rolling process to the winding process;
a batch annealing process of causing a secondary recrystallization in the steel
sheet coil;
a second continuous annealing process of unwinding and planarizing the steel
sheet coil; and
~
20
25
a continuous coating process of imparting a tension and an electrical insulation
properties to the surface ofthe silicon steel sheet,
wherein in the batch annealing process, a crystal grain boundary penetrating the
silicon steel sheet from a front surface to a back surface along the groove is generated,
and
when an average intensity ofthe laser beam is set to be P (W), a focusing
(Formula 4)
27
diameter in the sheet passing direction ofa focused spot ofthe laser beam is set to be DI
(rom), a focusing diameter in the sheet width direction is set to be Dc (mm), a scanning
speed in the sheet width direction ofthe laser beam is set to be Vc (rnm/s), an irradiation
energy density Up ofthe laser beam is represented by the following Formula 1, and an
5 instantaneous power density Ip ofthe laser beam is represented by following Formula 2,
following Formulae 3 and 4 are satisfied.
Up = (4/n)xP/(DlxVc) (Formula 1)
Ip = (4/n)xP/(DlxDc) (Formula 2)
1 s Up s 10 (J/mm2) (Formula 3)
100 (kW/mm2
) s Ip s 2000 (kW/mm2
10 )
2. The method ofmanufacturing a grain-oriented electrical steel sheet
according to Claim 1, wherein in the groove formation process, gas is blown onto a
portion ofthe silicon steel sheet, that is irradiated with the laser beam, at a flow rate of
15 greater than or equal to 10 Llminute and less than or equal to 500 Llminute.
3. A grain-oriented electrical steel sheet comprising:
a groove formed from a locus of a laser beam that performed scanning over an
area from one end edge to the other end edge in a sheet width direction; and
20 a crystal grain boundary extending along the groove and penetrating the
grain-oriented electrical steel sheet from a front surface to a back surface.
4. The grain-oriented electrical steel sheet according to Claim 3, further
comprising a crystal grain in which a grain diameter thereof in the sheet width direction
28
ofthe grain-oriented electrical steel sheet is greater than or equal to 10 rnm and less than
or equal to a sheet width and a grain diameter thereof in a longitudinal direction ofthe
grain-oriented electrical steel sheet exceeds 0 nun and is 10 nun or less,
wherein the crystal grain is present to over a range from the groove to the back
5 surface ofthe grain-oriented electrical steel sheet.
5. The grain-oriented electrical steel sheet according to Claim 3 or 4, wherein
( a glass coating is formed in the groove, and a X-ray intensity ratio Ir ofa characteristic
X-ray intensity ofMg at a portion ofthe grove in a case where an average value ofthe
10 characteristic X-ray intensity ofMg of portions other than the portion ofthe groove of
I the surface ofthe grain-oriented electrical steel sheet is set to be 1, in the glass coating, is
in a range of O~Ir~O.9.