Document Type] Specification
[Title of the Invention] GRAIN-ORIENTED MAGNETIC STEEL SHEET AND
METHOD OF PRODUCING THE SAME
[Technical Field of the Invention]
[OOOl]
The present invention relates to a grain-oriented magnetic steel sheet which is
used in an iron core material or the like of a winding transformer, and a method of
producing the same. In particular, the present invention relates to a grain-oriented
magnetic steel sheet in which iron loss is reduced by forming grooves in a surface
thereof by laser beam machining, and a method of producing the same.
Priority is claimed on Japanese Patent Application No. 2012-103212, filed on
April 27,2012, the content of which is incorporated herein by reference.
[Related Art]
[0002]
A grain-oriented magnetic steel sheet is an magnetic steel sheet which
contains Si and in which a magnetization easy axis ((110) <001> orientation) of a
crystal grain thereof is approximately aligned with a rolling direction in a production
process thereof. This grain-oriented magnetic steel sheet has a structure in which
multiple magnetic domains in which magnetization is directed in the rolling direction
are arranged with a magnetic domain wall interposed therebetween, and most of these
magnetic domain walls are 180" magnetic donlain walls. The magnetic domain of
this grain-oriented magnetic steel sheet is called a 180" magnetic domain and the
grain-oriented magnetic steel sheet is easily magnetized in the rolling direction. For
this reason, in a certain relatively small magnetizing force, magnetic flux density is
high and iron loss (energy loss) is low. Therefore, the grain-oriented magnetic steel
sheet is excellent as an iron core material of a transformer. As a parameter of the iron
loss, generally, W17150 (Wlkg) is used. W17150 is a value of iron loss which is
generated in a grain-oriented magnetic steel sheet when alternating-current excitation
is performed such that the maximum magnetic flux density becomes 1.7 T at a
frequency of 50 Hz. If W17150 is reduced, a more efficient transformer can be
manufactured.
[0003]
A normal method of producing a grain-oriented magnetic steel sheet will be
schematically described below. The thickness of a hot-rolled silicon steel sheet (a
hot-rolled sheet) containing a predetermined amount of Si is adjusted to a desired
thickness by annealing and cold rolling. Next, the silicon steel sheet is annealed in a
continuous annealing furnace to perform a primaly recrystallization (grain size: 20 pm
to 30 pm) together with decarburization and strain relief. Subsequently, an annealing
separator containing MgO as a major component is applied to a surface of the silicon
steel sheet (hereinafter also referred to simply as "steel sheet"), the steel sheet is coiled
into a coil shape (an outer shape is a cylindrical shape), batch annealing is performed at
a high temperature of about 1200°C for about 20 hours to thereby form a secondary
recrystallization texture in the steel sheet, and a glass film is formed on a surface of the
steel sheet.
[0004]
At that time, since the steel sheet contains, for example, an inhibitor such as
MnS or AlN, a so-called Goss grain in which a rolling direction and a magnetization
easy magnetic domain confornl to each other is preferentially subjected to crystal
growth. As a result, a grain-oriented magnetic steel sheet having a high crystal
orientation (orientation) after final annealing is obtained. After final annealing, the
coil is uncoiled, and the steel sheet is continuously transported into a separate
annealing furnace to perform flattening annealing, thereby eliminating unnecessary
strain in the steel sheet. In addition, a coating film is formed on a surface of the steel
sheet to impart tension and electric insulation thereto. As a result, a grain-oriented
magnetic steel sheet is produced.
[OOOS]
In the grain-oriented magnetic steel sheet produced through such a process,
even if an additional treatment is not cal~iedo ut, the iron loss is low. However, if
strain substantially perpendicular to a rolling direction (hereinafter also referred to as a
transportation direction) and having a constant period (a regular interval) is imparted,
the iron loss is further reduced. In this case, a 90° magnetic domain in which the
rolling direction and magnetization are orthogonal to each other is follned by local
strain and a magnetic domain wall intel-val of a substantially rectangular 180' magnetic
domain is narrowed (the width of a 180" magnetic domain is reduced) with
magnetostatic energy of the 90" magnetic domain as a source. Since the iron loss
(W17150) has a positive correlation with the interval between the 180' magnetic
domain walls, the iron loss is reduced based on this principle.
[0006]
For example, as disclosed in Patent Document 1, a method in which strain is
imparted to a steel sheet by laser irradiation has already been put to practical use.
Similarly, if a groove having a depth in a range of 10 pm to 30 pm is formed
substantially perpendicular to a rolling direction of a grain-oriented magnetic steel
sheet and at a constant period, the iron loss is reduced. This is because a magnetic
pole is generated in the periphery of the groove due to a change in permeability in a
void of the groove, the interval between the 180" magnetic domain walls is narrowed
with the magnetic pole as a source, and thus the iron loss is inlproved. Examples of a
method of forming a groove include a method disclosed in Patent Document 2 in
which a groove is formed in a cold rolled sheet using electrolytic etching, a method
disclosed in Patent Document 3 in which a tooth-shaped die is mechanically pressed on
a cold rolled sheet, and a method disclosed in Patent Docunient 4 in which a steel sheet
(a laser-irradiated portion) is melted and evaporated by laser irradiation.
[0007]
Incidentally, power transformers are roughly divided into laminated
transformers and winding transformers. Laminated transforniers are manufactured by
laminating and fixing multiple magnetic steel sheets. On the other hand, in a
manufacturing process of winding transformers, since a grain-oriented magnetic steel
slieet is coiled by performing lamination while coiling it, an annealing process to
release deformation strain (for example, strain due to bending) thereof is included.
Therefore, a grain-oriented magnetic steel sheet produced by the method disclosed in
Patent Document 1 in which strain is imparted to a steel sheet to improve the iron loss
can be used in the laminated transformer while maintaining an iron loss reduction
effect. However, the grain-oriented magnetic steel sheet cannot be used in the
winding transformer while maintaining an iron loss reduction effect. That is, in the
winding transformer, since strain disappears due to strain relief annealing, the iron loss
reduction effect also disappears. On the other hand, in a grain-oriented magnetic steel
sheet produced by the method of forming a groove to improve the iron loss, even if the
strain relief annealing is performed, the effect of improving the iron loss is not reduced.
Therefore, this grain-oriented magnetic steel sheet has an advantage effect in that it can
be used in both the laminated transformer and the winding transformer.
[0008]
Here, a method of forming a groove in the related art will be described. In
the method disclosed in Patent Document 2 in which a groove is formed in a cold
rolled sheet using electrolytic etching, a glass film is formed on a surface of the steel
sheet subjected to, for example, secondary recrystallization, the glass film on the
surface is linearly removed by laser irradiation or a mechanical method, and a groove
is formed in a portion where a matsix is exposed by etching. In this method, the
process is complicated, the manufacturing cost increases, and there is a limit to
treatment speed.
[0009]
In the method disclosed in Patent Document 3 in which a tooth-shaped die is
mechanically pressed on a cold rolled sheet, since a magnetic steel sheet is a very hard
steel sheet containing about 3% of Si, the tooth-shaped die is easily worn away and
damaged. If the tooth-shaped die is worn away, since the depth of the groove varies,
the iron loss reduction effect becomes non-uniform. In order to avoid this problem, it
is necessary to strictly manage the tooth-shaped die during an operation.
[OOl 01
The method using laser irradiation (referred to as a laser method) has an
advantageous effect in that high-speed groove machining can be performned by a
focused laser beam having high power density. Further, since the laser method is
non-contact machining, stable and uniform groove machining can be performed by
control of laser power or the like. Regarding the laser method, various attetnpts to
efficiently form a groove having a depth of 10 pm or more on a surface. of a steel sheet
have been made in the related art. For example, Patent Document 4 discloses a
method of fornling a groove by realizing high power density (energy density at a focal
point) of 2x10' w/& or more using a pulsed C02 laser (wavelength: 9 pm to 11 pm)
having high peak power. Here, in the method using the pulsed COz laser, a laser stop
time is present between successive pulses. Therefore, when a surface of a steel sheet
is scanned with a laser beam at high speed, holes (a row of points) which are formed
by the pulses are connected to each other on a scanning line of a laser beam, and thus a
groove is formed thereon.
[OOII]
On the other hand, Patent Document 5 discloses a method in which a
projection formed by a molten object generated at a peripheral portion of a groove is
significantly decreased by forming a groove which continuously extends using a
continuous-wave laser beam.
[Prior Art Docutnent]
[Patent Document]
[0012]
[Patent Document I] Japanese Examined Patent Application, Second
Publication No. S58-26406
[Patent Document 21 Japanese Examined Patent Application, Second
Publication No. S62-54873
[Patent Document 31 Japanese Examined Patent Application, Second
Publication No. S62-53579
[Patent Document 41 Japanese Unexamined Patent Application, First
Publication No. H06-57335
[Patent Document 51 PCT International Publication No. WO 20111125672
[Disclosure of the Invention]
[Problems to be Solved by the Invention]
[0013]
Incidentally, the laser method has the following problem. With the method
disclosed in Patent Document 5, a projection occurring on a surface of a steel sheet is
minimized. However, in a peripheral portion around the bottom of a groove, a meltresolidified
portion produced by laser irradiation is still present, which causes
deformation of the steel sheet, more specifically, warpage in a rolling direction (socalled
L-watpage). When a transformer is manufactured by combining mnltiple steel
sheets, a space factor decreases due to an effect of the above deformation, and there is
a problem of a decrease in the performance of the transformer. In addition, similarly,
due to an effect of the above deformation, local stress concentration occurs during
lamination and compression. As a result, the iron loss of the transformer may
increase.
[0014]
The present invention has been made in consideration of the above-described
circumstances, and an object thereof is to suppress deformation such as warpage in a
rolling direction derived from grooves in a grain-oriented magnetic steel sheet on
which the grooves are formed by laser beam machining to reduce iron loss.
[Measures for Solving the Problem]
[0015]
The present invention adopts the following measures to solve the abovedescribed
problems and to achieve the above-described object.
(1) According to an aspect of the present invention, there is provided a
grain-oriented magnetic steel sheet including grooves each of which extends in a
direction intersecting a transportation directioa, the grooves being formed at
predetermined pitches PL in the transportation direction by laser beam irradiation, in
which a relatiotiship between a sfandard deviation value D and the pitch PL satisfies
the following expression (I), the standard deviation value D being a standard deviation
of distances between a linear approximation line, which is obtained from a center line
of each of the grooves in a groove width direction by a least-squares method, and
respective positions on the center line, and an average angle formed between tangent
lines of the respective positions on the center line and a direction perpendicular to the
transportation direction is more than 0" to 30'.
[0016]
[Expression 11
0. 0 2 5 ( D / P L ) * . * ( I )
[0017]
(2) In the grain-oriented magnetic steel sheet according to (I), each of the
grooves may be formed to be curved on the grain-oriented magnetic steel sheet.
[0018]
(3) In the grain-oriented magnetic steel sheet according to (1) or (2), the
grooves may be formed on a front surface and a back surface of the grain-oriented
magnetic steel sheet.
[0019]
(4) In the grain-oriented magnetic steel sheet according to (3), positions of
the grooves formed on the front surface may be the same as positions of the grooves
formed on the back surface.
[0020]
(5) According to another aspect of the present invention, there is provided a
method of producing a grain-oriented magnetic steel sheet, the method including
irradiating a grain-oriented magnetic steel sheet with a laser beam to form grooves,
each of which extends in a direction intersecting a transportation direction, at
predetermined pitches PL in the transportation direction, in which a relationship
between a standard deviation value D and the pitch PL satisfies the following
expression (I), the standard deviation value D being a standard deviation of distances
between a linear approxin~ationli ne, which is obtained from a center line of each of the
grooves in a groove width direction by a least-squares method, and respective positions
on the center line, and an average angle formed between tangent lines of the respective
positions on the center line and a direction perpendicular to the transportation direction
is more than 0" to 30'.
[0021]
[Expression 21
0. o z ( u / P L ) + + + ( I )
[0022]
(6) In the method of producing a gain-oriented magnetic steel sheet
according to (5), a wavelength of the laser beam may be in a range of 0.4 pm to 2.1 pm.
[Effects of the Invention]
[0023]
According to the aspects, it is possible to suppress deformation such as
warpage in a rolling direction derived from grooves in a grain-oriented magnetic steel
sheet on which the grooves are formed by laser beam machining to reduce iron loss.
[Brief Description of the Drawing]
[0024]
FIG. 1 is a schematic diagram illustrating a state where grooves are formed by
laser beam machining on a surface of a grain-oriented magnetic steel sheet according
to an embodiment of the present invention.
FIG. 2 is a schematic diagram illustrating the details of the shape of a groove
(curve) which is formed in the grain-oriented magnetic steel sheet according to the
embodiment.
FIG. 3 is a schematic diagram illustrating an arrangement example of multiple
curve groups (groove groups) which are formed in the grain-oriented magnetic steel
sheet according to the embodiment.
FIG. 4A is a schematic diagram illustrating a first example of the groove shape
in the grain-oriented magnetic steel sheet according to the embodiment.
FIG. 4B is a schematic diagram illustrating a second example of the groove
shape in the grain-oriented magnetic steel sheet according to the embodiment.
FIG. 4C is a schematic diagram illustrating a third example of the groove
shape in the grain-oriented magnetic steel sheet according to the embodiment.
FIG. 4D is a schematic diagram illustrating a fourth example of the groove
shape in the grain-oriented magnetic steel sheet according to the embodiment.
FIG. 5.4 is a schematic diagram illustrating a first configuration example of a
laser scanner used for laser beam machining.
FIG. 5B is a schematic diagram illustrating a second configuration example of
a laser scanner used for laser beam machining.
FIG. SC is a schematic diagram illustrating a third configuration example of a
laser scanner used for laser beam machining.
FIG. 6 is a diagram illustrating a relationship between a standard deviation
value with respect to a linear approximation line of a center line of a groove; and a
space factor.
FIG. 7 is a schematic diagram illustrating the cross-sectional shape of a grainoriented
magnetic steel sheet according to another embodiment of the present
invention.
[Embodiments of the Inveiltion]
[0025]
Hereinafter, the details of a preferred embodiment of the present invention
will be described with reference to the accompanying drawings. In this specification
and the drawings, components having practically the same function are represented by
the same reference numerals, and the description thereof will not be repeated.
[0026]
A grain-oriented magnetic steel sheet according to an embodiment of the
present invention includes a steel sheet, a glass film that is formed on a surface of the
steel sheet, and an insulating film that is formed on the glass film. Typically, the steel
sheet is made from an iron alloy containing Si which is used as a material of the grainoriented
magnetic steel sheet. The composition of the steel sheet according to the
embodiment contains, for example, Si: 2.5 mass% to 4.0 mass%, C: 0.02 mass% to
0.10 mass%, Mn: 0.05 mass% to 0.20 mass%, acid-soluble Al: 0.020 inass% to 0.040
mass%, N: 0.002 mass% to 0.012 mass%, S: 0.001 mass% to 0.010 mass%, P: 0.01
mass% to 0.04 mass%, and a balance including Fe and unavoidable impurities. In
addition, the thickness of the steel sheet is, typically, 0.15 mm to 0.35 mm. The width
of the steel sheet is, for example, about 1 m.
In addition to the above-described elements, the grain-oriented magnetic steel sheet
according to the embodiment may further contain Cu, Cr, Sn, Sb, Ti, B, Ca, REM (rare
earth element such as Y, Ce, or La), or the like as an unavoidable impurity or as an
element for improving magnetic properties within a range not impairing mechanical
properties and magnetic properties of the grain-oriented magnetic steel sheet.
[0027]
In the grain-oriented magnetic steel sheet according to the embodiment, as
illustrated in FIG. 1, cu~vedg rooves G (refer to FIG. 2), each of which extends in a
direction (transverse direction) substantially perpendicular to a rolling direction, are
formed on a surface of the steel sheet 1 periodically in the rolling direction.
Regarding the cross-sectional shape of the groove for example, the groove depth is 5
pm to 50 pm, and the groove width is 10 pm to 300 pm as known. The pitch of the
grooves G is preferably 2 mm to 10 lmn. In the embodiment, each of the grooves G
is formed to be curved, not linear, on the surface of the steel sheet 1. Hereinafter, a
preferred shape of a curve which is drawn by a center line of the groove G in a groove
width direction (hereinafter, also referred to simply as "center line of the groove G )
will be described. In the following description, the curve drawn by the center line of
the groove G will also be referred to simply as "curve" for convenience of description.
Typically, as illustrated in FIG. 1, the total width of the steel sheet 1 which reaches
about 1 m is covered with multiple curve groups Gsl, Gs2, and Gs3, (the rest is
omitted) each of which is a group of multiple grooves G. Typically, since it is
difficult for one laser scanner to form the grooves over the total width, multiple laser
scanners LS 1, LS2, and LS3 (the rest is omitted) are used for the groove forming
process. As a result, the multiple curve groups Gsl, Gs2, and Gs3, (the rest is
omitted) are formed on the steel sheet 1. However, the present invention is not
limited to this configuration, and one laser scanner may form one curve group over the
total width. The structure of the laser scanner will be described below in detail. In
addition, hereinafter, w11en it is not necessary to specify any one of the curve groups
Gsl, Gs2, and Gs3, (the rest is omitted), the curve groups Gsl, Gs2, and Gs3, (the rest
is omitted) will be collectively referred to as "curve groups Gs".
[0028]
Each of the curve groups Gs includes multiple curves G (grooves G) which
are fonned at predetermined pitches PL. FIG. 2 illrlstrates only one curve G for
convenience of description. In the grain-oriented magnetic steel sheet according to
the embodiment, a relationship between a standard deviation value D with respect to a
linear approximation line C of each of the cullres G; and the pitch PL satisfies the
following expression (1). In the grain-oriented magnetic steel sheet according to the
embodiment, this expression (1) is satisfied for all the curves G included in each of the
cuve groups Gs.
[0029]
[Expression 31
0, 0 2 < ( D / P L ) . . . ( 1 )
[0030]
The standard deviation value D is obtained as follows. First, in a
coordination system in which an x axis represents the direction perpendicular to the
transportation direction of the steel sheet 1 and a y axis represents the transportation
direction, the curve G is expressed by a function of y=f(x). The linear approximation
line C with respect to the curve G which is expressed by y=ax+b is obtained using a
well-known least-squares method. Next, in a new coordinate system in which an X
axis represents a direction of the linear approximation line C and a Y axis represents a
direction perpendicular to the X axis, the curve G is expressed by Y=g(X). The X
and Y axes may be parallel to the x and y axes but, depending on the shape of the curve
G, may also be inclined to the x and y axes as illustrated in FIG. 2. The standard
deviation value D is defined by the following expression (2).
[003 11
[Expression 41
(wherein LC represents the length of the curve G in the X axis direction)
[0032]
In addition, in the embodiment, as illustrated in FIG. 2, an amplitude A of the
curve G is defined as the suln of a distance Au and a distance Ab (A=Au+Ab), the
distance Au ranging from the linear approximation line C of the cuwe G to a point
most distant from the linear approximation line C in a up direction (positive direction
of the Y axis), the distance Ab ranging from the linear approximation line C to a point
most distant from the linear approximation line C in a down direction (negative
direction of the Y axis).
[0033]
Next, the reason for setting (DIPL) to 0.02 or more as in the expression (1)
will be described. In a method of the related at in which the center line of the groove
G is linear @/PL=O), a center position of the groove which is a deformation starting
point, in a groove width direction is asranged to be linear on the linear approximation
line C. On the other hand, the present inventors found that, when the deformation
starting point is dispersed at positions of the linear approximation line C by allowing
the center line of the groove G to be curved (specifically, positions of respective points
on the curve G are dispersed in the Y axis direction when the cuwe G is seen from the
X axis direction of FIG. 2), the total warpage amount of the steel sheet can be reduced.
The standard deviation value D indicates the dispersion degree of the deformation
starting point, and for warpage, a ratio of this standard deviation value D having a
lengthwise dimension to the dimension of the groove pitch PL is important. As
described below in Examples, it is clarified that, when (DRL) is 0.02 or more, a space
factor can increase. In the embodiment, the shape of the groove G is not particularly
limited as long as it is not linear and various shapes including an arc shape of FIG. 4A
and a sectionally linear shape of FIG. 4B in which multiple straight lines are connected
to each other, not one continuously smooth curve shape, can be considered. However,
in either case, the above-described warpage mechanism is invariable, and the same
effects cat] be obtained by setting @RL) to be 0.02 or more.
[0034]
The upper limit of (DPL) for obtaining an effect of reducing the warpage
amount of the steel sheet 1 is not particularly present. However, when the upper limit
of (DIPL) is excessively high, the amplitude A of the curve G increases, and an angle
formed between the curve G and the direction perpendicular to the transportation
direction increases. In a magnetic domain refinement technique of the related art in
which one linear groove G is formed, it is known that, when the angle formed between
the direction of the groove G and the direction perpendicular to the transportation
direction is more than +30°, an effect of reducing the iron loss decreases. Likewise,
in the case of the curved groove G according to the embodiment, when an average
value of the angle formed between the direction of the groove G and the direction
perpendicular to the transportation direction is more than i30°, it is difficult to reduce
the iron loss. Therefore, it is preferable that the average value of the angle formed
between the direction of the groove G and the direction perpendicular to tlie
transportation direction be within *30°. More specifically, it is preferable that, when
an angle formed between tangent lines of tlie curve G defined at the respective points
on the curve G and the direction perpendicular to the transportation direction is
represented by 0 ("), f3 satisfy the following expression (3).
[0035]
[Expression 51
Further, from the viewpoint of reducing the iron loss, it is more preferable that
the groove G (curve G) be smooth; and that the angle formed with the tangent lines and
the direction perpendicular to the transportation direction be within i30° in all the
points of the groove G (cullre G).
[0036]
In the above-description, the description has been made on the assumption
that the groove G continuously extends. Such a groove G can be obtained by
continuously scanning the steel sheet 1 with a laser beam using a continuous-wave
laser as disclosed in Patent Document 5. On the other hand, according to another
embodiment of the present invention, for example, as disclosed in Patent Document 4,
there may be provided a magnetic steel sheet including a groove having a row of points
or a broken line-shaped groove which is obtained using a laser oscillating at
internlittent time intervals.
[0037]
In addition, in the embodiment, as illustrated in FIG. 3, curves groups Gs
which looks as if they are connected to forni one long cullre G can be obtained by
allowing an end of the culve of the curve group Gsl and an end of the cutlre G of the
curve group Gs2 to completely match with each other altliougli multiple laser scanners
are used. At this time, in a range where one long curve G is fornied, when the
standard deviation value D with respect to the linear approximation line C obtained
with completely the same ~lietlioda s above is within the range of the expression (I), a
grain-oriented magnetic steel sheet having the small warpage amount is obtained.
[0038]
Further, as illustrated in FIG. 7, the grooves G are formed on both front and
back surfaces of the steel sheet 1. Accordingly, the warpage amount of the steel sheet
1 can be furtlier reduced as compared to a case where the grooves G are formed on
only a single surface. FIG. 7 is a schematic diagram illustrating a cross-sectional
shape of the steel sheet 1 when the steel sheet 1 is seen from the transverse direction.
In FIG. 7, the grooves G are formed on a front surface la and a back surface lb of the
steel sheet 1, and positions of grooves G (cutves G) formed on the front surface la are
the same as positions of grooves G (curves G) formed on the back surface lb. Here,
the meaning of the positions being the same includes not only a case where the
positions of the grooves G of the front surface la are the same as the positions of the
grooves G of the back surface lb but a case where, even if the grooves G formed on
both the fiont and back surfaces are shifted from each other in either the rolling
direction or the transverse direction, the shift amount is less than or equal to the width
of the grooves G. In this way, when the positions of the curves G (grooves G) formed
on the front surface la and the back surface lb of the steel sheet 1 are the same, the
warpage amount of the steel slieet 1 can be further reduced as compared to a case
wliere the positions of the curves G formed on the front surface la and the back surface
lb of the steel sheet 1 are not the same.
[0039]
Next, an embodiment of a method of producing the grain-oriented magnetic
steel sheet according to the embodiment will be described in detail using the drawings.
First, typically, the grain-oriented magnetic steel sheet according to the embodiment is
produced, for example, by using silicon steel slab as a material and performing a
periodic groove forming process using laser irradiation in addition to a general
production process of a grain-oriented magnetic steel sheet, the general production
process including a hot rolling process, an annealing process, a cold rolling process, a
decarburization annealing process, a final annealing process, a flattening annealing
process, and an insulating film forming process which are performed in this order.
The groove forming process using laser irradiation is performed before the insulating
film forming process and after the cold rolling process or is performed after the
insulating film forming process. When the groove forining process is performed after
the insulating film forming process, a portion where an insulating film is peeled off is
generated in a peripheral portion of a laser-irradiated portion, and thus it is preferable
that the insulating film forming process be performed again. In the embodiment, a
case where the groove forming process using laser irradiation is performed before the
insulating film forming process and after the flattening annealing process is described
as an example, but the same irradiation method as below can be used in another
production process.
[0040]
Hereinafter, a method of forming a groove using laser irradiation will be
described in detail using a schematic diagram illustrating an example of a production
apparatus including laser light sources and laser scanners which are used in the
embodiment. FIG. 1 illustrates laser light sources and laser scanners. The steel
sheet 1 is transported in a rolling direction (transportation direction) at a constant
predetermined line speed VL. As illustrated in the drawing, light beams output from
multiple laser light sources L01, L02, and LO3 (the rest is omitted) are conducted to
multiple laser scanners LS1, LS2, and LS3 (the rest is omitted) through optical fibers 3
(refer to FIGS. 5A to 5C). By these laser scanners LSl, LS2, and LS3 (the rest is
omitted) irradiating the steel sheet 1 with laser beams LB1, LB2, and LB3 (the rest is
omitted), curve groups Gsl, Gs2, and Gs3, (the rest is omitted) are formed on the steel
sheet 1.
Hereinafter, when it is not necessary to distinguish the laser light sources L01,
L02, and LO3 (the rest is omitted) from each other, the laser light sources L01, L02,
and LO3 (the rest is omitted) will be collectively referred to as "the laser light source
LO". In addition, when it is not necessary to distinguish the laser scanners LSI, LS2,
and LS3 (the rest is omitted) from each other, the laser scanners LSI, LS2, and LS3
(the rest is omitted) will be collectively referred to as "the laser light scanner LS". In
addition, when it is not necessary to distinguish the laser beams LBI, LB2, and LB3
(the rest is omitted) from each other, the laser beams LBI, LB2, and LB3 (the rest is
omitted) will be collectively referred to as "the laser beam LB".
[0041]
As the laser light LO, a laser light source having a high light-focusing
property at a wavelength of 0.4 pm to 2.1 pm, that is, a laser light source such as a
fiber laser or a thin disk type YAG laser is preferably used. When the laser beam LB
output from such a laser light source LO is used, an effect of aplasma decreases, and
the occurrence of a projection can be suppressed.
[0042]
FIG. 5A is a diagram illustrating a configuration example of the laser scanner
LS. As this laser scanner LS, for example, a well-known galvano scanner may be
used. This laser scanner LS includes, as illustrated in FIG. 5A, a condensing lens 6
for focusing the laser beam LB which is output from a collimator 5 connected to the
laser light source LO through the optical fiber 3; and two galvano nlirrors GMI and
GM2 that reflects the laser beam LB.
By adjusting angles of the two galvano mirrors GM1 and GM2, the steel sheet
1 can be scanned at a high speed with the laser beam LB focused by the condensing
lens 6. In the configuration example of the laser scanner LS illustrated in FIG. 5A,
the scanning of the laser beam LB mainly in a direction (transverse direction)
perpendicular to the rolling direction can be performed by the rotation of the galvano
mirror GM2. In addition, the rotation of the galvano mirror GM1 has a function of
making an interval (amplitude) fiom the linear approxitnation line by the scanning of
the laser beam LB mainly in a direction (that is, rolling direction) perpendicular to the
transverse direction. The condensing lens 6 can operate while moving back and forth
in an optical axis direction of the laser beam LB to correct a change in work distance
depending on the combination of deflection angles of the two galvano mirrors GMl
and GM2. Of course, the configuration of the laser scanner LS is not limited to the'
configuration illustrated in FIG. 5A, and any configuration can be adopted as long as
the curves G (grooves G) can be two-dimensionally drawn in the steel sheet 1.
For example, as illustrated in FIG. 5B, a configuration in which one galvano
mirror is combined with a polygon mirror as disclosed in Patent Document 5 may also
be considered.
In the configuration example of the laser scanner LS illustrated in FIG. 5B, the
scanning of the laser beam LB mainly in the transverse direction can be performed by
the rotation of the polygon minor 10. In addition, the rotation of the galvano mirror
GMl has a function of making an interval (amplitude) from the linear approximation
line by the scanning of the laser beam LB mainly in the rolling direction. The fB lens
20 is used as the condensing lens. Even if the laser beam LB is obliquely incident on
the fB lens 20 along with the scanning of the laser beam LB, the focal point of the laser
beam LB on the steel sheet 1 can be maintained.
In addition, for example, as illustrated in FIG. 5C, in a configuration where
the polygon mirror 10 shared by two laser beams LB is used, when it is necessary that
multiple laser scanners LS be used to form the grooves G on the entire portion of the
steel sheet 1 in the transverse direction, the number of laser scanners LS can be
reduced. Therefore, the full size of a production apparatus can be reduced.
[0043]
The width and depth of the groove G are detennined depending on parameters
such as the power, the scanning speed, and the focused shape of the laser beam LB.
These parameters are adjusted such that the groove depth is 5 pm to 50 pm and the
groove width is 10 pm to 300 pm. In order to irradiate the laser beams at
predetermined pitches PL, the time required for one scanning, that is, the time T is set
as expressed in the following expression (4) (during the time T, laser inadiation starts
from a starting end of a scan width, laser scanning is performed to a finishing end of
the scan width, and the next laser irradiation starts from the next starting end).
PL=TxVL ... (4)
[0044]
FIGS. 4C and 4D illustrate examples of the shape of one curve G (groove G)
obtained by the scanning of the laser beam LB output from one laser scanner LS in the
embodiment. The values of (DJPL) calculated from these cu17.e~G are the same.
However, when the wavelength h of one period of the curve G is excessively short as
illustrated in FIG. 4C, high-speed scanning in the transportation direction is required,
and the scanner may be limited by the allowable maximum scanning speed. On the
other hand, in FIG. 4D, the wavelength h of the curve G is longer than that of FIG. 4C,
the scanner is not likely to be limited by the scanning speed. For example, in an
embodiment in which a sine wave-shaped cuwe G is formed as illustrated in FIGS. 4C
and 4D, it is preferable from the viewpoint of industrial production that the wavelength
h of the curve G be 10 mm or longer.
[Examples]
[0045]
Next, a confirmatory experiment for confirming the effects of the embodiment
will be described. First, a slab having a composition containing Si: 3.0 mass%, C:
0.05 mass%, Mn: 0.1 mass%, acid-soluble Al: 0.02 mass%, N: 0.01 mass%, S: 0.01
mass%, P: 0.02 mass%, and a balance including Fe and unavoidable impurities was
prepared. This slab was subjected to hot rolling at 1280°C, and a hot-rolled material
having a thickness of 2.3 mni was produced. Next, the hot-rolled material was heated
under a condition of 1000°Cxl min. After the heat treatment, a pickling treatment
was performed, and then cold rolling was performed. As a result, a cold-rolled
material having a thickness of 0.23 mm was produced. This cold-rolled material was
subjected to decarburization annealing under a condition of 800°Cx2 min, and then an
annealing separator containing magnesia as a major component was applied thereto.
In a state of being coiled into a coil shape, the cold-rolled material to which the
annealing separator was applied was charged into a batch furnace, followed by final
annealing under a condition of 1200°Cx20 hr. Next, flattening annealing was
perfornied, and then groove forming was performed by laser irradiation using a method
described below. Finally, an insulating film was formed on the material.
[0046]
As a production apparatus including the laser scanner LS and the like, those
illustrated in FIGS. 1 and 5A were used. An example where a fiber laser doped with
Yb as a laser medium is used as the laser light source LO will be described. In FIG. 1,
the steel sheet 1 is a grain-oriented magnetic steel sheet which is manufactured through
the above-described process, in which the width of the steel sheet after final annealing
is 1000 nlm, and a glass film is formed on a surface of a matrix. The steel sheet 1 is
transported in the rolling direction (transportation direction) at a constant line speed
VL.
[0047]
The laser beam intensity P was 1000 W, the focused beam diameter d was
0.04 mtn, and the pitch PL was 5 mm. Each instantaneous speed has a direction
following a tangent line of the cullre but the magnitude of the speed projected on the
linear approximation line was within a range of 80002~450d s . Under these laser
beam irradiation conditions, the substantially arc-shaped groove G of FIG. 4A was
formed. The length LC (refer to FIG. 2) of the groove determined depending on tlie
scan width of one scanner was 100 mm. In the experiment, by changing the
amplitude A as a parameter, grain-oriented magnetic steel sheets having different
curve-shaped grooves G were manufactured. Irrespective of the amplitude A, the
groove width was in a range of 55*5 pm, and the groove depth was in a range of 1553
pm.
[0048]
In addition, as a comparative example, grooves were formed on the same steel
plate materials using the method in which a tooth-shaped die is mechanically pressed.
At this time, the shape of the groove was linear, the pitch PL was 5 mm. The groove
width was 52 pm, the groove depth was 14 pm, and the groove substantially having the
same cross-sectional shape as that of the laser method was formed.
[0049]
In order to evaluate the effect of the warpage amount formed by the
irradiation of the laser beam LB, a space factor was measured according to JIS 2550.
As described above, an increase in space factor represents a reduction in the warpage
amount of the steel sheet 1.
[OOSO]
FIG. 6 illustrates the measurement results of the space factor. In a graph of
FIG. 6, the horizontal axis represents (D/PL) obtained using the above-described
method, and the vertical axis represents the space factor. In FIG. 6, the space factor of
the linear groove (D/PL=O) which was mechanically formed in the comparative
example is indicated by a white circle. It can be seen from FIG. 6 that, when (DRL)
is less than 0.02, the space factor of the groove G obtained using the laser method is
lower than that of the tnechanically formed linear groove; however, when (DIPL) is
0.02 or higher, the space factor of the groove G obtained using the laser method is
higher than that of the mechanically formed linear groove. In particular, when @RL)
is 0.05 or higher, the space factor shows a high value of 96.5% or higher. Further,
when (DJPL) is 0.1 or higher, the space factor shows a high value of 97% or higher
[0051]
It can be seen from the above results that, when a relationship between the
standard deviation value D and the groove pitch PL satisfies the above-described
expression (I), the warpage amount of the steel sheet 1 can be reduced. By reducing
the warpage amount, when the steel sheet is laminated and compressed as an iron core
material of a winding transformer, the space factor is high, the performance as a
transformer is high, and the effect of stress concentration is released. Therefore,
excellent iron loss characteristics can be realized.
[0052]
Hereinbefore, the preferred embodiments of the present invention have been
described. However, the present invention is not limited to these preferred
embodiments. Various additions, omissions, substitutions, and other modifications
can be made for the configuration within a range not departing fiom the scope of the
present invention. The present invention is not limited to the above description but is
only limited to the accompanying claims.
[Industrial Applicability]
[0053]
According to the present invention, when grooves are formed by laser beam
irradiation on a surface of a steel sheet, the deformation amount of the steel sheet
caused by the formation of the grooves can be reduced. Accordingly, a magnetic steel
sheet having the following advantageous effects can be provided. When the steel
sheet is laminated and compressed as an iron core material of a winding transformer,
the space factor is high, the performance as a transformer is high, and the effect of
stress concentration is released. Therefore, excellent iron loss characteristics can be
realized.
[Brief Description of the Reference Symbols]
[0054]
1 : GRAIN-ORIENTED MAGNETIC STEEL SHEET (STEEL SHEET)
3 : OPTICAL FIBER
5: COLLIMATOR
6: CONDENSING LENS
10: POLYGON MIRROR
20: fB LENS
LB: LASER BEAM
PL: GROOVE PITCH
LO: LASER LIGHT SOURCE
LS: LASER SCANNER
G: GROOVE (CURVE)
Gs: CURVE GROUP
[Document Type] CLAIMS
[Claim 11
A grain-oriented magnetic steel sheet comprising
grooves each of which extends in a direction intersecting a transportation
direction, the grooves being formed at predetermined pitches PL in the transportation
direction by laser beam irradiation,
wherein a relationship between a standard deviation value D and the pitch PL
satisfies the following expression (I), the standard deviation value D being a standard
deviation of distances between a linear approximation line, which is obtained from a
center line of each of the grooves in a groove width direction by a least-squares
method, and respective positions on the center line, and
an average angle formed between tangent lines of the respective positions on
the center line and a direction perpendicular to the transportation direction is more than
0" to 30°.
[Expression 11
0 . 0 2 < ( D / P L ) + + . ( 1 )
[Claim 21
The grain-oriented magnetic steel sheet according to Claim 1,
wherein each of the grooves is formed to be curved on the grain-oriented
magnetic steel sheet.
[Claim 31
The grain-oriented magnetic steel sheet according to Claim 1 or 2,
wherein the grooves are formed on a front surface and a back surface of the
grain-oriented magnetic steel sheet.
[Claim 41
The grain-or[ented magnetic steel sheet according to Claim 3, , I
I I I
wl~ereinp osiiions of the grooves formed on the front surface are the same as
I
positions of the groodes fornled on the back surface.
I
[claim 51 I
I
A method oflproducing a grain-oriented magnetic steel sheet, the method
I
grooves, each of whi h extends in a direction intersecting a transportation direction, at
direction,
between a standard deviation val~D~ ea nd the pitch PL
(I), the standard deviation value D beinlg a standard
comprising
irradiating a
linear approximation line, ~vl~icisli o btained from a
center line of each o grooves in a groove width direction by a leas;-squares
method, and on the center line, and
grain-oriented magnetic steel sheet wit11 a laser beain to fosn~
an average 1n gle formed between tangent lines of the respective positions on
I
the center line and a idirectiorl perpe~~diculator the transportation direction is more tlian
[Claim 61
The metlloh of producing a grain-o~iet~tetnda gnetic steel shekt according to
I Claim 5,
I
wherein a #avelength of the laser beain is in a range of 0.4 pm to 2.1 µm.