[Name of Document] DESCRIPTION
[Title of the Invention] GRAIN ORIENTED ELECTRICAL STEEL SHEET AND
METHOD OF PRODUCING GRAIN ORIENTED ELECTRICAL STEEL SHEET
[Technical Field]
5 [0001]
The present invention relates to a grain oriented electrical steel sheet having a
glass coating film formed on a surface thereof, and to a method of producing the grain
oriented electrical steel sheet.
[Background Art]
10 [0002]
The above mentioned grain oriented electrical steel sheet is produced by using, for
example, a silicon steel slab as a starting material in the following procedure: a hot rolling
step, an annealing step, a cold rolling step, a decarburization annealing step, a final
annealing step, a flattening annealing step, and an insulating film coating step.
15 [0003]
In the annealing prior to the final annealing step, silica (Si02)-based Si02 coating
films are formed on surfaces of the steel sheet. In the final annealing step, the steel sheet
is wound up in a coil shape, and in this state, the steel sheet is placed in a batch-type
annealing furnace so as to be subjected to heat treatment. In order to prevent seizing of
20 the steel sheet during the final annealing step, surfaces of the steel sheet is coated with a
magnesia (MgO)-based annealing separator prior to the final annealing step. In the final
annealing step, the Si02 coating film and the magnesia-based annealing separator react
with each other, thereby forming the aforementioned glass coating film.
[0004]
25 Here, the final annealing step will be described in detail. As shown in FIG. 1, in
the final annealing step, a coil 5 formed by winding up the steel sheet is placed on a coil
receiver 8 under an annealing furnace cover 9 with a coil axis 5a of the coil 5 positioned in
the vertical direction.
[0005]
As shown in FIG. 2, when the coil 5 positioned in this manner is annealed at high
5 temperatures, a lower edge portion 5z of the coil 5 in contact with the coil stand 8 is
plastically deformed because of the weight of the coil 5, a difference between the thermal
expansion coefficient of the coil receiver 8 and the thermal expansion coefficient of the
coil 5, and the like. Such a deformation cannot be completely removed even in the
subsequent flattening annealing step, and this deformation is usually referred to as a lateral
10 strain deformation. If the lateral strain deformation does not satisfy a requirement
specified by a customer, a lateral strained portion 5e in which the lateral strain deformation
occurs is trimmed. Hence, there is a problem of increase in the trimming width of the
lateral strained portion 5e as the lateral strained portion 5e increases, which deteriorates the
yield. When the steel sheet unwound from the coil 5 is placed on a flat surface plate, the
15 lateral strain is observed as a height h of a wave of the edge portion of the steel sheet lifted
up from the flat surface plate, as shown in FIG. 3. Normally, the lateral strained portion
5e is a deformation region in the edge portion of the steel sheet that satisfies a condition
that the wave height h is more than 2 mm, or a condition that a steepness s represented by
the following formula (1) is more than 1.5% (more than 0.015):
20 s = h/l (1),
where 1 denotes a width of the lateral strained portion.
[0006]
A mechanism of occurrence of the lateral strain at the time of the final annealing
can be explained by grain boundary sliding at high temperatures. Specifically,
25 deformation due to the grain boundary sliding becomes significant at high temperatures of
900°C or more; therefore, the lateral strain is likely to occur at the grain boundary portions.
In the lower edge portion of the coil in contact with the coil receiver, the growing of
secondary recrystallization occurs later than that in a central portion of the coil. Hence,
the grain size becomes smaller at the lower edge portion of the coil, which is likely to
generate a refined grain portion.
5 [0007]
It is considered that there are a large number of grain boundaries in such a refined
grain portion, so that the grain boundary sliding is likely to occur in this portion, which
causes lateral strain. Thus, there have been proposed various conventional methods of
controlling the growth of crystal grains at the lower edge portion of the coil so as to reduce
10 mechanical deformation (lateral strain) at the lower edge portion of the coil.
[0008]
Patent Document 1 discloses a method of applying a grain refiner to a strip
portion having a constant width from the lower edge of the coil in contact with the coil
receiver before the final annealing so as to refine grains in the strip portion during the final
15 annealing. Patent Document 2 discloses a method of applying mechanical deformation
strain using a roller with protrusions thereon or the like to a strip portion having a constant
width from the lower edge of the coil in contact with a coil receiver prior to the final
annealing so as to refine grains in this strip portion during the final annealing.
[0009]
20 In the methods of Patent Documents 1 and 2, in order to reduce lateral strain,
crystal grains at the lower edge portion of the coil are intentionally refined in the above
manners, thereby changing the mechanical strength at the lower edge portion of the coil.
[0010]
In the method disclosed in Patent Document 1, however, the grain refiner is liquid,
25 which makes it difficuh to accurately control a region where the grain refiner is applied.
The grain refiner may be diffused from the edge portion toward the central portion of the
steel sheet in some cases. Consequently, it becomes difficult to control the width of the
grain refinement region to be constant, and thus the width of the lateral strained portion
becomes greatly varied in the longitudinal direction of the coil. As the width of the
lateral strained portion having the greatest deformation determines a trimming width, if the
5 lateral strained portion has a great width even at a single position, the trimming width
increases, and the yield is deteriorated.
[0011]
In the method disclosed in Patent Document 2, grain refinement of crystals at the
lower edge portion of the coil is initiated by the strain generated through machining using a
10 roller or the like. The roller, however, wears out due to continuous machining for a long
time, which deteriorates the strain generated through mechanical deformation strain
(reduction ratio) applied to the steel sheet with time, resulting in deterioration of the grain
refining effect. In particular, the grain oriented electrical steel sheet is a hard material
containing a large amount of Si, and wear of the roller becomes significant, and thus it is
15 required to frequently replace the roller. Moreover, since machining induces the strain in
a wide range, there are limitations on the range of reducing the lateral strain.
[0012]
Patent Documents 3, 4, 5, and 6 disclose methods in which, in order to reduce
lateral strain, secondary recrystallization is encouraged in the strip portion having a
20 constant width extending from the lower edge of the coil so as to increase the grain size at
an early stage of the final annealing, thereby enhancing high temperature strength.
Patent Documents 3 and 4 disclose, as a solution to increase the grain size, a
method of heating the strip portion at the edge portion of the steel sheet through plasma
heating or induction heating prior to the final annealing. Patent Documents 3, 5, and 6
25 disclose a method of employing mechanical strain using shot blast, a roller, or a gear roller,
or the like.
[0013]
The plasma heating and the induction heating are suitable for heating a band
region because the plasma heating and the induction heating are heating processes having a
relatively wide heating range. However, the plasma heating and the induction heating
5 have a problem of difficulties in controlling a heating position and a heating temperature.
Another problem is that a wider range than a prescribed range is heated due to heat
conduction. Hence there arises a problem of failure to uniformly control a width of a
range where the grain size is increased through secondary recrystallization, and thus the
lateral strain reduction effect is likely to be non-uniform.
10 [0014]
As mentioned above, the mechanical method using a roller or the like has the
problem of deterioration of the strain applying effect (amount of strain) with time due to
wear of the roller. In particular, speed of the secondary recrystallization sensitively varies
depending on the strain amount; therefore, even a slight strain amount due to the wear of
15 the roller disadvantageously hinders attainment of a desired grain size, so that it becomes
impossible to attain stable lateral strain reduction effect. In addition, since machining
induces strain in a wide range, there are limitations on the range of reducing the lateral
strain.
[0015]
20 As described above, the methods disclosed in Patent Documents 1 to 6 have a
problem of difficulty in accurately controlling the grain size (range and size), and thus the
lateral strain reduction effect cannot be sufficiently attained.
[0016]
Patent Document 7 proposes a technique of generating an easy deformable portion
25 (groove or grain boundary sliding portion), or high-temperature deformable portion
extending parallel with the rolling direction in one of the side edge regions of the steel
#
sheet by radiating a laser beam, using water jet, or the like. In this case, the easy
deformable portion (groove or grain boundary sliding deformable portion) generated in the
one of the side edge regions of the steel sheet prevents propagation of the lateral strain,
thereby enabling reduction of the width of the lateral strained portion.
5 [Prior Art Documents]
[Patent Documents]
[0017]
[Patent Document 1] JP S63-100131A
[Patent Document 2] JP S64-042530A
10 [Patent Document 3] JP H02-097622A
[Patent Document 4] JPH03-177518A
[Patent Document 5] JP 2000-038616A
[Patent Document 6] JP 2001-323322A
[Patent Document 7] WO 2010/103761A
15 [Summary of the Invention]
[Problems to Be Solved by the Invention]
[0018]
In the method of generating the grain boundary sliding deformable portion as
disclosed in Patent Document 7, the easy deformable portion is directly generated in a base
20 metal iron portion of the steel sheet. This easy deformable portion is a linear region
including grain boundaries generated in the base metal iron portion of the steel sheet
during the final annealing, or is a sliding strip region including crystal grains generated in
the base metal iron portion of the steel sheet. Prior to the final annealing, a laser beam is
radiated onto the surface of the steel sheet so as to generate the easy deformable portion in
25 a heat afifected portion of the base metal iron portion. At this time, the base metal iron
portion of the region irradiated with the laser beam melts by heat of the laser beam, and is
then resolidified, so that abnormal grains whose axis of easy magnetization deviates from
the rolling direction of the steel sheet are generated at a high percentage in the easy
deformable portion generated during the final annealing. This deteriorates the magnetic
property in the base metal iron portion of the region where the easy deformable portion is
5 generated.
[0019]
As aforementioned, if the width of the lateral strained portion is reduced in a
small range, the grain oriented electrical steel sheet having the lateral strained portion may
satisfy quality required by a customer, and it may be unnecessary to carry out trimming of
10 the lateral strained portion. In the invention described in Patent Document 7, however,
even if the lateral strained portion is allowable, the abnormal crystal grains existing in the
base metal iron portion where the easy deformable portion is generated deteriorate the
magnetic property, which disadvantageously deteriorates the quality of the grain oriented
electrical steel sheet.
15 [0020]
In order to generate the easy deformable portion in the entire thickness direction
from the surface of the steel sheet, or down to a deep position inside the steel sheet, it is
required to apply great energy to the steel sheet. Consequently, preparation is
time-consuming prior to the final annealing, or a large-scale and high-power laser
20 apparatus is required, which disadvantageously hinders efficient production of the grain
oriented electrical steel sheet.
[0021]
An object of the present invention, which has been made in view of the
above-described circumstances, is to provide a grain oriented electrical steel sheet in which
25 propagation of lateral strain is securely suppressed by laser beam radiation onto a side edge
of the steel sheet, and deterioration of the magnetic property of the steel sheet by being
8
heat affected by the laser beam is reduced.
[Means for Solving the Problems]
[0022]
In order to solve the above problems, according to an aspect of the present
5 invention, a grain oriented electrical steel sheet having a glass coating film formed on a
surface thereof is provided, the grain oriented electrical steel sheet including a linearly
altered portion generated in the glass coating film at one of side edges of the steel sheet, in
a continuous line or in a discontinuous broken line in a direction parallel with a rolling
direction of the steel sheet, and having a composition different from a composition in other
10 portions of the glass coating film. An average value of a deviation angle of a direction of
an axis of easy magnetization of crystal grains relative to the rolling direction is 0° or more
and 20° or less in a base metal iron portion of the steel sheet at a position along a width
direction of the steel sheet, the position corresponding to the linearly altered portion.
[0023]
15 A characteristic X-ray intensity la of Mg in the linearly altered portion of the glass
coating film may be smaller than an average value Ip of the characteristic X-ray intensity
of Mg in the other portions of the glass coating film.
[0024]
The average value Ip of the characteristic X-ray intensity of Mg in the other
20 portions of the glass coating film and the characteristic X-ray intensity la of Mg in the
linearly altered portion may be obtained through an EPMA analysis, and the linearly
altered portion may be identified in the glass coating film as an Mg reduced portion whose
Mg reduction ratio Ir that is a ratio of the la relative to the Ip is 0.3 or more and less than
1.0.
25 [0025]
In addition, the linearly altered portion may be identified as the Mg reduced
portion whose Mg reduction ratio Ir is 0.3 or more and 0.95 or less.
[0026]
A laser beam may be radiated in a direction parallel with the rolling direction onto
a region at the one of the side edge regions of the steel sheet having an Si02 coating film
5 formed on a surface thereof, so as to generate a laser processed portion in a continuous line
or in a discontinuous broken line in a depth region from an outer layer of the Si02 coating
film toward a boundary between the SiOa coating film and the steel sheet, the laser
processed portion in the Si02 coating film may be altered, and the linearly altered portion
may be generated in the glass coating film.
10 [0027]
A distance WL from the one of the side edges of the steel sheet to a center with
respect to the width direction of the linearly altered portion may be 5 mm or more and 35
mm or less, and a width d of the linearly altered portion may be 0.3 mm or more and 5.0
mm or less.
15 [0028]
The linearly altered portion may be generated in a region of 20% or more and
100% or less of a total length in the rolling direction of the steel sheet, and the region starts
from one end in the rolling direction of the steel sheet corresponding to an outermost
periphery of the steel sheet when the steel sheet is wound up in a coil shape in a final
20 annealing step.
[0029]
According to another aspect of the present invention, a method of producing a
grain oriented electrical steel sheet having a glass coating film formed on a surface thereof
is provided, the method including a laser processing step of radiating, onto one of side
25 edge regions of a steel sheet having an SiOa coating film formed on a surface thereof, a
laser beam in a direction parallel with a rolling direction of the steel sheet so as to generate
10
a laser processed portion in a continuous line, or in a discontinuous broken line; an
annealing separator coating step of coating each surface of the steel sheet with an
annealing separator after the laser processing step; and a final annealing step of finally
annealing the steel sheet which is coated with the annealing separator so as to form the
5 glass coating film on each surface of the steel sheet. The laser processed portion is
generated in a depth region from an outer layer of the Si02 coating film toward a boundary
between the Si02 coating film and the steel sheet, in the final annealing step, the steel sheet
is wound up in a coil shape, the steel sheet in the coil shape is placed and finally annealed
with the one of the side edges thereof where the laser processed portion is directed
10 downward, the glass coating film is generated from the Si02 coating film and the annealing
separator, and a linearly altered portion having a composition different from a composition
in other portions of the glass coating film is formed in a portion corresponding to the laser
processed portion.
[0030]
15 In the laser processing step, the laser processed portion may be generated in such
a manner that a distance WL from the one of the side edges of the steel sheet to a center
with respect to the width direction of the laser processed portion is 5 mm or more and 35
mm or less, and a width d of the laser processed portion is 0.3 mm or more and 5.0 mm or
less.
20 [0031]
In the laser processing step, the laser processed portion may be generated in a
region of 20% or more and 100% or less of a total length in the rolling direction of the
steel sheet, and the region starts from one end in the rolling direction of the steel sheet
corresponding to an outermost periphery of the steel sheet when the steel sheet is wound
25 up in a coil shape in the final annealing step.
[0032]
11
According to the grain oriented electrical steel sheet and the producing method of
the same, the linearly altered portion extending in the rolling direction is generated in the
glass coating film in one of the side edge portions of the steel sheet, so that the linearly
altered portion is locally deformed, thereby suppressing propagation of the lateral strain.
5 Here, it is preferable to set a distance WL from the one of the side edges of the steel sheet
to the center with respect to the width direction of the linearly altered portion (laser
processed portion) as 5 mm or more and 35 mm or less, and to set a width d of the linearly
altered portion (laser processed portion) as 0.3 mm or more and 5.0 mm or less. Through
this configuration, it is possible to securely reduce the width of the lateral strained portion.
10 [0033]
The linearly altered portion is generated only in the glass coating film, and not
generated in the base metal iron portion of the steel sheet. In addition, in a portion of the
base metal iron portion of the steel sheet adjacently below the linearly altered portion, an
average value of the deviation angle of the direction of the axis of easy magnetization of
15 the crystal grains in the base metal iron portion of the steel sheet relative to the rolling
direction is adjusted to be 20° or less. Accordingly, the magnetic property becomes stable
not only in the portion of the base metal iron portion that does not correspond to the
linearly altered portion, but also in the portion adjacently below the linearly altered portion,
which allows the portion in which the linearly altered portion is generated to be available
20 as a product.
[0034]
In the present invention, the deviation angle is defined by a mean-square value 9a
of an angle 9t and an angle 9n, wherein the angle 9t is formed by the direction of the axis
of easy magnetization of the crystal grains, which are measured with the crystal orientation
25 measurement method (the Laue method) using X-ray diffraction, turning from the rolling
direction in the steel sheet face serving as a reference around a width directional axis of the
12
steel sheet, and the angle 9n is formed by the direction of the axis of easy magnetization of
the crystal grains turning from the rolling direction around an axis vertical to the face of
the steel sheet; and crystal grains having 9a of 20° or more are referred to as "abnormal
crystal grains".
5 [0035]
It is preferable that the characteristic X-ray intensity la of Mg in the linearly
altered portion is smaller than the average value Ip of the characteristic X-ray intensity of
Mg in the other portions of the glass coating film. It is also preferable that the linearly
altered portion is identified as the linear Mg reduced portion whose Mg reduction ratio Ir,
10 which is a ratio of la relative to Ip, is 0.3 or more and less than 1.0, in particular, 0.95 or
less. The amount of Mg is smaller in this linear Mg reduced portion than that in the other
portions of the glass coating film. Mg is a representative element in the glass coating film,
so that it is estimated that the thickness of the glass coating film itself is reduced in the
linear Mg reduced portion. Hence, the mechanical strength in the linear Mg reduced
15 portion is smaller than that in the other portions of the glass coating film, and the linear Mg
reduced portion becomes easily locally deformed; thus it is possible to suppress
propagation of the lateral strain.
[0036]
In the present invention, the thickness of the glass coating film is reduced in the
20 portion corresponding to the linear Mg reduced portion, but there is no problem in electric
insulation property as a transformer if an insulating coating film is formed on the glass
coating film.
[Effects of the Invention]
[0037]
25 As aforementioned, according to the present invention, the linearly altered portion
generated in the portion corresponding to the laser processed portion in the glass coating
13
film can suppress propagation of the lateral strain.
In addition, there is a low percentage of abnormal crystal grains also in the portion
of the base metal iron portion of the steel sheet adjacently below the linearly altered
portion, and thus it is possible to suppress deterioration of the magnetic property of the
5 steel sheet by being heat affected by the laser beam. Accordingly, it is possible to provide
a high-quality grain oriented electrical steel sheet whose crystal orientation is stable
through the entire steel sheet.
[Brief Description of the Drawings]
[0038]
10 [FIG. 1] FIG. 1 is a drawing explaining an example of a final annealing unit.
[FIG. 2] FIG. 2 is a schematic diagram showing a growing process of lateral strain
in a conventional coil having no solution to reduce lateral strain implemented for.
[FIG. 3] FIG 3 is an explanatory drawing showing an example of an evaluation
method of the lateral strain.
15 [FIG. 4] FIG. 4 is a cross sectional view of a grain oriented electrical steel sheet in
one embodiment of the present invention.
[FIG. 5] FIG. 5 is an explanatory drawing showing the grain oriented electrical
steel sheet in one embodiment of the present invention.
[FIG. 6A] FIG. 6A is an explanatory drawing showing a linearly altered portion in
20 the grain oriented electrical steel sheet shown in FIG. 4.
[FIG. 6B] FIG. 6B is an explanatory drawing showing the linearly altered portion
in the grain oriented electrical steel sheet shown in FIG 4.
[FIG. 7] FIG. 7 is a flow chart showing a producing method of the grain oriented
electrical steel sheet in one embodiment of the present invention.
25 [FIG 8] FIG. 8 is a schematic diagram explaining equipment that carries out a
decarburizing annealing step, a laser processing step, and an annealing separator coating
14
step.
[FIG 9] FIG. 9 is a schematic explanatory drawing showing a laser processing unit
that carries out the laser processing step.
[FIG 10] FIG 10 is a schematic explanatory drawing showing a steel sheet on
5 which the laser processing step is carried out.
[FIG. 11] FIG. 11 is a cross sectional view taken in the direction of arrows X-X of
FIG. 10.
[FIG 12] FIG 12 is an explanatory drawing showing the grain oriented electrical
steel sheet in one embodiment of the present invention, which is wound up into a coil
10 shape.
[FIG. 13] FIG. 13 is a schematic diagram showing a growing step of the lateral
strain in the grain oriented electrical steel sheet in one embodiment of the present
invention.
[FIG. 14] FIG. 14 is a graph showing a relation among a width of a laser processed
15 portion, a distance from an edge portion of the steel sheet, and a lateral strain width.
[FIG 15] FIG. 15 is a graph showing a relation between a position in the rolling
direction starting from an outermost peripheral portion of the finally annealed coil and the
lateral strain width in the case of using various lengths in the rolling direction of the laser
processed portion.
20 [FIG. 16] FIG 16 shows photographs of structures showing states of crystal grains
generated on the surface of the base metal iron portion of the steel sheet.
[FIG. 17] FIG 17 is an explanatory drawing showing the grain oriented electrical
steel sheet in another embodiment of the preset invention.
[FIG. 18] FIG 18 is an explanatory drawing showing crystal grains generated
25 around a linearly altered portion on the surface of the base metal iron portion of the steel
sheet.
t 15
[FIG 19] FIG 19 is a schematic diagram showing a state of crystal grains in a
cross section in a width direction of the steel sheet according to Comparative Examples.
[FIG 20] FIG 20 is a graph showing a relation among an Mg reduction ratio, the
lateral strain width, and an average value of a deviation angle of an axis of easy
5 magnetization relative to the rolling direction of the steel sheet.
[Modes for Carrying out the Invention]
[0039]
Hereinafter, referring to the appended drawings, a grain oriented electrical steel
sheet and a producing method of the grain oriented electrical steel sheet according to
10 preferred embodiments of the present invention will be described in detail. It should be
noted that, in this specification and the appended drawings, structural elements that have
substantially the same function and structure are denoted with the same reference numerals,
and repeated explanation thereof is omitted. The present invention is not limited to the
following embodiments.
15 [0040]
A grain oriented electrical steel sheet 10 of the present embodiment includes a
steel sheet 11, a glass coating film 12 formed on each surface of the steel sheet, and an
insulating coating film 13 formed on each glass coating film 12, as shown in FIG 4.
[0041]
20 The steel sheet 11 is made of an iron alloy containing Si, which is used as a
common material for a grain oriented electrical steel sheet. The steel sheet 11 according
to the present embodiment may include the following composition, for example:
[0042]
Si: 2.5 mass% or more and 4.0 mass% or less,
25 C: 0.02 mass% or more and 0.10 mass% or less,
Mn: 0.05 mass% or more and 0.20 mass% or less,
f
16
Acid-soluble Al: 0.020 mass% or more and 0.040 mass% or less,
N: 0.002 mass% or more and 0.012 mass% or less,
S: 0.001 mass% or more and 0.010 mass% or less,
P: 0.01 mass% or more and 0.04 mass% or less, and
5 Balance: Fe and inevitable impurities.
[0043]
The steel sheet 11 usually has a thickness of 0.15 mm or more and 0.35 mm or
less, and the thickness may be out of this range.
[0044]
10 The glass coating film 12 is made of complex oxide, such as forsterite (Mg2Si04),
spinel (MgAl204), or cordierite (Mg2Al4Si50i6), for example. The thickness of the glass
coating film 12 is 0.5 \xm to 3 fim for example, and in particular, is generally around 1 jum,
but it is not limited to these examples.
[0045]
15 The insulating coating film 13 is made of coating liquid mainly containing
colloidal silica and phosphate (such as magnesium phosphate or aluminum phosphate) (see
JP S48-39338A, JP S53-28375B), or coating liquid formed by mixing alumina sol and
boric acid (see JP H6-65754A, JP H6-65755A). In the present embodiment, the
insulating coating film 13 is made of aluminum phosphate, colloidal silica, chromium
20 trioxide, or the like (see JP S53-28375B), for example. The insulating coating film 13
generally has a thickness of approximately 2 jim, but this thickness is not limited to this
example.
[0046]
In the grain oriented electrical steel sheet 10 of one embodiment of the present
25 invention, as shown in FIG. 5, a linearly altered portion 14 into which a part of the glass
coating film 12 is altered is generated in one of the surfaces or both surfaces of the grain
1|B
17
oriented electrical steel sheet 10. The linearly altered portion 14 has a composition or
thickness different from that of the other portions of the glass coating film 12. Such a
difference in the linearly altered portion 14 of the glass coating film 12 can be identified as
a difference in content of elements constituting the glass coating film 12, such as Mg and
5 Fe.
[0047]
As shown in FIG 5, the linearly altered portion 14 is generated in a linear form in
a direcfion parallel with the rolling direction (longitudinal direction of the steel sheet 11)
inward of one of the side edges of the grain oriented electrical steel sheet 10 by a
10 prescribed distance WL. In the example of FIG. 5, the linearly altered portion 14 is
generated in a continuous line in a direction parallel with the rolling direction. The
linearly altered portion 14, however, is not limited to such an example, and may be formed
in a discontinuous line, for example, in a broken line periodically disconnected. Such a
linearly altered portion 14 is generated by converging a laser beam and radiating it onto the
15 surface of the steel sheet 11, as described later.
[0048]
As aforementioned, in the grain oriented electrical steel sheet 10 according to one
embodiment of the present invention, the linearly altered portion 14 is generated in the
rolling direction in the glass coating film 12 on the surface at the one of the side edges of
20 the steel sheet 11. This linearly altered portion 14 has a smaller mechanical strength, and
is more easily deformed than the other portions of the glass coating film 12. Therefore, in
the final annealing step, the linearly altered portion 14 is preferentially deformed locally in
the coil 5 formed by winding up the steel sheet 11, thereby suppressing propagation of the
lateral strain progressing upward of the coil 5 from a lower edge thereof Accordingly, in
25 the step subsequent to the final annealing step, it is possible to reduce the trimming width
of the grain oriented electrical steel sheet 10 as much as possible.
18
[0049]
The linearly altered portion 14 may be partially generated in the longitudinal
direction (rolling direction) of the steel sheet 11. In this case, it is preferable that the
linearly altered portion 14 is generated in a region of 20% or more and 100% or less of the
5 total longitudinal length of the steel sheet 11, starting from the outermost peripheral
portion of the coil 5 formed by winding up the steel sheet 11. Specifically, the
longitudinal length Lz of the linearly altered portion 14 extending from an end along the
longitudinal direction of the grain oriented electrical steel sheet 10 is preferably 20% or
more of the total length Lc of the grain oriented electrical steel sheet 10 (Lz > 0.2 x Lc).
10 [0050]
The lateral strain is more likely to be generated at the outer peripheral portion of
the coil 5 because this outer peripheral portion is heated at high temperatures during the
final annealing. Hence, it is preferable to generate the linearly altered portion 14 starting
from the outermost peripheral portion of the coil 5 in a region of 20% or more of the total
15 length Lc of the coil 5. Thereby, during the final annealing step, the linearly altered
portion 14 generated in the outermost peripheral portion of the coil 5 becomes locally
deformed, thereby securely suppressing propagation of the lateral strain in the outer
peripheral portion of the coil 5. To the contrary, if the region where the linearly altered
portion 14 is generated is less than 20% of the entire length Lc of the coil 5, the linearly
20 altered portion 14 having a sufficient length is not generated in the outer peripheral portion
of the coil 5, and thus the lateral strain reduction effect is deteriorated in the outer
peripheral portion of the coil 5.
[0051]
In order to further securely suppress propagation of the lateral strain, the linearly
25 altered portion 14 may be generated over the entire length in the longitudinal direction
(rolling direction) of the steel sheet 11.
9 19
[0052]
The linearly altered portion 14 is generated at a position where a distance WL
from the one of the side edges of the grain oriented electrical steel sheet 10 to the center
with respect to the width direction of the linearly altered portion 14 is 5 mm or more and
5 35 mm or less (5 mm < WL < 35 mm). In addition, the width d of the linearly altered
portion 14 is 0.3 mm or more and 5.0 mm or less (0.3 mm < d < 5.0 mm).
[0053]
In this manner, the linearly altered portion 14 is generated at the position that
satisfies 5 mm < WL < 35 mm, and the width d of the linearly altered portion 14 satisfies
10 0.3 mm < d < 5.0 mm, thereby generating the linearly altered portion 14 that becomes
easily deformed during the final annealing step at a position where reduction of the lateral
strain can be attained; thus it is possible to securely reduce the width of the lateral strained
portion.
[0054]
15 The linearly altered portion 14 is often difficult to be confirmed through a visual
observation, through a microscope observation, or the like on the surface of the grain
oriented electrical steel sheet 10. In the linearly altered portion 14, however, the
characteristic X-ray intensity of Mg of the glass coating film 12 obtained through an
EPMA analysis (Electron Probe Micro Analysis) tends to be smaller than that in the other
20 portions of the glass coating film 12. That is, as shown in FIG. 6A and FIG 6B, the
linearly altered portion 14 can be observed as a linear Mg reduced portion 14a that is
defined based on a Mg reduction ratio obtained through the EPMA analysis on the glass
coating film 12. Specifically, the linear Mg reduced portion 14a may be a region where
the Mg reduction ratio Ir (Ir = la/Ip) obtained through the EPMA analysis on the glass
25 coating film 12 is within a range of 0.3 < Ir < 1.0.
[0055]
p 20
Here, the Mg reduction ratio Ir is a value obtained by dividing the characteristic
X-ray intensity la of Mg in a portion of the glass coating film 12 where the linearly altered
portion 14 is generated (region corresponding to a laser processed portion 20 described
later) by an average value Ip of the characteristic X-ray intensity of Mg in the other
5 portions of the glass coating film 12, out of the region corresponding to the laser processed
portion 20 described later, where no linearly altered portion 14 is generated.
[0056]
Thus, the Mg reduction ratio Ir is a reduction ratio of the characteristic X-ray
intensity of Mg in the glass coating film 12, and the linear Mg reduced portion 14a is a
10 linear region in which the characteristic X-ray intensity of Mg is smaller than that in the
other portions of the glass coating film 12. In the grain oriented electrical steel sheet 10
according to the present embodiment, the linearly altered portion 14 can be identified as
the linear Mg reduced portion 14a in which the Ir is within the range of 0.3 < Ir < 1.0.
[0057]
15 In the linearly altered portion 14, the characteristic X-ray intensity of Fe of the
glass coating film 12 obtained through the EPMA analysis tends to be greater than that in
the other portions of the glass coating film 12. Hence, the linearly altered portion 14 can
also be identified by using this characteristic X-ray intensity of Fe. Alternatively, the
linearly altered portion 14 can be identified by using a characteristic X-ray spectrum of Al,
20 Si, Mn, O, or the like, which is contained as a glass component in the glass coating film 12.
[0058]
The EPMA analysis in FIGS. 6 was carried out using the spatially resolved EPMA
under the following conditions: the radiation intensity of electron beam of 15 keV, the
magnification of x50, the visual field area of 2.5 mm x 2.5 mm, the spatial resolution of 5
25 |um, and the X-ray analyzing crystal: TAP.
[0059]
0
21
In the present embodiment, in the base metal iron portion of the steel sheet 11
located at a portion inward of the linearly altered portion 14, an average value of a
deviation angle 9a between the direction of the axis of easy magnetization of the crystal
grains and the rolling direction is 0° or more and 20° or less, preferably 0° or more and 10°
5 or less.
[0060]
In the present embodiment, the deviation angle 6a between the direction of the
axis of easy magnetization of the crystal grains and the rolling direction is defined as
follows. That is, the deviation angle 6a is defined by a mean-square value of an angle 6t
10 and an angle 9n (9a = (9t^-i-6n'^)°^), wherein the angle 9t is formed by the direction of the
axis of easy magnetization of the crystal grains of interest turning from the rolling direction
in the steel sheet face serving as a reference around a width-directional axis of the steel
sheet, and the angle 9n is formed by the direction of the axis of easy magnetization of the
crystal grains of interest turning from the rolling direction around an axis vertical to the
15 face of the steel sheet. The 9t and On are measured with the crystal orientation
measurement method (the Laue method) using X-ray diffraction. In the present
embodiment, crystal grains of 6a > 20° are referred to as "abnormal crystal grains", and
this means crystal grains whose axis of easy magnetization greatly deviates from the
rolling direction of the steel sheet 11. To the contrary, crystal grains having 6a of less
20 than 20° are referred to as "normal crystal grains". If the axis of easy magnetization of
the crystal grains greatly deviates from the rolling direction, the direction of magnetization
at this portion is likely to be oriented to a direction greatly different from the rolling
direction, which hinders lines of magnetic force from passing in the rolling direction.
Consequently, the magnetic property in the rolling direction of the steel sheet 11 is
25 deteriorated.
[0061]
0 22
With respect to the crystal orientation of the grain oriented electrical steel sheet,
the easy direction of magnetization of a preferable product may sometimes deviate from
the rolling direction by several degrees. In the present embodiment, also considering the
magnetic property, as a reference for abnormal crystal grains whose axis of easy
5 magnetization greatly deviates from the rolling direction, the lower limit of the above 6a is
set to be 20°.
[0062]
In the present embodiment, as shown in FIG. 18, for crystal grains generated in
the base metal iron portion in the vicinity of the linearly altered portion 14 formed to be
10 substantially parallel with the rolling direction of the grain oriented electrical steel sheet 10,
an average value R of the deviation angle 9a is defined by the following Formula (1):
[0063]
[Math. 1]
^ = ^ 7— -(1)
i
15 [0064]
where i denotes a number of the crystal grains; Lj denotes a distance where the
linearly altered portion 14 overlaps or be in contact with the i-th crystal grain; Gai denotes
the above defined rotation angle 9a for the i-th crystal grain. As indicated by the crystal
grains other than the third and the fourth grains in FIG. 18, if a crystal grain is located
20 across the linearly altered portion 14, w, is defined to be Wi = 1. On the other hand, as
indicated by the third and fourth crystal grains in FIG. 18, if the linearly altered portion 14
is located at the boundary between two crystal grains, Wj is defined to be Wj = 0.5.
[0065]
As described later in Example, at the time of radiating a laser beam onto the
II 23
surface of the steel sheet before the final annealing, if the inside of the base metal iron
portion is so heat affected that the base metal iron portion melts and resolidifies, the crystal
growth of the steel sheet is influenced during the final annealing, so that the deviation
angle 0a becomes greater, resulting in increase in percentage of abnormal crystal grains.
5 Consequently, the magnetic property with respect to the rolling direction of the grain
oriented electrical steel sheet tends to be deteriorated. To the contrary, at the time of
radiating a laser beam during the final annealing, when only the Si02 coating film is heat
affected, the crystal growth in the portion irradiated with the laser beam can be
substantially equivalent to the crystal growth in the other portions which is not irradiated
10 with the laser beam. Accordingly, the deviation angle 6a becomes small, and thus it
becomes more lilcely to be able to obtain normal crystal grains.
[0066]
The producing method of the grain oriented electrical steel sheet of the present
embodiment will be described hereinafter.
15 The producing method of the grain oriented electrical steel sheet that is the
present embodiment includes a casting step SOI, a hot rolling step S02, an annealing step
803, a cold rolling step S04, a decarburizing annealing step S05, a laser processing step
S06, an annealing separator coating step S07, a final annealing step SOS, a flattening
annealing step S09, and an insulating film coating step SIO, as shown in a flow chart of
20 FIG. 7.
[0067]
In the casting step SOI, melted steel prepared to include the above composition is
supplied to a continuous casting machine so as to continuously produce ingots.
In the hot rolling step S02, each of the obtained ingots is heated at a prescribed
25 temperature (e.g. 1150 to 1400°C), and is hot-rolled. Through this step, a hot rolled
material having a thickness of 1.8 to 3.5 mm is produced, for example.
^
24
[0068]
In the annealing step 803, the hot rolled material is subjected to heat treatment
under the following conditions: the annealing temperature of 750 to 1200°C, and the
annealing time of 30 seconds to 10 minutes, for example.
5 In the cold rolling step S04, the surface of the hot rolled material after the
annealing step S03 is pickled, and is then cold-rolled. Through this step, the steel sheet
11 having a thickness of 0.15 to 0.35 mm is produced, for example.
[0069]
In the decarburizing annealing step S05, the steel sheet 11 is subjected to heat
10 treatment under the following conditions: the annealing temperature of 700 to 900°C and,
the annealing time of 1 to 3 minutes, for example. In the present embodiment, as shown
in FIG 8, the heat treatment is carried out by conveying the steel sheet 11 through a
decarburizing annealing fiimace 31 while the steel sheet 11 is kept traveling.
Through this decarburizing annealing step S05, a silica (Si02)-based Si02 coating
15 film 12a is formed on each surface of the steel sheet 11.
[0070]
In the laser processing step S06, as shown in FIG 10 and FIG. 11, a laser beam is
radiated in a direction parallel with the rolling direction onto the one of the side edge
regions of the steel sheet 11 having the Si02 coating film 12a formed thereon under the
20 laser radiation condition described in details later, thereby forming the laser processed
portion 20 in the Si02 coating film 12a for the purpose of obtaining the linearly altered
portion 14.
[0071]
In the example of FIG. 11, the laser processed portion 20 is linearly generated in
25 the rolling direction at the position corresponding to the aforementioned linearly altered
portion 14, and is generated in a depth region from the outer layer of the Si02 coating film
25
12a toward the vicinity of the boundary between the Si02 coating film 12a and the steel
sheet 11. In the example of FIG. 11, the laser processed portion 20 is a groove having a
V-shaped cross section, but the shape of the cross section of the laser processed portion 20
is not limited to this example, and it may also be U-shaped, semicircular, or the like. The
5 laser beam radiation condition will be described later; and depending on the laser beam
radiation condition, there is such a case that the Si02 coating film 12a is only heat affected,
so that physical change in shape, such as change in cross sectional shape, is hardly
confirmed in the Si02 coating film 12a.
[0072]
10 As shown in FIG 8, the laser processing step S06 is carried out with a laser
processing unit 33 positioned after the decarburizing annealing furnace 31. A cooling
unit 32 for cooling the steel sheet 11 after the decarburizing annealing step S05 may be
positioned between the decarburizing annealing fiimace 31 and the laser processing unit 33.
A temperature T of the steel sheet 11 to be subjected to the laser processing step S06 may
15 be set within a range of 0°C < T < 300°C with this cooling unit 32, for example.
[0073]
As shown in FIG. 9, the laser processing unit 33 includes a laser oscillator 33a, a
condensing lens 33b for condensing a laser beam emitted from the laser oscillator 33a, and
a gas nozzle 33c for injecting assist gas to the vicinity of a point irradiated with the laser
20 beam. The type of the assist gas is not limited to a specific one, and air or nitrogen may
be used for this gas, for example. The light source and the type of the laser beam are not
limited to specific ones.
[0074]
In the laser processing step S06, the laser beam radiation condition is
25 appropriately adjusted such that no heat affected layer due to the laser beam radiation is
generated in the base metal iron portion of the steel sheet 11 located inward of the portion
26
of the Si02 coating film 12a irradiated with the laser beam (laser processed portion 20).
For example, the laser beam radiation condition, such as the laser beam intensity (laser
power P), is adjusted such that no prominent heat affected zone, such as a melted portion
due to the laser beam radiation, is generated in the vicinity of the surface of the base metal
5 iron portion in the steel sheet 11, and the surface of the base metal iron portion at a portion
irradiated with the laser beam becomes as flat as the surface of the other portions of the
base metal iron portion.
[0075]
Let us consider a case where the following laser beam radiation conditions are
10 given: the light source and the type of a certain laser, the laser beam diameterdc (mm) in
the width direction of the steel sheet 11, the laser beam diameter dL (mm) in the traveling
direction (longitudinal direction) of the steel sheet 11, the traveling speed VL (mm/sec) of
the steel sheet 11, the sheet thickness t (mm) of the steel sheet, flow rate Gf (L/min) of the
assist gas, and the like. In this case, when the laser power P (W) is gradually increased
15 from zero while the above conditions are all fixed, the threshold value of the laser power P
that generates melting on the surface of the base metal iron portion of the steel sheet 11 is
set as PO (W). Under such a condition, in the laser processing step S06, it is desirable that
the laser power P is set to satisfy 0.3 x PO < P < PO, and the laser beam is radiated onto the
Si02 coating film 12a of the steel sheet 11. Through this configuration, it is possible to
20 appropriately generate the laser processed portion 20 through the laser beam radiation only
in the SiOi coating film 12a without generating any melted portion in the base metal iron
portion right below the irradiated position.
[0076]
In the annealing separator coating step S07, the Si02 coating film 12a is coated
25 with a magnesia (MgO)-based annealing separator, and the magnesia (MgO)-based
annealing separator is dried by heating. In the present embodiment, as shown in FIG. 8,
#
27
the annealing separator coating unit 34 is positioned after the laser processing unit 33, and
the surface of the steel sheet 11 that has been subjected to the laser processing step S06 is
continuously coated with the annealing separator.
[0077]
5 The steel sheet 11 that has passed through the annealing separator coating unit 34
is wound up in a coil shape to be the coil 5. The outermost peripheral end of this coil 5 is
to be a rear end of the steel sheet 11 that passes through the decarburizing annealing
furnace 31, the laser processing unit 33, and the annealing separator coating unit 34.
Hence, in the present embodiment, in the laser processing step S06, it is configured to
10 generate the laser processed portion 20 in a region on the longitudinal rear end of the steel
sheet 11.
[0078]
As shown in FIG. 12, in the final annealing step S08, the coil 5 formed by winding
up the steel sheet 11 which is coated with the annealing separator is placed on the coil
15 receiver 8 with the coil axis 5a positioned in the vertical direction, and is placed in a
batch-type final annealing furnace so as to apply heat treatment to the coil 5. The heat
treatment condition of the final annealing step SOS is the annealing temperature of 1100 to
1300°C, and the annealing time of 20 to 24 hours, for example.
[0079]
20 At this time, as shown in FIG. 12, the coil 5 (steel sheet 11) is placed on the coil
receiver 8 in such a manner that the one of the side edges portion of the coil 5 (lower edge
of the coil 5) where the laser processed portion 20 is generated comes into contact with the
coil receiver 8.
[0080]
25 During the final annealing step S08, the silica-based Si02 coating film 12a and the
magnesia-based annealing separator react with each other so as to form the glass coating
0 28
film 12 of forsterite (Mg2Si04) on each surface of the steel sheet 11.
[0081]
In the present embodiment, the laser processed portion 20 is generated in the
depth region from the outer layer of the Si02 coating film 12a toward the vicinity of the
5 boundary between the Si02 coating film 12a and the steel sheet 11. This region where the
laser processed portion 20 is generated is to be the linearly altered portion 14 of the glass
coating film 12 in the final annealing step S08. As aforementioned, in this linearly
altered portion 14, the characteristic X-ray intensity of Mg obtained through the EPMA
analysis tends to be smaller than that in the other portions of the glass coating film 12.
10 [0082]
Accordingly, the linearly altered portion 14 generated in the glass coating film 12
can be identified as the linear Mg reduced portion where the characteristic X-ray intensity
of Mg is reduced compared with that in the other portions of the glass coating film 12 (Ir <
1.0). Mg is a representative element in the glass coating film 12, so that it is estimated
15 that the thickness of the glass coating film itself is reduced in the linear Mg reduced
portion. Hence, the linear Mg reduced portion has a smaller mechanical strength than that
in the other portions, and becomes easy to be locally deformed, and thus it is possible to
suppress propagation of the lateral strain in the final annealing step SOS. As
aforementioned, according to the EPMA analysis of the glass coating film 12, the
20 characteristic X-ray intensity of Mg is easily reduced in the linearly altered portion 14, and
the characteristic X-ray intensity of Fe is easily increased as compared with the other
portions of the glass coating film 12. It can be considered that not only reduction in the
thickness of the glass coating film 12 but also change in the percentage of elements, such
as Mg and Fe (composition in a limited sense), contained in the glass coating film 12
25 contribute to reduction in the mechanical strength of the linearly altered portion 14. The
change in the composition in the limited sense also appears as the change in the
29
characteristic X-ray intensity through the EPMA analysis. The change in the thickness of
the glass coating film 12 also causes change in amount of elements, such as Mg and Fe,
contained in the glass coating film 12 having this thickness, and thus the characteristic
X-ray intensity through the EPMA analysis is changed.
5 [0083]
Accordingly, in the present invention, the "change in the thickness of the glass
coating film" and the "change in the percentage of elements (composition in a limited
sense) contained in the glass coating film", which appear as the change in the characteristic
X-ray intensity through the EPMA analysis, are both considered as the "change in
10 composition (composition in a broader sense) of the glass coating film". In the present
invention, the "composition" represented in the "linearly altered portion having a
composition different from that in the other portions of the glass coating film" denotes the
above composition in the broad sense, and the "linearly altered portion" denotes a portion
having the above composition in the limited sense or a thickness different from that in the
15 other portions of the glass coating film.
[0084]
In the flattening annealing step S09, the steel sheet 11 wound in a coil shape is
unwound, stretched in a sheet state by applying tension at an annealing temperature of
approximately 800°C, and conveyed so as to release the winding deformation of the coil,
20 thereby flattening the steel sheet 11. At the same time as the flattening annealing step
S09, in the insulating film coating step SIO, the glass coating film 12 formed on the both
surfaces of the steel sheet 11 is coated with an insulator material, and baking is performed
so as to form the insulating coating film 13 thereon.
[0085]
25 In ihis manner, the glass coating film 12 and the insulating coating film 13 are
formed on each surface of the steel sheet 11, thereby producing the grain oriented electrical
30
steel sheet 10 of the present embodiment.
Thereafter, the laser beam may be converged and radiated onto one surface of the
steel sheet 10 to apply linear strains that are substantially vertical to the rolling direction
and periodical in the rolling direction for the sake of magnetic domain control.
5 [0086]
In the above producing method of the grain oriented electrical steel sheet 10, as
described above, in the laser processing step S06, the laser processed portion 20 is
generated in the region at the one of the side edge regions of the steel sheet 11 where the
Si02 coating film 12a is formed. In the final annealing step SOS subsequent to the
10 annealing separator coating step S07, the glass coating film 12 is formed from the Si02
coating film 12a and the annealing separator, and the linearly altered portion 14 is also
generated in the region where the laser processed portion 20 is generated.
[0087]
Here, in the final annealing step SOS, as shown in FIG 13, the linearly altered
15 portion 14 is generated in the rolling direction of the coil 5 at a position on the coil 5 at a
prescribed distance from the contact position between the coil 5 and the coil receiver 8 (i.e.,
in the one side edge portion of the coil 5). In this linearly altered portion 14, as described
above, the composition in the limited sense, such as the composition ratio of Mg and Fe,
and the thickness are different from those in the other portions of the glass coating film, so
20 that it is considered that the mechanical strength thereof is also different from that in the
other portions.
In the final annealing step SOS, when the load is applied to the coil 5 by the
weight thereof or the like, the laser processed portion 20 generated in the Si02 coating film
12a in the laser processing step S06 is preferentially deformed.
25 [0088]
In the final annealing step SOS, as shown in FIG. 13, the lateral strained portion 5e
31
propagates from the contact portion between the coil 5 and the coil receiver 8 (one of the
side edges of the coil 5) toward the other side of the side edges of the coil 5, but the above
linearly altered portion 14 suppresses this propagation of the lateral strained portion 5e.
Accordingly, the width of the lateral strained portion 5e becomes decreased, so that the
5 trimming width can be reduced even in the case of removing this lateral strained portion 5e,
which enhances the production yield of the grain oriented electrical steel sheet 10.
[0089]
It is unnecessary to trim the lateral strained portion 5e if the produced grain
oriented electrical steel sheet 10 including this lateral strained portion 5e satisfies quality
10 required by a customer because the width and warp of the lateral strained portion 5e can be
sufficiently reduced. In this case, it is possible to further enhance the production yield of
the grain oriented electrical steel sheet 10. Because the base metal iron portion of the
steel sheet 10 located inward of the portion of the glass coating film 12 where the linearly
altered portion 14 is generated is hardly heat affected by the laser beam radiation, almost
15 no abnormal crystal grains are generated, and the magnetic property is not deteriorated in
the base metal iron portion at this position. Accordingly, even in the case of carrying out
no trimming of the lateral strained portion 5e, it is possible to use the grain oriented
electrical steel sheet 10 as it is as a product having an excellent magnetic property;
therefore it is possible to enhance the quality as well as the product yield of the grain
20 oriented electrical steel sheet 10.
[0090]
In the present embodiment, the laser processed portion 20 is generated in the
depth region from the outer layer of the Si02 coating film 12a toward the vicinity of the
boundary between the Si02 coating film 12a and the steel sheet 11. Note that, as
25 aforementioned, the radiation condition such as the intensity of the laser beam is adjusted
such that inside the steel sheet 11, no significant heat affected layer resulted from melting
32
due to the laser beam radiation is generated in the vicinity of the surface of the base metal
iron portion, and flatness nearly equal to the surface of the base metal iron portion in the
other portions is obtained. Consequently, as described later in detail, in the portion (base
metal iron portion) located inward of the linearly altered portion 14 in the steel sheet 11,
5 the average value R of the deviation angle 9a of the direction of the axis of easy
magnetization of the crystal grains of the steel sheet 11 deviating from the rolling direction
can be reduced to be 20° or less.
[0091]
Accordingly, the crystal orientation in the base metal iron portion located inward
10 of the linearly altered portion 14 has more preferable and stable orientation than that in the
prior art even if the width of the lateral strained portion 5e is so small that this lateral
strained portion 5e is unnecessary to be removed; thus it is possible to use this steel sheet
as the grain oriented electrical steel sheet 10 depending on the usage thereof
[0092]
15 Moreover, it is possible to reduce the power P of the laser beam to a low level in
the laser processing step S06, thereby eliminating necessity for a large-scale and
high-power laser apparatus, and this can attain efficient production of the grain oriented
electrical steel sheet 10.
[0093]
20 In the grain oriented electrical steel sheet 10 as one embodiment of the present
invention, the distance WL from the one of the side edges of the steel sheet 11 to the center
with respect to the width direction of the linearly altered portion 14 is set within 5 mm <
WL < 35 mm, and the width d of the linearly altered portion 14 is set within 0.3 mm < d <
5.0 mm, and thus propagation of the lateral strained portion 5e can securely be suppressed
25 by the linearly altered portion 14.
[0094]
33
Starting from the outermost peripheral portion of the coil 5, the length Lz in the
rolling direction of the linearly altered portion 14 (laser processed portion 20) is set as 20%
or more of the total length Lc of the coil 5; therefore, it is possible to securely suppress
propagation of the lateral strain even in the outer peripheral portion of the coil 5 where the
5 lateral strain is likely to be generated.
[0095]
Further, in one embodiment of the present invention, the linearly altered portion
14 includes the linear Mg reduced portion 14a. This linear Mg reduced portion 14a is a
region of the glass coating film 12 where the Mg reduction ratio Ir (Ir = la/Ip) is within the
10 range of 0.3 < Ir < 1.0. This linearly altered portion 14 (linear Mg reduced portion 14a) is
a portion of the glass coating film 12 where the thickness is smaller than that in the other
portions of the glass coating film 12, or where the composition of Mg, Fe, or the like (the
composition in the limited sense) is altered unlike in the other portions of the glass coating
film 12.
15 [0096]
In one embodiment of the present invention, in the laser processing step prior to
coating with the separator used for the final annealing, the laser beam with relatively low
intensity is radiated such that no significant heat affected zone such as a melted portion is
generated in the Si02 coating film 12a and in the vicinity of the surface of the base metal
20 iron portion located inward of the Si02 coating film 12a, and the linearly altered portion 14
is generated from the above laser processed portion 20 in the final annealing step.
Although a specific mechanism for this is not apparent, it can be considered that the
linearly altered portion 14 (linear Mg reduced portion 14a) has smaller mechanical strength
than the other portions, and thus this portion is more easily deformed. There also is such
25 a possibility that residual strain introduced in the Si02 coating film 12a by the laser beam
radiation may provide some influence. Consequently, it is estimated that, in the final
34
annealing step, the local deformation in the linearly altered portion 14 (linear Mg reduced
portion 14a) suppresses propagation of the lateral strained portion 5e.
[0097]
The grain oriented electrical steel sheet 10 and the producing method of the grain
5 oriented electrical steel sheet 10 have been described above as one embodiment of the
present invention, but the present invention is not limited thereto, and various
modifications can be appropriately made without departing from the technical ideas of the
invention.
[0098]
10 For example, the composition of the steel sheet 11 is not limited to the one
specified by the present embodiment, and the steel sheet having a different composition
may be used. It has been described that the decarburizing annealing step S05, the laser
processing step S06, and the annealing separator coating step S07 are carried out by using
the equipment shown in FIG. 8 and FIG. 9, but the present invention is not limited to this,
15 and these steps may be carried out by using other equipment having different structures.
The laser processing step S06 may be performed at any time between the decarburizing
annealing step 805 and the final annealing step S08, and may be performed after the
annealing separator coating step S07 and before the final annealing step 808, for example.
[0099]
20 Further, as shown in FIG. 5, the linearly altered portion 14 has been described by
using an example of generating the linearly altered portion 14 in a continuous line in a
direction parallel with the rolling direction, but the present invention is not limited to this.
For example, as shown in FIG. 17, the linearly altered portion 14 (laser processed portion
20) in a discontinuous broken line may periodically be generated in the rolling direction.
25 This case has an effect of reducing average power of the laser beam. In the case of
generating the periodical linearly altered portion 14, a rate r for the laser processed portion
35
20 per period is not limited to a specific one as far as the lateral strain reduction effect is
attained, and it is preferable to set this rate as r > 50%, for example.
[0100]
The laser beam may be radiated onto both surfaces of the steel sheet 10 so as to
5 generate the linearly altered portion 14 (laser processed portion 20) on both the surfaces of
the grain oriented electrical steel sheet 10.
[Example]
[0101]
Description will be provided on a validation test that has been carried out for
10 verifying the effects of the present invention.
[0102]
First, slabs each having the following composition were casted: 3.0 mass% of Si,
0.05 mass% of C, 0.1 mass% of Mn, 0.02 mass% of acid-soluble Al, 0.01 mass% of N,
0.01 mass% of S, 0.02 mass% of P, and balance being Fe and inevitable impurities (casting
15 step).
[0103]
Each of these slabs was subjected to hot rolling at a temperature of 1280°C so as
to produce a hot-rolled material having a thickness of 2.3 mm (hot rolling step).
[0104]
20 Then, the hot-rolled material was subjected to heat treatment under a condition of
1000°C X 1 minute (annealing step). The rolled material after the annealing step was
subjected to pickling treatment after the heat treatment, and was then subjected to cold
rolling so as to produce a cold-rolled material having a thickness of 0.23 mm (cold rolling
step).
25 [0105]
Decarburizing annealing was carried out on the cold-rolled material under a
36
condition of 800°C x 2 minutes (decarburizing annealing step). Through this
decarburizing annealing, the SiOa coating film 12a was formed on each surface of the steel
sheet 11, which was the cold-rolled material.
[0106]
5 A laser beam was radiated through the laser processing unit onto a surface of the
steel sheet 11 on which the Si02 coating film 12a was formed so as to generate the laser
processed portion 20 (laser processing step).
The laser processed portion 20 was generated in the Si02 coating film 12a in the
steel sheet 11 and each surface thereof was coated with the magnesia-based annealing
10 separator (annealing separator coating step).
[0107]
The steel sheet 11 which had been coated with the annealing separator was wound
up in a coil shape, and the steel sheet 11 in this state was placed in a batch-type final
annealing furnace so as to finally anneal this steel sheet 11 under a condifion of 1200°C x
15 20 hours (final annealing step).
[0108]
At this stage, various different conditions were used for generating the laser
processed portion 20, and a relation between these conditions and a width Wg of the lateral
strained portion 5e (hereinafter, referred to as a "lateral strain width Wg") after the final
20 annealing was evaluated.
[0109]
Moreover, the direction of the axis of easy magnetization of the crystal grains in
the base metal iron portion located inward of the linearly altered portion 14 in the steel
sheet 11 was measured using the X-ray diffraction so as to find an average value R of the
25 deviation angle 9a of this direction of the axis of easy magnetization relative to the rolling
direction. In addition, iron loss of Wl7/50 was also evaluated through an SST (single
37
sheet tester) test. Each test specimen for the SST measurement in a size of 100 mm in
width-directional length of the steel sheet, and 500 mm in length in the rolling direction of
the steel sheet was cut out from a 100 mm wide region along the edge of the steel sheet.
[0110]
5 The Mg reduction ratio Ir was measured in the linearly altered portion 14
generated in a portion corresponding to the laser processed portion 20 of the glass coating
film 12. In this quantitative analysis of Mg, using the steel sheet 10 having the insulating
coating film 13, which was a product, the insulating coating film 13 on the outermost layer
of the steel sheet 10 was removed with an NaOH aqueous solution, and the composition of
10 the glass coating film 12 was then analyzed through the EPMA. The characteristic X-ray
intensity la of Mg in the linearly altered portion 14 was defined by using an average value
obtained by averaging the X-ray intensity values of the Mg reduced portion at plural
positions in the width d. The above analysis may be carried out after the final annealing
step but before the insulating coating film forming step, thereby omitting a preparation step
15 of washing off the insulating coating film 13 of the steel sheet 10 with an alkali solution
such as NaOH prior to the analysis.
[0111]
A semiconductor laser was used as the laser unit. The laser processing was
carried out and evaluated under the following conditions: the laser beam diameter dL in the
20 traveling direction (longitudinal direction) of the steel sheet 11 was dL = 12 (mm), the
travelling speed VL of the steel sheet 11 was VL = 400 (mm/sec), the sheet thickness t of
the steel sheet 11 was t = 0.23 (mm), the flow rate Gf of the assist gas was Gf = 300
(L/min), the laser beam irradiated position WL in the width direction of the steel sheet 11
was WL = 20 (mm), by using as parameters the laser power P (W) and the laser beam
25 diameter dc (mm) in the width direction of the steel sheet 11. The length Lz in the rolling
direction of the laser processed portion 20 starting from the outermost peripheral portion of
38
the coil was set as Lz = 3000 m (total length Lc of the coil was Lc = 10000 m).
[0112]
Table 1 shows the radiation conditions of the laser beam and data on the
evaluation result. PO in Table 1 denotes a threshold value of the laser power P (W) that
5 generates melting on the surface of the base metal iron portion of the steel sheet 11 when
the laser power P was gradually increased from zero while the above conditions (dL, VL, t,
Gf, WL) and dc were fixed. The lateral strain width Wg shown in Table 1 was the
maximum value through the total length of the coil.
[0113]
10 In Table 1, Examples 1 to 6 satisfy 0°< R < 20°, and 0.3 < Ir < 0.95. Examples 7
and 8 satisfy 0° < R < 20°, but do not satisfy 0.3 < Ir < 0.95, and have 0.95 < Ir < 1.0. To
the contrary, Comparative Examples 1 to 3 do not satisfy 0° < R < 20°, and have R > 20°.
[0114]
[Table 1]
15 Table 1 Laser Radiation Conditions and Evaluation Results
No.
Example 1
Example 2
Example 3
Example 4
Example 5
Example 6
Example 7
Example 8
Comparative
Example 1
Comparative
Example 2
Comparative
Example 3
Laser
Beam
Diameter
dc(mm)
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
1
1
1
Laser
Power
P(W)
800
1000
1100
1200
1300
1400
450
600
1750
2000
1800
PO(W)
1420
1420
1420
1420
1420
1420
1420
1420
1700
1700
1700
Mg
Reduction
Ratio
Ir
0.95
0.90
0.80
0.70
0.50
0.30
0.99
0.97
0.24
0.05
0.15
Lateral
Strain Width
Wg(mm)
40
32
29
21
17
16
45
44
17
17
16
Average
Value of
Deviation
Angle
RO
5
6
6
7
10
20
5
5
25
52
43
Iron Loss
W17/50
(W/kg)
0.86
0.83
0.87
0.84
0.86
0.89
0.85
0.84
0.90
0.94
0.92
39
[0115]
The observation results of a microstructure in the base metal iron portion of each
steel sheet 11 are shown in FIG. 16. As shown in FIG 16, in the Comparative Examples 1
5 and 2, elongated crystal grains or grain boundaries extending in the rolling direction of
each steel sheet 11 can be observed at a position (indicated by arrows in the drawing)
corresponding to each laser processed portion 20 (linearly altered portion 14).
Aforementioned abnormal crystal grains having great deviation angle 0a of the direction of
the axis of easy magnetization from the rolling direction are generated around such
10 elongated crystal grains and grain boundaries. In the Comparative Examples 1 to 3, a
microstructure in the cross section in the width direction of each steel sheet immediately
after the laser beam radiation and before the final annealing was observed, and as
schematically shown in FIG. 19, a microstructure of abnormal crystal grains (melted and
resolidified portion 22) resulted from melted and resolidified base metal iron portion of the
15 steel sheet 11 due to the laser beam radiation was observed. In the Comparative
Examples 1 to 3, it is estimated that heat that had affected the inside of the base metal iron
portion of the steel sheet 11 also affected crystal growth of the steel sheet 11, thus the
abnormal crystal grains became likely to be generated.
[0116]
20 To the contrary, in the Examples shown in FIG. 16 (corresponding to "Example 5"
in Table 1), a portion of the base metal iron portion located at a position corresponding to
the laser processed portion 20 (linearly altered portion 14) has a microstructure of crystal
grains substantially equivalent to that in the other portions of the base metal iron portion.
In a manner similar to that in the Comparative Examples, a microstructure in the cross
25 section in the width direction of each steel sheet 11 after the laser beam radiation and
before the final annealing was observed under the condition of the Examples; and no
40
melted and resolidified portion 22 was observed even in the outermost layer of the base
metal iron portion. In the Examples, it is estimated that the significant heat affected zone
due to the laser beam radiation did not reach the base metal iron portion of the steel sheet
11, therefore, the crystal growth of the steel sheet 11 inward of the laser processed portion
5 20 progressed in the same manner as the crystal growth in the other portions of the steel
sheet 11 in the final annealing step.
[0117]
(Mg Reduction Ratio Ir)
FIG. 20 shows a relation among the Mg reduction ratio Ir of the linearly altered
10 portion 14 of the glass coating film 12 generated in a portion corresponding to the laser
processed portion 20, the width Wg of the lateral strained portion, and the average
deviation angle R of the axis of easy magnetization deviating from the rolling direction.
[0118]
The EPMA analysis was carried out using the spatial resolution EPMA under the
15 following conditions: the electron beam radiation intensity of 15 keV, the magnification of
x50, the visual field area of 2.5 mm x 2.5 mm, the spatial resolution of 5 ^m, and the
X-ray analyzing crystals: TAP.
[0119]
As shown in the Examples 1 to 6, if the Mg reduction ratio Ir is 0 < Ir < 0.95, the
20 lateral strain width Wg was reduced to be 40 mm or less. In the case of applying no laser
processing to the steel sheet 11 (i.e., generating no linearly altered portion 14), Wg was 50
mm. As shown in the Examples 4 to 6, if 0 < Ir < 0.70, the lateral strain width Wg
becomes 21 mm or less, and the lateral strain width was further reduced. Accordingly, it
is confirmed that in the linearly altered portion 14, it is preferable that the Mg reduction
25 ratio Ir is 0.95 or less, and more preferably 0.70 or less. On the other hand, as shown in
the Examples 7 and 8, in the case of 1.0 > Ir > 0.95, Wg was 45 or less, and there was
41
some more lateral strain reduction effect than in the case of applying no laser processing
(Wg = 50 mm), but Wg became greater than Wg in the Examples 1 to 6 by 10% or more,
and it is confirmed that the lateral strain reduction effect was decreased.
[0120]
5 FIG. 20 shows that the average value R of the deviation angle 0a of the axis of
easy magnetization relative to the rolling direction was quantified with respect to the
crystal grains in the base metal iron portion located inward of the linearly altered portion
14, and also shows results of studying a correlation between the above Mg reduction ratio
Ir and R. According to FIG. 20, it is understood that in the case of the Mg reduction ratio
10 Ir of 0.3 or more, R can be reduced to be 20° or less. It is also understood that in the case
of the Mg reduction ratio Ir of 0.5 or more, R can be reduced to be 10° or less.
[0121]
With respect to data regarding the iron loss shown in Table 1, if R is 10° or less,
the iron loss is equal to the reference value 0.85 ± 0.02 (W/kg), and the variation in the
15 iron loss is within a permissible error range, and thus it can be said that there is no
deterioration of the iron loss. The reference value of the iron loss here represents the iron
loss in the case of applying no laser processing to the steel sheet 11. The more the base
metal iron portion of the steel sheet 11 is heat affected by the laser processing, the more the
iron loss deviates from the reference value, which results in increase in the deterioration of
20 the iron loss. If R is 20° or less, the margin of the deterioration is less than 0.05 (W/kg)
relative to the reference value 0.85 (W/kg) although a tendency of deterioration of the iron
loss is exhibited. On the other hand, if R is more than 20° as shown in the Comparative
Examples 1 to 3, In particular, if R is 40° or more as shown in the Comparative Examples
2 and 3, deterioration of the iron loss becomes greater by 0.05 (W/kg) or more.
25 Deterioration of the iron loss by 0.05 (W/kg) corresponds to deterioration in the grain
oriented electrical steel sheet by one degree on the product grade basis. Hence, if R < 20°,
Jb 42
such an effect can be attained that a side edge portion of the steel sheet 10 including the
linearly altered portion 14 generated through the laser processing can be very likely to be
shipped together with the other inner portions of the steel sheet 10 at the same product
grade. To the contrary, if R > 20°, the side edge portion including the linearly altered
5 portion 14 of the steel sheet 10 has deterioration of the iron loss of 0.05 (W/kg) or more,
which results in deterioration of the product grade at this edge portion by one degree or
more. Consequently, this edge portion cannot be shipped together with the other inner
portions of the steel sheet 10 at the same product grade, and thus in order to secure the
product grade for the inner portions, this edge portion is required to be cut off, which
10 deteriorates the yield of the steel sheet 10.
[0122]
According to the results in FIG. 20, the smaller the Mg reduction ratio Ir becomes,
the smaller the lateral strain width Wg can become, but the greater R becomes. To the
contrary, the greater the Mg reduction ratio Ir becomes, the smaller R can become, but the
15 greater the lateral strain width Wg becomes. Hence, it is understood that in order to
achieve both goals of reduction of R in the base metal iron portion inward of the linearly
altered portion 14 and reduction of the lateral strain width Wg at the same time, it is
preferable to satisfy 0.3 < Ir < 1.0, and more preferable to satisfy 0.3 < Ir < 0.95, and even
more preferable to satisfy 0.5 < Ir < 0.70.
20 [0123]
Accordingly, in the case of applying no laser processing to the steel sheet 11, Wg
becomes 50 mm, which attains no lateral strain reduction effect. To the contrary, in the
case of applying the laser processing, it is possible to reduce the lateral strain without
deteriorating the magnetic property of the base metal iron portion of the steel sheet 10. In
25 particular, as shown in the Examples 1 to 6, through the laser processing under the
appropriate laser radiation condition, it is possible to generate the linearly altered portion
43
14 that satisfies the condition of 0.3 < Ir < 0.95; therefore, the lateral strain can be
significantly reduced (Wg < 40 mm) without deteriorating the magnetic property of the
base metal iron portion (R < 20°). In the case of the laser processing with smaller power
as shown in the Examples 7 and 8, the linearly altered portion 14 that satisfies 0.95 < Ir <
5 1.0 is generated, and thus the lateral strain reduction effect can be attained to some extent
(40 mm < Wg < 50 mm) without deteriorating the magnetic property of the base metal iron
portion (R < 20°).
[0124]
(Width d, distance WL, and length Lz in rolling direction of laser processed
10 portion 20 (linearly altered portion 14))
FIG 15 shows a relation between the position Z in the rolling direction of the steel
sheet 11 and the lateral strain width Wg using various different lengths Lz in the rolling
direction of the laser processed portion 20 (linearly altered portion 14) starting from the
outermost peripheral portion of the coil 5, in the case where the total steel sheet length Lc
15 = 10000 m. The origin of the position Z in the rolling direction of the steel sheet 11 is the
outermost peripheral portion of the coil 5. The laser condition was in accordance with
that in Example 2. The distance WL from the one of the side edges of the steel sheet 11
to the center with respect to the width direction of the laser processed portion 20 was set as
WL = 20 mm.
20 [0125]
In the case of Lz of 500 m (5% of Lc), or Lz of 1000 m (10% of Lc), the lateral
strain width Wg within the range of Z < 4000 m was the same as that in the Comparative
Examples having no laser processing. However, in the case of Lz of 2000 m or more, that
is, 20% or more of the total steel sheet length Lc, the lateral strain width Wg is reduced to
25 be approximately 30 mm across the total steel sheet length Lc. Hence, it can be said that
it is preferable to generate the laser processed portion 20 (linearly altered portion 14) in a
Jt
44
region of 20% or more from the outer peripheral portion of the coil where the lateral strain
deformation is significant, thereby eflficiently reducing the lateral strain in the outer
peripheral portion of the coil 5 where significant lateral strain is generated.
[0126]
5 In addition, FIG. 14 shows a relation between the distance WL from the one of the
side edges of the steel sheet 11 to the center with respect to the width direction of the laser
processed portion 20 (linearly altered portion 14), and the width Wg of the lateral strained
portion. The length Lz in the rolling direction of the laser processed portion 20 (linearly
altered portion 14) was set as Lz = 3000 m (total length of the coil Lc = 10000 m). The
10 width d of the laser processed portion 20 (linearly altered portion 14) was set to have five
levels: 0.5 mm, 1 mm, 2 mm, 3 mm, 5 mm, and 6 mm. The lateral strain width Wg
shown in FIG. 14 is the maximum value relative to the total length of the coil.
[0127]
As shown in FIG. 14, it is confirmed that in the case of the width d of the laser
15 processed portion 20 (linearly altered portion 14) as great as 6 mm, the lateral strain width
Wg becomes 45 mm or more, which exhibits a small effect of reducing the lateral strain
width Wg. To the contrary, it is understood that in the case of the width d of 0.5 mm, 1
mm, 2 mm, 3 mm, and 5 mm, the lateral strain width Wg becomes approximately 40 mm
or less, which exhibits that the lateral strain width Wg can appropriately be reduced. The
20 laser processed portion 20 having a too thin width d hinders the portion of the laser
processed portion 20 (linearly altered portion 14) from being deformed during the final
annealing; thus it is preferable to set the width d as 0.3 mm or more.
[0128]
Further, it was confirmed that in the case of the distance WL of 40 mm or more,
25 even if the width d is 5 mm or less, the lateral strain width Wg was increased to be 45 mm
or more, and the effect of reducing the lateral strain width Wg becomes decreased. To the
i> 45
contrary, if the distance WL is 35 mm or less, the lateral strain width Wg becomes
approximately 40 mm or less under the condition of the width d of 5 mm or less, which
exhibits that the lateral strain width Wg can appropriately be reduced. In particular, if the
distance WL is within the range of 10 to 20 mm, it is possible to significantly reduce the
5 lateral strain width Wg to be 35 mm or less under the condition of the width d of 3 mm or
less. If the distance WL is less than 5.0 mm, Wg tends to be slightly increased, and thus it
is preferable to set the distance WL as 5.0 mm or more.
[0129]
Accordingly, it is preferable that the width d of the laser processed portion 20
10 (linearly altered portion 14) is set as 0.3 mm or more and 5.0 mm or less, and the position
WL in the width direction is 5.0 mm or more and 35 mm or less. Through this
configuration, it is possible to preferably reduce the lateral strain width Wg to be a
permissible value (e.g. 40 mm) or less.
[Reference Signs List]
15 [0130]
5 Coil
5e Lateral strained portion
10 Grain oriented electrical steel sheet
11 Steel sheet
20 12 Glass coating film
12a Si02 coating film
14 Linearly altered portion
14a Linear Mg reduced portion
20 Laser processed portion
25 22 Melted and resolidified portion

[Name of Document] CLAIMS
[Claim 1]
A grain oriented electrical steel sheet having a glass coating film formed on a
surface thereof, comprising:
5 a linearly altered portion generated in the glass coating film at one of side edges
of the steel sheet, in a continuous line or in a discontinuous broken line in a direction
parallel with a rolling direction of the steel sheet, and having a composition different from
a composition in other portions of the glass coating film,
wherein an average value of a deviation angle of a direction of an axis of easy
10 magnetization of crystal grains relative to the rolling direction is 0° or more and 20° or less
in a base metal iron portion of the steel sheet at a position along a width direction of the
steel sheet, the position corresponding to the linearly altered portion.
[Claim 2]
The grain oriented electrical steel sheet according to claim 1,
15 wherein a characteristic X-ray intensity la of Mg in the linearly altered portion of
the glass coating film is smaller than an average value Ip of the characteristic X-ray
intensity of Mg in the other portions of the glass coating film.
[Claim 3]
The grain oriented electrical steel sheet according to claim 2,
20 wherein the average value Ip of the characteristic X-ray intensity of Mg in the
other portions of the glass coating film and the characteristic X-ray intensity la of Mg in
the linearly altered portion are obtained through an EPMA analysis, and
wherein the linearly altered portion is identified in the glass coating film as an Mg
reduced portion whose Mg reduction ratio Ir that is a ratio of the la relative to the Ip is 0.3
25 or more and less than 1.0.
[Claim 4]
47 \. \ ': ' . . nr-r. 1^^^
^^ I i - . . . uThe grain oriented electrical steel sheet according to claim 3,
wherein the linearly altered portion is identified as the Mg reduced portion whose
Mg reduction rafio Ir is 0.3 or more and 0.95 or less.
[Claim 5]
5 The grain oriented electrical steel sheet according to any one of claim 1 to claim
4,
wherein a laser beam is radiated in a direction parallel with the rolling direction
onto a region at the one of the side edge regions of the steel sheet having an SiOj coating
film formed on a surface thereof so as to generate a laser processed portion in a continuous
10 line or in a discontinuous broken line in a depth region from an outer layer of the Si02
coating film toward a boundary between the Si02 coating film and the steel sheet,
wherein the laser processed portion in the Si02 coating film is altered, and
wherein the linearly altered portion is generated in the glass coating film.
[Claim 6]
15 The grain oriented electrical steel sheet according to any one of claim 1 to claim
5,
wherein a distance WL from the one of the side edges of the steel sheet to a center
with respect to the width direction of the linearly altered portion is 5 mm or more and 35
mm or less, and
20 wherein a width d of the linearly altered portion is 0.3 mm or more and 5.0 mm or
less.
[Claim 7]
The grain oriented electrical steel sheet according to any one of claim 1 to claim
6,
25 wherein the linearly altered portion is generated in a region of 20% or more and
100% or less of a total length in the rolling direction of the steel sheet, and the region starts
,-.•!• I ' «i , * • • • /•-*
X
from one end in the rolling direction of the steel sheet corresponding to an outermost
periphery of the steel sheet when the steel sheet is wound up in a coil shape in a final
annealing step.
[Claim 8]
5 A method of producing a grain oriented electrical steel sheet having a glass
coating film formed on a surface thereof, the method comprising:
a laser processing step of radiating, onto one of side edge regions of a steel sheet
having an Si02 coating film formed on a surface thereof, a laser beam in a direction
parallel with a rolling direction of the steel sheet so as to generate a laser processed portion
10 in a continuous line or in a discontinuous broken line;
an annealing separator coating step of coating each surface of the steel sheet with
an annealing separator after the laser processing step; and
a final annealing step of finally annealing the steel sheet which is coated with the
annealing separator so as to form the glass coating film on each surface of the steel sheet,
15 wherein the laser processed portion is generated in a depth region from an outer
layer of the Si02 coating film toward a boundary between the Si02 coating film and the
steel sheet,
wherein, in the final annealing step, the steel sheet is wound up in a coil shape, the
steel sheet in the coil shape is placed and finally annealed with the one of the side edges
20 thereof where the laser processed portion is directed downward, the glass coating film is
generated from the Si02 coating film and the annealing separator, and a linearly altered
portion having a composition different from a composition in other portions of the glass
coating film is formed in a portion corresponding to the laser processed portion.
[Claim 9]
25 The method of producing a grain oriented electrical steel sheet, according to claim
wherein, in the laser processing step, the laser processed portion is generated in
such a manner that a distance WL from the one of the side edges of the steel sheet to a
center with respect to the width direction of the laser processed portion is 5 mm or more
and 35 ram or less, and a width d of the laser processed portion is 0.3 mm or more and 5.0
5 mm or less.
[Claim 10]
The method of producing a grain oriented electrical steel sheet, according to claim
8 or claim 9,
wherein, in the laser processing step, the laser processed portion is generated in a
10 region of 20% or more and 100% or less of a total length in the rolling direction of the
steel sheet, and the region starts from one end in the rolling direction of the steel sheet
corresponding to an outermost periphery of the steel sheet when the steel sheet is wound
up in a coil shape in the final annealing step.