GRAIN-ORIENTED ELECTRICAL STEEL SHEET
[Technical Field ofthe Invention]
[0001]
The present invention relates to a grain-oriented electrical steel sheet.
Priority is claimed on Japanese Patent Application No. 2015-086301, filed on
April20, 2015, the content of which is incorporated herein by reference.
[Related Art]
[0002]
In the related art, as a steel sheet for an iron core of a transformer, there is
known a grain-oriented electrical steel sheet that exhibits excellent magnetic
characteristics in a specific direction. The grain-oriented electrical steel sheet is a
steel sheet in which a crystal orientation is controlled so that a magnetization easy axis
of a crystal grain and a rolling direction match each other by a combination of a cold
rolling treatment and an annealing treatment. It is preferable that an iron loss of the
grain-oriented electrical steel sheet is as small as possible.
[0003]
The iron loss is classified into an eddy current loss and a hysteresis loss. In
addition, the eddy current loss is classified into a classical eddy current loss and an
anomalous eddy current loss. Typically, there is known a grain-oriented electrical
steel sheet in which an insulating film is formed on a surface of a steel sheet (base
metal) of which a crystal orientation is controlled as described above so as to reduce
the classical eddy current loss. The insulating film also plays a role of applying
electrical insulating properties, tensile strength, heat resistance, and the like to the steel
sheet. Furthermore, recently, there is also known a grain-oriented electrical steel
sheet in which a glass film is formed between the steel sheet and the insulating film.
- l -
[0004]
On the other hand, as a method of reducing the anomalous eddy current loss,
there is known a magnetic domain control method of narrowing a width of a 180°
magnetic domain (performing refinement ofthe 180° magnetic domain) by forming a
strain or a groove, which extends in a direction intersecting the rolling direction, at a
predetermined interval along the rolling direction. The magnetic domain control
method is classified into a non-destructive magnetic domain control method in which
the strain is applied to the steel sheet of the grain-oriented electrical steel sheet by nondestructive
means, and a destructive magnetic domain control method in which a
groove is formed in a surface ofthe steel sheet as an example.
[0005]
In a case of manufacturing a wound core for a transformer by using the grainoriented
electrical steel sheet, it is necessary to perform a stress relief annealing
treatment so as to remove a deformation strain that occurs when the grain-oriented
electrical steel sheet is coiled in a coil shape. In a case of manufacturing the wound
core by using a grain-oriented electrical steel sheet to which a strain is applied by using
the non-destructive magnetic domain control method, the strain is disappeared due to
execution of the stress relief annealing treatment. Therefore, a magnetic domain
refinement effect (that is, an anomalous eddy current loss reducing effect) is also lost.
[0006]
On the other hand, in a case of manufacturing the wound core by using a
grain-oriented electrical steel sheet to which a groove is applied in accordance with the
destructive magnetic domain control method, the groove is not lost due to execution of
the stress relief annealing treatment, and it is possible to maintain the magnetic domain
refinement effect. Accordingly, as a method of reducing the anomalous eddy current
- 2 -
loss, the destructive magnetic domain control method is typically employed with
respect to the wound core.
[0007]
For example, as disclosed in Patent Document 1, a method of applying a
strain to a steel sheet through laser irradiation is put into practical use. On the other
hand, when forming a groove having a depth of approximately 10 to 30 /-ill in a
direction, which is approximately perpendicular to a rolling direction of the grainoriented
electrical steel sheet, in a constant period in the rolling direction, the iron loss
is reduced. The reason for this is as follows. A magnetic pole occurs at the
periphery of the groove due to a variation of permeability in a void of the groove, and
an interval of a 180° magnetic wall is narrowed due to the magnetic pole. As a result,
the iron loss is improved.
[0008]
Exan1ples of a method of forming the groove in the electrical steel sheet
include an electrolytic etching method in which a groove is formed in a steel sheet
surface of the grain-oriented electrical steel sheet through the electrolytic etching
method (refer to Patent Document 2), a gear press method in which a groove is formed
in a steel sheet surface by mechanically pressing a gear on the steel sheet surface of the
grain-oriented electrical steel sheet (refer to the following Patent Document 3), and a
laser irradiation method in which the steel sheet (portion irradiated with a laser) is
melted and evaporated through laser irradiation (refer to Patent Document 4).
[Prior Art Document]
[Patent Document]
[0009]
[Patent Document I] Japanese Exan1ined Patent Application, Second
- 3 -
Publication No. S58-26406
[Patent Document 2] Japanese Examined Patent Application, Second
Publication No. S62-54873
[Patent Document 3] Japanese Examined Patent Application, Second
Publication No. S62-53579
[Patent Document 4] Japanese Unexamined Patent Application, First
Publication No. 2003-129135
[Disclosure of the Invention]
[Problems to be Solved by the Invention]
[0010]
In a case of forming the groove having the depth of approximately I 0 to 30
J.1l11 in a direction that is approximately perpendicular to the rolling direction by using
the related art, it is difficult to uniformly maintain a shape of an end of a groove
(groove end) on a surface (surface in which the groove is formed) of the electrical steel
sheet. Therefore, a variation in the shape of the groove end tends to increase. As a
result, when performing coating so as to apply electrical insulating properties to the
steel sheet surface after forming the groove, it is difficult to apply a coating agent to
every corner of the groove end. In addition, the variation in the shape of the groove
end is great. Therefore, adhesiveness ofthe coating agent may not be sufficient at
some sites of the groove end. As a result, since the groove end is not sufficiently
coated, the groove is exposed to the outside, and the exposure becomes a cause for
occurrence of rust. In addition, in a case of performing grooving by using a laser
method, there is a problem that a surface protrusion is likely to occur on the groove
end that is formed. For example, when rust occurs, a film at the periphery of the rust
is peeled off. Accordingly, when an interlayer current significantly flows, the iron
- 4 -
loss may increase. In addition, in a case where the steel sheet is corroded due to the
rust, a non-magnetic portion is diffused. Therefore, optimal magnetic domain
refinement conditions may not be maintained.
[0011]
The invention has been made in consideration of the above-described
problems, and an object thereof is to provide a grain-oriented electrical steel sheet
which includes a groove for a great improvement of an iron loss, and in which
adhesiveness of an insulating film and the like and rust resistance are improved in a
groove end.
[Means for Solving the Problem]
[0012]
The gist of the invention is as follows.
(I) According to an aspect of the invention, there is provided a grainoriented
electrical steel sheet including a steel sheet having a steel sheet surface in
which a groove, which extends in a direction intersecting a rolling direction and of
which a groove depth direction matches a sheet thickness direction, is formed. The
groove includes an inclined portion that is inclined from the steel sheet surface to a
bottom of the groove at a groove end in a longitudinal groove direction that is a
direction in which the groove extends. When an average value of a depth of the
groove in the sheet thickness direction from a height of the steel sheet surface at a
central portion in the longitudinal groove direction is set as an average groove depth D
in a unit of 11m, a straight line, which connects a first point at which the depth of the
groove in the sheet thickness direction from the height of the steel sheet surface
becomes O.OSxD, and a second point at which the depth of the groove in the sheet
thickness direction from the height of the steel sheet surface becomes 0.50xD, at the
- 5 -
inclined portion is set as a groove end straight line, an angle made by the steel sheet
surface and the groove end straight line is set as a first angle e in a unit of o, and in a
case where the groove is seen on a groove-width-direction cross-section perpendicular
to the longitudinal groove direction at the central portion of the groove, an average
value of a groove-width-direction length, which is a length of a line segment
connecting two points at which a depth of the groove in the sheet thiclmess direction
from the height of the steel sheet surface in a contour of the groove on the groovewidth-
direction cross-section becomes 0.05xD, is set as an average groove width W of
the groove in a unit of 11111, an aspect ratio A obtained by dividing the average groove
depth D by the average groove width W, and the first angle e satisf'y the following
Expression (1 ).
8<-2lxA+77 ... (1)
[0013]
(2) In the grain-oriented electrical steel sheet according to (1 ), the aspect
ratio A and the first angle e may satisfy the following Expression (2).
8<32xA2-55xA+73 ... (2)
[0014]
(3) In the grain-oriented electrical steel sheet according to (I) or (2), when
the average groove depth Dis 15 !Jll1 to 30 11m, the first angle e, the average groove
depth D, and the average groove width W may satisfy the following Expression (3).
8:S0.12xW-0.45xD+57.39 ... (3)
[00 15]
(4) In the grain-oriented electrical steel sheet according to (1) or (2), when
the average groove width W is 30 11m to 100 11m. the first angle 8, the average groove
depth D, and the average groove width W satisfy the following Expression (4).
- 6 -
8:S-0.37xD+O.I2xW+55.39 ... (4)
[0016]
(5) In the grain-oriented electrical steel sheet according to any one of (I) to
( 4 ), in the steel sheet, a grain size of a crystal grain that is in contact with the groove
may be 5 11m or greater.
[0017]
(6) In the grain-oriented electrical steel sheet according to any one of(!) to
(5), the average groove depth D may be 10 I-Illi to 50 fllli.
[Effects of the Invention]
[0018]
According to the aspect of the invention, it is possible to improve rust
resistance of a grain-oriented electrical steel sheet in which a groove is formed in a
steel sheet surface for magnetic domain refinement.
[Brief Description of the Drawings]
[0019]
FIG. 1 is a schematic view illustrating a groove that is formed in a steel sheet
surface of a grain-oriented electrical steel sheet according to an embodiment of the
invention.
FIG. 2 is a view illustrating a cross-sectional shape of the groove along line AA
in FIG. l.
FIG. 3 is a view illustrating a cross-sectional shape of the groove along line BE
in FIG. 1.
FIG. 4 is a view illustrating definition of a contour ofthe groove.
FIG. 5 is a view illustrating a cross-sectional shape of the groove in a
longitudinal groove direction.
- 7 -
FIG. 6 is a view illustrating definition of a first angle.
FIG. 7 is a view illustrating definition of the first angle.
FIG. 8 is a flowchart illustrating manufacturing processes of the grain-oriented
electrical steel sheet according to this embodiment.
FIG. 9 is a view illustrating laser irradiation in a grooving process in the
manufacturing processes of the grain-oriented electrical steel sheet according to this
embodiment.
FIG. 10 is a view illustrating the laser irradiation in the grooving process in
the manufacturing processes of the grain-oriented electrical steel sheet according to
this embodiment.
FIG. 11 is a view illustrating the laser irradiation in the grooving process in
the manufacturing processes of the grain-oriented electrical steel sheet according to
this embodiment.
FIG. 12 is a view illustrating the laser irradiation in the grooving process in
the manufacturing processes of the grain-oriented electrical steel sheet according to
this embodiment.
FIG. 13 is a graph illustrating a relationship between laser beam irradiation
output and time in the grooving process by a laser method according to this
embodiment.
[Embodiments of the Invention]
[0020]
Hereinafter, a preferred embodiment of the invention will be described in
detaiL However, the invention is not limited to configurations disclosed in this
embodiment, and various modifications can be made in a range not departing from the
gist of the invention. In addition, the lower limit and the upper limit are also included
- 8 -
in numerical value limiting ranges to be described later. However, the lower limit is
not included in a numerical value limiting range that is described as "greater than" the
lower limit, and the upper limit is not included in a numerical value limiting range that
is described as "less than" the upper limit.
[0021]
Hereinafter, a preferred embodiment ofthe invention will be described in
detail with reference to the accompanying drawings.
[0022]
FIG. 1 is a plan view of a grain-oriented electrical steel sheet 1 according to
this embodiment. FIG. 2 is an arrow cross-sectional view taken along line A-A in FIG.
1. FIG. 3 is an arrow cross-sectional view taken along line B-B in FIG. 1.
Furthermore, in FIG. 1 to FIG. 3, a rolling direction of the grain-oriented electrical steel
sheet l is defined as X, a sheet width direction (direction perpendicular to the rolling
direction in the same plane) of the grain-oriented electrical steel sheet 1 is defined as Y,
and a sheet thickness direction (direction perpendicular to an XY plane) of the grainoriented
electrical steel sheet 1 is defined as Z.
FIG. I is a schematic view illustrating a groove 3 when the grain-oriented
electrical steel sheet I according to this embodiment is seen from the sheet thickness
direction Z (hereinafter, may be described as "in a plan view"). Actually, in steel
sheet surface 2a and the groove 3 of an actual grain-oriented electrical steel sheet, a
surlace thereof is not uniformly formed, but in FIG. 1 to FIG 3, FIG. 5 to FIG. 8, and
FIG. 19, the steel sheet surface 2a and the groove 3 are schematically illustrated for
explanation of characteristics of the invention. In addition, the groove 3 may have an
arc shape when being seen from the sheet thickness direction Z (in a case of a plan
view of the groove 3). In this embodiment, the groove 3 having a linear shape is
- 9 -
exemplified for convenience of explanation.
[0023]
The grain-oriented electrical steel sheet 1 includes a steel sheet (base metal) 2
in which a crystal orientation is controlled by a combination of a cold-rolling treatment
and an annealing treatment so that a magnetization easy axis of a crystal grain and the
rolling direction X match each other, and the groove 3 is provided in a surface (steel
sheet surface 2a) of the steel sheet 2.
[0024]
The steel sheet 2 contains, as chemical components in terms of mass fraction,
Si: 0.8% to 7%, C: greater than 0% and equal to or less than 0.085%, acid-soluble AI:
0% to 0.065%, N: 0% to 0.012%, Mn: 0% to 1%, Cr: 0% to 0.3%, Cu: 0% to 0.4%, P:
O%to 0.5%, Sn: 0%to0.3%, Sb: O%to 0.3%, Ni: 0% to 1%, S: O%to 0.015%, Se: 0%
to 0.015%, and the remainder including Fe and unavoidable impurities.
[0025]
The chemical components of the steel sheet 2 are chemical components which
are preferable after integration to a {110} <001> orientation, that is, after a control to a
Goss texture. Among the elements, Si and C are basic elements, and acid-soluble AI,
N, Mn, Cr, Cu, P, Sn, Sb, Ni, S, and Se are selective elements. The selective elements
may be contained in correspondence with the purpose thereof. Accordingly, it is not
necessary to limit the lower limit, and the lower limit may be 0%. In addition, the
effect of this embodiment does not deteriorate even when the selective elements are
contained as impurities. In the steel sheet 2, the remainder of the basic elements and
the selective elements may be composed of Fe and impurities. In addition, the
impurities represent elements which are unavoidably mixed in due to ore and scrap as a
raw material, or a manufacturing environment and the like when industrially
- 10 -
manufacturing the steel sheet 2.
In addition, an electrical steel sheet is typically subjected to purification
armealing during secondary recrystallization. Discharge of an inhibitor forming
element to the outside of a system occurs in the purification armealing. Particularly, a
decrease in a concentration significantly occurs with respect to N and S, and the
concentration becomes 50 ppm or less. Under typical purification annealing
conditions, the concentration becomes 9 ppm or Jess, or 6 ppm or less. If the
purification armealing is sufficiently performed, the concentration reaches to a certain
extent (1 ppm or less) at which detection is impossible in typical analysis.
[0026]
The chemical component of the steel sheet 2 may be measured in accordance
with a typical steel analysis method. For example, the chemical components of the
steel sheet 2 may be measured by using inductively coupled plasma-atomic emission
spectrometry (ICP-AES). Specifically, it is possible to specifY the chemical
components by performing measurement for a test piece of 35 mm square, which is
obtained from the central position of the steel sheet 2 after film removal, by using an
ICP emission analyzing apparatus (for example, ICPS-81 00, manufactured by
Shimadzu Corporation) under conditions based on a calibration curve that is created in
advance. Furthermore, C and S may be measured by using a combustion-infrared ray
absorption method, and N may be measured by using inert gas fusion-thermal
conductivity method.
[0027]
The grain-oriented electrical steel sheet 1 according to this embodiment
includes the groove 3 for magnetic domain refinement in the steel sheet surface 2a, and
may include an insulating film (not illustrated) on the groove 3 and the steel sheet
- 11 -
surface 2a.
[0028]
In addition, a glass film (not illustrated) may be provided between the steel
sheet surface 2a and the insulating film. For example, the glass film is constituted by
a composite oxide such as forsterite (M~Si04), spinel (MgAb04), and cordierite
(Mg2Al4Si50 16). Although details will be described later, the glass film is a film that
is formed to prevent adhering to the steel sheet 2 in a final annealing process that is
one of manufacturing processes of the grain-oriented electrical steel sheet 1.
Accordingly, the glass film is not an essential element among constituent elements of
the grain-oriented electrical steel sheet L For example, the insulating film contains
colloidal silica and phosphate, and plays a role of applying electrical insulating
properties, a tensile force, corrosion resistance, heat resistance, and the like to the steel
sheet2.
[0029]
Furthermore, for example, the glass film and the insulating film of the grainoriented
electrical steel sheet I can be removed by the following method. The grainoriented
electrical steel sheet 1 including glass film or the insulating film is immersed
in an aqueous sodium hydroxide solution containing 10 mass% ofNaOH and 90
mass% of H20 at 80°C for 15 minutes. Then, the grain-oriented electrical steel sheet
1 is immersed in an aqueous sulfuric acid solution containing 10 mass% ofl-bS04 and
90 mass% of H20 at 80°C for 3 minutes. Then, the grain-oriented electrical steel
sheet 1 is immersed in an aqueous nitric acid solution containing 10 mass% of HN03
and 90 mass% of H20 at room temperature for a time period that is slightly shorter
than 1 minute, and is washed. Finally, the grain-oriented electrical steel sheet 1 is
dried by using a warm wind blower for a time period that is slightly shorter than 1
- 12 -
minute. Furthermore, in a case where the glass film or the insulating film is removed
from the grain-oriented electrical steel sheet I according to the above-described
method, it is confirmed that a shape or roughness ofthe groove 3 of the steel sheet 2 is
approximately the same as a shape or roughness before forming the glass film or the
insulating film.
[0030]
As illustrated in FIG. 1 and FIG. 2, the groove 3 is formed in such a manner
that the groove 3 extends in a direction L that intersects the rolling direction X and a
depth direction matches the sheet thickness direction Z. As illustrated in FIG. 2, in
the groove 3, an inclined portion 5, which is inclined so that a depth becomes deeper
from the steel sheet surface 2a to the bottom 4 of the groove 3, is formed on both ends
in the direction L. A detailed shape of the groove 3 will be described later.
[0031]
Terminologies in the following description will be defined. As illustrated in
FIG. 1, in a case where the groove 3 is seen from the sheet thickness direction Z (in a
case of a plan view of the groove 3), an extension direction (an arrow L illustrated in
FIG. 1) of the groove 3 is referred to as a longitudinal groove direction L. In addition,
in a plan view of the groove 3, a direction (an arrow Q illustrated in FIG. 1), which is
perpendicular to the longitudinal groove direction L of the groove 3, is referred to as a
groove width direction Q.
[0032]
(Average Groove Depth D)
The depth of the groove 3 represents a length from the height of the steel
sheet surface 2a to a surface (bottom 4) of the groove 3 in the sheet thickness direction
Z. The average groove depth D may be measured as follows. In a case where the
- 13 -
groove 3 is seen from the sheet thickness direction Z (in a case of a plan view of the
groove 3), an observation range is set to a part of the groove 3. It is preferable that
the observation range is set to a region excluding an end in the longitudinal groove
direction L of the groove 3 (that is, a region in which a shape of the groove bottom is
stable). For example, the observation region may be an observation region of which a
length in the longitudinal groove direction L becomes approximately 30 J.ll1l to 300 [till
at an approximately central portion in the longitudinal groove direction L. Next, a
height distribution (groove depth distribution) in the observation range is obtained by
using a laser microscope and the maximum groove depth is obtained in the observation
range. The same measurement is performed at least at three or greater regions, and
preferably 10 regions while changing the observation range. In addition, an average
value of the maximum groove depth at the respective observation regions is calculated,
and the average value is defined as an average groove depth D. For example, the
average groove depth D of the groove 3 in this embodiment is preferably 5 [till to 100
fJ.f11, and more preferably greater than 10 [till and equal to or less than 40 11m so as to
preferably obtain an effect of the magnetic domain refinement.
Furthermore, it is necessary to measure a position (height) of the steel sheet
surface 2a in the sheet thickness direction Z in advance so as to measure a distance
between the steel sheet surface 2a and the surface of the groove 3. For example, the
position (height) in the sheet thickness direction Z is measured with respect to a
plurality of sites on the steel sheet surface 2a in each of the observation ranges by
using a laser microscope, and an average value ofthe measurement results may be
used as the height of the steel sheet surface 2a. In addition, in this embodiment, when
measuring an average groove width W as described later, a transverse groove crosssection
is used. Accordingly, the steel sheet surface 2a may be measured from the
- 14 -
transverse groove cross-section. Furthermore, when observing a steel sheet sample
with a laser microscope, it is preferable that two sheet surfaces (an observation surface
and a rear surface thereof) of the steel sheet sample are approximately parallel to each
other.
[0033]
(Average Groove Width W)
The width of the groove 3 represents a length of a groove opening in the
transverse groove direction Q in a case where the groove 3 is seen on a cross-section (a
groove-width-direction cross-section or a transverse groove cross-section) that is
perpendicular to the longitudinal groove direction L. The average groove width W
may be measured as follows. As is the case with the average groove depth D, an
observation range is set to a part of the groove 3 in a case where the groove 3 is seen
from the sheet thickness direction Z (in a case of a plan view of the groove 3). It is
preferable that the observation range is set to a region excluding an end in the
longitudinal groove direction L of the groove 3 (that is, a region in which a shape of
the groove bottom is stable).
For example, the observation region may be an observation range of which a
length in the longitudinal groove direction L becomes approximately 30 Jllll to 300 11m
at an approximately central portion in the longitudinal groove direction L. Next, a
transverse groove cross-section that is perpendicular to the longitudinal groove
direction Lis obtained at arbitrary one site in the observation range (for example, a
position of the maximum groove depth in the observation region) by using a laser
microscope. A length of the groove opening is obtained from a contour curve of the
steel sheet surface 2a and the groove 3 on the transverse groove cross-section.
[0034]
- 15 -
Specifically, after obtaining a cross-section curve by applying a low-pass filter
(cut-off value: ?cs) to the steel sheet surface 2a and a measurement cross-section curve
MCL that constitutes a contour of the steel sheet surface 2a and the groove 3 that is
shown on the transverse groove cross-section, when a band filter (cut-off value: Af, ?cc)
is applied to the cross-section curve to remove long wavelength components and short
wavelength components from the cross-section curve, as illustrated in FIG. 3, a waving
curve WWC, which constitutes a contour of the groove 3 in the transverse groove
cross-section, is obtained. The waving curve is one kind of contour curve that is
suitable to simpli.(y the shape of the contour to a smooth line.
[0035]
As illustrated in FIG. 3, a length (groove opening) Wn of a line segment,
which connects two points (a third point 33 and a fourth point 34) at which the depth
from the steel sheet surface 2a to the surface of the groove 3 along the sheet thickness
direction Z becomes O.OSxD with respect to the average groove depth D of the groove
3, is obtained on the waving curve WWC of the groove 3 at the transverse groove
cross-section.
The same measurement is performed at least at three regions or greater
regions and preferably 10 regions while changing the observation range. In addition,
an average value of the groove opening at the respective observation regions is
calculated, and the average value is defined as an average groove width W. For
example, it is preferable that the average groove width W of the groove 3 in this
embodiment is 10 J.lm to 250 J.llll so as to preferably obtain the effect of the magnetic
domain refinement.
Furthermore, it is necessary to measure a position (height) of the steel sheet
surface 2a in the sheet thickness direction Z in advance so as to measure a depth,
- 16 -
which becomes 0.05xD, from the steel sheet surface 2a. For example, the position
(height) in the sheet thickness direction Z is measured with respect to a plurality of
sites on the steel sheet surface 2a on a waving curve in each transverse groove crosssection,
and an average value of the measurement results may be used as the height of
the steel sheet surface 2a.
[0036]
(First Angle 0)
The first angle 0 of the groove 3 represents an angle made by the steel sheet
surface 2a and the end of the groove 3. The first angle 0 may be measured as follows.
In a case where the groove 3 is seen from the sheet thickness direction Z (in a case of a
plan view of the groove 3 ), an observation range is set to a part of the groove 3 which
includes an end in the longitudinal groove direction L. In a plan view of the groove 3
from the sheet thickness direction Z, a plurality of (n) virtual lines L1 to Ln are virtually
set in the observation range along the longitudinal groove direction L (refer to FIG. 6).
It is preferable that the observation range is set to a region including the end of the
groove 3 (that is, a region including a starting point of the groove 3 in the longitudinal
groove direction L to a region in which a shape of the groove bottom is stable). Next,
when measuring a height distribution (groove depth distribution) of the groove 3 in the
observation range along the virtual line L1 by using a laser microscope (a laser type
surface roughness measuring device), as illustrated in FIG 4, a measurement crosssection
curve MCL 1, which constitutes a contour of the end of the groove 3 in the
longitudinal groove direction L, is obtained in a shape conforming to the virtual line
Ll.
[0037]
After obtaining a cross-section curve by applying a low-pass filter (cut-off
- 17 -
value: A-s) to the measurement cross-section curve MCLI obtained with respect to the
virtual line Ll, when a band filter (cut-off value: Af, A-c) is applied to the cross-section
curve to remove long wavelength components and short wavelength components from
the cross-section curve, as illustrated in FIG 5, a waving curve LWCl, which
constitutes a contour ofthe end of the groove 3 in the longitudinal groove direction L,
is obtained in a shape conforming to the virtual line L 1.
[0038]
As illustrated in FIG 5, when using the waving curve LWCl, distances
(depths dl to dn: unit is pm) in the sheet thickness direction Z between the steel sheet
surface 2a and the contour (that is, the waving curve LWCl) of the groove 3 are
obtained at a plurality of (n) positions along the virtual line Ll. In addition, an
average value (groove depth Dl) of the depths dl to dn is obtained. Groove depths
D2 to Dn of the groove end are also obtained with respect to other virtual lines L2 to
Ln according to the same measurement method.
Furthermore, it is necessary to measure a position (height) of the steel sheet
surface 2a in the sheet thickness direction Z in advance so as to measure the depths dl
to dn ftom the steel sheet surface 2a. For example, the position (height) in the sheet
thickness direction Z may be measured with respect to a plurality of sites on the steel
sheet surface 2a in the measurement range by using the laser microscope, and an
average value of the measurement results may be used as the height of the steel sheet
surface 2a.
[0039]
In this embodiment, among the virtual line Ll to Ln, a virtual line, which
conforms to the longitudinal groove direction Land satisfies a condition in which the
average depth of the groove 3 becomes the maximum, is selected as a groove reference
- 18 -
line BL. For example, among the groove depths Dl to Dn obtained with respect to
the virtnallines L1 to Ln illustrated in FIG. 6, the groove depth D2 is the maximum,
the virtnalline L2 is defined as the groove reference line BL.
[0040]
As illustrated in FIG. 7, on a waving curve shape based on the groove
reference line BL, a straight line, which connects a first point 51 at which the depth
from the steel sheet surface 2a in the sheet thickness direction Z becomes 0.05xD, and
a second point 52 at which the depth from the steel sheet surface 2a in the sheet
thickness direction Z becomes 0.50xD, is set as a groove end straight line 3E. In
addition, the first angle e of the groove 3 is defined as an inclination angle of the
groove end straight line 3E with respect to the steel sheet surface 2a.
Furthermore, it is necessary to subject the steel sheet surface 2a to linear
approximation so as to measure the first angle e.
For example, on a waving curve shape based on the groove reference line BL,
only a region of the steel sheet surface 2a except for the groove 3 may be subjected to
the linear approximation. An inclination angle between the steel sheet surface 2a
subjected to the linear approximation and the groove end straight line 3E may be
measured. An inclination angle (first angle 6) made by the groove end straight line
3E and the steel sheet surface 2a is obtained at both ends of the groove 3 in the
longitudinal groove direction L by the same method.
[0041]
The present inventors have repeated a thorough experiment to search a groove
shape in which an improvement of the magnetic characteristics and rust resistance are
compatible with each other. As a result, they found the following shape as the groove
shape. Specifically, as illustrated in FIG. 2, an end ofthe groove 3, which is provided
- 19 -
in the grain-oriented electrical steel sheet 1 according to this embodiment, may be
inclined so that in groove ends 31 a and 31 b of the groove 3 in the longitudinal groove
direction L, a relationship between an angle (first angle 8) made by the groove end
straight line 3E and the steel sheet surface 2a, and an aspect ratio A obtained by
dividing the average groove depth D by the average groove width W satisfy the
following Expression (1 ).
[0042]
8<-21xA+77 ... (I)
[0043]
The first angle 8, which represents an inclination angle of the inclined portion
5, is defined on the basis of an aspect ratio A ( =DIW) that is obtained by dividing the
average groove depth D by the average groove widtb W Typically, as the average
groove depth D is greater, the iron loss affected by the groove depth is improved. In
addition, as the average groove width W is smaller, a deterioration amount of a
magnetic flux density that deteriorates due to removal of a steel portion is suppressed
to be small. Accordingly, the iron loss can be improved. That is, as tbe aspect ratio
A is greater, it is possible to preferably control the magnetic characteristics. On the
other hand, as the aspect ratio A is greater, a coating solution is less likely to intrude
into the groove. Therefore, the rust resistance deteriorates. Particularly, the rust
resistance deteriorates at the groove end of the groove 3. Accordingly, it is necessary
to control the aspect ratio A and the first angle 8 in combination with each other so as
to make the magnetic characteristics and the rust resistance be compatible with each
other. Specifically, when the first angle 8 ofthe groove 3 deviates from the range of
Expression (1 ), the inclination angle of the groove end of the groove 3 with respect to
the aspect ratio becomes great. Therefore, it is difficult to coat the groove 3 with the
- 20 -
glass film or the insulating film at the groove end of the groove 3. As a result, rust is
likely to occur at the groove end of the groove 3.
[0044]
That is, as the average groove depth D is deeper, it is necessary make the
inclination angle (first angle 0) at the groove end be smaller so as to suppress
occurrence of rust. In addition, as the average groove width W is narrower, it is
necessary to make the inclination angle (first angle 0) at the groove end be smaller so
as to suppress occurrence of rust. In addition, when a relationship ofthe average
groove depth D, the average groove width W, and the first angle e satisfies Expression
( 1 ), it is possible to attain the effect of making a magnetic characteristic improvement
and rust resistance be compatible with each other in the groove 3.
[0045]
Furthermore, Expression (I) is a range suitable for a case where the average
groove depth D of the groove 3 is 5 JJl11 or greater. When the average groove depth D
of the groove 3 is less than 5 J.lm, a difference in a shape of the end of the groove 3 is
small, and a problem relating to the rust resistance is less likely to occur. On the
other hand, when the average groove depth D of the groove 3 is less than 5 J.lm,
refinement of the magnetic domain due to formation of the groove may not be
sufficient. The upper limit of the depth of the groove 3 is not particularly limited.
However, when the average groove depth D of the groove 3 becomes 30% or greater
with respect to the thickness of the grain-oriented electrical steel sheet in the sheet
thickness direction Z, the amount of the grain-oriented electrical steel sheet that is a
magnetic material, that is, the amount of the steel sheet decreases. Therefore, there is
a concern that the magnetic flux density may decrease. For example, the upper limit
of the average groove depth D of the groove 3 may be 100 run when considering that a
- 21 -
typical thickness of the grain-oriented electrical steel sheet for a wound transformer is
0.35 mm or less. The groove 3 may be formed in one surface of the grain-oriented
electrical steel sheet, or may be formed in both surfaces thereof
[0046]
From a result of an experiment, it becomes apparent that it is preferable for
the following Expression (2) to be satisfied in addition to Expression (1), because
occurrence of rust can be suppressed with higher accuracy.
[0047]
6<32xA2-55xA+73 ... (2)
[0048]
In addition, from a result of an experiment, it becomes apparent that in a case
where the average groove depth Dis in a range of 15 Jllll to 30 pm, it is more
preferable for the first angle e of the groove end of the groove 3 to satisfY the
following Expression (3) with respect to the average groove depth D and the average
groove width W from the viewpoint of improving the rust resistance.
[0049]
8:S0.12xW-0.45xD+57.39 ... (3)
[0050]
In addition, in a case where the average groove width W is greater than 30 1-lm
and equal to or less than 100 /-lm, from a result of an experiment, it becomes apparent
that it is more preferable for the first angle 8 of the groove end of the groove 3 to
satisfY the following Expression ( 4) with respect to the average groove depth D and the
average groove width W from the viewpoint of improving the rust resistance.
[0051]
8:S-037xD+O.J2xW+55.39 ... (4)
- 22 -
[0052]
In the grain-oriented electrical steel sheet 1 according to this embodiment,
even in a case where the average groove depth D is 15 Jlm to 30 Jlm, when the groove
3 is formed in such a manner that the first angle e satisfies Expression (3), covering
with the glass film or the insulating film is possible without a deviation, and it is
possible to make the magnetic characteristics and the rust resistance be compatible
with each other.
Similarly, even in a case where the average groove width W is greater than 30
Jlm and equal to or less than 100 Jlffi, when the first angle e satisfies Expression (4),
the magnetic characteristics and the rust resistance can be compatible with each other.
In a case where a plurality of grooves are formed in the grain-oriented electrical steel
sheet, when the above-described conditions are satisfied with respect to the entirety of
the grooves, a grain-oriented electrical steel sheet with high quality is obtained.
However, in a case where ends of the groove reach both end surfaces of the grainoriented
electrical steel sheet in the sheet width direction Y, the inclined portion is not
formed at the ends of the groove. Accordingly, it is needless to say that the abovedescribed
conditions are not applied.
[0053]
A glass film having an average thickness of 0 to 5 Jlffi and an insulating film
having an average thickness of l Jlm to 5 Jlm may be disposed in the groove 3. In
addition, a glass film having an average thickness of 0.5 Jlm to 5 Jlm and an insulating
film having an average thickness of I Jlffi to 5 11m may be disposed on the steel sheet
surface 2a. In addition, the average thickness of the glass film in the groove 3 may be
smaller than the average thickness of the glass film on the steel sheet surface 2a.
[0054]
- 23 -
Furthermore, when employing a configuration in which the glass film does
not exist in the groove 3 (that is, a configuration in which the average thickness of the
glass film in the groove 3 is zero), it is possible to further reduce a distance (groove
width) between groove wall surfaces which face each other. Accordingly, it is
possible to further improve the magnetic domain refinement effect (that is, the
anomalous eddy current loss reducing effect) due to the groove 3.
[0055]
In addition, as described above, in this embodiment, the glass film is not an
essential constituent element. Accordingly, when the embodiment is applied to with
respect to a grain-oriented electrical steel sheet that is constituted by only the steel
sheet 2 and the insulating film, it is also possible to obtain an effect of improving the
rust resistance. In the grain--oriented electrical steel sheet that is constituted by only
the steel sheet 2 and the insulating film, an insulating film having an average thickness
of 1 J.!m to 5 ).UTI may be formed in the groove 3, and an insulating film having an
average thickness of 1 ~ to 5 ~ may be formed on the steel sheet surface Za.
[0056]
In this embodiment, in the steel sheet 2, it is preferable that an average grain
size of a crystal grain (secondary recrystallized grain) that is in contact with the groove
3 is 5 J.!m or greater. In addition, the upper limit of the grain size ofthe crystal grain
that is in contact with the groove 3 is not particularly limited, but the upper limit may
be set to I OOx I 03 flm or less. In a case where a melted and resolidified region, which
is derived from formation of the groove 3, exists at the periphery of the groove 3, the
grain size of the crystal grain that is in contact with the groove 3 becomes fine.
In this case, there is a high possibility that the crystal orientation finally
deviates from the {II 0}<001> orientation. Therefore, there is a high possibility that
- 24 -
preferable magnetic characteristics are not obtained. Accordingly, it is preferable that
the melted and resolidified region does not exist at the periphery of the groove 3. In a
case where the melted and resolidified region does not exist at the periphery of the
groove 3, the average grain size of the crystal grain (secondary recrystallized grain)
that is in contact with the groove 3 becomes 5 J.lm or greater. In addition, the upper
limit ofthe grain size of the crystal grain that is in contact with the groove 3 is not
particularly limited, but the upper limit may be set to lOOxJ03 J.lm or less.
[0057]
Furthermore, the grain size of the crystal grain represents an equivalent circle
diameter. For example, the grain size of the crystal grain may be obtained in
accordance with a typical crystal grain size measurement method such as ASTM and
E 112, or may be obtained in accordance with an electron back scattering diffraction
pattern (EBSD) method. In addition, the crystal grain that is in contact with the
groove 3 may be observed on the transverse groove cross-section or a cross-section
that is perpendicular to the sheet thickness direction Z. For example, the groove that
does not include the melted and resolidified region may be obtained in accordance with
a manufacturing method to be described later.
[0058]
Particularly, in a case where the groove 3 is seen on the transverse groove
cross-section, it is preferable that a grain size of a crystal grain (secondary
recrystallized grain), which exists on a lower side of the groove 3 in the steel sheet 2,
in the sheet thickness direction is equal to or greater than 5 J.lill and equal to or less
than the sheet thickness ofthe steel sheet 2. This characteristic represents that a fine
grain layer (melted and resolidified region), in which a grain size of a crystal grain in a
sheet thickness direction is approximately I f.Lm, does not exist on a lower side ofthe
- 25 -
groove 3 in the steel sheet 2.
[0059]
Next, description will be given of a method of manufacturing the grainoriented
electrical steel sheet 1 according to this embodiment. FIG. 8 is a flowchart
illustrating manufacturing processes of the grain-oriented electrical steel sheet 1. As
illustrated in FIG. 8, in a first casting process SOl, molten steel, which has a chemical
composition including, in terms of mass fraction, Si: 0.8% to 7%, C: greater than 0%
and equal to or less than 0.085%, acid-soluble Al: 0% to 0.065%, N: 0% to 0.012%,
Mn: 0% to 1%, Cr: 0% to 0.3%, Cu: 0% to 0.4%, P: 0% to 0.5%, Sn: 0% to 0.3%, Sb:
0% to 0.3%, Ni: 0% to 1%, S: 0% to 0.015%, Se: 0% to 0.015%, and the remainder
including Fe and unavoidable impurities, is supplied to a continuous casting machine,
and a slab is continuously produced. Subsequently, in a hot-rolling process S02, the
slab obtained in the casting process SO 1 is heated under a predetermined temperature
condition (for example, 1150 to 1400°C), and hot-rolling is performed with respect to
the slab. According to this, for example, a hot-rolled steel sheet having the thickness
of 1.8 to 3.5 mm is obtained.
[0060]
Subsequently, in an annealing process S03, an annealing treatment is
perfonned with respect to the hot-rolled steel sheet obtained in the hot-rolling process
S02 under a predetermined temperature condition (for example, a condition in which
heating is performed at 750 to 1200°C for 30 seconds to I 0 minutes).
[0061]
Subsequently, in a cold-rolling process S04, pickling is performed as
necessary with respect to a surface of the hot-rolled steel sheet that is subject to the
annealing treatment in the annealing process S03, and then cold-rolling is performed
- 26 -
with respect to the hot-rolled steel sheet. According to this, for example, a coldrolled
steel sheet having the thickness of 0.15 to 0.35 mm is obtained.
[0062]
Subsequently, in a decarburization annealing process SOS, a heat treatment
(that is, a decarburization annealing treatment) is performed with respect to the coldrolled
steel sheet obtained in the cold-rolling process S04 under a predetermined
temperature condition (for example, a condition in which heating is performed at 700
to 900°C for 1 to 3 minutes) in a humid atmosphere. When the decarburization
annealing treatment is performed, in the cold-rolled steel sheet, carbon is reduced to a
predetermined amount or less, and primaty rectystallized structure is formed. In
addition, in the decarburization annealing process SOS, an oxide layer, which contains
silica (Si02) as a main component, is formed on a surface of the cold-rolled steel sheet
[0063]
Subsequently, in an annealing separating agent applying process S06, an
annealing separating agent, which contains magnesia (MgO) as a main component, is
applied to the surface (the surface of the oxide layer) of the cold-rolled steel sheet.
Subsequently, in final annealing process S07, a heat treatment (that is, a final annealing
treatment) is performed with respect to the cold-rolled steel sheet onto which the
annealing separating agent is applied under a predetermined temperature condition (for
example, a condition in which heating is performed at ll 00 to 1300°C for 20 to 24
hours). When the final annealing treatment is performed, secondaty recrystallization
occurs in the cold-rolled steel sheet, and the cold-rolled steel sheet is purified. As a
result, it is possible to obtain a cold-rolled steel sheet which has the above-described
chemical composition ofthe steel sheet 2 and in which a crystal orientation is
controlled so that a magnetization easy axis of a crystal grain and the rolling direction
- 27 -
X match each other (that is, the steel sheet 2 in a state before the groove 3 is formed in
the grain-oriented electrical steel sheet I).
[0064]
In addition, when the final annealing treatment is performed as described
above, an oxide layer containing silica as a main component reacts with the annealing
separating agent that contain magnesia as a main component, and the glass film (not
illustrated) including a composite oxide such as forsterite (Mg2Si04) is formed on a
surface of the steel sheet 2. In the fmal mmealing process S07, the final aJmealing
treatment is performed in a state in which the steel sheet 2 is coiled in a coil shape.
The glass film is formed on the surface of the steel sheet 2 during the final annealing
treatment. Accordingly, it is possible to prevent adhering to the steel sheet 2 that is
coiled in a coil shape.
[0065]
In an insulating fihn forming process S08, for example, an insulating coating
solution containing colloidal silica and a phosphate is applied to the steel sheet surface
2a from an upper side of the glass film. Then, when a heat treatment is performed
under a predetermined temperature condition (for example, 840 to 920°C), the
insulating film is formed on the surface of the glass film.
[0066]
Subsequently, in a grooving process S09, the groove 3 is formed in the steel
sheet surface 2a on which the glass film and the insulating film are formed. In the
grain-oriented electrical steel sheet 1 according to this embodiment, the groove can be
formed by a method such as a laser method, a press machine method, and an etching
method. Hereinafter, description will be given of a method of forming the groove 3
in a case of using the laser method, the press machine method, the etching method, and
- 28 -
the like in the grooving process S09.
[0067]
(Groove Fonning Method According to Laser Method)
Description will be given of a groove forming method according to the laser
method.
In the grooving process S09, the surface (only one surface) of the steel sheet,
on which the glass film is formed, is irradiated with a laser to form a plurality of the
grooves 3, which extend in a direction intersecting the rolling direction X, in the
surface of the steel sheet 2 along the rolling direction X at a predetermined interval.
[0068]
As illustrated in FIG 9, in the grooving process S09, a laser light YL emitted
from a laser light source (not illustrated) is transmitted to a laser irradiation device 10
through an optical fiber 9. A polygon mirror (not illustrated) and a rotary driving
device (not illustrated) of the polygon mirror are embedded in the laser irradiation
device 10. The laser irradiation device 10 irradiates the surface of the steel sheet2
with the laser light YL and scans the steel sheet 2 with the laser light YL in a direction
that is approximately parallel to the sheet width direction Y of the steel sheet 2 due to
rotation ofthe polygon mirror.
[0069]
An assist gas 25 such as air and an inert gas is sprayed to a portion of the steel
sheet 2 which is irradiated with the laser light YL in combination with the irradiation
with the laser light YL. Examples of the inert gas include nitrogen, argon, and the
like. The assist gas 25 plays a role of removing a component that is melted or
evaporated from the steel sheet 2 with the laser irradiation. The laser light YL stably
reaches the steel sheet 2 due to the spraying of the assist gas 25. Accordingly, the
- 29 -
groove 3 is stably formed. In addition, it is possible to suppress the component from
being attached to the steel sheet 2 due to the spraying ofthe assist gas 25. As a result,
the groove 3 is fom1ed along a scanning line of the laser light YL.
[0070]
The surface of the steel sheet 2 is irradiated with the laser light YL while the
steel sheet 2 is conveyed along a sheet travelling direction that matches the rolling
direction X. Here, a rotational speed of the polygon mirror is controlled in
synchronization with a conveying speed of the steel sheet 2 so that the groove 3 is
formed at a predetermined interval PL along the rolling direction X. As a result, as
illustrated in FIG 9, a plurality of the grooves 3, which intersect the rolling direction X,
are formed in the surface of the steel sheet 2 at the predetermined interval PL along the
rolling direction X.
[0071]
As the laser light source, for example, a fiber laser can be used. A high
output laser such as a YAG laser, a semiconductor laser, and a C02 laser, which are
typically used for industry, may be used as the laser light source. In addition, a pulse
laser or a continuous wave laser may be used as the laser light source as long as the
groove 3 can be stably formed. As irradiation conditions with the laser light YL, for
example, it is preferable that a laser output is set to 200 W to 2000 W, a lightcondensing
spot diameter of the laser light YL in the rolling direction X (that is, a
diameter including 86% of the laser output, hereinafter, referred to as 86% diameter) is
set to 10 11m to 1000 IJ.ill, a light-condensing spot diameter (86% diameter) in the sheet
width direction Y of the laser light YL is set to 10 11m to 4000 IJ.I11, a laser scanning
speed is set to I m/s to 100 m/s, and a laser scanning pitch (interval PL) is set to 4 mm
to 10 mm.
- 30 -
[0072]
As illustrated in FIG. 10, in the grooving process S09 of this embodiment, in a
plan view of the steel sheet 2 that is conveyed along the sheet travelling direction TD
parallel to the rolling direction X, the assist gas 25 is sprayed from a direction having
an inclination of an angle 92 with respect to the laser scanning direction SD (direction
parallel to the sheet width direction Y) of the laser light YL so as to conform to the
laser light YL. In addition, as illustrated in FIG. 11, when the steel sheet 2, which is
conveyed along the sheet travelling direction TD, is seen from the sheet width
direction Y (laser scanning direction SD), the assist gas 25 is sprayed from a direction
having an inclination of an angle 93 with respect to the steel sheet surface 2a to
conform to the laser light YL. It is preferable that the angle 92 is set in a range of 90°
to 180°, and the angle 63 is set in a range of 1 o to 85°. In addition, it is preferable
that a flow rate of the assist gas 25 is set in a range of 10 liters/minute to 1000
liters/minute.
In addition, it is preferable to perform an atmosphere control so that the
amount of particles, which exist in a sheet travelling atmosphere of the steel sheet 2
and have a diameter of0.5 J.Im or greater, becomes equal to or greater than 10 pieces
and less than 10000 pieces per 1 CF (cubic feet).
[0073]
Scanning with a laser beam over the whole width of the grain-oriented
electrical steel sheet may be performed by one scanning apparatus as illustrated in FIG.
9, or may be performed by a plurality of the scanning apparatuses as illustrated in FIG.
12. In a case of using one light source, laser beams emitted from the light source and
the resultant divided laser beams are used as the laser beam. In a case of using the
plurality oflaser irradiation devices 10, as illustrated in FIG. 12, the plurality oflaser
- 31 -
irradiation devices 10 are disposed along the rolling direction X at a predetermined
interval. In addition, when seen from the rolling direction X, positions of the
respective laser irradiation devices 10 in the sheet width direction Yare set so that laser
scanning lines of the respective laser irradiation devices 10 do not overlap each other.
[0074]
When using the laser irradiation method, a plurality ofthe grooves 3 can be
formed in the steel sheet surface 2a. When using the plurality of scanning
apparatuses, an irradiation region can be divided into a plurality of regions in the sheet
width direction Y Accordingly, scanning and irradiation time necessary for one laser
beam, are shortened. Accordingly, the method ofnsing the plurality of scanning
apparatuses is suitable for high-speed sheet conveying facility. In a case where the
plurality of scanning apparatuses are used, only one laser apparatus may be provided as
a light source of the laser beam incident to the respective scanning apparatuses, or the
laser apparatus may be provided to each of the scanning apparatuses.
[0075]
A surface of the grain-oriented electrical steel sheet is scanned with the laser
beam by one surface of the mirror, and the groove 3 having a predetermined length (for
example, 300 mm) is formed in the grain-oriented electrical steel sheet in an
approximately width direction. An interval of grooves adjacent to each other in the
rolling direction X, that is, an irradiation pitch PL in the rolling direction (conveying
direction) may be changed through adjustment of a velocity of a line VL and an
irradiation speed. As described above, the grain-oriented electrical steel sheet is
irradiated with the laser beam by using the laser irradiation device to form grooves in
the rolling direction X at a constant scanning interval PL (an irradiation pitch, a groove
interval). That is, the surface of the grain-oriented electrical steel sheet is irradiated
- 32 -
with the laser beam, which is condensed thereto, while being scanned with the laser
beam, thereby fonning a groove that has a predetermined length and extends in a
direction that is approximately perpendicular to the conveying direction of the grainoriented
electrical steel sheet (a direction that intersects the conveying direction, a
direction including a vector perpendicular to the conveying direction) at a
predetennined interval in the conveying direction. For example, the groove 3 is
fonned in a range of positive 45° to negative 45° with respect to a direction that is
approximately perpendicular to the conveying direction of the grain-oriented electrical
steel sheet.
[0076]
At both scanning ends, an output of the laser is subjected to a temporal
variation in synchronization with an operation of the mirror. According to this, the
depth of the groove 3 is allowed to vary, and the ends 3laand 3lb of the groove 3 are
inclined. That is, as illustrated in FIG 13, in the scanning direction, the output of the
laser is set to vary at positions which become ends of the groove 3. For example, a
groove width of the groove 3 is 100 Jllll, a groove depth is 20 Jllll, an irradiation pitch
is 3 mm, and a scanning speed on the steel sheet is 30 m/s, time 1'1 T, at which the
output of the laser is allowed to vary at fonnation initiation and fonnation tennination
of one groove, is set to 0. 0004 ms or longer so as to set the first angle e at a groove end
to 60° or less. According to this, the groove 3, which is inclined at the first angle eat
ends of the groove 3 in the longitudinal groove direction L, is formed.
[0077]
For example, as illustrated in FIG 9, in the irradiation with the laser beam,
scanning with the laser beam, which is emitted from the laser apparatus that is a light
source, is perfonned by the scanning apparatus in the sheet width direction Y that is
- 33 -
approximately perpendicular to the rolling direction X of the grain-oriented electrical
steel sheet at the predetermined interval PL. At this time, the assist gas such as air
and an inert gas is sprayed to a portion of the grain-oriented electrical steel sheet which
is irradiated with the laser beam. As a result, the groove 3 is formed at a portion on a
surface of the grain-oriented electrical steel sheet which is irradiated with the laser
beam. The rolling direction X matches the sheet travelling direction.
[0078]
A temperature ofthe grain-oriented electrical steel sheet when performing the
irradiation with the laser beam is not particularly limited. For example, the
irradiation with the laser beam can be performed with respect to the grain-oriented
electrical steel sheet that is set to approximately room temperature. It is not necessary
for a laser beam scanning direction to match the sheet width direction Y. However, it
is preferable that an angle made by the scanning direction and the sheet width direction
Y is in a range of oo to 90° and is 45° or less from the viewpoint of working efficiency
and the like, and when considering that a magnetic domain is subdivided into a
longitudinal strip shape in the rolling direction. It is more preferable that the angle
made by the scanning direction and the sheet width direction Y is 20° or less, and still
more preferably 10° or less.
[0079]
(Groove Forming Method According to Press Machine Method)
Description will be given of a method of forming the groove 3 of the grainoriented
electrical steel sheet 1 according to this embodiment according to a press
machine method. In a case of forming the groove 3 in the grain-oriented electrical
steel sheet by the press machine method, the groove is formed by using a tooth press
tool corresponding to the shape of the groove 3 according to a known press machine
- 34 -
method. That is, the groove 3 is formed by using a tooth press tool in which an
inclined portion having the same angle as the first angle e is formed at ends ofthe
tooth press tool in a length direction.
[0080]
(Groove Forming Method According to Electrolytic Etching Method)
Description will be given of a method of forming the groove in the grainoriented
electrical steel sheet 1 according to this embodiment according to an
electrolytic etching method.
An etching resist layer, of which a portion corresponding to the shape of the
groove is opened, is formed on the surface of the grain-oriented electrical steel sheet 1
after the insulating film forming process S08 tlnough printing and the like. With
regard to the opening of the etching resist layer, an etching resist is formed to be
inclined in such a manner that an opening width in a transverse direction gradually
decreases at sites corresponding to groove ends in order for the opening width at both
ends to be narrower in comparison to the central portion in the longitudinal groove
direction L. For example, the opening of the etching resist is formed in such a
manner that the opening width in the transverse groove direction Q is set to I 00 J.!m or
greater, and a length of the sites inclined in correspondence with the groove ends in the
longitudinal groove direction L becomes 14 J.llll to obtain a shape in which the average
groove depth D is 20 rtm, the groove width in the transverse groove direction Q is 50
rtm, and the first angle e is 55° or less. As a result, an inclined portion 5 is formed at
the groove ends in which the opening width of the etching resist is set to be narrow.
Then, an etching treatment is performed by using an etchant (NaCI and the like) at a
liquid temperature of 30°C for 20 seconds. Subsequently, the etching resist is peeled
off from the grain-oriented electrical steel sheet to form the groove 3 in the steel sheet
- 35 -
surface 2a.
[0081]
After forming the groove 3 in the grooving process S09, the same treatment as
in the insulating film forming process is performed again (insulating film re-forming
process SlO). The thickness of the insulating film that is obtained is 2 to 3 !lm.
According to the above-described processes, the grain-oriented electrical steel sheet
according to this embodiment is obtained.
[0082]
The steel sheet 2 of the grain-oriented electrical steel sheet 1 manufactured as
described above contains, as chemical components in terms of mass fraction, Si: 0.8%
to 7.0%, C: greater than 0% and equal to or less than 0.085%, acid-soluble Al: 0% to
0.065%, N: 0% to 0.012%, Mn: O%to 1%, Cr: 0% to 0.3o/o, Cu: O%to 0.4%, P: 0% to
0.5%, Sn: 0% to 03%, Sb: 0% to 03%, Ni: 0% to 1 o/o, S: 0% to 0.015%, Se: 0% to
0.015%, and the remainder including Fe and unavoidable impurities.
[0083]
Furthermore, the embodiment exemplifies a case of employing a
manufacturing process in which the groove 3 is fanned in the steel sheet surface 2a
after the insulating film is formed on the steel sheet surface 2a with laser irradiation.
In this case, the groove 3 immediately after laser irradiation is exposed to the outside.
Accordingly, it is necessary to form an insulating film again on the steel sheet 2 after
forming the groove 3. However, in this embodiment, it is possible to employ a
manufacturing process in which the groove 3 is formed in the steel sheet surface 2a by
irradiating the steel sheet surface 2a with the laser light YL before formation of the
insulating film on the steel sheet surface 2a, and then the insulating film is formed on
the steel sheet 2. Alternatively, in this embodiment, the glass film or the insulating
- 36 -
film may be formed after the groove 3 is formed in the steel sheet 2.
[0084]
Accordingly, the grain-oriented electrical steel sheet according to this
embodiment includes the grain-oriented electrical steel sheet 1 for which hightemperature
annealing for secondary recrystallization is completed and coating with
the glass film and the insulating film is completed. However, the grain-oriented
electrical steel sheet also includes a grain-oriented electrical steel sheet for which
coating with the glass film and the insulating film is not completed. That is, a final
product may be obtained by performing formation of the glass film and the insulating
film as a post process by using the grain-oriented electrical steel sheet according to this
embodiment Furthermore, as described above, in a case of executing the film
removing method, it is confmned that the shape or the roughness of the groove 3 after
removing the glass film or the insulating film is approximately the same as those
before forming the glass film or the insulating film.
[0085]
Furthermore, the embodiment exemplifies a case where the grooving process
(laser irradiation process) S09 is executed after the final annealing process S07, but the
grooving process may be executed between the cold-rolling process S04 and the
decarburization annealing process SOS. TI1at is, after forming the groove 3 in the
steel sheet surface 2a of the cold-rolled steel sheet by performing laser irradiation and
spraying of the assist gas with respect to the cold-rolled steel sheet obtained in the
cold-rolling process S04, the decarburization annealing may be perfonned with respect
to the cold-rolled steel sheet.
[0086]
This embodiment exemplifies a configuration in which the longitudinal
- 37 -
groove direction L that is the extension direction of the groove 3 is a direction that
intersects the rolling direction X and the sheet width direction Y. However, the
extension direction ofthe groove 3 of the grain-oriented electrical steel sheet 1
according to this embodiment is not limited thereto. For example, even when the
longitudinal groove direction L of the groove 3 is approximately perpendicular to the
rolling direction X, the improvement of the magnetic characteristic and the rust
resistance are compatible with each other.
[0087]
In this embodiment, the number of the groove 3 that is formed in the grainoriented
electrical steel sheet is not particularly limited. For example, a plurality of
the grooves 3 may be formed in the sheet width direction Y and the rolling direction X.
In addition, the groove 3 may be formed as one long groove of which both ends extend
to the vicinity of both ends of the steel sheet 2 in the sheet width direction Y, or a
plurality of the grooves 3 may be formed in the rolling direction at an equal interval.
[0088]
This embodiment exemplifies an example in which the shape of the groove 3
(shape of a boundary portion between the groove 3 and the steel sheet surface 2a) in a
plan view is an elongated ellipse. However, the shape of the groove in the grainoriented
electrical steel sheet is not limited thereto. For example, the groove may
have an arbitrary shape as long as the inclined portion is provided to the ends in the
longitudinal groove direction Land the relationship of Expression(!) is satisfied.
[0089]
FIG. 3 illustrates an example in which the shape of the groove 3 when seen
from the transverse groove direction Q is asymmetrical to the groove width center in
the transverse groove direction Q. However, the shape of the groove is not limited
- 38 -
thereto.
Examples
[0090]
Hereinafter, an effect of an aspect of the invention will be described more
specifically with reference to examples, but a condition in Examples is one conditional
example that is employed to confirm operability and an effect of the invention, and the
invention is not limited to the one conditional example. The invention may employ
various conditions as long as the object of the invention is accomplished without
departing from the gist of the invention.
[0091]
A slab, which has a chemical composition containing, in terms of mass
fraction, Si: 3.00/o, :u;id-soluble AI: 0.05%, C: 0.08%, N: 0.01%, Mn: 0.12%, Cr: 0.05%,
Cu: 0.04%, P: 0.01%, Sn: 0.02%, Sb: 0.01%, Ni: 0.005%, S: 0.007%, Se: 0.001%, and
the remainder including Fe and unavoidable impurities, was prepared. The hotrolling
process S02 was executed with respect to the slab to prepare a hot -rolled
material having a thickness of2.3 mm.
[0092]
Subsequently, a heat treatment was performed with respect to the hot-rolled
material under conditions of a temperature of 1 000°C for one minute (annealing
process S03). Pickling was performed after the heat treatment, and then cold-rolling
was performed (cold-rolling process S04) to prepare a cold-rolled material having the
thiclmess of0.23 mm.
[0093]
Decarburization annealing was performed with respect to the cold-rolled
material under a condition of a temperature of 800°C for two minutes ( decarburization
- 39 -
annealing process S05).
An annealing separating agent containing magnesia as a main component was
applied to both surfaces of the cold-rolled material after the decarburization annealing
(annealing separating agent applying process S06). The cold-rolled material to which
the annealing separating agent was applied was put in a furnace in a state of being
coiled in a coil shape, and the final annealing process S07 was performed at a
temperature of 1200°C for 20 hours to prepare steel sheet base metal on which the
glass film was formed on a surface thereof.
[0094]
Next, an insulating material containing a! uminum phosphate as a main
component was applied onto the glass film, and baking was performed at a temperature
of850°C for one minute to form the insulating film (insulating film forming process
S08).
[0095]
Subsequently, a groove, in which the average groove depth D, the average
groove width W in the longitudinal groove direction L, and the first angle 8 were set as
illustrated in Table l, was formed in the steel sheet surface 2a by using the laser
method under conditions in which the laser scanning pitch (interval PL) was set to 3
mm, the beam diameter was set to 0.1 mm in the rolling direction and 0.3 mm in the
scanning direction, and the scanning speed was set to 30 mm/s (grooving process S09).
After the grooving process S09, application ofthe insulating material including
aluminum phosphate as a main component was performed again, and baking was
performed at a temperature of 850°C for one minute to form the insulating film
(insulating film re-forming process S 1 0), thereby obtaining the grain-oriented electrical
steel sheet. In addition, as comparative examples, grain-oriented electrical steel
- 40 -
sheets, in which a steel sheet was formed in the same manner as in the grain-oriented
electrical steel sheet in the examples, was prepared. A groove, in which the average
groove depth D, the average groove width Win the longitudinal groove direction L,
and the first angle 6 were set as illustrated in Table 1, was formed in the grain-oriented
electrical steel sheet.
[0096]
The steel sheet (steel sheet in which a groove was formed) in the grainoriented
electrical steel sheet, which was finally obtained, mainly contained 3.0% of Si.
[0097]
Contours of the grooves of the examples and the comparative examples were
specified on the basis of the contour specifying method. First, a two-dimensional
height distribution on ten straight lines L1 to L 10 in the longitudinal groove direction L
was measured with respect to the grooves in the examples and the comparative
examples by using a non-contact laser meter (VK-9700, manufactured by Keyence
Corporation). Ten patterns of contours of the grooves on the longitudinal groove
cross-section were obtained on the basis of the measurement results. The average
groove depth D was calculated from each of the ten patterns of contours of the
longitudinal groove cross-section, and a contour of the longitudinal groove crosssection,
in which the average groove depth D was the deepest, was extracted as a
representative pattern. The average groove depth D of the representative pattern is
illustrated in a column of the groove depth Din Table 1.
[0098]
With regard to a contour on a cross-section in the transverse groove direction
Q, a two-dimensional height distribution of a groove at twenty straight lines in the
transverse groove direction Q was measured by using the same non-contact laser meter.
- 41 -
Twenty patterns of contours of the transverse groove cross-section of the groove were
obtained on the basis ofthe measurement results. In the obtained twenty patterns of
contours of the transverse groove cross-section, a depth from the steel sheet surface 2a
to the surface (contour) of the groove was measured to calculate an average transverse
groove depth Ds. In the contours of the transverse groove cross-section, two points
having an average transverse groove depth ofDsx0.05, were extracted, and a distance
between the two points was measured as the groove width W. An average value of
the groove width W obtained from the twenty patterns was calculated as an average
groove width. Average groove widths (unit: J.lm) obtained in the examples and the
comparative examples are illustrated in Table L
- 42 -
[0099]
[Table 1]
Average Average
8o;O.J2xW-
8<:.-
groove groove Aspect ratio First angle
-21xA+77 32xA1-55xA+73 0.45xD+57.39 in
0.37xD+0.12xW+ Rust Rust
depth D width W A~D!W 8 (degree)
case of 15<;Do;30
55.39 in case of occurrence resistance
(~m) (urn) 30o;D