U.S. patent application number 12/311756 was filed with the patent office on 2009-11-05 for grain-oriented electrical sheet superior in watt loss.
This patent application is currently assigned to NIPPON STEEL CORPORATION. Invention is credited to Hideyuki Hamamura, Keiji Iwata, Tatsuhiko Sakai.
Application Number | 20090272464 12/311756 |
Document ID | / |
Family ID | 39324497 |
Filed Date | 2009-11-05 |
United States Patent
Application |
20090272464 |
Kind Code |
A1 |
Hamamura; Hideyuki ; et
al. |
November 5, 2009 |
Grain-Oriented Electrical Sheet Superior in Watt Loss
Abstract
The present invention provides grain-oriented electrical sheet
more superior in watt loss compared with the past by dividing the
watt loss of grain-oriented electrical sheet introducing strain by
firing of a laser beam etc. into hysteresis loss and eddy current
loss and, in particular from the viewpoint of the eddy current
loss, quantitatively suitably controlling the distribution of the
strain and residual stress in the sheet thickness direction, that
is, grain-oriented electrical sheet obtained by firing a laser beam
etc. to introduce lines of strain substantially perpendicular to
the rolling direction uniformly in a sheet width direction and
cyclically in the rolling direction for magnetic domain control,
characterized in that in the two-dimensional distribution of a
rolling direction compressive residual stress occurring near one
location of the introduction of strain in a cross-section
perpendicular to the sheet width direction, the value of the
rolling direction compressive residual stress integrated in the
region of the cross-section where there is compressive residual
stress is within a predetermined range.
Inventors: |
Hamamura; Hideyuki; (Tokyo,
JP) ; Iwata; Keiji; (Tokyo, JP) ; Sakai;
Tatsuhiko; (Tokyo, JP) |
Correspondence
Address: |
KENYON & KENYON LLP
ONE BROADWAY
NEW YORK
NY
10004
US
|
Assignee: |
NIPPON STEEL CORPORATION
Tokyo
JP
|
Family ID: |
39324497 |
Appl. No.: |
12/311756 |
Filed: |
October 16, 2007 |
PCT Filed: |
October 16, 2007 |
PCT NO: |
PCT/JP2007/070507 |
371 Date: |
April 9, 2009 |
Current U.S.
Class: |
148/400 |
Current CPC
Class: |
H01F 1/14716 20130101;
C21D 9/46 20130101; C21D 8/1277 20130101; C21D 8/12 20130101; C21D
8/1294 20130101; C21D 10/005 20130101 |
Class at
Publication: |
148/400 |
International
Class: |
C22C 38/22 20060101
C22C038/22 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 23, 2006 |
JP |
2006-287709 |
Claims
1. A grain-oriented electrical sheet obtained by firing a
continuous wave laser beam to introduce strain uniformly in a sheet
width direction perpendicular to a rolling direction, cyclically in
the rolling direction, and in lines substantially perpendicular to
the rolling direction, characterized in that in the two-dimensional
distribution of a rolling direction compressive residual stress
occurring near one location of the introduction of strain in a
cross-section perpendicular to the sheet width direction, the value
of the rolling direction compressive residual stress integrated in
the region of the cross-section where there is compressive residual
stress is 0.20 N to 0.80 N.
2. A grain-oriented electrical sheet as set forth in claim 1,
characterized in that a cyclic pitch in said rolling direction of
the strain uniform in said sheet width direction due to firing of
the laser beam is 2 mm to 8 mm.
Description
TECHNICAL FIELD
[0001] The present invention relates to grain-oriented electrical
sheet superior in watt loss which uses laser firing or the like to
introduce residual stress for magnetic domain control.
BACKGROUND ART
[0002] Grain-oriented electrical sheet having an axis of easy
magnetization in the rolling direction of the steel sheet is mainly
being used for iron cores of transformers etc. In recent years, it
has been strongly demanded to reduce the watt loss of iron cores
from the viewpoint of energy savings.
[0003] The watt loss of electrical sheet may be roughly divided
into hysteresis loss and eddy current loss. It is known that the
hysteresis loss is influenced by the crystal orientation, defects,
grain boundaries, etc., while the eddy current loss is influenced
by the sheet thickness, electrical resistance, magnetic domain
width, etc. There are limits to the technique of controlling and
improving the crystal orientation so as to reduce the hysteresis
loss, so in recent years many proposals have been made of the art
of subdivision of the magnetic domain width so as to reduce the
eddy current loss accounting for most of the watt loss, that is,
the art of magnetic domain control.
[0004] As a method for this, Japanese Patent Publication (B2) No.
6-19112 discloses a method of production of grain-oriented
electrical sheet which uses YAG laser firing to introduce lines of
strain substantially perpendicular to the rolling direction
cyclically in the rolling direction and thereby reduce the watt
loss. The principle behind this method, called laser magnetic
domain control, is to use a laser beam to scan the surface and
produce surface strain due to which the 180.degree. magnetic domain
width is subdivided and the watt loss is reduced.
[0005] Further, Japanese Patent Publication (A) No. 2005-248291
makes a new proposal taking note of the maximum value of the
rolling direction residual stress formed at the steel sheet
surface.
DISCLOSURE OF THE INVENTION
[0006] Almost all proposals up to now relating to the introduction
of local strain to steel sheet surfaces and subdivision of the
180.degree. magnetic domain width to reduce the watt loss, that is,
laser magnetic domain control, including the prior art first patent
document, use trial and error to limit the type of the laser, the
shape of the focused spot of the laser beam, the laser energy
density, the laser firing pitch, and other laser firing parameters.
The proposals are extremely fragmentary and lack uniformity. The
reason is that no allusion is made to a quantitative discussion of
the main factors causing magnetic domain subdivision and watt loss
reduction, that is, strain or residual stress. Inherently, in
improvement of watt loss by laser firing, even under the same laser
firing conditions, due to the absorption rate of the steel sheet
(determined by laser wavelength or surface properties, shape, and
film composition) or film thickness, the conversion from laser
energy to heat energy (temperature distribution and temperature
history) will differ, so even if the laser firing conditions are
the same, the strain introduced will differ depending on the
properties of the steel sheet. Further, even with the same heat
energy (temperature distribution or temperature history), due to
the composition of the steel sheet (for example, amount of Si), the
physical property values (for example, Young's modulus or yield
stress value) will differ, so the residual stress will also differ.
Therefore, even if the optimal laser firing conditions with respect
to steel sheet of certain conditions are obtained, even a small
change in the state of the film will cause the way the strain is
introduced due to the laser to differ and the watt loss value to
change, so the laser firing conditions and reduction in watt loss
do not correspond to each other on a 1 to 1 basis. Therefore,
attempts have been made to find the inherent factors influencing
the watt loss. The second patent document quantitatively alludes to
the strain and residual stress, but there were limits to reduction
of the watt loss by just control of the strain or tensile residual
stress of the steel sheet surface.
[0007] The object of the present invention is to provide
grain-oriented electrical sheet more superior in watt loss compared
with the past by dividing the watt loss of grain-oriented
electrical sheet into hysteresis loss and eddy current loss and, in
particular from the viewpoint of the eddy current loss,
quantitatively controlling the distribution of the strain and
residual stress not only at the surface, but also inside in the
sheet thickness direction under suitable conditions.
[0008] The inventors ran experiments on magnetic domain control
introducing strain and residual stress into grain-oriented
electrical sheet by laser firing etc. and engaged in in-depth
research to investigate the distribution of residual stress
introduced into the obtained low watt loss grain-oriented
electrical sheet. As a result, the inventors discovered a
correlation between the residual stress and eddy current loss and
discovered that if controlling the compressive stress value and the
strain pitch, it is possible to realize a grain-oriented electrical
sheet superior in watt loss. The gist of the present invention is
as follows.
[0009] (1) A grain-oriented electrical sheet obtained by firing a
continuous wave laser beam to introduce strain uniformly in a sheet
width direction perpendicular to a rolling direction, cyclically in
the rolling direction, and in lines substantially perpendicular to
the rolling direction, characterized in that in the two-dimensional
distribution of a rolling direction compressive residual stress
occurring near one location of the introduction of strain in a
cross-section perpendicular to the sheet width direction, the value
of the rolling direction compressive residual stress integrated in
the region of the cross-section where there is compressive residual
stress is 0.20 N to 0.80 N.
[0010] (2) A grain-oriented electrical sheet as set forth in said
(1), characterized in that a cyclic pitch in said rolling direction
of the strain uniform in said sheet width direction due to firing
of the laser beam is 2 mm to 8 mm.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic view of an apparatus used for a method
of production of a grain-oriented electrical sheet of the present
invention.
[0012] FIG. 2 shows a two-dimensional distribution of a rolling
direction residual stress near a laser firing position at a rolling
direction/sheet thickness direction cross-section.
[0013] FIG. 3 is a view of a relationship between a maximum value
of a rolling direction tensile residual stress and a watt loss
W.sub.17/50.
[0014] FIG. 4 is a view of a relationship between a cumulative
compressive stress value .sigma.S and an eddy current loss We
(laser firing pitch of fixed 4 mm).
[0015] FIG. 5 is a view of a relationship between a cumulative
compressive stress value .sigma.S and a watt loss W.sub.17/50
(laser firing pitch of fixed 4 mm).
[0016] FIG. 6 is a view of a relationship between a laser firing
pitch PL and a watt loss W.sub.17/50 (rolling direction laser
firing diameter DL of 0.1 mm and scan direction laser firing
diameter DC of fixed 0.5 mm).
[0017] FIG. 7 is a view of a relationship between a maximum value
of a rolling direction compressive residual stress and a watt loss
W.sub.17/50.
BEST MODE FOR CARRYING OUT THE INVENTION
[0018] The inventors took note of the two-dimensional distribution
of rolling direction residual stress in the cross-section vertical
to the sheet width direction and the rolling direction laser firing
pitch for various laser firing conditions in the method of firing a
laser at the surface of grain-oriented electrical sheet so as to
introduce lines of strain substantially vertical to the rolling
direction at a constant pitch in the rolling direction so as to
improve the watt loss and discovered conditions by which
grain-oriented electrical sheet superior in watt loss can be
obtained. Here, the "sheet width direction" is a direction
perpendicular to the rolling direction. As the method for
introducing lines of strain like the above at the surface of
grain-oriented electrical sheet, in addition to the laser firing
method, ion injection, electrodischarge machining, local plating,
ultrasonic vibration, etc. may be mentioned. The conditions can be
applied to grain-oriented electrical sheet introducing strain by
any method. Below, drawings will be used to explain the
grain-oriented electrical sheet obtained by laser firing of the
present invention.
[0019] FIG. 1 is an explanatory view of the method of firing a
laser beam according to the present invention. In the present
embodiment, the continuous wave (CW) laser beam LB output from the
laser device 3 is used to scan a grain-oriented electrical sheet 1
using a polygonal mirror 4 and f.theta. lens 5. By changing the
distance between the f.theta. lens 5 and grain-oriented electrical
sheet 1, the rolling direction focused diameter dl of the laser
beam was changed. 6 is a cylindrical lens or a plurality of
cylindrical combination lenses. This is used in accordance with
need to change the focused diameter (scan direction length) dc of
the scan direction of the beam (sheet width direction perpendicular
to rolling direction) for the focused spot of the laser beam so as
to control the focused shape from a circular shape to an elliptical
shape. The average firing energy density Ua [mJ/mm.sup.2] is
defined using the laser power P [W], sheet width direction scan
speed Vc of the laser beam in the sheet width direction [m/s], and
rolling direction laser firing pitch PL (mm) as
Ua(mJ/mm.sup.2)=P/(Vc.times.PL)
The laser scan speed is determined by the rotational speed of the
polygonal mirror, so the average laser firing energy density can be
adjusted by changing the laser power, polygonal mirror rotational
speed, and laser firing pitch. FIG. 1 is an example of use of one
set of a laser and laser beam scan device. It is also possible to
set a plurality of similar devices in the sheet width direction in
accordance with the width of the steel sheet.
[0020] The inventors ran experiments using a 10 .mu.m fiber core
diameter continuous wave fiber laser device, changed the laser
firing conditions while combining the focused spot shape and
average laser firing energy density Ua in various ways, and made
the laser beam scan the surface of the grain-oriented electrical
sheet in lines in a direction substantially vertical to the rolling
direction so as to laser it. They measured the two-dimensional
distribution of the residual stress in the rolling direction in the
cross-section vertical to the sheet width direction and the watt
loss and hysteresis loss and divided the watt loss into hysteresis
loss and eddy current loss for study. For measurement of the
two-dimensional distribution of the residual stress in the rolling
direction in the cross-section vertical to the sheet width
direction, they used the X-ray diffraction method to measure the
lattice intervals and used the modulus of elasticity and other
physical property values to convert this to stress. The watt loss
was measured as W.sub.17/50 by an SST (Single Sheet Tester)
measuring device. W.sub.17/50 is the watt loss at the time of a
frequency of 50 Hz and a maximum magnetic flux density of 1.7 T. In
the grain-oriented electrical sheet sample used in this example,
when the sheet thickness is 0.23 mm, the W.sub.17/50 before laser
firing was 0.86 W/kg. The hysteresis loss was calculated by a
hysteresis loop, while the eddy current was made the value of the
watt loss minus the hysteresis loss.
[0021] FIG. 2 shows a typical example of the two-dimensional
distribution of the compressive residual stress of the rolling
direction occurring near the laser firing position in a
cross-section vertical to the sheet width direction. For steel
sheet where improvement in the watt loss is seen, there are
differences in the absolute value of the residual stress depending
on the laser firing conditions, but there is a large tensile stress
near the surface of the steel sheet and there is compressive stress
directly under the sheet thickness direction. Note that the width
of the rolling direction in which the residual stress and plastic
strain are present is substantially proportional to the rolling
direction diameter dl of the focused spot of the laser.
[0022] The inventors investigated the relationship between the
maximum value of the tensile residual stress and compressive
residual stress of the surface of the steel sheet and the watt
loss. The relationship between the maximum value of the tensile
residual stress and the watt loss is shown in FIG. 3, while the
relationship between the maximum value of the compressive residual
stress and the watt loss is shown in FIG. 7. For the maximum value
of the tensile residual stress, no correlation with the watt loss
or optimal value is seen. On the other hand, for the maximum value
of the compressive residual stress, the watt loss is good above the
100 MPa shown by the one-dot chain line, but the upper limit value
is not clear. As a result, the watt loss in magnetic domain control
by laser firing cannot be explained by the maximum value of the
tensile residual stress and cannot be completely explained even by
the maximum value of the compressive residual stress. The
possibility of the presence of separate particularly fine amounts
may be considered.
[0023] Therefore, the inventors studied the data in detail and as a
result noted, as a first point, that the maximum value of the
tensile residual stress is greater than the compressive residual
stress and the tensile residual stress concentrates in a narrow
region, that depending on the firing conditions, the yield stress,
that is, plastic strain region, is reached, that, on the other
hand, some relationship was seen between the maximum value of the
compressive residual stress and the watt loss, and, as a second
point, even if the maximum value of the compressive residual stress
is the same, there is a difference in the spread of the
distribution of compressive residual stress in the depth direction.
That is, they began to believe that as the main factors behind the
realization of reduction of watt loss and realization of magnetic
domain subdivision are, from the first point, not the tensile
stress, but the compressive stress has important meaning and, from
the second point, not the maximum value of the residual stress, but
the spread of the distribution has important meaning.
[0024] To express the distribution of compressive stress for
realizing reduction of the watt loss, the inventors defined the
characterizing quantity of the "cumulative compressive stress value
.sigma.S" as in the following formula (1):
.sigma. S = .intg. S .sigma. s ( 1 ) ##EQU00001##
That is, in the two-dimensional distribution of the rolling
direction compressive residual stress occurring near a lasered
part, that is, near a part where strain is introduced, in the
cross-section vertical to the sheet width direction, they defined
the cumulative compressive stress value .sigma.S [N] as the value
of the stress .sigma. integrated in the region S where the rolling
direction compressive residual stress is .sigma. [MPa], the region
in the cross-section in which there is compressive residual stress
is S [mm.sup.2], and the area element_is ds. That is, the
cumulative compressive stress value is the sum of the compressive
residual stress introduced by laser firing.
[0025] The inventors found the cumulative compressive stress by the
above method for grain-oriented electrical sheet obtained by
setting the rolling direction laser firing pitch PL at 4 mm
(fixed), setting the shape of the laser focused spot at
20.times.2500 .mu.m, 100.times.500 .mu.m, 100.times.2000 .mu.m, and
300.times.200 .mu.m, and changing the laser power for each in
stages for the laser firing. On the other hand, they subtracted the
hysteresis loss from the watt loss measured for each to find the
eddy current loss. FIG. 4 shows the relationship between the two
for each electrical sheet obtained by plotting the cumulative
compressive stress value .sigma.S on the abscissa and the eddy
current loss We on the ordinate. From the result, the cumulative
compressive stress value and the eddy current loss are in an
inversely proportional relationship regardless of the shape of the
focused spot. This means that the reduction in the eddy current
loss, that is, the magnetic domain subdivision effect, is
proportional to the sum of the introduced compressive residual
stresses. If considering this phenomenon from the physical
principles, the result becomes as follows. The magnetic elasticity
energy E is
E=-C.times..sigma..times.M.times.cos.sup.2 .theta.
where C is a constant, .sigma. is the residual stress, M is the
magnetic moment, and .theta. is the angle formed by .sigma. and M.
At this time, when there is compressive residual stress in the
rolling direction, since E becomes smallest when .theta. is 90
degrees, .sigma. is a negative value. If taking note of this, the
orientation of the magnetic moment becomes vertical to the rolling
direction. Therefore, due to the compressive stress, the axis of
easy magnetization can be made not only the rolling direction, but
also the vertical direction. In general, this is called a "reflux
magnetic domain". If there is a reflux magnetic domain, the
magnetostatic energy becomes higher and unstable, so it may be
considered to further divide the magnetic domains to lower the
magnetostatic energy and stabilize it. Accordingly, it is believed,
the greater the reflux magnetic domains, that is, the stronger and
broader the compressive residual stress generated, the higher the
magnetic domain subdivision effect becomes and the more the eddy
current loss is reduced.
[0026] FIG. 5 shows the relationship when using the data used in
FIG. 4 and the measured watt loss and plotting the cumulative
compressive stress value .sigma.S on the abscissa and the peak watt
loss W.sub.17/50 on the ordinate. From the results, in the range of
0.20 N.ltoreq..sigma.S.ltoreq.0.80 N shown by the dot-chain line,
compared with the watt loss W.sub.17/50=0.86 W/kg before magnetic
domain control, a good watt loss of a watt loss improvement rate of
13% or more (W.sub.17/50.ltoreq.0.75 W/kg) shown by the dotted line
can be realized. Note that, the watt loss improvement rate .eta. is
defined as .eta.(%)={(watt loss of material-peak watt loss)/watt
loss of material}.times.100. If the cumulative compressive stress
value .sigma.S is smaller than 0.20 N, the eddy current loss is
high, so the watt loss is not reduced. It is believed that, when
the cumulative compressive stress value .sigma.S is larger than
0.80 N, the eddy current loss is reduced, but the hysteresis loss
increases due to the plastic strain due to the tensile residual
stress near the surface, so the watt loss is not reduced. In the
above way, it is learned that if adjusting the cumulative
compressive stress value .sigma.S to the range of
0.20 N.ltoreq..sigma.S.ltoreq.0.80 N
a good improvement in the watt loss is obtained. More preferably,
it is learned that if adjusting the value to the range of 0.40
N.ltoreq..sigma.S.ltoreq.0.70 N, a further effect of improvement of
the watt loss can be obtained.
[0027] In the above, the rolling direction laser firing pitch PL
was fixed at 4 mm, but the inventors further investigated the
effects by changing the rolling direction laser firing pitch PL. At
this time, they made the shape of the focused spot of the laser
beam a rolling direction diameter of 0.1 mm and a scan direction
(sheet width direction) diameter of 0.5 mm and adjusted Ua so that
the cumulative compressive stress .sigma.S fell in the range of
0.20 N.ltoreq..sigma.S.ltoreq.0.80 N. FIG. 6 plots the rolling
direction laser firing pitch PL on the abscissa and the watt loss
W.sub.17/50 on the ordinate and shows the relationship between the
two. From the results, with a PL of 2 mm to 8 mm, a good watt loss
of a watt loss improvement rate of 13% can be realized. In a range
where PL is smaller than 2 mm, the hysteresis loss increases, so
the watt loss is not reduced. In a range where PL is larger than 8
mm, the eddy current loss is not reduced, so the watt loss is not
reduced. In the above way, it is learned that if adjusting the
rolling direction laser firing pitch PL to the range of
2 mm.ltoreq.PL.ltoreq.8 mm
a good improvement in the watt loss can be obtained.
Example 1
[0028] Using 0.23 mm thick grain-oriented electrical sheet, the
surface of the steel sheet was scanned using a continuous wave
laser under the laser firing conditions as shown in Table 1, the
residual stress was measured, then the cumulative compressive
stress value was calculated and the watt loss (W.sub.17/50) was
measured. The results are shown in together in the same Table 1.
Example 1 was performed fixing the laser power at 200 W and the
laser firing pitch in the rolling direction at 4 mm. The cumulative
compressive stress value was calculated by using the X-ray
diffraction method to measure the rolling direction residual stress
(strain) and finding the value with respect to the compressive
stress by formula (2).
[0029] As clear from Table 1, the electrical sheets shown in Test
No. 1 to No. 8 (invention examples) all had a rolling direction
cumulative compressive stress value .sigma.S in the range
prescribed by the present invention, that is, 0.20
N.ltoreq..sigma.S.ltoreq.0.80 N, so could be reduced in watt loss
to a low watt loss value (W.sub.17/50) of 0.75 W/kg, for a watt
loss improvement rate of 13%, or less. On the other hand, the
electrical sheets shown in Test No. 9 to No. 12 (comparative
examples) outside the range of conditions 0.20
N.ltoreq..sigma.S.ltoreq.0.80 N failed to achieve a low watt loss
value (W.sub.17/50) of 0.75 W/kg or less. In this way, if using the
present invention, it is possible to obtain grain-oriented
electrical sheet superior in watt loss.
TABLE-US-00001 TABLE 1 Rolling Scan Cumulative direction direction
Average Strain Maximum compressive Watt loss Watt loss diameter
diameter energy pitch tensile stress value improvement Test DL DC
density Ua PL stress value .sigma.S W17/50 rate No. mm mm
mJ/mm.sup.2 mm MPa N W/kg % Not lasered 0 -- -- -- -- 0 0 0.860 0
Inv. ex. 1 0.020 2.50 2.5 4 370 0.30 0.730 15.1 Inv. ex. 2 0.020
2.50 3.5 4 350 0.50 0.716 16.7 Inv. ex. 3 0.100 0.50 1 4 460 0.45
0.725 15.7 Inv. ex. 4 0.100 0.50 2 4 450 0.55 0.715 16.9 Inv. ex. 5
0.100 2.00 2 4 400 0.38 0.730 15.1 Inv. ex. 6 0.100 2.00 2.5 4 400
0.45 0.710 17.4 Inv. ex. 7 0.300 0.20 2 4 420 0.58 0.730 15.1 Inv.
ex. 8 0.300 0.20 3 4 410 0.70 0.735 14.5 Comp. ex. 9 0.020 2.50 1 4
330 0.10 0.820 4.7 Comp. ex. 10 0.100 0.50 4 4 440 0.85 0.755 12.2
Comp. ex. 11 0.100 2.00 1 4 390 0.14 0.800 7.0 Comp. ex. 12 0.300
0.20 4 4 410 0.90 0.765 11.0
Example 2
[0030] The surface of 0.23 mm thick grain-oriented electrical sheet
was scanned by a continuous wave laser beam under the laser firing
conditions as shown in Table 2, the residual stress of the lasered
part was measured, then the cumulative compressive stress value was
calculated and the watt loss (W.sub.17/50) was measured. These
values are shown in together in Table 2. Example 2 was performed
fixing the laser power at 200 W the same as Example 1.
[0031] As clear from Table 2, the electrical sheets shown in Test
No. 1 to No. 6 (invention examples) all have a rolling direction
cumulative compressive stress value .sigma.S and a rolling
direction laser firing pitch (strain pitch) PL in the ranges
prescribed in the present invention, that is, 0.20
N.ltoreq..sigma.S.ltoreq.0.80 N and 2 mm.ltoreq.PL.ltoreq.8 mm, so
could be reduced in watt loss to a low watt loss value
(W.sub.17/50) of 0.75 W/kg, for a watt loss improvement rate of
13%, or less. On the other hand, the electrical sheet shown in Test
No. 7 and No. 8 having a cumulative compressive stress value
.sigma.S satisfying the conditions, but off from the conditions of
the firing pitch PL failed to achieve a low watt loss value
(W.sub.17/50) 0.75 W/kg or less. In this way, if using the present
invention, it is possible to obtain grain-oriented electrical sheet
superior in watt loss.
TABLE-US-00002 TABLE 2 Rolling Scan Cumulative direction direction
Average Strain Maximum compressive Watt loss Watt loss diameter
diameter energy pitch tensile stress value improvement Test DL DC
density Ua PL stress value .sigma.S W17/50 rate No. mm mm
mJ/mm.sup.2 mm MPa N W/kg % Not lasered 0 -- -- -- -- 0 0 0.860 0
Inv. ex. 1 0.100 0.20 1.5 2 340 0.45 0.735 14.5 Inv. ex. 2 0.100
0.50 1.5 2 450 0.22 0.740 14.0 Inv. ex. 3 0.100 0.50 1.5 4 440 0.50
0.720 16.3 Inv. ex. 4 0.100 0.50 1.5 6 460 0.65 0.730 15.1 Inv. ex.
5 0.100 0.50 1.5 8 450 0.75 0.745 13.4 Inv. ex. 6 0.100 2.00 3 8
390 0.23 0.748 13.0 Inv. ex. 7 0.100 0.50 1.5 1 330 0.21 0.755 12.2
Inv. ex. 8 0.100 0.50 1.5 10 430 0.80 0.760 11.6
INDUSTRIAL APPLICABILITY
[0032] According to the present invention, by quantitatively
suitably controlling the residual stress introduced to the
grain-oriented electrical sheet, in particular the compressive
residual stress, it is possible to obtain to stably obtain
grain-oriented electrical sheet superior in watt loss compared with
the past. If using the grain-oriented electrical sheet of the
present invention as an iron core, a high efficiency, small-sized
transformer can be produced. The value of industrial application of
the present invention is extremely high.
* * * * *