Grain-oriented electrical steel sheet is steel sheet controlled in crystal orientation by a
combination of cold rolling and annealing so that the easy magnetization axes of crystal grains
15 and the rolling direction match.
[0003]
The crystal orientation is controlled by building in a primary recrystallization texture in
annealing treatment after cold rolling treatment and further annealing at a high temperature to
thereby cause preferential growth of an orientation preferable for the magnetic properties, that is,
20 so-called secondary recrystallization. This control of the crystal orientation enables the hysteresis
loss of the grain-oriented electrical steel sheet to be reduced.
[0004]
As art for reducing eddy current loss, one type of core loss, of grain-oriented electrical steel
sheet, grain-oriented electrical steel sheet comprised of a base steel sheet controlled in crystal
25 orientation and an insulating coating formed on the surface is known. The insulating coating
performs a role of not only providing electrical insulation, but also tension and rust resistance etc.
to the base steel sheet.
[0005]
Further, as another method for reducing abnormal eddy current loss, the method of control of
30 magnetic domains forming distorted regions or grooves in a direction crossing the rolling direction
at a predetermined pitch along the rolling direction to narrow the widths of the 180 magnetic
domains (the 180 magnetic domain refining) is known. Methods for control of magnetic domains
are classified into methods imparting distortion to a base steel sheet of grain-oriented electrical
steel sheet and methods forming grooves in the surface of a base steel sheet having a coating giving
35 tension at the base steel sheet.
[0006]
2
By using grain-oriented electrical steel sheet controlled in magnetic domains by grooves, even
if producing iron cores (wound cores) of transformers and applying straightening annealing, the
grooves will not disappear, so the effects of magnetic domain refining can be maintained. For this
reason, the method for control of magnetic domains using formation of grooves as the method for
5 reducing abnormal eddy current loss is sometimes employed for wound cores.
[0007]
FIG. 1 is a view showing an outline of electrical steel sheet formed with grooves. In FIG. 1,
the state is shown where the surface of the base steel sheet 1 is formed with a plurality of
grooves 2 at a pitch in the rolling direction of the base steel sheet 1. In FIG. 1, the notation 
10 shows the angle formed by the direction perpendicular to the rolling direction and sheet
thickness direction (sheet width direction) of the base steel sheet 1 and the longitudinal direction
of the grooves 2. The notation W shows the width of the grooves, the notation D shows the depth
of the grooves, and the notation P shows the pitch of the grooves 2 adjoining each other in the
rolling direction.
15 [0008]
Various methods for forming grooves in electrical steel sheet have been proposed.
For example, PTL 1 discloses an electrolytic etching method of using electrolytic etching to
form grooves in the steel sheet surface of grain-oriented electrical steel sheet.
[0009]
20 PTL 2 discloses a gear press method of mechanically pressing a gear against the steel sheet
surface of grain-oriented electrical steel sheet to thereby form grooves in the steel sheet surface.
[0010]
However, the gear press method suffers from wear of the gear teeth in a short period of time
due to the high hardness of electrical steel sheet. Further, from the viewpoint of high speed
25 processing, it is difficult to realize a line speed of 100 mpm or more like demanded in general
ferrous metal manufacturing processes. The method using electrolytic etching is free from the
problem of wear of the gear teeth, but steps of masking, etching, and mask removal are required.
Compared with mechanical methods, there is the problem that the process becomes complicated.
[0011]
30 PTL 3 discloses a lasering method of using lasering to melt and evaporate lasered parts of the
steel sheet surface of grain-oriented electrical steel sheet. The lasering method has no problem of
wear of gear teeth or a complicated process and also enables high speed processing.
[0012]
Further, even in the lasering method, there have been several proposals for the groove35 forming step. For example, PTL 4 is also a lasering method. Lasering a final product sheet
coated with a tension insulating coating is disclosed. However, in that case, it is necessary to