Provided is a method for refining magnetic domains of grain-oriented electrical steel plates including: a steel plate supporting roll position adjusting step of controlling a vertical direction position of the steel plate while supporting the steel plate; a laser radiating step of melting the steel plate by radiating a laser beam to form grooves on the surface of the steel plate; and a setting and maintaining step of setting and maintaining an internal operation environment of a laser room in which the laser radiation is performed, so as to increase magnetic domain refinement efficiency and improve workability by optimizing equipment and processes, thereby increasing the processing capacity.

A heat-resistant magnetic domain refined grain-oriented silicon steel, a single-sided surface or a double-sided surface of which has several parallel grooves which are formed in a grooving manner, each groove extends in the width direction of the heat-resistant magnetic domain refined grain-oriented silicon steel, and the several parallel grooves are uniformly distributed along the rolling direction of the heat-resistant magnetic domain refined grain-oriented silicon steel. Each groove which extends in the width direction of the heat-resistant magnetic domain refined grain-oriented silicon steel is formed by splicing several sub-grooves which extend in the width direction of the heat-resistant magnetic domain refined grain-oriented silicon steel. The manufacturing method for a heat-resistant magnetic domain refined grain-oriented silicon steel comprises the step of: forming grooves on a single-sided surface or a double-sided surface of a heat-resistant magnetic domain refined grain-oriented silicon steel in a laser grooving manner, a laser beam of the laser grooving is divided into several sub-beams by a beam splitter, and the several sub-beams form the several sub-grooves which are spliced into the same groove.

Vibration of an iron core is reduced to reduce transformer noise. An iron core for a transformer comprises a plurality of grain-oriented electrical steel sheets stacked together, wherein at least one of the plurality of grain-oriented electrical steel sheets: (1) has a region in which closure domains are formed in a direction crossing a rolling direction and a region in which no closure domains are formed; and (2) has an area ratio R of 0.10% to 30%, the area ratio R being an area ratio, to the whole grain-oriented electrical steel sheet, of a region in which a shrinkage amount at a maximum displacement point when excited in the rolling direction at a maximum magnetic flux density of 1.7 T and a frequency of 50 Hz is at least 210.sup.7 less than a shrinkage amount in the region in which no closure domains are formed.

Vibration of an iron core is reduced to reduce transformer noise. An iron core for a transformer comprises a plurality of grain-oriented electrical steel sheets stacked together, wherein at least one of the plurality of grain-oriented electrical steel sheets: (1) has a region in which closure domains are formed in a direction crossing a rolling direction and a region in which no closure domains are formed; (2) has an area ratio R.sub.0 of 0.10% to 3.0%, the area ratio R.sub.0 being defined as a ratio of S.sub.0 to S; and (3) has an area ratio R.sub.1a of 50% or more, the area ratio R.sub.1a being defined as a ratio of S.sub.1a to S.sub.1.

A method of manufacturing a stator is provided. The method may include stamping a fully-processed steel into a set of laminations having hardened outer edge areas. The method may further include flash annealing the laminations to concentrate thermal energy in the inner and outer edge areas relative to central areas of the laminations to drive a hardness of the inner and outer edge areas toward a hardness of the central areas to relieve residual stress and decrease iron loss of the laminations.

A grain-oriented electrical steel sheet according to the present embodiment is a grain-oriented electrical steel sheet having a groove formed on a surface, in which, in a cross section of the grain-oriented electrical steel sheet orthogonal to the groove, a KAM value is 0.1 or more and 3.0 or less in a region on a central side in a thickness direction of the grain-oriented electrical steel sheet with respect to the groove, the region being surrounded by a square having one side in contact with a groove bottom of the groove and having a length of 50 m in each side.

A grain-oriented electrical steel sheet according to the present invention includes a base steel sheet having plural grooves on a surface and a glass film formed on the surface of the base steel sheet. In case of viewing region including grooves in cross section orthogonal to groove longitudinal direction, a straight line passing through peak point present on profile line of glass film and parallel to groove width direction orthogonal to sheet thickness direction in cross section is defined as reference line, a point present on boundary line between glass film and base steel sheet and present at lowest location in sheet thickness direction is defined as deepest point, and a point present on boundary line and present at the highest location in the sheet thickness direction in region having the deepest point in a center and having length of 2 m in groove width direction is defined as shallowest point, a relationship between shortest distance A between reference line and deepest point and shortest distance B between reference line and shallowest point satisfies Expression (1).

0.1 mAB5.0 m(1)

A grain-oriented electrical steel plate of an exemplary embodiment of the present invention has a groove formed on a surface, wherein a curvature radius RBb at a position where a depth of the groove is maximum is 0.2 m to 100 m, and a curvature radius RSb on the groove surface from the position where the depth of the groove is maximum to a quarter-way position of the depth D of the groove is 4 m to 130 m.

This device scans a high-energy beam in a direction traversing a feed path of a grain-oriented electrical steel sheet having subjected to final annealing so as to irradiate a surface of the steel sheet being passed through with the high-energy beam to thereby perform magnetic domain refinement, the device including an irradiation mechanism for scanning the high-energy beam in a direction orthogonal to the feed direction of the steel sheet, in which the irradiation mechanism has a function of having the scanning direction of the high-energy beam oriented diagonally, relative to the orthogonal direction, toward the feed direction at an angle determined based on a sheet passing speed of the steel sheet on the feed path.

In a production of a grain-oriented electrical steel sheet by subjecting a steel slab containing a particular composition and further including an inhibitor-forming ingredient to hot rolling, hot-band annealing, cold rolling, primary recrystallization annealing combined with decarburization annealing and finish annealing, the steel slab satisfies a given relation between a content ratio of sol. Al to N and a final sheet thickness, and, in the finish annealing, the steel sheet is kept at a temperature zone of higher than 850 C. but not higher than 950 C. in heating process for 5 to 200 hours, heated to a temperature zone of 950 to 1050 C. at 5 to 30 C./hr and further subjected to purification treatment of keeping a temperature of not lower than 1100 C. for not less than 2 hours to provide a secondary recrystallization structure that has an average value of a diameter equivalent to a circle of 10 to 100 mm.