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.

A grain oriented electrical steel sheet includes the texture aligned with Goss orientation. In the grain oriented electrical steel sheet, when a grain size RAα.sub.L, a grain size RAβ.sub.L, and a grain size RAγ.sub.L are defined in a rolling direction L, the grain sizes satisfy RAβ.sub.L<RAα.sub.L and RAγ.sub.L<RAα.sub.L.

A grain-oriented electrical steel sheet according to the present invention has a steel sheet surface provided with grooves and includes two or more broken lines including the grooves having a length of 5 to 10 mm on a straight line intersecting a rolling direction on the steel sheet surface. In each of the broken lines including the grooves, the grooves are arranged at equal intervals, and a ratio of the length of the groove to a length of a non-groove is in a range of 1:1 to 1.5:1.

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 μm to 100 μm, 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 μm to 130 μm.

Disclosed herein are a method and a device for forming a groove in a surface of a steel sheet. In the method for forming a groove in a surface of a steel sheet, in order to form grooves at a depth of 10% or less of a thickness of the steel sheet in the surface of the steel sheet by irradiating a laser beam, in the case in which laser beams are irradiated from a plurality of laser oscillators to a scan mirror, pass through the scan mirror, and are then irradiated to the surface of the steel sheet, two or more laser beams share one scan mirror with each other to minimize a thermal influence of groove portions at a high line speed of 20 mpm or more, thereby accomplishing iron loss improvement characteristics before (after) heat treatment.

This grain-oriented electrical steel sheet is a grain-oriented electrical steel sheet including a base steel sheet and a tension coating, in which, when an average coating thickness of a flat surface coating portion is referred to as t1 (μm), a minimum coating thickness of a groove forming surface coating portion is referred to as t2.sub.Min (μm), and a maximum coating thickness of the groove forming surface coating portion is referred to as t2.sub.Max (μm), Expressions (1) and (2) are satisfied, and when a value of 0.95 times a distance D of the tension coating along a sheet thickness direction from a bottom surface position of the groove forming surface coating portion to a bottom surface position of the flat surface coating portion is referred to as an effective depth d (μm), Expression (3) is satisfied.

t2.sub.Min/t1≥0.4  (1)

t2.sub.Max/t1≤3.0  (2)

t2.sub.Max≤d/2  (3)

A grain oriented electrical steel sheet has a magnetic domain structure modified by strain introduction without a trace of treatment, in which noise generated when the grain oriented electrical steel sheet is used laminated on an iron core of a transformer is effectively reduced by: setting a magnetic flux density B.sub.8 to 1.92 T or higher; then setting a ratio of average magnetic domain width of treated surface after strain-introducing treatment W.sub.a to average magnetic domain width before strain-introducing treatment W.sub.0 as W.sub.a/W.sub.0<0.4; and setting a ratio of W.sub.a to average magnetic domain width of untreated surface W.sub.b as W.sub.a/W.sub.b>0.7; and further setting a ratio of average width of magnetic domain discontinuous portion W.sub.d in the untreated surface to average width of magnetic domain discontinuous portion in treated surface resulting from strain-introducing treatment W.sub.c as W.sub.d/W.sub.c>0.8; and setting W.sub.c<0.35 mm.

A grain oriented electrical steel sheet is subjected to a temperature holding treatment at a temperature T of 250-600° C. for 1-10 seconds in the primary recrystallization annealing and heated from temperature T to 700° C. at not less than 80° C./s and from 700° C. to a soaking temperature at not more than 15° C./s, wherein an oxygen potential from 700° C. to the soaking temperature is 0.2-0.4 and an oxygen potential during the soaking is 0.3-0.5 and an area ratio of secondary recrystallized grains is not less than 90% when an angle α deviated from {110}<001> ideal orientation is less than 6.5° and an area ratio is not less than 75% when a deviation angle is less than 2.5° and an average length [L] in the rolling direction is not more than 20 mm and an average value [β] of the angle β is 15.63×[β]+[L]<44.06.

A method for refining a magnetic domain of a grain-oriented electrical steel strip is provided, including a steel strip supporting roll position adjusting step of controlling a position of the steel strip in a vertical direction while supporting the steel strip proceeding along a production line, a laser irradiating step of forming a groove on a surface of the steel strip by irradiating a laser beam onto the surface of the steel strip to melt the steel strip, and a detecting step of detecting a defect in the groove formed on the surface of the steel strip while the steel strip proceeds, so as to be able to detect whether the groove is defective by confirming a machining state of a magnetic domain refined groove formed on the surface of the steel strip in a working process.

A grain-oriented electrical steel sheet includes a plurality of linear deformable portions formed on a surface of the electrical steel sheet in a rolling direction, wherein an interval between the deformable portions changes to correspond to a grain size of grains over the entire length of the steel sheet, and at least two regions in which intervals between the deformable portions are different exist.