A non-oriented electrical steel sheet with an average magnetostriction λ.sub.p-p at 400 Hz and 1.0 T of not more than 4.5×10.sup.−6, and area ratio of recrystallized grains at a section in rolling direction of steel sheet of 40 to 95% and an average grain size of 10 to 40 μm is obtained by subjecting a steel slab containing, in mass %, C: not more than 0.005%, Si: 2.8 to 6.5%, Mn: 0.05 to 2.0%, Al: not more than 3.0%, P: not more than 0.20%, S: not more than 0.005%, N: not more than 0.005%, Ti: not more than 0.003%, V: not more than 0.005% and Nb: not more than 0.005% and satisfying Si—2Al—Mn≥0 to hot rolling, hot-band annealing, cold rolling and finish annealing under adequate cold rolling and finish annealing conditions, and a motor core is manufactured by such a steel sheet.

A hot-rolled steel sheet includes, as chemical composition, C, Si, Mn, and sol.Al. In the hot-rolled steel sheet, an average of pole densities in crystal orientation group consisting of {110}<110> to {110}<001> in surface region is 0.5 to 3.0, a standard deviation of the pole densities in the crystal orientation group is 0.2 to 2.0, and the tensile strength is 780 to 1370 MPa.

According to an exemplary embodiment of the present invention, a method for manufacturing a grain-oriented electrical steel sheet includes: a step of hot-rolling a slab to manufacture a hot-rolled steel sheet; a step of performing hot-rolled sheet annealing on the hot-rolled steel sheet; a step of performing primary cold-rolling on the hot-rolled sheet annealed hot-rolled steel sheet; a step of performing primary decarburization annealing on the primarily cold-rolled steel sheet; a step of performing secondary cold-rolling on the decarburization-annealed steel sheet; a step of performing secondary decarburization annealing on the secondarily cold-rolled steel sheet; and a step of performing continuous annealing on the secondarily decarburization-annealed steel sheet.

A steel sheet includes: a predetermined chemical composition; and a steel structure represented by, in area %, first martensite in which two or more iron carbides each having a circle-equivalent diameter of 2 nm to 500 nm are contained in each lath: 20% to 95%, ferrite: 15% or less, retained austenite: 15% or less, and the balance: bainite, or second martensite in which less than two iron carbides each having a circle-equivalent diameter of 2 nm to 500 nm are contained in each lath, or the both of these, in which the total area fraction of ND//<111> orientation grains and ND//<100> orientation grains is 40% or less, and the content of solid-solution C is 0.44 ppm or more.

A grain-oriented electrical steel sheet having a metallographic structure after secondary-recrystallized annealing including matrix grains of Goss-oriented secondary recrystallized grains, wherein an existence frequency of Goss-oriented crystal grains having a major diameter of 5 mm or less in the matrix grains is 1.5 grains/cm.sup.2 or more and 8 grains/cm.sup.2 or less, and the magnetic flux density B8 is 1.88 T or more, and wherein deviation angles from a rolling direction of [001] direction of the Goss-oriented crystal grains having the major diameter of 5 mm or less are 7″ or less and 5° or less, in terms of a simple or arithmetic average of α angle and β angle, respectively, wherein the α angle represents an angle formed by a longitudinal direction and a projection of the [001] on a specimen surface, and the β angle represents a tilt of the [001] out of the specimen surface.

A grain oriented electrical steel sheet includes the texture aligned with Goss orientation. In the grain oriented electrical steel sheet, when (α.sub.1 β.sub.1 γ.sub.1) and (α.sub.2 β.sub.2 γ.sub.2) represent deviation angles of crystal orientations measured at two measurement points which are adjacent on the sheet surface and which have an interval of 1 mm, the boundary condition BA is defined as |γ.sub.2−γ.sub.1|≥0.5°, and the boundary condition BB is defined as [(α.sub.2−α.sub.1).sup.2+(β.sub.2−β.sub.1).sup.2+(γ.sub.2−γ.sub.1).sup.2].sup.1/2≥2.0°, the boundary which satisfies the boundary condition BA and which does not satisfy the boundary condition BB is included.

Grain-oriented electrical steel sheet excellent in magnetic properties and excellent in adhesion of a primary coating to the steel sheet is provided. The grain-oriented electrical steel sheet is provided with a base steel sheet having a chemical composition containing C: 0.005% or less, Si: 2.5 to 4.5%, Mn: 0.050 to 1.000%, a total of S and Se: 0.005% or less, sol. Al: 0.005% or less, and N: 0.005% or less and having a balance of Fe and impurities and a primary coating having Mg.sub.2 SiO.sub.4 as a main constituent formed on a surface of the base steel sheet. A peak position of Al emission intensity obtained when conducting elemental analysis by glow discharge spectrometry from a surface of the primary coating in a thickness direction is present in a range of 2.0 to 12.0 μm from a surface of the primary coating to the thickness direction. A sum of perimeters of the Al oxides at the peak position of Al emission intensity is 0.20 to 1.00 μm/μm.sup.2, and a number density of Al oxides is 0.02 to 0.20/μm.sup.2.

The present invention provides a steel material which has a plate shape and achieves both high strength and high rigidity by imparting large nonuniform deformation to the steel material utilizing rolling using a large-diameter work roll. The steel plate according to an embodiment of the present invention is produced by performing rolling using a rolling mill having a work roll diameter of 650 mm or more in a warm temperature region so that a nonuniform metallographic structure is formed in a plate thickness direction and thus the steel plate of the present invention is a high-strength and high-rigidity steel plate in which a yield strength is 580 MPa or more and a Young's modulus at a plate thickness center portion or a surface layer portion is 210 GPa or more and a difference in Young's moduli at the plate thickness center portion and the surface layer portion is 5 GPa or more in a case in which a tensile direction in a tensile test is at least any one of a rolling direction, a plate width direction, or a direction forming an angle difference of 45 degrees from the rolling direction and the plate width direction.

A grain-oriented electrical steel sheet according to an embodiment of the present invention has an average degree of orientation difference of 0.5 to 10° between recrystallized grains that are in contact with a groove present on the surface of the electrical steel sheet and the bottom of the groove, and other recrystallized grains.

A grain-oriented electrical steel sheet according to an exemplary embodiment of the present invention includes: a linear groove formed in one or both surfaces of the electrical steel sheet in a direction intersecting with a rolling direction; and a linear thermal shock portion formed in the one or both surfaces of the electrical steel sheet in a direction intersecting with the rolling direction. An angle between a longitudinal direction of the groove and a longitudinal direction of the thermal shock portion is 1 to 5°.