The present invention provides a grain-oriented electrical steel sheet with reduced iron loss over a wide range of sheet thickness by providing a grain-oriented electrical steel sheet with an actually measured sheet thickness t (mm) that includes a closure domain region extending linearly in a direction from 60 to 120 with respect to the rolling direction on a surface of the steel sheet, the closure domain region being formed periodically at a spacing s (mm) in the rolling direction, such that h74.9t+39.1 (0.26t), h897t174.7 (t>0.26), (wh)/(s1000)12.6t+7.9 (t>0.22), and (wh)/(s1000)40.6t+14.1 (t0.22), where h (m) is the depth and w (m) is the width of the closure domain region.

A method of producing a non-oriented electrical steel sheet by hot rolling and cold rolling a steel slab comprising by mass % C: not more than 0.0050%, Si: 2-7%, Mn: 0.05-2.0%, P: not more than 0.2%, S: not more than 0.005%, Al: not more than 3%, N: not more than 0.005%, Ti: not more than 0.003%, Nb: not more than 0.005% and V: not more than 0.005% and then subjecting to a finish annealing and a stress-relief annealing, conditions of the finish annealing and stress-relief annealing are adjusted so that a yield stress of the steel sheet after the finish annealing is not less than 400 MPa and a ratio of a magnetic flux density B.sub.50S of the steel sheet after the stress-relief annealing to a magnetic flux density B.sub.50H after the finish annealing is not less than 0.99.

This non-oriented electrical steel sheet contains a base material having a chemical composition including, in mass %, Si: 3.2 to 4.5%, wherein the tensile strength is 550 MPa or more, and a ratio (P.sub.120B/Fe.sub.700B).sub.B between a peak-to-peak height Fe.sub.700B of Fe at 700 eV and a peak-to-peak height P.sub.120B of P at 120 eV when crystal grain boundaries are measured through Auger electron spectroscopy is not more than twice a ratio (P.sub.120i/Fe.sub.700i).sub.i between a peak-to-peak height Fe.sub.700i of Fe at 700 eV and a peak-to-peak height P.sub.120i of P at 120 eV when the inside of crystals is measured through Auger electron spectroscopy.

Disclosed herein are a method for producing a hot-rolled steel sheet, a method for producing a cold-rolled full hard steel sheet, and methods for producing a heat-treated steel sheet that serve as the methods for producing intermediate products for obtaining a steel sheet having a tensile strength of 590 MPa or more, a particular composition and a particular steel structure.

Provided are a grain-oriented electrical steel sheet having excellent iron loss property without using magnetic domain refining treatment and an iron core produced using the same. The steel sheet comprises: a predetermined chemical composition; and a steel microstructure in which: crystal grains are made up of coarse secondary recrystallized grains of 5.0 mm or more, fine grains of more than 2.0 mm and less than 5.0 mm contained at a frequency of 0.2 to 5 grains per cm.sup.2, and very fine grains of 2.0 mm or less; for each coarse secondary recrystallized grain extending through the sheet in a thickness direction, an area ratio of a region in which projected surfaces of exposed areas of the coarse secondary recrystallized grain on a front side and a back side of the sheet coincide with each other to each of the exposed areas is 95% or more.

In the production of a non-oriented electrical steel sheet by subjecting a steel slab having a certain component composition to a hot rolling, a hot-band annealing, a cold rolling and a finish annealing, the conditions of the finish annealing are controlled such that a yield stress of the steel sheet after the finish annealing is not less than 480 MPa. Also, when a motor core is produced by using the above steel sheet, there can be provided a non-oriented electrical steel sheet capable of producing a rotor core and a stator core as the same raw material where the stator core is subjected to a stress relief annealing at a soaking temperature of 780 to 950? C. in an atmosphere having a nitrogen content of not more than 30 vol % and a dew point of not higher than ?20? C., while a motor core is produced with such a steel sheet.

A non-oriented electrical steel sheet has a chemical composition including C: not more than 0.0050 mass %, Si: 1.0-5.0 mass %, Mn: 0.03-3.0 mass %, P: not more than 0.2 mass %, S: not more than 0.005 mass %, Al: not more than 0.05 mass %, N: not more than 0.0050 mass %, 0: not more than 0.010 mass %, Ti: not more than 0.0030 mass %, Nb: not more than 0.0030 mass %, B: 0.0005-0.0050 mass % and the remainder being Fe and inevitable impurities, and is excellent in not only the recyclability, but also iron loss property after stress-relief annealing.

A motor core has multiple silicon steel sheets and multiple layers of electrically insulating colloid. Each one of the multiple layers of electrically insulating colloid is disposed between adjacent two of the silicon steel sheets. This reduces the chance of forming eddy currents, reducing the eddy current loss of the motor core during operation.

Disclosed is a method for manufacturing a grain-oriented electrical steel sheet using an inhibitor-less technique, in which cold rolling includes final cold rolling with a total cold rolling reduction being set to 85% or more and a rolling reduction per pass being set to 32% or more. The final cold rolling includes one or more passes and a final pass succeeding the one or more passes and uses work rolls having a surface roughness Ra of 0.25 m or less in at least one of the one or more passes other than the final pass. According to this method, it is possible to stably manufacture a grain-oriented electrical steel sheet exhibiting excellent magnetic properties at low cost.

A method of manufacturing a stator is provided. The method may include stamping steel into laminations each having an inner edge area defining a residual stress associated with a magnetic permeability. The method may also include exposing the laminations to a changing magnetic field such that, for each of the laminations, a density of resulting eddy currents is greatest near the inner edge area to heat the same relative to central areas of the lamination to decrease the residual stress and core loss.