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.

In a method of producing a grain-oriented electrical steel sheet comprising subjecting a steel slab containing no inhibitor-forming components to hot rolling, cold rolling, primary recrystallization annealing working also as decarburization and to final annealing causing secondary recrystallization after applying an annealing separator on the surface, the final cold rolling for cold rolling the steel sheet to the final thickness uses a warm rolling with a tandem rolling mill at a total rolling reduction of not less than 80% at 150 to 280° C. and is performed by extending a pass line length of the steel sheet between the stands so that T satisfies T≥1.3×L/V, where an distance between the stands is defined as L(m), a speed of the steel sheet passing between the stands is defined as V (mpm), and a pass time during which the steel sheet passes between the stands is defined as T(min).

The present disclosure has as its object the provision of non-oriented electrical steel sheet excellent in magnetic properties which is free from any drop in magnetic flux density even after stress relief annealing and a method for manufacturing the same.

Non-oriented electrical steel sheet having a chemical composition containing C: 0.0030 mass % or less, Si: 2.0 mass % or more and 4.0 mass % or less, Al: 0.010 mass % or more and 3.0 mass % or less, Mn: 0.10 mass % or more and 2.4% mass or less, P: 0.0050 mass % or more and 0.20 mass % or less, S: 0.0030 mass % or less, and one or more elements selected from the group comprising Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd: total 0.00050 mass % or more and having a balance of Fe and unavoidable impurities, where, when designating a mass % of Si as [Si], a mass % of Al as [Al], and a mass % of Mn as [Mn], a parameter Q shown by the following formula (1) is 2.0 or more, a random intensity ratio of the {100} orientation is 2.4 or more, and an average grain size is 30 μm or less:

Q=[Si]+2[Al]−[Mn]  (1)

Provided is a method of manufacturing a grain-oriented electrical steel sheet with which a grain-oriented electrical steel sheet with excellent magnetic properties and little variation in iron loss in the longitudinal direction of a coil can be stably manufactured. The method includes subjecting a steel slab to hot-rolling and optionally to annealing, then performing cold rolling once or twice or more to obtain a cold-rolled sheet with a final sheet thickness, and then subjecting the cold-rolled sheet to decarburization annealing and then secondary recrystallization annealing, where immediately before final cold rolling, a steel sheet is heated at a heating rate of 100° C./s or more to a heating temperature of 100° C. or higher and 350° C. or lower, and a time from when the steel sheet reaches the heating temperature to when it is bitten in a first pass of final cold rolling is set to within 5 seconds.

A hot-rolled steel plate has a predetermined chemical composition and a microstructure. In the microstructure, in a plate thickness 1/2 position, an area fraction of martensite is less than 3%, an area fraction of bainitic ferrite is 95% or greater, the bainitic ferrite has an average grain diameter of 6.0 μm or less, an amount of Nb precipitated as Nb carbonitride is 0.025 mass % or greater, and an amount of Nb precipitated as Nb carbonitride having a grain diameter of 20 nm or greater constitutes 50% or greater of a total mass of the Nb precipitated as Nb carbonitride. The hot-rolled steel plate has a tensile strength of 640 MPa or greater, a yield ratio of 85% or less, a Charpy impact absorbed energy at −40° C. of 300 J or greater, and a percent ductile fracture (SA value) of 85% or greater as determined by a DWTT test at −40° C.

There are provided a method for producing a non-oriented electrical steel sheet, a method for manufacturing a motor core from such a steel sheet, and a motor core. In the production of a non-oriented electrical steel sheet by subjecting a steel slab containing given amounts of C, Si, Mn, P, S, Al, N, Ti, Nb and V, provided that Si, Al and Mn satisfy Si-2Al—Mn≥0, to hot rolling, cold rolling, finish annealing and stress relief annealing, whereby a high-strength rotor core and a stator core having excellent magnetic properties after stress relief annealing can be obtained from the same steel material.

Provided is a grain-oriented electrical steel sheet, the core loss characteristics of which have been significantly improved without causing a deterioration in magnetic flux density. The grain-oriented electrical steel sheet: comprises 2.5-3.5% by mass of Si with the balance being Fe and inevitable impurities; has a sheet thickness of 0.18-0.35 mm; has a metallographic structure including matrix grains of Goss-oriented secondary recrystallized grains after secondary-recrystallized annealing, wherein Goss-oriented crystal grains existing in the matrix and having a major (long) diameter of 5 mm or smaller exist in the metallographic structure at a frequency of 1.5 grains/cm.sup.2 to 8 grains/cm.sup.2; and has a magnetic flux density B8 of 1.88T or greater. As for the orientations of the Goss-oriented crystal grains having a major (long) diameter of 5 mm or smaller, the <100> orientation of the Goss-oriented crystal grains deviate from the rolling direction by an angle of 7 degrees or smaller and by an angle of 5 degrees or smaller in terms of a simple average of an α angle and that of a ß angle, respectively.

α angle; the angle formed by the longitudinal direction and the projection of the [001] on specimen surface, and
ß angle; the tilt of the [001] out of the specimen surface

A component made of metallic composite material having high corrosion resistance and scale resistance. The metallic composite material contains as a core material an uncoated hardenable steel on which surface a corrosion resistance and scaling resistance layer is provided using heat resistant stainless steel, and has a yield strength Rp.sub.0,2 of at least 1000 MPa and a tensile strength R.sub.m of at least 1500 MPa for the core material and a critical scaling resistance temperature in air for the layer material is at least 850° C.

A hot-rolled steel plate has a predetermined chemical composition and a microstructure. In the microstructure, in a plate thickness 1/2 position, an area fraction of martensite is less than 3%, an area fraction of bainitic ferrite is 95% or greater, the bainitic ferrite has an average grain diameter of 6.0 m or less, an amount of Nb precipitated as Nb carbonitride is 0.025 mass % or greater, and an amount of Nb precipitated as Nb carbonitride having a grain diameter of 20 nm or greater constitutes 50% or greater of a total mass of the Nb precipitated as Nb carbonitride. The hot-rolled steel plate has a tensile strength of 640 MPa or greater, a yield ratio of 85% or less, a Charpy impact absorbed energy at 40 C. of 300 J or greater, and a percent ductile fracture (SA value) of 85% or greater as determined by a DWTT test at 40 C.

There are provided a method for producing a non-oriented electrical steel sheet, a method for manufacturing a motor core from such a steel sheet, and a motor core. In the production of a non-oriented electrical steel sheet by subjecting a steel slab containing given amounts of C, Si, Mn, P, S, Al, N, Ti, Nb and V, provided that Si, Al and Mn satisfy Si-2Al-Mn0, to hot rolling, cold rolling, finish annealing and stress relief annealing, conditions of the finish annealing and stress relief annealing are adjusted such that a yield stress after the finish annealing is not less than 400 MPa and iron loss W.sub.10/400 (W/kg) after the stress relief annealing in relation to a sheet thickness t (mm) satisfies W.sub.10/40010+25t and magnetostriction .sub.o-p (bake) after the stress relief annealing is not more than 5.010.sup.6 and a ratio (.sub.o-p (bake)/.sub.o-p (green)) of magnetostriction .sub.o-p (bake) after the stress relief annealing to magnetostriction .sub.o-p (green) before the stress relief annealing is less than 0.8, whereby a high-strength rotor core and a stator core having excellent magnetic properties after stress relief annealing can be obtained from the same steel material.