A method for manufacturing a grain-oriented electrical steel sheet, according to an embodiment of the present invention includes: heating a slab, based on 100 wt % of a total composition thereof, including N at 0.0005 wt % to 0.015 wt %, Ti at 0.0001 wt % to 0.020 wt %, V at 0.0001 wt % to 0.020 wt %, Nb at 0.0001 wt % to 0.020 wt %, B at 0.0001 wt % to 0.020 wt %, and the remaining portion including Fe and other impurities, and then hot rolling it to prepare a hot-rolled steel sheet; annealing the hot-rolled steel sheet; after the hot-rolled steel sheet is annealed, cooling the hot-rolled steel sheet, and then cold rolling it to prepare a cold-rolled steel sheet; decarburization-annealing the cold-rolled steel sheet and then nitriding-annealing it, or simultaneously performing the decarburization-annealing and the nitriding-annealing; and final-annealing the decarburization-annealed and nitriding-annealed steel sheet.

A method for manufacturing a grain-oriented electrical steel sheet, according to an embodiment of the present invention includes: heating a slab, based on 100 wt % of a total composition thereof, including N at 0.0005 wt % to 0.015 wt %, Ti at 0.0001 wt % to 0.020 wt %, V at 0.0001 wt % to 0.020 wt %, Nb at 0.0001 wt % to 0.020 wt %, B at 0.0001 wt % to 0.020 wt %, and the remaining portion including Fe and other impurities, and then hot rolling it to prepare a hot-rolled steel sheet; annealing the hot-rolled steel sheet; after the hot-rolled steel sheet is annealed, cooling the hot-rolled steel sheet, and then cold rolling it to prepare a cold-rolled steel sheet; decarburization-annealing the cold-rolled steel sheet and then nitriding-annealing it, or simultaneously performing the decarburization-annealing and the nitriding-annealing; and final-annealing the decarburization-annealed and nitriding-annealed steel sheet.

A grain-oriented electrical steel sheet that includes a base coating with a high TiN ratio advantageous for the application of tension to the steel sheet and has excellent magnetic property is provided. The grain-oriented electrical steel sheet includes: a base coating having a peak value PTiN of TiN in the form of osbornite, observed in a range of 42°<2θ<43° and a peak value PMg.sub.2SiO.sub.4 of Mg.sub.2SiO.sub.4 in the form of forsterite, observed in a range of 35°<2θ<36° of both more than 0 and satisfying a relationship PTiN≧PMg.sub.2SiO.sub.4, in thin-film X-ray diffraction analysis; and an iron loss W.sub.17/50 of 1.0 W/kg or less.

Provided are a high-strength steel sheet and a method for manufacturing the steel sheet. The high-strength steel sheet has a specified chemical composition with the balance being Fe and inevitable impurities, a microstructure including, in terms of area ratio, 30% or more of a ferrite phase, 40% to 65% of a bainite phase and/or a martensite phase, and 5% or less of cementite, in which, in a surface layer that is a region within 50 μm from the surface in the thickness direction, the area ratio of a ferrite phase is 40% to 55% and the total area ratio of a bainite phase having a grain diameter of more than 5 μm and/or a martensite phase having a grain diameter of more than 5 μm is 20% or less, and a tensile strength is 980 MPa or more.

Provided are a high-strength steel sheet and a method for manufacturing the steel sheet. The high-strength steel sheet has a specified chemical composition with the balance being Fe and inevitable impurities, a microstructure including, in terms of area ratio, 30% or more of a ferrite phase, 40% to 65% of a bainite phase and/or a martensite phase, and 5% or less of cementite, in which, in a surface layer that is a region within 50 μm from the surface in the thickness direction, the area ratio of a ferrite phase is 40% to 55% and the total area ratio of a bainite phase having a grain diameter of more than 5 μm and/or a martensite phase having a grain diameter of more than 5 μm is 20% or less, and a tensile strength is 980 MPa or more.

A high-strength galvanized steel sheet that includes a chemical composition containing, by mass %, C: 0.15% or more and 0.25% or less, Si: 0.50% or more and 2.5% or less, Mn: 2.3% or more and 4.0% or less, P: 0.100% or less, S: 0.02% or less, Al: 0.01% or more and 2.5% or less, and Fe and inevitable impurities. The steel sheet having a microstructure containing, by an area percentage basis, a tempered martensite phase: 30% or more and 73% or less, a ferrite phase: 25% or more and 68% or less, a retained austenite phase: 2% or more and 20% or less, and other phases: 10% or less (including 0%), the other phases containing a martensite phase: 3% or less (including 0%) and a bainitic ferrite phase: less than 5% (including 0%).

Provided are a high-strength steel sheet and a method for manufacturing the steel sheet. The high-strength steel sheet has a specified chemical composition with the balance being Fe and inevitable impurities, a microstructure including, in terms of area ratio, 25% or less of a ferrite phase, 75% or more of a bainite phase and/or a martensite phase, and 5% or less of cementite, in which, in a surface layer that is a region within 50 μm from the surface in the thickness direction, the area ratio of a ferrite phase is 5% to 20%, and a tensile strength is 1180 MPa or more.

A high-strength plated steel sheet sequentially includes an internal oxidized layer, a soft layer containing the internal oxidized layer, and a hard layer including a structure having metallic structure which contains a low-temperature-transformation produced phase in a proportion of 20 to 85% by area of the whole of the metallic structure, polygonal ferrite in a proportion more than 10% by area, and 70% or less by area of the whole of the metallic structure, and-retained austenite in a proportion of 5% or more by volume of the whole of the metallic structure. The high-strength plated steel sheet satisfies the average depth D of the soft layer being 20 μm or more, the average depth d of the internal oxidized layer being 4 μm or more and less than D, and a tensile strength being 980 MPa or more.

A non-oriented electrical steel sheet includes C: 0 to 0.0050 mass %, Si: 0.50 to 2.70 mass %, Mn: 0.10 to 3.00 mass %, Al: 1.00 to 2.70 mass %, and P: 0.050 to 0.100 mass %. In the non-oriented electrical steel sheet, Al/(Si+Al+0.5×Mn) is 0.50 to 0.83, Si+Al/2+Mn/4+5×P is 1.28 to 3.90, Si+Al+0.5×Mn is 4.0 to 7.0, the ratio of the intensity of {100} plane I{100} to the intensity of {111} plane I{111} is 0.50 to 1.40, the specific resistance is 60.0×10.sup.−8 Ω.Math.m or higher at room temperature, and the thickness is 0.05 mm to 0.40 mm.

The invention relates to a hot-rolled steel sheet having a tensile strength of greater than 1200 MPa, an R.sub.e/R.sub.m ratio of less than 0.75 and an elongation at break of greater than 10%, the composition of which contains, the contents being expressed by weight: 0.10%≦C≦0.25%; 1%≦Mn≦3%; Al≧0.015%; Si≦1.985%; Mo≦0.30%; Cr≦1.5%; S≦0.015%; P≦0.1%; Co≦1.5%; B≦0.005%; it being understood that 1%≦Si+Al≦2%; Cr +(3×Mo)≦0.3%, the balance of the composition consisting of iron and inevitable impurities resulting from the smelting, the microstructure of the steel consisting of at least 75% bainite, residual austenite in an amount equal to or greater than 5% and martensite in an amount equal to or greater than 2%.