Abstract: A method for producing Cu—Sn-containing steel includes a hot heating step of attaching a flux to a surface of a Cu—Sn-containing cast steel in such an amount that the mass per unit area is 50 g/m2 or more and 5000 g/m2 or less, and heating the Cu—Sn-containing cast steel at a temperature of 1000° C. or above and 1400° C. or below, the flux including at least any of B2O3, P2O5, K2O, PbO, Na2O—FeO, Na2O—SiO2, Na2O—TiO2, and Li2O—SiO2 components and being such that the liquid phase ratio at 1000° C. is 10 mass % or more; and a hot working step of hot working the Cu—Sn-containing cast steel.

Abstract: A mold powder which prevents surface defects from occurring on a surface of a cast slab of Al-containing hypo-peritectic steel having Al: 0.2% to 2.0%, by mass %, and, in a hypo-peritectic region, C: 0.08% to 0.17%, by mass %. The mold powder includes CaO, SiO2, Na2O, Li2O, F, and C. Li2O/Na2O is 0.6 or more, 1.0+0.05×Al?CaO/SiO2?2.0?0.35×Al, 10<Li2O+0.5×Na2O+0.8×F<20, and 1.00?F/(Li2O+0.5×Na2O+1.46)?1.24 are satisfied where Al is content by mass % of molten steel, and respective contents of the remaining elements are by mass %. A viscosity of the mold powder at 1,300° C. is in a range of 0.05 Pa·s to 0.20 Pa·s, and a crystallization temperature of the mold powder is in a range of 1,100° C. to 1,250° C.

Abstract: A method of evaluating central segregation in steel with excellent correlation with HIC susceptibility is provided. A method of evaluating central segregation in steel includes: taking a sample from a steel, the sample having a cross section including a central segregation area; measuring an area ratio of an inclusion containing a segregation metal element in a region to be measured including the central segregation area in the cross section; and evaluating central segregation in the steel based on the area ratio measured.

Abstract: A hot-pressed member has a predetermined chemical composition. In the hot-pressed member, a steel sheet has a microstructure in which a prior austenite average grain diameter is 8 ?m or less, and martensite is present in a volume fraction of 95% or greater in a region within 30 ?m of a surface; a Ni diffusion region having a thickness of 0.5 ?m or greater exists in a surface layer; a standard deviation of Vickers hardness values is 35 or less; Mndif (mass %) in a sheet thickness direction ?0.20, where Mndif (mass %) is a degree of Mn segregation; and a tensile strength is 1780 MPa or greater.

Abstract: A method for producing an ultra-low carbon steel product having a carbon concentration of 0.005% by mass or less includes, at least, a step of adjusting a carbon concentration of molten iron to obtain molten steel, a step of casting the molten steel into a slab, and a step of hot rolling the slab to obtain a hot-rolled steel sheet, in which the method further includes a width reduction step of performing width reduction on the slab with a reduction amount which is predetermined in accordance with the slab width in a direction orthogonal to the rolling direction of the slab.

Abstract: A mold powder which prevents surface defects from occurring on a surface of a cast slab of Al-containing hypo-peritectic steel having Al: 0.2% to 2.0%, by mass %, and, in a hypo-peritectic region, C: 0.08% to 0.17%, by mass %. The mold powder includes CaO, SiO2, Na2O, Li2O, F, and C. Li2O/Na2O is 0.6 or more, 1.0+0.05×Al?CaO/SiO2?2.0?0.35×Al, 10<Li2O+0.5×Na2O+0.8×F<20, and 1.00?F/(Li2O+0.5×Na2O+1.46)?1.24 are satisfied where Al is content by mass % of molten steel, and respective contents of the remaining elements are by mass %. A viscosity of the mold powder at 1,300° C. is in a range of 0.05 Pa·s to 0.20 Pa·s, and a crystallization temperature of the mold powder is in a range of 1,100° C. to 1,250° C.

Abstract: A hot-pressed member has a predetermined chemical composition. In the hot-pressed member, a steel sheet has a microstructure in which a prior austenite average grain diameter is 8 ?m or less, and martensite is present in a volume fraction of 95% or greater in a region within 30 ?m of a surface; a Ni diffusion region having a thickness of 0.5 ?m or greater exists in a surface layer; a standard deviation of Vickers hardness values is 35 or less; Mndif (mass %) in a sheet thickness direction ?0.20, where Mndif (mass %) is a degree of Mn segregation; and a tensile strength is 1780 MPa or greater.

Abstract: A high strength steel sheet having excellent surface quality and formability with a tensile strength of 980 MPa or more and a TS-El balance of 30000 MPa % or more is provided. A high strength steel sheet comprises: a chemical composition containing C: 0.08% to 0.30%, Si: 2.0% or less, Mn: more than 3.0% and 10.0% or less, P: 0.05% or less, S: 0.01% or less, Al: 1.5% or less, Ti: 0.010% to 0.300%, and N: 0.0020% to 0.0100% in a range satisfying 1.1?(Ti+Mn1/2/400)/(0.01+5N)?6.0; and a microstructure including a retained austenite phase and a ferrite phase, wherein a ratio ?Mn/?Mn of an average Mn concentration (?Mn) of the retained austenite phase to an average Mn concentration (?Mn) of the ferrite phase is 1.5 or more.

Abstract: A high strength steel sheet having excellent surface quality and formability with a tensile strength of 980 MPa or more and a TS-El balance of 30000 MPa % or more is provided. A high strength steel sheet comprises: a chemical composition containing C: 0.08% to 0.30%, Si: 2.0% or less, Mn: more than 3.0% and 10.0% or less, P: 0.05% or less, S: 0.01% or less, Al: 1.5% or less, Ti: 0.010% to 0.300%, and N: 0.0020% to 0.0100% in a range satisfying 1.1?(Ti+Mn1/2/400)/(0.01+5N)?6.0; and a microstructure including a retained austenite phase and a ferrite phase, wherein a ratio ?Mn/?Mn of an average Mn concentration (?Mn) of the retained austenite phase to an average Mn concentration (?Mn) of the ferrite phase is 1.5 or more.