Abstract: A hot-rolled steel sheet according to the present invention includes, as a chemical composition, by mass %: C: 0.030% to 0.250%; Si: 0.05% to 2.50%; Mn: 1.00% to 4.00%; Sol. Al: 0.001% to 2.000%; P: 0.100% or less; S: 0.0200% or less; N: 0.01000% or less; Ti: 0% to 0.20%; Nb: 0% to 0.20; B: 0% to 0.010%; V: 0% to 1.0%; Cr: 0% to 1.0%; Mo: 0% to 1.0%; Cu: 0% to 1.0%; Co: 0% to 1.0%; W: 0% to 1.0%; Ni: 0% to 1.0%; Ca: 0% to 0.01%; Mg: 0% to 0.01%; REM: 0% to 0.01%; Zr: 0% to 0.01%; and a remainder consisting of Fe and impurities, in which an area ratio of a scale damage portion, which is a portion lower than an average height of a surface of the steel sheet by 10 ?m or more, is 20% or less, and a tensile strength of the hot-rolled steel sheet is 780 MPa or more.

Abstract: High strength steel sheet having a tensile strength of 800 MPa or more comprising a middle part in sheet thickness and a soft surface layer arranged at one side or both sides of the middle part in sheet thickness, wherein each soft surface layer has a thickness of more than 10 ?m and 30% or less of the sheet thickness, the soft surface layer has an average Vickers hardness of 0.60 time or less the average Vickers hardness of the sheet thickness ½ position, and the soft surface layer has a nano-hardness standard deviation of 0.8 or less is provided.

Abstract: A hot-rolled steel sheet according to the present invention has a predetermined chemical composition, in which, when a height profile of a surface of the hot-rolled steel sheet is measured in each of five measurement ranges in a rolling direction and a direction perpendicular to the rolling direction, a distance in a height direction from an average height position which is an average of a height position of a point having a highest height position and a height position of a recessed part which is a point having a lowest height position to the recessed part is indicated as R1 (?m) in each of the height profiles, and an average of heights of two measurement points away from the recessed part in the rolling direction or the direction perpendicular to the rolling direction by 5 ?m is indicated as R2 (?m), an average value of radii of curvature r represented by Expression (1) is 10 ?m or more, and a tensile strength of the hot-rolled steel sheet is 500 MPa or more. r=(25+|R2?R1|2)/2|R2?R1| . . .

Abstract: A hot-rolled steel sheet includes, as chemical composition, C, Si, Mn, and sol.Al. In the hot-rolled steel sheet, a sum of an average of pole densities in a crystal orientation group consisting of {211}<111> to {111}<112> and a pole density in a crystal orientation of {110}<001> is 0.5 to 6.0 in the surface region, and the tensile strength is 780 to 1370 MPa.

Abstract: A steel sheet for hot stamping includes a steel structure represented by an area fraction of bainite, fresh martensite and tempered martensite: 80% or more in total, and a product of a number density (pieces/?m2) of carbides and a proportion of carbides precipitated into prior austenite grains in carbides: 0.50 or more.

Abstract: A steel sheet including an inner layer and a hard layer at one or both surfaces of the inner layer wherein the hard layer and the inner layer have predetermined compositions, each hard layer has a thickness of 20 ?m or more and ? of the total sheet thickness or less, the hard layer has an average micro-Vickers hardness of 400 HV or more and less than 700 HV, the hard layer has an N amount of 0.02% or less, the inner layer has an average micro-Vickers hardness of 80 HV or more and less than 400 HV, the inner layer has a carbide volume ratio of less than 2.00%, and the hard layer has a nanohardness standard deviation of 2.00 or less is provided.

Abstract: There is provided a steel sheet including an inner layer and a hard layer formed on one or both surfaces of the inner layer, wherein each content of C and Mn in the hard layer is more than each content of C and Mn in the inner layer, a thickness of the hard layer is 20 ?m or more and a total of the thickness of the hard layer is ? or less of the entire sheet thickness, an average micro-Vickers hardness of the hard layer is 400 HV or more and less than 800 HV, an average micro-Vickers hardness of the inner layer is 350 HV or more and is 50 HV or more smaller than a hardness of the hard layer, and a screw dislocation density of the inner layer is 2.0×1013 m/m3 or more.

Abstract: High strength steel sheet having a tensile strength of 800 MPa or more comprising a middle part in sheet thickness and a soft surface layer arranged at one side or both sides of the middle part in sheet thickness, wherein each soft surface layer has a thickness of more than 10 ?m and 30% or less of the sheet thickness, the soft surface layer has an average Vickers hardness of 0.60 time or less the average Vickers hardness of the sheet thickness ½ position, and the soft surface layer has a nano-hardness standard deviation of 0.8 or less is provided.

Abstract: The present invention provides a hot stamped body excellent in bendability, ductility, impact resistance, and hydrogen embrittlement resistance and small in scattering in hardness. The hot stamped body according to the present invention is provided with a middle part in sheet thickness and a softened layer arranged at both sides or one side of the middle part in sheet thickness.

Abstract: The present invention, in consideration of the problems in the prior art, provides a hot stamped body simultaneously achieving the high bendability and high ductility for realizing impact resistance and also hydrogen embrittlement resistance and kept down in scattering in hardness. The hot stamped body according to the present invention is provided with a middle part in sheet thickness and a softened layer arranged at both sides or one side of the middle part in sheet thickness.

Abstract: A hot-dip galvanized steel sheet includes: a predetermined chemical composition; and a steel structure represented by: in terms of area ratio, polygonal ferrite: 10% or less; upper bainite: 20% or less; retained austenite: 5% or less; and martensite: 70% or more, in which: martensite having Fe carbides at a number density of 1×106/mm2 or more is contained by 50% or more, in terms of area ratio, with respect to the entire amount of martensite; and the steel structure has an average effective crystal grain diameter of 5.0 ?m or less.

Abstract: A steel sheet for hot stamping includes a steel structure represented by an area fraction of bainite, fresh martensite and tempered martensite: 80% or more in total, and a product of a number density (pieces/?m2) of carbides and a proportion of carbides precipitated into prior austenite grains in carbides: 0.50 or more.

Abstract: A high strength steel sheet containing a large amount of Mn which has bendability suitable as a material for auto part use and a method of producing the same are provided. A high strength steel sheet comprising a center part in a sheet thickness and a softened surface layer part on one surface or both surfaces of the center part in the sheet thickness, characterized in that, the center part in the sheet thickness has an average Mn concentration of greater than 4.0 mass % and less than 10.0 mass %, each softened surface layer part has a thickness of 0.1% to 30% of the sheet thickness, and the softened surface layer part has an average Mn concentration of 2.5 mass % or less, a recrystallization rate of 90% or more, and recrystallized structures with an average crystal grain size of 0.1 ?m or more and 40 ?m or less.

Abstract: Steel sheet low in cost and improved in fatigue characteristics without causing a drop in the cold formability, characterized in that it comprises an inner layer and a hard layer on one or both surfaces of the inner layer, a thickness of the hard layer is 20 ?m or more and 40% or less of the thickness of the steel sheet, an average micro-Vickers hardness of the hard layer is 240 HV or more and less than 400 HV, an amount of C of the hard layer is 0.4 mass % or less, an amount of N is 0.02 mass % or less, a variation of hardness measured by a nanoindenter at a depth of 10 from the surface of the hard layer is a standard deviation of 2.0 or less, an average micro-Vickers hardness of the inner layer is 80 HV or more and less than 400 HV, a volume rate of carbides contained in the inner layer is less than 2.00%, and the average micro-Vickers hardness of the hard layer is 1.05 times or more the average micro-Vickers hardness of the inner layer.

Abstract: A steel sheet including an inner layer and a hard layer at one or both surfaces of the inner layer wherein the hard layer and the inner layer have predetermined compositions, each hard layer has a thickness of 20 ?m or more and ? of the total sheet thickness or less, the hard layer has an average micro-Vickers hardness of 400 HV or more and less than 700 HV, the hard layer has an N amount of 0.02% or less, the inner layer has an average micro-Vickers hardness of 80 HV or more and less than 400 HV, the inner layer has a carbide volume ratio of less than 2.00%, and the hard layer has a nanohardness standard deviation of 2.00 or less is provided.

Abstract: There is provided a hot stamped body including a middle part in sheet thickness and a surface layer arranged at both sides or one side of the middle part in sheet thickness, further including an intermediate layer formed between the middle part in sheet thickness and each surface layer so as to adjoin them, wherein the middle part in sheet thickness has a predetermined composition, the middle part in sheet thickness has a hardness of 500 Hv or more and 800 Hv or less, the surface layer has a hardness change ?H1 in the sheet thickness direction of 100 Hv or more and less than 200 Hv, and the intermediate layer has a hardness change ?H2 in the sheet thickness direction of 10 Hv or more and less than 50 Hv.

Abstract: High strength steel sheet having a tensile strength of 800 MPa or more comprising a middle part in sheet thickness and a soft surface layer arranged at one side or both sides of the middle part in sheet thickness, wherein each soft surface layer has a thickness of more than 10 ?M and 30% or less of the sheet thickness, the soft surface layer has an average Vickers hardness of more than 0.60 time and 0.90 time or less the average Vickers hardness of the sheet thickness 1/2 position, and the soft surface layer has a nano-hardness standard deviation of 0.8 or less is provided.

Abstract: There is provided a hot stamped body including a middle part in sheet thickness and a surface layer arranged at both sides or one side of the middle part in sheet thickness, further including an intermediate layer formed between the middle part in sheet thickness and each surface layer so as to adjoin them, wherein the middle part in sheet thickness has a predetermined composition, the middle part in sheet thickness has a hardness of 500 Hv or more and 800 Hv or less, the surface layer has a hardness change ?H1 in the sheet thickness direction of 10 Hv or more and less than 200 Hv, and the intermediate layer has a hardness change ?H2 in the sheet thickness direction of 50 Hv or more and less than 200 Hv.

Abstract: A blank material is formed from a steel sheet, a first quenching of the blank material is performed, and a second quenching of the blank material is performed after the first quenching. When the first quenching is performed, the blank material is heated to a first temperature of not lower than (Ac3 point—50)° C. nor higher than 1200° C. at an average heating rate of 2° C./sec or more, and the blank material is cooled from the first temperature to a second temperature of 250° C. or lower. When the second quenching is performed, the blank material is heated from the second temperature to a third temperature of not lower than (Ac3 point—50)° C. nor higher than 1200° C. at an average heating rate of 2° C./sec or more, and the blank material is cooled from the third temperature to a fourth temperature of 250° C. or lower. Forming of the blank material is performed in the first quenching or the second quenching or both of the above.

Abstract: A hot-dip galvanized steel sheet includes: a predetermined chemical composition; and a steel structure represented by: in terms of area ratio, polygonal ferrite: 10% or less; upper bainite: 20% or less; retained austenite: 5% or less; and martensite: 70% or more, in which: martensite having Fe carbides at a number density of 1×106/mm2 or more is contained by 50% or more, in terms of area ratio, with respect to the entire amount of martensite; and the steel structure has an average effective crystal grain diameter of 5.0 ?m or less.