Abstract: A steel member according to an aspect of the present invention has a predetermined chemical composition, in which a metallographic structure includes, by a volume %, 60.0% to 85.0% of martensite, 10.0% to 30.0% of bainite, 5.0% to 15.0% of residual austenite, and 0% to 4.0% of a remainder in microstructure. A length of a maximum minor axis of the residual austenite is 30 nm or longer. A number density of a carbide which exist in the steel member and has a circle equivalent diameter of 0.1 ?m or more and an aspect ratio of 2.5 or less is 4.0×103 pieces/mm2 or less.

Abstract: A steel sheet has a predetermined chemical composition containing, in mass %, C: more than 0.18% and less than 0.30%, Mn: more than 2.50% and 4.00% or less, and other elements. The steel micro-structure at a position at a depth of ¼ of the sheet thickness from the surface in an L cross section of the steel sheet is, in area %, tempered martensite: 25 to 90%, ferrite: 5% or less, retained austenite: 10 to 50%, and bainite: 5% or less. At a position at a depth of ¼ of the sheet thickness from the surface of the L cross section, the proportion of a total area of retained austenite grains having an area of 1 ?m2 or more and having a grain shape circularity of 0.1 or more is less than 50% with respect to the entire area of retained austenite. The steel sheet satisfies the formula CMn?/CMn??1.2.

Abstract: A cold-rolled steel according to the present invention has a predetermined chemical composition, satisfies (5×[Si]+[Mn])/[C]>10 when [C] is the amount of C by mass %, [Si] is the amount of Si by mass %, and [Mn] is the amount of Mn by mass %, includes 40% to 95% ferrite and 5% to 60% martensite in area fraction, and optionally further includes 10% or less pearlite in area fraction, 5% or less retained austenite in volume fraction, and less than 40% bainite in area fraction. The total of the area fraction of ferrite and the area fraction of martensite is 60% or more, the hardness of martensite measured with a nanoindenter satisfies H2/H1<1.10 and ?HM<20.

Abstract: Grain-oriented electrical steel sheet excellent in coating adhesion and magnetic properties is provided. The method for manufacturing grain-oriented electrical steel sheet excellent in coating adhesion and magnetic properties includes a process of heating to 1280° C.

Abstract: A high-strength steel sheet having a microstructure represented by, in area %, martensite: 5% or more; ferrite: 20% or more; and pearlite: 5% or less. A ratio of the number of bulging type martensite grains to the number of martensite grains on grain boundary triple points of a matrix is 70% or more, wherein: the bulging type martensite grain is on one of the grain boundary triple points of the matrix; and at least one of grain boundaries of the bulging type martensite grain, the grain boundaries connecting two adjacent grain boundary triple points of the bulging type martensite grain and grains of the matrix, has a convex curvature to an outer side with respect to line segments connecting the two adjacent grain boundary triple points. An area ratio VM/A0 is 1.0 or more.

Abstract: A steel member according to an aspect of the present invention has a predetermined chemical composition, in which a metallographic structure includes, by a volume %, 60.0% to 85.0% of martensite, 10.0% to 30.0% of bainite, 5.0% to 15.0% of residual austenite, and 0% to 4.0% of a remainder in microstructure. A length of a maximum minor axis of the residual austenite is 30 nm or longer. A number density of a carbide which exist in the steel member and has a circle equivalent diameter of 0.1 ?m or more and an aspect ratio of 2.5 or less is 4.0×103 pieces/mm2 or less.

Abstract: A heat-treated steel sheet member having a chemical including, by mass %: C: 0.05 to 0.50%; Si: 0.50 to 5.0%; Mn: 1.5 to 4.0%; P: 0.05% or less; S: 0.05% or less; N: 0.01% or less; Ti: 0.01 to 0.10%; B: 0.0005 to 0.010%; Cr: optional amounts of Ni, Cu, Mo, V, Ca, Al, Nb, and REM, with the balance: Fe and impurities. The steel sheet member has a microstructure comprising: mainly martensite; and retained austenite of which a volume ratio is 5.0% or higher, a number density of retained carbide in the steel sheet member having circle-equivalent diameters of 0.1 mm or larger is 4.0×103/mm2 or lower, [(log fg0?log fg(0.02))/0.02<20.0] is satisfied when mechanical properties are measured using a sheet specimen specified in ASTM E8, a tensile strength is 1.4 GPa or higher, and a total elongation is 8.0% or higher.

Abstract: A steel sheet for heat treatment having a chemical composition including, by mass %: C: 0.05 to 0.50%; Si: 0.50 to 5.0%; Mn; 1.5 to 4.0%; P: 0.05% or less; S: 0.05% or less; N: 0.01% or less; Ti: 0.01 to 0.10%; B: 0.0005 to 0.010%; Cr: 0 to 1.0%; Ni: 0 to 2.0%; Cu: 0 to 1.0%; Mo: 0 to 1.0%; V: 0 to 1.0%; Ca: 0 to 0.01%; Al: 0 to 1.0%; Nb: 0 to 1.0%; REM: 0 to 0.1%; and the balance: Fe and impurities, wherein a maximum height roughness Rz on a surface of the steel sheet is 3.0 to 10.0 ?m, and a number density of carbide being present in the steel sheet and having circle-equivalent diameters of 0.1 ?m or larger is 8.0×103/mm2 or lower.

Abstract: A cold-rolled steel according to the present invention has a predetermined chemical composition, satisfies (5×[Si]+[Mn])/[C]>10 when [C] is the amount of C by mass %, [Si] is the amount of Si by mass %, and [Mn] is the amount of Mn by mass %, includes 40% to 95% ferrite and 5% to 60% martensite in area fraction, and optionally further includes 10% or less pearlite in area fraction, 5% or less retained austenite in volume fraction, and less than 40% bainite in area fraction. The total of the area fraction of ferrite and the area fraction of martensite is 60% or more, the hardness of martensite measured with a nanoindenter satisfies H2/H1<1.10 and ?HM<20.

Abstract: A heat-treated steel sheet member having a composition including, by mass %: C: 0.05 to 0.50%; Si: 0.50 to 5.0%; Mn: 1.5 to 4.0%; P: 0.05% or less; S: 0.05% or less; N: 0.01% or less; Ti: 0.01 to 0.10%; B: 0.0005 to 0.010%; Cr: 0 to 1.0%; Ni: 0 to 2.0%; Cu; 0 to 1.0%; Mo: 0 to 1.0%; V: 0 to 1.0%; Ca: 0 to 0.01%; Al: 0 to 1.0%; Nb: 0 to 1.0%; REM: 0 to 0.1%; and the balance: Fe and impurities. The steel sheet member has a microstructure comprising mainly martensite and retained austenite of which a volume ratio is 0.2 to 1.0%, a number density of retained carbide in the steel sheet member having circle-equivalent diameters of 0.1 mm or larger is 4.0×103/mm2 or lower, a tensile strength is 1.4 GPa or higher, and a yield ratio is 0.65 or higher.

Abstract: A hot-stamped steel according to the present invention has a predetermined chemical composition, satisfies (5×[Si]+[Mn])/[C]>10 when [C] is the amount of C by mass %, [Si] is the amount of Si by mass %, and [Mn] is the amount of Mn by mass %, includes 40% to 95% ferrite and 5% to 60% martensite in area fraction, and optionally further includes 10% or less pearlite in area fraction, 5% or less retained austenite in volume fraction, and less than 40% bainite in area fraction. The total of the area fraction of ferrite and the area fraction of martensite is 60% or more, the hardness of martensite measured with a nanoindenter satisfies H2/H1<1.10 and ?HM<20, and TS×? which is product of tensile strength TS and hole expansion ratio ? is 50000 MPa·% or more.

Abstract: This high-strength cold-rolled steel sheet contains, in mass %, C: 0.02% to 0.20%; Si: 0.001% to 2.5%; Mn: 0.01% to 4.0%; P: 0.001% to 0.15%; S: 0.0005% to 0.03%; Al: 0.001% to 2.0%; N: 0.0005% to 0.01%; and O: 0.0005% to 0.01%; in which Si+Al is limited to less than 1.0%, and a balance being composed of iron and inevitable impurities, in which an area ratio of bainite in a metal structure is 95% or more, at a sheet thickness center portion being a range of ? to ? in sheet thickness from the surface of the steel sheet, an average value of pole densities of the {100}<011> to {223}<110> orientation group is 4.0 or less, and a pole density of the {332}<113> crystal orientation is 5.0 or less, and a mean volume diameter of crystal grains in the metal structure is 7 ?m or less.

Abstract: A heat-treated steel sheet member having a chemical including, by mass %: C: 0.05 to 0.50%; Si: 0.50 to 5.0%; Mn: 1.5 to 4.0%; P: 0.05% or less; S: 0.05% or less; N: 0.01% or less; Ti: 0.01 to 0.10%; B: 0.0005 to 0.010%; Cr: optional amounts of Ni, Cu, Mo, V, Ca, Al, Nb, and REM, with the balance: Fe and impurities. The steel sheet member has a microstructure comprising: mainly martensite; and retained austenite of which a volume ratio is 5.0% or higher, a number density of retained carbide in the steel sheet member having circle-equivalent diameters of 0.1 mm or larger is 4.0×103/mm2 or lower, [(log fg0?log fg(0.02))/0.02<20.0] is satisfied when mechanical properties are measured using a sheet specimen specified in ASTM E8, a tensile strength is 1.4 GPa or higher, and a total elongation is 8.0% or higher.

Abstract: This high-strength hot-rolled steel sheet having excellent local deformability contains, in mass %, C: 0.07% to 0.20%; Si: 0.001% to 2.5%; Mn: 0.01% to 4.0%; P: 0.001% to 0.15%; S: 0.0005% to 0.03%; Al: 0.001% to 2.0%; N: 0.0005% to 0.01%; and O: 0.0005% to 0.01%; and a balance being composed of iron and inevitable impurities, in which an area ratio of bainite in a metal structure is 95% or more, at a sheet thickness center portion being a range of ? to ? in sheet thickness from the surface of the steel sheet, an average value of pole densities of the {100}<011> to {223}<110> orientation group is 4.0 or less, and a pole density of the {332}<113> crystal orientation is 5.0 or less, and a mean volume diameter of crystal grains in the metal structure is 10 ?m or less.

Abstract: A high-strength steel sheet includes a specific chemical composition, and a microstructure represented by, in area %, martensite: 5% or more; ferrite: 20% or more; and perlite: 5% or less. An average diameter of martensite grain is 4 ?m or less in equivalent circle diameter. A ratio of the number of bulging type martensite grains to the number of martensite grains on grain boundary triple points of a matrix is 70% or more, wherein: the bulging type martensite grain is on one of the grain boundary triple points of the matrix; and at least one of grain boundaries of the bulging type martensite grain, the grain boundaries connecting two adjacent grain boundary triple points of the bulging type martensite grain and grains of the matrix, has a convex curvature to an outer side with respect to line segments connecting the two adjacent grain boundary triple points. An area ratio represented by VM/A0 is 1.

Abstract: A heat-treated steel sheet member having a composition including, by mass %: C: 0.05 to 0.50%; Si: 0.50 to 5.0%; Mn: 1.5 to 4.0%; P: 0.05% or less; S: 0.05% or less; N: 0.01% or less; Ti: 0.01 to 0.10%; B: 0.0005 to 0.010%; Cr: 0 to 1.0%; Ni: 0 to 2.0%; Cu; 0 to 1.0%; Mo: 0 to 1.0%; V: 0 to 1.0%; Ca: 0 to 0.01%; Al: 0 to 1.0%; Nb: 0 to 1.0%; REM: 0 to 0.1%; and the balance: Fe and impurities. The steel sheet member has a microstructure comprising mainly martensite and retained austenite of which a volume ratio is 0.2 to 1.0%, a number density of retained carbide in the steel sheet member having circle-equivalent diameters of 0.1 mm or larger is 4.0×103/mm2 or lower, a tensile strength is 1.4 GPa or higher, and a yield ratio is 0.65 or higher.

Abstract: A steel sheet for heat treatment having a chemical composition including, by mass %: C: 0.05 to 0.50%; Si: 0.50 to 5.0%; Mn; 1.5 to 4.0%; P: 0.05% or less; S: 0.05% or less; N: 0.01% or less; Ti: 0.01 to 0.10%; B: 0.0005 to 0.010%; Cr: 0 to 1.0%; Ni: 0 to 2.0%; Cu: 0 to 1.0%; Mo: 0 to 1.0%; V: 0 to 1.0%; Ca: 0 to 0.01%; Al: 0 to 1.0%; Nb: 0 to 1.0%; REM: 0 to 0.1%; and the balance: Fe and impurities, wherein a maximum height roughness Rz on a surface of the steel sheet is 3.0 to 10.0 ?m, and a number density of carbide being present in the steel sheet and having circle-equivalent diameters of 0.1 ?m or larger is 8.0×103/mm2 or lower.

Abstract: A steel sheet for hot stamping includes a composition including at least, in mass %, C: 0.100% to 0.600%, Si: 0.50% to 3.00%, Mn: 1.20% to 4.00%, Ti: 0.005% to 0.100%, B: 0.0005% to 0.0100%, P: 0.100% or less, S: 0.0001% to 0.0100%, Al: 0.005% to 1.000%, and N: 0.0100% or less, with a balance of Fe and impurities, surface roughness of the steel sheet satisfies Rz>2.5 ?m, and 50 mg/m2 to 1500 mg/m2 of coating oil is applied to a surface.

Abstract: The present invention provides a high-strength steel sheet including: C: 0.03 to 0.25 mass %, Si: 0.1 to 2.0 mass %, Mn: 0.5 to 3.0 mass %, P: not more than 0.05 mass %, T.O: not more than 0.0050 mass %, S: 0.0001 to 0.01 mass %, N: 0.0005 to 0.01 mass %, acid-soluble Al: more than 0.01 mass %, Ca: 0.0005 to 0.0050 mass %, and a total of at least one element of Ce, La, Nd, and Pr: 0.001 to 0.01 mass %, with a balance including iron and inevitable impurities, in which the steel sheet contains a chemical component on a basis of mass that satisfies 0.7<100×([Ce]+[La]+[Nd]+[Pr])/[acid-soluble Al]?70 and 0.

Abstract: This high-strength cold-rolled steel sheet contains, in mass %, C: 0.02% to 0.20%; Si: 0.001% to 2.5%; Mn: 0.01% to 4.0%; P: 0.001% to 0.15%; S: 0.0005% to 0.03%; Al: 0.001% to 2.0%; N: 0.0005% to 0.01%; and O: 0.0005% to 0.01%; in which Si+Al is limited to less than 1.0%, and a balance being composed of iron and inevitable impurities, in which an area ratio of bainite in a metal structure is 95% or more, at a sheet thickness center portion being a range of ? to ? in sheet thickness from the surface of the steel sheet, an average value of pole densities of the {100}<011> to {223}<110> orientation group is 4.0 or less, and a pole density of the {332}<113> crystal orientation is 5.0 or less, and a mean volume diameter of crystal grains in the metal structure is 7 ?m or less.