Abstract: There is provided a steel sheet having a chemical composition comprising, in mass %, C: 0.05 to 0.25%, Si: 0.2 to 2.0%, Mn: 1.2 to 3.0%, P: 0.030% or less, S: 0.050% or less, Al: 0.01 to 0.55%, N: 0.0100% or less, and Ti: 0.010 to 0.250%, with the balance: Fe and impurities, wherein a random intensity ratio of a texture in a near-surface portion of the steel sheet is 8.0 or less, and a minimum angle formed between a maximum strength orientation in a {110} pole figure of the texture and a normal direction of a rolled surface of the steel sheet is 10° or less.

Abstract: A high-strength steel sheet includes a chemical composition including: by mass %, C: 0.080 to 0.500%, Si: 2.50% or less, Mn: 0.50 to 5.00%, P: 0.100% or less, S: 0.0100% or less, Al: 0.001 to 2.500%, N: 0.0150% or less, O: 0.0050% or less, and the balance: Fe and inevitable impurities. The high-strength steel sheet satisfying a predetermined formula has a microstructure in a region from ?t to ?t from a steel sheet surface. The microstructure includes: by volume %, 20% or more of acicular ferrite, 20% or more of an island-shaped hard structure including residual austenite, 2% to 25% of residual austenite, and 20% or less of aggregated ferrite.

Abstract: This steel sheet has a predetermined chemical composition, has a microstructure in which a number density of alloy carbides present at grain boundaries and having a major axis of 10 to 100 nm is 1.0×108 to 1.0×1011/cm2 and a number density of alloy carbides present in grains and having a major axis of 10 nm or less is 1.0×1016 to 1.0×1019/cm3, and has a tensile strength of 1,030 MPa or more.

Abstract: This steel sheet for gas soft nitriding has a predetermined chemical composition and metallographic structure, in which, when a sheet thickness is indicated as t, a sheet width, which is a width in a direction perpendicular to a rolling direction, is indicated as w, and effective grain sizes are measured at seven positions of w/8, w/4, 3w/8, w/2, 5w/8, 3w/4, and 7w/8 in a width direction from an end portion in the width direction at a t/4 depth position from a surface, an average effective grain size, which is an average of the effective grain sizes at the seven positions, is 8.0 to 35.0 ?m, and an effective grain size difference, which is a difference between a maximum value and a minimum value among the effective grain sizes at the seven positions, is 10.0 ?m or less.

Abstract: This steel sheet has predetermined chemical composition and microstructure, in a crystal orientation distribution function of a texture at a sheet thickness ¼ position, when A/B that is a ratio of a maximum value A of pole densities at ?=20° to 60° and ?1=30° to 90° in a cross section of ?2=45° to a maximum value B of pole densities at ?=120° to 60° and ?1=30° to 90° in the cross section of ?2=45° is 1.50 or less, a total of the maximum value A and the maximum value B is 6.00 or less, and a tensile strength is 1030 MPa or more.

Abstract: Provided is a hot rolled steel sheet having a tensile strength of 780 MPa or more, a sheet thickness of 1.2 to 4.0 mm, and a sheet width of 750 mm or more, and satisfying -15?(?W 1 +?W2)/2-?C ?15 (where ?W1 and ?W2 respectively indicate hole expansion ratios (%) at ? positions of the sheet width from one end of the hot rolled steel sheet in a sheet width direction perpendicular to a rolling direction and the other end at an opposite side, and ?C indicates a hole expansion ratio (%) of a sheet width center part).

Abstract: This steel sheet has a predetermined chemical composition, in which a steel structure of an inside of the steel sheet contains, by volume fraction, soft ferrite: 0% to 30%, retained austenite: 3% to 40%, fresh martensite: 0% to 30%, a sum of pearlite and cementite: 0% to 10%, and a remainder includes hard ferrite, a number proportion of the retained austenite having an aspect ratio of 2.0 or more in the total retained austenite is 50% or more, a soft layer having a thickness of 1 to 100 ?m from a surface in a sheet thickness direction is present, in ferrite contained in the soft layer, a volume fraction of grains having an aspect ratio of 3.0 or more is 50% or more, a volume fraction of retained austenite in the soft layer is 80% or less of the volume fraction of the retained austenite in the inside of the steel sheet, and a peak of an emission intensity at a wavelength indicating Si appears in a range of more than 0.2 ?m and 10.0 ?m or less from the surface.

Abstract: This hot-rolled steel sheet has a predetermined chemical composition and predetermined metallographic structure, a ratio between a maximum depth of a region where, on one surface, a rotation angle between a normal line of the one surface and a (011) pole near the normal line of the one surface is 5° or less and a maximum depth of a region where, on the other surface, a rotation angle between a normal line of the other surface and a (011) pole near the normal line of the other surface is 5° or less is 1.00 to 1.20, and a tensile strength is 1150 MPa or more.

Abstract: Adopted are a hot-rolled steel sheet having a predetermined chemical composition, in which a region, where a rotation angle between a normal line of a surface and a (011) pole near the normal line becomes 5° or less, is 0.150 or less from the surface in terms of a sheet thickness direction position standardized by a sheet thickness, and a region, where the rotation angle becomes 20° or more, is 0.250 or more from the surface in terms of the sheet thickness direction position standardized by the sheet thickness and a manufacturing method thereof.

Abstract: A steel sheet includes a predetermined chemical composition and a metal structure represented by, in area fraction, ferrite: 50% to 95%, granular bainite: 5% to 48%, martensite: 2% to 30%, and upper bainite, lower bainite, tempered martensite, retained austenite, and pearlite: 5% or less in total.

Abstract: This hot-rolled steel sheet has a predetermined chemical composition, a microstructure includes 80% or more of tempered martensite by a volume percentage and a remainder consisting of one or more of ferrite, pearlite, bainite, fresh martensite, and residual austenite, the tempered martensite includes 5×109 pieces/mm3 or more of precipitates containing Ti and having an equivalent circle diameter of 5 nm or less per unit volume, in a surface layer region that is a range from a surface to a 1/10 position of a sheet thickness, a sum of an average pole density of a crystal orientation group consisting of {211}<111> to {111}<112> and a pole density in a crystal orientation of {110}<001> is 6.0 or less, and a tensile strength is 980 MPa or more.

Abstract: A steel sheet has a predetermined chemical composition and a metal structure represented by, in area fraction, polygonal ferrite: 40% or less, martensite: 20% or less, bainitic ferrite: 50% to 95%, and retained austenite: 5% to 50%. In area fraction, 80% or more of the bainitic ferrite is composed of bainitic ferrite grains that have an aspect ratio of 0.1 to 1.0 and have a dislocation density of 8×102 (cm/cm3) or less in a region surrounded by a grain boundary with a misorientation angle of 15° or more. In area fraction, 80% or more of the retained austenite is composed of retained austenite grains that have an aspect ratio of 0.1 to 1.0, have a major axis length of 1.0 ?m to 28.0 ?m, and have a minor axis length of 0.1 ?m to 2.8 ?m.

Abstract: A steel sheet wherein a steel structure of an inside of the steel sheet contains, by volume fraction, soft ferrite: 0% to 30%, retained austenite: 3% to 40%, fresh martensite: 0% to 30%, a sum of pearlite and cementite: 0% to 10%, and a remainder including hard ferrite. In the steel sheet, in a ? to ? thickness range, a proportion of retained austenite having an aspect ratio of 2.0 or more is 50% or more, and a soft layer having a thickness of 1 to 100 ?m from a surface in a sheet thickness direction is present. When an emission intensity at a wavelength indicating Si is analyzed in the sheet thickness direction from the surface by a radio-frequency glow discharge analysis method, a peak of the emission intensity appears in a range of more than 0.2 ?m and 5.0 ?m or less from the surface.

Abstract: A steel sheet includes a predetermined chemical composition and a metal structure represented by, in area fraction, ferrite: 50% to 95%, granular bainite: 5% to 48%, tempered martensite: 2% to 30%, upper bainite, lower bainite, fresh martensite, retained austenite, and pearlite: 5% or less in total, and the product of the area fraction of the tempered martensite and a Vickers hardness of the tempered martensite: 800 to 10500.

Abstract: A steel sheet has a chemical composition with a steel structure containing, by volume fraction, soft ferrite: 0-30%, retained austenite: 3-40%, fresh martensite: 0-30%, pearlite and cementite: 0-10%, and a remainder including hard ferrite. In the steel sheet, a number proportion of retained austenite having an aspect ratio of 2.0 or more in the total retained austenite is 50% or more, and a soft layer having a thickness of 1-100 ?m is present. In the soft layer, a volume fraction of ferrite grains having an aspect ratio of less than 3.0 is 50% or more, and a volume fraction of retained austenite is 50% or more of the volume fraction of the retained austenite of the inside of the steel sheet. A peak of an emission intensity at a wavelength indicating Si appears in a range of more than 0.2 ?m to 5 ?m or less from the surface.

Abstract: A high-strength steel sheet includes a predetermined chemical composition, a microstructure contains, by volume percentage, 95% or more of tempered martensite and bainite in total, and a remainder consists of ferrite and pearlite, the microstructure contains 5.0×109 pieces/mm or more of, per unit volume, precipitate having an equivalent circle diameter of 5.0 nm or less and containing Ti, Hvs/Hvc which is a ratio of an average hardness Hvs at a position of a depth of 20 ?m from a surface to an average hardness Hvc at a position of 0.20 to 0.50 mm from the surface is 0.85 or more, a tensile strength is 980 MPa or more, and a product of the tensile strength and elongation is 12,000 MPa×% or more.

Abstract: A high-strength steel sheet includes a chemical composition including: by mass %, C: 0.080 to 0.500%, Si: 2.50% or less, Mn: 0.50 to 5.00%, P: 0.100% or less, S: 0.0100% or less, Al: 0.001 to 2.500%, N: 0.0150% or less, O: 0.0050% or less, and the balance: Fe and inevitable impurities. The high-strength steel sheet satisfying a predetermined formula has a microstructure in a region from ?t to ?t from a steel sheet surface. The microstructure includes: by volume %, 20% or more of acicular ferrite, 20% or more of an island-shaped hard structure including residual austenite, 2% to 25% of residual austenite, and 20% or less of aggregated ferrite.

Abstract: A high-strength steel sheet includes a predetermined chemical composition, a microstructure contains, by volume percentage, 80% or more of tempered martensite, and a remainder consists of ferrite and bainite, the microstructure contains 5.0×1011 pieces/mm3 or more of, per unit volume, precipitate containing Ti and having an equivalent circle diameter of 5.0 nm or less, Hvs/Hvc which is a ratio of an average hardness Hvs at a position of a depth of 20 ?m from a surface to an average hardness Hvc at a position of 0.20 to 0.50 mm from the surface is 0.85 or more, and the tensile strength is 1,180 MPa or more.

Abstract: A high-strength cold-rolled steel sheet which is a steel sheet having a tensile strength of 980 MPa or more has a predetermined chemical component composition, a metallographic microstructure of the steel sheet contains, by area ratio, ferrite and granular bainite: 10% or more and 50% or less in total, one or both of upper bainite and lower bainite: 10% or more and 50% or less in total, tempered martensite: more than 0% and 30% or less, retained austenite: 5% or more, and one or more of pearlite, cementite, and martensite: 0% to 10% in total, and an area ratio of the ferrite with respect to a total area ratio of the ferrite and the granular bainite is 25% or less.

Abstract: A high-strength steel sheet excellent in formability, toughness and weldability has a chemical composition including: by mass %, C: 0.05 to 0.30%, Si: 2.50% or less, Mn: 0.50 to 3.50%, P: 0.100% or less, S: 0.0100% or less, Al: 0.001 to 2.500%, N: 0.0150% or less, O: 0.0050% or less, and the balance consisting of Fe and inevitable impurities. The high-strength steel sheet has a microstructure in a region from ?t (t: sheet thickness) to ?t (t: sheet thickness) from a steel sheet surface, the microstructure including: by volume %, acicular ferrite (3): 20% or more, and martensite (4):10% or more, aggregated ferrite: 20% or less, residual austenite: 2.0% or less, and the martensite satisfies a formula (A), ? i = 1 5 ? ? d i a i 1.5 ? 10.