Abstract: The present invention provides a high-strength steel sheet, which can be used in various applications including automobile parts and exhibits excellent collision safety and excellent moldability, and a method for manufacturing the high-strength steel sheet. The high-strength steel sheet according to an aspect of the present invention satisfies a predetermined chemical composition and has a metallographic microstructure having ferrite fraction: 0% to 10%, MA fraction: 0% to 30%, hard phase other than ferrite and MA: 70% to 100% in terms of area proportion and retained austenite fraction: 5% to 30% in terms of volume proportion, and in the high-strength steel sheet, the skewness of IQ as analyzed by the EBRD method is ?1.2 to ?0.3 when the skewness is expressed by a predetermined relational expression in a case where crystal grains having a bcc structure and a bct structure are regarded as an aggregation of regions having an area of 0.05 ?m2.

Abstract: The present invention provides a high-strength steel sheet, which can be used in various applications including automobile parts and exhibits excellent collision safety and excellent moldability, and a method for manufacturing the high-strength steel sheet. The high-strength steel sheet according to an aspect of the present invention satisfies a predetermined chemical composition and has a metallographic microstructure having ferrite fraction: 0% to 10%, MA fraction: 0% to 30%, hard phase other than ferrite and MA: 70% to 100% in terms of area proportion and retained austenite fraction: 5% to 30% in terms of volume proportion, and in the high-strength steel sheet, the skewness of IQ as analyzed by the EBRD method is ?1.2 to ?0.3 when the skewness is expressed by a predetermined relational expression in a case where crystal grains having a bcc structure and a bct structure are regarded as an aggregation of regions having an area of 0.05 ?m2.

Abstract: Disclosed is a high-strength sheet containing: C: 0.15% by mass to 0.35% by mass, a total of Si and Al: 0.5% by mass to 3.0% by mass, Al: 0.01% by mass or more, N: 0.01% by mass or less, Mn: 1.0% by mass to 4.0% by mass, P: 0.05% by mass or less, and S: 0.01% by mass or less, with the balance being Fe and inevitable impurities, wherein the steel structure satisfies that: a ferrite fraction is 5% or less, the total fraction of tempered martensite and tempered bainite is 60% or more, the amount of retained austenite is 10% or more, MA has an average size of 1.0 ?m or less, retained austenite has an average size of 1.0 ?m or less, retained austenite having a size of 1.5 ?m or more accounts for 2% or more of the total amount of retained austenite, and the amount of solute nitrogen in a steel sheet is 0.002% by mass or less.

Abstract: Disclosed is a high-strength sheet containing: C: 0.15% by mass to 0.35% by mass, a total of Si and Al: 0.5% by mass to 3.0% by mass, Mn: 1.0% by mass to 4.0% by mass, P: 0.05% by mass or less (including 0% by mass), S: 0.01% by mass or less (including 0% by mass), and Ti: 0.01% by mass to 0.2% by mass, with the balance being Fe and inevitable impurities, wherein the steel structure satisfies that: a ferrite fraction is 5% or less, a total fraction of tempered martensite and tempered bainite is 60% or more, a retained austenite fraction is 10% or more, a fresh martensite fraction is 5% or less, retained austenite has an average grain size of 0.5 ?m or less, retained austenite having a grain size of 1.0 ?m or more accounts for 2% or more of the total amount of retained austenite, and a prior austenite grain size is 10 ?m or less.

Abstract: Disclosed is a high-strength sheet containing: C: 0.15% by mass to 0.35% by mass, a total of Si and Al: 0.5% by mass to 3.0% by mass, Al: 0.01% by mass or more, N: 0.01% by mass or less, Mn: 1.0% by mass to 4.0% by mass, P: 0.05% by mass or less, and S: 0.01% by mass or less, with the balance being Fe and inevitable impurities, wherein the steel structure satisfies that: a ferrite fraction is 5% or less, the total fraction of tempered martensite and tempered bainite is 60% or more, the amount of retained austenite is 10% or more, MA has an average size of 1.0 ?m or less, retained austenite has an average size of 1.0 ?m or less, retained austenite having a size of 1.5 ?m or more accounts for 2% or more of the total amount of retained austenite, and the amount of solute nitrogen in a steel sheet is 0.002% by mass or less.

Abstract: Disclosed is a high-strength sheet containing: C: 0.15% by mass to 0.35% by mass, a total of Si and Al: 0.5% by mass to 3.0% by mass, Mn: 1.0% by mass to 4.0% by mass, P: 0.05% by mass or less (including 0% by mass), S: 0.01% by mass or less (including 0% by mass), and Ti: 0.01% by mass to 0.2% by mass, with the balance being Fe and inevitable impurities, wherein the steel structure satisfies that: a ferrite fraction is 5% or less, a total fraction of tempered martensite and tempered bainite is 60% or more, a retained austenite fraction is 10% or more, a fresh martensite fraction is 5% or less, retained austenite has an average grain size of 0.5 ?m or less, retained austenite having a grain size of 1.0 ?m or more accounts for 2% or more of the total amount of retained austenite, and a prior austenite grain size is 10 ?m or less.

Abstract: Disclosed is a high-strength sheet including: C: 0.15% to 0.35% by mass, total of Si and Al: 0.5% to 3.0% by mass, Mn: 1.0% to 4.0% by mass, P: 0.05% by mass or less, and S: 0.01% by mass or less, with the balance being Fe and inevitable impurities, wherein the steel structure satisfies that: a ferrite fraction is 5% or less, the total fraction of tempered martensite and tempered bainite is 60% or more, the amount of retained austenite is 10% or more, MA has an average size of 1.0 ?m or less, retained austenite has an average size of 1.0 ?m or less, retained austenite having a size of 1.5 ?m or more accounts for 2% or more of the total amount of retained austenite, and a scattering intensity at the q value of 1 nm?1 in X-ray small angle scattering is 1.0 cm1 or less.

Abstract: Disclosed is a high-strength sheet including: C: 0.15% by mass to 0.35% by mass, total of Si and Al: 0.5% by mass to 3.0% by mass, Mn: 1.0% by mass to 4.0% by mass, P: 0.05% by mass or less, and S: 0.01% by mass or less, with the balance being Fe and inevitable impurities, wherein the steel structure satisfies that: a ferrite fraction is 5% or less, the total fraction of tempered martensite and tempered bainite is 60% or more, the amount of retained austenite is 10% or more, MA has an average size of 1.0 ?m or less, a half-width of the concentration distribution of Mn in the carbon-concentrated region that is equal to the amount of retained austenite is 0.3% by mass or more, and a scattering intensity at the q value of 1 nm?1 in X-ray small angle scattering is 1.0 cm?1 or less.

Abstract: One aspect of the present invention is a high strength steel sheet having a specific component composition, wherein a metal structure of the steel sheet comprises polygonal ferrite, bainite, tempered martensite, and retained austenite; when the metal structure is observed with a scanning electron microscope, the metal structure satisfies polygonal ferrite: 10 to 50 area %, bainite: 10 to 50 area %, and tempered martensite: 10 to 80 area % with respect to the metal structure overall; and when the metal structure is measured by X-ray diffractometry, the metal structure satisfies retained austenite: 5.0 volume % or more, retained austenite with a carbon concentration of 1.0 mass % or less: 3.5 volume % or more, and retained austenite with a carbon concentration of 0.8 mass % or less: 2.4 volume % or less with respect to the metal structure overall.

Abstract: A high-strength steel sheet comprising, as component composition, by mass: C: 0.15 to 0.35%; total of Si and Al: 0.5 to 2.5%; Mn: 1.0 to 4.0%; P: more than 0% and 0.05% or less; and S: more than 0% and 0.01% or less, with the balance being Fe and inevitable impurities, wherein a steel structure satisfies, in ratio with respect to the whole structure: ferrite: more than 5 area % and 50 area % or less; total of tempered martensite and bainite: 30 area % or more; and retained austenite: 10 volume % or more, the steel structure further includes MA, and the steel structure satisfies: an average circle equivalent diameter of the MA: 1.0 ?m or less; an average circle equivalent diameter of the retained austenite: 1.0 ?m or less; and a volume ratio of retained austenite with a circle equivalent diameter of 1.5 ?m or more to the whole retained austenite: 5% or more.

Abstract: A high-strength steel sheet of the present invention is a steel sheet satisfying a predetermined component composition. A metal structure of the steel sheet is composed of polygonal ferrite, high-temperature region generated bainite, low-temperature region generated bainite and retained austenite each having a predetermined area percent, and a distribution using each average IQ of predetermined crystal grains determined by electron backscatter diffraction satisfies Equations (1) and (2) below. According to the present invention, a high-strength steel sheet having excellent ductility and low-temperature toughness can be realized even at a tensile strength of 780 MPa or more. (IQave?IQmin)/(IQmax?IQmin)?0.40??(1) (?IQ)/(IQmax?IQmin)?0.

Abstract: Disclosed herein is a high-strength cold-rolled steel sheet, in which the metal structure at a position of ¼ of the sheet thickness satisfies (1) to (4): (1) an area ratio of ferrite is more than 10% to 65% or less, with a balance being a hard phase including quenched martensite and retained austenite and including at least one selected from the group consisting of bainitic ferrite, bainite, and tempered martensite; (2) a volume ratio V? of retained austenite is 5% to 30%; (3) an area ratio VMA of an MA structure in which quenched martensite and retained austenite are combined is 3% to 25%, and an average circle-equivalent diameter of the MA structure is 2.0 ?m or less; and (4) a ratio VMA/V? of the area ratio VMA of the MA structure to the volume ratio V? of the retained austenite is 0.50 to 1.50.

Abstract: A high-strength cold-rolled steel sheet, in which the metal structure at a position of ¼ of the sheet thickness satisfies (1) to (4) below. (1) The area ratio of ferrite is 0% or more and 10% or less, with the balance being a hard phase including quenched martensite and retained austenite and including at least one selected from the group consisting of bainitic ferrite, bainite, and tempered martensite. (2) The volume ratio V? of retained austenite is 5% to 30%. (3) The area ratio VMA of an MA structure in which quenched martensite and retained austenite are combined is 3% to 25%, and the average circle-equivalent diameter of the MA structure is 2.0 ?m or less. (4) The ratio VMA/V? of the area ratio VMA of the MA structure to the volume ratio V? of the retained austenite is 0.50 to 1.50.

Abstract: A high-strength steel sheet of the present invention is a steel sheet satisfying a predetermined component composition. A metal structure of the steel sheet is composed of polygonal ferrite, high-temperature region generated bainite, low-temperature region generated bainite and retained austenite each having a predetermined area percent, and a distribution using each average IQ of predetermined crystal grains determined by electron backscatter diffraction satisfies Equations (1) and (2) below. According to the present invention, a high-strength steel sheet having excellent formability and low-temperature toughness can be realized even at a tensile strength of 590 MPa or more. (IQave?IQmin)/(IQmax?IQmin)?0.40??(1) (?IQ)/(IQmax?IQmin)?0.

Abstract: A high-strength steel sheet of the present invention is a steel sheet satisfying a predetermined component composition. A metal structure of the steel sheet is composed of polygonal ferrite, high-temperature region generated bainite, low-temperature region generated bainite and retained austenite each having a predetermined area percent, and a distribution using each average IQ of predetermined crystal grains determined by electron backscatter diffraction satisfies Equations (1) and (2) below. According to the present invention, a high-strength steel sheet having excellent ductility and low-temperature toughness can be realized even at a tensile strength of 780 MPa or more. (IQave?IQmin)/(IQmax?IQmin)?0.40??(1) (?IQ)/(IQmax?IQmin)?0.

Abstract: An injection-compression molding apparatus includes a stationary mold provided with a nozzle for injecting molten resin, and a movable mold driven by a servo motor. In compressing the resin, high-speed position control of the movable mold is first performed, which is then switched to speed feedback control which enables delicate regulation of clamping pressure in accordance with pressure fluctuations in the resin.

Abstract: An injection device includes a cylinder, a plunger and a driving device. The cylinder has a port for supplying molding material into the cylinder, and the molding material supplies into the cylinder is compressed by the plunger. The plunger has a groove extending circumferentially around an outer wall of a large-diameter portion of the plunger, and the clearance between the outer wall of the large-diameter portion of the plunger and the inner wall of the cylinder is determined by a specified equation.

Abstract: An injection-compression molding apparatus includes a stationary mold provided with a nozzle for injecting molten resin, and a movable mold driven by a servo motor. In compressing the resin, high-speed position control of the movable mold is first performed, which is then switched to speed feedback control which enables delicate regulation of clamping pressure in accordance with pressure fluctuations in the resin.

Abstract: A method of manufacturing the peripheral wall of a tank for an oil-immersed electric apparatus which comprises manufacturing a panel unit through the steps of:fabricating a panel by pressing a thin steel sheet to form an upward extending flange along both edges of the panel and provide a plurality of reinforcement depressions concaved toward the backside of the flat portion of said panel;folding the panel into two parts with the surface of the panel kept outside along the central line extending between both edges of the panel to fabricate a hollow fin;joining both sides of the folded fin by spot welding the reinforcement depressions; andwelding together the closely facing edges of both sides of the fin,and constructing the peripheral wall of the tank by joining together a plurality of panel units fabricated through the above-mentioned steps by welding the flanges of said panel units.