A zinc-plated steel sheet of an aspect of the present invention includes a steel sheet having a predetermined chemical composition and a zinc-plated layer. In the steel sheet, steel microstructures in a range of ⅛ thickness to ⅜ thickness, having the center at ¼ thickness from a steel sheet surface, include, by vol %, ferrite: 0% to 10%, bainite: 0% to 20%, tempered martensite: 70% or more, fresh martensite: 0% to 10%, retained austenite: 0% to 10%, and pearlite: 0% to 5%. In the zinc-plated steel sheet, the amount of hydrogen emitted when the steel sheet is heated to 200° C. from a room temperature after removal of the zinc-plated layer is 0.40 ppm or less per mass of the steel sheet, the tensile strength is 1470 MPa or more, and no cracking occurs in a U-shape bending test where a stress equivalent to 1000 MPa is applied for 24 hours.

This coated steel member includes: a steel sheet substrate having a predetermined chemical composition; and a coating formed on a surface of the steel sheet substrate and containing Al and Fe, in which the coating has a low Al content region having an Al content of 3 mass % or more and less than 30 mass % and a high Al content region formed on a side closer to a surface than the low Al content region and having an Al content of 30 mass % or more, a maximum C content of the high Al content region is 25% or less of a C content of the steel sheet substrate, a maximum C content of the low Al content region is 40% or less of the C content of the steel sheet substrate, and a maximum C content in a range from an interface between the steel sheet substrate and the coating to a depth of 10 μm on a side of the steel sheet substrate is 80% or less of the C content of the steel sheet substrate.

The present invention provides steel sheet products having controlled compositions that are subjected to two-step annealing processes to produce sheet products having desirable microstructures and favorable mechanical properties such as high strength and ultra-high formability. Steels processed in accordance with the present invention exhibit combined ultimate tensile strength and total elongation (UTS.Math.TE) properties of greater than 25,000 MPa-%. Steels with these properties fall into the category of Generation 3 advanced high strength steels, and are highly desired by various industries including automobile manufacturers.

A hot-pressed member having excellent bending collapsibility, a method for manufacturing the same, and a method for manufacturing a steel sheet for the hot-pressed member. The hot-pressed member includes a steel sheet as a base material, the steel sheet having a specified chemical composition. The hot-pressed member has a microstructure in which a martensite microstructure is present in a volume fraction of 70% or greater, and a number density of inclusions having a longest diameter of 25 μm or greater is 0.02/mm.sup.2 or less. The hot-pressed member has a tensile strength of 1.8 GPa or greater.

The present invention relates to a high-strength steel sheet and, more specifically, to a dual-phase steel sheet having excellent formability, so as to be appropriately applied to vehicle panels and the like, and a manufacturing method therefor.

A high strength interstitial free low density steel and method for producing the steel.

A high strength low alloy steel. The high strength low alloy steel strip, sheet or blank, coated with zinc or a zinc alloy, has the following composition in weight %: C: 0.03-0.07, Mn: 0.70-1.60, Si: ≦0.2, Al: 0.005-0.1, Cr: ≦0.1, Cu: ≦0.2, N: ≦0.008, P: ≦0.03, S: ≦0.025, O: ≦0.01, Ti: 0.02-0.07, V: 0.04-0.15 Mo: ≦0.03, Nb: ≦0.03, Ca: ≦0.05, the remainder being iron and unavoidable impurities,
wherein the steel strip, sheet or blank has a yield strength Rp0,2 of at least 420 MPa.

A high-strength galvanized steel sheet comprising a cold-rolled steel sheet, an intermetallic compound formed on the cold-rolled steel sheet, and a galvanizing layer formed on the intermetallic compound, the cold-rolled steel sheet having a specific composition and a microstructure having a martensite area ratio of 7% or more and less than 25% and a ferrite area ratio of 50% or more and which includes a base metal surface portion in which the amount of internal oxides per single side is 0.05 g/m.sup.2 or less.

The invention relates to a method for producing a high strength coated steel sheet having a yield stress YS>550 MPa, a tensile strength TS>980 MPa, and improved formability and ductility. The steel contains: 0.15%≦C≦0.25%, 1.2%≦Si≦1.8%, 2%≦Mn≦2.4%, 0.1%≦Cr≦0.25%, Al≦0.5%, the balance being Fe and unavoidable impurities. The sheet is annealed at a temperature between TA1=Ac3−0.45*(Ms−QT) and TA2=830° C. for at least 30s then quenched by cooling it to a quenching temperature QT between 180° C. and 300° C., then heated to a partitioning temperature PT between 380° C. and 480° C. and maintained at this temperature for a partitioning time Pt between 0 sec and 300 sec, then either hot dip coated and cooled to the room temperature with a cooling rate of at least 25° C./s below 300° C., or directly cooled to the room temperature with a cooling rate of at least 25° C./s and further electro-galvanized, or cooled to the room temperature with a cooling rate of at least 25° C./s without coating. The steel according to the invention contains 5% to 25% of intercritical ferrite, at least 50% of partitioned martensite, at least 10% of residual austenite, less than 10% of fresh martensite, and bainite, the sum of partitioned martensite and bainite being at least 60%. It also relates to the obtained coated or non coated sheet.

This coated steel member includes: a steel sheet substrate having a predetermined chemical composition; and a coating formed on a surface of the steel sheet substrate and containing Al and Fe, in which the coating has a low Al content region having an Al content of 3 mass % or more and less than 30 mass % and a high Al content region formed on a side closer to a surface than the low Al content region and having an Al content of 30 mass % or more, a maximum C content of the high Al content region is 25% or less of a C content of the steel sheet substrate, a maximum C content of the low Al content region is 40% or less of the C content of the steel sheet substrate, and a maximum C content in a range from an interface between the steel sheet substrate and the coating to a depth of 10 μm on a side of the steel sheet substrate is 80% or less of the C content of the steel sheet substrate.