A welded component having mechanical properties in a welding seam region comparable or better to those in the non-influenced base material via a method including producing a hot-rolled steel product made of a high-strength air-hardenable steel with a material thickness of at least 1.5 mm having a chemical composition by mass in one embodiment of: C: 0.03 to 0.4; Mn: 1.0 to 4.0; Si: 0.09 to 2.0; Al: 0.02 to 2.0; P<=0.1; S<=0.1; N: 0.001 to 0.5; Ti: 0.01 to 0.2; Cr: 0.05 to 2.0; B: 0.001 to 0.1; Mo: 0.01 to 1.0; V: 0.01 to 0.2; optionally: Ni: 0.02 to 1.0; Nb: 0.01 to 0.1; and residual iron including conventional steel-accompanying elements, subsequently air hardening the produced hot-rolled steel product, then deforming the hot-rolled steel product in the air-hardened state to form a component, and producing welding connections using a fusion welding process on the component.

A high-strength high-ductility steel sheet has a specific component composition and a steel microstructure containing, in terms of an area ratio relative to the entire microstructure, 8% or more of a retained austenite, with the remainder being at least one of bainite, martensite, tempered bainite, and tempered martensite. With respect to the carbon concentration in the retained austenite, an average carbon concentration is from 0.9 to 1.2 mass %, a standard deviation of the carbon concentration distribution is 0.35 mass % or more, and an area ratio of a region having the carbon concentration of 1.5 mass % or more, relative to the entire microstructure, is 1.0% or more.

A high-strength cold-rolled steel sheet having a specified chemical composition and a microstructure including ferrite having an average crystal grain diameter of 2 μm or less in an amount of 10% to 25% in terms of volume fraction, retained austenite in an amount of 5% to 20% in terms of volume fraction, martensite having an average crystal grain diameter of 2 μm or less in an amount of 5% to 15% in terms of volume fraction, and the balance being a multi-phase structure including bainite and tempered martensite having an average crystal grain diameter of 5 μm or less, in which a relational expression, 0.35≦V2/V1≦0.75 (1), is satisfied, where V1 is a volume fraction of phases which are different from ferrite and V2 is a volume fraction of tempered martensite.

A nitrided packaging steel in the form of a flat steel product and method for producing a nitrided packaging steel with a carbon content of 10-1000 ppm and uncombined nitrogen, dissolved in the steel, of more than 100 ppm. The nitriding is performed in two stages: a first stage, in which a molten steel is nitrided to a nitrogen content of at most 160 ppm by introducing a nitrogen-containing gas and/or a nitrogen-containing solid into the molten steel, and a second stage, in which a flat steel product produced from the nitrided molten steel by cold rolling is treated with a nitrogen-containing gas in order to increase further the amount of uncombined nitrogen in the flat steel product. The second stage is performed in an annealing furnace, in which the flat steel product is at the same time annealed in a recrystallizing manner. The packaging steels produced are distinguished by great strength, in excess of 600 MPa, and good elongation to fracture, regularly in excess of 5%, as well as by good forming properties.

A martensitic steel including the following elements, expressed in percentage by weight 0.1%≤C≤0.4%; 0.2%≤Mn≤2%; 0.4%≤Si≤2%; 0.2%≤Cr≤1%; 0.01%≤Al≤1%; 0%≤S≤0.09%; 0%≤P≤0.09%; 0%≤N≤0.09%; and can contain one or more of the following optional elements 0%≤Ni≤1%; 0%≤Cu≤1%; 0%≤Mo≤0.1%; 0%≤Nb≤0.1%; 0%≤Ti≤0.1%; 0%≤V≤0.1%; 0.0015%≤B≤0.005%; 0%≤Sn≤0.1%; 0%≤Pb≤0.1%; 0%≤Sb≤0.1%; 0%≤Ca≤0.1%; the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of said steel having microstructure by area percentage including cumulative presence of residual austenite and bainite between 0% and 25%, the remaining microstructure being martensite at least 70%, and with an optional presence of ferrite between 0% and 10%.

The present invention has as its object the provision of a steel member and steel sheet having high tensile strength and toughness and excellent in hydrogen embrittlement resistance in a corrosive environment and methods for manufacturing the same. The steel member of the present invention has predetermined chemical constituents and has a maximum value of content of Cu in a range from the surface to a depth of 0 to 30 μm of 1.4 times the content of Cu at a depth of 200 μm.

A hot-stamping formed body includes: a steel sheet having a predetermined chemical composition; and a plating layer provided on a surface of the steel sheet, the plating layer having an adhesion amount of 10 g/m.sup.2 to 90 g/m.sup.2 and a Ni content of 10 mass % to 25 mass %, and containing a remainder consisting of Zn and impurities. The hot-stamping formed body includes, in a surface layer region of the steel sheet, an average grain size of prior austenite grains to 10.0 μm or less, a Ni concentration per unit area at grain boundaries having an average crystal orientation difference of 15° or more is 1.5 mass %/μm.sup.2 or more.

Provided is a hot-pressed member that combines both high strength of 1850 MPa or more in TS and excellent delayed fracture resistance. A hot-pressed member comprises: a predetermined chemical composition; a microstructure in which a prior austenite average grain size is 8 μm or less, a volume fraction of martensite is 95% or more, and a volume fraction of granular carbide of 0.1 μm or more in grain size is 0.10% to 4.0%; a Ni diffusion region of 2.0 μm or more in a depth direction in a surface layer; and a tensile strength of 1850 MPa or more.

The present invention has as its object the provision of a steel member and steel sheet having high tensile strength and toughness and excellent in hydrogen embrittlement resistance in a corrosive environment and methods for manufacturing the same. The steel member of the present invention has predetermined chemical constituents and has a maximum value of content of Cu in a range from the surface to a depth of 0 to 30 μm of 1.4 times the content of Cu at a depth of 200 μm.

A roll-bonded clad metal sheet and a method for producing a roll-bonded clad metal sheet is provided. The roll-bonded clad sheet includes a metallic base material layer and a metallic cladding material layer which are joined to one another by a metallurgical bond. The metallic cladding material layer includes a nickel-based material whose chemical composition includes, in % by mass, a proportion of more than 50% of Ni and a proportion of 3.1% of Nb. The metallurgical bond is obtained by a thermomechanical rolling process including a first rolling phase for prerolling, a second rolling phase for final forming and a cooling time between the first rolling phase and the second rolling phase, wherein a final rolling temperature of the second rolling phase is set to a value equal to or less than 880° C.