A method for forming a cold rolled, coated and post batch annealed steel sheet is provided. The method includes cold rolling a steel sheet; coating the cold rolled steel sheet with a zinc or zinc alloy coating, the cold rolled, coated steel sheet having an initial hole expansion and an initial yield strength and post batch annealing the cold rolled, coated steel sheet at a tempering temperature in a range from 150 to 650° C., the post batch annealed steel sheet having a final hole expansion and a final yield strength. The steel sheet includes (in wt. %)C-0.1-0.3%, Mn-1-3%, Si-0.5-3.5%, Al-0.05-1.5% and Mo+Cr being between 0-1.0%. The final hole expansion is at least 80% greater than the initial hole expansion and the final yield strength is at least 30% greater than the initial yield strength.

The present invention relates to a method for the manufacture of a hot-dip coated steel sheet coated with a zinc or an aluminum based coating including the provision of a specific steel sheet, a recrystallization annealing with specific heating, soaking and cooling sub-steps using an inert gas and a hot-dip coating; the hot dip coated steel sheet and the use of the hot-dip coated steel sheet.

A galvannealed steel sheet having a steel substrate coated with a first alloy layer with iron and nickel directly topped by a second alloy layer based on zinc, the first and second alloyed layers being alloyed through diffusion such that the second alloy layer includes from 5 to 15 wt.% of iron, from 0 to 15 wt.% of nickel, a balance being zinc.

Zn alloy plated steel material having excellent weldability and processed-part corrosion resistance and a method for production of Zn alloy plated steel material are provided. In the Zn alloy plated steel material comprising base steel material and a Zn alloy plating layer, the Zn alloy plating layer includes, by wt %, Al: 0.1-5.0%, Mg: 0.1-5.0%, as well as a remainder of Zn and inevitable impurities. The Zn alloy plated steel material includes a lower interface layer and an upper interface layer between the base steel material and the Zn alloy plating layer, wherein the lower interface layer is formed on the base steel material and has a dense structure, and the upper interface layer is formed on the lower interface layer and has a network-type or island-type structure.

Method for the manufacture of a coated steel sheet including the following step of A) the provision of a pre-coated steel sheet coating with a first coating including iron and nickel, B) the thermal treatment of such pre-coated steel sheet at a temperature between 600 and 1000° C., and C) the coating of the steel sheet obtained in step B) with a second coating based on zinc.

This joint component is a joint component including a first steel member, a second steel member, and a spot-welded portion that joins the first steel member and the second steel member, in which the first steel member includes a steel sheet substrate having a predetermined chemical composition and a coating that is formed on a surface of the steel sheet substrate, contains Al and Fe, and has a thickness of 25 μm or more, in a cross section in a thickness direction of the first steel member and the second steel member including the spot-welded portion, a filled metal containing Al and Fe is present in a gap between the first steel member and the second steel member in a periphery of the spot-welded portion, in the cross section, the filled metal has a cross-sectional area of 3.0×10.sup.4 μm.sup.2 or more, and has a filling ratio of 80% or more in the gap in a range of 100 μm from an end portion of a corona bond formed in the periphery of the spot-welded portion, and includes a first region and a second region.

The present invention has as its object the provision of a coated steel member and coated steel sheet excellent in hydrogen embrittlement resistance in a corrosive environment and methods for manufacturing the same. The coated steel member of the present invention is provided on its surface with an Al—Fe-based coating containing Cu and one or more of Mo, Ni, Mn, and Cr in a total by mass % of 0.12% or more by heating, cooling, and manufacturing a coated steel sheet having a layer containing Cu on its surface under predetermined conditions.

The present invention relates to a method for the manufacture of a coated steel sheet comprising the following successive steps: A. the coating of the steel sheet with a first coating consisting of nickel and having a thickness between 600 nm and 1400 nm, the steel sheet having the following composition in weight: 0.10<C<0.40%, 1.5<Mn<3.0%, 0.7<Si<3.0%, 0.05<Al<1.0%, 0.75<(Si+Al)<3.0%, and on a purely optional basis, one or more elements such as Nb≤0.5%, B≤0.010%, Cr≤1.0%, Mo≤0.50%, Ni≤1.0%, Ti≤0.5%, the remainder of the composition making up of iron and inevitable impurities resulting from the elaboration, B. the recrystallization annealing at a temperature between 820 to 1200° C., C. the coating with a second coating based on zinc not comprising nickel.

A flat steel product for production of a sheet metal component by hot forming includes a steel substrate consisting of a steel including 0.1-3% by weight of Mn and optionally up to 0.01% by weight of B, an aluminium-based coating disposed on at least one side of the steel substrate. A coating here has an applied layer weight of 15-30 g/m.sup.2. In addition, the coating has an Al base layer consisting of 1.0-15% by weight of Si, optionally 2-4% by weight of Fe, 0.1-5.0% by weight of alkali metals or alkaline earth metals, and optional further constituents, the contents of which are limited to a total of not more than 2.0% by weight, and aluminium as the balance.

A steel sheet for the manufacture of a press hardened part is provided, having a composition of: 0.15%≤C≤0.22%, 3.5%≤Mn<4.2%, 0.001%≤Si≤1.5%, 0.020%≤Al≤0.9%, 0.001%≤Cr≤1%, 0.001%≤Mo≤0.3%, 0.001%≤Ti≤0.040%, 0.0003%≤B≤0.004%, 0.001%≤Nb≤0.060%, 0.001%≤N≤0.009%, 0.0005%≤S≤0.003%, 0.001%≤P≤0.020%. A microstructure has less than 50% ferrite, 1% to 20% retained austenite, cementite, such that the surface density of cementite particles larger than 60 nm is lower than 10{circumflex over ( )}7/mm.sup.2, and a complement of bainite and/or martensite, the retained austenite having an average Mn content of at least 1.1*Mn %. Press-hardened steel part obtained by hot forming the steel sheet, and manufacturing methods thereof.