ArcelorMittal S.A.
A method for the manufacturing of liquid metal embrittlement resistant galvannealed steel sheet

Abstract:

The present invention relates to a method for the manufacture of a galvannealed steel sheet including the steps of A.) coating of the steel sheet with a first coating consisting of nickel and having a thickness between 150 nm and 650 nm, the steel sheet having the following composition in weight percentage 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.ltoreq.0.5%, B.ltoreq.0.010%, Cr.ltoreq.1.0%, Mo.ltoreq.0.50%, Ni.ltoreq.1.0%, Ti.ltoreq.0.5%., the remainder of the composition is made up of iron and inevitable impurities resulting from the elaboration, B.) annealing of the coated steel sheet being annealed at a temperature between 600 to 1200.degree. C., C.) coating of the steel sheet obtained in step B.) with a second coating based on zinc and D.) an alloying heat treatment to form a galvannealed steel sheet.