HIGH-STRENGTH MOLTEN-ZINC-PLATED STEEL SHEET HAVING EXCELLENT BENDABILITY AND WELDABILITY, AND PROCESS FOR PRODUCTION THEREOF

摘要

A steel sheet is coated with a molten zinc plating layer, wherein the steel sheet comprises, in mass%, not less than 0.05% and less than 0.12% of C, 0.001 to 0.040% of P and 0.0050% or less of S, has a steel sheet surface layer part (which is a part lying between each of surfaces of the steel sheet and a depth of 10 µm of the steel sheet) and a steel sheet inner layer part (which is a inside part from the depth of 10 µm from each of the surfaces of the steel sheet), and has a tensile strength of 980 MPa or more, wherein the steel sheet surface layer part has a structure that contains a ferrite phase at a volume fraction of more than 70% and the steel sheet inner layer part has a structure that contains a ferrite phase having an average crystal particle diameter of 5 µm or less at a volume fraction of at least 20 to 70%. In this manner, it is possible to produce a high-strength molten-zinc-plated steel sheet having a tensile strength (TS) as high as 980 MPa or more and also having excellent bendability and weldability.