high strength and high ductility hot-dip galvanized steel sheet excellent in workability and coating adhesion of the friction stir welding method

摘要

PROBLEM TO BE SOLVED: To provide a high strength and high ductility hot-dip galvanized steel sheet which has strength and ductility required as the steel sheet for automobile and exhibits excellent workability in the case of applying a friction-stir welding process etc., and further, is excellent in plating adhesion property.;SOLUTION: This steel sheet has a composition composed of 0.05-0.40% C, ≤1.5% Si, 0.5-3.0% Mn, ≤0.4% Al and satisfying (Si+Al)≥0.5% and the balance Fe with inevitable impurities, wherein a secondary phase containing retained austenite of ≥5% volume ratio in a main phase of pro-eutectoid ferrite is formed and further, the sum of a temperature range width of the ferrite single phase and the temperature range width of two-phases of the austenite phase and the ferrite phase, in an equilibrium state of ≥600°C, is made ≥200°C.;COPYRIGHT: (C)2010,JPO&INPIT