the tensile strength corrosion resistance in more than 700MPa, hole expandability and excellent ductility was alloyed hot-dip galvanized high-strength steel sheet and method of manufacturing the same

摘要

PROBLEM TO BE SOLVED: To provide a hot dip galvannealed high strength steel sheet having a tensile strength of ≥700 MPa, and jointly having corrosion resistance, hole expansibility and high ductility, and to provide a method for producing the same.;SOLUTION: Disclosed is a steel sheet obtained by applying hot dip galvannealing to a steel sheet having a composition comprising, by mass, 0.01 to 0.2% C, 0.001 to 0.200% Si, 1.0 to 3.0% Mn, 0.01 to 1.0% Al, 0.001 to 0.3% P, 0.0001 to 0.1% S, 0.0005 to 0.01% N and 0.01 to 0.5% Mo, and the balance Fe with inevitable impurities. The steel has a microstructure comprising, by area ratio, 30 to 90% tempered martensite, 5 to 50% ferrite and ≤50% bainite, an in which the ratio (Hv)₁/(Hv)₂ between the hardness (Hv)₁ of the tempered martensite and the hardness (Hv)₂ of the ferrite lies in the range of 1.3 to 2.4 times.;COPYRIGHT: (C)2009,JPO&INPIT