High strenght steel sheet having superior ductility and method for manufacturing the same

摘要

A high strength steel sheet and a method for manufacturing the same are proposed, the high strength steel sheet having superior phosphatability properties and hot-dip galvannealed properties besides a tensile strength of 950 MPa or more and a high ductility, and also having a small variation in mechanical properties with the change in annealing conditions. The high strength steel sheet described above has a component composition which includes 0.05 to 0.20 mass percent of C, 0.5 mass percent or less of Si, 1.5 to 3.0 mass percent of Mn, 0.06 mass percent or less of P, 0.01 mass percent or less of S, 0.3 to 1.5 mass percent of Al, 0.02 mass percent or less of N, 0.01 to 0.1 mass percent of Ti, and 0.0005 to 0.0030 mass percent of B; at least one of 0.1 to 1.5 mass percent of Cr and 0.01 to 2.0 mass percent of Mo; and the balance being Fe and inevitable impurities, and in addition, this high strength steel sheet is composed of a microstructure including ferrite and martensite and has a tensile strength of 950 MPa or more.