DUAL-PHASE STEEL SHEET AND PROCESS FOR PRODUCING SAME

摘要

A dual phase steel sheet including: in mass%, C: 0.01 to 0.1%; Mn: 0.2 to 3%; Al: 0.04 to 1.5%; Ti: 0.015 to 0.2%; P: 0.01% or less; S: 0.005% or less; N: 0.01% or less, in which [Ti] - 48/14 x [N] - 48/32 x [S] ‰§ 0% is satisfied and when Ex.C (%) = [C] - 12/48 x {[Ti] + 48/93 x [Nb] - 48/14 x [N] - 48/32 x [S]} is set, 0.001 ‰¦ Ex.C (%)/fsd (%) ‰¦ 0.01 is satisfied, and a balance being composed of Fe and impurities, in which at the position of 1/4 thickness of a sheet thickness, a microstructure is a dual phase with its main phase composed of polygonal ferrite precipitation-strengthened by carbide of Ti and its second phase composed of 1 to 10% in area fraction (fsd (%)) of low-temperature transformation products dispersed plurally, and an average crystal diameter of the low-temperature transformation product is 3 to 15 µm and an average value of a distance of closest approach between the low-temperature transformation products is 10 to 20 µm.