HIGH-STRENGTH STEEL SHEET EXERTING EXCELLENT DEEP DRAWABILITY AT ROOM TEMPERATURE AND WARM TEMPERATURES, AND METHOD FOR WARM WORKING SAME

摘要

This high-strength steel sheet has a component composition containing, in mass %, 0.02 to 0.3% C, 1 to 3% Si, 1.8 to 3% Mn, 0.1% or less P, 0.01% or less S, 0.001 to 0.1% Al, and 0.002 to 0.03% N, the remainder being iron and impurities. The high-strength steel sheet has a structure containing, in terms of area ratio relative to the entire structure, each of the following phases: 50 to 85% bainitic ferrite; 3% or more retained austenite (); 10 to 45% martensite and the aforementioned retained austenite (); and 5 to 40% ferrite. The ratio between the Mn concentration (MnR) in the retained austenite () and the average Mn concentration (Mnav) in the entire structure is 1.2 or more (MnR/ Mnav) based on the Mn concentration distribution obtained by means of EPMA line analysis. As a consequence, the high-strength steel sheet exhibits strength of 980 MPa or more and exerts excellent deep drawability.