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

摘要

The high strength steel according to the present invention comprises 0.02 to 0.3% of C, 1 to 3% of Si, 1.8 to 3% of Mn, 0.1% or less of P, 0.01% or less of S, 0.001 to 0.1% , And N: 0.002 to 0.03%, the balance being iron and an impurity, and having an area ratio with respect to the whole structure: bainitic ferrite: 50 to 85%, residual _gamma : 3% The Mn concentration in the retained austenite Mn _{粒 R} and the total Mn concentration in the retained austenite based on the Mn concentration distribution obtained by line analysis of EPMA and having a structure comprising the residual _{γ of} 10 to 45% and the ferrite of 5 to 40% the Mn ratio _γR / Mn _av of average Mn concentration of the Mn is at least 1.2 _av. As a result, the deep drawability is excellent while the strength of 980 MPa or more is secured.