HIGH STRENGTH STEEL SHEET EXHIBITING GOOD BURRING WORKABILITY AND EXCELLENT RESISTANCE TO SOFTENING IN HEAT-AFFECTED ZONE AND METHOD FOR PRODUCTION THEREOF

摘要

A high strength steel sheet exhibiting good burring workability and excellent resistance to the softening in a heat-affected zone, characterized in that it has a chemical composition, in mass %: C: 0.01 to 0.1 %, Si: 0.01 to 2 %, Mn: 0.05 to 3 %, P <= 0.1 %, S <= 0.03 %, Al: 0.005 to 1 %, N: 0.0005 to 0.005 %, Ti: 0.05 to 0.5 %, Cr <= 0.5 %, Mo <= 0.5 %, with the proviso that 0 % < C - (12/48Ti - 12/14N - 12/32S) <= 0.05 % and Mo + Cr >= 0.2 %, and the balance: Fe and inevitable impurities, and has a microstructure comprising ferrite or ferrite and bainite; and a method for producing the high strength steel sheet.