HIGH-STRENGTH HOT-ROLLED STEEL SHEET HAVING MAXIMUM TENSILE STRENGTH OF 980 MPA OR MORE, AND HAVING EXCELLENT AND BAKING HARDENABILITY AND LOW-TEMPERATURE TOUGHNESS

摘要

Provided is a high-strength hot-rolled steel sheet consisting of, in mass%, C: 0.01% to 0.2%, Si: 0% to 2.5%, Mn: 0% to 4.0%, Al: 0% to 2.0%, N: 0% to 0.01%, Cu: 0% to 2.0%, Ni: 0% to 2.0%, Mo: 0% to 1.0%, V: 0% to 0.3%, Cr: 0% to 2.0%, Mg: 0% to 0.01%, Ca: 0% to 0.01%, REM: 0% to 0.1%, B: 0% to 0.01%, P: less than or equal to 0.10%, S: less than or equal to 0.03%, O: less than or equal to 0.01 %, one or both of Ti and Nb: 0.01% to 0.30% in total, and the balance being Fe and inevitable impurities. The steel sheet has a structure in which a total volume fraction of tempered martensite or lower bainite is 90% or more, a dislocation density thereof is greater than or equal to 5×10 13 (1/m 2 ) and less than or equal to 1×10 16 (1/m 2 ), and 1×10 6 (numbers/mm 2 ) or more iron-based carbides are included therein.