HIGH-TENSION HOT-ROLLED STEEL SHEET AND HIGH-TENSION PLATED STEEL SHEET WHICH ARE EXCELLENT IN BAKE HARDENABILITY AND DUCTILITY AND THEIR PRODUCTION METHODS

摘要

PPROBLEM TO BE SOLVED: To provide a high-tension hot-rolled steel sheet and a high-tension plated steel sheet which are excellent in non-aging property at room temperature whose bake hardenability and ductility can be improved without further decreasing the crystal grain size or increasing the amount of solid solution N. PSOLUTION: The high-tension hot-rolled steel sheet has a composition comprising, by mass, 0.05-0.15% C, 0.5% Si, 1.2-3.0% Mn, 0.05-1.0% Mo, 0.05% P, 0.001-0.1% Al, 0.005-0.02% N and the balance being Fe and unavoidable impurities and has a steel structure comprising, by area, 10-50% low-temperature transformed ferrite phase and the balance substantially being polygonal ferrite phase. The average crystal grain size of the two phases, i.e. the low-temperature transformed ferrite phase and the polygonal ferrite phase, is 8 m. PCOPYRIGHT: (C)2004,JPO&NCIPI