| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-strength hot-rolled steel sheet which has tensile strength (TS) of 540-780 MPa, and is excellent in the strength uniformity wherein variance in strength is small by using an inexpensive Ti series general-using steel sheet. SOLUTION: The component composition of this steel sheet contains, by mass, 0.05-0.12% C,≤0.5% Si, 0.8-1.8% Mn,≤0.030% P,≤0.01% S, 0.005-0.1% Al,≤0.01% N, 0.030-0.080% Ti and the balance Fe with inevitable impurities. And, in the structure, a polygonal-ferrite is contained in faction ratio of≥70% and the quantity of Ti existing in the precipitation having size of <20 nm, is≥50% of Ti* value calculated with the following formula (1)...T*=[Ti]-48/14×[N]. Wherein, [Ti] and [N] each represent the component-compositions (mass%) of Ti ans N in the steel sheet. COPYRIGHT: (C)2009,JPO&INPIT
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