HIGH-TENSILE-STRENGTH HOT-ROLLED STEEL SHEET AND METHOD FOR PRODUCING SAME

摘要

To provide a high strength hot rolled steel sheet and method for producing the high strength hot rolled steel sheet that has high strength, excellent formability (stretch-flange formability), a tensile strength of 780 MPa or more, and excellent material uniformity. The hot rolled steel sheet has the composition comprising : C: 0.03% or more to less than 0.07%; Si: 0.3% or less; Mn: 0.5% or more to 2.0% or less; P: 0.025% or less; S: 0.005% or less; N: 0.0060% or less; Al: 0.1% or less; Ti: 0.07% or more to 0.11% or less; and V: 0.08% or more to less than 0.15% on a mass percent basis, such that Ti and V contents satisfy the following formula: 0.18 ‰¤ Ti + V ‰¤ 0.24 (where Ti and V are respective contents of the elements (by mass%)). Balance comprises Fe and inevitable impurities. A matrix has an area ratio of 95% or more with respect to an overall structure of a ferrite phase. In the structure, fine carbide is dispersedly precipitated, the fine carbide containing Ti and V has an average particle size of less than 10 nm in the matrix, and a volume fraction of the fine carbide is 0.0020 or more with respect to an overall structure.