| 摘要 |
Provided are a high-strength hot-rolled steel sheet having good punchability in mass production and a tensile strength TS of 900 MPa or more and a method for manufacturing the high-strength hot-rolled steel sheet. A steel slab having a composition containing C: more than 0.07% and 0.2% or less, Si: z or less, Mn: 1.0% to 3.0%, Al: 0.1% or less, Ti: 0.05% to 0.3%, and V: 0.05% to 0.3% on a mass percent basis is heated to 1100°C or more and is subjected to rough rolling and finish rolling. In the finish rolling, the total rolling reduction of two final passes is 30% or more, and the finish rolling temperature ranges from (A r3 transformation temperature) to (A r3 transformation temperature + 120°C) . Cooling is started within 2 seconds after the finish rolling. Coiling is performed at an average cooling rate of 40°C/s or more at a coiling temperature in the range of 300°C to 500°C. The resulting high-strength hot-rolled steel sheet has a microstructure in which a bainite phase constitutes more than 90% by volume, the average lath interval of bainite is 0.45 µm or less, and the ratio of Fe-based carbide precipitated in bainite lath to all Fe-based carbide is 10% or more, has a high tensile strength of 900 MPa or more, and has significantly improved punchability in mass production. |
