| 摘要 |
<p>A high tensile hot-rolled steel sheet which has a chemical composition, in mass %, wherein C: 0.15 % or less, Si: 2.0 % or less, Mn: 3.0 % or less, P: 0.08 % or less, S: 0.02 % or less, Al: 0.02 % or less and N: 0.0050 to 0.0250 %, and optionally more than 0.02 % and not more than 0.1 % of Nb and/or more than 0.02 % and not more than 0.1 % of V are contained in a total amount of 0.1 % or less and wherein N (mass %)/Al (mass %) is 0.3 or more, and which has a tensile strength of 440 Mpa or more and exhibits a BH of 80 Mpa or more and a ΔTS of 40 Mpa or more. The steel sheet is produced by a method which comprises heating a slab having the above composition to a temperature of 1000°C or higher, followed by rough rolling, to provide a sheet bar, subjecting the sheet bar to a finish rolling under a condition wherein an output temperature is 800°C or higher, cooling the resultant product within 0.5 sec after the finish rolling at a cooling rate of 20°C to 40°C/s or more, and reeling it at a temperature of 650°C to 450°C or lower. The high tensile hot-rolled steel sheet is excellent in strain aging hardening properties, has high formability and stable quality characteristics, and thus can provide various automobile parts having a satisfactory strength and allows the achievement of the lightweight of an automobile body.</p> |
