| 摘要 |
PURPOSE:To produce a high-tensile strength steel sheet excellent in workability and weldability, by adding specified elements to a low-carbon steel, finish-rolling the steel in a specified temperature range, and then quenching and optionally annealing the steel. CONSTITUTION:A steel slab containing 0.02-0.10% C, 0.05-0.40% Si, 0.50- 3.00% Mn, and 0.005-0.10% sol. Al as basic components, and one or more of 0.005-0.050% Nb, 0.01-0.10%V and 0.005-0.10% Ti and optionally one or more of 0.05-1.00% Mo, 0.05-1.00% Cr and 0.10-1.00% Ni is rolled into a sheet. In this case, the upper limit of a rolling temperature is controlled at a level just above its Ar3 transition point, while the lower limit is controlled at a level where a ferrite rate, directly precipitated from an austenite phase having a work-strain during rolling, is at 40% or less. After completion of rolling, the steel sheet is quenched from a temperature range where a ferrite rate will be 50-90%, and then optionally tempered. |
