| 摘要 |
PURPOSE:To obtain a steel sheet having >=70kg/mm.<2> high tensile strength, superior workability, superior toughness at low temp. and superior bending crack resistance especially during edging by shearing by subjecting a Ti added steel having a specified composition to controlled rolling and by coiling the rolled sheet at a specified low temp. CONSTITUTION:A killed steel consisting of, by weight, 0.05-0.20% C, 0.04- 0.20% Ti, <=1.2% Si, 0.5-2.0% Mn, <=0.025% P, <=0.015% S, 0.005-0.15% sol. Al, <=0.008% N and the balance Fe or further contg. one or more among <=0.0100% Ca, <=0.0030% B and <=1.0% Cr is hot rolled at >=30% total draft in the temp. range of 900-800 deg.C. After finishing the rolling at >=800 deg.C, the rolled sheet is rapidly cooled at >=5 deg.C/sec cooling rate and coiled at 500-200 deg.C. By carrying out the coiling at said low temp., the precipitation of TiC is properly inhibited, and transformation hardening is mainly caused in place of precipitation hardening, so the purpose can be attained. |
