| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for producing a high tension steel plate having≥30 mm plate thickness, excellent in earthquake-proof and weldability having a strength of≥570 MPa class of tension strength. SOLUTION: The steel composed by mass% of 0.03-0.15% C, 0.01-0.50% Si, 0.15-1.30% Mn. 0.05-0.40% Mo, 0.001-0.050% Nb and the balance Fe with inevitable impurities and 0.23-0.45% To Ceq=C+Mn/6+Si/24+Mo/4+Cr/5+Ni/40+V/14, and≤0.25% to Pcm=C+Si/30+(Mn+Cu+Cr)/20+Ni/60+Mo/15+V/10+5B, is as it is after casting or reheated after once cooling, and held at 850-1,050°C. Thereafter, rolling is applied in the rolling temperature range of 850-1,050°C so as to become to 50-95% total rolling-reduction ratio between 850-950°C, and after completing the rolling, cooling is performed from≥750°C to <350°C at 2-100°C/s average cooling speed and thereafter, air-cooling is performed to <250°C and tempering is performed at 250-550°C and thereafter, the air-cooling is performed. COPYRIGHT: (C)2006,JPO&NCIPI
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