| 摘要 |
PURPOSE:To obtain a high tension thick steel plate having excellent toughness without a reheating treatment by subjecting a specifically composed steel to controlled rolling and controlled cooling after rolling under specific conditions. CONSTITUTION:A steel is composed, by weight %, of 0.1-0.25 C, 0.01-0.5 Si, 0.9-1.5 Mn, 0.02-0.1 Al, 0.002-0.008 N, 0.0003-0.002 B, <0.01 S, <0.03 P, and the balance Fe with inevitable impurities. Such steel is heated to <=1,050 deg.C, and rolled at >=30% cumulative draft with respect to the final plate thickness in the uncrystallization temp. region in such a way that the rolling finish temp. is maintained within the temp. range of the ferrite transformation temp. or above and the ferrite transformation temp. +20 deg.C or below. The steel after the final rolling is allowed to cool or is subjected to cooling at <=5 deg.C/sec cooling rate down to the temp. range of the ferrite transformation temp. -60 deg.C or above and the ferrite transformation temp. -20 deg.C or below and is quickly cooled at 15 deg.C/ sec cooling rate immediately thereafter. |
