| 摘要 |
PURPOSE:To produce a strong and tough steel usable in low-temp. environment at a low cost by subjecting a specifically composed steel to hot rolling then further to hot rolling and hardening under specific conditions followed by heating and hardening under specific conditions and subjecting the steel plate to tempering. CONSTITUTION:A steel contg., by weight, 0.15-0.45% C, 0.05-1.00% Si, 0.3- 2.0% Mn, 0.01-0.10% Al, 0.005-0.150% one or two kinds of Nb and Ti and the balance Fe and unavoidable impurities and contg. the impurities limited to <=0.025% P and <=0.015% S is subjected to primary hot rolling in an austenite state and is then subjected immediately in the austenite state to holding or reheating at or to the temp. region of the Ac3 point -(Ac3 point+200 deg.C) and thereafter the steel is subjected to secondary hot rolling. The rolled steel is directly hardened in the auxtenite state and is subjected repeatedly >=1 time of the treatment in which the steel plate is heated to the temp. region of the Ac3 point -(Ac3 point+200 deg.C) and is hardened. The steel plate is thereafter subjected to a tempering treatment at the Ac1 point or below. |
