| 摘要 |
PURPOSE:To obtain the objective thick steel plate for welded structure excellent in the toughness of the electron beam weld zone by specifying a compsn. constituted of C, Si, Mn, P, S, Al, N, Ni, Cr, Mo, O and Fe and controlling the distribution of the P concn. in the steel. CONSTITUTION:Molten steel contg., by weight, 0.07 to 0.20% C, 0.05 to 0.20% Si, 0.20 to 1.80% Mn, <=0.008% P <=0.005% S, 0.005 to 0.040% SolAl, 0.0020 to 0.0070% N, 0.05 to 1.50% Ni, 0.05 to 0.50% Cr, 0.05 to 1.00% Mo and <=0.0040% O as well as 0.11 to 0.40 N/Al, furthermore contg., at need, one or two kinds of 0.0005 to 0.0050% Ca and 0.0005 to 0.0050% rare earth metals, and the balance Fe with inevitable impurities is subjected to continuous casting. At this time, the crater ends of the continuously cast slab are subjected to forging to regulate P/P0, i.e., the ratio of the P content P on the central part of the plate thickness to the P content P0 in the molten steel in a ladle to <=1.3. This slab is subjected to hot rolling or casting into a thick steel plate and is thereafter subjected to hardening and tempering. |
