| 摘要 |
PROBLEM TO BE SOLVED: To provide a thick steel plate simultaneously satisfying high basic material strength, good toughness at the center part in the thickness, good large heat-input weld HAZ (Heat Affect Zone) toughness and high rolling efficiency at high dimensions. SOLUTION: To a cast slab composed of 0.01-0.07% C,≤0.2% Si, 0.2-1.8% Mn,≤0.015% P, 0.0005-0.005% S, 0.0003-0.003% B, >0.02% to 0.06% Nb, 0.001-0.0034% Al, 0.005-0.02% Ti, 0.001-0.008% N, 0.001-0.004% O and further, one or more kinds of 0.0003-0.004% Ca and 0.003-0.004% Mn and satisfying a prescribed condition to the effective B content and Ceq, rough rolling is applied after cooling to Ar<SB>3</SB>-200°C and then successively reheating at 1000-1250°C and thereafter, a finish-rolling satisfying the following the formula (3) is applied at 800-900°C and further, thereafter, an accelerating cooling is performed from≥Ar<SB>3</SB>point temperature. COPYRIGHT: (C)2008,JPO&INPIT
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