| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength hot rolled steel plate having excellent toughness without causing deterioration in HIC (hydrogen-induced cracking) resistance in a thick material with a plate thickness of≥18 mm; and to provide a method for advantageously producing the same. SOLUTION: The thick hot rolled steel plate has a steel composition comprising, by mass, 0.01 to 0.05% C,≤1.0% Si, 0.3 to 1.5% Mn,≤0.025% P,≤0.001% S, 0.005 to 0.10% Al,≤0.0050% N, 0.0001 to 0.0020% B, 0.005 to 0.03% Ti, 0.030 to 0.10% Nb, 0.001 to 0.005% Ca and≤0.003% O, and also satisfying 0.8Si≤Mn≤Si+1.2, 0.5<(Ti+Nb/2)/C<4.0, and 1.2≤äCa-(130×Ca+0.18)×O}/(1.25×S)≤3.6, and the balance Fe with inevitable impurities, and has a metallic structure composed of bainitic ferrite and/or ferrite. Further, by controlling the amount of precipitation of B to≤10 ppm, the remarkable improvement of strength and weld zone toughness are imparted, and also, the variation in the toughness and hardness of the electric resistance weld zone after seam annealing can be reduced. COPYRIGHT: (C)2007,JPO&INPIT
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