PRODUCTION OF THICK STEEL PLATE EXCELLENT IN TOUGHNESS IN WELD HEAT-AFFECTED ZONE AND LAMELLAR TEAR RESISTANCE

摘要

PURPOSE:To produce a thick steel plate having the characteristics by subjecting a cast slab with a specific composition prepared by successively adding Ti, Zr, and Ca to a molten steel under respectively specified conditions and carrying out casting to reheating at specific temp. and then forming this cast slab into a steel plate. CONSTITUTION:Ti is added by 0.010-0.040% to a molten steel with 0.003-0.020% dissolved oxygen content and 0.005-0.030% Zr is added within 30min after the above Ti addition and, further, 0.001-0.010% Ca is added within 15min after the above Zr addition, and then, solidification is completed by a continuous casting method, and the resulting cast slab practically free from Al which has a composition consisting of, by weight, 0.03-0.15% C, =0.6% Si, 0.8-2.0% Mn, =0.025% P, =0.005% S, 0.004% Al, 0.003-0. 060% Nb, 0.0020-0.0060% N, 0.005-0.020% Ti, 0.003-0.015% Zr, 0.0005-0.0050% Ca, 0.001-0.006% O, and the balance iron with inevitable impurities and satisfying an inequality is reheated at =1250 deg.C and formed into a steel plate. By this method, a high tensile strength steel plate excellent in toughness at low temp. in weld heat-affected zone can be obtained.