PURPOSE: To produce an extremely thick high tensile strength steel plate free from defects caused by hydrogen even without dehydrating treatment in the production of a steel plate.
CONSTITUTION: An extremely thick high tensile strength steel plate having a compsn. contg., by weight, 0.02 to 0.25% C, 0.05 to 1.0% Si, 0.50 to 2.5% Mn, ≤0.02% P, ≤0.01% S, 0.001 to 0.05% Al and ≤0.01% N, contg. one or ≥two kinds among 0.01 to 1.5% Cr, 0.01 to 1,0% Mo, 0.002 to 0.1% Nb, 0.1 to 5.0% Ni, 0.01 to 2.5% Cu and 0.0005 to 0.0050% B, contg. one or both of 0.08 to 0.50% V and 0.01 to 0.10% Ti and contg. ≤0.20% sol.V, and the balance iron with inevitable impurities and free from defects caused by hydrogen is produced. Thus, the steel plate high in reliability can be obtd. at a low cost.
TAKEDA TETSUJIRO
OKAMOTO KENTARO
