| 摘要 |
PURPOSE: To produce an extremely thick high tensile strength steel plate high in the toughness of the base metal and the weld heat affected zone by specifying its compsn. constituted of C, Si, Mn, Ni, Cr, Mo, Nb, B, Ti, Al, N, Cu, V and Fe and its structure. CONSTITUTION: In a steel having a compsn. contg., by weight, 0.02 to 0.15% C, <=0.30% Si, 0.6 to 2.0% Mn, <=1.50% Ni, <=1.0% Cr, <=1.0% Mo, 0.01 to 0.07% Nb, <=0.002% B, 0.005 to 0.030% Ti, <=0.08% SolAl, <=0.006% N, C×(Cu+5V); 0.02 to 0.20, and the balance Fe with inevitable impurities, the average lath length of bainite in the structure is regulated to <=15μm, and the volume rate of ferrite is regulated to <30%. The extremely thick high tensile strength steel plate of this steel can be obtd. by heating a slab having the above compsn. at 1000 to 1250 deg.C, thereafter executing cumulative rolling at >=30% in a recrystallized austenitic region and at >=50% in an unrecrystallized austenitic region, subjecting it to accelerated cooling to <=580 deg.C and transforming the same.
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