LOW YIELD RATIO TYPE HIGH TENSILE STRENGTH STEEL PLATE EXCELLENT IN WELD CRACKING RESISTANCE AND HAVING =440N/ MM2 YIELD RATIO AND =590N/MM TENSILE STRENGTH AND ITS PRODUCTION

摘要

PURPOSE: To produce a low yield ratio type tensile strength steel plate excellent in weld cracking resistance by specifying the compsn. constituted of C, Si, Mn, P, S, Al, Mo, V, Nb and Fe and furthermore specifying the content of ferrite having high hardness. ;CONSTITUTION: As the one having a compsn. contg., by mass, 0.05 to 0.15% C, 0.05 to 0.50% Si, 0.30 to 1.80% Mn, ≤0.015% P, ≤0.005% S, 0.005 to 0.10% Al, 0.05 to 1.00% Mo, 0.005 to 0.070% V and 0.006 to 0.040% Nb, furthermore contg. prescribed amounts of Cu, Ni, Cr, B, Ca, Ti and rare earth metals, and the balance Fe with inevitable impurities, and in which PCM=C+Si/30+Mn/20+ Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B≤0.22%, and furthermore, ferrite in which microhardness in 10kg loads is regulated to ≥180HV is contained by 10 to 50 vol.%, the steel plate having about ≤80% yield ratio, ≥440N/mm² yield strength and ≥590N/mm² tensile strength and excellent in weld cracking resistance can be obtd.;COPYRIGHT: (C)1997,JPO