STEEL WITH LOW YIELD RATIO AND HIGH TENSILE STRENGTH, EXCELLENT IN BRITTLE FRACTURE RESISTANCE UNDER HIGH SPEED DEFORMATION, AND ITS PRODUCTION

摘要

PROBLEM TO BE SOLVED: To provide steel with low yield ratio and high tensile strength, excellent in brittle fracture resistance even under high speed deformation occurring at the time, e.g. of a big earthquake of active fault type, and particularly high tensile strength steel having ≥780MPa tensile strength and ≤85% yield ratio. ;SOLUTION: This steel has a composition which contains, by weight ratio, 0.05-0.2% C, 0.05-1.50% Si, 0.5-2.0% Mn, 0.05-2.0% Cr, 0.05-1.0% Mo, 0.01-0.1% V, and 0.005-0.1% Al and in which the contents of S and O are limited to ≤0.005% and ≤0.002%, respectively. Further, this steel has ≥30% value of reduction of area under static loading condition at a tensile test using a test piece having a notch producing ≥5 coefficient of stress concentration.;COPYRIGHT: (C)1998,JPO