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

摘要

PROBLEM TO BE SOLVED: To provide a steel material free from a brittle fracture surface ratio increasing phenomenon in a stress concentration part even under high speed deformation and excellent in brittle fracture resistance. ;SOLUTION: This steel has a composition which contains, by weight ratio, 0.05-0.2% C, 0.05-0.7% Si, 0.5-2.0% Mn, and 0.005-0.1% Al and in which the contents of S and O are controlled to ≤0.005% and ≤0.0025%, respectively, and also has a metallic structure consisting of ferrite in ≥25% by area fraction and the balance bainite or bainite + martensite. Further, this steel has ≥30% value of reduction of area under static loading condition at the tensile test using a test piece having a notch giving ≥5 coefficient of stress concentration.;COPYRIGHT: (C)1998,JPO