STEEL FOR HIGH STRENGTH BOLT, EXCELLENT IN HOT DIP GALVANIZING RESISTANCE, AND HIGH STRENGTH BOLT

摘要

PROBLEM TO BE SOLVED: To provide a steel for high strength bolt, having ≥F10T strength, free from deterioration in strength after plating, and excellent in hot dip galvanizing resistance (plating crack, plating yellowing), and a high strength bolt. ;SOLUTION: The steel for high strength bolt has a composition which contains, by weight, 0.15-0.30% C, ≤0.30% Si, 0.3-1.5% Mn, 0.5-1.5% Cr, 0.1-0.5% Mo, 0.01-0.05% Al, 0.007-0.030% N, and 0 or 0.0010-0.0100% Ca and in which B content is specified to ≤0.0003% and the ratio between Al content and N content, Al/N, is regulated to 1.5-2.8. Further, the high strength bolt is obtained by subjecting this steel for high strength bolt to tempering at 500°C after hardening and regulating austenite grain size to No.8 or above.;COPYRIGHT: (C)1997,JPO