Spring with excellent spring steel to hydrogen embrittlement resistance and fatigue characteristics, the manufacturing method and the spring steel of the spring steel

摘要

PROBLEM TO BE SOLVED: To obtain a spring steel, improved in hydrogen embrittlement resistance while promoting the increase of strength and stress and further improved in fatigue durability, by controlling the number of large-size MnS inclusions of a specific length or above in an inspection plane to a specific value. ;SOLUTION: This spring steel has a composition consisting of, by mass, 0.25-0.70% C, 1.0-2.1% Si, 0.05-0.49% Mn, 0.05-2.0% Cr, ≤0.02% S, 10-200ppm N, at least one element selected from the group consisting of 0.001-0.2% Ti, 0.05-0.5% Cu, 0.0002-0.01% Ca, and 0.001-0.10% Zr, and the balance iron with inevitable impurities. Further, the number of sulfides composed essentially of Mn or multiple compounds based on the sulfides, having ≥8μm major axis, existing within the following inspection plane is regulated to ≤20 pieces: at this time, the inspection plane means the cross section with an area of 20mm², set up from the region being at a depth of ≥0.3mm from the surface and excluding the central part.;COPYRIGHT: (C)1998,JPO