Precipitation Strengthened Spring Steel for Automotive Suspensions

A spring steel with a small amount of niobium and vanadium added simultaneously into AISI9260 or SUP7 of the Japanese Industrial Standards is found to have a good sag resistance or resistance to a small deformation, during service for automotive suspension springs. The two alloying elements bring about a retarded softening when quenched and tempered, which is the result of the precipitation of carbides of the two elements. Besides good sag resistance, which is evaluated by two methods, the steel has comparable characteristics to SUP7 in many respects, such as hardenability, fatigue properties, and so on. Reduction in the weight of the suspension springs is about 15 pct. The new spring steel has been used for some Japanese new models for two years, and the application is increasing.