Vanadium - Transforming Possibilities

Precipitation Strengthened Spring Steel for Automotive Suspensions

Abstract:

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.
The current trend toward lighter automotive suspension springs requires higher working stresses, with sag as the primary obstacle for suspension designers. Prior investigations1,2,3 have revealed that silicon has an advantageous effect of reducing sag on spring steels. For this reason, a higher-silicon steel, AISI9260 or JIS-SUP7 (0.6 pct C−2.0 pct Si−0.85 pct Mn), has become widely used as a sag-resistant spring steel in place of JIS-SUP6 (0.6 pct C−1 .65 pct Si−0.85 pct Mn) in Japan. Since improved sag resistance was needed, especially for the suspension springs for modern lightweight FF cars, we investigated various strengthening effects for steels and have designed a precipitation-strengthened spring steel.

Keywords:

vanadium, spring steel. 

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