The effect of tempering temperature on the high cycle fatigue properties of high strength spring steels

Abstract

The high cycle fatigue behavior of a high strength spring steel has been investigated in relation to the microstructural variation through austenizing followed by tempering at different temperatures. The results have been compared with those of SAE9254 alloy which is widely used as an suspension coil spring material. The crack initiation resistance and crack growth resistance of high strength steel, regardless of the microstructure (tempering temperature), were superior to those of SAE9254. The highest fatigue limit, ductility and toughness were achieved by tempering the alloy at 450 degrees C which resulted in a microstructure composed of predominately the tempered martensite with a favorable precipitation distribution. At lower tempering temperatures the existence of retained austenite induced inhomogeneous slip while at higher tempering temperatures the excessive precipitation softened the martensitic matrix. These both lead to a loss in ductility and fatigue strength.