THE EFFECT OF TEMPERING TEMPERATURE ON THE HIGH CYCLE FATIGUE PROPERTIES OF HIGH STRENGTH SPRING STEELS

摘要

The high cycle fatigue behavior of a highstrength spring steel has been investigated in relation to themicrostructural variation through austenizing followed bytempering at different temperatures. The results have beencompared with those of SAE9254 alloy which is widely usedas an suspension coil spring material.The crack initiation resistance and crack growth resistance ofhigh strength steel, regardless of the microstructure (temperingtemperature), were superior to those of SAE9254. The highestfatigue limit, ductility and toughness were achieved bytempering the alloy at 450 deg C which resulted in amicrostructure composed of predominately the temperedmartensite with a favorable precipitation distribution. At lowertempering temperatures the existence of retained austeniteinduced inhomogeneous slip while at higher temperingtemperatures the excessive precipitation softened themartensitic matrix. These both lead to a loss in ductility and fatigue strength.