Effects of Retained Austenite and Softened Martensite on High‐Cycle Fatigue Behavior of Spring Steel under Two Loading Modes

Abstract

A novel quenching-partitioning-tempering (Q-P-T) process is applied to 60Si2Mn spring steel, resulting in multiphase microstructures consisting mainly of retained austenite (RA) and softened martensite (SFM). The influence of multiphase microstructures on the high-cycle fatigue behavior of Q-P-T and traditional quenching and tempering (Q&T) spring steels are investigated under rotating-bending and tensiontension loading. The results indicate that the fatigue strength of Q-P-T spring steel with RA, SFM, and lower quenching stress increases by 23.9 and 14.4% under cyclic rotating-bending and tension-tension loadings, respectively, compared with that of Q&T spring steel. Under both loading modes, the fatigue crack of the Q-P-T spring steel is mainly initiated from the interface between the martensitic matrix and inclusions or carbides. In contrast, the fatigue crack of the Q&T spring steel is mainly initiated from the plastic area around the martensitic matrix rather than inclusions. The RA, SFM, and lower quenching stress of the Q-P-T spring steel are conducive to the formation of dimples and tear ridges in the crack propagation and ultimate failure areas, whereas the inadequate SFM and higher quenching stress of the Q&T spring steel are prone to the formation of quasi-cleavage facets and secondary cracks.