Microstructure evolution of Fe-33Mn-4Si steel during low-cycle fatigue deformation

Abstract

The microstructure evolution and mechanical behavior of an Fe-33Mn-4Si alloy steel under low-cycle fatigue deformation were investigated by using the X-ray diffraction and electron backscatter diffraction techniques.Results show that the experimental steel has an initial microstructure consisting of austenite and thermally induced ε-martensite. The initial microstructure remarkably affects the low-cycle fatigue property of the experimental steel through influencing the ε-martensitic transformation during deformation. At the early stage of fatigue deformation (first 100 deformation cycles), with increasing deformation cycles, a rapid increase in the volume fraction of ε-martensite and the frequency of the intersection of ε-martensite with different variants result in a quick rise in cyclic average peak stress and work hardening degree. With the continuation of cyclic deformation up to fatigue fracture, the ε-martensite becomes the dominant constituent phase in the deformation microstructure, and the volume fraction of ε-martensite and the frequency of the intersection of ε-martensite increase at an appreciably slower rate, thereafter significantly slowing the increase in cyclic average peak stress and work hardening degree.

Keywords

• fe-mn-si steel
• low-cycle fatigue deformation
• microstructure evolution
• ε-martensite
• annealing twin