Fatigue properties and plastically deformed microstructure of Fe-15Mn-10Cr-8Ni-4Si alloy in high-cycle-fatigue regime

Tension compression axial fatigue tests in the high cycle fatigue regime were conducted on the Fe-15Mn-10Cr-8Ni-4Si (wt.%) alloy, and the microstructure beneath the fracture surface was investigated using EBSD to characterize the fatigue crack path in terms of the plastically deformed microstructure. The fatigue limit was relatively high and enough to cause macroscopic plastic deformation. It was found that epsilon-martensitic transformation can occur below the fatigue limit. The fracture surface morphology changed from a relatively smooth region with straight stripes close to the crack origin to three-dimensional step-like morphologies followed by striations at a distance from the origin. The epsilon-martensite were found near the crack origin region, where crack growth along epsilon-martensite seemed to occur, while there are reports that neither mechanical twins nor e-martensite were observed in high cycle fatigue of some high-Mn steels. Contrarily, less e-martensite were found in the region where the striations were formed on the fracture surface. In conclusion, the e-martensite might affect the small crack growth in high cycle fatigue regime of Fe-15Mn-10Cr-8Ni-4Si.