Correlation between microstructure evolution and mechanical response in a moderately low stacking-fault-energy austenitic Fe–Mn–Si–Al alloy during low-cycle fatigue deformation

Through in-depth microstructural and mechanical characterization, a mechanism for low-cycle fatigue (LCF) deformation of an Fe-30.7Mn-4.3Si-1.8Al (in wt%) austenitic transformation-induced-plasticity (TRIP) steel at a total strain range of 2% was investigated. The LCF deformation of the steel was performed through two main deformation modes which were planar slip of Shockley partials, and ε-martensitic transformation and its reverse transformation. The varying significance of each deformation mode as well as the relevance between the two modes determined the microstructures evolved during fatigue deformation and resulted in a four-stage cyclic hardening behavior. With increasing fatigue cycles, the LCF deformation was dominated sequentially by the multiplication of partial dislocations, development of slip bands, reversible ε-martensitic transformation, and formation of more thick and crossed ε-martensite along with enhancement of planar dislocation slip, thus generating the characteristic deformation stages of primary cyclic hardening, cyclic softening, cyclic saturation, and secondary cyclic hardening correspondingly. In general, the superior LCF resistance of the steel was attributed to appreciably high plasticity reversibility during the entire fatigue deformation which was caused by reversible planar dislocation slip and ε-martensitic transformation.