Deformation-induced martensitic transformation and strain hardening in a nanocrystalline FeMn alloy processed by severe austenite pre-deformation

Abstract The FeMn alloy is processed by the surface mechanical rolling treatment when being heated beyond 200°C for an austenitic state. The nanocrystalline microstructure mainly consisting of austenite phase is resulted in by the severe austenite pre-deformation, which is attributed to the significant mechanical stabilization. This is in contrast with the coarse-grained counterpart that is dominated by epsilon-martensite. The nanocrystalline microstructure in the graded specimen can undergo a large tensile deformation. Martensitic transformation occurs during mechanical loading, and strain hardening of the nanocrystalline microstructure is achieved. Microscopic observations show the growth of epsilon-martensite plates, indicating the multiplication of stacking faults in the nanograins. This study demonstrates a novel approach combining alloy design and plastic processing to produce nanocrystalline materials with strain hardening capacity.