Effect of grain size on the intrinsic mechanical stability of austenite in transformation-induced plasticity steels: The competition between martensite transformation and dislocation slip

An austenitic stainless steel was employed to clarify the effect of grain size on the intrinsic mechanical stability of austenite in transformation-induced plasticity (TRIP) steels. Contrary to the general impression in TRIP-assisted steels with multi-phase microstructure, grain refinement decreases the mechanical stability of austenite in the single-phase austenitic steel. The unexpected phenomenon was explained in the essence of austenite mechanical stability by theoretical calculation and experimental verification: dislocation slip and martensite transformation are two competing deformation mechanisms during plastic deformation of austenite, the stress for martensite transformation will be lower than that for dislocation slip when the grain size is smaller than a critical value. Therefore, the yielding mechanism of austenite will transit from dislocation slip to martensite transformation with the refinement of austenite grains.