Enhanced Mechanical Properties of Microalloyed Austenitic Stainless Steel Produced by Martensite Treatment

A thermomechanical treatment based on the reversion of strain‐induced martensite (SIM) was employed to produce ultrafine‐grained structures in a microalloyed austenitic stainless steel (ASS). The smallest average grain size of ≈480 nm was achieved by annealing the heavily‐rolled samples at 650 °C for 240 min while an outstanding combination of strength and ductility was acquired by annealing at 850 °C for 1 min due to the synergic effects of the following phenomena: refinement of austenite matrix grains down to an average grain size of 620 nm, presence of small amount of thermally‐induced martensite, formation of a bimodal grain size distribution by primary and secondary recrystallization processes, and dislocation accumulation. The kinetics of strain‐induced martensitic transformation was studied and the classical rule of mixtures was used to elucidate the hardening contribution of martensite. Subsequently, it was shown that the Hall–Petch relation is valid for a wide range of grain size for AISI 304 type stainless steel.