Mechanical properties and strain hardening behavior of phase reversion-induced nano/ultrafine Fe-17Cr-6Ni austenitic structure steel

Nano/ultrafine-grained (Nano/UFG) structure was obtained in Fe-17Cr-6Ni austenitic steel using a combination of severe cold deformation and reverse-transformation annealing. The microstructural evolution during severe cold reduction and annealing was studied to elucidate the effect of grain size on mechanical properties and strain hardening behavior. Austenitic steel with the smallest average grain size of ∼220 nm was obtained and exhibited a good combination of high strength and high ductility when the cold reduction was ∼75% and annealing was carried out at 700 °C for 20 s. The relationship between grain size and yield strength was in good agreement with Hall-Petch relationship until ∼200 nm grain size. For coarse-grained steel, the strain hardening rate (SHR) plots comprised of 4 stages and the increase of SHR was attributed to deformation-induced martensite transformation (DIMT). While for Nano/UFG ASS, the SHR plots contained only 3 stages and the increase of SHR was attributed to the comprehensive effect of DIMT and twining.