Hot deformation behavior and dynamic recrystallization of Mn18Cr18N steel with as-cast versus wrought starting structures

Hot deformation behavior and dynamic recrystallization of Mnl 8Crl 8N austenitic stainless steel with as-cast and wrought starting microstructures were investigated by isothermal hot compression tests at temperatures from 950 C to 1200 C under strain rates of 0.001-1/s up to the true strain of 0.7. The true stress-strain curves were characterized by hardening and subsequent softening varied with temperatures and strain rates both for as-cast and wrought samples. However, the hot deformation activation energy of as-cast samples is 672KJ/mol, which is higher than 478KJ/mol of the wrought samples. It implies that dynamic recrystallization is more difficult due to as-cast coarse structure. Hot processing maps were established both for as-cast and wrought samples. There are two domains with peak power-dissipating efficiency at the high strain rate of 1/s and the low strain rate of 0.001/s respectively for as-cast samples. For wrought samples, the above two domains merged as one with peak power efficiency at lower strain rates. Two dynamic recrystallization mechanisms, dislocation and twinning, were demonstrated at the lower strain rate and the higher strain rate domains in the processing map respectively for the as-cast steel. DRX controlled by dislocation mechanism occurs mainly in the peak efficiency domain of the wrought steel at higher strains. (C) 2017 The Authors. Published by Elsevier Ltd.