The operative dynamic recrystallization mechanism of austenite during the transient deformation in a Ni-30%Fe model alloy

Abstract

Effect of strain rate and its discontinuous changes on dynamic recrystallization (DRX) behaviours of a Ni-30%Fe austenitic model alloy were investigated by hot compression tests. The results show that, during deformation at slow strain rates, DRX occurs with discontinuous nature, i.e. the DRX nuclei preferentially appear along initial grain boundaries followed by a quick growth through the strain-induced boundary migration (SIBM). Interestingly, during the further deformation after an abrupt increase in the strain rate, it can be found that the subgrains which developed in the first stage of deformation would gradually transform into new DRX grains. Therefore, in spite of the low stacking fault energy austenite, the continuous DRX (CDRX) is indeed possible to be activated during the transient deformation. The strain-induced sub-boundaries developed in the first deformation stages are believed to transform into higher-angle boundaries easily in further straining after abrupt increase of the strain rate. By this way, the CDRX mechanism in austenite is significantly promoted. Moreover, the local growth of new grains also plays an important role in this dynamic softening process.