Microstructural evolution during hot deformation of duplex stainless steel

The microstructure evolution during hot deformation of a 23Cr-5Ni-3Mo duplex stainless steel was investigated in torsion. The presence of a soft delta ferrite phase in the vicinity of austenite caused strain partitioning, with accommodation of more strain in the delta ferrite. Furthermore, owing to the limited number of austenite/austenite grain boundaries, the kinetics of dynamic recrystallisation (DRX) in austenite was very slow. The first DRX grains in the austenite phase formed at a strain beyond the peak and proceeded to < 15% of the microstructure at the rupture strain of the sample. On the other hand, the microstructure evolution in delta ferrite started by formation of low angle grain boundaries at low strains and the density of these boundaries increased with increasing strain. There was clear evidence of continuous dynamic recrystallisation in this phase at strains beyond the peak. However, in the delta ferrite phase at high strains, most grains consisted of delta/delta and delta/gamma boundaries.