Dynamic Restoration Processes in a 23Cr-6Ni-3Mo Duplex Stainless Steel: Effect of Austenite Morphology and Interface Characteristics

The austenite and ferrite microstructure evolution and restoration mechanisms were studied during hot uniaxial compression of a 23Cr-6Ni-3Mo duplex stainless steel with two markedly different austenite morphologies (i.e., equiaxed and Widmanstatten). The deformation was performed at a temperature of 1273 K (1000 A degrees C) at a strain rate of 0.1 s(-1). The strain was preferentially partitioned in ferrite for both the microstructures studied. Both austenite morphologies displayed frequent splitting into complex-shaped deformation bands, containing dislocation cells and local stacking faults. Equiaxed austenite was favorable to the local development of microbands (MBs), while its Widmanstatten counterpart appeared to be completely resistant to their formation. This was attributed to the complexity of deformation inside the irregularly shaped Widmanstatten plates precluding the formation of self-screening MB arrays. The MB boundaries were typically aligned along highly stressed slip planes. The presence of discontinuous dynamic recrystallization (DDRX) within both the austenite morphologies was very limited. A slightly higher fraction of DDRX was detected in Widmanstatten austenite, compared to equiaxed austenite, which was ascribed to its higher contribution to the overall deformation and lower fraction of low-mobility coherent twin boundaries. Furthermore, it was demonstrated that continuous dynamic recrystallization (CDRX) was the main restoration mechanism within ferrite for both the microstructure types studied. The CDRX development within ferrite was accelerated in the microstructure with equiaxed austenite. This was related to the comparatively lower fraction of coherent interphases in this microstructure, which would hinder the slip transmission across the interphase and make the strain concentrate within ferrite.