Dynamic Recrystallization and Phase-Specific Corrosion Performance in a Super Duplex Stainless Steel

Super duplex stainless steel specimens were subjected to controlled (in a deformation simulator) thermal and thermal plus deformation treatments. The objective was to relate the corrosion performance with hot (1000-1300°C) deformed microstructures. The microstructural evolutions were quantified with extensive microtextural characterization and measurements of phase-specific micro-hardness. The corrosion behavior was investigated by anodic polarization and phase-specific selective dissolution methods. Though the thermal treatment imposed an increasing degradation in corrosion performance with holding temperature, the associated deformation at that temperature brought a non-monotonic behavior. The best corrosion performance (or the lowest passivation current density) was noted in the specimen deformed at ~1100°C. This superior corrosion behavior was attributed to the grain size refinement in the austenite phase. Finally, a combination of transmission Kikuchi diffraction (TKD) plus transmission electron microscopy (TEM) clearly related the grain size refinement to discontinuous dynamic recrystallization. The overall corrosion behavior was shown to be determined by a balance between decreasing austenite fraction and dynamic recrystallization-induced grain size refinement of the austenite phase.