Microstructural evolution and sensitization behaviour of thermo-mechanically processed low-nickel high-manganese austenitic stainless steel

The present study investigates the effects of cold working (CW) and subsequent thermal ageing (TA) on microstructural evolution and sensitization behaviour of low-nickel high-manganese austenitic stainless steel (NMASS; AISI 201 grade). Two sets of specimens were considered to evaluate the influence of deformation and thermal exposure. In first set, 201-grade NMASS specimens were subjected to 15%, 30% and 50% cold deformation followed by solution annealing. In second set, the cold-worked and solution-annealed specimens were subsequently thermally aged at 700 °C for 30, 60, 120 and 180 min. The specimens were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM), while the electrochemical sensitization behaviour was evaluated using double-Loop Electrochemical Potentiokinetic Reactivation (DLEPR) technique. The investigation is aimed at establishing the relationship between the extent of cold deformation, TA, microstructural evolution and sensitization susceptibility of 201-grade NMASS. Particular attention is given to deformation-induced phase evolution and the changes associated with TA that may influence intergranular corrosion (IGC) susceptibility. The DLEPR results likewise varied non-monotonically with deformation and ageing. The maximum reported degree of sensitization (DOS) was 94.45% for 50% cold-worked specimen aged for 60 min, followed by 72.62% and 66.51% after 120 and 180 min, respectively. Post-test morphology indicates that the electrochemical response cannot be interpreted solely as sensitization because attack also occurs within grain interiors in several cold-worked and aged conditions. The results provide a basis for understanding the processing–microstructure–corrosion relationship of NMASS and for identifying processing conditions that can improve its resistance to sensitization in engineering applications.