Influence of Thermal Aging Treatments on Intergranular Corrosion and Cyclic Oxidation Behavior of Low Nickel and Nickel-Free Austenitic Stainless Steels

The present study aims to investigate the influence of thermal aging treatments on the intergranular corrosion and cyclic oxidation behavior of low nickel and nickel-free austenitic stainless steels (Cr–Mn and Cr–Mn–N ASSs). From the findings, Microstructural features of Cr–Mn–N and Cr–Mn austenitic stainless steels in As received (AR) condition resulted in an austenite grain matrix along with concurrent twinning, and it is also observed that the nickel free austenitic stainless steels (Cr–Mn–N ASS) with fine grain structure than low nickel austenitic stainless steels (Cr–Mn ASS). In the solution annealing (SA) condition, both alloys were observed to have a coarser austenite grain matrix with a reduced number of twins. Further, austenite grain coarsening with wider twins and chromium-rich inter-metallic phases was revealed in the solution annealing followed by aging (SA + A) conditions. The hardness was higher in AR condition, followed by SA and SA + A treatments in both Cr–Mn–N and Cr–Mn ASSs. This could be due to the grain coarsening effect with thermal aging treatments. In AR and SA conditions there was no evidence of intergranular corrosion (IGC) attack was observed, whereas in SA + A condition with higher durations, i.e., from 180 min onwards, ditch structure was observed in both Cr–Mn–N and Cr–Mn ASS. The Cr–Mn–N ASS shows poor % DOS than Cr–Mn ASS. This could be due to high rate of Cr-rich precipitates development. A higher rate of oxidation kinetics (i.e., weight gain per unit area and spallation rate) was observed in SA + A than in AR and SA conditions in both alloys.