Effect of high-energy shot peening process on the oxidation behaviour of AISI 321 stainless steel at 900 °C

Abstract

ABSTRACT The present work comparatively investigates the oxidation behaviour of AISI 321 austenitic stainless steel at 900 °C in Ar-21vol.%O2 in two conditions of solution annealed (SAed) and after a high-energy shot peening process (HESPed). Kinetic observations indicated that during the initial 25 h of oxidation, the HESPed sample exhibits higher oxidation kinetics. However, as oxidation progresses, the kinetics of the SAed sample surpasses in a way that after 150 h, the weight gain for SAed is 0.93 mg/cm2, and for HESPed, it is 0.71 mg/cm2. GI-XRD results after 150 h of oxidation revealed similar oxide phases on both samples, including (Cr,Fe)2O3, Mn(Fe,Cr)2O4, and Fe2O3. An important point is that the oxide formed on the surface of the SAed sample, unlike HESPed, undergoes severe spallation and cracking after 150 h, leading to sub-surface oxidation and the formation of Ni-rich oxide phases such as Ni(Fe,Cr)2O4. The enhancement observed in the oxidation performance of the HESPed sample can be ascribed to the augmented density of high-diffusivity paths, a consequence of the high-energy shot peening process, and the prompt development of uniform inner Si-rich and intermediate Cr-rich oxide layers.