Oxidation behaviour of austenitic stainless steel 304HCu in Advanced Ultra Supercritical (AUSC) steam and the efficacy of shot-peening treatment

Effect of shot-peening on the oxidation behaviour of alloy 304HCu in controlled advanced ultra-supercritical (AUSC) steam at 650 ◦C, 31MPa for 600h was investigated. Non-shot peened surfaces form thick Fe-rich oxides, undergo internal oxidation, and suffer oxide spallation sooner than those reported in literature. Shot-peened surfaces form a thin, external chromia scale with Mn(Cr,Fe)2O4 and MnCr2O4 spinels growing above and below it respectively. Shot-peening enhances Cr and Mn diffusivity through grain refinement and increased dislocation density, which aids in resisting chromia scale breakdown, eliminating iron oxides, and preventing oxide spallation. Oxide growth mechanism in AUSC steam is discussed.