A combined experimental and first-principle study on the oxidation mechanism of super austenitic stainless steel S32654 at 900 °C

Abstract

Abstract A combined experimental and first-principle study on the oxidation mechanism of super austenitic stainless steel S32654 at 900 °C for a short time period (1, 3, and 5 h) in air is presented. The samples exhibit excellent oxidation resistance because of the initial and gradual formation of the denser Fe- and Cr-rich layer with increasing oxidation time. Meanwhile, the Mo-rich layer gradually forms because of the Mo diffusion, which results in the formation of the oxide layer with two distinct regions: an inner Fe- and Cr-rich layer and an outer Mo-rich layer. Density functional theory is applied to investigate the diffusion behaviour of Mo atom in the Fe-Cr-Ni/Cr2O3 interface and the effects of alloying elements (Fe, Ni, and Mn) on the Mo diffusion. The Mo originating from the alloy matrix tends to diffuse into the Cr2O3 part, thereby resulting in the formation of the continuous Mo-rich layer, which is consistent with the experimental behaviour. Moreover, the introduction of Ni to the Cr2O3 part can promote the Mo diffusion and the formation of the Mo-rich oxide layer, whereas Fe and Mn can hinder the Mo diffusion. The calculated results provide a microcosmic explanation of the experimental results.