Oxidation behavior of 9Cr-4.5Al ODS steel in 600 °C supercritical water and the effect of pre-oxidation

The oxidation behavior of a 9Cr-4.5Al ODS steel in 600℃ supercritical water with 200 ppb dissolved oxygen was investigated with and without a pre-oxidation heat treatment. In general, results suggest that all samples follow the “available space model” oxidation mechanism as exposure time is extended. Based on the microstructural analysis, it is found that a thin alumina layer formed by pre-oxidation treatment is initially protective up to approximately 100 h. However, this passive film becomes ineffective due to the existence of M23C6 (M = Cr, Fe) and the insufficient content of Al or/and Cr in the steel.