Early oxidation mechanism of austenitic stainless steel TP347H in supercritical water

The initial corrosion behaviour of austenitic TP347H exposed to supercritical water was investigated. The early oxidation can be categorized into three stages (rapid oxidation, transitory, and diffusion-controlled stages). Higher temperature resulted in a transformation towards the subsequent stage earlier and less oxidation resistance. Cr⁶⁺ species (likely CrO₂(OH)₂) were only generated on the surface in the very early phase, and then they gradually disappeared as the exposure time increased. Compared with a complete outer Fe-rich oxide layer, the formation priority of a continuous inner Cr-rich layer was observed at 540 °C within 35 h. A corresponding early oxidation process was determined.