Oxidation of 316 stainless steel in supercritical water

The oxide scales of 316 stainless steel (316 SS) have been examined after exposure to supercritical water (SCW) with 2.0% H₂O₂ for up to 250 h. The exposed samples were analyzed using weight measurement, scanning electron microscopy (SEM), and X-ray diffraction analysis (XRD). It was found that mass gain of all samples increased with increasing temperature and exposure time. Higher temperature SCW resulted in rougher surfaces and thicker oxide scales. Duplex layer oxide structures with Ni-enrichment at the oxide/metal interface developed on all samples exposed to SCW, which were identified as Fe₂O₃/Fe₃O₄ + spinel/Cr₂O₃/Ni-enrichment/316 SS from the outer to inner layer. The possible oxidation mechanisms are also discussed.