Characterization of oxide films grown on 316L stainless steel exposed to H2O2-containing supercritical water

The characterization of microstructure and chemical compositions of oxide films formed on surfaces of stainless steels is necessary for understanding of corrosion processes and environmentally assisted cracking. In this study, the morphologies, microstructure and chemical compositions of oxide films grown on 316L stainless steel exposed to H2O2-containing supercritical water (SCW) were investigated using a scanning electron microscope equipped with an energy-dispersive X-ray spectrometer (EDX), an X-ray photoelectron spectroscopy (XPS) analyzer and an X-ray diffraction (XRD) analyzer. A duplex-layer structure was identified in the oxide films. The loose outer layer was rich in Fe, while the compact inner layer was rich in Cr and Fe. In addition, Ni enrichment was observed at the interface between the metal matrix and oxides. The surface oxides tended to change with an increase in water temperature. The possible growth mechanism of the oxide films on 316L stainless steel in SCW environments is believed to be similar to that in high-temperature water, namely metal dissolution/oxide precipitation mechanism and solid-state growth mechanism.