Early oxidation of Super304H stainless steel and its scales stability in supercritical water environments

The early oxidation of Super304H stainless steel exposed to supercritical water at 450 °C, 540 °C, and 580 °C was characterized. After a 40 h exposure, distribution density of oxide grains produced on samples increased with experimental pressures, while initial aqueous pH had a negligible influence on short-term corrosion morphologies, implying that the outer oxide layer of scales may form via solid growth mechanism rather than by metals dissociation/oxides precipitation process. After a repeated 24 h cycles of exposure at condition of 540 °C/25 MPa followed by that of 500 °C/23 MPa up to 5 cycles, partial spallation of the scales appeared along inner and outer layer interface, not substrate/scales interface due to the enhanced adhesion of scales on the substrate by pinning effects and production and convergence of cavities at the inner/outer layer interface.