Corrosion Resistance of 9Cr Oxide Dispersion Strengthened Steel in Supercritical Water

The oxidation behavior of a 9Cr oxide dispersion strengthened (ODS) steel exposed to supercritical water at 500 ℃ and 25 MPa was examined. For comparison, two non-ODS steels K1 (12Cr) and K2 (9Cr) were also examined. The oxidized samples were characterized using gravimetry, scanning electron microscopy/energy dispersive X-ray spectroscopy and X-ray diffraction. The oxide scales were rather porous in two non-ODS steels K1 and K2, while the porosity in 9Cr-ODS almost couldn′t be observed. A three-layered oxide scale formed on 9Cr-ODS steel, which was mainly composed of an outer oxide layer (Fe3O4), an inner oxide layer (Fe3O4 + FeCr2O4) and an internal oxide zone which was featured by gradual variation of alloying elements and oxygen from the oxide to the matrix. The kinetic data of 9Cr-ODS, two non-ODS steels showed that oxide scale formation obeyed a parabolic rate law. The oxidation rate of 9Cr-ODS steel was lower than that of K2 (9Cr), even more it was lower than that of K1 (12Cr).