General corrosion rates were studied in water at 300-650 °C at supercritical pressure using weight gain measurements. Oxide thicknesses were determined from cross-section samples. The compositions of the oxide layers were analyzed using scanning electron microscope (SEM) in conjuction with energy dispersive spectroscopy (EDS). The layers of selected samples were analyzed also by X-ray diffraction (XRD). The test matrix included 10 materials from four alloy classes: ferritic/martensitic (F/M) steels, ODS steels, austenitic stainless steels and nickel base alloys. A high oxidation resistance was seen in Ni base alloy 625, austenitic stainless steels with high Cr content, and an ODS steel containing 20% Cr at all applied test temperatures (300-650°C). The oxidation rates of austenitic stainless steels with lower Cr content, 15-18%, increase considerably at temperatures higher than 500°C. The oxidation rates of 9% Cr ODS steels were moderate or high at all temperatures. Ferritic/martensitic steels showed high oxidation rates at all temperatures.
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