High-temperature oxidation of Fe-Cr alloys in wet oxygen

Fe-Cr binary alloys have been oxidized in a stream of oxygen containing different amounts of water vapor at 900–1000°C to study the effects of water vapor. The Fe-Cr alloys exhibit an initial protective behavior due to formation of a Cr-rich scale and followed by a nonprotective breakaway oxidation due to formation of iron-rich scale. The appearance of the breakaway oxidation was very sensitive to the water vapor content in the atmosphere. The higher the water vapor content, the earlier the breakaway oxidation takes place. Increasing the oxidizing temperature or decreasing the Cr content in the alloys facilitate an earlier breakaway oxidation. The breakaway oxidation was inhibited effectively by surface-applied CeO₂ particles before oxidation. The oxide scales were examined and analyzed by optical metallography, X-ray diffraction, SEM, and EPMA. A mechanism of the effects of water vapor has been proposed.