HIGH-TEMPERATURE OXIDATION OF FE-CR ALLOYS IN WET OXYGEN

Fe-Cr binary alloys have been oxidized in a stream of oxygen containin g different amounts of water vapor at 900-1000 degrees 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 nonpro tective breakaway oxidation due to formation of iron-rich scale. The a ppearance of the breakaway oxidation was very sensitive to the water v apor content in the atmosphere. The higher the water vapor content, th e earlier the breakaway oxidation takes place. Increasing the oxidizin g temperature or den easing the Cr content in the alloys facilitate an earlier breakaway oxidation. The breakaway oxidation was inhibited ef fectively by surface-applied CeO2 particles before oxidation. The oxid e scales were examined and analyzed by optical metallography, X-ray di ffraction, SEM, and EPMA. A mechanism of the effects of water vapor ha s been proposed.