Effects of pre-oxidation on selective oxidation behaviour of Fe-25Cr-7Ni-N alloy

Abstract

Pre-oxidation has been studied in an effort to improve the oxidation resistance of alloys. An alloy, Fe-25Cr-7Ni-N, was pre-oxidised at 400°C, and the effect of pre-oxidation on the selective oxidation behaviour of this alloy at 1000°C was studied. It was found that low temperature pre-oxidation significantly improved the oxidation resistance of the alloy at high temperature. SEM and EDS analysis showed that a Fe-rich oxide scale preferentially formed on the surface of the alloy during the pre-oxidation treatment, creating an oxide-alloy interface with an increased Cr content and decreased oxygen pressure. Thus the pre-oxidation promotes the selective oxidation of Cr at the oxide-alloy interface during oxidation at 1000°C. Compared with Fe-18Cr-9Ni-Ti stainless steel, Fe-25Cr-7Ni-N showed lower improvement in oxidation resistance, but needs a relatively short time of pre-oxidation.