Effect of Fe on Steam Oxidation of the Newly Designed Fe–Ni-Base Alloys

Several newly designed Fe–Ni-base alloys with different Fe content are prepared and the steam oxidation resistance of these alloys in high-temperature steam at 650°C and 700°C was investigated by oxidation mass gain method, SEM observation and XRD analysis. The results show that the oxidation kinetics of 37Fe and 42Fe alloys at 650°C and 700°C both conform to the parabolic rule, the outer Ni–Fe spinel and the inner Cr₂O₃ are formed after oxidized for 1000 h, also accompanied by the internal oxidation of Al. The protective oxides containing external Cr₂O₃ and internal Al₂O₃ were obtained faster and more by the acceleration of Cr diffusion rate, which made the alloys have excellent steam oxidation resistance at 700°C. The 47Fe alloy loses mass after oxidation at 650°C for 60 h due to the formed iron oxides are easy to peel off at the initial oxidation stage, but follow the parabolic rule of stable oxidation at 700°C. When the Cr content in Fe–Ni–Cr alloy is lower than 18%, the corresponding Fe content should be lower than 42% to achieve the transformation of internal oxidation to external oxidation for Cr₂O₃ oxide. The oxidation mechanism and the influence of constituent elements were elucidated.