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

ABSTRACT 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 Cr 2 O 3 are formed after oxidized for 1000 h, also accompanied by the internal oxidation of Al. The protective oxides containing external Cr 2 O 3 and internal Al 2 O 3 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 Cr 2 O 3 oxide. The oxidation mechanism and the influence of constituent elements were elucidated.