Development of 1100 °C Capable Alumina-Forming Austenitic Alloys

Recently developed alumina-forming austenitic (AFA) alloys based on ~12–32 weight % (wt%) Ni offer an attractive combination of oxidation resistance and creep resistance at relatively low alloy cost. However, they exhibit a transition to internal oxidation and nitridation of Al above ~750–950 °C depending on composition and exposure environment. In order to identify AFA compositions capable of higher-temperature operation for applications such as ethylene cracking, the oxidation behavior of a series of developmental, as-cast nominal Fe–(25–45)Ni–(10–25)Cr–(4–5)Al–1Si–0.15Hf–0.07Y–0.01B wt% base alloys with and without Nb, Ti, and C additions was evaluated at 1100 °C in air with 10% water vapor. Protective alumina scale formation was observed at levels of 35Ni, 25Cr, and 4Al with additions of Nb and C, indicating promise for 1100°C capable cast AFA alloys.