The relative wet oxidation reactivity of two centrifugally-cast, heat-resistant Ni-Cr alloys is presented for an isothermal (900 °C) in wet (10% H2O) air up to 500 h. Both 48Ni-45Cr and 41Ni-32Cr exhibit a similar weight loss after 500 h, which suggests a similar relative reactivity. However, there are three aspects that suggest there is a difference in the relative wet oxidation reactivity. These include: (i) a different kinetic rate law (cubic for 41Ni-35Cr and parabolic for 48Ni-45Cr), (ii) a different susceptibility to internal oxidation (deeper in 48Ni-45Cr) and (iii) a difference in the degree of oxide spallation observed upon cooling to room temperature (significantly higher for 41Ni-35Cr). These relative differences are discussed by establishing links to the oxide scale morphology for (i) above and the underlying microstructure for (ii) and (iii) above.

Key words: High temperature oxidation, ethylene cracking, Ni-Cr superalloys, water vapor, alloying elements.