Comparing effects of Si and Mn on isothermal and cyclic oxidation of a ferritic chromia former in water vapour

Model alloys, Fe-20Cr-(1Si, 2Mn), were exposed to isothermal and cyclic oxidation in Ar-5H 2 O (vol.%) mixtures at 650 °C. The binary Fe-20Cr alloy formed thick Fe-rich scales and an internal oxidation zone under both isothermal and cyclic conditions. Manganese additions reduced oxidation rates under both conditions, but did not prevent breakaway corrosion. Silicon addition led to protective behaviour, forming a duplex scale of Cr 2 O 3 and SiO 2 , even during thermal cycling. Differences in reaction outcomes were discussed in terms of reaction product phases and the diffusion processes supporting their formation. • Corrosion behaviors of Fe-20Cr-(1Si,2Mn) alloys were investigated in both isothermal and cyclic conditions in H 2 O at 650 °C. • Cyclic reaction accelerated Fe-20Cr corrosion and changed oxide morphologies. • Mn addition reduced oxidation rate and modified scale structure, but fails to prevent breakaway corrosion. • Si addition formed a duplex Cr 2 O 3 /Si-rich oxide scale, preventing breakaway oxidation under both isothermal and cyclic exposures.