|Cite this article as:|
|Hailong Zhao, Longfei Li, and Qiang Feng, Isothermal oxidation behavior of Nb-bearing austenitic cast steels at 950°C, Int. J. Miner. Metall. Mater.,(2021). https://doi.org/10.1007/s12613-021-2314-2|
The oxidation behaviors of three austenitic cast steels with different morphology of primary carbides at 950°C in air was investigated using SEM, EDS, XRD and FIB/TEM. It was found that their oxidation kinetics followed a logarithmic law and the oxidation rate could be significantly decreased as long as a continuous silica layer formed at the scale/substrate interface. When the local Si concentration was inadequate, the internal oxidation beneath the oxide scale occurred. The spallation of oxides during cooling could be inhibited with the formation of internal oxidation, owing to the reduced mismatch stress between the oxide scale and the substrate. The "Chinese-script" primary Nb(C,N) was superior to the dispersed primary Nb(C,N) in suppressing the oxidation penetration in the interdendritic region by supplying a high density of Cr quick-diffusion channels. In addition, the innermost and the outermost oxidation layers were both found to be enriched with Cr, while the Cr evaporation in the outermost layer was significant when the water-vapor concentration in the environment was high enough. These findings further the understanding regarding the oxidation behavior of austenitic cast steels and will promote the alloy development for exhaust components.