Carburisation of ferritic Fe-Cr alloys by low carbon activity gases

Thomas Gheno (1, 2) , Daniel Monceau (2) , Jianqiang Zhang (1) , David J. Young (1)

1 UNSW - University of New South Wales [Sydney]
2 CIRIMAT - Centre interuniversitaire de recherche et d'ingenierie des matériaux

Model Fe-Cr alloys were exposed to Ar-CO2-H2O gas mixtures at 650 and 800 °C. At equilibrium, these atmospheres are oxidising to the alloys, but decarburising (aC ≈ 10−15 to 10−13). In addition to developing external oxide scales, however, the alloys also carburised. Carbon supersaturation at the scale/alloy interface relative to the gas reflects local equilibrium: a low oxygen potential corresponds to a high pCO/pCO2 ratio, and hence to a high carbon activity. Interfacial carbon activities calculated on the basis of scale-alloy equilibrium are shown to be in good agreement with measured carburisation rates and precipitate volume fractions, providing support for the validity of the thermodynamic model.

Mots clés: Steel; Carburisation; High temperature corrosion; Oxidation

Domaines: Matériaux

Thomas Gheno, Daniel Monceau, Jianqiang Zhang, David J. Young. Carburisation of ferritic Fe-Cr alloys by low carbon activity gases. Corrosion Science, 2011, vol. 53, pp. 2767-2777. ⟨10.1016/j.corsci.2011.05.013⟩. ⟨hal-00726316⟩