Simultaneous oxidation and carburization of a Fe-9Cr alloy under different oxygen pressures at 800 °C

A model Fe-9Cr alloy was exposed to various H2CO2CH4 mixtures providing different oxygen pressures and carbon activities at 800 °C. Three oxidation modes and three oxygen pressure ranges have been observed. At low pressures (Range I) only thin external Cr2O3 scales formed. An intermediate range (Range II) produced an internal precipitation of Cr2O3 and Cr carbide without an external scale. Higher pressures (Range III) produced external FeOx scales plus an internal oxidation of Cr. Two critical oxygen pressures for the transitions between the three oxidation modes were observed and also calculated in reasonable agreement with the experimental results.