Dispersion of complex carbides at the oxidation front during the oxidation of 9Cr-1Mo steel

To better understand oxidation and carburisation processes taking place during exposure of 9Cr-1Mo steel experimental samples have been exposed at 600°C and 620°C to a CO2 rich atmosphere for various exposure times. Complex multi-elemental carbides form showing a range of compositions, with some showing coring/elemental segregation. Certain carbides show both M7C3 and M23C6 within a single multi-component carbide. At the oxidation front some carbides resist oxidation through growth of a Cr rich oxide shell. Carbides within both substrate and oxide have been characterised with mechanisms being proposed for the complex interactions taking place within both the substrate and oxide.