The selective oxidation of three CMnSi steels with differentC levels was studied by XPS. The formation of a graduallycovering SiO2 film is observed until a transition temperatureabove which the oxide film disappears, resulting in a renewedappearance of metallic iron at the surface. This change inoxidation behavior is thought to be due to the SiO2 reductionby solute C which is thermodynamically favorable at hightemperature. At the same time the precipitation of a BN filmon the metallic surface was observed which prevented anyfurther oxidation.