Thermodynamics and Kinetics of Surface Oxidation of Steels during Annealing in H2-N2 Atmospheres

Kinetic and thermodynamic calculations were performed on some low and high carbon steels in order to study the oxidation behaviour of the alloying elements, manganese, Mn, and silicon, Si, during annealing in H-2-N-2 atmospheres. In these calculations external and internal oxidation of the alloying elements were predicted where conditions of annealing were specified. The bulk external and internal oxidation as well as grain boundary oxidation of these alloying elements were predicted at a constant annealing temperature of 600 degrees C and in H-2-N-2 gas mixtures containing up to 5 vol.%H-2. The calculations showed that oxidation of Si and Mn in all annealing conditions is possible and that annealing in gas mixtures containing (1 vol.%H-2), (3 vol.%H-2) and (5 vol.%H-2) will prevent the oxidation of iron. In high carbon steel both external and grain boundary oxidation of Si may take place.