Oxidation kinetics of Fe-(2-10)Mn-xSb alloys during annealing

The selective oxidation kinetics of a series of Fe-(2-10)Mn-(0.00/0.01/0.03)Sb (at. pct) were determined and a model was proposed for analyzing oxide growth during intercritical annealing prior to galvanizing. The annealing conditions (temperature and isothermal holding time) affected the thickness and depth of the oxidation zone, which in turn influenced the MnO growth rate. Increasing the alloy bulk Mn content increased the Mn elemental flux to the external surface, thereby increasing the oxidation parabolic rate constant and decreasing the oxidation activation energy. Micro-additions of Sb to the Fe-Mn alloys reduced the parabolic rate constant, which was attributed to the reduction of oxygen permeability at the surface and interfaces by Sb segregation at both the external and internal oxide interfaces. This reduction was more significant in the Fe-10Mn alloys due to higher Sb segregation at the interfaces. The average activation energy of internal oxidation for the Fe-2Mn, Fe-6Mn and Fe-10Mn alloys were determined to be 216 ± 15 kJ/mol, 178 ± 18 kJ/mol and 152 ± 10 kJ/mol, respectively, which are consistent with the activation energy of oxygen diffusion through MnO interfaces and the bulk diffusion of oxygen in austenite. Furthermore, the average activation energy for external oxide growth was ∼113 ± 18 kJ/mol, which was attributed to the diffusion of Mn cations along the grain boundaries of the external Mn oxides.