The oxidation and reduction kinetics of a 1.7 wt.% Mn steel alloy with 0.1 wt.% C was studied in different ?CO?_2/CO mixtures and at different temperatures. The external iron oxide growth, the internal alloying element oxide formation and the reduction of iron oxides were observed with thermogravimetry (TG). The oxidation at 750 ? follows a logarithmic growth rate law, which suggests that transport of electrons from the metal through the oxide determines the kinetics. However, the oxidation rate of a linear growth at 950 ? obeys a linear growth rate law, which suggests that the dissociation of ?CO?_2 into CO and adsorbed oxygen atoms or ions determines the kinetics. The kinetics of the reduction of external iron oxide by hydrogen follows a First-Order model. A Wüstite scale with internal Manganese oxide was formed during the thermal oxidation in different ?CO?_2/CO mixtures. After reduction with H_2at 950 ?, an iron layer with internal Manganese oxide was obtained at the surface of the steel. The depth of the internal Manganese oxide zone increased during the reduction.