Yttrium implanted and unimplanted low manganese and low manganese-carbon steel samples were analyzed at T s 7008C and under an oxygen partial pressure P s 0.04 Pa for 24 h to show the yttrium implantation effect on sample O 2 high temperature oxidation resistances. Sample oxidation weight gains were studied by thermogravimetry and structural Ž . analyses were performed by in-situ high temperature X-ray diffraction XRD with the same experimental conditions. The aim of this paper is to show the initial nucleation stage of the main compounds induced by oxidation at high temperature Ž . according to the initial sample treatment yttrium implanted or unimplanted . The results obtained by in-situ high temperature XRD will be compared to those by thermogravimetry to a better understanding of the weight gain curves observed during the oxidation test at 7008C and P s 0.04 Pa. This study allows us to show the improved corrosion O 2 resistance of yttrium implanted low manganese and low manganese-carbon steel at high temperature.