Characterization of selective oxidation of manganese in surface layers of Fe-Mn alloys by different analytical methods

Since selective oxidation of alloying elements on the surface of steel products influences their surface properties, characterization of the surface oxides which can be considered as non-metallic inclusions is of great importance. In this study, X-ray photoelectron spectroscopy (XPS), X-ray diffractometry (XRD) and X-ray absorption spectroscopy (XAS) were used for characterizing the formation process of Mn oxides on the surface of annealed Fe-Mn alloys under a low partial pressure of oxygen. The results obtained by XPS showed that the enrichment and oxidation of Mn occurs on the surface of the Fe-Mn alloys annealed under low oxygen partial pressure, and Mn oxides are formed in the metallic Fe matrix in the surface layers. XAS spectra using grazing-exit X-ray fluorescence measurements showed depth-resolved information on chemical state of Mn. These Mn oxides were identified as MnO (manganosite) by grazing-incident XRD measurements. It was found using in situ XRD measurements at high temperatures that the lattice constant of MnO increased with increasing annealing temperature, which attributed to the non-stoichiometry of MnO. These oxidation characteristics of Mn in the Fe-Mn alloys are discussed on the basis of thermochemical properties of Mn.