In the present work, a selective oxidation process of HP40 alloy at 1050 °C under a H2–H2O environment were studied in detail by means of SEM, EDS, GD-OES, XRD, Raman spectra and XPS. The results revealed that selective oxidation of Mn and Cr elements was realized, and the oxide scale preferentially grew via grain boundary rather than via grain lattice. The oxide scales were composed of a majority of MnCr2O4 spinel and a spot of Cr2O3 throughout the oxidation process. Mn existed in the form of Mn2+ ions on the surface, while Cr existed in various species. Metal hydroxides appeared on the surface approved by spectra of the O 1s region, and the relative amount of them decreased with oxidation time.
