Surface oxidation in Maraging-350 plates

Full text: Maraging steel is used as pieces and tools in the nuclear, aeronautics and aerospace industries. Often, the steel works in corrosive environment or oxidizing atmosphere. For this reason, is important to investigate the corrosion or oxidation reaction occurring on the steel surface, for different reacting atmospheres and other pertinent conditions. In this study, Maraging-350 steel polished plates were heat-treated in air, in the 100°C - 500°C temperature range, during periods of time from 1h to 12h. The objective was to identify the oxide phase formed at the plate surface and describe the evolution of the oxidized layer. For that, the surfaces were characterized by glazing angle X-ray diffraction and by conversion electron Mössbauer spectroscopy. It was shown that no oxidation took place for samples annealed at temperatures lower than 300°C. Differently, at 300°C and above, a layer of oxide was detected on the maraging surface, as first evidenced by its coloration, varying from golden to the black. >From the diffractometer analysis, applying the Rietveld method, it was possible to identify and quantify the fraction of phases formed on the maraging surface, i.e., hematite on the top,a Fe-Ni alloy underneath and spinel phase between them. The Mössbauer spectra confirmed the nature of the topmost oxide. Based on the above results, a model for the surface oxidation on the maraging surface is proposed. (author)