A corrosion study of austenitic and martensitic steels under boiler conditions by means of 57Fe conversion electron Moessbauer spectroscopy

The growth of protective oxide layers on a martensitic Fe-Cr (1.4122) and two austenitic Fe-Cr-Ni steel samples (1.4550 and Incoloy 800) was studied by means of the 57Fe Conversion Electron Moessbauer Spectroscopy (CEMS). Scanning electron microscopy was applied to characterize the topographical nature of the oxide layers. The steel specimens were oxidized in oxygen-free water at 2950C, 142 bar and a pH value between 9 and 10 for periods up to 70 h. In the case of the steels 1.4122 and 1.4550 the only oxide phase detected was non-stoichiometric magnetite, whereas nickel ferrite of non-stoichiometric composition was found on Incoloy 800. The study of the kinetics of the oxide layer growth revealed that the oxidation process is most probably controlled by short-circuit diffusion. (author)