Investigation of oxide film formation on 316L stainless steel in high-temperature aqueous environments

Oxide films were grown on the surface of 316L stainless steel subjected to high temperatures and a high-pressure aqueous environment (250 °C and 7 MPa). The morphology, chemical compositions and corrosion properties of oxide films were investigated by scanning electron microscopy (SEM), auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. The results indicated that oxide films formed at 250 °C were more corrosion resistant and thicker than were oxide films formed in air at room temperature (25 °C). These distinctions are correlated with the structure and chemical compositions of oxide films. It was found that both films contained a double-layer structure comprised of mixed iron–nickel oxides and chromium oxides. Iron was present as FeO, Fe2O3 and FeOOH; Cr was present as Cr2O3, Cr(OH)3 and CrO3; and Ni existed as Ni(OH)2 within the oxide films formed at 250 °C.

► Oxide films formed in high temperature and high pressure aqueous environment (250 °C and 7 MPa) is much thicker than air-formed films (25 °C).
► Oxide films formed at 250 °C have higher charge transfer resistance and smaller passive current density than air-formed films.
► Fe exists in the form of FeO, Fe2O3 and FeOOH, Cr of Cr2O3, Cr(OH)3 and CrO3 and Ni of Ni(OH)2 in oxide films formed at 250 °C.