13Cr martensitic stainless steel is widely used in oil and gas industry. It is well known that addition of molybdenum (Mo) enhances the passivity of steel. However, the role of Mo in passive film has not been clarified completely. The aim of the present research was to reveal role of Mo in terms of semi-conductivity. The Mott–Schottky plot, obtained by impedance spectroscopy, revealed the effect of Mo addition on the semiconducting property of a passive film under an H2S environment in a pH 4.0 solution at 25 °C. The results revealed that Cr-O of the inner film and sulfide of the outer film exhibited semiconductor p-type and n-type characteristics, respectively. The number of defects in the film on 2.5 mass% Mo-added steel was approximately half of that in the film on Mo free steel. The role of Mo was discussed through investigation using X-ray photoelectron spectrometric analysis based on the existent state of the passive films.

Subject
Thin films, Steel surfaces, Marine environments, Passive films, Sulfide films, Oxide films, X-ray spectroscopy, Density, Film formation, Steel, Sulfides, Corrosion resistance, Martensitic steel
Keywords:
Martensitic Stainless Steels, Sour environment, Corrosion mechanisms, Molybdenum, Thin films, Electrochemistry
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2022
Association for Materials Protection and Performance (AMPP)
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