Corrosion resistance and semiconductor properties of passive films formed on super 13Cr stainless steel

The electrochemical behavior and semiconductor properties of passive films formed on super 13Cr martensitic stainless steel in a corrosion solution which contains CO2 and Cl^- soaked for 7d at 100,130,150 and 170℃ were examined using polarization curves and Mott-Schottky curves.The valence states of elements in the passive films were analyzed by X-ray photoelectron spectroscopy.It is shown that Mo and Ni in the forms of sulfides concentrate respectively in the surface layer of the passive films,but Cr in form of oxides enriches on the surface layer.The passive films formed at 100℃ and 130℃ are in possession of superior corrosion resistance,but the corrosion resistance of the passive films formed at 150℃ and 170℃ decreases.The reason for this phenomenon is concerned with the semiconductor properties of the passive films.A typical n-p-type semiconductor behavior is observed for the passive films formed at 100℃ and 130℃,the doping quantity increases with increasing temperature;but a p-type semiconductor behavior is observed for the passive films formed at 150℃ and 170℃.For this reason,the corrosion resistance of the martensitic stainless steel decreases with increasing temperature.