Pit initiation mechanism of modified martensitic 13Cr stainless steel exposed to CO2 saturated acidic environments at elevated temperatures induced by Ti(C,N) inclusions

The influence of temperature (25, 75, and 150 degrees C) on the passivation behavior of Modified Martensitic 13Cr Stainless Steel (M13Cr) in CO2 saturated acidic salt brine environments was investigated. The material was found to contain Ti(C,N) inclusions and Volta potential maps obtained through scanning Kelvin probe force microscopy (SKPFM) identified them to be more anodic (60 mV lower) than the matrix. Cyclic polarization (CP) showed a shift in pitting and repassivation potentials to more negative values at higher temperatures. Electrochemical impedance spectroscopy (EIS) and Mott-Schottky tests showed that the passive film formed was more defective with increasing temperature. X-ray photoelectron spectroscopy (XPS) confirmed the presence of a defective passive film with reduced repassivation capabilities due to higher contents of soluble CrO3/Cr6+ species at temperatures exceeding 75 degrees C. These results offer valuable insights into understanding the pit initiation mechanisms and performance of M13Cr.