Mechanism of the dual effect of Te addition on the localised corrosion resistance of 15–5PH stainless steel

The effect of tellurium (Te) on the localised corrosion mechanism in 15–5PH stainless steel is studied in a simulated marine environment. The addition of Te changed the composition and size of the inclusions, which significantly affected the localised corrosion mechanism of the steel. Scanning Kelvin probe force microscopy and current-sensing atomic-force microscopy results show that the inclusions have good electrical conductivity and are always electrochemically dissolved. During the corrosion process, MnS acted as the anodic phase and was preferentially dissolved. The portion of Te in Te-containing complex inclusions increased the Volta potential of the inclusions and changed the localised corrosion mechanism. The appropriate addition of Te increased the pitting potential of 15–5PH stainless steel, thereby improving its localised corrosion resistance. However, superfluous addition of Te resulted in corrosion-resistance attenuation. This can be attributed to the continuous cathodic effect of the larger Te portion in the complex inclusion. The dissolution of Te oxides destabilised the passivation film.