Sohrab Pahlavan - M.Sc. student, Materials and metallurgical engineering department, Ferdowsi University of Mashhad.
Mohammad Hadi Moayed - Professor, Materials and metallurgical engineering department, Ferdowsi University of Mashhad,
Mostafa Mirjalili - Assistant professor, Materials and metallurgical engineering department, Ferdowsi University of Mashhad,

This work aims to examine the effect of different halide anions on the pitting corrosion of 316 austenitic stainless steel. Investigated halide anions are chloride, bromide and iodide. Stable pitting was investigated by means of potentiodynamic experiments. Metastable pitting characteristics were also evaluated by using potentiostatic experiments. Initiation and propagation steps of pitting were then compared according to the obtained results. The results confirmed that the aggressivity of halides increases in the following order: Cl-> Br-> I-. In the other word, for a constant concentration, the pitting potential of 316 austenitic stainless steel has the highest value for iodide and the lowest for chloride. Bromide also stands in the intermediate place. It was also found that the occurrence frequency of metastable pits decreases in the following order: Cl-> Br-> I-. The anionic radius found to be possibly related to the metastable nucleation. According to pitting mechanisms, anions with smaller radii can promote pitting nucleation, more than others which have larger ionic radii. Statistical investigations carried out for metastable pits also show that the most stability product value pertains to the Cl- bearing solution. Lowest stability product however, belongs to the NaI solution and NaBr solution has again the intermediate value

Pitting corrosion, Stainless steel, Halides, Metastable pits, Stability product