The effect of dichromate ion on the pitting corrosion of AISI 316 stainless steel Part II: Pit initiation and transition to stability

• Effect of dichromate ion on pitting corrosion of 316 SS is investigated by a statistical approach.
• Dichromate ion increases the value of both corrosion and breakdown potentials.
• Dichromate ion decreases the initiation frequency of metastable pitting.
• Dichromate hinders the transition from metastable to stale pitting.
• Survival probability of stable pits is increased in dichromate containing solution.

The effect of dichromate ions on the corrosion behaviour of 316 stainless steel was investigated in 0.1 M NaCl solution by electrochemical measurements and electron microscopy. The results revealed that the addition of dichromate increases the resistance to pitting corrosion as the pitting corrosion does not occur in the presence of 0.05 M dichromate ions at room temperature. The mechanistic studies showed that the increase in pitting corrosion resistance in presence of Cr2O72− is due to the decrease in the metastable pit initiation, lower kinetics of metastable pit dissolution and increase in the survival probability of the pit formation.