The effect of dichromate ion on the pitting corrosion of AISI 316 stainless steel. Part I: Critical pitting temperature

•Effect of dichromate ion on critical pitting temperature of SS316 is investigated.•The CPT of 316 SS is increased up to 38 °C in the presence of 0.05 M dichromate.•Dichromate ion decreases the maximum current density in simulated pit solution.•Diffusion controlled limiting current density is decreased by dichromate addition.•Dichromate decreases the pores in lacy cover over the pits mouths.

This article provides a better understanding of dichromate effect on the critical pitting temperature (CPT) of 316 SS in chloride solution. Potentiostatic measurements revealed that dichromate effectively improves the CPT. In the presence of dichromate ion, a remarkable decrease in the anodic dissolution in simulated pit environment and a slight decrease in the saturation concentration of cations in pit solution were defined in pencil electrode experiments. Scanning electron microscopy showed that, in compare with pure chloride solution, the pits formed on the metal surface in dichromate containing solution, have finer lacy covers.