Decrease in Pitting Corrosion Resistance of Extra-High-Purity Type 316 Stainless-Steel by Cu2+ in NaCl

The effect of Cu2+ in bulk solution on pitting corrosion resistance of extra-high-purity type 316 stainless-steel was investigated. Pitting occurred in 0.1 M NaCl-1 mM CuCl2, whereas pitting was not initiated in 0.1 M NaCl. Although deposition of Cu2+ on the surface occurred regardless of a potential region in 0.1 M NaCl-1 mM CuCl2, Cu2+ in bulk solution had no influence on the passive film formation. The decrease in pitting corrosion resistance in 0.1 M NaCl-1 mM CuCl2 resulted from the deposited Cu or Cu compound and continuous supply of Cu2+ on the surface.