Effect of Copper on Active Dissolution and Pitting Corrosion of 25% Cr Duplex Stainless Steels

Electrochemical studies were made of the influence of Cu on pitting behavior and active dissolution of 25% Cr duplex stainless steels (DSS) in chloride-containing neutral and acid solutions. Alloys with increased Cu content showed higher pitting potentials (Ep) in 1 M hydrochloric acid (HCl) and 3.5% sodium chloride (NaCl) solutions. In HCl, the current density in the active state also was lower for the Cu-containing alloys. However, the critical pitting temperature (CPT) in ferric chloride (FeCl3) was not improved significantly by addition of Cu. Pitting in all environments took place preferentially in the ferrite phase.