On the corrosion mechanism of AISI 204Cu stainless steel in chlorinated alkaline media

Electrochemical techniques (CV, SECM, CPT) and surface analysis techniques (EDX, SEM) have been employed to assess the corrosion behaviour of the AISI 204Cu stainless steel. The behaviour of this steel has been compared with that of AISI 304 and AISI 434 stainless steels in chlorinated alkaline media. All samples performed well at room temperature under potentiodynamic polarisation up to a chloride to hydroxyl ratio of 10. At this ratio the AISI 204Cu and the AISI 434 steels presented pitting potential at +0.47 V vs. SCE and +0.31 V vs. SCE, respectively. Moreover, the critical pitting temperature was higher for the AISI 204Cu steel than for the AISI 434 steel, respectively 58 °C and 28 °C.In terms of corrosion performance of the AISI 204Cu stainless steel can be classified better than the AISI 434 steel and worse than the AISI 304 steel.Local electrochemical and chemical examinations allowed evidencing the local activity of some pits over long period, and to conclude that the improved corrosion performance of the low nickel alloy AISI 204Cu stainless steel should be ascribed to copper cementation at active corrosion sites.