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The origins of the second anodic current peak in polarization curves of AISI 430 (UNS S43000) stainless steel in deaerated 0.1 M sulfuric acid (H2SO4) have been investigated by potentiodynamic polarization and atomic emission spectroelectrochemistry (AESEC). The elemental dissolution rates of Fe, Cr, Ni, Cu, and Mn were measured in real time during linear potential sweep voltammetry, revealing the formation and dissolution of a copper-rich corrosion product layer. The deposition and subsequent dissolution of this copper layer is proposed to be the main cause of the second anodic current peak. The negative current loop observed after the first anodic peak is attributed to the cathodic reduction of H+ ion on the copper-enriched layer. Other factors such as the oxidation of the adsorbed H atoms on the copper-enriched layer and the presence of chromium-impoverished grain boundaries are shown to have a negligible effect on the second anodic current peak.

The Critical Pitting Temperature of a 22-05 type duplex stainless is investigated using both potentiodynamic and potentiostatic techniques. The potentiodynamic technique leads to a lower CPT value than the potentiostatic one. The pitting potential distribution near the CPT is determined using a multichannel device. A 10°C transition temperature interval is evidenced in which pitting probability gradually increases from 0 to 1. A conservative CPT should then be defined as the lowest boundary of this temperature interval.

International audienceThe depassivation of UNS S32304, S32202, and S32101 lean duplex stainless steels (DSS) in 26 wt% sodium chloride (NaCl) was investigated by potentiodynamic polarization to understand the selective dissolution processes in localized corrosion phenomena. Results showed that the depassivation of the three grades proceeds in two stages. First, the austenite is the only phase depassivated within the range of no more than 0.3 pH units, providing a single corrosion peak on the polarization curves of the DSS. Subsequently, the ferrite is also depassivated and provides a second corrosion peak at a more cathodic potential. Results are discussed in terms of the partitioning of alloying elements