Scanning electrochemical microscopic observation of corrosion reactions on a duplex stainless steel

The objective of this study is to clarify the preferential dissolution mechanism of a duplex stainless steel (DSS) at its corrosion potential (about -0.15 V vs.SHE) by means of Scanning Electrochemical Microscope (SECM) observation of the corrosion reactions on the ferritic phase (α phase) and the austenitic phase (γ phase) of a DSS, respectively. Probe electrode was fixed above α and γ each phase of DSS at corrosion potential in 1 mol/l HCl aqueous solution. Potential of the probe electrode was polarized toward noble direction, from - 0.10 V to 1.4 V (SHE), at a potential scan rate of 20 mV/s, and probe current was measured. In a probe potential range of 0∼0.70 V (SHE), anodic current due to hydrogen oxidation reaction could be detected. This anodic current was larger above y phase than that above α phase. In a probe potential range of 0.70∼1.2 V (SHE), anodic current due to Fe²⁺ oxidation reaction to Fe³⁺ could be detected. This anodic current was larger above a phase than that above y phase. On the α phase, the anodic dissolution reaction occurred preferentially at the DSS corrosion potential, while on the γ phase, the cathodic reduction reaction of hydrogen ion occurred preferentially.