Effect of Grain Size on the Anodic Dissolution of Lean Duplex UNS S32202 Austenitic-Ferritic Stainless Steel

Abstract

The effect of grain size on the anodic dissolution of lean duplex UNS S32202 dual-phase austenitic-ferritic stainless steel was evaluated. Grain coarsening was achieved by heat treatment, and grain size and grain boundary densities determined by automatic image analysis after etching. Potentiodynamic electrochemical testing in acidic chloride medium allowed isolating the anodic dissolution behavior of the crystallographic phases of the material. A relationship between grain boundary density (for grain sizes in the micrometer range) and dissolution rate has been found, showing that reducing grain size enhances active corrosion rates in environments that promote active behavior. This leads to new possibilities of industrial adjustment of the corrosion behavior of duplex stainless steels via grain size control.

Application of bipolar electrochemistry to assess the ambient temperature corrosion resistance of solution annealed type 2205 duplex stainless steel

“…Longer heat treatment at these temperatures can intermittently produce fully ferritic microstructures [39]. The resulting grain size has been reported to influence the overall corrosion behaviour, with for example, DSS 2202 (22%Cr-2%Ni) showing higher current densities potentio-static polarisation tests with larger grain sizes [40]. The larger the difference of Cr, Mo, and Ni within the two phases, the higher was the observed Volta potential difference between the two phases, resulting in lower corrosion resistance [18].…”