New High-Resolution Solution for Measuring Degree of Sensitization of Duplex Stainless Steel 2205 Using Double-Loop Electrochemical Potentiodynamic Reactivation Technique

In the present work, a new high-resolution solution for measuring degree of sensitization (DOS) of duplex stainless steel (DSS) 2205 (UNS S31803) by double loop-electrochemical potentiodynamic reactivation (DL-EPR) technique was obtained and the solution parameters were optimizing using the Taguchi method. Sensitized samples in three different conditions were chosen and five solution main factors including acid and two types of depassivator concentrations, scan rate, and surface roughness were considered. To reduce the number of experiments, Taguchi orthogonal array (OA) was used. The resulting optimal condition was to be 0.5 M sulfuric acid (H₂SO₄), 0.002 M sodium thiosulfate (Na₂S₂O₃), 0.02 M sodium chloride (NaCl), and 120 grid in surface roughness and 30 mV/min scan rate. By introducing the new solution, a DOS value of 78% was obtained in the DSS2205 sample sensitized at 850°C for 40 min. Moreover, topography variations of non-sensitized and sensitized samples measured by atomic force microscopy elucidated the mechanism of austenite/ferrite boundary attack and carbide precipitates formation in sensitized samples extended to the ferrite phase.