Detection of deleterious phases in duplex stainless steel by weak galvanostatic polarization in alkaline solution

A novel electrochemical procedure has been developed to quantify the presence of secondary phases (nitride, χ, σ) in duplex stainless steel. This is based on anodic galvanostatic polarization in a weakly alkaline solution to detect the transpassive dissolution of Cr- and Mo-rich phases. By adjusting the current density, an almost linear relation can be obtained between the “time to reach a given potential” and impact toughness. The material used was UNS S32760 (Zeron 100), isothermally aged at 650, 750, 825 and 850 °C. Distinctive features on the potential–time curves were correlated with the microstructure by examining reacted surfaces with backscattered imaging in the SEM.