Sigma Phase Detection in Stainless Steels

Sigma phase is an intermetallic phase that can form in duplex stainless steel during forming, welding, heat treating, and operational exposure. Depending on its amount, morphology, distribution, and use environment, sigma phase can result in degradation of mechanical properties and loss of corrosion resistance. Metallurgical analysis of color etched samples is the most common analysis method to evaluate whether it is present and, if so, the amount of sigma phase present. However, due to the small size of sigma phase domains compared to other phases and their location primarily along grain boundaries, quantification is difficult and often considered to be only semi-quantitative. Recently, numerous studies have focused on evaluating the amount of sigma phase utilizing electrochemical methods (single loop EPR, double loop EPR, and potentiodynamic). This presentation will explore the use of electrochemical methods compared to metallurgical methods on aged duplex stainless steel samples.