Characterization of Sigma Phase Duplex Stainless Steels Using Nondestructive Ultrasonic Techniques

Duplex stainless steels have wide applications in industry due to their high mechanical strength, excellent toughness, and high corrosion resistance regarding to other types of steels. However, these steels are susceptible to form brittle phases during heat treatment associated to manufacture or welding processes, in particular the negative effect of sigma-phase into ferrite-austenitic microstructure has to be pointed out. In this work, a study is carried out about the use of ultrasonic nondestructive technique to establish a relationship between sigma phase signal percentages in 2507 duplex stainless steel and more relevant features of the collected ultrasonic signal in an equation. Thus, a novel method is obtained to perform the inspection of these materials in-situ in order to avoid the loss of mechanical resistance and to increase the susceptibility to localized corrosion in service.