Post-weld Heat Treatment and Nitrogen Application in Welding of Super Duplex Stainless Steels

In this study, the microstructure and mechanical characteristics of a super duplex stainless steel (SDSS), S32750 welded by gas tungsten arc welding (GTAW) after post-weld heat treatment (PWHT), were investigated. Microstructure observations after PWHT indicated an increase in the size of austenite laths and globularity due to solution annealing at a high temperature and complete austenite with a few small ferrite islands in the fusion zone (FZ) due to the presence of nitrogen as a strong austenite stabilizer. The phase percentage obtained based on ASTM E562 indicated an almost equivalent ratio for austenite and ferrite after using nitrogen as the shielding gas and PWHT. No evidence of undesired intermetallic phases such as σ, χ, and nitride was detected based on X-ray diffraction (XRD) analysis. According to mechanical characteristics, tensile strength increases after the usage of nitrogen gas, while the elongation of samples increases after PWHT.