Influence of Ni and PWHT on microstructure evolution and mechanical properties of GTA-welded duplex stainless steel and super duplex stainless steel joints: A comparative investigation

In the present investigation, a new endeavor has been made to analyze the impact of the secondary process (post-weld heat treatment (PWHT)) as well as Ni addition on the microstructure and mechanical characteristics of welds. Welds between similar joining materials from duplex stainless steels (DSS), as well as super DSS (SDSS), were made by the gas tungsten arc welding (GTAW) process. For DSS, after PWHT with the addition of Ni element, the amount of austenite rises and becomes more uniformly distributed with curved boundaries, while for SDSS, the microstructure mainly consists of intergranular and Widmanstätten austenite. According to the comparison of phase percentages obtained based on both ASTM E1245 and ASTM E562, a good balance between ferrite and austenite phases of joint materials was achieved. X-ray diffraction analyses on both joints revealed that phases are mainly ferrite and austenite with different lattice parameters without evidence of unwanted intermetallic phases. The addition of Ni increases the hardness values of DSS weld metal compared to the base metal due to an increased amount of Widmanstätten austenite and ferrite in the microstructure. The lowest ductility was obtained for the SDSS weld sample with the addition of Ni and PWHT because of the existence of secondary austenite in the weld metal and the Widmanstätten morphology of the austenite. The effect of PWHT on the development of microstructure and mechanical behaviors was more than the effect of nickel powder on weld samples.