Effect of Post Weld Heat Treatment and Filler Wire on Mechanical Properties and Microstructure of Tungsten Inert Gas Welded AISI 2507 Super Duplex Stainless Steel

In this study, AISI 2507 super duplex stainless steel sheets were joined by Tungsten Inert Gas welding. The welding process was carried out without filler wire and using austenitic filler wire. In addition, welded joints were subjected to post-weld heat treatment, and two different cooling procedures were applied to heat-treated samples: air-cooling and water-cooling. The highest ferrite content and a finer microstructure morphology were obtained in the weld metal of the sample joined without filler wire and heat treatment. Due to heat treatment (especially under air-cooling conditions) and using an austenitic filler wire, the weld microstructure became coarser, and a microstructure formation in favor of austenite occurred. Energy-dispersive spectroscopy analysis results showed that the element contents in the heat-affected zone and weld metal of the additional wire welded joints tended to decrease due to the effect of the welding heat input. Still, the impact of the additional wire balanced this decrease in the element content. Some chromium–nitride formations were detected together with ferrite and austenite grains in the weld microstructure. Chromium nitrides had an adverse effect, especially on the ductility properties of the welded samples. While the ductility properties improved in base materials applied with water-cooling and air-cooling, a similar improvement in ductility was obtained only without filler wire joints. While the toughness properties improved in the air-cooling samples due to the microstructure developing in favor of austenite, the increase in austenite caused a decrease in microhardness. After the tensile and impact tests, it was determined that the fractures on the base material surfaces and welded samples occurred in ductile mode.