Effect of Welding Processes on the Microstructure and Mechanical Properties of Duplex Stainless Steel Weld Joints

The objective of the present investigation involves studying the microstructure and mechanical properties of duplex stainless steel (DSS) alloy 2205 and super DSS (SDSS) alloy 2507 weld joints fabricated by tungsten inert gas (TIG) welding and its variant, activated TIG (A-TIG) welding. Square butt weld joints were fabricated from 10-mm-thick plates of DSS and SDSS using single pass A-TIG and multi-pass TIG welding processes. The filler wire ER2209 was used for multi-pass TIG welding of DSS 2205, and ER2594 filler wire was used for multi-pass TIG welding of SDSS 2507. The microstructure in the A-TIG weld metals was found to be coarser, which was caused by high peak temperatures during A-TIG welding. The microstructures exhibited different forms of austenite, including grain boundary allotriomorphs, Widmanstatten side plates, and intragranular precipitates in the weld metal. In the A-TIG weld metals, the microstructure exhibited a balanced ferrite-to-austenite ratio. The hardness values of multi-pass TIG weld joints were higher compared to A-TIG weld joints. The tensile and yield strengths of multi-pass TIG weld joints were higher compared to A-TIG weld joints, which was mainly due to higher delta ferrite content and finer microstructure. The toughness values obtained by Charpy impact testing were higher in A-TIG weld joints compared with multi-pass TIG weld joints at room temperature, which was mainly due to the balanced ferrite-to-austenite ratio in the weld microstructure. However, at subzero temperatures, the A-TIG weld joints exhibit lower impact toughness because of their coarser weld metal structure.