Characterization of the microstructure and mechanical properties of activated tungsten inert gas welded and hot-wire tungsten inert gas welded super austenitic stainless steel AISI 904L

Super austenitic stainless steel AISI 904L is a premium stainless steel variant known for its superior properties and ability to retain the same in highly challenging conditions. This study investigates the feasibility of welding 10-mm thick plates of AISI 904L through activated tungsten inert gas welding and hot-wire tungsten inert gas welding methods. The fabricated joints are then subjected to solidification mode study, ferrite number analysis, microstructural characterization, and mechanical tests. Results of the solidification mode study indicated primary austenitic solidification in both the weld joints. The ferrite number measurement revealed that the hot-wire tungsten inert gas weld joint had a higher delta-ferrite content of 1.58 over 0.99 of the activated tungsten inert gas weld joint. A microstructure study confirmed the presence of refined equiaxed grains in the fusion zone of the hot-wire tungsten inert gas weld joint, while the activated tungsten inert gas weld joint displayed equiaxed grains crammed between the columnar grains and dendrites. Liquid penetrant inspection of bend-tested samples proved the soundness and quality of both weld joints. The hot-wire tungsten inert gas weld joint excelled over the activated tungsten inert gas weld joint with a higher microhardness value. During tensile tests, activated tungsten inert gas and hot-wire tungsten inert gas weld joints displayed average ultimate tensile strength values of 521 and 514 MPa, respectively. The impact toughness of the activated tungsten inert gas weld joint was 248 J, while it was 220 J for the hot-wire tungsten inert gas weld joint. Field emission scanning electron microscope analysis equipped with energy-dispersive spectroscopy and elemental color mapping provided details about weld microstructure and the reasons for the material's failure. The study proved the efficiency and soundness of the 10-mm thick joints of AISI 904L fabricated by activated tungsten inert gas and hot-wire tungsten inert gas welding techniques.