A comparative investigation on the mechanical properties and process performance of conventional and advanced TIG welding for austenitic stainless steel joints

Tungsten inert gas (TIG) welding is extensively employed for joining steel products in several manufacturing fields, partly thanks to the high mechanical weld quality achievable. However, the low efficiency represents its main drawback in industrial applications. A high-productivity alternative is the keyhole TIG method. This research is aimed at investigating and comparing the metallurgical characteristics and mechanical quality of single-pass keyhole TIG welding and conventional multi-pass TIG technique for welding medium-thickness steel parts. For this purpose, the two welding techniques were employed for joining 10-mm-thick 316L austenitic stainless steel plates. The influence of the welding processes on the metallurgical and mechanical characteristics of the joints was investigated through microstructural analysis, hardness measurements as well as tensile, bending and impact tests. Furthermore, the fracture surfaces after tensile and impact tests were analysed using scanning electron microscopy technique. The results reveal sound and defect-free welds with a dendritic weld zone microstructure consisting of a matrix of austenite and δ-ferrite, with a reduction of the latter in keyhole mode welding. Hardness measurements resulted slightly lower in the weld zone produced through the keyhole technique than those achieved by conventional TIG, while the weld tensile and bending strength properties were comparable. Moreover, keyhole TIG welding revealed excellent fracture toughness properties in the weld zone, even better than those of conventional TIG technique. Fractographic analysis of the joints showed a ductile fracture mechanism in both welds. Finally, experiments prove a drastic reduction in welding time by employing the keyhole TIG technique compared with conventional TIG, as well as a significant saving on welding consumables.