Investigation of the residual stresses and strains, microstructure and mechanical properties of stainless steel multipass welds produced using dual wire-tungsten inert gas process

Tungsten inert gas welding of thick components, such as baseplates or tubes, requires chamfering and multipass welding, which can induce significant residual strains and stresses. Strain might then be responsible for misalignments during welding and deviations from the desired part geometry while stress can compromise the integrity and service life. This study investigates the residual stresses, strains, microstructure, and mechanical properties of stainless steel multipass welds using the Dual-Wire Tungsten Inert Gas (DW-TIG) process. Two filler metals, austenitic 304 L and martensitic 415 stainless steels, were used to weld 20 mm thick 304 L baseplates, employing alternated and graded filling strategies compared to single-wire reference welds. Residual stress was determined using neutron diffraction and the contour method, with macroscopic distortion evaluated via profilometry. Microstructure was analyzed via electron backscatter diffraction, micrographs and Vickers hardness tests. Weld mechanical performances were assessed trough tensile tests and compared to standards. The results show strong agreement between the contour method and neutron diffraction, with discrepancies below 100 MPa. The alternated strategy achieved the most significant strain reduction (18 %) without amplifying stress, providing the best compromise between residual stress, strain, and mechanical performance. Martensitic transformation emerged as a key mechanism, introducing compressive stresses. The findings demonstrate the potential of DW-TIG welding to reduce distortions, minimize material waste, and enhance stress field control, making the process applicable to industrial settings (for thick components welding or part reloading). Future work will explore alternative filling strategies and lower-energy welding parameters to further enhance grain refinement and mechanical performance further.