Effects of gas tungsten arc welding on the mechanical properties and microstructure of 316L stainless steel by powder bed fusion

Laser-based powder bed fusion (LPBF) is a widely utilized technique for additive manufacturing (AM) of metal components. The size of LPBF-produced parts is restricted by machine dimensions. Welding emerges as a feasible solution for connecting smaller parts generated via PBF. Nevertheless, the weldability of PBF parts differs from conventional ones due to the unique thermal history of PBF components. This paper investigated the weldability of stainless steel 316L and tensile behavior of welded samples, comparing samples produced through LPBF and the conventional wrought method. Tensile testing, grain size analysis, microhardness test, and assessment of secondary dendrite arm spacing were conducted on every welded combination of materials (AM-AM, wrought-wrought, and AM-wrought) using gas tungsten arc welding (GTAW). The findings indicate that the wrought material demonstrates a higher maximum strength (577.5 MPa) and a lower yield strength (231.7 MPa) compared to the AM material (with a maximum strength of 548.2 MPa and a yield strength of 399.9 MPa). This difference may be attributed to the annealing process applied to the wrought material, which has not been applied on the AM material. Additionally, welded wrought samples have a significantly lower tensile strength compared to non-welded samples. The wrought samples exhibit a larger average grain size (11.14 to 31.12 \(\mu {\text{m}}\) $\mu \text{m}$ ) in the heat affected zone (HAZ) compared to non-heat affected regions (8.13 \(\mu {\text{m}}\) $\mu \text{m}$ ). In contrast, it is found that grain coarsening does not occur in PBF samples, which exhibit a similar grain size in the HAZ (15.04 \(\mathrm{\mu m}\) $\mu \mathrm{m}$ ) vs 13.97 \(\mathrm{\mu m}\) $\mu \mathrm{m}$ outside of the HAZ. Larger grain sizes within the HAZ correspond to a larger reduction in tensile strength for the wrought samples, compared to PBF samples. Similar secondary dendrite arm spacing has been observed in the weld regions of both PBF and wrought materials. Microhardness test results indicated that the AM base material has the highest microhardness and gradually decreases as transitioning to the HAZ and weld region. In summary, the PBF samples exhibit less reduction of strength and ductility after welding than wrought samples. Therefore, it is determined that additively manufactured 316L stainless steel has a higher weldability than traditionally manufactured wrought 316 stainless steel.