Effect of building orientation on weld characteristics of additively manufactured 316L stainless steel: Microstructure and mechanical properties

Abstract

In this study, the influence of building orientation of additively manufactured 316L stainless steel (SS) welded joints was investigated. Laser powder bed fusion (LPBF) technique was employed to print 316L SS plates in three different building orientations (BO): horizontal, inclined at 45°, and vertical directions. Subsequently, the welding processing of the printed 316L plates were conducted in various directions to the building orientations, i.e., the weld directions were perpendicular to the built layer (W90D) in horizontal specimens, parallel (W0D) in the vertical specimens, and oriented with 45° (W45D) to the inclined layers. The microstructure features were characterized using electron backscattered diffraction (EBSD) and laser confocal scanning microscopy (LCSM). The mechanical properties were evaluated through tension tests and hardness measurements. Fracture mode after tensile testing was examined by scanning electron imaging. The microstructural analysis revealed that the fusion zone (FZ) consisted of a predominantly austenitic matrix with the presence of 1–4% δ-ferrite. The FZ of the W0D joints exhibited fine grain structure and lowest dendrites arm spacing as compared to W90D and W45D. The hardness measurements in the FZ of W90D and W45D are 143 ± 5 and 155 ± 6 HV, respectively. These values were lower than the hardness of W0D joints, which measured 180 ± 7 HV. During tensile testing, the W90D and W45D joints were observed to fracture at the FZ, recording ultimate tensile strength (UTS) of 531 and 548 MPa, respectively. In contrast, the W0D joints fractured outside the FZ, displaying a lower UTS of 492 MPa. Furthermore, the welded joints displayed a ductile fracture mode, while W0D joints showed a very fine dimple structure, indicative of a different failure mechanism.