## 3 Results and Discussion
It is believed that the larger porosities (Figure 12b, red arrow) are the voids remaining between the filaments during production. Additionally, the predominantly spherical morphology of the microporosities indicates that these voids are regions where particle densification was incomplete during sintering [45]. The literature suggests that spherical micro-voids can positively influence mechanical properties due to their crack-stopping effects [46]. No orientation related to the printing direction was detected in the grains, suggesting isotropic properties. Furthermore, no significant relationship between layer thickness and grain size was observed. [PERSON] and [PERSON] [47] reported a grain size of 252 \(\upmu\)m for cast stainless steel of similar composition, while [PERSON] et al. [48] reported an average grain size of 94.51 \(\upmu\)m for 316L stainless steel parts produced via powder injection molding. The microstructures obtained in this study reveal that the grain structure is much finer compared to casting and similar to that achieved through injection molding. Figure 5.0 Graph of porosity size as a function of layer thickness. Figure 5.1 Density variation with respect to layer thickness. Another factor influencing the microstructure in additive manufacturing is the build direction [49]. In some cases, due to differences in bonding and cooling rates between layers, different microstructures can be observed on various surfaces (xz, yz) of the produced parts. The Vickers microhardness measurements that support this statement are shown in Figure 5.2 To assess whether there are microstructural differences between surfaces, images from different surfaces of the parts were taken (Figure 13). In SEM images, spherical pores appear more prominently. The images were taken in Backscattered Electron mode to enhance the visibility of grain boundaries. Figure 13a,b shows the microstructure of the front and side surfaces, respectively, of a part produced with a low layer thickness. The spherical pores observed in both intra-grain and inter-grain regions are considered to be due to trapped gas pockets during sintering. It is believed that these voids formed because the argon gas used during sintering became trapped before escaping, due to the closing of exit paths and its inability to react with surrounding particles since it is an inert gas [50]. In the microstructure image of the front surface of the part produced with a high layer thickness (Figure 13c), a higher amount of microporosity was observed compared to the other sample. The side surface of the same part (Figure 13d) shows larger, irregularly shaped pores. However, no significant differences were observed between surfaces. Unlike the SLM method, the much longer sintering time in FDM metal part production prevents the formation of heterogeneous structures between surfaces. EDS analyses of the parts support this conclusion. The amounts of major alloying elements such as Cr, Ni, and Fe in the grain boundary and intra-grain regions are very similar. However, segregation of alloying elements was observed in some areas. For instance, regions with a relatively white color, indicated by white arrows in Figure 13a,d, show higher amounts of Si compared to other regions. The presence of more Si at grain boundaries indicates a greater presence of ferrite in these regions, as Si is a ferrite stabilizer [51]. Additionally, since the BCC structure of ferrite allows easier dissolution of alloying elements compared to the denser FCC austenite structure, higher Si concentrations in ferrite regions are expected. Some regions with relatively wider grain boundaries were identified, and EDS analyses revealed higher oxygen content in these areas. [PERSON] et al. [52] found similarly high oxygen concentrations at grain boundaries in their study with 316L stainless steel, attributing it to the formation of Fe\({}_{3}\)O\({}_{4}\) phase at the grain boundaries.