## 3 Results and Discussion
In this study, the presence of various iron oxide phases at the grain boundaries is also considered, but due to their low amounts, these phases were not detectable in the XRD analyses (Figure 8). Figure 5.3 Optical microstructure images of parts produced with different layer thicknesses. (**a**) 100 \(\upmu\)m; (**b**) 400 \(\upmu\)m. Red arrows display the voids remaining between the filaments during production. Figure 14 shows the variation in layer hardness values depending on layer thickness. According to the data, the highest average hardness value of approximately 199 Hv was observed in the part produced with a layer thickness of 100 \(\upmu\)m, while the lowest average hardness value of approximately 170.5 Hv was found in the part produced with a layer thickness of 400 \(\upmu\)m. The measured values are close to the hardness of AISI 316L stainless steel. As previously mentioned, the presence of certain secondary phases dispersed in specific regions of the structure may lead to locally higher hardness values. Higher hardness values were achieved in grain boundary regions due to the increased hardness of oxygen-rich phases. Nonetheless, the difference between the hardness of the sample with the lowest average value and the sample with the highest value is approximately 14%. The lack of correlation between density values and hardness values is attributed to the measurement of hardness in terms of microhardness. [PERSON] et al. achieved a hardness value of approximately 15 Hv with a layer thickness of 200 \(\upmu\)m [53]. [PERSON] et al. [12] obtained a hardness value of 132 Hv in 316L parts produced with a layer thickness of 100 \(\upmu\)m. While the values obtained in this study are similar, minor differences are attributed to variations in the debinding and sintering process parameters. In FDM-produced parts, variability in mechanical properties (anisotropy) between layers is frequently observed. A high number of layers can lead to weak interlayer bonding, especially in directions perpendicular to the loading direction, which may result in reduced hardness, particularly in scenarios with low layer thickness [28]. Even with low layer thickness in FDM production, anisotropy in mechanical properties can adversely affect hardness. Mechanical strength in directions perpendicular to the layers is generally weaker, and low layer thickness may not fully compensate for this weakness [26]. Figure 5.4 SEM images of parts produced with different layer thicknesses: **(a)** 100 \(\upmu\)m front surface; **(b)** 100 \(\upmu\)m side surface; **(c)** 400 \(\upmu\)m front surface; **(d)** 400 \(\upmu\)m side surface. White arrows point to the regions in which there are higher amounts of Si compared to other regions. Stress-strain graphs of the produced specimens are presented in Figure 5.5 According to the obtained data, the highest tensile strength was achieved with the part produced at the lowest layer thickness (100 \(\upmu\)m, 432 MPa). Low layer thickness implies a greater accumulation of layers, which can enhance interlayer bonding. [PERSON] et al. [54] observed that thinner layer thicknesses provide strong interlayer bonding, thereby increasing tensile strength. No necking was observed in the tensile specimens after the test. However, fracture points varied for each specimen, which is thought to be due to voids or gas bubbles remaining from the production stages or residual stresses formed during thermal processes [55; 56]. The lower-than-expected tensile strength may be attributed to delamination occurring between the layers [56]. The specimens were produced according to the ASTM E8 [22] standard. The highest tensile strength obtained from the material was 432 MPa at a layer thickness of 100 \(\upmu\)m. [PERSON] and colleagues [55] also reported achieving tensile strengths in the range of 400 to 485 MPa in their study. The hardness and tensile strength are influenced by variations during the heat treatment processes. In additive manufacturing using 316L austenitic stainless steel, [PERSON] et al.