PSI - Issue 68

Yasith H. Rajashilpage et al. / Procedia Structural Integrity 68 (2025) 981–987 Y.H. Rajashilpage, R.A. Yildiz, M. Malekan / Structural Integrity Procedia 00 (2025) 000–000

986 6

resistance to dislocation motion, thereby lowering the material's hardness. Increased layer thickness also contributes to higher porosity and insufficient adhesion between layers, both of which compromise hardness (Dabwan et al, 2021, Huang et al, 2022). Porosity introduces stress concentrations, while inadequate bonding weakens the material structural integrity. The effect of higher scanning speed on hardness mirrors its impact on tensile properties. The observed reduction in hardness was linked to changes in cooling rates, reduced laser energy input, and the occurrence of lack-of-fusion defects. A faster cooling rate from increased scanning speed could induce residual stresses, further diminishing hardness. These residual stresses, combined with insufficient fusion and lower energy input, account for the overall decrease in hardness at the higher scanning speeds. Table 3. Hardness properties of the SS 316L and IN625 alloys. Layer thickness – Scanning speed SS 316L IN625 temperature (°C) HRB temperature (°C) HRB

700 900 1100 700 900 1100 700 900 1100 700 900 1100 700 900 1100 700 900 1100 700 900 1100 700 900 1100 700 900 1100

78.69 75.41 77.61 76.59 74.81 72.93 79.55 73.74 74.9 77.27 73.39 74 74.67 72.09 70.85 67.72 65.27 62.98 68.22 71.47 72.19 66.01 60 62.7 52.84 51.25 44.6

900 1000 1100 900 1000 1100 900 1000 1100 900 1000 1100 900 1000 1100 900 1000 1100 900 1000 1100 900 1000 1100 900 1000 1100

87.47 85.55 78.72 83.65 85.06 82.13 87.43 86.48 82.46 80.98 78.71 72.16 79.65 74.27 72.74 72.93 71.38 68.81 76.26 75.1 70.43 64.49 70.97 73.52 59.84 57.82 56.34

30 µ m - 1400mm/s

30 µ m - 1700mm/s

30 µ m - 2000mm/s

55 µ m - 1400mm/s

55 µ m - 1700mm/s

55 µ m - 2000mm/s

80 µ m - 1400mm/s

80 µ m - 1700mm/s

80 µ m - 2000mm/s

4. Conclusion This study highlights key findings on the effects of annealing temperatures on the mechanical properties of stainless steel 316L (SS 316L) and Inconel 625 (IN625) alloys. At lower annealing temperatures (700°C for SS 316L and 900°C for IN625), elongation significantly decreased, while ultimate tensile strength (UTS) showed a slight increase. However, as the annealing temperature increased up to 1100°C, elongation recovered substantially, reaching up to 95% for SS 316L and 78% for IN625, compared to the as-built samples. At 700°C, elongation recovery was lower, around 75% for SS 316L and 34% for IN625. In contrast, UTS tend to decrease with higher annealing temperatures. Additionally, increasing layer thickness and scanning speed generally reduced both UTS and elongation for both materials, with the most adverse effects observed at a layer thickness of 80 μm and scanning speed of 2000 mm/s. Hardness also decreased with increasing annealing temperatures, thicker layers, and faster scanning speeds. The observed trends in elongation, UTS, and hardness with increasing annealing temperatures can be explained by several factors, including recrystallization and grain growth, reduction in dislocation density, decrease in residual stresses, stabilization of the austenitic phase (in SS 316L), dissolution of brittle phases (γ'' and delta phases in IN625), and increased porosity.