*3.2. Mechanical Properties*

Table 4 shows the mechanical properties of specimens processed with different conditions. The S1 specimen has high strength, hardness and relative density, relatively low ductility and toughness [15]. The strength and ductility of the S2 samples decrease rapidly due to the precipitation of the σ phases. In the temperature range of 1100–1200 ◦C, the strength and hardness decreased gradually while the elongation and section shrinkage increased gradually due to recrystallization and grain growth with the increase of solution annealing temperature. Lastly, the table also shows that the sample solution treated at 1150◦C for one hour had better comprehensive mechanical properties compared to the others. Figure 5 is the tensile fracture and impact fracture morphology of the S4 specimen, which is characterized by ductile fracture. There are some pores in the parts prepared by SLM with relative density of 98.2%. The laser energy density, laser scanning strategy, and powder properties will affect relative density. In order to obtain fully compact parts, further densification by hot isostatic pressing can further improve the mechanical properties. Therefore, it is understandable that the mechanical properties prepared by SLM are lower than that of welded and seamless pipe required in ASTM A790 standard.


**Table 4.** The mechanical properties of specimens processed under different conditions.

**Figure 5.** The fracture morphology of the S4 specimen (**a**) tensile fracture; (**b**) impact fracture.
