# Wire Arc Additive Manufacturing of Stainless Steels: A Review
## 6 Mechanical Properties
### Tensile Strength  
High quality WAAM components can be achieved with proper process parameters and a comprehensive understanding of the solidification phenomenon [105]. [PERSON] et al. [123] stated that geometry of the final part, the thermal history, and the localized solidification phenomena have an essential influence on the microstructure, which in turn affects the mechanical properties of the deposited parts. In this sense, studies have been carried out on the influence of process parameters on tensile strength. [PERSON] et al. [100] studied the relationship between the scanning speed, microstructure and ultimate tensile strength. They found that CGEF grains contributed to an increase in the ultimate tensile strengths and elongation rates of the Cr-Ni stainless steel samples manufactured by DWF-PAM or SWF-PAM, while the scanning speeds were ranging from 30 cm/min to 60 cm/min. Yield strengths and  
Figure 14: Average micro hardness values of different deposited specimens (316L Stainless Steel) [96]. Figure 15: Hardness distribution of the oscillated pass samples (17-4 PH stainless) deposited in different shielding gas under different heat treatment conditions (SG1: 38% He + 2% CO\({}_{2}\) + Ar; SG2: 2.5% CO\({}_{2}\) + Ar; AD represents as-deposited; ST: as-deposited followed by solution treatment only; AD+H900: as-deposited plus H900 ageing treatment; ST+H900: as-deposited followed by solution treatment and H900 ageing) [91]. ultimate tensile strengths are also dependent on the deposition direction, which leads to the upward growth of the coarse columnar crystals resulting in anisotropy [124; 125]. As stated by [PERSON] et al. [96], there is no obvious difference in the mean values of the horizontal and vertical tensile strengths between samples. However, the tensile strengths are indeed different in the horizontal and vertical orientations in the same build [88; 96]. Tables 7 and 9 list the tensile strength of stainless steel structures from different WAAM processes. The tensile strength of WAAM 316L steel is comparable to the wrought one. The 316 stainless steel samples fabricated by CMT and TopTIG with different current programs (continuous or pulsed) have comparable elongations (EL). Besides, the elongation is similar in horizontal (X) and vertical (Z) orientations [88]. However, samples deposited by MIG welding [96], CMT, and TopTIG based WAAM [88] are anisotropic in terms of yield strength (YS) and ultimate tensile strength (UTS). Yield strength of CMT samples in vertical orientation is lower than that in horizontal orientation owing to preferential growth of austenite grains [88]. Furthermore, research on anisotropy of MIG welding depositions shows that short heat dissipation time, severe heat accumulation, and cooling rate decline made the structure more uniform. A higher scanning speed can accelerate the cooling rate, leading to distinct anisotropy in sample G3510. Moreover, the relatively low thermal input of the bottom transient current (sample T3010) can cause a more pronounced anisotropy [96]. According to [PERSON] et al. [91], post-deposition heat treatment can help to obtain the required tensile properties. However, direct aging (without prior solution treatment) on as-deposited condition can lead to \(\delta\)-ferrite phase embrittlement, making the martensitic stainless-steel (17-4 PH stainless-steel) parts brittle. The localized brittle facets found in the fractographs can serve as evidence of possible localized \(\delta\)-ferrite embrittlement (see Figure 16). The anisotropy of tensile strength has an important effect on the performance of additive manufacturing components. Even though some studies have been conducted on the anisotropy of mechanical properties of WAAM stainless steels, further studies are needed for deeper understanding its mechanism and then properly control it. WAAM+in-situ rolling and post heat treatments could be useful approaches to reduce the anisotropy.