# Wire Arc Additive Manufacturing of Stainless Steels: A Review
## 2 Macroscopic Characteristics of Samples
The surface of CMT- base additive manufacturing parts is rather smooth as mentioned by the work of Fronius International GmbH [57; 58], [PERSON] et al. [59], [PERSON] et al. [60], and [PERSON] et al. [61]. To investigate the ability of CMT in terms of surface condition, [PERSON] et al. [55] adopted CMT to manufacture blade-like geometries of duplex stainless steel. With consistent welding parameters for all layers, they achieved quite smooth surface comparable to that obtained by hot rolling, flame cutting, or sand casting. The absolute surface roughness (R\({}_{\text{a}}\)) of duplex stainless steel geometry was 24.5 \(\upmu\)m, and the average distance between the highest peak and lowest valley (R\({}_{\text{z}}\)) was 135.3 \(\upmu\)m, which can be seen in Figure 4 of [55]. Other factors, such as deposition path and wire material, also affect the surface condition. During wire-arc additive manufacturing of duplex stainless steel blocks, an alternating direction path generated the uniform layer height, while a one-direction deposition path yielded uneven sides due to the heat accumulation at the stop point during the deposition of each layer [101]. [PERSON] et al. [88] applied multi-bead CMT deposition parameters to build 316L stainless steel walls. The R\({}_{\text{z}}\) of CMT-based WAM parts was 220 \(\upmu\)m.  
In summary, macroscopic characteristics are closely related to wire feeding speed and scanning speed, welding current mode, cooling time, and interlay temperature. The influences of main process parameters on the macroscopic morphology of WAM stainless steel parts are listed in Table 6. Further studies on optimizing the above-mentioned process parameters are needed for achieving better dimensional accuracy and surface quality of WAM parts. Figure 4: Photographs of different deposited wall samples [100]: (**a**), (**b**), and (**c**) showing the DWF-PAM samples prepared at speeds of 30 cm/min, 50 cm/min, and 60 cm/min, respectively; (**d**), (**e**), and (**f**) demonstrate the SWF-PAM samples prepared at speeds of 30 cm/min, 50 cm/min, and 60 cm/min, respectively. \begin{table}
\begin{tabular}{c c c c c} \hline
**WSAM Techniques** & **Material** & **Process Parameters** & **Macroscopic Characteristics** & **Reported by** \\ \hline \multirow{2}{*}{MIG} & 316L (austenitic) stainless steel & Welding current mode & Gradual reduction of bottom current & Improves bottom formation & [PERSON] et al. [96] \\ \cline{3-5}  & & Increasing scanning speed & Uneverenness of both ends & \\ \hline \multirow{2}{*}{PAM} & H00 Cr21 Nil10 (austenitic) stainless steel & SWF-PAM: single-wire feed and plasma additive manufacturing & Slightly better surface-quality than that of Double-wire feed and plasma additive manufacturing & [PERSON] et al. [100] \\ \cline{3-5}  & & DWF-PAM: double-wire feed and plasma additive manufacturing & / & \\ \hline PAM: SWF-PAM, DWF-PAM & & Increasing scanning speed & Better surface quality & \\ \hline \multirow{2}{*}{GMAW} & Type-220 (duplex) stainless steel & Deposition path & Alternating direction deposition path & Uniform layer height & [PERSON] et al. [101] \\ \cline{3-5}  & & One-direction deposition & Uneveren sides: the start side was higher than the end side. & \\ \hline \multirow{2}{*}{GMAW} & H08 Mn2 Si low-carbon steel & Decreasing interlay temperature & Surface roughness decreases & \\ \cline{3-5}  & & Increasing scanning speed & Surface roughness increases & [PERSON] et al. [95] \\ \cline{3-5}  & & Increasing wire feeding speed & Surface roughness increases & \\ \hline \end{tabular}
\end{table} 
Table 6: Process parameters affecting the macro morphology of WSAM stainless steel parts