# Wire Arc Additive Manufacturing of Stainless Steels: A Review
## 1 Introduction
Moreover, studies on AM of stainless steel 316 indicate that the arc power of WAAM (also known as directed energy deposition with gas-metal-arc, DED-GMA) is 5-10 times higher than that of laser in PBF-L and DED-L [74; 75; 76; 77; 78; 79; 80; 81; 82; 83; 84; 85; 86; 87; 88], which leads to much higher printing speed of WAAM, as shown in Figure 2[26]. Recently, there have been a number of investigations on wire arc additive manufacturing of stainless steels, including filler metals' chemical composition, process parameters, process modeling, defects, residual stress and distortion, microstructure, and mechanical properties. Stainless steels are usually classified as: ferritic stainless steel (409, 430, etc. ), austenitic stainless steel (316, 304, etc. ), austenitic-ferrite duplex stainless steel (2205, 2209) and martensitic stainless steel (420, 17-4). Their microstructure features and mechanical properties are quite different after WAAM. [PERSON] et al. found that mixing different filler metals can reduce the nickel equivalent and increase the ferrite content in GMAW duplex stainless steel specimens [89]. Moreover, appropriate process parameters can help to \begin{table}
\begin{tabular}{l l l l} \hline \hline \multicolumn{1}{c}{**Country**} & \multicolumn{1}{c}{**Research Groups**} & \multicolumn{1}{c}{\begin{tabular}{c} **Synonyms of Wire Arc Additive** \\ **Manufacturing (WAAM)** \\ \end{tabular} } & \multicolumn{1}{c}{**Ref.**} \\ \hline \multirow{3}{*}{United States} & Southern Methodist & Rapid prototyping (RP) based on & \\  & University & gas tungsten arc welding (GTAW) & \\ \cline{2-3}  & Tufts University & Near-Net Shape Manufacturing & [PERSON] et al. [37] \\ \hline \multirow{2}{*}{South Korea} & Korea Institute of Science and & 3D welding & [PERSON] et al. [35; 36] \\ \cline{2-3}  & Technology & 3D micro welding & [PERSON] et al. [38] \\ \hline \multirow{3}{*}{United Kingdom} & University of Sheffield & Shaped metal deposition & [PERSON] et al. [39] \\ \cline{2-3}  & Cranfield University & Wire Arc Additive Manufacturing & [PERSON] et al. \\ \cline{2-3}  & University of Manchester & Wire Arc Additive Manufacturing & [PERSON] et al. \\ \cline{2-3}  & Coventry University & Wire Arc Additive Manufacturing & [PERSON] et al. \\ \cline{2-3}  & University of Wales Swansea & Shaped metal deposition & [PERSON] et al. [40] \\ \hline \multirow{3}{*}{China} & Harbin Institute of Technology & \
\begin{tabular}{c} GMAW-based rapid \\ manufacturing \\ \end{tabular} & [PERSON] et al. [41; 42] \\ \cline{2-3}  & Harbin Institute of Technology &
\begin{tabular}{c} GMAW based additive \\ manufacturing \\ \end{tabular} & [PERSON] et al. [43] \\ \cline{2-3}  & Xi An Jiao Tong University & MPAW—based rapid prototyping & [PERSON] et al. [44] \\ \hline India & Indian Institute of Technology & Hybrid Layered Manufacturing & [PERSON] et al. [45] \\ \hline \multirow{3}{*}{Australia} & \multirow{3}{*}{University of Wollongong} & Wire and arc additive & \\  & manufacturing (WAAM) & [PERSON] et al. [46; 47] \\ \cline{1-1} \cline{3-3}  & & Wire-feed additive manufacturing & [PERSON] et al. [48] \\ \cline{1-1} \cline{3-3}  & & GTAW based-additive & [PERSON] et al. [49] \\ \cline{1-1} \cline{3-3}  & manufacturing & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Main research groups working on WAAM. achieve a high-quality WAAM structure. Heat input, cooling rate and reheating effect can impact the morphology, microstructure, and mechanical properties in WAAM components [86; 90]. [PERSON] et al. found that the cooling rate during deposition has an essential influence on retained austenite formation. Direct ageing on the as-deposited condition leads to a reduction of ductility by nearly 50% [91]. [PERSON] and [PERSON] et al. studied the printability of 316 stainless steel by heat transfer fluid flow model. They concluded that DED-GMA has deep penetration, which makes DED-GMA components have the lowest probability of lack of fusion defects compared to PBF-L and DED-L parts [26].