# Monotonic and Fatigue Properties of Steel Material Manufactured by Wire Arc Additive Manufacturing
## 2 Specim Materials and Experiments
### Manufacturing and Preparation of Specimen Material  
To investigate the above-mentioned influences, cuboids were manufactured by the WAAM process, Figure 1a. These consisted of 40 layers, each approximately 2.8 mm thick. A metal inert gas (MIG) welding robot was used for production (see Table 1 for process parameters). The welding filler material was ISO 14341-A-G 50 7 M21 4 Mo in accordance with ISO Standard 14341 [10]. In conventional welding, it is used to generate weld material with a minimum yield strength of R\({}_{\text{p,min}}\) = 500 MPa, a tensile strength in the range of R\({}_{\text{m}}\) = 560-720 MPa, and minimum elongation at rupture of A\({}_{\text{min}}\) = 18%. The filler material is usually used to weld low-alloyed high strength structural steels with a correspondent strength of about 560 MPa. Welding was carried out with a pendulum movement in order to produce the largest possible weld pool and to enable adequate melting of the deposited layer. Thus, a good connection of the newly formed layer to the previous one should be ensured. A large energy input was used to achieve high melting rates and thus shorter manufacturing times (process optimization mentioned previously). In this way, WAAM material was produced using two different interlayer temperatures, 150 and 300 \({}^{\circ}\)C. It was measured at three points distributed over the layer with sheath tip on thermocouples in \begin{table}
\begin{tabular}{c c} \hline \hline
**Welding Parameters.** & **Value** \\ \hline Welding Current & 112 A \\ Voltage & 23.1 V \\ Wire Feed & 4.5 \(\frac{\text{m}}{\text{min}}\) \\ Wire-\(\varnothing\) & 1.2 mm \\ Inert Gas Quantity & 12 \(\frac{\text{l}}{\text{min}}\) \\ Width of Pendulum Movement & 24 mm \\ Frequency of Pendulum Movement & 0.7 Hz \\ Feed & 50 \(\frac{\text{min}}{\text{min}}\) \\ Path Velocity & 2.1 \(\frac{\text{min}}{\text{min}}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameters of the manufacturing process. Figure 1: Wire arc additive manufacturing (WAAM) material: (**a**) semi-finished block products, (**b**) sampling plan for tensile specimens with directional designation related to the weld layers, (**c**) regions for micrographs (A and C), path for hardness measurements (B), and points for residual stress determinations (D1 to D3). combination with a hand-held device for data acquisition. Thereby, temperature differences between the beginning and end of a layer of maximum 20 \({}^{\circ}\)C resulted. A recording of the temperature at the three thermocouples throughout the entire manufacturing process was not made, as the thermocouples had to be reattached after each layer applied to avoid their destruction. Due to the shorter waiting times between layer application for the interlayer temperature of 300 \({}^{\circ}\)C, the production of these cuboids took about a factor of 2 shorter compared to the interlayer temperature of 150 \({}^{\circ}\)C.  
To prepare the manufactured material for further examination, first, measurements of residual stresses were taken on some of the semi-finished product cuboids. Three measuring points per cuboid were distributed over the cuboid's height (see D1 to D3 in Figure 1c). After that, the semi-finished product cuboids were sawn to obtain cross-section X in Figure 1b,c in order to carry out microstructural investigations (see regions A and C in Figure 1c) and hardness measurements along path B in Figure 1c. The cuboids were divided into quadrants, Figure 1b, from which sample blanks were extracted lengthwise and crosswise to the welding direction. From these, the following unnotched tensile specimens were taken by CNC (Computerized Numerical Control) machining:  
1. Fatigue specimens with a diameter in the test range of 3 mm. The surfaces of the specimens in the test area were polished, Figure 2a;
2. Proportional tensile specimens with a diameter in the test range of 5 mm for monotonic tensile tests at room temperature, according to [11], Figure 2b;
3.