# Monotonic and Fatigue Properties of Steel Material Manufactured by Wire Arc Additive Manufacturing
## 3 Results
### Monotonic and Fatigue Properties
#### 3.3.1 Monotonic Tensile Properties
However, the properties R\({}_{\text{eH}}\) or R\({}_{\text{p0.2}}\), R\({}_{\text{m}}\), and A could still be evaluated. For each case of test temperature and interlayer temperature, three tensile tests were conducted. The evaluated average tensile properties are given in Table 3 and the stress-strain curves are shown in Figure 8. Since only three tests were conducted for each average property, no standard deviation is calculated. While a pronounced yield strength R\({}_{\text{eH}}\) is found at room temperature and 150 \({}^{\circ}\)C, at 300 \({}^{\circ}\)C the yield strength R\({}_{\text{p0.2}}\) is used instead (see italic values in Table 3). This need to be kept in mind for the comparison of the yield strength R\({}_{\text{p}}\)--depending on the test temperature, the two different properties R\({}_{\text{eH}}\) and R\({}_{\text{p0.2}}\) are used. Figure 9 shows the dependencies between the determined average properties and the test temperature. To facilitate comparison, for room temperature, the properties determined from the stress-strain curves in Figure 7 have also been added to this diagram (triangle markers in Figure 9). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Interlayer** & **Test** & **Tensile Strength** & **Yield Strength** & **Elongation at Rupture A** \\
**Temp/\({}^{\circ}\)C** & **Temp/\({}^{\circ}\)C** & **R\({}_{\text{m}}\)/MPa** & **R\({}_{\text{p0.2}}\)/MPa** & **R\({}_{\text{p0.2}}\)**/MPa** & **R\({}_{\text{p0.2}}\)** \\ \hline
150 & 20 & 549 & 385 & 31.3\%  
While for the yield strength, a slight decrease with increasing test temperature is found, the tensile strength shows lower values at 150 \({}^{\circ}\)C compared to at room temperature. However, an increase at 300 \({}^{\circ}\)C over the value at room temperature is observed. This tendency is found for both interlayer temperatures. It may be explained by effects of dynamic strain aging (DSA). DSA is a dynamical interaction between solute atoms and dislocations that may occur for certain strain rates and temperatures, [23]. It is known to appear for both ferritic and pearlitic structures and causes a local increase of tensile strength at about 350 \({}^{\circ}\)C. Above the temperature at which this maximum occurs, the tensile strength decreases with increasing temperature again, [24]. In addition, the Portevin-Le Chatlier (PLC; [25])  
Figure 8: Stress–strain curves (engineering stresses and strains) from monotonic tensile tests for crosswise extraction direction and interlayer temperatures of 150 \({}^{\circ}\)C (**a**) and 300 \({}^{\circ}\)C (**b**). Figure 9: Average tensile properties for different test temperatures: (**a**) tensile strength, (**b**) yield strength, (**c**) elongation at rupture. effect, often observed in association with DSA, could be witnessed at the test temperature of 150 \({}^{\circ}\)C. It manifests itself in kinks in the stress-strain curve, as shown in the enlargement of these curves in Figure 8a. The effect is observed at a test temperature of 150 \({}^{\circ}\)C for both interlayer temperatures, but is more pronounced for the interlayer temperature of 150 \({}^{\circ}\)C.  
Due to the large scattering for the elongation at rupture, a clear dependency is hard to determine. However, it seems reasonable to state that there is a decreasing tendency with an increasing test temperature for both interlayer temperatures. While no clear trend is found for the elongation at rupture between the two interlayer temperatures, the average strength properties R\({}_{\rm p}\) and R\({}_{\rm m}\) for the material manufactured with an interlayer temperature of 300 \({}^{\circ}\)C are below those for 150 \({}^{\circ}\)C for all testing temperatures. These differences are below a factor of 1.07 for R\({}_{\rm m}\) and below a factor of 1.15 for R\({}_{\rm p}\).