# Monotonic and Fatigue Properties of Steel Material Manufactured by Wire Arc Additive Manufacturing
## 4 Discussion
### Comparison of the WAAM Material with Conventional Materials  
One of the aims of this study is to compare the performance of the WAAM material under investigation to conventional steel material. First of all, the monotonic properties are examined. It could be expected that the generated material would reach properties within the requirements for weld materials, as specified in the standard for the welding filler material. However, except for the elongation at rupture, the WAAM material is not found to reach these specifications:  
* The yield strength is smaller than the specification by a factor of 1.4 to 1.5;
* The tensile strength is slightly below the specified minimal value;
* The elongation at rupture is larger than the specified minimal value by a factor of about 1.6. It can be stated that monotonic properties of WAAM material should not be expected to show the same properties as weld material from conventional weldments. This finding is not surprising as the manufacturing process and cooling conditions may vary considerably for the WAAM process. Second, the performance of WAAM material concerning the fatigue life is compared. Since WAAM material is a new class of material and only few experimental findings are known for this class in general, a rating of the fatigue performance can only be done by looking at conventional steel materials. For this, a study by [PERSON] and [PERSON] [27] that determined the average statistical dependencies between the monotonic tensile strength and cyclic properties on a large database of experimental results is considered. From that study, a method for estimating cyclic properties originated, amongst others, for steel materials (Table 6). The estimation method just needs the tensile strength R\({}_{\text{m}}\) to estimate the cyclic properties of the strain-life curve. For steel, two subgroups are distinguished: steel (rolled and forged) and cast steel. To get an insight of how the WAAM material under investigation behaves in relation to other steel materials, the cyclic material characteristics are estimated from the tensile strength of the WAAM material using the method shown in Table 6. The determined average values for the R\({}_{\text{m}}\) of the WAAM materials vary over a range from 531 to 539 MPa, Table 2. This range has no noticeable influence on the estimated values when plotted in a diagram. Therefore, the average tensile strength R\({}_{\text{m}}\) = 536 MPa is used for the estimation. The estimated strain-life curves are plotted in Figure 14 beside the results of the strain-controlled tests. The study presented in [27] also contains a deviation range between the 10% and 90% quantiles for the estimation method. This scatter parameter describes the scattering of experimental values compared with the estimated curves and is also included in Figure 14. It can be seen that the fatigue life of the WAAM material is below the estimated strain-life curve for rolled and forged steel material in most experimental results, while it fits the estimated curve and rated scatter band for cast steel quite well. With both the estimated values for the strain-life curve as well as Equations (3) and (4), it is possible to estimate the properties for the cyclic stress-strain curves. These are plotted in the same way as the strain-life curve, Figure 15. Since the two estimated curves do not differ much between steel and cast steel, the deformation behavior for the WAAM material is in good agreement with both material groups.