## 3 Results and Discussion  
### Experimental Data  
An additively manufactured wall structure is shown in Figure 7. The parameter set with 4 kJ/cm is displayed in this figure. On the left side there is a size comparison of the different structure widths with one, two and three adjacent weld tracks. The right side shows a side view of the wall structure with 4 kJ/cm with a single weld track. In order to generate data sets for unknown parameter sets a regression equation in relation with the \(\mathrm{t_{8/5}}\) cooling times is needed for all parameters which should be predicted. A welding TTT diagram can be used to evaluate the type of regression equation which is suitable to describe the relation between \(\mathrm{t_{8/5}}\) cooling time and hardness. Therefore, the hardness values and the \(\mathrm{t_{8/5}}\) cooling times to create Figure 8 was read out of Figure 3.  
Figure 7: Samples of additively manufactured wall structures 4 kJ/cm: (1) single weld track; (2) two adjacent weld tracks; (3) three adjacent weld tracks. The \(\mathrm{t_{8/5}}\) cooling times and their corresponding hardness values can be used to determine the general form of the regression equation. In Figure 8 a curve with these corresponding values, which were taken from the TTT diagram of G4 Si1 in [PERSON] et al. (2018), is shown. Hardness decreases with increasing \(\mathrm{t_{8/5}}\) cooling times. For smaller values the changes in hardness are quite high, but the hardness change is lower for higher \(\mathrm{t_{8/5}}\) cooling times. The change in hardness is due to a differing amount of bainite and ferrite, whereas the ferrite content increases for higher \(\mathrm{t_{8/5}}\) cooling times according to the TTT-diagram in Figure 3 [(51)]. Moreover, the increase in \(\mathrm{t_{8/5}}\) cooling times leads to a coarser grain structure and therefore decreasing mechanical properties. The general course of the values shows a logarithmic character. Therefore, a logarithmic regression equation will be used for all mechanical properties. The hardness of the welded structures (Figure 9) decreases with increasing \(\mathrm{t_{8/5}}\) cooling times. Hardness decreases from 200 HV1 at 8 s cooling time to 175 HV1 at 35.1 s, which is a decrease of 12.5%. This decreasing hardness is due to the formation of lower amounts of bainite and higher amounts of perlite and ferrite, due to longer cooling times [(51; 52)]. The measured hardness values fit well in the logarithmic equation within their margin of error. Therefore, hardness is a mechanical property which could be predicted by interpolation, even for parameter sets with differing number of weld bead, thicknesses and travel speeds. In Figure 10 the measured yield and tensile strength and the elongation at break are shown. They were measured using the tensile samples according to Figure 3. Samples in buildup direction and across were combined due to a low difference between both values, as shown in a previous study [(18)]. The measured tensile and yield strengths are in the same order of magnitude as stated in [(53; 54; 22; 55)]. [PERSON] et al. stated that a heat treatment such as normalization can lead to a change in mechanical properties. Tensile and yield strengths are decreasing in a similar manner to the hardness with increasing \(\mathrm{t_{8/5}}\) cooling times, due to varying proportions [(22)] of ferrite and bainite and a coarser grain structure [(51; 52)]. It was observed that the tensile strength decreased and the elongation at break was increased after normalization. The hardness values are generally linked to the mechanical strength [(55)]. The tensile test does not fit as good as the hardness values. This is probably due to a higher dependency on differing geometric properties and thickness of the tensile samples. Therefore, a different test methodology might be necessary to  
Figure 8: Hardness as a function of \(\mathrm{t_{8/5}}\) cooling time (values for hardness and \(\mathrm{t_{8/5}}\) cooling time according to the welding TTT diagram shown in Figure 3).