## 3 Results
### Evaluation of AM_A, AM_B, and Forging_C Mechanical Properties
#### 3.1.3 Unnotched Impact Test Evaluation of AM_A, AM_B, and Forging_C  
The impact test is important for evaluating the toughness of mold steel materials. For this test, each impact specimen was prepared according to the heat treatment and nonheat treatment conditions of the AM materials. Moreover, to quantitatively evaluate the impact test values of the AM and forged materials, Forging_C was selected as the comparative material, and the impact values of all the materials were evaluated through an unnotched impact test. Figure 19 shows the shape and detailed dimensions of the impact specimen. The specimens for impact testing were prepared on the S45C substrate using heterogeneous metal AM. Additionally, with the surface roughness after AM taken into consideration, the specimens were prepared with a processing allowance. As a result, 55 \(\times\) 10 \(\times\) 7 mm unnotched impact specimens were manufactured via wire processing and abrasive processing. Seven test specimens were prepared for each combination of material and condition.  
An MPX-700 Charpy impact tester was used for the impact tests. For each material-condition combination, after five samples (from among the seven specimens) were tested, the minimum and maximum values were discarded, and the average of the remaining  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{
\begin{tabular}{c} **Specimen** \\ **No** \\ \end{tabular} } & \multicolumn{2}{c}{**AM\_B**} & \multicolumn{2}{c}{**AM\_B**} \\ \cline{2-5}  & **Tensile Strength** & **Elongation (\%)** & **Tensile Strength** & **Elongation (\%)** \\ \hline
1 & 646 & 9.70 & 635 & 9.52 \\
2 & 647 & 9.89 & 506 & 9.40 \\
3 & 648 & 9.65 & 584 & 9.48 \\ Average & 647 & 9.75 & 575 & 9.47 \\ \hline \hline \end{tabular}
\end{table}
Table 15: AM specimen bonding-strength test results.  
Figure 19: Shape and dimensions of unnotched impact test specimens.  
three was recorded. Table 16 outlines each material and manufacturing condition with the corresponding test results. The heat-treated Forging_C exhibited the highest impact value, whereas the AM_B laminated material exhibited superior impact properties, equivalent to 85% that of Forging_C. By contrast, the impact test value of AM_A was very low, at 20% of the Forging_C value. Generally, the impact properties of forging materials are improved when a material that has undergone quenching is tempered. However, in the case of the tested laminated materials, the impact values of the non-heat-treated materials were higher than those of the tempered specimens. Furthermore, generally, high-temperature tempering conditions yield higher impact values than those produced in low-temperature tempering conditions. By contrast, the hardness and impact test values of the tested AM materials were high under the low-temperature tempering condition. This was expected as a result of the quenching of the AM material through the additional heat treatment process, in which primary quenching occurred during AM. This is considered to have been caused by differences in the alloy compositions and manufacturing processes of the forging and laminate materials.