The formation of microstructure at the center zone.

The microstructure analysis process associated with this research was carried out on the surface and the center zone. The microstructure found in the center zone for all samples as has been given the codes S1, S2, S3, and S4 (Table 2) shows that graphite nodules are uniformly and roundly formed, with a ferrite and perlite structure phase, as shown in Fig. 4. This graphite structure is under the specifications of the nodular cast iron material according to the ASTM A 536 standard which is carried out through an inoculation process. In this nodularization process, magnesium (Mg) alloy elements will be added to get a round of the graphite nodule so that the ductile iron base material can withstand tensile loads and impact loads according to research Yamamoto S et al and Sasaki et al. [32, 33].