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].本研究所涉及的显微组织分析工作分别在试样表面与中心区域开展。所有编号为S1、S2、S3、S4的中心区域试样（见表2）的显微组织均显示，石墨球均匀圆润地析出，基体组织为铁素体与珠光体相，如图4所示。该石墨组织符合采用孕育处理工艺制备的ASTM A 536标准规定的球墨铸铁材料规范。在该球化处理工序中，需添加镁（Mg）合金元素以实现石墨球化，使球墨铸铁基体可承受拉伸载荷与冲击载荷，相关研究结论引自Yamamoto S等人与Sasaki等人的文献[32,33]。