The figure shows the graphite morphology and distribution of three grades of gray cast iron samples. It can be seen from the figure that the graphite morphology of the three grades of gray cast iron samples is mainly A-type graphite, with a small amount of D-type graphite and E-type undercooled graphite. At present, it is considered that the mechanical properties of type a graphite are good, and the mechanical properties of type D and e graphite are adversely affected. It can also be seen in the photos that there are casting holes in the three gray cast iron samples. The existence of these casting holes will cause stress concentration and induce crack initiation, so as to reduce the tensile and fatigue properties of gray cast iron.
The graphite grade of ordinary HT250 has both grade I and grade II, while the graphite grade of low alloy HT250 and HT300 added with trace alloying elements is grade II. The results show that the addition of trace alloying elements not only refines the flake graphite in gray cast iron, but also makes the structure of gray cast iron more uniform.