According to the outer contour, the eutectic group of gray cast iron can be divided into three types: spherical eutectic group, pot tooth eutectic group and bamboo leaf eutectic group. Among them, globular eutectic clusters are formed under the condition of large undercooling, and the solid-liquid interface is relatively smooth; The eutectic group of most gray cast iron belongs to serrated eutectic group, which is formed when the undercooling is small, and there are few branches of graphite; Bamboo like eutectic clusters are formed under very low undercooling conditions, and the branches of graphite are smaller.
By comparing the eutectic structure of low carbon equivalent gray cast iron treated with different rare earth addition amounts, it can be found (as shown in the figure): with the addition of rare earth alloy in the melting process of low carbon equivalent gray cast iron, the number of eutectic clusters per unit area increases with the increase of rare earth alloy addition amount. The number of eutectic clusters in gray cast iron is related to the nucleation and growth conditions during eutectic transformation. The more heterogeneous nuclei and the slower growth rate, the more eutectic clusters will be formed. Due to the inoculation of rare earth alloy, a large number of heterogeneous nodule cores are added, and the crystallization time of eutectic is increased, resulting in the refinement effect of eutectic clusters. After eutectic refinement, the mechanical properties of gray cast iron can be effectively improved under the same matrix conditions.