Abstract: Aiming at the failure and fracture of a ductile iron part, SEM scanning electron microscope and metallographic microscope were used to analyze the fracture morphology and the metallographic structure respectively. The results show that there are a large number of directionally distributed chilled carbides in the casting, which improves the tensile strength and yield strength of the material, but the plasticity is greatly reduced, which is the main reason for its fracture failure. By studying the formation mechanism of chilled carbide in ductile iron matrix, heat treatment technology was adopted to eliminate chilled carbide and increase pearlite content and distribute it evenly in matrix, thus improving the strength and plasticity of the material. The experimental results show that the chilled carbides in ductile iron castings can be effectively eliminated by two-stage high temperature graphitization annealing. For pearlite-ferrite ductile iron, the pearlite content in the matrix can be controlled and distributed evenly by accurately controlling its cooling rate and tapping temperature.