D uctile iron is an indispensable engineering material with excellent mechanical performances. Its tensile strength is even comparable to that of steel because the existence of graphite in a spherical shape reduces the cleavage effect of stress concentration in the matrix [1, 2]. In recent years, it has been found that austempered ductile iron (ADI) and carbidic austempered ductile iron (CADI), which are obtained by the austempering process, have higher strength and shock absorption, as well as good wear resistance and plastic toughness, giving rise to ductile iron being more widely used [3-5]. The quantity and morphology of graphite have a great influence on the properties of ductile iron. For examples, graphite nodules with small diameter and high roundness can significantly improve

C ADI (Carbidic Austempered Ductile Iron) is a new kind of wear-resistant material developed on the basis of ADI [1] (Austempered Ductile Iron). There are many studies concerning CADI, such as on chemical composition [2][3][4][5] , microstructure [6,7] , properties [8][9][10][11] and heat treatment [12][13][14][15] . The matrix structure of ADI is composed of the acicular ferrite with high hardness, and the strong and ductile retained austenite. Increasing the carbides can greatly improve the wear-resistance of CADI, so that the application of CADI in the mining industry with great wear and tear consumption is increasing day by day. Wear-resistant metal materials such as grinding balls, liners, bucket teeth and drill bits are consumed at a rate of more than 4.05 million tons every year in China, among which grinding balls are the largest part, accounting for 43% of the total of wear-resistant materials [16] . Compared with steel balls (such as medium carbon steel balls, high carbon steel balls) and other iron balls (such as ordinary white iron balls, high chromium iron balls), the grinding ball made of CADI has the advantages of light weight, low cost, energy saving, and low rate of consumption, so the