In recent years, Austempered ductile iron (ADI, CADI) has made great progress in the selection of grinding ball materials due to its excellent mechanical properties. However, there are two important constraints for stable production of excellent ADI or CADI grinding balls:
1) Add precious alloy elements. Due to the hardenability of the grinding ball, in order to ensure the uniformity of the internal and external structures of the grinding ball and the stability of production, when the diameter of the grinding ball is greater than 80 mm, the traditional nodular cast iron ball must be added with valuable alloy elements such as Mo, Cu, and the amount of alloy elements must be increased with the increase of the diameter of the grinding ball, greatly increasing the production cost of the traditional nodular cast iron grinding ball.
2) Salt bath isothermal heat treatment. In the case of adding precious alloy elements to obtain stable austenite bainite structure, the grinding ball must be isothermal treated in salt bath. Due to the huge investment in salt bath isothermal equipment, the melting and heat preservation of salt bath need to consume a lot of electric energy, and the limited volume of salt pond, the production can not be effectively operated continuously, which makes the production cycle longer and the production cost higher. At the same time, the heating of nitrate can be decomposed into nitrite, which will cause adverse effects on the environment and operators. In order to meet the environmental requirements, corresponding environmental protection equipment must be invested, further increasing the cost.
Therefore, high cost and environmental protection are two important limiting factors for the development of traditional ADI and CADI.