Our cast iron grinding balls can be divided into three categories including the high chromium type, medium chromium type and the low chromium type. 1. The quality index of the high chromium type The chromium content of the high chromium type product is greater than or equal to 10.0%. And the carbon content is between 1.80% and 3.20%. It is required by the national standard that the hardness of the high chromium type product must be no less than 58hrc, and that the impact value should be greater than or equal to 3.0j/cm. This type of product must go through the hot quenching and the tempering treatment to come up to the hardness. Currently at home, there are two quenching methods for this type of product including oil quenching and wind quenching. If the tested hardness of this type of product is below 54hrc, then it shows that the quenching treatment is omitted. 2.The quality index of the medium chromium type The medium chromium type cast iron grinding ball is defined as the chromium content ranging from 3.0% to 7.0%, and the carbon content coming between 1.80% and 3.20%. Its impact value should be no less than 2.0j/cm. . The national standard requires the hardness of this type of product should be greater than or equal to 47hrc. For ensuring the quality, the medium chromium type product should be processed with high temperature tempering to eliminate the casting stress. If the surface of the steel ball assumes the dark red color, it proves that the steel ball has been processed with high temperature tempering. If the surface of the steel ball still comes with the metal color, then, we can judge that the steel ball doesn’t go through the high temperature tempering treatment.