Analysis of the influence of the chemical composition and metallurgical quality of grinding balls on their operational properties

Abstract

On the basis of a complex of researches carried out in laboratory and industrial conditions using standard methods of metallographic analysis and impact testing of balls, the regularities of the formation of the quality of the macro- and microstructure of grinding balls in relation to their operational resistance in the production of rail steels and specialized ball steels of various chemical compositions are determined. When studying samples of five different compositions, it was
 BULLETIN «FERROUS METALLURGY» • Vol. 79 • 6• 2023 ―――――――――――――――――――――――――――――― 485
 determined that grinding balls made of 76XF steel have an optimal homogeneous microstructure that provides high impact resistance in combination with increased hardness after heat treatment. Additional alloying of the specified rail steel with chromium and nickel in excess of the requirements of regulatory documentation leads to the formation of dendritic liquation in the cast structure, which decreases, but is not completely eliminated after heat treatment of the produced balls. This mi-crostructure is defective and causes a reduced impact resistance of grinding balls. In the production of balls made of 90HAF grade hypereutectoid rail steel, cementite is present in the microstructure, which reduces the balls' resistance to shock loads; at the same time, there is no noticeable increase in the hardness of heat-treated balls compared to balls made of 76XF steel. With regard to balls made of specialized steels of grades Sh2.1 and Sh2.3, the determining effect on their impact resistance of macrostructure defects passing from the initial cast blanks has been established. The features of the quenching microstruc-ture of grinding balls made of specialized steels of the specified grades, formed by varying the modes of their heat treatment, does not significantly affect the impact resistance of the balls