Relationship between microstructure, hardness, impact toughness and wear performance of selected grinding media for mineral ore milling operations

Investigations were conducted to determine the microstructure–property–wear performance relationships of five selected commercial grinding mill ball types in laboratory scale milling experiments. The results obtained show a general increase in hardness and wear resistance of the grinding media with an increase in carbon content reflecting a transition from a wholly pearlitic structure in steels to one dominated by hard carbides in a pearlite and retained austenite matrix in cast irons. The impact toughness of the medium chromium cast iron as indicated by the drop test results improve significantly after the heat treatment. This is attributed to the disruption of the crack sensitive continuous carbide network leaving behind discrete carbides surrounded by a tough matrix comprising pearlite and retained austenite. Medium chromium cast iron ball type in the heat-treated condition has the desired microstructure–mechanical property–wear performance combination. Economic consideration and the ease of production favour the use of unalloyed white cast iron, particularly in the grinding of abrasive mineral ores.