G. H. Akbari, M. A. Sheikhi,
Volume 4, Issue 1 (6-2007)
Abstract
Abstract: Ball mills are used in the last stage of ore processing for grinding raw materials. Forged
70Cr2 alloy steel and Austempered Ductile Iron (ADI) balls are materials from which grinding
balls are made for Sarcheshmeh Copper Plant (SCP) ball mills. In the present study wear and
impact properties of these two kinds of balls have been investigated. Some balls randomly were
selected as samples. They were cut to investigate the cross section under optical and scanning
electron microscopes. The microstructure of the sample balls was studied and quantitative
measurements of microstructural features were performed. The hardness of different parts of cross
sections of balls was measured. The wear resistance of the balls was measured by Pin on Disc
method. Repeated dropt test was employed to evaluate impact resistance of the balls. The
microstructure of ADI balls consisted of bianitic matrix with graphite nodules and some retained
austenite and martensite. Micro cracks and porosities in the cast structure were frequently
observed. In the case of forged steel balls the microstructure composed of tempered martensite in
outer area and bianitic structure with some tempered martensite in central areas. The wear and
impact resistance of forged steel balls were markedly higher than those of ADI balls. The
difference was consistent with the differences between the microstructures of the two kinds of balls.
Cast structure with microcracks and shrinkage porosities in ADI balls gives rise to lower impact
resistance.
