Materials Engineering, Sharif University of Technology
The secondary cone crusher's shields at Sarcheshmeh Copper Complex of Iran are made of Hadfield steel with a nominal composition of Fe-1.3 % C-12 % Mn. They have a cut-off in the shape of a cone with an upper end diameter of 80cm and an approximate lower end diameter of 200 cm whose main problem is an unexpected early failure under normal working condition. In this paper, the results of metallographic and fractographic studies carried out on a failed shield at various depths and analytical examinations of the fractured regions are presented. It is revealed that crack propagation starts from the pre-existing microcracks in the internal regions of the shield and results in a catastrophic failure. Analytical examinations indicated other problems associated with the chemical composition of the shield. An Mn/C ratio of < 10 and high sulfur and phosphorus concentrations in the inclusions as compared to that of bulk are typical examples. The latter together with the carbide precipitation in the grain boundaries can be regarded as the pre-existing crack path in these high energy regions of the shield substructure.