Failure analysis of a crusher jaw

Abstract This article reports the outcome of an investigation made to uncover the premature failure of crusher jaws produced in a local foundry. The investigation was conducted using a systematic approach by assembling background information; performing visual, fractographic and metallographic examinations; performing chemical analysis; and conducting mechanical tests. Hardness changes with depth were analyzed to determine the extent of plastic flow during work-hardening, and various heat-treatment operations were carried out on samples of ASTM A128 grade B-4 to determine the heat-treatment operations that would give better microstructure and mechanical properties. The study revealed that the failure of locally produced crusher jaws was not due to wrong chemical composition but to the precipitation of carbides at grain boundaries and in grains. This led to the formation of microcracks and their propagation under impact action of crushing, which effectually led to early brittle fracture failure. The carbides presence also causes nonuniform plastic flow during work-hardening and hence was not able to withstand the shock load due to crushing. These carbides were found in the as-cast, and water-quenched and tempered samples. However, the solution heat-treated and martempered samples were free from theses carbides. The absence of these carbides was found to give good combination of hardness and toughness required for crushing. The study concluded that failure occurred as a result of improper heat treatment and not because of a deficiency in composition.