Some Case Histories Of Surface Finish Related Failures

Helical compression springs experienced occasional fatigue failures during service in cable transportation plants operating at relatively low temperatures. The springs were made of UNI 50CrV4 steel quenched and tempered to obtain high strength level. A high intensity shot-peening treatment gave rise to surface defects that acted as nucleation sites for fatigue cracks which rapidly propagated in a material embrittled by a number of factors. In a paper-mill plant, rolls failed in service after more than 10? cycles. The cracks leading to these failures were nucleated at surfacial pits brought about by environmental corrosive attack. Propagation by fatigue developed in a ferriticpearlitic microstructure that was not the most suitable condition to sustain fatigue loading.