Fracture failure analysis in compression spring of a wagon torpedo

Abstract This work aimed to identify and evaluate the reasons that led to a compression spring to fail. The compression spring was operating in a wagon torpedo, a vehicle that transported pig iron in a liquid state from the blast furnace to the steel mill. For this purpose, optical microscopy (OM), scanning electron microscopy (SEM), quantitative chemical analysis by combustion and x-ray fluorescence, Vickers microhardness test (HV), Rockwell superficial hardness with N scale (HRN), and residual stress analysis by x-ray diffraction were used. The industrial quenching, tempering heat treatment, and shot peening process, were also redone for the spring under analysis, all in order to simulate the treatments that were supposedly done on the original spring. It can be concluded that the process that led to spring fracture was a mechanism of fatigue failure that originated from a defect in the spring surface. Although residual stresses on the spring surface were expected to prevent fatigue failures from surface defects, the hardness in this region of the material was lower than specified due to a decarburizing process.