Análise de falha por fratura em mola de carro torpedo: estudo de caso

Abstract

This paper analyzed the possible causes that led to the premature failure of a spring that made up a torpedo truck, a vehicle used to transport pig iron from the blast furnace to the steelworks of a large steel mill. For this purpose, optical microscopy (MO), scanning electron microscopy (SEM), semi-quantitative chemical analysis by Energy Dispersive Spectroscopy (EDS), quantitative fluorescence chemical analysis, Vickers microhardness test (HV), Rockwell hardness at the N measuring scale (HR) and residual stress analysis measured by X - ray diffraction in the region where the fracture occurred were used. The industrial quenching, tempering heat treatments and shot peening were also redone for the spring under analysis, all in order to simulate the treatments that were supposedly done on the original spring. Comparing the results, it can be concluded that the process that led to spring fracture was a mechanism of fatigue failure originated from a defect in the spring surface. Although residual stresses on the spring surface were as 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.