High cycle fatigue, low cycle fatigue and failure modes of a carburized steel

An experimental investigation is conducted for better understanding fatigue and fracture of carburized steel used in the construction of vehicle transmission elements such as gears and shafts. Fatigue tests of case hardened specimens are carried out in low and high cycle regimes. The effect of hard layer thickness in fatigue life and fatigue strength is investigated. It is observed that case depth has influence in fatigue properties of carburized steels. The greater the case depth the higher the fatigue strength. The analysis of the fracture surface shows a combination of fracture mechanisms, i.e. brittle fracture is observed in the hard layer and ductile fracture is observed at specimen core. Fatigue properties developed here, are needed in fatigue crack initiation models for carburized steels used in the design methodologies of gears and shafts.