Influence of Carbide Morphology on the Fatigue Strength of Carburized Steel

Carbide-dispersion carburizing is a promising method to strengthen automobile parts, especially for carburized gears and shafts. A study was made on the influence of carbide morphology in the case on bending fatigue strength and contact fatigue strength. The results obtained are as follows:(1) Coarse carbide in the case deteriorates both rotating bending fatigue strength and roller pitting fatigue life.(2) For the bending fatigue test, the fatigue crack tend to originate from the pre-austenite grain boundaries at the surface, which is covered with the coarse carbides.(3) The contact fatigue life is improved with the increase in the area fraction of finely dispersed carbide. The reason can be explained by prevention of softening in the case during the test.