Rolling Contact Fatigue in Carburized Steel (SCM415) and Crack Initiation Depth
Katsuyuki KIDA, Hiroyuki Asou, Makoto SAITOU, Noriyasu OGUMA, Koshiro YAMAKAWA and Hisashi HARADA
Abstract:Fatigue strength and crack initiation depth were investigated in carburized SCM415 steel under rolling contact fatigue (RCF). RCF tests were carried out until the number of cycles reached 1.2~108. The fatigue strength of carburized SCM415 was found to be more than 4000MPa. Observation of a flaking surface showed that the crack initiated around an inclusion or a defect, the depth of which was about 50m. Based on the observations, we concluded that the subsurface crack was propagated when its shape remained circular. We evaluated the crack growth behavior in terms of contact stresses and stress intensity factors. The contact stresses and the stress intensity factors were calculated by using Hanson and Fabrikant's analytical method. It is found that the absolute values of KUmax and KUmin were larger than other stress intensity factors and the subsurface crack was dominantly propagated in modeU. The flaking depths vary depending on the KU peak curbing slightly. The friction between crack faces causes the flaking failure which is shallower than predicted by the maximum shear stress. Key Words:Rolling contact fatigue, Carburized steel, Crack initiation, Flaking failure, Flaking depth