Observation of flaking process in rolling contact fatigue of bearing steel with spheroidal inclusions by laminography using ultrabright synchrotron radiation X-rays

Rolling contact fatigue tests were performed on specimens containing spheroidal inclusions to clarify the effect of the orientation of inclusions, and the results were compared with those of specimens containing stringer-shaped inclusions. For all types of inclusion, cracks first formed on the rolling surface and then propagated in the depth direction, and an internal crack parallel to the rolling surface formed from the deepest point of the vertical crack, which led to flaking. The flaking life of the specimens with spheroidal inclusions was longer than that of the specimens with stringer-shaped inclusions, where the initiation and propagation lives of cracks were affected by the inclusion shape and size. The surface crack initiation life was shorter for specimens with longer surface inclusions, whereas the crack propagation life decreased with the depth of surface inclusion. The greater the scatter of the size of inclusions, the greater the scatter of flaking life. In every orientation, formation of surface crack precedes formation of interior crack.Flaking life of spheroidal inclusion was longer than that of stringer-shaped inclusion.Surface crack initiation life was shorter for longer inclusions at the surface.Lateral crack propagation life was shorter with increasing inclusion depth.

Automated summary

Rolling contact fatigue tests were conducted to investigate the effect of inclusion orientation on the fatigue life, and the results were compared with those of specimens containing stringer-shaped inclusions. The study found that cracks first formed on the rolling surface and then propagated in the depth direction, leading to flaking. The flaking life of specimens with spheroidal inclusions was longer than that of specimens with stringer-shaped inclusions, and the initiation and propagation lives of cracks were influenced by the shape and size of inclusions.