Magnetooptical Analysis of the Subsurface Region in a Bearing Ring Subjected to Rolling Contact Fatigue

It has been known for decades that high contact load in bearings leads to fatigue alterations of subsurface material, which can be optically visualized on etched samples. In the literature, these alterations are termed dark etching regions and white etching bands, due to their peculiar patterns and contrast. In the current work, it is proposed to study these alterations by the magnetooptical Kerr effect, expecting that the material changes associated with rolling contact fatigue also affect the magnetic properties of bearing steel. The advantage of this method is that it has good spatial resolution, allowing recording of magnetic properties on microscopic scales. Samples containing dark etching regions and white etching bands were compared in the magnetooptical test with the reference sample containing no optically visible changes. It was found that the coercive force of material reduces as result of microstructural changes caused by rolling contact fatigue.