Recent improvements in steel-making techniques have greatly decreased the content of nonmetallic inclusions in steels. Inclusions are known to be detrimental to the rolling contact fatigue life of bearings. While bearing life has improved because of advances in steelmaking techniques, the conventional method for evaluating nonmetallic inclusions is losing its effectiveness. A new method for evaluating the nonmetallic inclusion content of steels used for rolling bearings has been developed. In ring-type rotating fatigue fracture tests on quench-hardened specimens a crack usually initiates on the inside surface of the ring specimen. However, a crack initiates near the outside surface when the specimen has been treated, to produce a large residual tensile stress on the outside surface before the test. In this case, the fractured surface remains protected from damage caused by rubbing of the mating fracture surfaces until the test rig stops.
