Steel purity refers to how much non metallic inclusions contained in the steel.The higher the degree of purity, the less the non metallic inclusions in steel. The oxides, silicate and other harmful inclusions in bearing steel is the main reason which caused  bearing early fatigue peeling, bearing life significantly reduce. Particular the brittle inclusion harmful, because it's easy peeled down from the metal substrate in the process, and affect the INA bearing parts surface quality after finishing seriously. Therefore, in order to improve the service life and reliability of the bearing, so its must reduce the inclusions content in bearing steel.