Ball Bearing Materials

Ball bearings are generally made of high carbon steels, such as AISI 52100 (fifty-two, one hundred). One of the factors that determines the life of the bearing steel (thus the bearing itself) is the purity or cleanliness of the steel. The 52100 steel is subjected to a rigorous purification process with stringent controls in order to meet the ever increasing standards for cleanliness-- eliminating nonmetallic inclusions or impurities. These impurities are removed through various processes such as vacuum degassing and consumable- electrode vacuum melting (CEVM), to name just two of the processes referred to when discussing the merits and cleanliness of bearing steel. The hardening of the steel is achieved by a heat treating process in which the steel microstructure is manipulated by cycles of heating and quick cooling to obtain the optimum hardness range for the steel—usually on the order of 60 to 64 on the Rockwell C Hardness scale. Penetration hardness tests (such as Rockwell or Brinell) provide the means to estimate the actual hardness of metals.