The majority of bearing designs use steel and are classified as either bearing steels (actually high-carbon material like 52100, 100Cr6 or SUJ2 families) or case-carburized grades (5120, 8620 or 4320).
There are really three key questions (and other sub-questions along the way) when it comes to application-based material selection.
• Do you need case-carburized or through-hardened properties?
• What material to select? The material must have the proper hardenability to meet engineering requirements and the heat-treat process selected. The selected material must also deal with any special circumstances of the application: marginal lubrication conditions (low lubricant film thickness to surface-roughness ratio, called lambda ratio), severe cold, high toughness, high operating temperatures, etc.
• What is the desired performance target? The cleanness of the material is very important as well. There are very different steelmaking practices that produce different inclusion populations. Not only is this important to the application with regard to performance, it can be important to the heat treater as well.