Metallurgy Case hardening or through hardening grades of bearing-quality steel are satisfactory for raceways. Steels which are modified for free machining, such as those high in sulfur content and particularly those containing lead, are seldom satisfactory for raceways.
To realize full bearing capacity, the raceway area must be at least surface hard with a reasonable core strength. The preferred surface hardness is equivalent to 58 Rockwell C (ref. ASTM E18).
Shaft raceways for all needle roller bearings, in diameters up to 3.5 inches or 90mm should have an effective case depth of 0.030 inch or 0.8mm. (Effective case depth is defined as the distance from the surface, after final grinding, to the 50 HRC hardness level.) For raceways larger than 3.5 inches or 90mm in diameter the effective case depth should be 0.050 inch or 1.3 mm.