Degree of hardness
This is initially determined by the material used to manufacture the sprocket but hardness levels may be reduced by subsequent tempering to meet specified levels.
The majority of sprockets are made from K1042 plate which contains 0.45% carbon. The as-hardened hardness of this material is 45-55 Rockwell “C” (HRc) and it may be tempered back to any specified hardness level below this.
Example: If the application requires the sprocket to wear preferentially to the chain the hardness level specified for the sprocket would be 5 HRc points lower than the chain. A typical sprocket hardness specified for this type of application is 35-40 HRc.
Occasionally 4140 or 4340 is the specified material. This requires particular care when hardening. An oil or polymer quenchant is used and sprockets must be tempered after hardening.
1.5 – 2.0 mm is typical however deeper cases may be obtained for special applications.