Depth of the transition of the surface layer to the core

The core hardness at reference circle H_KH is defined as the local Vickers hardness at the transition from the hardness layer to the core (i.e., the depth of the transition of the surface layer to the core y_KH) halfway up the active flank. The values H_KH and y_KH can be determined from measured hardness curves according to FVA 240/II. If no measured values are available, the following initial reference values are recommended:

H_KH = 350 ... 400 HV
y_KH = 1,7 ... 2 * Eht