There are many methods for determining hardness limits. Therefore, there are also many methods for calculating CHD values. The program you choose depends on the hardening process used. The particularly common calculation methods are as follows.

    Carburization or carbon components (EN ISO 2639)

    Hardness limit=550 HV

    CHD (Eht)=distance from the surface to a point with a hardness of 550 HV

    Induction hardened or flame hardened components (EN 10328 and ISO 3754)

    Hardness limit=80%× Surface hardness (minimum)

    CHD (Rht)=distance from the surface to the point where the hardness is 80% of the surface hardness (minimum value)

    Nitrided parts (DIN 50190-3)

    Hardness limit=core hardness+50 HV

    CHD (Nht, NCD)=distance from the surface to the point where the hardness is the core hardness+50 HV (maximum)

    Example of continuous CHD values

    CHD measurement, with a CHD value of 0.95 mm at a hardness limit of 550 HV1