This International Standard defines the case-hardened depth, and specifies methods for the determination of this depth, in steel. It is applicable to a) carburized cases and carbonitrided cases; b) parts that, when heat treated to final hardness, have a hardness of less than 450 HV 1 at a distance of three times the case-hardened depth, from the surface. The case-hardened depth is defined by special agreement where these conditions are not met. For steels that, in the part under test, and at a distance of three times the case-hardened depth from the surface, present a hardness greater than 450 HV 1, the criterion can still be used, provided that a limiting hardness value greater than 550 HV 1 – in steps of 25 units – be selected for the case-hardened depth.