Determination of the nitriding hardness depth is defined in standard DIN 50190-3. This is ascertained from the hardness curve and lies at a hardness limit of 50 HV below the core hardness, see illustration (Nhd).
Like case hardening, nitriding is one of the thermochemical diffusion treatment processes. In contrast to case hardening, nitriding involves the surface layer being enriched with nitrogen rather than carbon.
Workpieces made of ferrous materials exhibit better wear, strength and corrosion properties after nitriding. The increase in nitrogen content also leads to an increase in hardness.
Nitriding is customarily conducted preferably in a temperature range of 500 to 550°C. As long as it is thermally stable, the original structure remains unchanged. Then the nitrogen donor is transported to the workpiece surface and adsorbed. This results in a release of nitrogen atoms at the specimen surface. The nitrogen atoms are absorbed and diffuse further into the workpiece interior. The nitriding layer is created.