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Nitriding hardness depth definition

  • 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 preferably conducted 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.

Determining nitriding hardness depth to DIN 50190-3

  • The determination of nitriding hardness depth is described in the DIN 50190-3 standard. This is ascertained from the hardness curve and lies at a hardness limit of 50 HV above the core hardness, see illustration (NHD).
  • The surface of the specimen on which the measurement is performed must be finely machined.
  • First, the core hardness must be determined. This is ascertained from a minimum of three hardness test indents and allows the hardness limit to be obtained. Subsequently, hardness indents are applied from the edge to the workpiece interior at precisely defined distances. The test method to be used is Vickers hardness testing in the low-load range.
  • The nitriding hardness depth is derived from the curve representing the hardness over distance from the surface by measuring the distance from the surface to the calculated hardness limit.

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