Nitrocarburising is a variation of the case hardening process. It is a thermochemical diffusion process where nitrogen, carbon, and to a very small degree, oxygen atoms diffuse into the surface of the steel part, forming a compound layer at the surface, and a diffusion layer. This process is done mainly to provide an anti-wear resistance on the surface layer and to improve fatigue resistance. The process also increases abrasion and wear resistance and improves bending and contact fatigue properties. The process also decreases a part’s coefficient of friction. It also forms a thin, corrosion-resistant layer of iron oxide which significantly increases corrosion resistance.


  • Relative low cost
  • High resistance to wear
  • Excellent scuffing and seizure resistance
  • Fatigue properties improved by up to 120%
  • Considerably improved corrosion resistance
  • Good surface finish
  • Negligible shape distortion
  • Predictable growth characteristics
  • Alloy substitution – plain carbon steels replacing low alloy steels.

Application & materials

Advantages of the process include the ability to harden materials which are not pre-hardened, the relatively low temperature of the process which minimises distortion, and relative low cost in comparison to carburising or other case hardening processes.


A hardness range of 300–1300 Vickers is obtained through this process. It depends on the steel alloy used.  The hardness of the compound layer will determine how resistant the alloy is to wear.

Examples of applications are:

  • Cylinders
  • Pistons
  • Gears
  • Crankshafts
  • Cams
  • Barrels

Nitriding and nitrocarburizing can replace surface treatments like chromizing or black oxidizing. It also looks good.


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