Diffusionshärdning

Diffusionshärdning, known in English as diffusion hardening, is a thermochemical surface hardening process that increases the hardness of the outer layers of a metal component while maintaining a relatively soft core. The technique employs hydrogen, carbon, or nitrogen gases, which diffuse into the surface when the part is exposed to high temperature. A hardening agent is introduced into a furnace or reactor, typically at temperatures between 900 °C and 1100 °C, to promote diffusion into the steel. As the metal cools, the hardening agent forms martensitic or pearlitic surface layers, depending on the alloy and cooling rate.

The most common variation of diffusion hardening is case hardening, which is applied to low‑carbon steels such as AISI 1045, AISI 4140 and AISI 4540. A more specialized technique, hydrogen embrittlement, is avoided because it can compromise toughness. In automotive, aerospace and railway applications, diffusion hardening ensures wear resistance on gear teeth, camshafts and crankshafts while preserving the ductility needed for load‑bearing cores.

Typical advantages include uniform surface hardness, reduced distortion compared to conventional heat treatments, and the ability to harden complex geometries. Disadvantages are the long processing times and high operating temperatures, which can increase energy cost and may cause contamination through alloy loss. Diffusion hardening is often combined with other surface finishing or coating processes, such as shot peening or nitriding, to achieve optimal performance for a given application.