Nitriding steels

Nitriding steels are used in investment casting mainly for components which require high wear resistance and are subject to severe mechanical stress. Piston rods, for instance, are made of nitriding steel. The chemical composition of nitriding steel is very similar to that of heat treatable steel, since it is also quenched and tempered. The components are not nitrided until after the machining process.
The nitriding temperature is lower than the annealing temperature. This ensures that the mechanical properties achieved by quenching and tempering are not changed. Due to the low temperatures the diffusion processes during nitriding take place very slowly. As a result, the nitriding process may take up to 100 hours. The required wear resistance is brought about by the formation of a very hard nitrided case. Therefore, nitriding steels contain nitride formers such as chromium (Cr), aluminium (Al), vanadium (V), etc.