Gaseous nitriding is a thermochemical surface treatment aiming surface strengthening of steels. The diffusion of nitrogen atoms in the ferritic matrix involves the precipitation of nano-scale alloying elements nitrides MN (M = Cr, V, Al…) that leads to secondary phase hardening and the generation of compressive residual stresses. Prior to nitriding, steels are quenched and tempered for industrially practical interests in controlling the machining process, microstructure, and mechanical properties. Nitriding of steels has then been performed at a temperature lower than tempering to avoid core softening during nitriding, especially in case of deep nitriding. Therefore, surface properties depend on the kinetics of nitriding related to as quenched-tempered microstructure.
The present work aims investigating the direct application of nitriding on as quenched steel 33CrMoV12-9. Properties such as the chemical, hardness or residual stresses in-depth profiles will be compared between quenched and quenched-tempered specimens. Optimization of the nitriding process will then be discussed.