Wear behaviour of diffusion and compound layers in nitrided steels

The wear behaviour of two nitrided steels was studied in order to evaluate the tribological properties of the compound layer and of the diffusion layer. The specimens were treated in different conditions, in order to obtain different microstructural and compositional characteristics of the nitrided surfaces. Concerning the diffusion layer, microstructural homogeneity tends to prevail over the microhardness profile in affecting wear resistance, since grain boundary carbonitrides worsen the mechanical properties and oxidation behaviour of the subsurface layers and contribute to abrasion of the counterface. As far as the compound layer is concerned, the effect of thickness and compactness is at least as significant, if not more so, than that of composition. The results demonstrate the importance of designing the microstructure of nitrided layers to maximise the wear resistance of the treated components.