Nitride layers consist of a compound and a diffusion layer.
Both layer components possess different properties and provide the component with various usage behaviours. With the right combination of both layers, the component can be prepared perfectly for the stress during use.
Properties of the compound layer:
The compound layer exhibits a high level of hardness and a hexagonal structure which leads to a high resistance to adhesive and abrasive wear. Thanks to the passivatability of the iron nitride, the nitride layer provides the nitrided component with an increased level of corrosion resistance. 
Properties of the diffusion layer:
The precipitation of nitrides in the diffusion layer leads to an increase in strength and to a build-up of compressive residual stresses. This results in increased vibration resistance and a higher resistance to contact fatigue.
Since the nitride precipitates that form are also stable at temperatures above the nitriding temperature, nitrided components have considerably greater heat resistance and tempering resistance compared to the base material. 
 Spies, H-J: Einfluss des Gasnitrierens auf die Eigenschaften von Eisenwerkstoffen, Freiberger Forschungshefte B249, Deutscher Verlag für Grundstoffindustrie, Leipzig 1986.