- GAS NITRIDING NITREG® -

Nitriding is a process of diffusing nitrogen atoms into the metal surface. Nitrogen is plentiful on Earth, however, in nature it exists as a two-atom molecule, chemically inert and too large to penetrate the surface. Hence nitriding technologies focus on the source of nascent (atomic) nitrogen.

The main objective of nitriding is to increase the hardness of the component’s surface by enriching it with nitrogen. Regardless of the method, nitriding is a process of diffusing nitrogen into the metal and such diffusion, once individual atoms of nitrogen have penetrated the surface, continues as long as the temperature is high enough, and there is a fresh supply of nascent nitrogen on the surface. In other words, the diffusion is basically the same in all nitriding, while the difference lies in the supply of nitrogen. The latter has a fundamental influence on the resultant properties of the surface.

Generally speaking all ferrous alloys, including stainless steels, cast irons, and even titanium alloys, are capable of being nitrided. However, the various alloys have different characteristics with regard to surface conditions, the natural speed of diffusion and propensity to form nitrides. It is important to understand that even a properly run nitriding process will produce significantly different results on dissimilar materials. Consequently, some users may have insurmountable difficulties, particularly if their methodology is primitive and/or their knowledge and experience inadequate.

A surface exposed to a nitriding medium will generally form two distinct layers. The outside layer is called a compound layer (or white layer) and its thickness generally falls between zero and 0.001” (25 µm). Underneath the white layer we have a diffusion case or diffusion zone. Both together comprise what is generally referred to as the case. However, depending on the material and its original pre-process hardness there will be very significant differences between the properties of these layers.