What is Nitriding?

Nitriding is still one of the most common surface treatment processes world-wide and was developed in the early 1900’s. Basically, elemental nitrogen is diffused into a steel surface to provide a hard, nitrogen saturated structure which forms two distinct metal nitride layers:

a. surface compound zone or white layer (WL), and
b. the diffusion zone (DZ) underneath the WL

Each of these layers provide particular properties in an application. For example the WL provides wear and corrosion resistance, whereas the DZ supplies fatigue resistance, wear resistance and support for the surface WL. The thickness, depth and composition of these layers also have a major influence on the performance of a part.

Conventional nitriding processes do not allow for the tailor-made formation of the surface layers and this is where our specialized nitriding is different. In some cases a thick WL and deep DZ is required, whereas in other cases different thicknesses of layers provide the correct performance.  Our WL is also ductile rather than brittle and with the correct steel selection and heat treatment it treatment ensures the correct thickness WL and DZ is formed. The WL is also low in porosity which is essential for certain applications.

Mould and Tool Steel Nitriding

For injection moulds and other tooling, the formation of a thicker white layer is not desired as this increases surface roughness and may spall under high shear. Our mould nitriding process minimizes the formation of a thin WL to provide a smoother surface and improved polishability. Dies can be used straight from the process but can also the mirror finish can also be restored easier.  

Diffox vs Black Nitriding, QPQ

When sufficient white layer is formed it can be given an additional high temperature black oxide layer which helps improve both corrosion and wear resistance. This is commonly known as Black Nitriding. QPQ stands for Quench-Polish-Quench whereby the parts are given pre-, intermediate and final polish process to create a smooth, black surface which the benefits of improved corrosion and wear resistance vs. black nitriding. Our Diffox coating is a combination of 1. controlled WL and DZ. 2. a pre-polished surface and 3. a blackening cycle giving the best combination of all properties.

Nitriding for Stainless Steel

Nitriding of stainless steels require a special process. Find out more about it here.