Plasma nitriding is a modern and environmentally-friendly nitriding and nitro-carburizing process, adopted to steel quality and surface.
Boundary layer properties
Plasma nitriding allows nitriding layers to be structured, which can be adapted to the respective component loading in an optimum manner. The forced nitriding-caused decrease of the ductility in the boundary layer is controlled during plasma nitriding, so that in spite of a hardness increase ductility also remains in the boundary layer. Specialists therefore speak of the plasma-nitriding-type hard layer ductility. A nitriding layer consists in general of a diffusion layer and compound layer located above it, whose formation is depending on the steel quality and the processing parameters of temperature, duration and gas composition. The compound layer primarily determines the properties of plasma nitrided component parts. The iron-nitrogen compounds Fe4N and Fe2-3N can be generated purposefully and reproducibly on the diffused layer and supporting it. They are monophase and low-pore, resist wear stressing and offer corrosion protection. Also in case of overlaid dynamic loading, these properties are maintained. The diffusion layer underneath the compound layer can be structured with low nitride linings and to a large extent free from grain boundary nitriding, which contributes to the embrittlement of the boundary layers as it is generally known. It determines the strength characteristics of plasma-nitrided workpieces. The diffusion layer can also be generated without forming a connecting layer and finds application in certain cases.
Also component parts with complex geometry, bores or cylinders are provided with the plasma-nitriding-type boundary layers. The process engineering of plasma nitriding in vacuum guarantees good dimensional stability and low distortion. Stress relieve annealing is especially useful before the mechanical finishing. With paste and solid coverings, workpieces can be plasma-nitrided partially. The vacuum processing saves the following cleaning of the plasma nitrated charge. Roughness changes are so small that a mechanical after treatment can be dispensed with. Highly polished tools, which should be slightly finished after the processing, form exceptions. Annealing sensitive steels are plasma nitrided with comparably low treatment temperatures. High-alloy steels and special materials can also be plasma nitrided above the usual treatment temperatures.