nitrocarburizing
what is nitrocarburizing?
Nitrocarburizing is a process for surface hardening of materials. The surface layer of the material is enriched with nitrogen and carbon through thermochemical diffusion. This contrasts with nitriding, a process in which only nitrogen is deposited in the surface layer. The compound layer formed on the component surface by nitrocarburizing has a certain corrosion resistance and shows a high resistance to wear caused by abrasion, deformation, scuffing and bonding.
nitrocarburizing process
Nitrocarburizing can be carried out in various media, e.g. in gas, a salt bath or plasma. In addition, the process takes place at relatively low temperatures. The result is a very hard surface layer, a thin compound layer only a few µm thick and the remaining soft core of the material used. The compound layer is particularly resistant to corrosion and wear.
The advantages of the process can be seen in the high wear resistance of the material and the low treatment costs.
nitrocarburizing and oxidation
In order to further improve the corrosion resistance already improved by nitrocarburizing, subsequent oxidation, known as post-oxidation, can be carried out directly after the nitrocarburizing process. This involves applying an approx. 2 µm thick oxide layer to the compound layer. The oxide layer should generally consist of Fe3O4 oxides. This results in an attractive black surface.
gas nitrocarburizing
Nitrocarburizing in a gas stream, also known as gas nitrocarburizing, is the most widely used method in industry. The treatment is carried out in an atmosphere consisting of ammonia, nitrogen and a carbon donor and usually takes no longer than 5 hours. Gas nitrocarburizing is therefore an alternative to salt bath nitrocarburizing due to the short treatment time.
salt bath nitrocarburizing
Salt bath nitrocarburizing has been used successfully for the surface treatment of workpieces since 1929 and is still used today. The molten salts suitable for nitrocarburizing contain toxic cyanides and cyanates, which release nitrogen and carbon at a treatment temperature of around 570 to 580°C via various reaction steps. Treatment times are around 1 to 3 hours, depending on the material and desired coating thickness. The advantage of salt bath nitrocarburizing lies in its applicability to practically all ferrous materials, as well as sintered materials.
plasma nitrocarburizing
In terms of process technology, plasma nitrocarburizing is comparable to plasma nitriding. In plasma nitrocarburizing, a gas mixture of nitrogen and carbon dioxide or a gaseous hydrocarbon (usually methane) is introduced into a vacuum reactor where it is ionized under the effect of a strong electric field. Several chemical and physical processes ultimately lead to nitrogen and carbon absorption of the workpiece surface and thus to nitride formation.
ferritic and austenitic nitrocarburizing
Ferritic and austenitic nitrocarburizing are two variants of nitrocarburizing, each of which offers advantages tailored to the specific material requirements.
Ferritic nitrocarburizing: In ferritic nitrocarburizing, ferrous alloys are treated at lower temperatures with a higher carbon potential, resulting in the formation of a diffusion layer consisting predominantly of iron nitrides within a ferritic microstructure. This process increases surface hardness and wear resistance and is therefore particularly suitable for applications where robust wear performance is required.
Austenitic nitrocarburizing: Austenitic nitrocarburizing, on the other hand, is characterized by a diffusion layer of nitrogen and carbon within an austenitic microstructure. This variant is often preferred when components require a balance between wear and corrosion resistance, extending its applicability to a wider range of materials, including stainless steels.
special advantages of nitrocarburizing
Nitrocarburizing has a number of advantages over conventional heat treatment processes:
- The surfaces of nitrocarburized components have a significantly higher hardness, as the nitrided layer is harder than martensite.
- Nitrided layers have a high hot hardness, which is maintained until close to the nitriding temperature of around 500°C.
- Nitrocarburized coatings have good corrosion resistance.
suitable materials for nitrocarburizing
Nitriding steels are particularly suitable for nitrocarburizing. They contain alloying elements such as Cr, Al, Mo, V, Ti and Nb, which are particularly prone to nitride formation and form nitrides with high hardness. Nitriding steels are heat-treatable steels and belong to the alloyed stainless steels.
nitrocarburizing in various industries
Nitrocarburizing is a heat treatment process that is used in almost every industry. The process is most commonly used in the automotive industry and in mechanical engineering.
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frequently asked questions about nitrocarburizing
What considerations should be taken into account when choosing nitrocarburizing, especially with regard to possible disadvantages?
The outer part of the nitrocarburized layer (compound layer) is relatively brittle. For this reason, nitrocarburized components can crack or flake off without significant deformation under excessive stress (high surface pressure, impact stress).
What is the difference between carbonitriding and nitrocarburizing?
Carbonitriding is a variant of case hardening. Here, mainly carbon with small amounts of nitrogen is introduced into the component surface. Nitrocarburizing is a variant of nitriding. Here, mainly nitrogen with small amounts of carbon is introduced into the component surface.
Which materials are suitable for nitrocarburizing?
All ferrous materials are suitable for nitrocarburizing. However, if a certain high surface hardness is required, materials with nitride-forming alloying elements such as Cr, Al and Mn must be used.
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