The process and its advantages
During nitrocarburising, both nitrogen and carbon penetrate the surface of a workpiece. The surface hardens, while the core retains its softness. The process also produces a thin compound layer that provides a high degree of protection against corrosion and wear. Moreover, the diffusion layer underneath improves fatigue strength.
While similar in name, nitrocarburising and carbonitriding are two completely different processes. Carbonitriding is classified as case hardening, because it does not create a compound layer and only small amounts of nitrogen are used.
Three different types of nitrocarburising
Nitrocarburising can be carried out using different media. Gas is used for gas nitrocarburising, a salt bath for salt bath nitrocarburising and, finally, plasma for plasma nitrocarburising.
Good candidates for gas nitrocarburising are low- and non-alloy steel whose wear and corrosion resistance needs to be improved. This process uses a gas mixture such as ammonium and carbon dioxide, which releases both nitrogen and carbon. The treatment temperature is 500°C to 600°C. If the workpiece is quenched in an oxidising atmosphere, corrosion protection can be improved even further.
Salt bath nitrocarburising
Cast iron, as well as low-, medium-, and high-alloy steel, can be subjected to salt bath nitrocarburising, to achieve exceptionally high resistance to wear and corrosion. For this, the workpieces are dipped in a salt melt at temperatures between 550°C and 630°C. This is a blend of alkaline cyanates and alkaline carbonates. Here too, if the workpiece is quenched in an oxidising atmosphere during a post-treatment, corrosion protection can be improved further.
High-alloy steel is suitable for plasma nitrocarburising. If its chromium content is less than 13 per cent, the steel can be subjected to both gas nitrocarburising and plasma nitrocarburising. The workpieces are enveloped by ionised gas at temperatures between 480 and 580°C. No passivation layer is formed. Warping is low, and rework is usually unnecessary.
Nitriding vs. nitrocarburising
Both nitriding and nitrocarburising improve the wear resistance of a component. However, nitrocarburising is capable of achieving substantially greater surface hardness. This makes the process better suited for optimising corrosion protection and vibration resistance. Nitriding, on the other hand, works well in enhancing the wear resistance, as well as sliding and emergency running properties.
Pros and cons of nitriding
- Improved wear protection (abrasive, adhesive, and corrosive)
- Option to precision-harden the edge zones
- Plasma nitriding is the most environmentally friendly process (toxic gases not used)
- Partial hardening possible
Pros and cons of nitrocarburising
- More cost-efficient than carburising and other surface hardening processes
- Improved protection against wear and corrosion
- Optimised sliding properties
- Improved emergency running properties
- Minimum warping thanks to low process temperatures – no need for rework
- Also suitable for treatment of bulk material
Areas of application
Nitrocarburising and nitriding are processes that can be used for the same materials. This also includes non-alloy steel. Because it is exceptionally cost-efficient, the process is used, for instance, instead of classic hard coatings for punching tools.
- Gate valves
- Ball seats and ball heads
- Valve shafts
- Control valves
- Impeller housings
- Pump cases
- Pistons and cylinders
- combine harvester separators, crop transfer stations, and crop cutting units
- Oil pump gears for diesel engines
- Gear wheels
- Crankshafts and cam shafts
- Press jaws and cutting dies
- Cam drums
- Extruder and injection moulding machines
- Press drills, enclosures, and press mould components
- Guide tracks for automatic small arms
Surface hardness and nitriding hardness depth of various materials
The table below tells you the surface hardnesses that nitrocarburising can achieve on various materials.
The following applies:
- The higher the treatment temperature, the lower the intrinsic hardness of the nitrided layer.
- The longer the nitriding time, the greater the nitriding hardness depth (NHD).
- The higher the temperature (480°C - 630°C), the deeper the nitrogen diffuses into the material in the same treatment time.
- The higher the alloy content of the material, the higher the nitriding hardness of the material. However, the nitrogen’s penetration depth into the material is also decreased.
Check list: Ordering nitrocarburising
If you would like us to nitrocarburise your workpieces or materials, we will gladly advise you on the best procedure. You can use the check list below to make your preparations for the order.
- Which material is to be treated, and what is its condition?
- What is the target hardness (including tolerance range in HV)?
- What is the desired nitriding hardness depth (including tolerance range in mm)?
- If applicable, which areas should be nitrided, and where can the hardness be measured?
- If applicable, how thick should the compound layer be (including tolerance range in μm)?
We use a sample that we take ourselves to measure the thickness of the compound layer and/or the nitriding hardness depth. For measurements that are specifically related to your order, we need you to provide us with a reference component that is intended for the hardening treatment.