Case Hardening by Carburising, Carbonitriding

Carburising and Carbonitriding are thermo-chemical heat treatment processes nominally carried out in the temperature range 800°c to 950°c.

These processes change the chemical composition of the surface of a steel component so that subsequent fast cooling, by quenching, produces a hard “case” combined with a softer/ tougher core.

The processes are commonly known as Case Hardening and are normally applied after machining although there are variations which can involve multiple stages defined within the manufacturing process to create differing case depths or areas that are required to remain soft.

Make contact with our sales co-ordinator

For Technical or Sales enquiries:


As a rule, case hardening comprises three working steps. In the first step, the workpieces are exposed to a carbon rich environment usually at a temperature of 800°c to 950°c, depending on material and/ or geometry of the part.

In the second step, the quenching takes place either directly from the application temperature or after intermediate cooling and reheating to a material-specific hardening temperature.

The third step, the tempering treatment serves essentially to relieve the highest stresses in the material structure and to reduce sensitivity to grinding cracks.


Carbonitriding results in a very hard case of the component. Specifically, this is useful in the case hardening of gears and similar components which are subject to a great deal of wear in hostile environments.
This heat treatment process is especially useful if there is a requirement for a hard, wear resistant surface, overlying a much softer and tougher core. A good example for its application is a gear wheel.
The surface of the teeth needs to be extremely hard so that they can withstand constant metal-to-metal contact, without undue wear. The underlying material needs to be tough so that the teeth can tolerate occasional impact loads, without the risk of fracture.


The carbonitriding process is applied to low carbon and mild steels to give a hard case onto the cheapest steels which are often not capable of being case hardened because of their chemical composition.

specialised case hardening and low pressure vacuum heat treatments

We constantly seek to improve, and will value your feedback: especially if you have used one of our plants: click on the link


Aalberts Surface Technologies Heat Ltd | Disclaimer

Registered Address.: Aalberts Surface Technologies Heat Ltd, Blackhorse Road, Letchworth. SG6 1HD 

Tel: 01462 472147