Rohdetherm

Carbo-Nitriding

As the name suggests this process presents a combination of the gas carburizing method with an adapted nitriding process. Carbo-nitriding is a particular type of case hardening. It is most often used with low to medium degrees of hardening. Along with carbon, nitrogen is simultaneously diffused into the surface layer. In this process nitrogen operates primarily as an alloying element in the surface areas. This improvement in the hardening ability of the surface allows more economical steels to be utilised for example. It is thus possible to achieve the full hardness with unalloyed steel using oil quenching.

Optimum control of this process is possible in gas carburizing plants. An approx. 5 % ammonia (NH3) is added to the gas composition standard with gas carburizing.
In principle, carbo-nitriding is rather more comparable with carburizing than with nitriding, as the treatment temperature lies in the carburizing range. Following carbo-nitriding, quenching is also generally required. Temperatures between 700 and 900 °C are used most often for carbo-nitriding. The vast majority of the carbo-nitriding work is carried out within the temperature range of 780 to 850 °C. In general, carbo-nitriding reaches a depth range of between 0.06 and 0.6 mm, whereby the duration of the treatment is temperature dependent – just as with gas carburizing. Thanks to the low temperature of austenite-ferrite conversion, the workpieces can be quenched to harden them at very low temperatures and this causes less hardening distortion.

Most materials that are carbo-nitrided are unalloyed or low-alloyed steels. Equally, machining steel and deep-drawing steel can be treated very successfully with this process.
Due to the higher manganese content in these steels there is however a risk that austenite residue can form.

The abrasion resistance and emergency running properties of the nitrogen enriched surface layer are improved and the tempering resistance is also greater. It is common to temper carbo-nitrided parts after quenching. The higher the nitrogen content in the surface layer the higher the possible tempering temperature.