Everything You Need to Know About Carbonitriding

20 July 2021

Metals and alloys undergo various heat treatment processes to obtain changes in terms of their general properties and microstructures. Most of the time, these processes can strengthen the structure of the mentioned materials by heating and cooling activities. They can likewise relieve stresses, increase surface hardness, amplify strength, and make them easier to machine or weld.

A wide array of heat treatment processes can now be utilised in altering the properties of metals and alloys. Some of these processes include annealing, case hardening, precipitation strengthening, quenching, and tempering. Another process that can be done to specific types of metals is carbonitriding.

An Overview of Carbonitriding

Before knowing what carbonitriding is, you should understand two concepts first. One of these concepts is the case hardening process. The case hardening process is a process of granting metals additional thin layer of harder metal on their surfaces while retaining their softness underneath. Another concept that you should know about is carburising. Carburising is a thermochemical process wherein low carbon steels are diffused with carbon, yielding a durable surface layer.

And with these two concepts, carbonitriding can now be easily understood. Carbonitriding is a case hardening process that closely resembles the carburising technique. Just like carburising, carbonitriding also integrates carbon into metals for them to have durable surfaces. Nitrogen, however, is also added during the carbonitriding process, further increasing the wear resistance and surface hardness of metals being processed. A hardened surface layer is expected out of this process.

Carbonitriding Main Processes

When conducting the carbonitriding process, metal workpieces are often heated in a sealed chamber before adding the nitrogen and carbon elements. The temperature of the heating process typically ranges between 820 to 900°C. During the heating, the workpieces are expected to generate some phase changes on their crystal structure, allowing carbon and nitrogen elements to diffuse into them easily.

The amount of carbon that is added to the workpieces typically ranges between 0.5 to 0.8%, while the amount of nitrogen added to the same workpieces would range between 0.2 to 0.4%. Most metal workpieces that undergo carbonitriding are plain carbon steel or low alloy steel since they do not harden well with other heat treatment processes.

To ensure metal workpieces will obtain high surface hardness and ductile core, the entire carbonitriding process should take from a few hours up to a day. Once the diffusion process is completed, the workpieces are then directly quenched in oil.

Key Benefits and Applications

As previously stated, the carbonitriding process helps metals attain a strong, durable, and wear-resistant case. Distortion and quench cracking among metal workpieces are likewise reduced as carbonitriding only requires lower temperature and slower quenching speed compared to other processes. Aside from obtaining this type of case, this process can also benefit industries since it can cater to a cleaner mass production of small metal components.

All these benefits of carbonitriding make them great for producing small components such as gears, shafts, rollers, bearings, pistons, and levers in various systems.

To know more about carbonitriding, you can call us at Alpha Detroit Heat Treatment.

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