Improve the Qualities of Metal Workpieces through Carbonitriding

20 February 2023

Metal workpieces require delicate processes before they can achieve the properties needed by industries. One of the processes they must undergo is heat treatment.

Heat treatment is comprised of industrial, thermal, and metalworking methods that can alter the physical properties of metal workpieces. These methods may sometimes change the chemical properties of the same materials. Some properties of metal workpieces that are expected to improve during heat treatment are strength, hardness, ductility, elasticity, and wear resistance.

Many heat treatment methods can be maximised by manufacturers in processing metal workpieces. One of these methods is case hardening, particularly carbonitriding.

An Introduction to Carbonitriding

Carbonitriding is a part of the case hardening process, a heat treatment method wherein the surfaces of metal workpieces are enhanced. Case hardening often ensures that surfaces can be resistant to wear. It then preserves the toughness and strength of the core.

Given the general benefits of case hardening, it is not surprising for carbonitriding to provide the same thing. With the addition of nitrogen, carbonitriding can increase the wear resistance and surface hardness of metal workpieces as it generates a hardened surface layer over metals.

During the carbonitriding process, carbon and nitrogen atoms diffuse into metal workpieces. The diffusion of these things then creates barriers to the workpieces, increasing their hardness and modulus near their surface. Most of the time, this process is applied to metal workpieces made from low-carbon steel, which are mostly inexpensive and easy to machine.

The Specifics of Carbonitriding

To produce parts and products with more durable surfaces, certain conditions must be met during the process of carbonitriding. First, the process must be done at lower temperatures. It should also be carried out for shorter times, ensuring that components will not be prone to distortion. To reduce distortion further, less severe quenching media like oil can be used.

The temperature range of carbonitriding is between 820 and 900 degrees Celsius in a gaseous atmosphere. Around 0.5 to 0.8% carbon and 0.2 to 0.4% nitrogen can then be added to the surface of plain carbon steel or low alloy steel workpieces. Once the diffusion time is over, the components must then be quenched directly in oil. The case-hardened depth will often be around 0.7 mm. However, it can still vary depending on the hardening temperature, the hardenability of the steel, the quench rate, and the dimensions of the component.

Low-temperature tempering between 150 to 200 degrees Celsius is, ultimately, necessary to complete the carbonitriding process.

Carbonitriding Primary Benefits

Given the effects of carbonitriding on workpieces, this process can be utilised by industries that want products with hard and wear-resistant surfaces. In this case hardening method, it can easily improve the hardenability of the workpieces. Distortion is likewise reduced with carbonitriding as it can already be processed in lower temperatures.

The whole process of carbonitriding makes it effective in mass-producing small components. Keep in mind that the mild quenching speed must be reduced during processing to reduce the risk of cracking. Some products that can be processed through carbonitriding are gears, shafts, pistons, rollers, bearings, hydraulic levers, pneumatic systems, and mechanical systems.

Aside from low-carbon steel, carbonitriding can also be used for workpieces made from mild steels, low alloy steels with around 0.25% carbon, free-cutting steels, and sintered steels.

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