Carbonitriding is a heat-intensive thermo-chemical process. Within the framework of this process, the surface layer of components is enriched with carbon and nitrogen, in order to improve the mechanical properties of the component surface layer. For this process, there are various furnace technologies, such as chamber furnaces and continuous furnaces.
As a rule, carbonitriding comprises three working steps. In the first step, the workpieces are exposed to a carbon and nitrogen rich environment at a temperature of 750 to 900 °C. In the second step, the quenching takes place after the workpiece was exposed to the target temperature for a certain time. The third step, the tempering treatment serves essentially to relieve the highest stresses in the material structure and to reduce sensitivity to grinding cracks.
1. process: carbon and nitrogen exposure
After pretreatment (component cleaning) of the workpieces, they are taken to a heat treatment facility containing a clearly defined gas atmosphere consisting, among other things, of carbon and nitrogen. Heating the workpieces to temperatures of 750 °C to 900 °C allows carbon and nitrogen atoms to diffuse into the workpiece surface. The exact temperature is determined on the basis of various factors such as the material used, the desired layer thickness and other mechanical properties to be set.
2. process: quenching
After the workpiece has been exposed to the treatment temperature for a sufficient time, it is quenched. Quenching is usually performed by rapid cooling of the workpiece, either by immersion in a suitable cooling medium such as water, oil, or air, or by using specific cooling methods that ensure sufficient quenching speed.
3. process: tempering treatment
After carbonitriding and quenching, internal stresses occur in the workpiece which make the material brittle and increase the risk of fracture. To reduce these stresses and adjust the mechanical properties, a tempering treatment is carried out. The workpiece is heated to a certain temperature and then slowly cooled. This process aims to reduce stresses, optimize hardness and improve fracture strength. The exact tempering parameters are determined based on the specific material and requirements.
Gas carbonitriding is a method in which the workpiece is placed in a gaseous environment containing a mixture of carbon and nitrogen. Typically, a mixture of ammonia (NH3) and hydrocarbon gases such as methane (CH4) or propane (C3H8) is used. The workpiece is placed in a furnace where the desired temperatures and gas compositions are controlled. The heating causes carbon and nitrogen atoms to diffuse into the surface of the workpiece and, after sufficiently rapid cooling, form a hard and wear-resistant layer.
Liquid carbonitriding is based on immersing the workpiece in a liquid mixture of salts. The workpiece is placed in a container with a heat source and the salt. The heating increases the carbon and nitrogen potential of the liquid and the carbon and nitrogen atoms diffuse into the surface of the workpiece. This process is often used for high alloy steels where gas carbonitriding does not work.
carbonitriding and its advantages
✓ Improved hardness: The incorporation of carbon and nitrogen into the workpiece surface creates a hard layer. This increases wear resistance and extends the service life of the workpiece.
✓ Increased wear resistance: The carbonitrided layer forms a resistant barrier against abrasion, friction and wear.
✓ Good fatigue resistance: The hardening of the workpiece surface can reduce stresses and cracks, resulting in improved fatigue resistance.
appropriate materials for carbonitriding
Some of the most commonly used materials for carbonitriding are:
Unalloyed carbon steels (e.g., C10, St2, C22): These steels contain about 0.10% to 0.25% carbon and are well suited for carbonitriding to provide increased hardness and wear resistance.
Alloy steels (e.g., 16MnCr5, 20CrMo4): These steels contain additional alloying elements such as chromium, molybdenum and nickel. They are often used for applications requiring high strength and toughness and can be given improved surface properties by carbonitriding.
benefits of carbonitriding in various industries
Carbonitriding is used in various industries where it offers numerous advantages.
With these advantages, carbonitriding has established itself as a proven method to improve the performance and service life of workpieces, predominantly unalloyed materials, from various industries.
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