Carburizing and Carbonitriding
What is the case hardening (carburizing) process?
Carburizing process is a thermochemical process performed between 800-950°C degrees. In the carburizing process, the temperature of the steel is raised above the austenitic point by heating, carbon diffusion from the surface to the core of the steel is provided by creating a carbon-rich protective atmosphere in the environment where the process is carried out. The steel, whose carbon is enriched on its surface, is then immersed in oil and quickly cooled. The quenching process (rapid cooling) can be done directly or with different intermediate steps in order to reduce waste. After these processes, starting from the surface of the steel to a certain depth, martensitic transformation is achieved in the material. While the regions with this transformation are hardened, the core part has a lower hardness value compared to the surface depending on the type of steel. In this process, hardness is given to the steel up to a depth of 0.05-2 mm, depending on the usage characteristics.
After the carbonitriding process, the steel is tempered and the stresses in the material are reduced and the desired final hardness value is obtained.
What is the carbonitriding process?
The carbonitriding process is a modified form of the carburizing process. In addition to carburizing, ammonia is added to the furnace atmosphere, thus adding nitrogen along with carbon to the steel surface. The difference in the process compared to carburizing is that it is performed at lower temperatures and shorter processing times and as a result, a thinner hardness layer is formed. Carbonitriding process, usually 0.05-0.5 mm. It is applied when the depth of hardness is desired and if steels that are not suitable for carburizing are selected.
After the carbonitriding process, the steel is tempered and the stresses in the material are reduced and the desired final hardness value is obtained.
Carburizing and Carbonitriding Processes at Önerler
Atmosphere controlled chamber type furnaces are used for carburizing and carbonitriding processes in our company. Diffusion is provided to the steel surface by enriching the carbon and nitrogen in the ambient atmosphere in the heating chamber.
With various furnaces with charging capacities of 600 - 1000 - 2000 kg, we offer our customers the opportunity of flexible charging.
All of our 5 furnaces in total are of German origin and the IPSEN brand, which is a world leader in its field.
With the Carb-o Prof program in our furnaces, parameters such as gas flow, temperature, protective atmosphere composition, oil temperature, cooling rate, which are critical for the process, are controlled and thus high repeatability and traceability is provided.
Thanks to the Rapid-quench system, materials gain the maximum hardness value that can be achieved by cooling faster.
Since the establishment of our company in 1967, we have been providing the best quality to our customers with our expert staff, state-of-the-art equipment and experience in the carburizing process we have been doing for 50 years.
Benefits of the processes
High tensile strength
High wear resistance
High surface hardness
High toughness
High fatigue strength
Low carbon steels can be processed easily and are cheaper than other steels in terms of cost. The mechanical properties (hardness, strength, etc.) and wear resistance required by such steels are provided by the carburizing and carbonitriding processes. After the case hardening and carbonitriding processes, high wear resistance and high toughness values are obtained with a hard surface and relatively low core hardness.
Another feature of the case hardening and carbonitriding processes is that the part is partially hardened. With the special paste applied to the surface, carbon or nitrogen diffusion can be prevented and only the desired areas can be hardened.
Steels Applicable to Processes
The nitriding process is generally applied to steels containing %0.2 and below carbon. In the table below, the steels that are used extensively in the market and which are hardened and the maximum hardness values that can be obtained after the carburizing process are given in Rockwell.
1010 58 - 62 HRc Carburizing
1020 58 - 62 HRc Carburizing
9SMnPb28 60 - 63 HRc Carburizing
11SMnPb30 60 - 63 HRc Carburizing
16MnCr5 62 - 65 HRc Carburizing
20MnCr5 62 - 65 HRc Carburizing
20MoCr 4 62 - 65 HRc Carburizing
25MoCr 4 62 - 65 HRc Carburizing
15CrNi6 62 - 65 HRc Carburizing
18CrNi8 62 - 65 HRc Carburizing
17CrNiMo6 62 - 65 HRc Carburizing
8620 62 - 65 HRc Carburizing
20 MnB5 62 - 65 HRc Carburizing
St 52 58 - 63 HRc Carburizing
1010 700 - 800 HV Carbonitriding
1020 700 - 800 HV Carbonitriding
9SMnPb28 750 - 850 HV Carbonitriding
11SMnPb30 750 - 850 HV Carbonitriding
16 MnCr5 750 - 850 HV Carbonitriding
8620 750 - 850 HV Carbonitriding
20 MnB 5 750 - 850 HV Carbonitriding
St 52 750 - 850 HV Carbonitriding
Problems That May Occur After The Procedure
One of the most troublesome problems in the carburizing process is the change in the size of the materials, in other words, distortion. Carburizing process is a thermal process. The material is heated to high temperatures and cooled very quickly, and in this case, the material naturally expands and then shrinks rapidly, and when the material reaches the maximum hardness it can reach, the stresses in the material increase excessively. Even if the material is heated homogeneously, the shape of the material (especially thin-thick sections), the inhomogeneous stresses that occur in the material as a result of the processes performed before the heat treatment can increase the distortion and even crack the material.
In the carburizing process, after martensitic transformation, hardness is at maximum and internal stresses are at the highest level. If steel in this situation contains residual stresses due to processes before heat treatment, there may be more distortion or cracking in the material.
If a steel with high internal stress needs to be treated, then the internal stresses of the steel should be relieved by applying stress relief annealing beforehand.