What is Carburization in Heat Treatment?

07 April 2020

Case hardening is a process of reinforcing the surface of some types of soft metal, making them more durable and tough. This process forms a thin layer of durable metal coating that allows the metal underneath to remain soft. One type of case hardening is carburization, which involves introducing steel items to carbon atoms. 

The Essence of Carburization

Carburization is a process that transforms a specific type of metal like iron or steel into a highly carbonized metal. The transformation is done by exposing and heating the soft type of metal to a carbon-dense atmosphere such as charcoal or carbon monoxide. Once the carbon atoms have attached to the surface of the involved metal, it will ultimately develop improved hardness and strength.

The temperature and duration of the whole carburization process typically determines the overall strength acquired by the soft metal. A metal that is exposed to longer carburizing times and higher temperatures generally has a higher concentration of carbon. When this metal is quickly cooled by quenching, its outer surface becomes hard and resistant to wear, while the core will remain soft and tough. 

Types of Carburization Process

To date, there are four different types of carburization that are used in metal manufacturing industries. 

  • Vacuum Carburization: Vacuum carburization involves the placement of steel alloys in an oxygen-free, low-pressure environment like a furnace. This environment is pumped with hydrocarbon molecules that allow the involved alloys to be attached to carbon molecules. The absence of oxygen on this process makes the oxidation of steel alloys almost impossible, permitting the acceleration of the carburization process once the high heats are injected into the atmosphere.
  • Liquid Carburization: Liquid carburization takes place in a liquid vat, which is normally filled with a mixture of cyanide and salt. The metal alloys will then be submerged in this mixture, allowing them to be into contact with a collection of carbon molecules. The rapid diffusion of carbon molecules into the alloyed items makes the alloys form a hard case in a short time. This process enables steels to possess high levels of carbon and low levels of nitrogen.
  • Pack Carburization: Pack carburization is a process that places steel items into a furnace together with high-carbon items like carbon powder and cast-iron particles. Once they together, the furnace will then be heated by carbon monoxide, a gas that causes carbon to detach from the surface of the carbon-dense items. Afterward, the carbon molecules will be attached to the surfaces of steel items that are to be carburized.
  • Gas Carburization: The process involved in gas carburization is quite similar to pack carburization. The only difference between them is the absence of carbon-dense items. This type of carburization will instead continuously pump carbon monoxide into an enclosed high-temperature environment. The presence of high heat and carbon molecules allows the carburization of steel items that are being hard-cased.

Benefits of Carburization

The process of carburization can be advantageous for steel materials. For one, the whole carburization process can make the steels more durable. The formation of a very hard exterior out of this process allows the steel alloys to deal with immense physical trauma without damaging their soft interior. Speaking of the soft interior, the process of carburization can maintain this core part. The presence of this metal part allows the metals to be easily manipulated into different shapes. Lastly, steels that are carburized are much affordable than other types of steel. 

The carburization in heat treatment allows the metal to gain a surface that is difficult to get damaged. It also maintains important properties of metal even with the presence of an outer protective layer. If you want to know more about this process, you can always ask us at Alpha Detroit Heat Treatment.

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