What Is Carburizing: Benefits, Process, Types and Applications

Every application has a different requirement for the hardness of the material used in the making of its components. However, to achieve the relevant level of hardness, a carburizing process is done to harden metals.

There are different types of metals that may require hardening, and this is achieved through the carburization process. If you want to know what is carburizing, read the guide below.

What is Carburizing?

Carburizing is a process of heat treatment that enhances the properties of materials like hardness by adding the content of carbon to the surface of the metal. The surface of the metal may lack carbon, and hence, the need for carbon is essential to add a hard coating around it.

Benefits of Carburizing

There are several versatile benefits of carburizing, and some of these are as follows:

• The process of carburizing is very simple and can be performed in no time, and doesn't even need excessive skills. It is also compatible with multiple types of materials, like cast iron and carbon steel. It is suitable for complex shapes and designs.
• Carburizing is a process that is not costly, and at a limited expense, it can offer components hardness.
• Carburization is suitable for mass volume as it is automated and hardens larger batches of products.
• It offers better control of dimensions, and even after the hardening process, the deformation is negligible.
• It improves the wear resistance and ductility of the workpiece.
• Carburization gives components high fatigue strength, and hence, the hard layer on the outside allows the component to withstand high loads.

Processes of Carburizing

The process of carburizing consists of the following steps:

Addition of Carbon

In the first step, the component is cleaned and then placed in a box that is tightly sealed and contains the carbonaceous materials. To seal the box, fire clay can be used. The box is then kept in the furnace at a temperature of 925 degrees Celsius for a time span of around 10 hours.

The carbon dioxide comes from the carbonaceous material, which breaks down into carbon and carbon monoxide. The carbon diffuses with the component, which is carburized. The part absorbs carbon in layers, and then the box is removed from the furnace.

Heat Treatment

The part is then placed in the furnace again for the heat treatment stage. It is kept in the furnace for around 15 minutes at a temperature of 790 degrees Celsius. It helps to transform the metal into austenite, and then, after removing it from the furnace, the part is kept in water. This leads to quick cooling and the development of hard structures.

Tempering

The internal stresses are formed due to rapid cooling, and hence, it is important to relieve these stresses by tempering. You can heat the part at a low temperature and leave it to cool in the air after it has been under heat for an hour.

Types of Carburizing

There are different types of carburizing processes, and they are discussed below.

Gas Carburizing

Gas carburizing consists of heating carbon steel to the austenitizing temperature in an atmosphere that is carbon-rich. It uses a carrier gas, and the component is kept in an oven that has propane and methane. It is a mixture of CO2, CH4, CO, etc.

At the carburizing temperature, propane decomposes on the surface of the part, and the carbon diffuses on the surface. The temperature is around 925 degrees Celsius, and the time required for carburizing is 2 hours.

Vacuum Carburizing

The process of vacuum carburizing involves using an environment that is oxygen-free and uses low pressure. The process uses hydrocarbons, which are gases like methane. The surroundings are free from oxygen, and the temperature can be increased if needed. The higher the temperature, the higher the diffusion rate of carbon.

Liquid Carburizing

Liquid carburizing is a process that is used for carburizing steel or iron components. These parts are kept at a temperature that is more than Ac1 in the salt in a melted condition, and nitrogen and carbon are added. The liquid carburizing uses cyanide, which is composed of nitrogen as well as carbon.

The component is kept in a salt bath, which has a temperature of around 900 degrees Celsius, and the salt is highly toxic. The salt incorporated nitrogen on the component’s surface, which made it hard.

Solid Carburizing (Pack Carburizing)

Solid carburizing is a process in which carbon monoxide is derived from the solid compound, which decomposes on the surface of the metal into carbon dioxide and nascent carbon. The carburizing containers are made using aluminum-coated carbon steel, carbon steel, or iron nickel-chromium alloys that resist heat.

The components are kept in a sealed box with a carburizing medium, which can be charcoal or coke. The process uses gas carburization, and the carbon monoxide is dissociated into carbon dioxide, which then fuses carbon on the surface of the part. The process takes as little as 2 hours and as much as 36 hours under a temperature of 800 to 845 degrees Celsius.

Plasma Carburizing

The plasma carburizing process uses the direct current glow distance, which adds a layer of carbon to one component. The direct current voltage is applied between the component and the electrode, and the workpiece is kept in the carburizing chamber. The carbon is then released in the form of plasma discharge.

Drip Carburizing

Drip carburizing uses organic agents, such as methanol, which is added to the carburizing furnace. It produces the gas, which decomposes the components and their surface, leaving behind a hard layer of carbon.

Carbonitriding

Carbonitriding is also conducted on steel and has a carbon mass of 0.4 to 0.5 percent. It helps to harden the surface of the part, and these parts may include shafts and gears. The process modifies gas in which methane and ammonia are present.

Carburizing vs Nitriding

Carburizing and nitriding are both processes that help to harden steel and other metals. However, the only difference between them is the material used during the process.

Carburizing is used for diffusing carbon on the surface of the metal by heating it in the presence of a carbon-associated material. Nitriding, on the other hand, uses nitrogen on the component and exposes it to high temperatures.

Applications of Carburizing

The process of carburizing is observed in many applications for hardening the metals used in components; some of these applications are given below:

Aerospace: The parts of aircraft, like engine parts and landing gears, need high strength, which requires carburized steel.

Maritime: Components, like gear systems and engines in the shop, are made using carburized parts that offer corrosion resistance and wear resistance.

Automobile: In the automobile sector, the parts with high strength and resistance to wear, such as bearings, gears, shafts, and carburizing, are used for it.

Agriculture: The machinery used for agriculture uses carburized steel as it needs parts to withstand harsh surroundings.

Start Your CNC Machining Steel Project at DEK

The carburizing steel parts are used widely in many applications, and if you are looking to have components manufactured and carburized for your upcoming project, contact us at DEK. We offer high-quality parts that are designed to meet your custom specifications and can be used in different projects.

Conclusion

Carburizing process has various types, and each type has its own characteristics. It is very important to understand each type of carburizing process and its suitability so that you can choose it according to your application requirements.