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Vacuum Carburizing vs. Gas Carburizing

December 16th, 2020

Carburizing is a valuable treatment process that hardens metals. It is used because many low-carbon steels are not able to withstand the stresses and wear required in industrial and many other applications.

At Specialty Steel Treating, Inc., we offer a few carburizing methods including vacuum and gas carburizing. Understanding how these methods work and the different benefits and drawbacks of each will help you to make the right decisions for how you want your steel products to be treated.

Understanding the Methods of Carburizing

The general process for carburizing steel involves heating it with a nearby supply of carbon-rich material. This will cause the carbon content of the steel to increase.

Carburizing can be achieved with a solid carbon source (such as charcoal), a liquid source or a gaseous source (such as carbon monoxide). Although early versions of this process used charcoal, nearly all carburizing today is done with gas because it is significantly more uniform and easier to control.

The process can be achieved at atmospheric pressure. It can also be done at low pressure in a vacuum. The latter provides some useful characteristics, particularly related to control.

Currently, atmospheric gas carburizing is the most commonly used process by far. Although both atmospheric and vacuum carburizing can use gas, the term “gas carburizing” is typically used to refer to the atmospheric version. Despite the popularity of this option, vacuum carburizing has a lot of potential and may be the best choice in many circumstances.

Vacuum Carburizing

The process for vacuum carburizing is a modified version of gas carburizing that can be done at pressures significantly below atmospheric. Atmospheric pressure is around 760 Torr whereas vacuum carburizing is done at pressures as low as one Torr.

Advantages

The result of doing this is a cleaner and more consistent carburizing process. It also tends to be faster. Compared to atmospheric gas carburizing, there are several practical advantages:

• Easy Integration: The parts are significantly cleaner after being vacuum carburized. This makes it easy to integrate into the manufacturing process because of the superior results.
• Greater Automation Control: This process can be highly controlled because the vacuum pressure eliminates many variables. This can result in more accurate and specific treatments.
• Increased Temperatures: This process allows for higher temperatures. Some applications can benefit from higher heat.
• Consistent Results: The cleanliness of the process means that the results are very consistent.

Disadvantages

Of course, using vacuum pressures is not without drawbacks. These are some of the disadvantages:

• Greater Initial Investment: The equipment for vacuum carburizing is costly. Although this is not as much of a concern for Specialty Steel Treating customers, it is the reason for slow adoption.
• Cleanliness Is Essential: The equipment needs to be kept very clean to achieve optimal results. Also, the process can produce a lot of soot and tar that need to be removed.

Gas Carburizing

Gas carburizing shares a lot of process similarities with vacuum carburizing. However, it is done at atmospheric temperatures instead.

Advantages

This can be an excellent option in many cases. These are some of the advantages:

• Low Cost: The initial cost of much lower for this type of carburizing.
• Adequate Control: Using gases can give a lot of control, even at atmospheric pressure. So, in many cases, this process provides ample treatment control.
• Excellent Results: Compared to solid or liquid carburizing, the gas process delivers excellent results. Your steel products will be hardened very effectively.

Disadvantages

Compared to vacuum carburizing, there are some drawbacks. These are the most notable:

• Post-Processing Requirements: The reduced accuracy may require some post-processing and finishing. This can add cost in some cases.
• Reduced Control: Compared to vacuum carburizing, it is hard to get truly minute control over the process. So, it may be insufficient in some cases.