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Carburizing is a type of case-hardening process in which carbon is diffused into a part at elevated temperatures and then quenched to form a hard outer surface layer. This is used on low-carbon steels to transform them into high-carbon steel, giving intricately shaped parts a strength and toughness they otherwise wouldn’t have.


  • Gears
  • Bearings
  • Tooling
  • Cams
  • ​Shafts

Common Alloys that we heat treat through Carburizing

  • Low-Carbon Carbon Steels, e.g., 1018, 1020, 12L14
  • Low-Carbon Structural Steels, e.g., A36, A572
  • Low-Carbon Alloy Steels, e.g., 8620, 4130



TMT’s Equipment and variations of Carburizing

We heat parts in a protective endothermic atmosphere to above the critical point of steel. Additions of methane and trim air are then introduced and controlled via an oxygen probe. The parts undergo a high-carbon “boost” cycle followed by a lower-carbon “diffuse” cycle for a determined time based on the desired case depth.

Once the cycles are complete, the parts are quenched in oil or polymer to harden. They, they’re tempered to ensure that parts are at the correct hardness level. Case depths generally range from .015-.125 inches.

Applications of Carburizing

Carburizing is frequently used on low-carbon steels that need to have a hard outer surface. Due to the low-carbon content of the steel, traditional quench and temper processing will not produce a hard surface. The diffusion of carbon into the steel allows for maximum surface hardness in excess of 60 HRC. For some alloy steels, carburizing can promote a hard, wear-resistant surface while still retaining a tough core.

Carburizing is generally used over carbonitriding in parts that have enough alloy content to not require nitrogen diffusion to increase the hardenability. This allows higher process temperatures and, therefore, shorter cycle times.

Associated Specs/Standards

  • AMS 2759/7

What To Consider When Specifying for Heat Treatment

  • Hardness
  • Case Depth
  • Material
  • Spec (if required)
  • Masking (if required)

Do you have more technical questions?

If you have technical questions for us, you can contact one of our engineers here. We would be happy to discuss all of the heat-treating options that we have available for you!