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Gas Carburising Process

Gas Carburising Process is a surface chemistry process, which improves the case depth hardness of a component by diffusing carbon into the surface layer to improve wear and fatigue resistance.  The work pieces are pre-heated and then held for a period of time at an elevated temperature in the austenitic region of the specific alloy, typically between 820 and 940°C. 

During the thermal cycle the components are subject to an enriched carbon atmosphere such that nascent species of carbon can diffuse into the surface layers of the component.

Typical continuous carburising furnace
 

The rate of diffusion is dependent on the alloy and carbon potential of the atmosphere. Care must be taken to ensure that only sufficient carbon is available in the atmosphere at any one time to satisfy the take up rate of the alloy to accept the carbon atoms.

 

In practice, this is defined in a carbon potential setpoint profile which runs concurrently with the temperature cycle. The setpoint may give a boost phase where the carbon potential would be typically set above 1.0% carbon but, as the cycle progresses and the effective case depth increases, the carbon setpoint will be reduced to complete the diffusion stage.

 

Depending on the final requirement for effective case depth, the whole cycle may take many hours.   

Once the heating and carbon diffusion part of the process are complete it is necessary to rapidly quench the components to a defined alloy recipe. The recipe will specify the quench method, the quenchant temperature and time. 

 

The purpose of the quench process is to provide the required hardness of the component by completing a Martensitic phase change in the alloy.

Typical Features of Batch Sealed Quench Furnace
 

Gas carburising and other surface chemistry treatments can be carried out in batch or continuous furnaces dependent on the parts under treatment and the user requirements.

Eurotherm provides heat treat control solutions for both types of furnaces, as well as other metal treating processes such as:

 

  • Nitriding

  • Carbonitriding

  • Nitrocarburising

  • Tempering

  • Stress relieving