Carburising or Carburisation is a heat treatment process by which carbon is introduced into a metal.

Carburised machine components have higher endurance limit because carburisation introduces a compressive layer on the surface.



Carburisation is a heat treatment process in which carbon is diffused into the surface of a metal component, typically steel. The purpose of carburisation is to increase the carbon content near the surface, thereby improving the hardness and wear resistance of the component.

During the carburisation process, the component is heated in a carbon-rich environment, such as a furnace with a carbonaceous atmosphere or a bath of molten carbon-rich material. The high temperature allows carbon atoms to diffuse into the metal matrix, forming a layer of high-carbon content near the surface.



The diffusion of carbon atoms into the metal matrix during carburisation leads to the formation of a hardened layer on the surface. This hardened layer is typically martensitic in nature, which is characterized by high hardness and strength.

However, the carburisation process also results in the expansion of the surface layer due to the introduction of carbon atoms. As the surface layer expands, it exerts compressive stresses on the underlying material. This compressive stress acts as a beneficial residual stress, counteracting the applied tensile stresses during operation.



The presence of a compressive layer on the surface of carburised machine components has a significant impact on their endurance limit, which is the maximum cyclic stress that a component can withstand without failure.

The compressive stresses introduced by carburisation help to suppress any stress concentrations that may be present in the component. Stress concentrations are areas of localized stress that are higher than the average stress level. They can arise from geometric features, such as notches or sharp corners, or from material defects.

By introducing compressive stresses, carburisation helps to distribute the applied cyclic stresses more evenly throughout the component, reducing the likelihood of stress concentration and crack initiation. This results in a higher endurance limit for carburised machine components compared to untreated components.

In summary, carburised machine components have a higher endurance limit because carburisation introduces a compressive layer on the surface, which helps to suppress stress concentrations and improve the overall fatigue resistance of the component.