Gas Nitriding by Alpha Detroit: Enhanced Strategies to Control White Layer Formation05 September 2023
Explore the essence of successful gas nitriding by Alpha Detroit and the strategies for controlling white layer formation. Call 03 9555 3682.
Gas nitriding is a surface hardening process used to improve the surface properties of various materials. The process involves exposing the material to a high-temperature atmosphere of ammonia gas, which later introduces a hard, wear-resistant layer to its surface.
One of the challenges associated with gas nitriding, however, is the formation of a brittle white layer on its surface. It is normally caused by the excessive diffusion of nitrogen atoms into the material. As this layer forms, it can negatively affect the performance and fatigue life of the component. It can also make the material more susceptible to corrosion.
Strategies to Control White Layer Formation
A white layer on processed materials often occurs due to variations in the nitriding temperature, time, and nitrogen potential. Hence, nitriding parameters should be controlled to avoid a white layer. Here are some strategies to effectively control its formation.
• Utilise a lower nitriding temperature: The nitriding temperature is one of the critical parameters affecting the formation of the white layer. It should be selected based on the material composition and the desired properties. However, a lower nitriding temperature is expected to slow down the diffusion of nitrogen atoms into the material, which can reduce the formation of the white layer.
• Use a lower nitrogen partial pressure: The nitrogen potential is the ratio of the partial pressure of nitrogen to the partial pressure of hydrogen in the nitriding atmosphere. Now, a lower nitrogen partial pressure can slow down the diffusion of nitrogen atoms into the steel. Therefore, it must be maintained to minimise or prevent white layer formation.
• Take advantage of pre-treatment processes: Pre-treatment processes can likewise affect the formation of the white layer. Some of these processes include cleaning, degreasing, and surface preparation. Conducting them can help remove any contaminant from the material, preventing the formation of the white layer.
• Integrate post-treatment processes: Post-treatment processes like quenching, tempering, and stress relieving can be used to temper the material after nitriding. These processes can reduce the brittleness of the white layer, which then helps minimise the residual stress and improve the fatigue life of the component.
Key Factors to Regulate During Gas Nitriding
The success of these strategies can be enhanced further once the composition of the material, its surface finish, and the nitriding time are all considered and controlled during gas nitriding. Controlling them helps minimise white layer formation, which then improves the fatigue strength and corrosion resistance of the nitrided components.
Minimising the white layer formation on an object that will be used in a fatigue-critical application can be achieved by using a lower nitriding temperature and a lower nitrogen partial pressure. A pre-treatment can then be utilised to ensure a component that is to be used in a corrosive environment will not have any white layer. A post-treatment, ultimately, is useful for components intended for a high-temperature application.
White layer formation during the gas nitriding process can be a vital concern that affects the performance and durability of treated components. However, by implementing strategies like precise process control, thorough surface preparation, and controlled nitriding atmosphere and conditions, it is possible to easily control white layer formation.
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