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Gas & Plasma Nitriding, Nitrocarburizing & Post Oxidation |
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Nitriding is a ‘case hardening’ process whereby nitrogen is introduced into the surface of a ferrous alloy by retaining the component to be treated at a suitable temperature in contact with a nitrogenous atmosphere. The comparatively low temperatures employed in the process (500 - 560°C) and the absence of a quenching operation account for the lower distortion and deformation normally experienced in either carburising or conventional bulk hardening treatments.
| The principal reasons for Nitriding are to: |
- Achieve a high surface hardness
- Enhance wear resistance and anti-galling properties
- Improve fatigue life
- Improve the corrosion resistance of low alloy and carbon steels
- Increase the temperature at which the surface softens
- Eliminate adhesive wear
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| Compared to the gas process, Plasma Nitriding: |
- Yields a deeper case for the same process duration
- Allows closer control of the surface chemistry
- Is a more environmentally friendly process
- It is however less suitable for complex components
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| Typical applications of the Nitriding Process: |
- Plastic injection moulds, cutting tools and forming dies
- Parts for hydraulic components
- Internal combustion components
- Feed screws
- High pressure nozzles
- Steam valve components
- Shafts and sleeves
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Nitrocarburizing is a thermochemical treatment that involves the addition by diffusion of both nitrogen and carbon to the surface of ferrous materials at temperatures below 675"C. The primary objective of nitrocarburizing is usually to improve anti-scuffing, fatigue and corrosion characteristics in components which need to be assembled and which therefore, cannot tolerate distortion. The process is used for a wide range of engineering components such as rocker-arm spacers, textile machinery gears, pump cylinder blocks, jet nozzles and crank and drive shafts.
Gaseous or Plasma Post-Oxidation involves the introduction in the furnace of an oxidation medium such as oxygen or water. The resulting surface has a black aesthetically pleasing colour which is also wear and corrosion resistant.
CASE STUDY POST- OXIDATION
A polymer component manufacturer was experiencing extensive adhesion to the metal mould. This was leading to rapid tool wear and loss of production. Post oxidation was used to reduce chemical surface activity, minimizing corrosion and adhesion to the surface. The period between cleaning operations was increased by 50%
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