Nitriding gas: what it is and why it is used

Gaseous nitriding is a low-temperature thermochemical treatment process used to improve the surface properties of metal components, particularly alloy steel containing elements such as chromium, vanadium, molybdenum and aluminium, capable of forming nitrides. In this process, the object to be treated is exposed to a gaseous environment containing active nitrogen. During exposure, a chemical reaction takes place between the nitrogen and the elements on the metal surface, creating a reinforced surface layer.

How does gas nitriding work?

As mentioned earlier, gas nitriding treatment is a thermochemical process involving the exposure of metal components, mostly steels such as tool steels or quenched and tempered steels, to an environment rich in active nitrogen. The treatment takes place in a controlled atmosphere furnace, where the material to be treated is placed in a sealed chamber together with a source of nitrogen, such as ammonia (NH3) or molecular nitrogen (N2). For stainless steels, on the other hand, ion nitriding treatment is preferred.

Once the furnace reaches the desired temperature, usually between 500°C and 600°C, the ammonia decomposes into active nitrogen (N) and hydrogen (H). The reactive active nitrogen gas interacts with the surface elements of the metal, creating compounds such as nitrite and iron nitride. These compounds accumulate on the surface of the metal, forming a surface layer known as the nitrided layer. This layer is characterised by greater hardness and wear resistance than the base material.

The depth of the nitrided layer depends on the duration and conditions of the nitriding treatment, as well as the composition of the metal itself. Precise control of temperature, chemical composition and treatment duration is essential to achieve uniform and consistent results. Once the treatment phase is complete, the components are cooled gradually to avoid unwanted deformation. Subsequently, they can be subjected to additional processes, such as tempering, to further improve mechanical properties and dimensional stability.

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The advantages of gas nitriding treatment

Gas nitriding offers a number of significant advantages that make it an optimal choice for improving the surface properties of metal components. 

  1. Increased wear resistance: The nitrided surface layer has a higher hardness than the base material, significantly improving the component’s resistance to wear and abrasion. This results in a longer service life and reduced need for maintenance and replacement.
  2. Increased surface hardness: The formation of nitrite and iron nitride during the gaseous nitriding process increases the hardness of the treated metal surface. This makes the components more resistant to scratches, surface deformation and impact damage, helping to extend their service life.
  3. Improved fatigue resistance: components subjected to the gas nitriding treatment show improved fatigue resistance. This means that they can withstand repeated dynamic loads without suffering damage or permanent deformation, improving the reliability and safety of applications.
  4. Enhanced corrosion resistance: the nitrided layer offers additional protection against the corrosive action of external agents, such as moisture, aggressive chemicals and adverse weather conditions. This helps prevent rust and other types of corrosion, maintaining the structural and functional integrity of components over time.
  5. Improved seizure resistance: The gas nitriding treatment reduces the risk of seizing and adhesion between moving parts due to the formation of nitrite and iron nitride on the metal surface. This is especially important in applications where there is friction and direct contact between moving parts, such as in automotive and mechanical engineering.

Applications of gas nitriding

Gas nitriding finds application in various industries to improve the strength and durability of critical components. In the automotive industry, it is used to increase the wear resistance and service life of components such as camshafts, drive shafts, pistons, cylinders and gears, which are subjected to high loads during vehicle operation. In the aerospace industry, it improves the wear resistance and durability of parts such as gears, shafts, engine housings and aircraft structural components, which are subjected to extreme environmental conditions and high mechanical stress. In the oil and gas industry, it is used to increase the corrosion and abrasion resistance of critical components such as valves, pipes, drill shafts and offshore equipment, which are exposed to aggressive environmental conditions and corrosive chemicals.

In moulding processes, gas nitriding extends the life of moulds used in the production of plastic and metal parts, increasing their resistance to wear and corrosion and enabling more efficient and higher quality production. In the machine tool industry, it improves the life and performance of components such as guides, shafts, cutting tools and gears, which are subject to mechanical and thermal stress during use. Finally, in the food industry, it increases the wear and corrosion resistance of equipment used in the processing, packaging and transportation of food products, ensuring the safety and hygiene of end products.

Protecting components during gas nitriding with ATP-Europe’s Stop Off coatings

During gas nitriding treatment, protecting components is essential for several reasons. First of all, it is aimed at preserving the integrity of delicate surfaces, which may suffer undesirable alterations due to the process, and also at maintaining the size of the components, avoiding deformations that could compromise their functionality. There are also sensitive components, such as seals and o-rings, that must be protected to avoid irreversible damage. Finally, optimisation of the gas nitriding process can be achieved by using Stop Off coatings that allow customised masks to be created, protecting only the necessary areas and thus reducing overall treatment time and costs.

With ATP-Europe’s Stop Off metal surface coatings, metal parts that do not need to be treated can be precisely protected during gas nitriding, guaranteeing high quality results and maximum efficiency. In particular, our METSEAL 100 is suitable for this process. For more information on ATP-Europe products, please do not hesitate to contact our team of experts. We are available to provide personalised advice and technical support for your specific metal heat treatment needs!