The effects of Nitrogen Embrittlement on steel fasteners and coatings used to protect them

Nitrogen embrittlement is a phenomenon that can occur in certain types of steel and other metals when they are exposed to high concentrations of nitrogen, either in the form of nitrogen gas or as a component of certain materials. This can result in the metal becoming more brittle and prone to cracking or failure, even at lower stresses than it would normally be able to withstand.

The mechanism by which nitrogen embrittlement occurs is not fully understood, but it is thought to involve the formation of nitrogen-rich zones or pockets within the metal’s microstructure. These pockets can disrupt the normal flow of stresses within the metal, leading to the formation of cracks. Nitrogen embrittlement is more likely to occur in materials that have a high degree of ductility, or the ability to deform under stress without breaking because these materials are more susceptible to the formation of microcracks.

Nitrogen embrittlement can be a problem in a number of industrial applications, such as the manufacturing of high-pressure gas cylinders, pipelines, and other structural components. It is important for designers and engineers to take into account the potential for nitrogen embrittlement when selecting materials for these types of applications, and to carefully control the levels of nitrogen exposure during fabrication and use. In some cases, it may be necessary to use special heat treatment processes or other techniques to mitigate the risk of nitrogen embrittlement.

There are a number of coatings that can be used to protect materials from nitrogen embrittlement. The most effective coatings will depend on the specific requirements of the application and the properties of the substrate material. Some of the coatings that have been shown to be effective at preventing or mitigating nitrogen embrittlement include:

Ceramic coatings

Ceramic coatings, such as alumina, zirconia, and silicon carbide, are highly resistant to chemical attack and can provide a barrier to the penetration of nitrogen.

Metal coatings

Metal coatings, such as nickel and chrome, can provide a barrier to the penetration of nitrogen and can also improve the corrosion resistance of the substrate material.

Composite coatings

Composite coatings, which are made from a combination of materials, can be tailored to provide specific properties and can be effective at preventing the penetration of nitrogen.

Polymer coatings

Polymer coatings, such as epoxy, can provide a barrier to the penetration of nitrogen and can also improve the corrosion resistance of the substrate material.

 

The best coating for a steel fastener will depend on the specific requirements of the application and the environment in which the fastener will be used. Some of the factors to consider when selecting a coating for a steel fastener include:

Corrosion resistance

If the fastener will be exposed to corrosive environments, such as saltwater or high humidity, it may be necessary to use a coating that provides excellent corrosion resistance. Coatings that are commonly used for this purpose include galvanized coatings, chrome plating, and nickel plating.

Abrasion resistance

If the fastener will be subject to wear and tear, such as in a high-stress or high-vibration environment, it may be necessary to use a coating that provides excellent abrasion resistance. Coatings that are commonly used for this purpose include hard chrome plating, nickel-boron coatings, and titanium nitride coatings.

Ease of application

If the fasteners will be mass-produced, it may be necessary to use a coating that can be easily applied using an automated process. Coatings that are commonly used in this context include zinc electroplating, black oxide coatings, and phosphate coatings.

Cost

The cost of the coating will also be a factor to consider, as some coatings may be more expensive than others. It may be necessary to trade off performance and durability against cost in order to find the most appropriate coating for a given application.

Corrosion resistance coatings are thin layers of material that are applied to the surface of a metal in order to protect it from corrosion. Corrosion is a process that occurs when a metal reacts with its environment, resulting in the formation of oxide or other degradation products on the surface of the metal. This can lead to the weakening and failure of the metal over time. Corrosion resistance coatings are designed to provide a barrier between the metal and its environment, preventing or slowing the process of corrosion.

There are many different types of corrosion resistance coatings available, each with its own unique properties and characteristics. Some common types of corrosion resistance coatings include:

Galvanized coatings

Galvanized coatings are thin layers of zinc that are applied to the surface of steel or other metals in order to provide corrosion protection. The zinc reacts with the oxygen in the air to form a thin layer of zinc oxide, which provides a barrier to the penetration of corrosive substances.

Chrome plating

Chrome plating is a process in which a thin layer of chromium is applied to the surface of a metal in order to provide corrosion protection. Chromium is highly resistant to corrosion and is often used as a coating for automotive parts and other components that are exposed to the elements.

Nickel plating

Nickel plating is a process in which a thin layer of nickel is applied to the surface of a metal in order to provide corrosion protection. Nickel is highly resistant to corrosion and is often used as a coating for aircraft and marine components.

Anodized coatings

Anodized coatings are thin layers of oxide that are formed on the surface of the metal through an electrochemical process. Anodized coatings are highly resistant to corrosion and are commonly used on aluminum and other metals that are prone to corrosion.

Ultimately, the best coating for a steel fastener will depend on the specific requirements of the application and the environment in which the fastener will be used. It is important to carefully evaluate the suitability of different coatings for a given application and to consider factors such as the cost, durability, and performance of the coating in order to select the most appropriate option. 

The standard coatings used by Schmid Schrauben are chrome-free zinc electroplated, however, a zinc-nickel coating can be requested which has up to twice the tested protection.