Cast iron is an excellent material type for piston rings because it’s strong and durable. However, when it comes to piston and sealing rings, cast iron can benefit from a secondary treatment or coating to minimise the impact of wear and tear.

Read on to discover the types of secondary treatments we have available for piston rings and metallic sealing rings at PPUK.

Why do cast iron piston rings require secondary treatments?

While cast iron is a great material choice for metallic rings in industrial and marine applications, it also has some inherent weaknesses that can make it prone to cracking and breaking. One of these weaknesses is its tendency to corrode or rust when exposed to moisture. To prevent this from happening, cast iron piston rings must be treated with a secondary coating or finish to protect them from the elements. 

There are many factors that can affect the performance of piston rings, including the type of engine, the operating conditions, and the quality of the rings themselves. Applying a secondary treatment to the rings can help to mitigate some of these factors and improve their performance.

However, it is important to carefully consider the type of treatment that is used and ensure that it is suitable for the intended application. Some treatments are used as a running-in coating, while others will support the ongoing lifespan of the engine. 

Discover more about the reasons behind piston ring coatings in our previous article: Why are different coatings used for piston rings?

Secondary treatments for cast iron rings

When exploring secondary treatments for metal rings, it’s also vital to ensure the coating is appropriate for the metal type — bear in mind that not all secondary treatments are ideal for cast iron. Here are a few options that are suitable for this type of metal.


This process involves applying a thin layer of phosphate to the surface of the rings to create a barrier between the cast iron and the environment to prevent rust and corrosion and improve the rings’ overall wear resistance. 


Another common secondary treatment is known as ‘nitriding’. This is a heat treatment process that involves introducing nitrogen into the surface layer of the metal, forming a hard, wear-resistant nitride layer that protects the metal underneath from wear and damage.


Chroming is another effective secondary treatment to improve the performance and extend the lifespan of cast iron rings. Our C4 Hard Chrome is a wear-resisting coating that’s great for rings used in 2 and 4 stroke engines


Molybdenum is a chemical element that has excellent lubricating properties and can help to reduce friction and wear on piston rings. It’s resistant to high temperatures and can withstand the harsh operating conditions found in internal combustion engines.

This treatment can be used as a standalone — such as our C7 Molybdenum coating — or layered with Nickel Graphite. The combination of Molybdenum and Nickel Graphite is known as RIAS, our C5 coating.

Treatments and coatings for metallic rings

At Precision Products, we cater for a broad range of marine and industrial applications. Our piston rings, sealing rings, and valve rings are designed to be robust and long-lasting in all conditions.

If you need support with finding the right metallic ring material or coating, get in touch with the PPUK team today, and we’ll be happy to help.