Valve Nitriding
The nitriding process and it’s many benefits have been around for around 100 years and it has been widely used in various fields including performance engine parts such as valves, valve springs, crankshafts, camshafts, gearboxes, piston rings and other parts.
The first aspect that we must clarify is that the nitriding process isn’t actually a coating because it doesn’t adhere to the parent metal, it bonds with it. In this sense it is considered a heat treatment that produces a case-hardened surface.
The principle behind this heart treatment is the deposition of nitrogen on the stainless steel creating a nitrided layer that has increases its hardness, wear and fatigue resistance, lower coefficient of friction and corrosion resistance.
Nitriding Process
There are different methods to nitride the metal: Gas Nitriding, Salt Bath Nitriding and Plasma Nitriding. Where they differ is the medium that is used to transfer the nitrogen to the metal. Our valves undertake a gas nitriding treatment that occurs at relatively lower temperature than the other methods.
In the gas nitriding process, nitrogen-rich gas (ammonia), when in contact with the heated valve, dissociates into nitrogen and hydrogen. The nitrogen combines with the stainless steel to create a hard smooth layer of nitrided steel on and immediately below the surface of the valve.
Nitriding Valves and its Advantages
​ Engine valves operate in extremely harsh environments, subject to very high temperature and oxygen rich environments while dealing with various types of fuel for extended periods – all these conditions contribute to a highly corrosive environment. One of the advantages of the nitriding treatment is exactly improving this corrosion resistance to increase valve life and maintain engine performance for longer.
Nitriding is also responsible for reducing the friction coefficient. This is particularly important in the valve stem where a smoother surface will result in lower temperatures, reduced frictional losses and more importantly less wear and longer lifespan for the valve and the guide. This is even more important on racing engines subject to high RPM conditions for long periods of time as well as forced induction engines.
Increased hardness and tensile strength are important for those areas subject to high shock loads such as the valve seat area and the valve tip. Here, if the valves have a lower hardness and strength, they will deform or mushroom out of shape. In extreme instances, higher hardness may require other modifications such as Stellite Tips – as we use and recommend for all the valves actuated by rocker arms such as those used on most of the oil cooled GSXR family of engines.
Alternatives to Nitriding
A common alternative to the Nitriding process is Chrome Plating. Chrome plating serves basically the same purposes: reduce friction, improve durability through abrasion tolerance and wear resistance in general.
There are differences however between the two:
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Nitriding produces a smoother surface than chrome plating, hence further reducing heat production, wear and frictional losses
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Nitriding bonds to a valve's base material at a microscopic level, so it can not flake or brake off whereas chrome plating deposits a chrome layer onto the base metal
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Nitride treatment is applied to the whole valve while the use of a traditional chrome coating is only applied to the valve stem
Both represent a significant improvement over an uncoated / untreated valve and are recommended in any high performance application.
Conclusion
The nitriding treatment we apply to our valves greatly complements their high strength and temperature resistant 21-4N material, widely regarded as the gold standard in stainless steel valves, producing a longer wearing, smoother and higher performance valve ideal for high performance and racing engines alike.
