Gas Nitriding is a thermo-chemical case hardening process. Disassociated Ammonia is the source of atomic Nitrogen that is diffused into the part surface to create a hardened case that is wear resistant and corrosion resistant.
The process temperature for Gas Nitriding is below the transformation temperature of the material. Generally, parts are heat treated to the required mechanical properties, then final machined prior to Gas Nitriding. The Nitriding temperature and atmosphere is controlled to produce targeted phases and thicknesses of diffusion that meet various application demands.
As the process is carried out below the tempering temperature of the steel, the base steel properties are not affected. As a result, high strength parts with extremely good wear and corrosion resistant properties with little to no distortion is produced.
To further enhance corrosion resistance properties, Gas Nitriding is often combined with post oxidization/black oxide. For some applications, the compound layer/white layer produced by Gas Nitriding is brittle and needs to be removed afterwards. For example, Gas Nitrided gears need to be post ground to remove white layer. Although Gas Nitriding provides great wear and fatigue resistance for gears, the brittle white layer, if not removed will chip off and cause surface damage during operation. For applications that need the white layer removed, Plasma Nitriding should be considered. The white layer produced in Plasma Nitriding is ductile/crack resistant.
Gas Nitriding is not the optimal Nitriding process for Stainless Steels, except Martensitic Stainless Steels. The mechanically or chemically removed chrome oxide layer (layer prevents Nitriding) grows back prior to Nitriding, causing the the Nitride case to be non-uniform. For stainless steels, Plasma Nitride is preferred.
Materials Suited for Gas Nitriding:
- Alloy Steels that are quenched & tempered: 4140, 4150, 4340, P20
- Nitriding Steel: Nitralloy 135
- Low Alloy Steels that are Carburized and need Nitriding for added corrosion resistance: 5120, 9310
Advanced Nitriding Solutions is Nadcap accredited* and can certify to AMS 2759/6, AMS 2759/10 specification.