Definition - What does Gas Nitriding mean?
Gas nitriding is a thermochemical case-hardening process that increases wear resistance, surface hardness and fatigue life by dissolution of nitrogen and hard nitride precipitations.
It is suitable for components that are subjected to heavy loading and increased fatigue.
Ferrous materials can generally be gas nitrided up to 5% chromium. For higher contents of alloying elements and for gas nitriding of stainless steel, plasma nitriding might be considered. Gas nitriding of sintered steels with low density is not recommended.
Corrosionpedia explains Gas Nitriding
In the process of gas nitriding, nitrogen is introduced into the surface of a solid ferrous alloy by maintaining the metal at a suitable temperature while in contact with a nitrogenous gas, usually ammonia. The nitriding temperature for all steels is between 923 and 1050°F (495 and 565°C).
Principal reasons for nitriding are:
- Obtaining high surface hardness
- Increasing wear resistance and anti-galling properties
- Improving fatigue life
- Improving corrosion resistance
- Obtaining a surface that is resistant to the softening effect of heat at temperatures up to the nitriding temperature
Gas nitriding develops a very hard case at a relatively low temperature, without the need for quenching. Nitriding of steels produces less distortion and deformation than either carburizing or conventional hardening.
Materials or parts to be nitrided are heat treated to the proper strength level, and final machined. The parts are then exposed to active nitrogen at a carefully controlled temperature. This temperature is typically below the final tempering temperature of the steel so that nitriding does not affect the base metal's mechanical properties. As a result, a very high-strength product with extremely good wear resistance can be produced, with little or no dimensional change.
Typical applications include:
- Extrusion screws
- Die-cast tooling
- Forging dies
Gas nitriding is most effective when applied to steels containing nitride-forming elements. The process is applicable to:
- Tool steels
- Hot-work steels
- Cold-work steels
- Mold steels
For optimum results, the material should be in a hardened and tempered condition prior to gas nitriding.