Nitriding is a thermochemical surface-hardening treatment. The part is heated to a relatively low temperature, typically between 500 and 580 °C, in a medium that releases nitrogen: gas (ammonia), plasma (ion nitriding) or a salt bath. The nitrogen diffuses into the steel surface and forms very hard nitrides. The result is a skin resistant to wear, galling and fatigue, to a depth of a few tenths of a millimetre at most, around an unchanged core.
Its main advantage is low distortion: because there is no sudden cooling, a part already machined to final dimensions can be nitrided, which sets it apart from case hardening followed by quench hardening. The treatment mainly suits alloy steels containing chromium, molybdenum, aluminium or vanadium, such as 42CrMo4; some stainless steels can be plasma nitrided. Parts are often supplied in the quenched and tempered condition before nitriding, so that the core is strong.
It is used for extrusion screws, crankshafts, gears, shafts, dies and moulding tools. One point to watch: the layer is thin, so it tolerates heavy grinding after treatment poorly, and sharp edges can become brittle. The part grows very slightly, which should be allowed for in tight fits.
In a quote request
State the steel grade and its condition before treatment, the process wanted if one is imposed (gas, plasma, salt), the surface hardness targeted with its unit (HV) and the case depth, and the areas to protect. Specify whether there is an operation after nitriding (light polishing or no rework) and the checks required: microhardness, metallographic section, treatment certificate. These choices are made at part design stage, with a CNC machining workshop that knows the treatment.