Nitriding is a surface hardening process in which nitrogen atoms are diffused into the surface of ferrous materials at sub-critical temperatures and react with the base metal to form a hard, wear resistant, and fatigue resistant nitrided case below the surface. The combination of subcritical temperatures, minimal distortion, and protective atmospheres make nitriding a good choice for precision parts.
Applicable Materials
Most ferrous materials can be nitrided in theory, but the process is most effective when applied to alloy steels containing nitride-forming elements such as Cr, Al, Mo, V, W, and Ti. The best response in terms of hardness is realized when these "nitriding steels" are selected for the process as the nitrogen that enters the surface is able to form alloy nitride precipitates and increase the hardness of the case.
The most commonly used nitriding steels include 4130, 4140, 4150, 4340, Nitralloy 135, and 8640. Other chrome and chrome-vanadium steels such as the 51xx, 52xx, 61xx families also are good candidates for nitriding. Tool steels and high speed tool steels may also be nitrided. Stainless steel may also be nitrided (formerly called malcomizing) where an extra chemical surface activation step must be employed prior to nitriding. Some nickel-based superalloys are also candidates for nitriding as well.
Nitriding Features
•Superior wear resistance •Improved fatigue life
•High hardness (700-1000 HV depending on material being treated)
•Case depths typically .058 to .762 mm deep depending on material being treated and cycle selected
Applications
•Forging dies / Die-casting dies
•Extrusion dies
•Gears
•Bearings
•Extrusion dies
