What is Nitriding?

Legal Definition
Nitriding is a heat treating process that diffuses nitrogen into the surface of a metal to create a case-hardened surface. These processes are most commonly used on low-carbon, low-alloy steels. They are also used on medium and high-carbon steels, titanium, aluminium and molybdenum. In 2015, nitriding was used to generate unique duplex microstructure (Martensite-Austenite, Austenite-ferrite), known to be associated with strongly enhanced mechanical properties

Typical applications include gears, crankshafts, camshafts, cam followers, valve parts, extruder screws, die-casting tools, forging dies, extrusion dies, firearm components, injectors and plastic-mold tools.
-- Wikipedia
Legal Definition
Ammonia decomposition releases nitrogen that reacts with metal to make iron nitride, an hardening substance. In the presence of ammonia, a nitrogen and hydrogen compound, this specific metallurgical process hardens the alloy steel surfaces with heat.