Nitriding

Nitriding is a surface-hardening heat treatment that diffuses nitrogen into the outer layer of a steel or alloy part while it is held at a moderate temperature, well below the metal's melting or even hardening-transformation point, forming hard nitride compounds within that surface layer without requiring the rapid quenching that carbon-based case hardening methods need. The German metallurgist Adolph Fry developed the modern gas nitriding process in the early 1920s while working for the Krupp steelworks, discovering that certain alloy steels containing aluminum, chromium or molybdenum formed an especially hard nitrided layer. Because nitriding causes little distortion compared to quench-hardening methods, it became particularly valued for precision components such as gears, crankshafts and gun barrels that must hold a hardened surface while keeping tight dimensional tolerances, and it remains a standard heat-treatment option in modern metallurgical engineering.