Case hardening at about 495 to 565 °C in which nitrogen from cracked ammonia, plasma or salt diffuses into the surface and forms hard nitrides with chromium, aluminum, molybdenum and vanadium. No quench is needed and the core is hardened and tempered beforehand, so distortion is small. Cases run about 0.1 to 0.6 mm after cycles of 10 to 80 hours, with surface hardness above 900 HV on aluminum-bearing nitriding steels.
4140 crank gets nitrided after Q&T, 48 hours in ammonia, and comes out with about 0.015 total case.
Temper the core at least 30 °C above the nitriding temperature, or the core softens during the long cycle.
Also heard as
- gas nitriding
- nitride
- nitrided
Related terms
White layer
The thin, hard compound layer of iron nitrides that forms on the surface during nitriding.
Ion nitriding
Nitriding with a glow-discharge plasma in a vacuum vessel, which allows close control of the white layer.
FNC
Ferritic nitrocarburizing: adding nitrogen and carbon below the critical temperature for a thin, hard layer.
Case depth
Thickness of a hardened surface layer, measured from the surface to a specified hardness or structure.