Nitriding
Nitriding is a thermochemical surface-hardening process that diffuses nitrogen into the surface of a metal, creating hard nitrides and a hardened case while largely preserving core properties and dimensions. It improves wear resistance, fatigue life, and corrosion resistance with low distortion. Common variants include gas, salt bath, and plasma nitriding, typically at 480–580°C.
On the shop floor, nitriding is used as a post-machining surface treatment for precision parts that must maintain close fits. Unlike more aggressive heat treatments, it adds a hard case with minimal bulk dimensional changes, making it ideal for gears, shafts, dies, and wear pads. The typical workflow involves machining the part to near-net geometry, then nitriding, and often finishing with grinding, honing, or lapping to restore tight tolerances on functional surfaces. Plasma nitriding offers the advantage of localized control, allowing masked areas, precise case depths, and the ability to treat only specific zones like bearing seats or threads. This low-distortion process is critical in CNC cells where subsequent assembly requires exact dimensions, and the hardened surface prolongs component life under sliding contact, repeated loading, or mild adhesive wear.
Does nitriding change the core hardness?
No; the core retains its original mechanical character because the process is diffusion-based at relatively low temperature.
Why is nitriding favored for precision parts?
It is favored because it is low distortion and provides high fit accuracy compared with more shape-altering heat treatments.
What does 'white layer' mean?
It refers to the compound layer that forms on the surface during nitriding. While extremely hard, excessive thickness can hurt fatigue performance or finish quality.