Industry Knowledge, Surface Finishing, Surface Treatment Related

Surface Finishing：What is Nitriding?

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Nitriding

Key Benefits of Nitriding

  • Exceptional Wear Resistance: The nitride layer has a hardness of 800–1200 HV (compared to 200–300 HV for untreated steel), ideal for components subject to friction or abrasion.
  • Improved Fatigue Strength: Nitrogen diffusion creates compressive stresses in the surface, reducing the risk of crack formation and propagation under cyclic loading.
  • Corrosion Resistance: The compound layer acts as a barrier against moisture and oxidation (especially for stainless steels).
  • No Distortion: Processing below the metal’s critical temperature avoids phase changes, so parts retain their original dimensions (critical for precision components).
  • No Post-Processing: The finished surface is smooth and requires no additional grinding or polishing (unlike hardening + tempering).

Material Compatibility

Nitriding is a thermochemical surface hardening process that diffuses nitrogen atoms into the surface of ferrous metals (e.g., steel, cast iron) at elevated temperatures (typically 450–550°C, below the metal’s austenitization temperature). The result is a hard, wear-resistant surface layer (consisting mainly of iron nitrides like Fe₃N and Fe₄N) while preserving the metal’s core toughness—making it ideal for cnc components requiring both surface durability and internal strength.

 

Nitrogen is introduced to the metal surface via three common methods, all achieving atomic diffusion into the substrate:
  1. Gas Nitriding: Parts are heated in an atmosphere of ammonia (NH₃), which decomposes to release nitrogen atoms that bond with the metal surface.
  2. Plasma (Ion) Nitriding: A low-pressure plasma environment ionizes nitrogen gas, accelerating nitrogen ions toward the metal surface for deeper, more controlled diffusion.
  3. Salt Bath Nitriding: Parts are immersed in a molten salt bath containing nitrogen-rich compounds (e.g., cyanates), which react with the metal to form the nitride layer.

Material Compatibility

Nitriding works best on nitride-forming steels—alloys containing chromium, aluminum, vanadium, or molybdenum (e.g., 4140, 4340, H13 tool steel, and stainless steels like 316). These elements form stable nitrides that enhance layer hardness and adhesion. Low-carbon steels can be nitrided but yield less durable layers.

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