Gas Nitriding

Hard, wear-resistant case with good lubricity.

When specifications require heat treatment of parts that must retain precise shapes or parts that must have hard surfaces but softer, more ductile cores, Paulo’s gas nitriding process is right for the job. While parts sometimes require additional machining after heat treating because the stress of rapid cooling and transformation during hardening causes distortion, gas nitriding eliminates that risk because it’s carried out at lower temperatures and there is no transformation.

Gas nitriding is a case hardening process where nitrogen is imparted to workpieces heated in furnaces at around 1,000 degrees Fahrenheit. Ammonia (NH3) is injected into the furnace during heating and breaks apart upon contact with the workpiece. The nitrogen —which is soluble in iron at nitriding temperatures— then diffuses into the piece. The process is controlled by monitoring how much of the ammonia has broken apart during the process.

The hardness that the part achieves is dictated by the alloy composition and prior microstructure. More complex alloys respond better, and are usually hardened and finished machined before processing. The hardness is added at the part’s surface, but its core remains comparatively soft and ductile.

Distortion is significantly limited in gas nitriding because it is conducted at low enough temperatures for workpieces to remain in their ferritic stage rather than transforming into austenite. That’s opposed to methods like austempering or martempering where parts are heated to the point of triggering the phase change in the microstructure of the steel.

Because gas nitriding achieves the desired part qualities without a phase change, there’s no need for quenching. Parts also do not need to be tempered following gas nitriding because the specified hardness, strength and wear resistance levels can be achieved based on adjustments made to the furnace temperature, gas content, gas flow and process time.

Depending on the specified finished qualities, gas nitriding can take anywhere from 12 hours to a few days to complete.

Paulo’s gas nitriding process delivers:

  • Higher surface hardness
  • Higher impact and fatigue strengths
  • Increased wear resistance
  • Moderate corrosion control
  • Lower friction coefficient

Workpieces that respond best to gas nitriding include finished machined parts like tool steels or forging dies. Gas nitriding also improves automotive components like crankshafts and valve parts and firearm components like slides and barrels.

Gas nitriding is a good case hardening option for these types of parts because they must retain precise shapes to perform as designed. Heat treatment methods carried out at higher temperatures increase the risk that a part will distort. Distortion can lead to the need to remachine parts, which adds to costs and timelines.

Paulo’s state-of-the-art computer-controlled systems ensure consistency across all batches and finished parts that always meet stated specifications.

Key features:

  • Pit furnace at the St. Louis Division measures 25 inches in diameter and 55 inches deep.
  • Our state-of-the-art computer-controlled systems deliver precise temperatures and gas flow to suit any specification.

Locations offering this service:

Heat treating 101: An Introduction to Heat Treating Procedures