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Nitriding's Impact on Compressive Stress, Bending Fatigue & Wear Resistance

Authored by Dr. Edward Rolinski

posted On Wednesday, September 13, 2023 in Blog

Manufacturing long parts requires strong steels, which are very expensive and sometimes difficult to obtain. Therefore, heat and thermochemical treatments are very important and needed to enhance the performance as well as the longevity of the parts.


Advanced Heat Treat Corp. is known for its ability to ion nitride some of the largest parts in the country, parts such as shafts, tubes, feedscrews and stamping dies, made of various steels like Nit135M, 4140 as well as stainless steels, pictured.

Between AHT’s three locations that offer nitriding and nitrocarburizing, it has the capabilities to nitride up to:

  • 160” in diameter
  • 360” in length and
  • 60,000 lbs.

Gamma Prime Compound Zone for Bending Fatigue

Proper control of the nitriding processes allows for enhancing surface properties of the treated objects. It has been known that formation of the nitrided layer with the gamma prime compound zone/layer is beneficial where bending fatigue properties of the treated component need to be increased. That is when the nitriding process is used for high-performance crankshafts and other components.

Epsilon Compound Zone for Wear Resistance

When wear resistance is required, the ferritic nitrocarburizing (FNC) process is used to form the epsilon compound zone. Additional enhancement of corrosion properties of the surface is achieved when this compound zone is post-oxidized and a 1-µm-thick magnetite layer is formed. This layer is often impregnated with a proper chemical to further increase its corrosion resistance.

FNC & Gas Nitriding

FNC and gas nitriding processes allow for the all-over treatment of the components and for formation of the ɛ-type iron nitrides and nitro-carbides containing up to 9% of nitrogen and carbon needed for achieving maximum corrosion resistance and also excellent tribological properties. Thickness of the ɛ-type compound zone/white layer (WL) can exceed 0.001”, if needed. Thickness of this zone, when produced in ion/plasma FNC, is smaller because the process in a “low-nitriding potential”. Nevertheless, quality of the white layer produced this way is also excellent.

White layer

SEM picture of the structure of plasma nitrided and post-oxidized actuator shafts used in glass-making machines. Note a black oxide at the surface.

Nitriding or FNC processes allow for significant increase of the compressive stresses in the surface and increased hardness.

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Microhardness profile in a typical 4140 steel after nitriding. Note that the hardness values near the surface exceeds 60 HRc equivalent.

Nitriding and FNC techniques have been growing very intensely in recent years and their commercial potential is huge. This is the result of significant modernizations of the equipment, allowing use of this low temperature process in its full capacity. AHT has all the necessary controlling instruments for producing the optimum case depth, its hardness and the structure based on the percentage of nitrogen in the white/compound layers, and their anti-corrosion properties are additionally enhanced by our proprietary UltraOx® treatment.

Continued Investments in Nitriding at AHT

AHT continues to add additional nitriding equipment, increasing size capabilities and improving in expanding its gas nitriding services in Waterloo, Iowa increased significantly our ability to gas nitride similar long parts.

AHT’s nitriding and ferritic nitrocarburizing (FNC) capabilities were recently increased by investing in four new gas nitriding units and adding more accreditations and specifications such as Nadcap, AMS 2759/6, AMS 2759/10, and AMS 26759/12.

All our units allow us to do regular nitriding and FNC using ion/plasma and gas methods as well as a post-oxidizing method, UltraOx®.

For more information on AHT's nitriding and nitrocarburizing processes, follow the corresponding hyperlinks below. 


  1. ferritic nitrocarburizing
  2. gas nitriding
  3. ion nitriding
  4. nitriding
  5. plasma nitriding
  6. wear resistance