Gas nitriding

Gas nitriding, or long-term gas nitriding, is a thermochemical heat treatment process. It is a particularly good choice for hardening materials that are prone to warping or are exposed to high loads. During gas nitriding, nitrogen penetrates the steel surface and improves numerous component properties. Partial nitriding is possible as well. Regardless whether you require gas nitriding or other state-of-the-art processes: we optimise even the most challenging technical components for you. As a single part, in custom sizes, or as series production - whatever your requirements are. Feel free to contact us for a personal, no-obligation consultation. We operate several chamber and shaft furnace systems up to 1,100 x 3,300 mm in diameter.

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The process and its advantages

Gas nitriding improves the surfaces of iron-based workpieces that are subjected to high loads. Gas nitriding increases fatigue strength as well as wear resistance and resistance to wear due to scoring. It is carried out at low temperatures around 520°C. This ensures that warping is extremely low. Another version of gas nitriding is gas nitrocarburising, which involves the use of a gas atmosphere which provides carbon.

Gas nitrocarburising creates deeper layers than the Tenifer QPQ process (salt bath nitrocarburising). The treatment times can be extensive in some cases. Components that are sensitive to warping should be pre-treated beforehand by stress-free annealing.

Gas nitriding forms a compound layer on the workpieces that is composed of nitrides. A thin layer improves fatigue resistance. Thick layers improve resistance to wear and corrosion. Dissolved nitrogen atoms and nitride precipitates form the diffusion layer underneath the compound layer. The diffusion layer extends the service life of the components.

NIOX and ALDOX: A special variation of gas nitrocarburising with post-oxidation

If workpieces of premium quality are to undergo gas nitrocarburising and post-oxidation, they can be treated using the NIOX or ALDOX process. The surface receives a refined black look and significantly improved corrosion protection.

Gas nitriding offers a particularly wide range of applications, because different nitriding depths and temperatures can give the workpieces highly diverse properties.

The advantages of gas nitriding at a glance

  • Higher bending fatigue resistance and fatigue strength
  • Enhanced wear and scoring resistance
  • Lower friction coefficient
  • Good temperature resistance
  • Reliably reproducible results
  • Partial hardening possible
  • Minimum warping makes reworking the components unnecessary

Surface hardness and nitriding hardness depth of various materials

The table below shows the surface hardnesses that gas nitriding can achieve on various materials.
The following applies:

  • The higher the treatment temperature, the lower the intrinsic hardness of the nitrided layer
  • The longer the nitriding time, the greater the nitriding hardness depth (NHD).
  • The higher the temperature (500°C - 600°C), the deeper the nitrogen diffuses into the material in the same treatment time
  • The higher the alloy content of the material, the higher the nitriding hardness of the material. However, the nitrogen’s penetration depth into the material is also decreased.

Areas of application

Gas nitriding is particularly suitable for alloy materials, as they contain nitride-forming elements. Examples include chromium, molybdenum, vanadium, and aluminium. These materials include tool steels (cold worked and hot worked steels as well as sectional steels) and spring steel, which is widely used in the automotive industry. Materials previously hardened or tempered will produce the best results. In contrast, plasma nitriding is more commonly used for stainless steel or high-alloy materials.

Typical components:

  • Gearboxes
  • Valve components
  • Springs
  • Gear wheels
  • Drive shafts
  • Guide rails
  • Extruder screws
  • Spindles
  • Cam discs
  • Hydraulic cylinders
  • Forging dies
  • Bending punches
  • Die plates
  • Injection moulding tools
  • Camshafts
  • Crankshafts
  • Injection nozzles


Summary: Which materials are suitable?

  • Nitriding steels (for high surface hardness alloyed with aluminium, chromium, molybdenum, and vanadium)
  • Quenched and tempered steels
  • Steel materials
  • Cast materials
  • Sintered materials


Check list: Ordering gas nitriding

If you would like us to treat your workpieces or materials using gas nitriding, we will gladly advise you on the best procedure. You can use the check list below to make your preparations for the order.

  • Which material is to be treated, and what is its condition?
  • What is the target hardness (including tolerance range in HV)?
  • What is the desired nitriding hardness depth (including tolerance range in mm)?
  • If applicable, which areas should be nitrided, and where can the hardness be measured?
  • If applicable, how thick should the compound layer be (including tolerance range in μm)?

For gas nitriding to be successful, the surface of the workpiece must additionally meet the following requirements:

  • Free of oil, grease, and rust
  • Metallically blank
  • Neither decarbonised nor oxidised
  • No edge layers
  • Ideally no surface compaction present, as this hinders the formation of the nitrided layer


Key technical figures:

  • Temperature: up to 600 °C
  • Size of furnace: Diameter up to 1,100 X 3,300 mm
  • Processing time: 12 hours or longer
  • Nitriding hardness depth: up to 0.6 mm

Suitable materials

Select material table
    Quenched and tempered steels / structural steels
    Nitriding steels
    Case-hardened steels
    Cold-work steels / Hot-work steels
Material groupShort nameNumberNitriding hardness depth in mm
Structural steelsSt52-3/S355J2G31.05700,20-0,40
Quenched and tempered steelsC351.05010,20-0,40
C60 1.06010,20-0,40
Material groupShort nameNumberNitriding hardness depth in mmHardness in HV
Nitriding steels31CrMo12185150,20-0,30750-900
Material groupShort nameNumberNitriding hardness depth in mmHardness in HV
Case-hardened steelsC15104010,20-0,40300-500
Material groupShort nameNumberNitriding hardness depth in mmHardness in HV
Cold-work steels100Cr61.20670,20-0,30500-700
Hot-work steels55NiCrMoV61.27130,20-0,30550-700