# Plasma nitriding

Plasma-assisted nitrogen diffusion, process variants, layer requirements and component-specific acceptance.

Reviewed: 2026-11-01

Tags: processes, heat-treatment, nitriding

The example defines depth at **core hardness + 50 HV** at a stated force. With **340 HV core**, the threshold is **390 HV**. A traverse of **430 HV at 0.300 mm** and **350 HV at 0.400 mm** interpolates to **0.350 mm**. Removing **0.020 mm** normally leaves **0.330 mm** if the profile is unchanged. Verify the finished reference surface and ordered method.

## Mechanism and process boundary

Plasma nitriding uses glow discharge to supply nitrogen for diffusion. ASM distinguishes direct-current, pulsed-current and active-screen methods. Control atmosphere, pressure and part temperature. [Elwar and Hunger, ASM Handbook volume 4A, 2013, pages 690–703](https://dl.asminternational.org/handbooks/edited-volume/18/chapter-abstract/275906/Plasma-Ion-Nitriding-and-Nitrocarburizing-of)

Gas and plasma nitriding share nitrogen diffusion as an objective but provide the reactive environment differently. TWI describes nitrogen/hydrogen gas in its plasma-nitriding explanation; Nitrex contrasts plasma equipment with ammonia-based gas nitriding. A matching surface-hardness result does not authorize substitution between routes, because layer structure, treatment distribution and the rest of the qualified process still matter. [TWI plasma treatment](https://www.twi-global.com/technical-knowledge/faqs/faq-what-is-plasma-carburising-plasma-nitriding), [Nitrex gas/plasma comparison](https://www.nitrex.com/en/ion-plasma-nitriding-versus-gas-nitriding/)

## Direct, pulsed and active-screen arrangements

| Arrangement | Bounded distinction | Information to preserve |
| --- | --- | --- |
| Direct cathodic treatment | The workpiece acts as a cathode in the discharge | Electrical contact, positioning, discharge and temperature controls |
| Pulsed plasma | Electrical power is applied intermittently | Approved pulse/control arrangement; this is not a universal time-temperature recipe |
| Active-screen process | A surrounding screen supports the discharge in the identified system | Screen geometry, load arrangement, part electrical condition and heating method |

A plasma-equipment manufacturer's glossary describes the direct workpiece-cathode arrangement. As a separate named example, AMP's **Nitro-Tool** places the plasma discharge on an active screen, with no discharge on its workpieces and resistance heaters maintaining temperature. Other screen-assisted arrangements need not share that exact configuration. Specify the actual system rather than treating “active screen” as a guarantee of identical heating or surface chemistry. [Diener plasma-nitriding glossary](https://www.plasma.com/en/plasma-technology-glossary/plasma-nitriding/), [AMP Nitro-Tool](https://amphtt.com/en/azotowanie-nitro-tool)

Uddeholm describes pulsed plasma as reducing over-tempering risk through improved local temperature control and identifies sharp-corner layer thickening as a concern with conventional nitriding. Those observations support geometry-specific development; they do not prove that pulsing or a screen eliminates every edge effect, overheating risk or inaccessible-feature limitation. [Uddeholm heat-treatment guide, printed page 13](https://www.uddeholm.com/app/uploads/sites/239/2024/06/Tech-Uddeholm-Heat-treatment-EN.pdf)

## Compound layer, diffusion zone and material response

Nitrex distinguishes the outer compound or white layer from the underlying diffusion zone. A specification should identify both where relevant, rather than reporting one ambiguous “case thickness.” Required compound-layer thickness, porosity or phase constitution can differ from the hardness-depth requirement. Surface hardness, diffusion-zone support and final component performance are separate acceptance questions. [Nitrex layer explanation](https://www.nitrex.com/en/solutions/furnaces-technologies/process-technologies/nitreg-technologies/gas-nitriding-nitreg/)

A bounded producer example illustrates the importance of labels: RUBIG's **Typical Results After Plasma Nitriding**, printed **©03/2020**, gives its Ck45 row a surface-hardness range of **250–500 HV1**, nitriding-hardness depth **0.2–0.6 mm** and white-layer thickness **2–10 µm**. The sheet explicitly calls these guidelines influenced by many factors. They are neither guaranteed properties for every Ck45 part nor interchangeable measurements of one layer. Its cross-standard steel-name columns should not replace the ordered material specification. [RUBIG typical-results sheet](https://cdn.rubig.com/assets/rubig.com/dokumente/Anlagentechnik/rubig-anlagentechnik-dokument-plasmanitrierergebnisse-en.pdf)

Supply alloy, product form, incoming heat treatment/core hardness, cold work, surface condition and previous processing. Uddeholm's hardened-tool-steel guidance requires a mechanically and microstructurally stable core and prior tempering above the nitriding temperature to avoid softening. Apply the actual alloy's requirements; this is not a complete cycle for all materials. [Uddeholm, printed page 12](https://www.uddeholm.com/app/uploads/sites/239/2024/06/Tech-Uddeholm-Heat-treatment-EN.pdf)

Stainless steel needs a separate corrosion assessment. Uddeholm warns that conventional nitriding can impair corrosion resistance of high-chromium corrosion-resistant steel. ELTROPULS's **Eltro-Corr** instead describes a controlled low-temperature route intended to avoid chromium precipitation and substantially retain corrosion behavior. That named process does not establish that every plasma-nitrided stainless component preserves its original corrosion performance. Specify the alloy, service exposure and corresponding qualification. [Uddeholm corrosion caution](https://www.uddeholm.com/app/uploads/sites/239/2024/06/Tech-Uddeholm-Heat-treatment-EN.pdf), [Eltro-Corr](https://www.eltropuls.de/en/eltro-corr/)

## Geometry and manufacturing sequence

Discuss bores, close gaps, edges, thin sections, contact points and mixed-section loads with the processor. Identify significant and protected surfaces on the drawing and establish representative inspection locations. The glow visible on an accessible face is not proof of acceptable depth, temperature or layer constitution throughout a complex component.

Keep surface preparation, activation, nitriding, any post-oxidation or finishing and subsequent coating in the approved route. RUBIG's service description treats post-oxidation as an additional process used to modify sliding and corrosion behavior. A nitrided-and-oxidized surface is therefore a specified system, not an automatic property of every plasma-nitrided part. [RUBIG plasma-nitriding service](https://www.rubig.com/en/heat-treatment/steel/plasma-nitriding)

Retain final dimensional inspection even where low distortion is expected. Establish permitted polishing or grinding, masking transitions and any later thermal exposure. Material removal changes the layer remaining at the surface; a final dimension alone does not prove the required compound layer or hardness-depth profile survived.

## Measurement and original depth example

**ISO 18203:2026**, edition 2, January 2026, covers determination of surface-hardened-layer thickness quantities, including nitriding-hardness depth. Its record identifies the 2016 edition as withdrawn. Use the applicable ordered definition and test conditions rather than borrowing a carburized-case threshold or treating a metallographic compound-layer thickness as nitriding-hardness depth. [ISO 18203:2026](https://www.iso.org/standard/89021.html)

Struers describes cross-sectional hardness traverses and a nitriding limit related to core hardness. Record the actual specified criterion, force, spacing, preparation, section location and reference surface. The public guidance does not set one acceptance depth for all parts. [Struers Vickers/depth guidance](https://www.struers.com/en/knowledge/hardness-testing/vickers)

**Original illustration:** assume the purchaser explicitly defines the threshold as core hardness plus **50 HV at a stated force**, and the measured core value is **340 HV**. The example threshold is **390 HV**. Assume a descending traverse reads **430 HV at 0.300 mm** and **350 HV at 0.400 mm**. Linear interpolation gives:

`depth = 0.300 + (430 − 390)/(430 − 350) × 0.100 = 0.350 mm`.

If approved finishing removes **0.020 mm normal to the surface**, and the remaining hardness profile and core value are assumed unchanged, the ideal remaining depth is **0.330 mm**. These assumptions do not establish a permissible finishing allowance, ISO test procedure or growth factor. The separately measured compound layer and finished dimensions still need their own acceptance.

## Release information and source versions

Provide part/material traceability, starting condition, selected equipment/route, significant and masked surfaces, compound-layer and depth requirements, hardness/core limits, final dimensions and functional tests. Agree representative sections, lot sampling and permitted rework. Preserve actual process and inspection records against the delivered parts.

Uddeholm's guide prints **Edition 10, 04.2018**, despite its 2024 hosting path. RUBIG's sheet prints **©03/2020**; the ASM chapter is published **2013**. Undated supplier web examples remain separate from contractual process limits. The arithmetic above is original and deliberately bounded.

## Related reference

[Grades, tempers and conditions](../../materials/grades-tempers-and-conditions.md)