AMS 2759/8
Ion Nitriding
Ion (plasma, glow-discharge) nitriding of steel parts — low-alloy, tool, martensitic and precipitation-hardening stainless and, with sputter activation, austenitic stainless — including pre-treatment, process control and verification of case depth, surface hardness and compound layer.
What AMS 2759/8 specifies
AMS 2759/8 covers nitriding in a low-pressure nitrogen–hydrogen glow discharge (pulsed DC plasma) at roughly 750–1050 °F (400–565 °C), where the part is the cathode and the plasma both heats the surface and sputters away the passive oxide that blocks conventional gas nitriding of stainless steels. It applies to low-alloy steels (4140, 4340, Nitralloy), tool steels (H13, D2, A2), martensitic and PH stainless (410, 17-4PH, 15-5PH) and, with adequate depassivation, austenitic grades. The sheet requires prior hardening and tempering above the nitriding temperature, clean oxide-free surfaces, and control of gas ratio, pressure, voltage, current and time so that the compound layer can be specified as none (diffusion zone only), thin monophase gamma-prime, or epsilon. Case depth and surface hardness are verified by microhardness traverse and light-load hardness on coupons processed with the lot, compound-layer thickness by metallography. Geometry limits — hollow-cathode overheating in narrow slots and blind holes, mechanical rather than paint masking — are part of the process qualification.
Tests and the drawing call-out
Tests the document imposes
- Effective case depth by microhardness traverse per ASTM E384 (HK or HV, 100–500 gf) on a lot coupon
- Surface hardness per ASTM E18 superficial scale (HR15N) or ASTM E384 with light load
- Compound (white) layer thickness and phase by metallographic cross-section (ASTM E3 / E407); XRD for gamma-prime / epsilon when specified
- Core hardness per ASTM E18 after nitriding
- Process records: gas composition, pressure, voltage / current, part temperature (thermocouple in a dummy part), time; pyrometry per AMS 2750
How to cite it
Drawing call-out
ION NITRIDE PER AMS 2759/8, 4140 PREHARDENED 28–32 HRC, EFFECTIVE CASE DEPTH 0.010–0.015 IN, SURFACE 60 HRC MIN (HR15N), COMPOUND LAYER 0.0002 IN MAX; MASK THREADSAngle brackets mark the choices the drawing must make; every finish page shows a completed example.
Heat treatments specified to AMS 2759/8
| Treatment | Role | Cost |
|---|---|---|
Plasma nitriding uses a glow discharge to clean, heat, and diffuse nitrogen into ferrous surfaces. | Governing | $$$$ |
AMS 2759/8 — frequently asked
What does plasma do that gas nitriding cannot?
Ion bombardment strips the chromium oxide from stainless steels so they nitride without chemical depassivation, and the nitrogen activity is set by the N2:H2 ratio rather than ammonia dissociation, so the compound layer can be dialled from zero to a few micrometres. Lower temperatures (down to about 750 °F / 400 °C) let PH stainless and tool steels be nitrided below their tempering temperature.
How deep is a plasma-nitrided case?
Similar to gas nitriding for the same alloy and time: about 0.004–0.020 in (0.1–0.5 mm) effective in 10–60 h on low-alloy steels, but only 0.001–0.004 in (25–100 µm) on austenitic stainless because chromium nitrides slow diffusion. Surface hardness runs about 900–1100 HV on H13 and Nitralloy and over 1000 HV on nitrided austenitic stainless.
Why does the drawing need to show masking?
Plasma cannot be stopped with paint; areas are masked mechanically with fitted caps, plugs or shields, and small blind holes and narrow slots (below a few millimetres) can overheat by the hollow-cathode effect or receive no case at all. Call out the masked and non-critical zones so the fixtures can be designed.
Does plasma nitriding distort parts?
Very little: the treatment runs below the prior temper with no quench, so growth is a few micrometres per surface from nitrogen uptake and the compound layer, and shape is retained. Parts are normally finished before nitriding, with only a light polish afterwards if the surface finish is critical.
AMS 2759/8 is copyrighted by SAE International. This page explains the document so a drawing can be read; it does not reproduce the standard. Purchase the current edition from the publisher. Official source ↗