AMS 2759/10
Automated Gaseous Nitriding Controlled by Nitriding Potential
Gas nitriding of steel parts in which the furnace atmosphere is controlled automatically by nitriding potential (KN), with the compound layer and diffusion zone specified as process targets.
What AMS 2759/10 specifies
AMS 2759/10 is the modern counterpart of AMS 2759/6: the same dissociated-ammonia nitriding at about 900–1075 °F (480–580 °C), but the atmosphere is measured continuously with hydrogen or ammonia sensors and the nitriding potential KN = p(NH3) / p(H2)^1.5 is held to a programmed set-point instead of being inferred from a manual dissociation reading. Using the Lehrer diagram the heat treater selects KN and temperature to produce a specified surface structure — no compound layer, a thin gamma-prime layer, or a thicker epsilon-rich layer — reproducibly on Nitralloy 135M, 4140, 4340, H11/H13 and PH stainless. The sheet requires the same prior hardening and tempering above the nitriding temperature, clean activated surfaces and coupons per lot; acceptance covers effective case depth by microhardness traverse, surface hardness, and compound-layer thickness and porosity by metallography. KN, temperature and time records form part of the certification.
Tests and the drawing call-out
Tests the document imposes
- Effective case depth by microhardness traverse per ASTM E384 on a lot coupon
- Surface hardness per ASTM E18 superficial scale (HR15N) or ASTM E384 with light load
- Compound layer thickness and porous zone by metallographic cross-section (ASTM E3)
- Core hardness per ASTM E18 after nitriding
- KN / temperature / time record from the atmosphere controller; sensor calibration; pyrometry per AMS 2750
How to cite it
Drawing call-out
NITRIDE PER AMS 2759/10, 4140 PREHARDENED 28–32 HRC, EFFECTIVE CASE 0.012–0.018 IN, SURFACE 88 HR15N MIN, COMPOUND LAYER 0.0002–0.0005 INAngle brackets mark the choices the drawing must make; every finish page shows a completed example.
Heat treatments specified to AMS 2759/10
| Treatment | Role | Cost |
|---|---|---|
Cryogenic treatment cools a previously hardened alloy below room temperature to transform retained austenite and improve dimensional stability. | Governing | $$ |
Martempering is an interrupted quench that equalizes austenitized steel just above its martensite-start temperature before cooling through martensite formation. | Governing | $$$ |
Spheroidize annealing converts lamellar cementite into rounded carbide particles in a ferrite matrix. | Governing | $$ |
Gas nitriding diffuses nitrogen into finished ferrous parts below the transformation temperature, producing a hard compound layer and diffusion zone without quenching. | Alternative | $$$$ |
AMS 2759/10 — frequently asked
What is nitriding potential?
KN = p(NH3) / p(H2)^1.5, the atmosphere ratio that fixes the nitrogen activity at the steel surface for a given temperature. A high KN builds a compound layer quickly; a low KN keeps the surface in the alpha or gamma-prime field of the Lehrer diagram and gives a diffusion zone with little or no white layer.
Why control KN instead of dissociation?
Dissociation percentage depends on flow, load surface area and furnace condition, so a fixed 25 % setting can give different nitrogen activity from run to run. KN calculated from measured hydrogen ties the process to the phase diagram, so compound-layer thickness repeats within a few micrometres and the certification carries an actual controlled variable.
Can I specify "no white layer"?
Yes — that is the main reason to cite /10. Running at low KN in the alpha field after an initial boost gives a diffusion-zone-only case that needs no post-grinding on gear teeth and fatigue-critical fillets. The trade is a slightly slower case build-up and lower surface hardness on low-alloy steels.
Is the case the same as under AMS 2759/6?
Same metallurgy and depth-time relationship — about 0.008–0.025 in (0.2–0.6 mm) in 20–80 h on 4140 or Nitralloy — but with the compound layer specified instead of merely accepted. Drawings citing /6 can move to /10 by adding a compound-layer range; the hardness and depth callouts do not change.
AMS 2759/10 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 ↗