AMS 2759/5
Heat Treatment, Martensitic Corrosion-Resistant Steel Parts
Annealing, hardening, tempering and sub-zero treatment of martensitic corrosion-resistant steel parts such as 410, 416, 420, 431, 440A/B/C, 418 (Greek Ascoloy) and 422.
What AMS 2759/5 specifies
AMS 2759/5 covers the hardenable stainless steels used for valve parts, bearings, cutlery-grade tooling and fasteners: 410, 416, 420, 431, 440A/B/C, Greek Ascoloy and 422. It tabulates per-alloy annealing, austenitizing (about 1750–1850 °F / 955–1010 °C for 410 and 420, 1850–1950 °F / 1010–1065 °C for 440C), quenchant (oil or air/gas) and tempering temperatures for each hardness or tensile class. Because these steels lose corrosion resistance and toughness when tempered in the 750–1050 °F (400–565 °C) range, that band is avoided unless the drawing accepts it; 440C is normally tempered at 300–400 °F (150–205 °C) and may receive a -100 °F (-73 °C) sub-zero treatment before tempering to transform retained austenite, followed by a double temper. A protective atmosphere or vacuum is required to prevent scale and decarburization, and tempering must follow the quench promptly. Acceptance is by Rockwell hardness on every lot, with tensile tests where specified.
Tests and the drawing call-out
Tests the document imposes
- Rockwell C hardness per ASTM E18 on each lot (superficial HR15N / HR30N on thin sections)
- Tensile test per ASTM E8/E8M when the drawing specifies a tensile class (410 / 431 structural parts)
- Decarburization and scale check by metallographic cross-section
- Sub-zero treatment time and temperature record when specified
- Furnace TUS / SAT per AMS 2750
How to cite it
Drawing call-out
HEAT TREAT PER AMS 2759/5, 440C, 58 HRC MIN; SUB-ZERO TREAT; DOUBLE TEMPER; HARDNESS TEST PER ASTM E18Angle brackets mark the choices the drawing must make; every finish page shows a completed example.
Heat treatments specified to AMS 2759/5
| Treatment | Role | Cost |
|---|---|---|
Cryogenic treatment cools a previously hardened alloy below room temperature to transform retained austenite and improve dimensional stability. | Governing | $$ |
Quench and temper transforms hardenable steel to martensite and then tempers it to the required balance of strength and toughness. | Governing | $$ |
AMS 2759/5 — frequently asked
Why avoid the 750–1050 °F tempering range?
In that range chromium carbides precipitate at grain boundaries and the martensite passes through a temper-embrittlement trough: impact strength drops and pitting resistance falls sharply. 410 and 420 are therefore tempered either low (below about 750 °F) for hardness or high (above about 1050 °F) for toughness, and several fastener specifications forbid the intermediate band outright.
What hardness can 440C reach?
Austenitized around 1900 °F (1040 °C), oil or gas quenched and tempered at 300–400 °F it reaches 58–62 HRC. A sub-zero hold at -100 °F before the first temper converts retained austenite, adds about one HRC point and stabilises dimensions; tempering at 600 °F drops hardness to about 55 HRC.
Is an air furnace allowed?
Not for hardening. Martensitic stainless scales and loses chromium and carbon from the surface in air, so austenitizing is done in vacuum or a dry inert atmosphere; vacuum furnaces with high-pressure gas quench are the common route for 440C bearings and 420 mould parts because the parts come out bright.
Should I order 410 by tensile class or by hardness?
Structural 410 and 431 parts are usually ordered to a tensile class (for example 431 at 180–200 ksi) with hardness as the lot check; wear parts are ordered by HRC only. Give one or the other unless the material specification correlates them, otherwise the heat treater has two acceptance criteria that may disagree.
AMS 2759/5 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 ↗