AMS 2759
Heat Treatment of Steel Parts, General Requirements
General requirements for the heat treatment of carbon, low-alloy, corrosion-resistant, maraging and tool steel parts, applied together with the alloy-specific AMS 2759 slash sheets.
What AMS 2759 specifies
AMS 2759 is the base document for the AMS 2759/1 through /12 slash sheets: it carries the requirements common to every steel heat treatment so that each slash sheet only adds alloy-specific temperatures, quenchants and property tables. It sets furnace pyrometry through AMS 2750, defines heat-treat lots, and requires protective atmosphere, vacuum or salt where the slash sheet demands them. It limits surface damage: total decarburization is not permitted, partial decarburization and carburization are held to depth limits that depend on strength class and on whether stock is removed afterwards, and intergranular oxidation is controlled. It also covers cleaning before heat treatment, racking, quench media and quench delay, prompt tempering, straightening restrictions, hydrogen-embrittlement baking after plating (AMS 2759/9), and lot acceptance by hardness (ASTM E18, E10, E384) or tensile test. Drawings cite AMS 2759 together with the slash sheet, the alloy and the target hardness or tensile class.
Tests and the drawing call-out
Tests the document imposes
- Hardness per ASTM E18 (Rockwell), ASTM E10 (Brinell) or ASTM E384 (microindentation) on each lot after final temper
- Tensile test per ASTM E8/E8M when the drawing specifies a tensile class
- Decarburization and carburization depth by metallographic cross-section or microhardness traverse
- Furnace temperature uniformity survey and system accuracy test records per AMS 2750
- Process-record review: load chart, quench delay, temper delay, time at temperature
How to cite it
Drawing call-out
HEAT TREAT PER AMS 2759 AND AMS 2759/<SLASH SHEET>, <ALLOY>, <HRC RANGE OR TENSILE CLASS>; HARDNESS TEST PER ASTM E18 AT LOCATION SHOWNAngle brackets mark the choices the drawing must make; every finish page shows a completed example.
Heat treatments specified to AMS 2759
| Treatment | Role | Cost |
|---|---|---|
Austempering forms bainite by quenching austenitized steel or ductile iron into a hot bath and holding isothermally. | Governing | $$$ |
Cryogenic treatment cools a previously hardened alloy below room temperature to transform retained austenite and improve dimensional stability. | Governing | $$ |
Full annealing heats steel through its critical transformation range and then furnace-cools it slowly. | Governing | $$ |
Martempering is an interrupted quench that equalizes austenitized steel just above its martensite-start temperature before cooling through martensite formation. | Governing | $$$ |
Normalizing heats steel above its critical range and cools it in air. | Governing | $ |
Process annealing is a subcritical softening cycle inserted between cold-working operations. | Governing | $ |
Quench and temper transforms hardenable steel to martensite and then tempers it to the required balance of strength and toughness. | Governing | $$ |
Solution annealing dissolves detrimental precipitates and restores a single-phase matrix in austenitic stainless and many nickel alloys. | Governing | $$$ |
Spheroidize annealing converts lamellar cementite into rounded carbide particles in a ferrite matrix. | Governing | $$ |
Stress relief reduces residual stress from welding, machining, forming, casting, or additive manufacture without intentionally changing the bulk microstructure. | Governing | $ |
Carbonitriding diffuses both carbon and nitrogen into low-carbon steel in the austenitic range, then quenches and tempers the surface to martensite. | Related | $$ |
Flame hardening rapidly austenitizes selected steel surfaces with an oxy-fuel flame and immediately quenches them to martensite. | Related | $$ |
Induction hardening uses an alternating magnetic field to austenitize selected steel surfaces, followed immediately by quenching. | Related | $$ |
AMS 2759 — frequently asked
Do I cite AMS 2759 alone or with a slash sheet?
Always with the slash sheet. AMS 2759 has no alloy tables; the temperatures, quenchants and property tables live in /1 (carbon and low-alloy below 220 ksi), /2 (220 ksi and up), /3 (PH and maraging), /4 (austenitic), /5 (martensitic stainless) and so on. A note reading only "HEAT TREAT PER AMS 2759" leaves the heat treater to pick the sheet from the alloy, which most quality systems reject.
Does AMS 2759 allow any decarburization?
Total decarburization (a fully ferritic surface layer) is not permitted. Partial decarburization is allowed only to a depth that depends on the strength class and on whether finish machining or grinding will remove the surface afterwards. Parts finished before heat treatment should be processed in a protective atmosphere or vacuum so the allowance is not consumed.
How does AMS 2759 relate to MIL-H-6875?
MIL-H-6875 was the DoD specification for heat treating steel; it was republished as AMS-H-6875 and then cancelled in favour of AMS 2759 and its slash sheets. Older drawings still cite MIL-H-6875; the accepted substitution is AMS 2759 with the slash sheet that matches the alloy and strength.
Who performs the hardness test and on how many parts?
The heat treater tests each lot after final tempering per the sampling plan in the slash sheet, using ASTM E18 (Rockwell), ASTM E10 (Brinell) or ASTM E384 where sections are thin. The test location must be on the part or on a coupon of the same heat, product form and section that went through the furnace with the lot.
AMS 2759 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 ↗