AMS 2759/1
Heat Treatment of Carbon and Low-Alloy Steel Parts, Minimum Tensile Strength Below 220 ksi (1517 MPa)
Heat treatment of carbon and low-alloy steel parts (1045, 4130, 4140, 4340, 8740 and similar) to minimum tensile strengths below 220 ksi (1517 MPa), including normalizing, annealing, hardening, tempering and stress relief.
What AMS 2759/1 specifies
AMS 2759/1 is the slash sheet behind most quenched-and-tempered aerospace steel: carbon and low-alloy grades such as 4130, 4140, 4340, 8740 and 1045 finished below 220 ksi. Its tables give, for each alloy, the normalizing and annealing temperatures, the austenitizing range with the permitted quenchant (water, polymer, oil or salt), and the tempering bands that produce each tensile-strength class, together with the hardness equivalent the heat treater may use for lot acceptance (160–180 ksi is about 36–41 HRC, 180–200 ksi about 39–43 HRC). It requires furnace pyrometry per AMS 2750, a protective atmosphere or vacuum when the surface will not be machined afterwards, prompt tempering after the quench, and it limits partial decarburization by strength class and stock removal. Acceptance is by Rockwell or Brinell hardness on every lot, with tensile tests when the drawing calls for them.
AMS 2759/1 types and classes
Every designation the document defines, with the thickness it requires and the tests it imposes.
| Designation | Meaning | Requirement / test |
|---|---|---|
125–145 ksi | Minimum tensile 125 ksi (860 MPa), maximum 145 ksi (1000 MPa); the lowest quenched-and-tempered class in the sheet, typical for 4130 and 1045 fittings. | Hardness per ASTM E18 / E10 against the hardness-equivalent band in the sheet |
140–160 ksi | Minimum tensile 140 ksi (965 MPa), maximum 160 ksi (1105 MPa). | Hardness per ASTM E18 / E10 against the hardness-equivalent band in the sheet |
150–170 ksi | Minimum tensile 150 ksi (1035 MPa), maximum 170 ksi (1170 MPa). | Hardness per ASTM E18 / E10 against the hardness-equivalent band in the sheet |
160–180 ksi | Minimum tensile 160 ksi (1105 MPa), maximum 180 ksi (1240 MPa); the common class for 4140 shafts and fittings, hardness equivalent about 36–41 HRC. | Hardness per ASTM E18 / E10 against the hardness-equivalent band in the sheet |
180–200 ksi | Minimum tensile 180 ksi (1240 MPa), maximum 200 ksi (1380 MPa); typical for 4340 and 8740 structural parts, hardness equivalent about 39–43 HRC. | Hardness per ASTM E18 / E10 against the hardness-equivalent band in the sheet |
200–220 ksi | Minimum tensile 200 ksi (1380 MPa), maximum 220 ksi (1517 MPa); the top class of the sheet — anything with a 220 ksi minimum moves to AMS 2759/2. | Hardness per ASTM E18 / E10 against the hardness-equivalent band in the sheet |
Tests and the drawing call-out
Tests the document imposes
- Rockwell C or Brinell hardness per ASTM E18 / ASTM E10 on each lot after final temper
- Tensile test per ASTM E8/E8M when the drawing specifies tensile properties
- Partial decarburization depth by metallographic cross-section (ASTM E1077)
- Furnace class and instrumentation per AMS 2750 (TUS / SAT records)
- Microindentation hardness per ASTM E384 on thin sections
How to cite it
Drawing call-out
HEAT TREAT PER AMS 2759/1, 4140, 160–180 KSI (36–41 HRC); 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 2759/1
| Treatment | Role | Cost |
|---|---|---|
Full annealing heats steel through its critical transformation range and then furnace-cools it slowly. | Governing | $$ |
High-temperature tempering reheats quenched steel around 500–650 °C to produce tempered martensite with high toughness and moderate hardness. | Governing | $ |
Low-temperature tempering reheats freshly quenched steel at about 150–250 °C to relieve stress while retaining high martensitic hardness. | Governing | $ |
Martempering is an interrupted quench that equalizes austenitized steel just above its martensite-start temperature before cooling through martensite formation. | Governing | $$$ |
Medium-temperature tempering reheats quenched steel around 300–450 °C to trade some hardness for strength, elasticity, and improved toughness. | Governing | $ |
Normalizing heats steel above its critical range and cools it in air. | Governing | $ |
Quench and temper transforms hardenable steel to martensite and then tempers it to the required balance of strength and toughness. | Governing | $$ |
AMS 2759/1 — frequently asked
Should I specify a tensile class or an HRC range?
Specify the tensile class from the sheet (for example 160–180 ksi) when the material specification is written in tensile terms, and let the heat treater accept by the hardness equivalent in the table (about 36–41 HRC for that class). If you specify only an HRC range, pick one that maps to a single tensile class; a range like 38–46 HRC spans three classes and two very different tempering temperatures.
Can 4140 be heat treated to 220 ksi under this sheet?
No. Anything with a minimum tensile of 220 ksi (1517 MPa) or higher falls under AMS 2759/2, which adds tighter atmosphere, temper-delay, straightening and hydrogen controls. 4140 rarely reaches 220 ksi in useful sections anyway; 4340, 300M and D6AC are the /2 alloys.
Does the sheet allow an air furnace?
Yes, when enough stock is left for finish machining to remove the decarburized layer; the sheet limits partial decarburization by strength class and by whether stock is removed. Parts finished before heat treatment need endothermic gas, nitrogen-methanol, neutral salt or vacuum.
What happens if the lot fails hardness?
Parts that read soft may be re-hardened and re-tempered as a new lot; parts that read hard may be re-tempered at a higher temperature. Re-heat-treat cycles are limited and recorded on the certification, and a second re-austenitize normally needs purchaser approval because each cycle adds decarburization and distortion.
AMS 2759/1 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 ↗