AMS 2759/3
Heat Treatment, Precipitation-Hardening Corrosion-Resistant and Maraging Steel Parts
Solution treating, transformation, precipitation hardening and annealing of precipitation-hardening corrosion-resistant steels (17-4PH, 15-5PH, PH13-8Mo, 17-7PH, PH15-7Mo, AM350/355, Custom 450/455, A-286) and of 18Ni maraging steel parts.
What AMS 2759/3 specifies
AMS 2759/3 governs the heat treatment of precipitation-hardening stainless — martensitic 17-4PH, 15-5PH, PH13-8Mo, Custom 450/455, the semi-austenitic 17-7PH, PH15-7Mo, AM350/355, and iron-base A-286 — and of 18Ni maraging steels (200, 250 and 300 grades). For the martensitic grades it sets the solution (Condition A) temperature, 1900 °F (1040 °C) for 17-4PH and 15-5PH, and the ageing cycles that give the H conditions: H900 (900 °F / 480 °C, 1 h) through H925, H1025, H1075, H1100 and H1150 (4 h each) to the H1150M double cycle (1400 °F for 2 h, then 1150 °F for 4 h). For semi-austenitic grades it defines austenite conditioning, refrigeration (for example -100 °F / -73 °C for the RH950 condition of 17-7PH) and ageing; for maraging steel the 1500 °F (815 °C) solution anneal and 900 °F (480 °C) age. Ageing furnaces need tight AMS 2750 uniformity because properties shift quickly with temperature. Each lot is accepted by hardness, with tensile tests where specified.
Tests and the drawing call-out
Tests the document imposes
- Rockwell C hardness per ASTM E18 on each lot after ageing (Brinell per ASTM E10 on large sections)
- Tensile test per ASTM E8/E8M when the drawing specifies properties (H1150M and semi-austenitic conditions are commonly tensile tested)
- Refrigeration time and temperature record for R conditions
- Furnace TUS / SAT per AMS 2750, with load thermocouples where the sheet requires them
- Microstructure / delta-ferrite check when the material specification requires it
How to cite it
Drawing call-out
HEAT TREAT PER AMS 2759/3, 17-4PH (AMS 5643) TO CONDITION H1025, 35 HRC MIN; 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 2759/3
| Treatment | Role | Cost |
|---|---|---|
Q+T H1025 is a precipitation-hardening condition for 17-4 PH (S17400) and 15-5 PH (S15500). | Governing | $$ |
Q+T H1075 is a precipitation-hardening condition for 17-4 PH (S17400) and 15-5 PH (S15500). | Governing | $$ |
Q+T H1150 is a precipitation-hardening condition for 17-4 PH (S17400) and 15-5 PH (S15500). | Governing | $$ |
Q+T H900 is a precipitation-hardening condition for 17-4 PH (S17400) and 15-5 PH (S15500). | Governing | $$ |
AMS 2759/3 — frequently asked
What is the practical difference between H900 and H1150?
H900 gives the highest strength (190 ksi / 1310 MPa minimum tensile, about 40 HRC) but the lowest toughness and the poorest stress-corrosion resistance; H1025 (155 ksi, 35 HRC) and H1150 (135 ksi, 28 HRC) trade strength for toughness and corrosion behaviour. Most aerospace 17-4PH is used at H1025 or above, and H1150M where impact strength at low temperature matters.
Can I age directly from the bar supplier's Condition A?
Yes. AMS 5643 and ASTM A564 bar is supplied solution treated (Condition A, 363 HB maximum) so the part can be machined and then aged once under AMS 2759/3. Re-solution treating is needed only if the part has been welded, over-aged or otherwise had its Condition A structure disturbed.
Why is ageing furnace uniformity so tight?
A shift of 25 °F (14 °C) in an H900 age moves hardness by roughly one to two HRC points and can move the part out of its strength class, so the sheet requires ageing furnaces to meet a tight AMS 2750 class with load thermocouples where specified. Solution treating tolerates a wider band.
Does the sheet cover maraging steel?
Yes. The 18Ni maraging grades are solution annealed at about 1500 °F (815 °C) and aged near 900 °F (480 °C) for 3 to 6 h, with a small and predictable contraction, so parts can be finish machined before ageing. No quench is required, which is why maraging steels distort so little.
AMS 2759/3 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 ↗