AMS 2774
Heat Treatment of Wrought Nickel Alloy and Cobalt Alloy Parts
Solution treatment, stabilisation, precipitation (ageing), annealing and stress relief of wrought nickel-base and cobalt-base alloy parts such as Inconel 718, 625, X-750, Waspaloy, Hastelloy X, René 41, Haynes 25 (L-605) and 188.
What AMS 2774 specifies
AMS 2774 sets the heat-treatment controls for wrought nickel and cobalt superalloy parts, whose properties depend on precisely timed precipitation. It requires vacuum or protective-atmosphere furnaces with AMS 2750 pyrometry, strict cleanliness — no sulfur-bearing marking inks, lubricants or fingerprints, since sulfur embrittles nickel alloys at temperature — and cooling after solution treating fast enough to hold the strengthening elements in solution. Cycle parameters come from the material specification and are reproduced as controls: for Inconel 718 (AMS 5662/5663) solution at 1700–1850 °F (925–1010 °C) then age at 1325 °F (718 °C) for 8 h, furnace cool to 1150 °F (620 °C) and hold for a total of 18 h; Waspaloy is solution treated, stabilised at 1550 °F (845 °C) and aged at 1400 °F (760 °C); Hastelloy X and L-605 are solution annealed near 2150–2250 °F (1175–1230 °C). Acceptance is by hardness, tensile and, where the material specification requires, stress-rupture tests on lot coupons.
Tests and the drawing call-out
Tests the document imposes
- Hardness per ASTM E18 (Rockwell C) or ASTM E10 on each lot
- Room-temperature tensile per ASTM E8/E8M and elevated-temperature tensile per ASTM E21 when specified
- Stress-rupture per ASTM E139 (for example Inconel 718 at 1200 °F / 100 ksi, 23 h minimum) when the material specification requires it
- Grain size per ASTM E112 and microstructure (delta phase) check when specified
- Surface cleanliness and discoloration inspection; furnace TUS / SAT per AMS 2750
How to cite it
Drawing call-out
HEAT TREAT PER AMS 2774: SOLUTION TREAT AND PRECIPITATION HARDEN INCONEL 718 PER AMS 5663, 36 HRC MINAngle brackets mark the choices the drawing must make; every finish page shows a completed example.
Heat treatments specified to AMS 2774
| Treatment | Role | Cost |
|---|---|---|
Age (Inconel 718) is a precipitation-hardening condition for Inconel 718 (UNS N07718) and Alloy 718 AM. | Governing | $$$$ |
Solution annealing dissolves detrimental precipitates and restores a single-phase matrix in austenitic stainless and many nickel alloys. | Governing | $$$ |
AMS 2774 — frequently asked
Why the fuss about sulfur?
Sulfur diffuses along nickel grain boundaries above about 1200 °F and forms a low-melting nickel sulfide that causes intergranular cracking; a fingerprint or a sulfurised cutting oil is enough. AMS 2774 requires parts to be cleaned of all oils, inks and residues and heat treated in vacuum or clean inert atmosphere on sulfur-free fixtures.
What does the 718 age actually do?
After solution treating, which sets grain size and dissolves the strengthening phases, the 1325 °F step nucleates fine gamma-double-prime Ni3Nb and gamma-prime precipitates; the slow cool and 1150 °F hold grow them to peak strength. The result is at least 36 HRC, 185 ksi (1275 MPa) tensile and 150 ksi (1035 MPa) yield per AMS 5663.
Can 718 be machined before ageing?
Yes, and it usually is: solution-treated 718 (AMS 5662) is markedly softer and more machinable, and the age produces only a small, predictable dimensional change, so finish-machined parts are aged to size with an allowance from the heat treater's data. Threads and bores are commonly finished before the age.
Which furnace should be used?
Vacuum is standard: it avoids oxidation and chromium depletion, and fan-forced gas cooling meets the "air cool or faster" requirement after solution treating. Air furnaces are acceptable only when the oxide will be removed and the material specification allows it; AMS 2769 gives the vacuum practice.
AMS 2774 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 ↗