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Exotic Alloys · Inconel · AMS Specifications
Inconel Heat Treatment Conditions
and AMS Specifications
The AMS specifications for Inconel are not interchangeable. The spec you call out on your drawing determines the alloy, the product form, the heat treatment condition, and the mechanical property minimums your parts must meet. Getting this wrong — or leaving it unspecified — creates ambiguity that results in wrong material, incorrect properties, and potential nonconformances on a finished part.
Key AMS Specifications — Inconel 625
Inconel 625 is a solid-solution alloy — it cannot be precipitation hardened. The AMS specifications cover different product forms, all in annealed condition.[1]
AMS 5599Inconel 625 — Sheet, Strip, and Plate (Annealed)
Alloy
Inconel 625 (UNS N06625)
Product form
Sheet, strip, and plate in annealed condition
Condition
Annealed (mill anneal, roughly 1750–1900°F / 954–1038°C). No aging cycle.
UTS minimum
120 ksi (827 MPa)
Yield minimum
60 ksi (414 MPa)
Hardness max
241 HB (annealed)
Solution-annealed grade
AMS 5869: solution annealed at 1093°C (2000°F) minimum with rapid cool; 100 ksi (689 MPa) UTS / 40 ksi (276 MPa) yield minimum. Lower strength, better creep and thermal stability for high-temperature service. Specify it, not AMS 5599, when the part runs hot.
Not to be confused with
AMS 5596, which is Inconel 718 sheet, strip, and plate, not 625.
Typical applications
Chemical processing equipment, heat exchangers, marine components, exhaust systems, welded fabrications
AMS 5666Inconel 625 — Bar, Rod, Wire, Forgings
Alloy
Inconel 625 (UNS N06625)
Product form
Bar, rod, wire, and forgings in annealed condition
Condition
Annealed. Same condition and minimums as AMS 5599 (120 ksi UTS / 60 ksi yield / 30% elongation).
UTS minimum
120 ksi (827 MPa)
Yield minimum
60 ksi (414 MPa)
Typical applications
Precision machined components, shafts, fittings, fasteners, offshore structural members
625 drawing callout
For machined bar stock: Nickel Alloy Bar, Inconel 625 (N06625), Annealed, per AMS 5666. For plate: Nickel Alloy Plate, Inconel 625, Annealed, per AMS 5599. For plate in high-temperature service: Nickel Alloy Plate, Inconel 625, Solution Annealed, per AMS 5869. Since 625 cannot be aged, there is no aging condition to specify; the only choice is annealed (AMS 5599/5666) or solution annealed (AMS 5869).
Key AMS Specifications — Inconel 718
Inconel 718 has multiple governing specifications based on product form and heat treatment condition. The most important distinction for machined components is between AMS 5662 (annealed — for machining before aging) and AMS 5663 (solution treated and aged, the standard finished-part condition). AMS 5664 is a different, 1950°F solution treatment, covered below.[2][3]
AMS 5662Inconel 718 — Bar, Annealed (Pre-Machining Condition)
Alloy
Inconel 718 (UNS N07718)
Condition
Solution treated at 968°C (1775°F), precipitation hardenable. NOT aged; delivered soft. Softest machineable condition for 718.
UTS (typical, annealed)
150 ksi (1034 MPa). A typical as-delivered value, not a spec minimum: AMS 5662's tensile minimums are verified on test coupons after aging.
Yield (typical, annealed)
75 ksi (517 MPa), typical
Hardness max
363 HB (38 HRC); typically about 20–25 HRC as delivered
Why it's specified
Parts that will be rough machined, then sent out for double aging (AMS 2774) before final machining. This is the
preferred machining sequence.
Availability
Widely stocked — most common 718 bar form in distributors
AMS 5663Inconel 718 — Bar, Solution Treated and Aged (Standard Aged Condition)
Alloy
Inconel 718 (UNS N07718)
Condition
Solution treated at 968°C (1775°F) + double aged per AMS 2774: 718°C (1325°F) / 8 h, furnace cool to 621°C (1150°F), hold until 18 h total, air cool. This is exactly what AMS 5662 stock becomes after aging.
UTS minimum
185 ksi (1276 MPa)
Yield minimum
150 ksi (1034 MPa)
Hardness minimum
331 HB (about 36 HRC); typical aged 36–44 HRC. Extremely hard and work-hardening.
Availability
Requires aging cycle per AMS 2774 — typically not stocked aged; parts are rough machined from AMS 5662 stock and aged, or bar is ordered from the mill already aged
Typical applications
Jet engine discs, structural aerospace fasteners, turbine shafts, downhole tooling, high-temp structural components
AMS 5664Inconel 718 — Bar, 1950°F Solution Treated and Aged (Notch-Rupture / Creep Condition)
Condition
Solution treated at 1066°C (1950°F) + aged 760°C (1400°F) / 10 h, furnace cool to 649°C (1200°F), hold until 20 h total, air cool. The higher solution temperature and hotter age give better stress-rupture (notch) ductility and creep resistance at a small cost in tensile strength.
UTS minimum
180 ksi (1241 MPa)
Yield minimum
150 ksi (1034 MPa)
When specified
Where notch-rupture ductility and creep matter more than peak tensile strength: oil and gas, some turbine hardware. It is not a "peak" condition, and it cannot be produced by aging AMS 5662 bar; the 1950°F solution treatment has to be done before the age, so order the material to AMS 5664.
Availability
Specialty — confirm lead time
One more condition exists: direct aged (DA) bar, aged straight from the hot-working temperature with no separate solution treatment, is covered by AMS 5962. Typical DA properties are about 200 ksi UTS / 170 ksi yield with lower ductility. It is a mill product for specialty aerospace parts such as turbine discs; there is no AMS 5663 basis for direct aging, and a heat treater cannot produce it from stock bar.
The Double Aging Cycle — What Happens in the Furnace
The precipitation hardening cycle for Inconel 718 is a two-step process — often called a "double aging" or "two-stage aging" cycle — that produces two distinct strengthening precipitate phases: γ″ (gamma double prime, Ni₃Nb) and γ′ (gamma prime, Ni₃(Al,Ti)). The two-step process is designed to nucleate γ″ at the higher temperature and grow it at the lower temperature, producing an optimal precipitate size distribution.[2]
AMS 5663 Double Aging Cycle (AMS 2774)
Step 1
1325°F / 718°C
8 hours
Nucleate γ″ precipitates
→
Transition
Furnace cool
to 1150°F / 621°C
Controlled rate
→
Step 2
1150°F / 621°C
Hold until 18 h total, then air cool
Grow and stabilize γ″
Total thermal cycle: approximately 20–24 hours including heat-up, hold, and cool times. Performed in vacuum or inert atmosphere furnace to prevent oxidation.
AMS 2774 double aging cycle
Furnace temperature against elapsed time for the AMS 5663 cycle shown above: 1325°F for 8 h, furnace cool to 1150°F, hold until 18 h total, then air cool. Hold times and temperatures are from the flow above; the furnace-cool slope and the air-cool end point are drawn schematically. Hover a point for the step.
All 718 Condition Options — At a Glance
Critical drawing callout note — always specify the condition
A drawing that calls out "Inconel 718" without specifying the AMS specification and condition is ambiguous. The shop or distributor cannot determine whether you want annealed bar for rough machining (AMS 5662) or aged bar in its standard heat-treated condition (AMS 5663). The correct callouts are:
For bar to be machined then aged: Nickel Alloy Bar, IN718, Annealed, AMS 5662
For bar already in final condition: Nickel Alloy Bar, IN718, Solution Treated and Aged, AMS 5663
If your part will be rough machined from AMS 5662 stock, then sent out for the double aging cycle per AMS 2774, then final machined — which is the recommended sequence — the material note on the drawing should reference AMS 5662, and the required final condition (AMS 5663 properties) should be stated as a post-process requirement. If the drawing calls for AMS 5664, that is a different 1950°F solution treatment that cannot be produced by aging AMS 5662 stock; the material has to be ordered to AMS 5664.
Need help specifying the right Inconel condition?
Our engineering team reviews material and heat treatment callouts as part of every quote. We coordinate with certified heat treat vendors and verify certs on receipt.