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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 5596Inconel 625 — Sheet, Strip, and Plate
Alloy
Inconel 625 (UNS N06625)
Product form
Sheet, strip, and plate in annealed condition
Condition
Annealed — 1093°C (2000°F) min, rapid cool. No aging cycle.
UTS minimum
120 ksi (827 MPa)
Yield minimum
60 ksi (414 MPa)
Hardness max
241 HB (annealed)
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 thermal requirements as AMS 5596.
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 5596. Since 625 cannot be aged, there is no condition suffix to specify — annealed is the only available state.
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 5664 (solution treated and double aged — final strength condition).[2][3]
AMS 5662Inconel 718 — Bar, Annealed (Pre-Machining Condition)
Alloy
Inconel 718 (UNS N07718)
Condition
Solution annealed only — NOT aged. Softest machineable condition for 718.
UTS minimum
150 ksi (1034 MPa)
Yield minimum
75 ksi (517 MPa)
Hardness max
363 HB (~38 HRC)
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 5664Inconel 718 — Bar, Solution Treated and Double Aged (Peak Condition)
Alloy
Inconel 718 (UNS N07718)
Condition
Solution annealed at 980°C (1800°F) + double aged: 718°C (1325°F) / 8 hr furnace cool to 621°C (1150°F) / 8 hr + air cool
UTS minimum
185 ksi (1276 MPa)
Yield minimum
150 ksi (1034 MPa)
Hardness
≤444 HB (≈45 HRC) — extremely hard and work-hardening
Availability
Requires aging cycle per AMS 2774 — typically not stocked aged; parts are aged after rough machining
Typical applications
Jet engine discs, structural aerospace fasteners, turbine shafts, downhole tooling, high-temp structural components
AMS 5663Inconel 718 — Bar, Direct Aged (DA) Condition
Condition
Direct aged without prior solution anneal. Higher yield strength than AMS 5664, lower ductility.
UTS minimum
200 ksi (1379 MPa)
Yield minimum
170 ksi (1172 MPa)
When specified
When maximum yield strength is required above AMS 5664 capability. Rarely called out outside of specific aerospace and defense applications.
Availability
Specialty — confirm lead time
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 5664 Double Aging Cycle (per 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
8 hours + 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.
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 at peak strength (AMS 5664). 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 5664
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 5664 properties) should be stated as a post-process requirement.
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.
