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Incoloy A286 / (1.4980) / UNS S66286 / AMS 5731 / AMS 5732

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Incoloy A286, also widely known as Alloy A286, is an alloy that resembles stainless steel both in the elements it contains and in the proportions of those elements. Formed essentially from an iron-nickel-chromium alloy, the material also contains elements such as molybdenum and titanium. Molybdenum and titanium make the material more resistant to corrosion while also giving it extra mechanical strength.

Alloy A-286 is also designated UNS S66286, and the number 1.4980 is likewise used for Incoloy A-286. The material can be age hardened by heat treatment, and through this heat treatment A-286 gains a more durable mechanical structure. The alloy shows good mechanical properties and corrosion resistance up to 700 °C. It belongs to the austenitic group of materials and preserves that austenitic structure under all conditions.​‌​​‌​

Mechanically very strong and with good corrosion resistance at the same time, the material is frequently chosen for aerospace components and gas turbine blades. Also used in many fasteners, Incoloy A-286 is frequently used in vehicle engine components, in various special screws, in vehicle manifold systems, in parts subjected to high temperature and high load at the same time, and on oil and gas platforms.

Identity First — A-286 Is Not a Nickel Alloy​‌​​‌​

A-286 (UNS S66286 / W.Nr. 1.4980 / AISI Type 660) is an iron-based austenitic precipitation-hardening superalloy. The S that opens its UNS number places it in the stainless steel series — not the nickel-alloy N series (alloy 718 = N07718). ASTM’s own title reads “Precipitation Hardening Iron Base Superalloy…”. “Incoloy A-286” is a trade-name styling, and it is the single biggest reason buyers file this material as a nickel alloy.

The AMS Specifications — by Product Form AND Heat-Treat Condition​‌​​‌​

This table is the core of the page. The AMS set splits on two axes simultaneously: solution temperature (899 / 954 / 982 °C) and whether the mill ages it (supplied solution-treated, or supplied solution-treated and aged). Getting one axis right and the other wrong is the most common ordering error.​‌​​‌​

Composition (AMS 5525L Table 1): C ≤0.08 % · Mn ≤2.00 % · Si ≤1.00 % · P ≤0.025 % · S ≤0.025 % · Cr 13.50–16.00 % · Ni 24.00–27.00 % · Mo 1.00–1.50 % · Ti 1.90–2.35 % · V 0.10–0.50 % · B 0.003–0.010 % · Al ≤0.35 % · Co ≤1.00 % · Fe balance. Divergences: Mo max 1.50 % (four sources) or 1.75 % (one) — use 1.50; Ti max 2.35 % (specification) or 2.30 % (two mills running a tighter internal band); B min 0.003 % (three sources) or 0.0010 % (ASTM A638). One site’s 0.0003 % boron is almost certainly a decimal typo — do not repeat it.

What the additions do. Titanium (1.90–2.35 %) is the strengthening element: it combines with nickel to precipitate coherent fcc γ′-Ni₃(Ti,Al) inside the austenite matrix. Without titanium there is no precipitation hardening at all — A-286 would be a plain austenitic stainless at about 620 MPa. Aluminium (≤0.35 %) is deliberately held LOW: it raises the γ′ volume fraction, but keeping total (Al+Ti) modest is a major reason A-286 is more weldable than the high-γ′ nickel superalloys — it is the alloy’s defining design compromise. Boron (0.003–0.010 %) is a grain-boundary strengthener; it raises creep life but aggravates weld hot cracking, which is exactly why the welding-wire specification (AMS 5805) trims boron to 0.004 %. Nickel (24–27 %) keeps the structure fully austenitic and non-magnetic. The specific metallurgical function of vanadium (0.10–0.50 %) could not be verified in any source reviewed — no mechanism is asserted here.​‌​​‌​

The γ′ mechanism and its clock. Solution treatment dissolves titanium into the austenite; ageing at 700–760 °C precipitates fine coherent γ′-Ni₃(Ti,Al), which obstructs dislocation motion. But γ′ in A-286 is metastable: over extended ageing it transforms into the stable hcp η (eta) Ni₃Ti phase, and that transformation degrades the mechanical properties. This is the metallurgical clock that sets A-286’s real service limit — and grain-boundary η also drives its hydrogen sensitivity (below).

Heat Treatment — There Are Three Solution Treatments, Not Two​‌​​‌​

Elevated-temperature tensile and rupture (AMS 5732, aged — single-sourced): 143/93 ksi at 204 °C, 138/93 at 427 °C, 131/87 at 538 °C, 103/88 at 649 °C, 64/62 ksi at 760 °C. The 1000-hour rupture strength falls from 607 MPa at 538 °C to 317 MPa at 649 °C — a 48 % collapse over 111 °C. Design note: one mill states it plainly — “creep and stress rupture properties, rather than short time tensile properties, are the limiting design criteria“.

Welding, Machining and Forming​‌​​‌​

Welding — the honest version

Processes: GTAW, GMAW, SMAW. Filler: AMS 5804 or AMS 5805 A-286 welding wire; 5805 adds VIM melting, environment-controlled packaging and lower boron. No verified AWS ER classification was found — specify the filler by AMS 5804/5805, not by an AWS number. One mill separately notes that “nickel-base electrodes are preferred“, so matching-composition filler is not automatic; confirm with the design authority.​‌​​‌​

Pre-weld condition: weld in the SOLUTION-TREATED condition, not aged. That is precisely why AMS 5895 (954 °C, bar products) and AMS 5858 (982 °C, sheet) exist as dedicated “welding grade” solution-treated specifications. Cracking behaviour: one mill calls A-286 “susceptible to hot cracking”; another is blunter — “prone to heat affected zone cracking when welded with any of the fusion processes. If welding is absolutely necessary, consideration should be given to using JBK-75 alloy instead“. Two mills independently flagging weld cracking makes it verified. JBK-75 is a modified A-286 developed specifically for improved weldability, with ageing characterised as “8 hours at 948 K, followed by 8 hours at 873 K” — an option almost no competitor names.

Inert shielding gas is required, “to prevent titanium loss”. Burning off titanium directly removes the γ′ former, so a weld made with inadequate shielding will not age-harden properly. No numeric preheat or interpass guidance could be verified in any source. The claim “no preheat or post-weld heat treatment is required” is disputed: it comes from a single distributor and conflicts with the practice of welding solution-treated and then ageing the assembly. Do not publish it as fact. Brazing is successful in a pure, dry hydrogen atmosphere or in vacuum — but read that alongside the hydrogen section below.​‌​​‌​

Machining and forming

Machinability rating 40 % (free-machining steel = 100 %) at about 250 HB. A useful, verified comparison: A-286 is easier to machine than the nickel-base precipitation-hardening grades such as alloy 718. There is a genuine disagreement: one mill says A-286 is gummy in the soft solution-treated condition and is “generally machined after it has been partially or fully aged”; a distributor advises the opposite (“rough machine in the solution-annealed state; finish machine after heat treatment”). Know both. The alloy work-hardens rapidly in the solution-treated condition and is “somewhat stiffer than stainless steels such as Types 316 and 310”. The practical rule: select the cutting depth so that the previous consolidation zone is undercut, and keep the tool constantly engaged if possible — never dwell, never rub. Use sharp, positive-geometry coated carbide inserts.​‌​​‌​

Hot working: 1038–1121 °C (1900–2050 °F), with a SHORT soaking period. Do not forge below 927 °C (1700 °F). The short-soak instruction matters: prolonged soaking in the hot-work range coarsens the grain and degrades the fine-grain tensile route. Cold forming is done in the solution-treated condition; expect rapid work hardening and plan interstage solution anneals for severe draws. Controlled cold work is a deliberate strengthening route in its own right — AMS 5853 (160 ksi) and AMS 5726 (200 ksi) are both work-strengthened, not aged.​‌​​‌​

Service Limits, Magnetism and Hydrogen

Hydrogen Embrittlement — the Reputation Is Half Right

The claim “A-286 resists hydrogen embrittlement” is half true, and the half that is false is the half that bites fasteners.​‌​​‌​

Where the reputation comes from — and it is real: “A-286 that has been tested in tension in external hydrogen gas is not embrittled”; slow strain-rate tensile tests in gaseous hydrogen show no effect; and A-286 is the designated control material for high resistance to hydrogen embrittlement under ASTM G142.

Where it fails: internal hydrogen — introduced by electroplating, pickling, cathodic charging or hydrogen-atmosphere brazing — is severely damaging: smooth specimens show “typically 50 to 60 % loss in reduction in area” at room temperature, with strength relatively unaffected — meaning a tensile test will not catch it. At 40 wppm internal hydrogen, notched tensile strength drops about 20 % and reduction of area 50 %; above 100 wppm, fracture toughness decreases by about half. Even in external hydrogen gas, precracked and fatigue testing tells a different story: “for resistance to crack propagation in hydrogen, A-286 is similar to other austenitic stainless steels“.​‌​​‌​

Directly actionable heat-treat dependence: “Materials in solution heat-treated condition show little ductility loss in tensile tests with internal hydrogen, while ageing results in significant reduction in ductility.” The mechanism: embrittlement correlates with grain-boundary η-Ni₃Ti precipitation. Verified mitigation: “shorter aging times and lower aging temperatures result in microstructures that are less susceptible to hydrogen effects.” In practice: avoid electroplating A-286 fasteners where possible; if plated, bake; treat hydrogen-atmosphere brazing as a hydrogen-charging operation; and if hydrogen service is the driver, do not let a smooth-bar tensile qualification stand in for fracture and fatigue data.

Physical properties: density 7.92 g/cm³ (solution treated) / 7.94 (aged) · melting range 1371–1427 °C · modulus of elasticity 199–201 GPa at room temperature, about 149 GPa at 704 °C · mean CTE (21–760 °C) 18.6 × 10⁻⁶/°C · thermal conductivity (150 °C) about 15.0 W/m·K · electrical resistivity about 91 µΩ·cm · specific heat 420 J/kg·K or 461 J/kg·K (sources diverge; both are given). Outlier warning: one major distributor publishes density 0.303 lb/in³ and a melting range of 1288–1349 °C; three independent mills agree on 0.286 lb/in³ and 1371–1427 °C — use the three-source consensus.​‌​​‌​

Frequently Asked Questions

Which solution-treat temperature should I order, and what fails if I get it wrong?​‌​​‌​

A-286 has two production solution treatments, and they are not interchangeable. The 982 °C (1800 °F) treatment produces a slightly coarser grain and superior creep and stress-rupture properties; the 899 °C (1650 °F) treatment produces a finer grain and superior room- and elevated-temperature short-time tensile and fatigue properties. In AMS terms: 982 °C aged = AMS 5732 (minimum 895 MPa tensile, 585 MPa yield, 15 % elongation); 899 °C aged = AMS 5737 (minimum 965 MPa tensile, 655 MPa yield, 12 % elongation). ASTM mirrors this as A453 Grade 660 Class B (982 °C) against Class A (899 °C). Order 899 °C / AMS 5737 for bolts, studs, fasteners and fatigue-loaded parts — you gain about 10 ksi of yield and the fine grain that carries fatigue. Order 982 °C / AMS 5732 for turbine wheels, rotating discs, casings and anything whose design case is creep or rupture at 593–704 °C. What fails if you swap them: specify 899 °C for a creep-limited rotating part and you get a fine-grained bar that passes every tensile test on the certificate and then creeps in service — because creep and rupture, not short-time tensile, are the limiting design criteria for A-286. Specify 982 °C for a highly loaded bolt and you are 10 ksi short of yield with coarser grain and reduced fatigue life, while the certificate still reads “A-286, aged”. The certificate will not catch this. The solution temperature must be on the purchase order.

A-286, Inconel 718 or 17-4 PH for high-strength fasteners and rotating parts​‌​​‌​

These three are not a ladder — each owns a distinct window. 17-4 PH (S17400) is a martensitic precipitation-hardening stainless. It is the cheapest and strongest at room temperature, but it is ferromagnetic, and the NASA fastener design manual lists 17-4 PH and 17-7 PH among the stress-corrosion-susceptible fastener materials. Its temperature ceiling is far below the other two. Choose it for cost-driven, moderate-temperature, non-critical fastening where magnetism and SCC are acceptable. A-286 (S66286) is iron-based, fully austenitic and non-magnetic — relative permeability 1.010 solution-treated, 1.007 aged — and it stays non-magnetic after hardening because γ′ is non-magnetic. The NASA manual is unambiguous: “Of the stainless steels, A286 is the best fastener material for aerospace usage. It is not susceptible to stress corrosion,” usually supplied at 160 ksi (220 ksi on special order), useful −253 to 649 °C, with high strength and good corrosion resistance to 704 °C. Inconel 718 (N07718) is genuinely nickel-based and sits a class above on strength: roughly 1275 MPa tensile / 1034 MPa yield minimum against A-286’s 895/585, in a ~700 °C window. Decision rule: need non-magnetic or the best SCC behaviour → A-286. Need strength above what A-286 gives, or fatigue capability at temperature → 718, and accept the cost. Need only room-temperature strength cheaply → 17-4 PH. Size on measured fastener metal temperature, not gas or flange temperature.

“A-286 is hydrogen-embrittlement proof, right?”​‌​​‌​

Half right — and the wrong half is the dangerous one. A-286’s reputation is real and earned: it is the designated control material for high resistance to hydrogen embrittlement under ASTM G142, and “A-286 that has been tested in tension in external hydrogen gas is not embrittled”. If your qualification is a smooth-bar tensile test in hydrogen gas, A-286 passes brilliantly. But that test is measuring the wrong thing. Data on internal hydrogen — the kind introduced by electroplating, pickling, cathodic protection or hydrogen-atmosphere brazing — shows “typically 50 to 60 % loss in reduction in area” at room temperature, with strength relatively unaffected. At 40 wppm internal hydrogen, notched tensile strength drops about 20 % and reduction of area 50 %; above 100 wppm, fracture toughness “decreased by about half”. And even in external hydrogen gas, precracked and fatigue testing shows “a significant effect on resistance to crack growth”, with the conclusion that “for resistance to crack propagation in hydrogen, A-286 is similar to other austenitic stainless steels“. Two actionable consequences. First, condition matters: solution-treated A-286 shows little ductility loss, but ageing makes it significantly more susceptible, because embrittlement tracks grain-boundary η-Ni₃Ti precipitation — “shorter aging times and lower aging temperatures result in microstructures that are less susceptible”. Second, do not let a tensile certificate stand in for hydrogen qualification; a hydrogen-damaged A-286 bolt can meet every number on its certificate and still fail from a crack.

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