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( Incoloy A-286 (S66286) is a precipitation hardening iron-based superalloy. Learn its chemical composition, mechanical properties, heat treatment and common industrial uses here.)
In aerospace engines, industrial gas turbines, and high-temperature fastener applications, ordinary stainless steels lose strength rapidly above 400°C, while premium nickel-base superalloys may exceed budget or formability constraints. Incoloy A-286 (UNS S66286 / AISI Type 660 / W.Nr. 1.4980 / GH2132) fills this gap as a precipitation-hardenable (PH) iron-nickel-chromium superalloy. It is strengthened primarily by gamma-prime [γ′, Ni₃(Al,Ti)] precipitates formed during aging, delivering useful tensile and creep strength up to 650°C (1200°F) with good oxidation resistance and fabricability. Shanghai COCESS Special Alloys Co., Ltd supplies Incoloy A-286 in round bar, forging stock, plate, sheet, and seamless tube, fully compliant with ASTM A638 Grade 660, AMS 5731–5737, and AMS 5525, with EN 10204 3.1 certification and global export support.
Metallurgical Background — Why A-286 is Different
Unlike solid-solution strengthened alloys (econel 600/625), A-286 must be solution treated and aged to achieve design strength. Its key metallurgical features are:
Precipitation Hardening via γ′ Phase: Ti (1.90–2.35%) and Al (0.35–0.70%) combine with Ni to form coherent Ni₃(Ti,Al) precipitates during aging at 700–718°C.
Austenite Stability: ~25% Ni ensures a fully austenitic matrix (non-magnetic in annealed condition, weakly magnetic after heavy cold work).
Grain Boundary Strengthening: Trace Boron (0.001–0.010%) and Vanadium (0.10–0.50%) improve creep-rupture life.
Mo Addition (1.0–1.5%): Provides solid-solution strengthening and enhances creep resistance.
The alloy is not intended for use above 705–760°C in load-bearing service—γ′ coarsening and reduced creep strength limit long-term stressed application to ≤650°C, although oxidation resistance in air is acceptable up to ~705°C.
Chemical Composition (wt%, per ASTM A638 Gr. 660 / AMS 5737)
|
Element |
Content (wt%) |
Function |
|---|---|---|
|
Iron (Fe) |
Balance (≈ 50–56) |
Austenite-stabilized base; cost reduction vs Ni-base alloys |
|
Nickel (Ni) |
24.0 – 27.0 |
Forms γ′ with Ti & Al; stabilizes austenite |
|
Chromium (Cr) |
13.5 – 16.0 |
Oxidation/corrosion resistance (similar to 430 SS) |
|
Molybdenum (Mo) |
1.0 – 1.5 |
Solid-solution creep strengthening |
|
Titanium (Ti) |
1.90 – 2.35 |
Primary γ′ former (Ni₃Ti); controls peak aged strength |
|
Aluminum (Al) |
0.35 – 0.70 (typ. 0.40) |
Secondary γ′ former (Ni₃Al); refines precipitate distribution |
|
Vanadium (V) |
0.10 – 0.50 (typ. 0.25–0.30) |
Refines grain structure; improves rupture ductility |
|
Boron (B) |
0.001 – 0.010 (typ. 0.004–0.006) |
Segregates to grain boundaries; raises creep-rupture strength |
|
Carbon (C) |
≤ 0.08 (typ. 0.04–0.06) |
Forms MC-type carbides; excess consumes Ti/Al |
|
Manganese (Mn) |
≤ 2.0 (typ. ≤ 1.0) |
Deoxidizer |
|
Silicon (Si) |
≤ 1.0 (typ. ≤ 0.50) |
Deoxidizer |
|
Sulfur (S) |
≤ 0.025 (premium ≤ 0.010) |
Strictly controlled—hot shortness & grain boundary weakening |
|
Phosphorus (P) |
≤ 0.040 |
Residual impurity |
Recommended Heat Treatment (Critical for Properties)
A-286 does NOT reach specification strength in the as-rolled or as-forged condition.
|
Step |
Typical Cycle |
Purpose |
|---|---|---|
|
Solution Treating |
930–955°C × (sufficient time for section) → oil quench or rapid water quench |
Dissolve γ′ & carbides; produce supersaturated austenite |
|
Aging (Precipitation Hardening) |
700–718°C (commonly 710°C) × 16–18 h → air cool |
Fine, uniform γ′ precipitation → Rm ≥ 895 MPa, Rp0.2 ≥ 585 MPa |
|
Stress Relieving (non-load) |
595–705°C × 1–2 h → air cool |
Reduce machining residual stress; slight strength reduction |
Material may be supplied in solution-annealed condition (for customer to age after machining) or solution-annealed + aged.
Avoid prolonged exposure in 540–760°C withoutproper aging schedule—sigma phase (FeCr) embrittlement possible in long-term isothermal holds > 650°C.
Mechanical Properties (Solution Treated + Aged)
Room Temperature (Minimum per ASTM A638 Gr. 660):
|
Property |
Minimum Requirement |
Typical Range |
|---|---|---|
|
Tensile Strength (Rm) |
≥ 895 MPa (130 ksi) |
930–1050 MPa |
|
Yield Strength (Rp0.2) |
≥ 585 MPa (85 ksi) |
620–750 MPa |
|
Elongation (A5, 4D) |
≥ 15% |
18–25% |
|
Reduction of Area (Z) |
≥ 18% |
25–40% |
|
Hardness |
— |
28–36 HRC (≈ 270–330 HB) |
|
Charpy V-notch Impact (RT) |
— |
Typically 40–80 J (grain-size dependent) |
Elevated Temperature Trend (Aged Condition, Typical):
|
Temp (°C) |
Rm (MPa) |
Rp0.2 (MPa) |
A5 (%) |
|---|---|---|---|
|
20 |
930–1050 |
620–750 |
18–25 |
|
300 |
≈ 860 |
≈ 580 |
≈ 20 |
|
540 |
≈ 790 |
≈ 555 |
≈ 19 |
|
650 |
≈ 690 |
≈ 490 |
18–22 |
|
700 |
≈ 620 |
≈ 430 |
20–25 |
Creep-Rupture Reference (typical): 650°C / 440 MPa → ~1000 h; 650°C / 340 MPa → ~10,000 h.
Long-term load-bearing design limit is commonly cited as 650°C max; short-time or unstressed oxidation exposure to 705–760°C is permissible.
Physical Constants
|
Property |
Value |
|---|---|
|
Density |
7.93 g/cm³ (0.287 lb/in³) |
|
Melting Range |
~1364°C (solidus) to ~1420°C (liquidus) |
|
Thermal Conductivity @ 20°C |
~15.0 W/m·K; @ 650°C ~23 W/m·K |
|
CTE (20–650°C, mean) |
~16.1 × 10⁻⁶ /K |
|
Specific Heat @ 20°C |
~460 J/kg·K |
|
Electrical Resistivity @ 20°C |
~0.91 µΩ·m |
|
Magnetic Behavior |
Weakly magnetic possible after cold work; essentially non-magnetic annealed |
Corrosion & Environmental Resistance
Oxidation: Good up to ~705°C in air (Cr₂O₃ scale); inferior to Inconel 600/601 due to lower Cr and Fe-rich base.
Aqueous Corrosion: Better than martensitic SS (410/431), but inferior to 300-series austenitics and Ni-Cr-Mo alloys. Not recommended for seawater immersion or strong reducing acids.
Chloride SCC: More susceptible than 304/316 in hot chloride solutions; best used in air/gas/superheated steam, not chloride-rich aqueous service.
Typical Applications
Aerospace & Gas Turbine: High-temperature fasteners (bolts, nuts, studs), compressor case components, turbine blade roots, lock pins—primary use segment.
Power Generation: Steam turbine main studs & nuts (HP/IP casing), bolting for headers & manifolds.
Industrial Furnace / Heat Treat: Fixtures, retorts, and load-bearing pins where oxidation resistance + strength to 650°C is required.
Automotive Racing / Performance: Turbocharger mounting studs, exhaust manifold bolts.
