Discover the latest trends and innovations in the nickel alloy industry. We provide expert insights and in-depth analysis on the newest developments in nickel alloys.
(Incoloy A-286 features remarkable high temperature strength and creep resistance. Perfect for components working under sustained high heat and pressure.)
Inconel 600 and 625 rely on solid-solution strengthening and excel in corrosive media, but when the design calls for sustained load-bearing capability above 400°C with a cost-effective iron-nickel base, those alloys may be over-spec or lack sufficient creep strength at equivalent temperatures. Incoloy A-286 (UNS S66286 / AISI Type 660 / W.Nr. 1.4980 / GH2132) is a precipitation-hardenable (PH) iron-nickel-chromium superalloy whose chief distinction is its ability to retain useful tensile and creep-rupture strength up to 650°C (1200°F) in the aged condition—performance that ordinary austenitic stainless steels (even 316) cannot match. Shanghai COCESS Special Alloys Co., Ltd supplies Incoloy A-286 bar, forging stock, plate, and custom-machined components in full compliance with ASTM A638 Grade 660 and AMS 5731–5737, supported by EN 10204 3.1 certification and technical guidance on heat treatment and high-temperature application.
Strengthening Mechanism — Why A-286 Retains High-Temp Strength
Unlike solid-solution alloys, A-286 owes its high-temperature strength to coherent γ′ precipitates [Ni₃(Al,Ti)] formed during aging (700–718°C):
Ti (1.90–2.35%) & Al (0.35–0.70%): Combine with Ni to form nanoscale γ′ phase that impedes dislocation motion—even at elevated temperatures.
Mo (1.0–1.5%): Provides solid-solution strengthening and improves creep resistance.
B (0.001–0.010%) & V (0.10–0.50%): Segregate to grain boundaries, delaying creep cavitation and raising rupture life.
~25% Ni & ~15% Cr: Maintain a fully austenitic matrix with oxidation resistance up to ~705°C in air.
The γ′ phase is thermally stable to approximately 700°C; above this, coarsening reduces its pinning effect, which defines the practical long-term stressed service limit at ≤650°C.
Typical Chemical Composition (wt%, ASTM A638 Gr. 660 / AMS 5737)
|
Element |
Content (wt%) |
Role in High-Temp Performance |
|---|---|---|
|
Fe |
Balance (≈ 50–56) |
Austenite-stabilized base; economical alternative to full Ni-base |
|
Ni |
24.0 – 27.0 |
Forms γ′ with Ti/Al; stabilizes austenite |
|
Cr |
13.5 – 16.0 |
Oxidation resistance; indirect effect on surface stability at temp |
|
Mo |
1.0 – 1.5 |
Solid-solution creep strengthening |
|
Ti |
1.90 – 2.35 |
Primary γ′ former (Ni₃Ti); controls peak aged strength |
|
Al |
0.35 – 0.70 (typ. 0.40) |
Secondary γ′ former (Ni₃Al) |
|
V |
0.10 – 0.50 (typ. 0.25–0.30) |
Grain refinement; improves rupture ductility |
|
B |
0.001 – 0.010 (typ. 0.004–0.006) |
Grain boundary strengthening → ↑ creep-rupture life |
|
C |
≤ 0.08 (typ. 0.04–0.06) |
MC carbides pin grain boundaries |
|
Mn / Si / S / P |
≤ 2.0 / ≤ 1.0 / ≤ 0.025 / ≤ 0.040 |
Controlled residuals |
Room & Elevated Temperature Tensile Strength (Aged Condition)
Values below are typical for properly solution-treated + aged material (per ASTM A638 Gr. 660 minimum: Rm ≥ 895 MPa, Rp0.2 ≥ 585 MPa, A5 ≥ 15%).
|
Temp (°C) |
Tensile Strength Rm (MPa) |
Yield Strength Rp0.2 (MPa) |
Elongation A5 (%) |
|---|---|---|---|
|
20 |
930 – 1050 |
620 – 750 |
18 – 25 |
|
200 |
≈ 880 |
≈ 590 |
≈ 20 |
|
400 |
≈ 840 |
≈ 570 |
≈ 20 |
|
540 |
≈ 790 |
≈ 555 |
≈ 19 |
|
650 |
≈ 690 |
≈ 490 |
18 – 22 |
|
700 |
≈ 620 |
≈ 430 |
20 – 25 |
|
760 |
≈ 480 |
≈ 300 |
25 – 30 |
Strength remains usable to 650°C; beyond 700°C, γ′ coarsening causes noticeable softening.
Elongation stays acceptable even at temperature, supporting formability of aged blanks in limited applications.
Creep & Stress-Rupture Performance (Key Differentiator)
Creep resistance is the principal reason A-286 is selected over 300-series stainless steels for high-temperature fasteners and turbine hardware.
Typical Stress-Rupture Data (Trend Values — Design Must Use Certified Allowables):
|
Temp (°C) |
Stress (MPa) |
Approx. Rupture Life |
|---|---|---|
|
650 |
440 |
~1000 h |
|
650 |
340 |
~10,000 h |
|
595 |
515–550 |
~1000 h |
|
705 |
240–275 |
~1000 h (not for long-term design) |
Design Limit: For sustained loaded components (bolting, casings, lock pins), 650°C is the accepted long-term design ceiling; short-term or intermittent exposure to 700–705°C may be tolerated in lightly loaded applications.
Compared to Type 316 SS (which typically loses useful creep strength above ~400–450°C), A-286 offers a 150–200°C extension in serviceable temperature range for stressed parts.
Recommended Heat Treatment to Achieve High-Temp Strength
A-286 will NOT exhibit specification high-temp strength unless properly heat treated:
|
Step |
Typical Cycle |
Effect on High-Temp Properties |
|---|---|---|
|
Solution Treat |
930–955°C × (time per section) → oil quench or rapid water quench |
Dissolves γ′ & carbides; produces supersaturated matrix |
|
Age (Precipitation Harden) |
700–718°C (commonly 710°C) × 16–18 h → air cool |
Fine γ′ precipitation → peak Rm/Rp0.2 & optimized creep strength |
|
Stress Relieve (optional, non-load) |
595–705°C × 1–2 h → air cool |
Reduces machining residual stress; slight strength reduction |
Material can be supplied solution annealed only (for customer to age after finish machining to avoid distortion) or solution + aged.
Avoid prolonged isothermal holds in 540–760°C outsidethe aging cycle — sigma (FeCr) phase embrittlement risk.
Oxidation Resistance vs. Load-Bearing Limit
Oxidation / Scaling Limit: Good in air to ~705°C (Cr₂O₃ scale); inferior to Inconel 601/600 due to lower Cr and Fe-rich base.
Load-Bearing Limit: Defined by creep-rupture — ≤ 650°C for long-term stressed service.
Components exposed to > 705°C andunder load should consider Inconel 718 (to ~650–700°C load-bearing, higher oxidation resistance) or higher Ni-base alloys.
Typical High-Temperature Applications
Aerospace / Gas Turbine: High-temp fasteners (bolts, nuts, studs), compressor case components, blade root locks — primary application sector.
Power / Steam Turbine: HP/IP casing main studs & nuts, header bolting, manway fasteners.
Industrial Heat / Furnace: Load-bearing pins, fixture components, retort hardware operating ≤ 650°C under load + oxidizing atmosphere.
High-Perf Auto / Racing: Turbocharger studs, exhaust manifold bolts (where 316 would relax/creep excessively).
