What Is A286 Superalloy?
A286 (UNS S66286, also DIN 1.4980) is an iron-nickel-chromium precipitation-hardening austenitic superalloy. It is the strongest iron-base superalloy available in commercial production today — and it fills a performance gap that neither standard stainless steel nor expensive nickel-base alloys can fill cost-effectively.
Developed in the 1950s for jet engine applications, A286 has become the workhorse superalloy for elevated-temperature service in oil and gas, power generation, aerospace, and nuclear industries. Its defining characteristic is the combination of high tensile strength at temperatures up to 704°C, a fully austenitic (non-magnetic) microstructure, and excellent cryogenic toughness — a combination that no other iron-base alloy fully matches.
Unlike solid-solution-strengthened stainless steels, A286 achieves its strength through precipitation hardening: a controlled two-stage heat treatment causes fine intermetallic particles (called gamma-prime, or γ') to form within the austenite matrix. This dramatically increases resistance to dislocation motion — and therefore to plastic deformation and creep at high temperatures.
A286 sits precisely between 316 stainless steel (too weak at elevated temperature) and Inconel 718 (superior performance but 1.8–2.5× the cost). For service temperatures between 400°C and 704°C where creep or fatigue is a concern, A286 is typically the most cost-effective qualified alloy available. Jiangsu Liangyi manufactures A286 open-die forgings and seamless rolled rings from 30 kg to 30,000 kg per piece, certified to AMS 5731 and ASTM B637.
Common Names and Designations
A286 is referenced under many designations across different standards systems. All of the following refer to the same alloy:
| Standard System | Designation | Scope |
|---|---|---|
| UNS (USA) | S66286 | Unified Numbering System — primary identifier |
| AMS (SAE) | 5731 / 5732 / 5737 | Bars, wire, forgings, tubing — different heat treatment conditions |
| ASTM | A453 Gr 660 / A638 Gr 660 / B637 | High-temperature bolting, bars, forgings |
| DIN / EN (Europe) | 1.4980 / X5NiCrTiMoVB25-15-2 | German and European material standard |
| Trade Names | Incoloy® A286, Pyromet® A286, ATI A286™ | Brand-specific; chemically and mechanically identical |
| AISI | 660 | Used in older US engineering documents |
A286 Chemical Composition (UNS S66286)
A286's composition is the engineered foundation of all its key properties. Each element serves a specific metallurgical role — understanding these roles helps engineers evaluate whether the alloy is correctly melted and whether substitutions are feasible.
What Each Element Does
Iron (Fe) — Matrix Backbone
At roughly 55%, iron forms the primary austenitic matrix. The relatively high iron content compared to nickel-base superalloys is what keeps A286 cost-effective — iron is approximately 4–6× cheaper per kilogram than nickel.
Nickel (Ni) — Austenite Stabilizer
Nickel at 24–27% is critical for stabilizing the face-centered cubic (FCC) austenite phase at all service temperatures, including cryogenic. It prevents the martensite transformation that would occur in lower-nickel iron alloys on cooling, and it suppresses brittle fracture at low temperatures.
Chromium (Cr) — Oxidation and Corrosion Resistance
Chromium at 13.5–16% forms the protective Cr₂O₃ passive layer that provides oxidation resistance to 700°C and corrosion resistance in steam, H₂S/CO₂ environments, and dilute acids.
Titanium (Ti) and Aluminum (Al) — Precipitation Strengtheners
These elements combine with nickel during aging to form γ' (Ni₃(Ti,Al)) precipitate particles. Titanium is the primary strengthener in A286. The tight 1.90–2.35% Ti specification is critical — too low reduces strength; too high risks embrittling phases forming at grain boundaries.
Boron (B) — Grain Boundary Strengthener
Boron at 30–100 ppm segregates to grain boundaries, reducing grain boundary sliding at elevated temperatures and improving creep rupture ductility. This is one reason A286's creep performance at 700°C significantly exceeds what its basic composition alone would predict.
A286 Mechanical Properties
| Property | Metric | Imperial | Standard |
|---|---|---|---|
| 0.2% Proof Stress (min) | 590 N/mm² | 85 ksi | AMS 5731 |
| Tensile Strength (min) | 900 N/mm² | 130 ksi | AMS 5731 |
| Elongation A₅ (min) | 13–15% | 13–15% | AMS 5731 |
| Reduction of Area | 25–40% | 25–40% | Typical |
| Hardness | 248–302 HB | 26–32 HRC | Typical |
| Charpy Impact (RT) | ≥ 50 J | ≥ 37 ft·lb | Typical |
Elevated Temperature Strength Retention
The most critical advantage of A286 over austenitic stainless steel is its strength retention at elevated temperature. 316 SS loses more than 40% of room-temperature strength above 500°C, while A286 maintains useful structural properties through 700°C. Engineers specifying custom A286 forged bars, rings, and shafts should request material certified to these minimum values per AMS 5731 or ASTM B637.
| Temperature | 100 hours | 1,000 hours | 10,000 hours |
|---|---|---|---|
| 538°C (1000°F) | ~690 MPa | ~590 MPa | ~490 MPa |
| 593°C (1100°F) | ~480 MPa | ~380 MPa | ~290 MPa |
| 649°C (1200°F) | ~280 MPa | ~200 MPa | ~140 MPa |
| 704°C (1300°F) | ~145 MPa | ~95 MPa | ~60 MPa |
For rotating parts (turbine disks, compressor rotors) and pressure-retaining joints (bolted flanges, valve bodies), the design-limiting property is usually creep rupture life at operating temperature — not room-temperature tensile strength. Always size A286 components against the creep data for the actual operating temperature and required service life.
A286 Heat Treatment: The Two-Stage Cycle
A286 requires a precise two-stage thermal cycle to develop target mechanical properties. Skipping or incorrectly performing either stage results in either an understrength part (under-aged) or a brittle part with reduced creep life (over-aged).
"In our production process, the grain size developed during forging has a significant influence on high-temperature performance. For A286, we target an ASTM grain size of 5–8. Even a 50°C deviation from the 720°C aging target — either over-aging or under-aging — results in a measurable reduction in creep rupture life. For this reason, our heat treatment furnaces are calibrated monthly to ±5°C."Jiangsu Liangyi Engineering Team — Chief Forging Engineers, Superalloy Division, Jiangyin China
A deviation of just 50°C from the 720°C aging target — either too high (over-aging) or too low (under-aging) — produces a measurable reduction in creep rupture life at service temperature. Furnace calibration accuracy of ±5°C or better is mandatory. At Jiangsu Liangyi, all heat treatment furnaces are calibrated monthly and all heat treatment operators hold Level II qualifications.
AMS 5731 vs AMS 5732 vs AMS 5737
| Specification | Solution Temp | Aging | Typical Use |
|---|---|---|---|
| AMS 5731 | 982°C / 1800°F | 718°C / 16h, AC | Bars, forgings — highest strength (most common specification) |
| AMS 5732 | 899°C / 1650°F | 718°C / 16h, AC | Higher ductility, lower solution temp, fastener applications |
| AMS 5737 | 899°C / 1650°F | 718°C / 16h, AC | Similar to 5732 but emphasizes tensile-based acceptance criteria |
When writing a purchase order, specify the AMS number explicitly. Dual certification (e.g. AMS 5731 + ASTM B637) is possible for material that simultaneously meets both standards and is available from qualified forging suppliers on request at no extra cost.
A286 vs Inconel 718 vs 316L SS — Which Alloy?
After 25 years of forging A286, the most frequent question from design engineers is: "Why not just use Inconel 718?" or "Can't 316L handle this?" Here is an honest engineering answer.
When to Specify A286 — Quick Decision Guide
- Service temperature is 400–704°C with sustained load
- Part must be permanently non-magnetic
- Cryogenic service below −100°C is required
- Budget cannot justify Inconel 718 (1.8–2.5×)
- Fasteners or bolts must retain preload at elevated temperature
- Sour gas / H₂S environments — confirm NACE MR0175
- Creep resistance over 10,000+ hours is required
- Tensile >1,100 MPa at temperature → Inconel 718
- Service temp <400°C, no creep concern → 316L or 17-4PH
- Spec mandates nickel-base classification → Inconel 718
- Extreme aerospace combustion zone → Inconel 718
- Budget is primary constraint, low stress → 316L SS
- Magnetic properties acceptable → 17-4PH may suffice
Machining and Welding A286 Superalloy
Machining A286
A286 has a machinability rating of approximately 20–25% relative to free-cutting carbon steel — comparable to 316 stainless but significantly more demanding than carbon steel. The primary challenge is work hardening: A286 rapidly strain-hardens during cutting. If a tool dwells on the surface rather than shearing cleanly, it creates a surface layer of 40–50 HRC hardness in a single pass, chipping subsequent carbide inserts.
| Operation | Tooling | Speed | Feed Rate |
|---|---|---|---|
| Rough Turning | TiAlN coated carbide P20–P30 | 20–35 m/min | 0.3–0.5 mm/rev |
| Finish Turning | PVD-coated carbide or CBN | 25–40 m/min | 0.1–0.2 mm/rev |
| Face / End Milling | TiAlN, positive rake geometry | 15–30 m/min | 0.05–0.12 mm/tooth |
| Drilling | Solid carbide or TiAlN HSS-Co | 8–15 m/min | 0.05–0.12 mm/rev |
| Grinding | Al₂O₃ wheel, 46–60 grit | 25–30 m/s wheel | 0.005–0.015 mm depth |
When possible, perform rough machining while the material is in the solution-annealed condition (soft, ~180 HB), then age to final hardness before finish machining. This sequence dramatically extends tool life. Aged A286 at ~300 HB accelerates insert wear on roughing passes by 3–4× compared to machining in the annealed condition.
Welding A286
A286 is weldable, but requires more process discipline than austenitic stainless steel. The two main risks are heat-affected zone (HAZ) liquation cracking and strain-age cracking if post-weld heat treatment is not performed correctly.
| Parameter | Specification |
|---|---|
| Preferred Process | TIG (GTAW) or plasma arc; MIG acceptable for non-critical joints |
| Filler Metal | AMS 5804 (matching A286 wire) or AMS 5798 (Inconel 625 for dissimilar joints) |
| Preheat | 150–200°C minimum; interpass temperature not to exceed 200°C |
| Heat Input | Maximum 1.0 kJ/mm — stringer beads only, no weave passes |
| Post-Weld Heat Treatment | Mandatory for pressure and rotating parts: solution at 980°C (≥1h) + age at 720°C (≥16h) |
| Post-Weld Inspection | Liquid penetrant (PT) all weld surfaces; UT volumetric for thickness >25mm |
A286 Corrosion and Oxidation Resistance
A286's corrosion resistance comes from its chromium content (13.5–16%), which forms a self-repairing Cr₂O₃ passive film. While not as corrosion-resistant as Inconel 718 in the most aggressive media, it outperforms standard austenitic grades in high-temperature steam, oxidizing atmospheres, and moderate sour-gas environments.
| Environment | A286 | 316L SS | Inconel 718 |
|---|---|---|---|
| Oxidizing atmosphere to 700°C | Excellent | Good | Excellent |
| High-pressure steam (>300°C) | Excellent | Good | Excellent |
| Seawater / chloride solution | Good | Limited | Excellent |
| Sour gas (H₂S + CO₂, NACE MR0175) | Good* | Not qualified | Excellent |
| Liquid nitrogen / cryogenic | Excellent | Good | Excellent |
| Nitric acid (HNO₃) | Excellent | Excellent | Good |
| Dilute HCl (<5%) | Limited | Poor | Good |
* Sour gas suitability: confirm with application-specific NACE MR0175 testing. General industry experience is positive for downhole environments within specified hardness limits.
A286 Applications by Industry
Oil & Gas
For oil and gas, the key drivers for A286 selection are resistance to stress relaxation at elevated temperature (critical for bolted flange integrity at wellhead), NACE MR0175 sour-gas suitability, and API 6A material compliance. Mill test certificates to EN 10204 3.2 with third-party inspection are standard in this sector.
Power Generation
In gas and steam turbines, A286 is specified for rotating components where creep resistance over 25,000–100,000 operating hours is the primary constraint. For nuclear applications, the non-magnetic property and radiation resistance make A286 suitable for coolant pump internals and reactor instrumentation housings.
Aerospace
Industrial
Why A286 Critical Parts Should Be Forgings
A286 is commercially available as bar, sheet, plate, and wire — but critical structural parts should be specified as forgings when operating under sustained load at elevated temperature. Here is why.
Grain Flow and Directionality
Open-die forging works the material in a controlled direction, creating a fibrous grain structure that follows the contour of the part. Compared to a part machined from bar or plate, a forged A286 part has higher fatigue resistance in the designed loading direction and more consistent properties across the entire cross-section.
Grain Size Control
Forging reduction ratio and finishing temperature directly control grain size. For A286, a target ASTM grain size of 5–8 is typically specified. Coarser grains (lower ASTM number) improve creep resistance; finer grains improve fatigue life. The ability to deliberately engineer grain size across the part cross-section is unique to the forging process and cannot be replicated with bar or plate conversion.
Melt Quality for Critical Applications
For the most demanding applications — aerospace disks, nuclear pump casings, downhole BOP bodies — A286 forgings should be produced from double or triple melt stock: VIM + ESR (double melt) or VIM + ESR + VAR (triple melt). Each remelting step reduces inclusions, segregation, and oxygen content. This level of material cleanliness is not achievable with standard single-melt bar stock. For full dimensional capability, available delivery conditions, and lead times, see the A286 forged parts specifications page.
Need A286 Forged Parts?
Jiangsu Liangyi has produced A286 open-die forgings and seamless rolled rings for over 25 years, delivering to 50+ countries with full MTC 3.1/3.2 documentation and third-party inspection.
Frequently Asked Questions About A286
Is A286 the same as Incoloy A286?
Can A286 be used above 704°C?
What is the difference between A286 and 17-4PH?
What does "precipitation hardening" mean for A286?
What standards do A286 forgings typically meet?
What is the typical lead time for A286 forged parts?
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