A-286 / Alloy 660 – UNS S66286
Precipitation-hardenable Fe-Ni-Cr superalloy
Austenitic Fe-25Ni-15Cr alloy hardened by precipitation of γ' (Ni3Ti) after solution treatment and aging. It keeps high strength up to ≈ 650–700 °C; widely used in high-temperature fasteners and turbine components.
Designations and equivalents
| System | Designation |
|---|---|
| UNS | S66286 |
| W.Nr./EN | 1.4980 (X6NiCrTiMoVB25-15-2) |
| DIN | X6NiCrTiMoVB25-15-2 |
| JIS | SUH660 |
| Trade names | A-286, Alloy 660 |
| Others | ASTM A453 Gr. 660 |
Standards by product form
| Form | Standard |
|---|---|
| Bar/fastener | ASTM A453 Gr. 660 (Classes A, B, C, D) |
| High-temperature bar/forging | ASTM A638 Gr. 660 |
| Aerospace bar | AMS 5731 / 5732 / 5737 |
| Sheet | AMS 5525 |
Tolerances and HS codes
- Forged bars (round and square): machining allowance from 2 mm (Ø 6–16 mm) to 24 mm (Ø 400–500 mm) on the diameter. E.g. Ø 100–125 mm finished: +7 mm, tolerance +6 / −0 (length up to 3,500 mm).
- Forged discs: allowance of 4 to 9 mm on the diameter and 3 to 11 mm on the height, plus-only tolerance.
- Cutting and machining: band saw −0 / +5 to +15 mm on length; waterjet +10 % of thickness on the diameter (min. 2 mm); machined parts −0 / +2 to +5 mm on the diameter. See the full tables (INF 002 and INF 003, the same for every alloy).
| Form | NCM (Brazil, 8 digits) | HS (international, 6 digits) | HTS (USA, 10 digits)* | CN (European Union, 8 digits)* |
|---|---|---|---|---|
| Forged bar | 7222.30.00 | 7222.30 | 7222.30.0024 | 7222 30 51 |
| Hot-rolled bar | 7222.11.00 | 7222.11 | 7222.11.0059 | 7222 11 11 |
| Plate (> 10 mm, width ≥ 600 mm) | 7219.21.00 | 7219.21 | 7219.21.0020 | 7219 21 10 |
| Flange and fitting | 7307.21.00 | 7307.21 | 7307.21.5000 | 7307 21 00 |
Tariff class: stainless steel (by chemical composition, under the Chapter 72 Notes and Section XV Note 5).
*: US and EU codes for reference. NCM per current legislation (General Rules of Interpretation, Notes to Chapters 72, 74 and 75 and Section XV Note 5). Confirm the final code with your customs broker according to the item size and finish. HS = first 6 digits of the NCM.
Chemical composition (%)
ASTM A453 Gr. 660
| Element | Range (%) |
|---|---|
| C | ≤ 0.08 |
| Mn | ≤ 2.00 |
| P | ≤ 0.040 |
| S | ≤ 0.030 |
| Si | ≤ 1.00 |
| Cr | 13.5 – 16.0 |
| Ni | 24.0 – 27.0 |
| Mo | 1.00 – 1.50 |
| Ti | 1.90 – 2.35 |
| Al | ≤ 0.35 |
| V | 0.10 – 0.50 |
| B | 0.001 – 0.010 |
| Fe | balance |
Mechanical properties
Solution treated + aged (ASTM A453 Gr. 660)
| Property | Value |
|---|---|
| Yield strength (0.2%) | ≥ 585 MPa (Class D: ≥ 725) |
| Tensile strength | ≥ 895 MPa |
| Elongation | ≥ 15% |
| Reduction of area | ≥ 18% |
| Hardness | ≈ 248 – 341 HB (24 – 37 HRC) |
| Stress rupture (A, B, C) | 650 °C / 385 MPa: ≥ 100 h |
Typical physical properties
| Property | Value |
|---|---|
| Density | 7.94 g/cm³ |
| Melting range | 1,370 – 1,430 °C |
| Modulus of elasticity | 201 GPa |
| Thermal conductivity (20 °C) | 12.7 W/m·K |
| Thermal expansion (0–200 °C) | 16.5 µm/m·K |
Aging conditions
| Class (ASTM A453 Gr. 660) | Solution treatment | Aging | Stress rupture (650 °C / 385 MPa, ≥ 100 h) |
|---|---|---|---|
| A | 900 °C ± 14 °C, min. 2 h, rapid liquid quench | 720 °C ± 14 °C, 16 h, air | Required |
| B | 980 °C ± 14 °C, min. 1 h, rapid liquid quench | 720 °C ± 14 °C, 16 h, air | Required |
| C | 980 °C ± 14 °C, min. 1 h, oil | 775 °C ± 14 °C, 16 h, air + 650 °C ± 14 °C, 16 h, air | Required |
| D | 900 °C (min. 2 h) or 980 °C (min. 1 h), rapid liquid quench | 720 °C ± 14 °C, 16 h, air; if the properties are not reached, re-age at 650 °C ± 14 °C, 16 h | Waived |
Heat treatment, welding and machining
| Item | Usual practice |
|---|---|
| Service temperature | Long-term continuous load up to ≈ 540–650 °C; short term up to ≈ 700–815 °C. Oxidation up to ≈ 815 °C continuous. |
| Heat treatment | Solution treatment at 900 °C or 980 °C (per class/AMS: 900 °C → fine grain and higher tensile strength; 980 °C → coarse grain and better creep), oil or water cooling; aging 705 – 760 °C for 16 h, air cooling. Class C: 775 °C/16 h + 650 °C/16 h. |
| Welding | Limited: risk of hot cracking in the HAZ due to the high Ti. When necessary, TIG before aging, with a matching consumable or ERNiCr-3 in non-structural joints (typical). |
| Machining | Difficult, similar to nickel superalloys: preferably machine solution treated, carbide tooling, low speed and firm feed. |
Filler metal for welding
The wire composition is usually not identical to the material: each page explains why.
Typical applications
- High-temperature bolts, studs and nuts (A453)
- Gas turbine and jet engine components
- Turbochargers
- Turbine discs, shafts and casings
- Steam and petrochemical flange fasteners
- Cryogenic and non-magnetic fasteners
Alternatives: B16/B8 for lower temperature and load; Inconel 718 for higher strength up to ≈ 650 °C; Waspaloy/Nimonic 80A above ≈ 700 °C.
A-286 / Alloy 660: complete guide
What A-286 / Alloy 660 is
A-286 belongs to the family of special stainless steels, in the group of precipitation-hardenable austenitic iron-nickel alloys, and sits at the border with the nickel alloys. A-286 is the alloy's name; there is no "ASTM A286" standard. The product standards are ASTM A453 Gr. 660, for high-temperature bolts and studs, and ASTM A638 Gr. 660, for bar and forgings. It should also not be confused with Inconel 600, a nickel-chromium alloy without precipitation hardening.
Chemical composition and role of the elements
Nickel, from 24 to 27%, stabilizes the austenite; chromium, from 13.5 to 16%, gives oxidation resistance; titanium, from 1.90 to 2.35%, forms the gamma-prime precipitate that hardens the alloy during aging; molybdenum (1.00 to 1.50%), vanadium (0.10 to 0.50%) and boron (0.001 to 0.010%) raise creep resistance. Iron is the balance, about half of the alloy.
Temperature, corrosion and applications
A-286 keeps useful strength up to about 700 °C in fasteners and up to about 650 °C in creep-designed components, with oxidation and aqueous corrosion resistance similar to the austenitic 304 / 316. It is used in bolts, studs and nuts of steam and gas turbines, compressor discs and casings, jet engine and turbocharger components, springs for temperature and non-magnetic cryogenic parts. For higher strength or higher temperature, the choice moves to Inconel 718.
Supply forms and Dustre services
Round bars and blocks forged in open die, cut to size on a band saw, with rough or finish machining, heat treatment (quenching and tempering, annealing, solution annealing and aging) in our own furnaces and hardness, tensile and impact testing. All material is supplied with a 3.1 inspection certificate and heat traceability.
Frequently asked questions
What is the chemical composition of A-286 / Alloy 660?
Per ASTM A453 Gr. 660: C ≤ 0.08; Mn ≤ 2.00; P ≤ 0.040; S ≤ 0.030; Si ≤ 1.00; Cr 13.5 – 16.0.
Which standards cover A-286 / Alloy 660?
Bar/fastener: ASTM A453 Gr. 660 (Classes A, B, C, D). High-temperature bar/forging: ASTM A638 Gr. 660. Aerospace bar: AMS 5731 / 5732 / 5737. Sheet: AMS 5525.
Up to what temperature can A-286 / Alloy 660 be used?
Long-term continuous load up to ≈ 540–650 °C; short term up to ≈ 700–815 °C. Oxidation up to ≈ 815 °C continuous.
Which materials can replace A-286 / Alloy 660?
B16/B8 for lower temperature and load; Inconel 718 for higher strength up to ≈ 650 °C; Waspaloy/Nimonic 80A above ≈ 700 °C.
What is the difference between classes A, B, C and D of A453 Gr. 660?
The chemistry is the same; the heat treatment changes. Class A is solution treated at 900 °C, B and C at 980 °C, and D allows either. Class D has a minimum yield strength of 725 MPa, versus 585 MPa for the others, and is the only one exempt from the stress rupture test (650 °C / 385 MPa, ≥ 100 h). Check the current edition of ASTM A453.
Is A-286 a stainless steel or a nickel alloy?
It is an austenitic iron-nickel-chromium alloy: about half iron, 24 – 27% Ni and 13.5 – 16% Cr. Because of the high nickel it sometimes appears among the nickel alloys, but the product standards (ASTM A453 and A638 Gr. 660) treat it as a precipitation-hardenable stainless steel.
