Stainless Steel 660
AISI/SAE 660 · UNS S66286 · JIS SUH660
660 (A286, SUH660, UNS S66286, ASTM A453 Grade 660, GH2132) is an austenitic precipitation-hardening heat-resistant alloy based on Fe-25Ni-15Cr, strengthened by γ′ formed from its Ti and Al additions.
Values for the Solution Annealed condition
660 tempers and conditions
660 is supplied in 7 conditions, soft to hard. Solution Annealed is the default FabDigit quotes; the values on this page are for it.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
980–1010 °C anneal, softest supply condition | Choose for maximum cold formability of sheet/strip and for wire before drawing; must be aged afterwards to develop strength. | 280 | 640 | 45 | 150 HB | — |
Solution AnnealedDefault 980 °C/1 h + oil or water quench (AMS 5731/5737 pre-age) | Standard stock condition for bar, sheet and wire that will be machined or formed and then age hardened by the user. | 310 | 690 | 40 | 160 HB | — |
ASTM A453 Gr 660 Class A | Order this class when a pressure-vessel/flange bolting certificate to A453 Gr 660 Class A minima is required. | 585 | 895 | 15 | 29 HRC | 1.9 % IACS |
solution 980 °C + age 720 °C/16 h (AMS 5731/5737, A453 Gr 660 Cl A) | The normal service condition: γ′ precipitation gives ~1000 MPa tensile with good 540–700 °C strength and stress-relaxation resistance for bolts and turbine hardware. | 690 | 1,000 | 20 | 32 HRC | — |
solution treated then cold drawn bar/wire (unaged) | Pick for close-tolerance bright bar and wire feedstock where strength above the solution-annealed level is wanted before final ageing. | 700 | 900 | 18 | 23 HRC | 1.9 % IACS |
STA | Lower solution temperature keeps a finer grain size for higher room-temperature yield strength in bolting; slightly lower creep/rupture capability than the 980 °C treatment. | 760 | 1,035 | 17 | 34 HRC | — |
Cold Worked + Aged | Highest strength form, used for high-temperature springs, retaining rings and fasteners where 1300–1500 MPa with 500–600 °C relaxation resistance is required. | 1,250 | 1,400 | 6 | 44 HRC | 1.9 % IACS |
Supply forms, finishes and certifications
Ways 660 is supplied — form, process route, surface or paperwork — without a datasheet of their own. The property values above apply.
| Option | What it is | Type |
|---|---|---|
A453-660-B | ASTM A453 Gr 660 Class B | Certification |
What is 660?
660 (A286, SUH660, UNS S66286, ASTM A453 Grade 660, GH2132) is an austenitic precipitation-hardening heat-resistant alloy based on Fe-25Ni-15Cr, strengthened by γ′ formed from its Ti and Al additions. It combines stainless-steel fabricability with nickel-alloy strength at 540–700 °C and is supplied as bar, wire and forgings for turbine bolting, gas-turbine discs and rings, exhaust valves and springs. Solution-treated bar gives 310 MPa yield, 690 MPa tensile and 40 % elongation at 160 HB, with service to 540 °C. Aged material cuts slowly (machinability 28), pitting and chloride resistance is only comparable to 304/316, and welds are prone to strain-age cracking and need re-solution plus ageing. 660 has a density of 7.94 g/cm³ (0.287 lb/in³), heavier than 78% of stainless steel grades. It melts at 1,370°C (2,498 °F). 660 has a yield strength of 310 MPa (45 ksi) and a tensile strength of 690 MPa (100 ksi) — weaker than 63% of stainless steel grades. Elongation at break is 40% and the elastic modulus is 201 GPa (29.2 Msi).
What is 660 used for?
- Aircraft engine fasteners and turbine bolting
- Gas-turbine discs and ring parts
- Exhaust valves
- High-temperature springs
- Turbocharger components
- Jet engine casings and housings
- Non-magnetic high-strength shafts
Limitations
- High embodied carbon — 6.8 kg CO₂/kg, worse than 95% of stainless steel grades
- Low electrical conductivity — 1.9 % IACS, worse than 84% of stainless steel grades
660 properties
Typical room-temperature values for 660-Solution Annealed; bars are the position among stainless steel grades.
Physical3
660 has a density of 7.94 g/cm³ (0.287 lb/in³), heavier than 78% of stainless steel grades. It melts at 1,370°C (2,498 °F).
Mechanical13
660 has a yield strength of 310 MPa (45 ksi) and a tensile strength of 690 MPa (100 ksi) — weaker than 63% of stainless steel grades. Elongation at break is 40% and the elastic modulus is 201 GPa (29.2 Msi).
Thermal5
660 is rated for continuous service to 540°C (1,004 °F). It conducts heat at 13.4 W/m·K (7.74 BTU/hr·ft·°F), worse than 84% of stainless steel grades. Thermal expansion is 16.6 µm/m·K (9.22 µin/in·°F).
Electrical3
660 conducts electricity at 1.9 % IACS, worse than 84% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is good (62/100), worse than 52% of stainless steel grades.
Sustainability4
Producing a kilogram of 660 takes about 95 MJ of energy and emits 6.8 kg of CO₂ — more than 96% of stainless steel grades. Typical recycled content is 30%.
Manufacturability7
660's machinability is poor (28/100, worse than 79% of stainless steel grades); weldability good (55/100); formability good (60/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the stainless steel family
Yield strength against density for every stainless steel grade FabDigit runs. 660 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 660
Is 660 easy to machine?
Gummy and highly work-hardening — machine in the solution-treated condition where possible with rigid setups, positive-rake carbide, heavy flood coolant, low speed (15–25 m/min) and constant feed to avoid glazing; aged material typically cut at ~15 % of AISI 1212 rates.
Can 660 be welded?
GTAW/EBW with matching A286 or Ni-base filler works, but the alloy is prone to hot cracking and strain-age cracking; weld in the solution-treated state, restrain minimally, and re-solution plus age the weldment for full properties.
Can 660 be formed, bent or molded?
Cold form and draw only in the annealed/solution-treated condition, allowing for high springback and ~2× the load of 304; hot work at 1100–950 °C then solution treat, and never form aged material.
Manufacturability
The process limits FabDigit applies to 660. Every 660 part is priced by an engineer; design inside these and the quote comes back without a redesign loop.
CNC machining
| Machinability | Fair28 / 100 |
|---|---|
| ISO material group | M.1 |
| Cutting speed (rough / finish) | 150 / 180 m/min |
| Minimum wall | 0.8 mm |
| Minimum internal radius | 1.5 mm |
| Drill depth limit | 4× diameter |
| Best surface (machined / polished) | Ra 1.6 / — |
| Hardenable after machining | No |
Sheet metal
| Formability | Fair60 / 100 |
|---|---|
| Weldability | Better55 / 100 |
| Bendable | Yes |
660 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| C | ≤ 0.08 | 0.05 |
| Si | ≤ 1 | 0.5 |
| Mn | ≤ 2 | 1.3 |
| P | ≤ 0.04 | |
| S | ≤ 0.03 | |
| Cr | 13.5 – 16 | 14.8 |
| Ni | 24 – 27 | 25.5 |
| Mo | 1 – 1.5 | 1.25 |
| Tiγ′ (Ni3Ti) former | 1.9 – 2.35 | 2.1 |
| V | 0.1 – 0.5 | 0.3 |
| Al | ≤ 0.35 | 0.2 |
| Bgrain-boundary strengthener | 0 – 0.01 | 0.01 |
| Febalance, ~53 % | balance |
What surface finishes work on 660?
Not anodizable — passivate per AMS 2700/ASTM A967, electropolish or mechanically polish; oxide films from ageing must be pickled or blasted off before plating, and silver or MoS2 coatings are common on fasteners to prevent galling.
Surface treatments FabDigit runs on stainless steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Plating
Organic Coating
CVD Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Stainless Steel 660 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- S66286
- JIS
- SUH660
How much does 660 cost?
660 is a premium-cost stainless steel ($$$), pricier than about 58% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
660 — frequently asked
What is 660 used for?
660 is typically used for aircraft engine fasteners and turbine bolting, gas-turbine discs and ring parts, exhaust valves, high-temperature springs, turbocharger components and jet engine casings and housings. In short: high-temp aerospace stainless.
What is the yield strength of 660?
660 has a typical yield strength of 310 MPa (45 ksi) and a tensile strength of 690 MPa (100 ksi) — weaker than 63% of stainless steel grades. Strength varies by condition: see the 7 listed tempers.
Is 660 easy to machine?
Not especially — machinability is rated poor (28/100, worse than 79% of stainless steel grades). Gummy and highly work-hardening — machine in the solution-treated condition where possible with rigid setups, positive-rake carbide, heavy flood coolant, low speed (15–25 m/min) and constant feed to avoid glazing; aged material typically cut at ~15 % of AISI 1212 rates.
Can 660 be welded?
Yes — weldability is rated good (55/100). GTAW/EBW with matching A286 or Ni-base filler works, but the alloy is prone to hot cracking and strain-age cracking; weld in the solution-treated state, restrain minimally, and re-solution plus age the weldment for full properties.
What surface finishes work on 660?
Not anodizable — passivate per AMS 2700/ASTM A967, electropolish or mechanically polish; oxide films from ageing must be pickled or blasted off before plating, and silver or MoS2 coatings are common on fasteners to prevent galling.
Can 660 be formed, bent or molded?
Cold form and draw only in the annealed/solution-treated condition, allowing for high springback and ~2× the load of 304; hot work at 1100–950 °C then solution treat, and never form aged material.
What is the maximum service temperature of 660?
660 is rated for continuous use to about 540°C (1,004 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 660 Solution Annealed and 660 STA-900?
Solution Annealed is the default condition — standard stock condition for bar, sheet and wire that will be machined or formed and then age hardened by the user. STA-900: lower solution temperature keeps a finer grain size for higher room-temperature yield strength in bolting; slightly lower creep/rupture capability than the 980 °C treatment. Yield strength is 310 MPa in Solution Annealed versus 760 MPa in STA-900.
How much does 660 cost?
660 is a premium-cost stainless steel ($$$), pricier than about 58% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Can FabDigit make parts in 660?
Yes — 660 is available for CNC machining and sheet metal; every part is priced by an engineer rather than instantly. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM A453/A453M Grade 660 — Bolting with Expansion Coefficients Comparable to Austenitic Stainless Steels — ASTM International (2021)
- AMS 5731 / 5732 / 5734 / 5737 — Alloy Bars, Forgings and Rings, 15Cr-25.5Ni-1.2Mo-2.1Ti-0.3V-0.005B — SAE International (2018)
- JIS G 4311 SUH660 / GB/T 1221 (0Cr15Ni25Ti2MoAlVB, GH2132) — JISC / SAC (2016)
- ASM Specialty Handbook: Heat-Resistant Materials — ASM International (1997)
- MMPDS-17, Metallic Materials Properties Development and Standardization — Battelle/FAA (2022)
- A286 / Alloy 660 technical data sheet — Specialty steel producers (e.g. Carpenter, Aubert & Duval, VDM) (2023)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.