Stainless Steel 660 · heat-treated state
Stainless Steel 660 Age Hardened
Properties of the Age Hardened condition, compared with the other 660 tempers.
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.
What is 660 Age Hardened?
660 Age Hardened is 660 heat treated to Age Hardened — 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. 660 Age Hardened has a yield strength of 690 MPa (100 ksi) and a tensile strength of 1,000 MPa (145 ksi) — stronger than 92% of stainless steel grades. Elongation at break is 20% and the elastic modulus is 201 GPa (29.2 Msi). 660 Age Hardened 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). Solution Annealed is the default condition FabDigit quotes; Age Hardened is available on request or by drawing note.
Advantages
- High strength — 690 MPa (100 ksi), better than 92% of stainless steel grades
Limitations
- Difficult to machine — 20/100, worse than 98% of stainless steel grades
- High embodied carbon — 6.8 kg CO₂/kg, worse than 95% of stainless steel grades
- Limited formability — 15/100, worse than 91% of stainless steel grades
- Low electrical conductivity — 1.9 % IACS, worse than 84% of stainless steel grades
- Difficult to weld — 40/100, worse than 83% of stainless steel grades
660 Age Hardened properties
Typical room-temperature values for 660 Age Hardened — 18 properties are specific to this condition; the rest are grade-level values shared by every 660 temper. Each bar shows where the value sits among the stainless steel grades in FabDigit's library — further right is higher.
Physical3
660 Age Hardened 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 Age Hardened has a yield strength of 690 MPa (100 ksi) and a tensile strength of 1,000 MPa (145 ksi) — stronger than 92% of stainless steel grades. Elongation at break is 20% and the elastic modulus is 201 GPa (29.2 Msi).
Thermal5
660 Age Hardened is rated for continuous service to 700°C (1,292 °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 Age Hardened conducts electricity at 1.9 % IACS, worse than 84% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is good (60/100), worse than 58% of stainless steel grades.
Sustainability4
Producing a kilogram of 660 Age Hardened 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 Age Hardened's machinability is poor (20/100, worse than 98% of stainless steel grades); weldability fair (40/100); formability poor (15/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other 660 tempers and conditions
660 is also supplied in 7 other conditions. The full side-by-side table is on the 660 overview.
- Solution AnnealedDefaultStandard stock condition for bar, sheet and wire that will be machined or formed and then age hardened by the user.310 MPa yield · 160 HB
- CW+AgedHighest 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 MPa yield · 44 HRC
- STA-900Lower 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 MPa yield · 34 HRC
- Cold DrawnPick for close-tolerance bright bar and wire feedstock where strength above the solution-annealed level is wanted before final ageing.700 MPa yield · 23 HRC
- Age HardenedThe 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 MPa yield · 32 HRC
- AnnealedChoose for maximum cold formability of sheet/strip and for wire before drawing; must be aged afterwards to develop strength.280 MPa yield · 150 HB
Working with 660 Age Hardened
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.
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.
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 | — |
660 Age Hardened — frequently asked
What is 660 Age Hardened used for?
660 Age Hardened 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 Age Hardened?
660 Age Hardened has a typical yield strength of 690 MPa (100 ksi) and a tensile strength of 1,000 MPa (145 ksi) — stronger than 92% of stainless steel grades. Strength varies by condition: see the 8 listed tempers.
Is 660 Age Hardened easy to machine?
Not especially — machinability is rated poor (20/100, worse than 98% 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 Age Hardened be welded?
With care — weldability is rated fair (40/100). 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 Age Hardened?
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 Age Hardened 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 Age Hardened?
660 Age Hardened is rated for continuous use to about 700°C (1,292 °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.
Can FabDigit make parts in 660 Age Hardened?
Yes — 660 Age Hardened is available for CNC machining and sheet metal with instant online pricing. 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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.