Steel SUH660 · heat-treated state
Steel SUH660-ST
Properties of the ST condition, compared with the other SUH660 tempers.
Soft supply condition for forming, deep machining or welding before final ageing.
What is SUH660-ST?
SUH660-ST is SUH660 heat treated to ST — soft supply condition for forming, deep machining or welding before final ageing. SUH660-ST has a yield strength of 285 MPa (41.3 ksi) and a tensile strength of 655 MPa (95 ksi) — weaker than 89% of steel grades. Elongation at break is 45% and the elastic modulus is 201 GPa (29.2 Msi). SUH660-ST has a density of 7.94 g/cm³ (0.287 lb/in³), heavier than 93% of steel grades. It melts at 1,370°C (2,498 °F). STA is the default condition FabDigit quotes; ST is available on request or by drawing note.
Advantages
- Ductile — tolerates forming and impact — 45%, better than 100% of steel grades
- Good corrosion resistance — 58/100, better than 99% of steel grades
- High service temperature — 600°C (1,112 °F), better than 98% of steel grades
- Polishes to a fine finish — 75/100, better than 94% of steel grades
- Tough — resists crack growth — 130 MPa·√m (118.3 ksi·√in), better than 89% of steel grades
Limitations
- Low electrical conductivity — 1.9 % IACS, worse than 100% of steel grades
- Poor heat conductor — 13 W/m·K (7.51 BTU/hr·ft·°F), worse than 99% of steel grades
- High embodied carbon — 6.5 kg CO₂/kg, worse than 98% of steel grades
- Low strength — 285 MPa (41.3 ksi), worse than 89% of steel grades
- Difficult to machine — 30/100, worse than 89% of steel grades
SUH660-ST properties
Typical room-temperature values for SUH660-ST — 13 properties are specific to this condition; the rest are grade-level values shared by every SUH660 temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
SUH660-ST has a density of 7.94 g/cm³ (0.287 lb/in³), heavier than 93% of steel grades. It melts at 1,370°C (2,498 °F).
Mechanical16
SUH660-ST has a yield strength of 285 MPa (41.3 ksi) and a tensile strength of 655 MPa (95 ksi) — weaker than 89% of steel grades. Elongation at break is 45% and the elastic modulus is 201 GPa (29.2 Msi).
Thermal6
SUH660-ST is rated for continuous service to 600°C (1,112 °F). It conducts heat at 13 W/m·K (7.51 BTU/hr·ft·°F), worse than 99% of steel grades. Thermal expansion is 16.4 µm/m·K (9.11 µin/in·°F).
Electrical3
SUH660-ST conducts electricity at 1.9 % IACS, worse than 100% of steel grades.
Chemical & Environmental3
Corrosion resistance is good (58/100), better than 99% of steel grades.
Sustainability4
Producing a kilogram of SUH660-ST takes about 90 MJ of energy and emits 6.5 kg of CO₂ — more than 98% of steel grades. Typical recycled content is 30%.
Manufacturability6
SUH660-ST's machinability is poor (30/100, worse than 89% of steel grades); weldability good (65/100); formability good (55/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other SUH660 tempers and conditions
SUH660 is also supplied in 4 other conditions. The full side-by-side table is on the SUH660 overview.
- STADefaultStandard stocked condition: best balance of room-temperature strength, ductility and 650–700 °C creep/rupture life.725 MPa yield · 30 HRC
- CD+AFastener wire/bar route: cold work before ageing lifts strength well above 1150 MPa at the cost of ductility and toughness.1,030 MPa yield · 38 HRC
- STA-900Choose for fasteners and highly stressed parts needing maximum room- and mid-temperature strength (finer grain, lower creep capability than 980 °C solution).790 MPa yield · 33 HRC
- STSoft supply condition for forming, deep machining or welding before final ageing.285 MPa yield · 190 HB
Working with SUH660-ST
Is SUH660 easy to machine?
Machine like a superalloy: rigid setups, sharp positive-rake carbide or ceramic, low speed / heavy positive feed, flood coolant — it work-hardens fast and glazes if the tool dwells; rough in ST condition and finish after ageing where possible.
Can SUH660 be welded?
GTAW/EBW with matching A286 or Ni-base filler works, but keep heat input low and weld in the solution-treated state, then re-solution and age to avoid strain-age (post-weld) cracking in the HAZ.
Can SUH660 be formed, bent or molded?
Cold form only in the solution-treated condition with generous radii and high press loads; hot work at 1010–1150 °C and always finish above ~950 °C to avoid Ti-rich phase and cracking.
What surface finishes work on SUH660?
Takes a good mechanical polish and can be passivated (nitric or citric) like a stainless; not anodizable — for high-temperature threads use silver, Cu-Ni or dry-film lubricant coatings to prevent galling.
SUH660 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 | 1.2 |
| P | ≤ 0.04 | — |
| S | ≤ 0.03 | — |
| Ni | 24 – 27 | 25.5 |
| Cr | 13.5 – 16 | 15 |
| Mo | 1 – 1.5 | 1.25 |
| Tiγ′ Ni₃(Ti,Al) former | 1.9 – 2.35 | 2.1 |
| V | 0.1 – 0.5 | 0.3 |
| Al | ≤ 0.35 | 0.2 |
| Bgrain-boundary strengthening | 0 – 0.01 | 0.01 |
| Febalance ≈ 53 % | balance | — |
SUH660-ST — frequently asked
What is SUH660-ST used for?
SUH660-ST is typically used for aircraft engine fasteners, gas turbine bolts and studs, high-temperature springs, turbocharger wheel shafts, exhaust valves and aero-engine discs and rings. In short: high-temp aerospace bar.
What is the yield strength of SUH660-ST?
SUH660-ST has a typical yield strength of 285 MPa (41.3 ksi) and a tensile strength of 655 MPa (95 ksi) — weaker than 89% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is SUH660-ST easy to machine?
Not especially — machinability is rated poor (30/100, worse than 89% of steel grades). Machine like a superalloy: rigid setups, sharp positive-rake carbide or ceramic, low speed / heavy positive feed, flood coolant — it work-hardens fast and glazes if the tool dwells; rough in ST condition and finish after ageing where possible.
Can SUH660-ST be welded?
Yes — weldability is rated good (65/100). GTAW/EBW with matching A286 or Ni-base filler works, but keep heat input low and weld in the solution-treated state, then re-solution and age to avoid strain-age (post-weld) cracking in the HAZ.
What surface finishes work on SUH660-ST?
Takes a good mechanical polish and can be passivated (nitric or citric) like a stainless; not anodizable — for high-temperature threads use silver, Cu-Ni or dry-film lubricant coatings to prevent galling.
Can SUH660-ST be formed, bent or molded?
Cold form only in the solution-treated condition with generous radii and high press loads; hot work at 1010–1150 °C and always finish above ~950 °C to avoid Ti-rich phase and cracking.
What is the maximum service temperature of SUH660-ST?
SUH660-ST is rated for continuous use to about 600°C (1,112 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between SUH660-STA and SUH660-ST?
STA is the default condition — standard stocked condition: best balance of room-temperature strength, ductility and 650–700 °C creep/rupture life. ST: soft supply condition for forming, deep machining or welding before final ageing. Yield strength is 725 MPa in STA versus 285 MPa in ST.
Can FabDigit make parts in SUH660-ST?
Yes — SUH660-ST 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
- JIS G 4311 — Heat-resisting steel bars — JSA (2019)
- AMS 5737 / AMS 5732 — Alloy Bars, Forgings (UNS S66286) — SAE International (2021)
- ASTM A453/A453M Grade 660 — ASTM International (2022)
- ASM Specialty Handbook: Heat-Resistant Materials — ASM International (1997)
- A286 (UNS S66286) alloy datasheet — specialty alloy producers (2023)
- GH2132/SUH660 (2025)
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.