Nickel Alloy Alloy 684 STA3
Precip hard
UNS N07500 · EN 2.4983
STA3 = full triple heat treatment
Turbine-blade / long-life creep condition: extra stabilising step maximises rupture life above 750 °C at some loss of RT ductility.
Values for the STA3 condition
Other Alloy 684 tempers and conditions
Alloy 684 is listed in 5 conditions; see the grade overview at Alloy 684.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Softest supplied state — use when heavy machining, hot/cold forming or fabrication must precede final ageing. | 585 | 965 | 35 | 26 HRC | — |
As hot forged / hot rolled | Mill-supplied forged stock intended for further solution treatment and ageing by the part maker. | 700 | 1,100 | 22 | 32 HRC | 1.5 % IACS |
Investment cast + solution and aged | Equiaxed investment-cast blades/vanes and integral wheels where forging is impractical; lower ductility than wrought. | 790 | 1,035 | 6 | 36 HRC | — |
STADefault Solution treated and aged | Standard commercial bar/forging condition for disks, rings and high-temperature fasteners; best balance of strength and ductility. | 860 | 1,310 | 16 | 38 HRC | — |
STA3This page Full triple heat treatment | Turbine-blade / long-life creep condition: extra stabilising step maximises rupture life above 750 °C at some loss of RT ductility. | 900 | 1,350 | 13 | 40 HRC | 1.4 % IACS |
What is Alloy 684 STA3?
Alloy 684 STA3 is Alloy 684 in the STA3 condition — turbine-blade / long-life creep condition: extra stabilising step maximises rupture life above 750 °C at some loss of RT ductility. Alloy 684 STA3 has a yield strength of 900 MPa (131 ksi) and a tensile strength of 1,350 MPa (196 ksi) — stronger than 94% of nickel alloy grades. Elongation at break is 13% and the elastic modulus is 215 GPa (31.2 Msi). Alloy 684 STA3 has a density of 8.02 g/cm³ (0.29 lb/in³), lighter than 84% of nickel alloy grades. It melts at 1,300°C (2,372 °F). STA is the default condition FabDigit quotes; STA3 is available on request or by drawing note.
Advantages
- High strength — 900 MPa (131 ksi), better than 94% of nickel alloy grades
Limitations
- Difficult to machine — 10/100, worse than 93% of nickel alloy grades
- Difficult to weld — 12/100, worse than 90% of nickel alloy grades
- Limited formability — 12/100, worse than 83% of nickel alloy grades
- Limited ductility — 13%, worse than 82% of nickel alloy grades
- Low fracture toughness — 78 MPa·√m (71 ksi·√in), worse than 78% of nickel alloy grades
Alloy 684 STA3 properties
Typical room-temperature values for Alloy 684 STA3; 22 are specific to this condition. Other listed values are Alloy 684 reference data and may not represent this condition. Bars are the position among nickel alloy grades.
Physical3
Alloy 684 STA3 has a density of 8.02 g/cm³ (0.29 lb/in³), lighter than 84% of nickel alloy grades. It melts at 1,300°C (2,372 °F).
Mechanical16
Alloy 684 STA3 has a yield strength of 900 MPa (131 ksi) and a tensile strength of 1,350 MPa (196 ksi) — stronger than 94% of nickel alloy grades. Elongation at break is 13% and the elastic modulus is 215 GPa (31.2 Msi).
Thermal6
Alloy 684 STA3 is rated for continuous service to 900°C (1,652 °F). It conducts heat at 10.7 W/m·K (6.18 BTU/hr·ft·°F), worse than 68% of nickel alloy grades. Thermal expansion is 12.1 µm/m·K (6.72 µin/in·°F).
Electrical3
Alloy 684 STA3 conducts electricity at 1.4 % IACS, worse than 80% of nickel alloy grades.
Chemical & Environmental3
Corrosion resistance is very good (70/100), worse than 77% of nickel alloy grades.
Sustainability4
Producing a kilogram of Alloy 684 STA3 takes about 165 MJ of energy and emits 14 kg of CO₂ — more than 54% of nickel alloy grades. Typical recycled content is 35%.
Manufacturability8
Alloy 684 STA3's machinability is not recommended (10/100, worse than 93% of nickel alloy grades); weldability not recommended (12/100); formability not recommended (12/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Alloy 684 STA3
Is Alloy 684 easy to machine?
Machine solution-treated where possible; rigid setups, positive-rake carbide or ceramic tools, 8–20 m/min for carbide, heavy flood coolant, constant feed to avoid work-hardened glaze.
Can Alloy 684 be welded?
Weld only in the solution-treated state with matched or Waspaloy/Alloy 625 filler, low heat input and immediate post-weld solution + age; high Al+Ti makes strain-age cracking a real risk.
Can Alloy 684 be formed, bent or molded?
Hot work between about 1090 and 1150 °C with reheats; cold forming is limited to gentle bends in the solution-treated condition due to very high work-hardening rate.
What surface finishes work on Alloy 684?
Grind/belt with SiC or ceramic abrasives and shot peen loaded surfaces; protect hot-gas parts by aluminide or MCrAlY coating — no anodising applies.
Alloy 684 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 |
|---|---|---|
| Croxidation resistance | 17 – 20 | 18.5 |
| Co | 15 – 20 | 18 |
| Mosolid-solution strengthening | 3.5 – 5 | 4 |
| Tiγ′ former | 2.5 – 3.25 | 2.9 |
| Alγ′ former | 2.5 – 3.25 | 2.9 |
| C | 0.05 – 0.12 | 0.08 |
| Bgrain-boundary ductility | 0 – 0.01 | 0.01 |
| Zr | ≤ 0.1 | 0.05 |
| Feresidual | ≤ 4 | 1 |
| Mn | ≤ 0.75 | 0.1 |
| Si | ≤ 0.75 | 0.15 |
| S | ≤ 0.02 | — |
| Nibalance, typically 50–55 % | balance | — |
Alloy 684 STA3 — frequently asked
What is Alloy 684 STA3 used for?
Alloy 684 STA3 is typically used for gas turbine fasteners and studs, high-temperature bolting, turbine disks and rotor hardware, hot-section blade retention parts, heat-treated cast turbine components and high-temperature spring and washer stacks. In short: turbine-disk strength class; 870 °C service limit; very difficult to weld.
What is the yield strength of Alloy 684 STA3?
Alloy 684 STA3 has a typical yield strength of 900 MPa (131 ksi) and a tensile strength of 1,350 MPa (196 ksi) — stronger than 94% of nickel alloy grades. Strength varies by condition: see the 5 listed tempers.
Is Alloy 684 STA3 easy to machine?
Not especially — machinability is rated not recommended (10/100, worse than 93% of nickel alloy grades). Machine solution-treated where possible; rigid setups, positive-rake carbide or ceramic tools, 8–20 m/min for carbide, heavy flood coolant, constant feed to avoid work-hardened glaze.
Can Alloy 684 STA3 be welded?
Not readily — weldability is rated not recommended (12/100). Weld only in the solution-treated state with matched or Waspaloy/Alloy 625 filler, low heat input and immediate post-weld solution + age; high Al+Ti makes strain-age cracking a real risk.
What surface finishes work on Alloy 684 STA3?
Grind/belt with SiC or ceramic abrasives and shot peen loaded surfaces; protect hot-gas parts by aluminide or MCrAlY coating — no anodising applies.
Can Alloy 684 STA3 be formed, bent or molded?
Hot work between about 1090 and 1150 °C with reheats; cold forming is limited to gentle bends in the solution-treated condition due to very high work-hardening rate.
What is the maximum service temperature of Alloy 684 STA3?
Alloy 684 STA3 is rated for continuous use to about 900°C (1,652 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between Alloy 684-STA and Alloy 684-ST?
STA is the default condition — standard commercial bar/forging condition for disks, rings and high-temperature fasteners; best balance of strength and ductility. ST: softest supplied state — use when heavy machining, hot/cold forming or fabrication must precede final ageing. Yield strength is 860 MPa in STA versus 585 MPa in ST.
Sources
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- ASM Superalloys: A Technical Guide, 2nd ed. — ASM International (2002)
- AMS 5751 / UNS N07500 nickel alloy bar and forging specifications — SAE International (2018)
- DIN EN 10302 / W.-Nr. 2.4983 creep-resisting alloys — DIN/CEN (2008)
- ASM Handbook Vol.13B — Corrosion: Materials — ASM International (2005)
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.