Nickel Alloy Alloy 684-ST (Solution annealed)
Heat-treated state
UNS N07500 · EN 2.4983
Softest supplied state — use when heavy machining, hot/cold forming or fabrication must precede final ageing.
Values for the ST 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 |
|---|---|---|---|---|---|---|
STThis page 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 | — |
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-ST?
Alloy 684-ST is Alloy 684 heat treated to ST — softest supplied state — use when heavy machining, hot/cold forming or fabrication must precede final ageing. Alloy 684-ST has a yield strength of 585 MPa (84.8 ksi) and a tensile strength of 965 MPa (140 ksi) — stronger than 81% of nickel alloy grades. Elongation at break is 35% and the elastic modulus is 213 GPa (30.9 Msi). Alloy 684-ST 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; ST is available on request or by drawing note.
Advantages
- High strength — 585 MPa (84.8 ksi), better than 81% of nickel alloy grades
Limitations
- Difficult to weld — 32/100, worse than 77% of nickel alloy grades
Alloy 684-ST properties
Typical room-temperature values for Alloy 684-ST; 12 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-ST 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-ST has a yield strength of 585 MPa (84.8 ksi) and a tensile strength of 965 MPa (140 ksi) — stronger than 81% of nickel alloy grades. Elongation at break is 35% and the elastic modulus is 213 GPa (30.9 Msi).
Thermal6
Alloy 684-ST is rated for continuous service to 700°C (1,292 °F). It conducts heat at 11 W/m·K (6.36 BTU/hr·ft·°F), worse than 60% of nickel alloy grades. Thermal expansion is 12.1 µm/m·K (6.72 µin/in·°F).
Electrical3
Alloy 684-ST conducts electricity at 1.4 % IACS, worse than 65% of nickel alloy grades.
Chemical & Environmental3
Corrosion resistance is very good (72/100), worse than 71% of nickel alloy grades.
Sustainability4
Producing a kilogram of Alloy 684-ST 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-ST's machinability is poor (18/100, worse than 61% of nickel alloy grades); weldability poor (32/100); formability fair (40/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Alloy 684-ST
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-ST — frequently asked
What is Alloy 684-ST used for?
Alloy 684-ST 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-ST?
Alloy 684-ST has a typical yield strength of 585 MPa (84.8 ksi) and a tensile strength of 965 MPa (140 ksi) — stronger than 81% of nickel alloy grades. Strength varies by condition: see the 5 listed tempers.
Is Alloy 684-ST easy to machine?
Not especially — machinability is rated poor (18/100, worse than 61% 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-ST be welded?
Not readily — weldability is rated poor (32/100). 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-ST?
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-ST 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-ST?
Alloy 684-ST 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 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.