Nickel Alloy Alloy 684
UNS N07500 · EN 2.4983
Alloy 684 is a precipitation-hardenable Ni-Cr-Co superalloy (UNS N07500, 2.4983) strengthened by gamma-prime from a high Al+Ti content, supplied solution-treated (ST), solution-treated and aged (STA, STA3), hot-finished or as heat-treated castings.
Reference datasheet — Alloy 684 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the STA condition
Alloy 684 tempers and conditions
Alloy 684 is supplied in 5 conditions, soft to hard. STA is the default FabDigit quotes; the values on this page are for it.
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 | — |
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?
Alloy 684 is a precipitation-hardenable Ni-Cr-Co superalloy (UNS N07500, 2.4983) strengthened by gamma-prime from a high Al+Ti content, supplied solution-treated (ST), solution-treated and aged (STA, STA3), hot-finished or as heat-treated castings. Engineers select it for turbine fasteners and disks that need 860 MPa yield, 1310 MPa tensile, 16 % elongation and 355 HB (38 HRC) with service to 870 °C, normally as bar, forgings or castings. The limits are poor machinability (score 12) and low weldability (score 20) driven by strain-age cracking risk. Alloy 718 is the easier alternative to weld and machine where its lower temperature capability is acceptable. Alloy 684 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). Alloy 684 has a yield strength of 860 MPa (125 ksi) and a tensile strength of 1,310 MPa (190 ksi) — stronger than 91% of nickel alloy grades. Elongation at break is 16% and the elastic modulus is 213 GPa (30.9 Msi).
What is Alloy 684 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
- High-temperature spring and washer stacks
Advantages
- High strength — 860 MPa (125 ksi), better than 91% of nickel alloy grades
Limitations
- Difficult to weld — 20/100, worse than 84% of nickel alloy grades
- Limited ductility — 16%, worse than 79% of nickel alloy grades
- Limited formability — 20/100, worse than 75% of nickel alloy grades
Alloy 684 properties
Typical room-temperature values for Alloy 684-STA; bars are the position among nickel alloy grades.
Physical3
Alloy 684 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 has a yield strength of 860 MPa (125 ksi) and a tensile strength of 1,310 MPa (190 ksi) — stronger than 91% of nickel alloy grades. Elongation at break is 16% and the elastic modulus is 213 GPa (30.9 Msi).
Thermal6
Alloy 684 is rated for continuous service to 870°C (1,598 °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 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 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's machinability is not recommended (12/100, worse than 86% of nickel alloy grades); weldability poor (20/100); formability poor (20/100).
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 nickel alloy family
Yield strength against density for every nickel alloy grade FabDigit runs. Alloy 684 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with Alloy 684
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.
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 |
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.
Surface treatments FabDigit runs on nickel alloy 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
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Nickel Alloy Alloy 684 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- N07500
- EN / DIN / Werkstoff-Nr.
- 2.4983
How much does Alloy 684 cost?
Alloy 684 is a high-cost nickel alloy ($$$$), pricier than about 78% 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.
Alloy 684 — frequently asked
What is Alloy 684 used for?
Alloy 684 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?
Alloy 684 has a typical yield strength of 860 MPa (125 ksi) and a tensile strength of 1,310 MPa (190 ksi) — stronger than 91% of nickel alloy grades. Strength varies by condition: see the 5 listed tempers.
Is Alloy 684 easy to machine?
Not especially — machinability is rated not recommended (12/100, worse than 86% 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 be welded?
Not readily — weldability is rated poor (20/100). 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?
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 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?
Alloy 684 is rated for continuous use to about 870°C (1,598 °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.
How much does Alloy 684 cost?
Alloy 684 is a high-cost nickel alloy ($$$$), pricier than about 78% 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.
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; 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.