Cobalt-Chrome Alloy S-816-AC (Spheroidize annealed)
Heat-treated state
UNS R30816 · also Haynes S-816
Investment-cast blades, vanes and nozzle parts used directly in the as-cast condition; coarse carbide network, lower ductility.
Values for the AC condition
Other S-816 tempers and conditions
S-816 is listed in 6 conditions; see the grade overview at S-816.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Softest supplied condition — used before final forming/machining, or where maximum ductility and homogeneity are needed prior to aging. | 345 | 830 | 38 | 220 HB | — |
Hot Rolled + Annealed | Mill condition for bar/billet stock destined for forging or re-heat-treatment; moderate strength, good ductility. | 400 | 870 | 30 | 24 HRC | 1.9 % IACS |
ACThis page Spheroidize annealed | Investment-cast blades, vanes and nozzle parts used directly in the as-cast condition; coarse carbide network, lower ductility. | 430 | 745 | 9 | 29 HRC | 1.9 % IACS |
Cast + Heat Treated | Castings homogenised and aged to refine carbide distribution — better creep-rupture consistency than as-cast. | 460 | 800 | 11 | 30 HRC | 1.9 % IACS |
STADefault Solution treated and aged | Standard service condition for wrought bar/forgings: carbide precipitation gives peak elevated-temperature strength and creep life. | 480 | 1,000 | 18 | 31 HRC | — |
Cold drawn | Cold-drawn small bar and wire where higher room-temperature strength and tight tolerance matter more than ductility. | 900 | 1,250 | 8 | 38 HRC | 1.9 % IACS |
What is S-816-AC?
S-816-AC is S-816 heat treated to AC — investment-cast blades, vanes and nozzle parts used directly in the as-cast condition; coarse carbide network, lower ductility. S-816-AC has a yield strength of 430 MPa (62.4 ksi) and a tensile strength of 745 MPa (108 ksi) — weaker than 96% of cobalt-chrome alloy grades. Elongation at break is 9% and the elastic modulus is 195 GPa (28.3 Msi). S-816-AC has a density of 8.68 g/cm³ (0.314 lb/in³), heavier than 79% of cobalt-chrome alloy grades. It melts at 1,330°C (2,426 °F). STA is the default condition FabDigit quotes; AC is available on request or by drawing note.
Limitations
- Low strength — 430 MPa (62.4 ksi), worse than 96% of cobalt-chrome alloy grades
- Low stiffness — 195 GPa (28.3 Msi), worse than 96% of cobalt-chrome alloy grades
- Hard to polish — 65/100, worse than 96% of cobalt-chrome alloy grades
S-816-AC properties
Typical room-temperature values for S-816-AC; 22 are specific to this condition. Other listed values are S-816 reference data and may not represent this condition. Bars are the position among cobalt-chrome alloy grades.
Physical3
S-816-AC has a density of 8.68 g/cm³ (0.314 lb/in³), heavier than 79% of cobalt-chrome alloy grades. It melts at 1,330°C (2,426 °F).
Mechanical14
S-816-AC has a yield strength of 430 MPa (62.4 ksi) and a tensile strength of 745 MPa (108 ksi) — weaker than 96% of cobalt-chrome alloy grades. Elongation at break is 9% and the elastic modulus is 195 GPa (28.3 Msi).
Thermal6
S-816-AC is rated for continuous service to 870°C (1,598 °F). It conducts heat at 12.5 W/m·K (7.22 BTU/hr·ft·°F), worse than 77% of cobalt-chrome alloy grades. Thermal expansion is 13.9 µm/m·K (7.72 µin/in·°F).
Electrical3
S-816-AC conducts electricity at 1.9 % IACS, worse than 52% of cobalt-chrome alloy grades.
Chemical & Environmental3
Corrosion resistance is very good (72/100), worse than 61% of cobalt-chrome alloy grades.
Sustainability4
Producing a kilogram of S-816-AC takes about 190 MJ of energy and emits 13 kg of CO₂ — more than 70% of cobalt-chrome alloy grades. Typical recycled content is 30%.
Manufacturability7
S-816-AC's machinability is not recommended (12/100, better than 61% of cobalt-chrome alloy grades); weldability poor (22/100); formability not recommended (5/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with S-816-AC
Is S-816 easy to machine?
Very difficult — rigid setups, positive-rake carbide or ceramic tooling, low speed (10–20 m/min carbide), heavy constant feed and flood coolant to avoid work hardening and glazing; grinding preferred for finish.
Can S-816 be welded?
GTAW with matched or Co-base filler in the solution-treated condition only; high carbon makes it crack-sensitive, so preheat is unnecessary but low heat input, minimal restraint and a full post-weld solution+age are required.
Can S-816 be formed, bent or molded?
Hot work 1100–1200 °C with frequent reheats; cold forming limited to gentle bends on annealed sheet — plan interstage anneals, and investment casting is the usual route for complex airfoils.
What surface finishes work on S-816?
Not anodizable; use abrasive blast plus pickling for scale removal, and aluminide/MCrAlY diffusion coatings for hot-gas surfaces; polishes to a bright finish though carbides can pull out.
S-816 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 |
|---|---|---|
| Chigh carbon — carbide strengthening | 0.32 – 0.42 | 0.38 |
| Mn | 1 – 2 | 1.2 |
| Si | ≤ 1 | 0.4 |
| Cr | 19 – 21 | 20 |
| NiFCC matrix stabiliser | 19 – 21 | 20 |
| Mo | 3.5 – 4.5 | 4 |
| W | 3.5 – 4.5 | 4 |
| NbCb; may include incidental Ta | 3.5 – 4.5 | 4 |
| Fe | ≤ 5 | 4 |
| S | ≤ 0.03 | — |
| P | ≤ 0.04 | — |
| Cobalance, ~42 % | balance | — |
S-816-AC — frequently asked
What is S-816-AC used for?
S-816-AC is typically used for turbine blades and vanes, afterburner components and high-temp fasteners. In short: legacy cobalt turbine alloy; carbide-strengthened to 870 °C; very difficult to machine.
What is the yield strength of S-816-AC?
S-816-AC has a typical yield strength of 430 MPa (62.4 ksi) and a tensile strength of 745 MPa (108 ksi) — weaker than 96% of cobalt-chrome alloy grades. Strength varies by condition: see the 6 listed tempers.
Is S-816-AC easy to machine?
Not especially — machinability is rated not recommended (12/100, better than 61% of cobalt-chrome alloy grades). Very difficult — rigid setups, positive-rake carbide or ceramic tooling, low speed (10–20 m/min carbide), heavy constant feed and flood coolant to avoid work hardening and glazing; grinding preferred for finish.
Can S-816-AC be welded?
Not readily — weldability is rated poor (22/100). GTAW with matched or Co-base filler in the solution-treated condition only; high carbon makes it crack-sensitive, so preheat is unnecessary but low heat input, minimal restraint and a full post-weld solution+age are required.
What surface finishes work on S-816-AC?
Not anodizable; use abrasive blast plus pickling for scale removal, and aluminide/MCrAlY diffusion coatings for hot-gas surfaces; polishes to a bright finish though carbides can pull out.
Can S-816-AC be formed, bent or molded?
Hot work 1100–1200 °C with frequent reheats; cold forming limited to gentle bends on annealed sheet — plan interstage anneals, and investment casting is the usual route for complex airfoils.
What is the maximum service temperature of S-816-AC?
S-816-AC 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 S-816-STA and S-816-CD?
STA is the default condition — standard service condition for wrought bar/forgings: carbide precipitation gives peak elevated-temperature strength and creep life. CD: cold-drawn small bar and wire where higher room-temperature strength and tight tolerance matter more than ductility. Yield strength is 480 MPa in STA versus 900 MPa in CD.
Sources
- Superalloys Source Book / ASM Handbook Vol.1 — Cobalt-Base Heat-Resistant Alloys — ASM International (1990)
- Aerospace Structural Metals Handbook — S-816 (Grade 671) — CINDAS/Purdue (1998)
- SAE AMS 5765 — Cobalt Alloy Bars, Forgings and Rings 20Cr-20Ni-4W-4Mo-4Cb — SAE International (2012)
- SAE/ASTM UNS R30816 alloy designation — SAE/ASTM (2018)
- Machining Data Handbook — heat-resistant cobalt alloys — Metcut Research (1980)
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.