Cobalt-Chrome Alloy Stellite 21 · finish state · default condition
Cobalt-Chrome Alloy Stellite 21 As Cast
Properties of the As Cast condition, compared with the other Stellite 21 tempers.
Default form for valve trim, nozzles, pump and hot-work parts; best balance of toughness and wear resistance.
What is Stellite 21 As Cast?
Stellite 21 As Cast is Stellite 21 supplied in the As Cast condition — default form for valve trim, nozzles, pump and hot-work parts; best balance of toughness and wear resistance. Stellite 21 As Cast has a yield strength of 495 MPa (71.8 ksi) and a tensile strength of 710 MPa (103 ksi) — weaker than 70% of cobalt-chrome alloy grades. Elongation at break is 9% and the elastic modulus is 248 GPa (36 Msi). Stellite 21 As Cast has a density of 8.33 g/cm³ (0.301 lb/in³), lighter than 66% of cobalt-chrome alloy grades. It melts at 1,186°C (2,167 °F).
Advantages
- Low embodied carbon — 10 kg CO₂/kg, better than 83% of cobalt-chrome alloy grades
- Readily welded — 55/100, better than 81% of cobalt-chrome alloy grades
- Forms and bends easily — 20/100, better than 78% of cobalt-chrome alloy grades
Stellite 21 As Cast properties
Typical room-temperature values for Stellite 21 As Cast — 9 properties are specific to this condition; the rest are grade-level values shared by every Stellite 21 temper. Each bar shows where the value sits among the cobalt-chrome alloy grades in FabDigit's library — further right is higher.
Physical3
Stellite 21 As Cast has a density of 8.33 g/cm³ (0.301 lb/in³), lighter than 66% of cobalt-chrome alloy grades. It melts at 1,186°C (2,167 °F).
Mechanical14
Stellite 21 As Cast has a yield strength of 495 MPa (71.8 ksi) and a tensile strength of 710 MPa (103 ksi) — weaker than 70% of cobalt-chrome alloy grades. Elongation at break is 9% and the elastic modulus is 248 GPa (36 Msi).
Thermal6
Stellite 21 As Cast is rated for continuous service to 760°C (1,400 °F). It conducts heat at 14.8 W/m·K (8.55 BTU/hr·ft·°F), better than 84% of cobalt-chrome alloy grades. Thermal expansion is 14.2 µm/m·K (7.89 µin/in·°F).
Electrical3
Stellite 21 As Cast conducts electricity at 2 % IACS, better than 78% of cobalt-chrome alloy grades.
Chemical & Environmental3
Corrosion resistance is very good (80/100), better than 60% of cobalt-chrome alloy grades.
Sustainability4
Producing a kilogram of Stellite 21 As Cast takes about 145 MJ of energy and emits 10 kg of CO₂ — less than 74% of cobalt-chrome alloy grades. Typical recycled content is 25%.
Manufacturability8
Stellite 21 As Cast's machinability is poor (15/100, better than 79% of cobalt-chrome alloy grades); weldability good (55/100); 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.
Other Stellite 21 tempers and conditions
Stellite 21 is also supplied in 4 other conditions. The full side-by-side table is on the Stellite 21 overview.
- As CastDefaultDefault form for valve trim, nozzles, pump and hot-work parts; best balance of toughness and wear resistance.495 MPa yield · 32 HRC
- Hot WorkedChoose for wrought bar or forgings needing higher strength, ductility and sounder structure than castings.700 MPa yield · 35 HRC
- AgedSelect when maximum hardness and creep/wear resistance are wanted and reduced ductility is acceptable.650 MPa yield · 40 HRC
Working with Stellite 21 As Cast
Is Stellite 21 easy to machine?
Very difficult and work-hardening — use rigid setups, negative-rake carbide or CBN at low speed with heavy positive feed, or finish by grinding/EDM.
Can Stellite 21 be welded?
The most weldable Stellite: GTAW/PTA/SMAW with 250–500 °C preheat, low dilution, slow cooling; avoid interpass cracking on thick sections.
Can Stellite 21 be formed, bent or molded?
Practically no cold formability — produce by investment casting, HIP powder consolidation, hot forging above ~1050 °C, or weld overlay/AM.
What surface finishes work on Stellite 21?
Not anodizable; passivate or electropolish, and it takes a mirror polish for valve seats and implant surfaces; hard coatings rarely needed.
Stellite 21 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 |
|---|---|---|
| Clow carbon vs Stellite 6/12 → tougher, weldable | 0.2 – 0.35 | 0.25 |
| Cr | 25 – 29 | 27 |
| Mosolid-solution strengthener | 4.5 – 6 | 5.5 |
| Ni | 1.75 – 3.75 | 2.5 |
| Fe | ≤ 3 | 1 |
| Si | ≤ 1 | 0.6 |
| Mn | ≤ 1 | 0.6 |
| Wmax, incidental | ≤ 0.5 | — |
| Cobalance, ~60–63 % | balance | — |
Stellite 21 As Cast — frequently asked
What is Stellite 21 As Cast used for?
Stellite 21 As Cast is typically used for hot forging dies, pump shafts and sleeves, valve seats and trim, weld-overlay hardfacing on steel substrates, cast surgical implant components and hot shear and trim blades. In short: tougher hardfacing cobalt.
What is the yield strength of Stellite 21 As Cast?
Stellite 21 As Cast has a typical yield strength of 495 MPa (71.8 ksi) and a tensile strength of 710 MPa (103 ksi) — weaker than 70% of cobalt-chrome alloy grades. Strength varies by condition: see the 5 listed tempers.
Is Stellite 21 As Cast easy to machine?
Not especially — machinability is rated poor (15/100, better than 79% of cobalt-chrome alloy grades). Very difficult and work-hardening — use rigid setups, negative-rake carbide or CBN at low speed with heavy positive feed, or finish by grinding/EDM.
Can Stellite 21 As Cast be welded?
Yes — weldability is rated good (55/100). The most weldable Stellite: GTAW/PTA/SMAW with 250–500 °C preheat, low dilution, slow cooling; avoid interpass cracking on thick sections.
What surface finishes work on Stellite 21 As Cast?
Not anodizable; passivate or electropolish, and it takes a mirror polish for valve seats and implant surfaces; hard coatings rarely needed.
Can Stellite 21 As Cast be formed, bent or molded?
Practically no cold formability — produce by investment casting, HIP powder consolidation, hot forging above ~1050 °C, or weld overlay/AM.
What is the maximum service temperature of Stellite 21 As Cast?
Stellite 21 As Cast is rated for continuous use to about 760°C (1,400 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between Stellite 21 As Cast and Stellite 21 Aged?
As Cast is the default condition — default form for valve trim, nozzles, pump and hot-work parts; best balance of toughness and wear resistance. Aged: select when maximum hardness and creep/wear resistance are wanted and reduced ductility is acceptable. Yield strength is 495 MPa in As Cast versus 650 MPa in Aged.
Can FabDigit make parts in Stellite 21 As Cast?
Yes — Stellite 21 As Cast is available for CNC machining with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- Stellite 21 alloy data sheet — Kennametal Stellite (2023)
- AMS 5385 — Cobalt Alloy Castings, Corrosion and Heat Resistant (Co-27Cr-5.5Mo-2.5Ni) — SAE International (2019)
- ASTM A494/A494M — Castings, Nickel and Nickel Alloy (related Co-Cr-Mo grades) — ASTM (2022)
- ASM Handbook Vol. 2 — Properties and Selection: Nonferrous Alloys (Cobalt-base alloys) — ASM International (1990)
- 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.