Cobalt-Chrome Alloy Stellite 21
UNS R30021 · also CoCrMo Stellite
Stellite 21 is a low-carbon cast and weld-overlay Co-Cr-Mo alloy (UNS R30021, also matching the ASTM F75 implant composition) strengthened mainly by molybdenum in solid solution rather than by heavy carbide content.
Reference datasheet — Stellite 21 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 As Cast condition
Stellite 21 tempers and conditions
Stellite 21 is supplied in 5 conditions, soft to hard. As Cast 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 |
|---|---|---|---|---|---|---|
hardfacing overlay (PTA/GTAW/SMAW), undiluted deposit | Use for cladding valve seats, dies and shafts; hardness rises substantially by work hardening in service. | 490 | 700 | 8 | 32 HRC | 2 % IACS |
As CastDefault investment/sand cast, no post-heat-treatment | Default form for valve trim, nozzles, pump and hot-work parts; best balance of toughness and wear resistance. | 495 | 710 | 9 | 32 HRC | 2 % IACS |
Hot isostatic pressed | Pick when near-net-shape parts need fine uniform carbides, isotropic properties and no casting porosity. | 640 | 950 | 16 | 34 HRC | 2 % IACS |
Solution treated + aged | Select when maximum hardness and creep/wear resistance are wanted and reduced ductility is acceptable. | 650 | 900 | 4 | 40 HRC | 2.1 % IACS |
hot rolled / forged and annealed bar | Choose for wrought bar or forgings needing higher strength, ductility and sounder structure than castings. | 700 | 1,000 | 14 | 35 HRC | 2.1 % IACS |
What is Stellite 21?
Stellite 21 is a low-carbon cast and weld-overlay Co-Cr-Mo alloy (UNS R30021, also matching the ASTM F75 implant composition) strengthened mainly by molybdenum in solid solution rather than by heavy carbide content. It is chosen for the best weldability and toughness in the Stellite family together with good corrosion resistance, and is supplied as overlay wire and electrode, investment castings, HIP powder parts and hot-worked bar; 495 MPa yield, 710 MPa tensile, 9 % elongation, 32 HRC, service to 760 °C. Abrasion resistance is lower than carbide-rich grades such as Stellite 6, and with a machinability rating of 15 most finishing is done by grinding or EDM. Stellite 21 has a density of 8.33 g/cm³ (0.301 lb/in³), lighter than 64% of cobalt-chrome alloy grades. It melts at 1,186°C (2,167 °F). Stellite 21 has a yield strength of 495 MPa (71.8 ksi) and a tensile strength of 710 MPa (103 ksi) — weaker than 65% of cobalt-chrome alloy grades. Elongation at break is 9% and the elastic modulus is 248 GPa (36 Msi).
What is Stellite 21 used for?
- Hot forging dies
- Pump shafts and sleeves
- Valve seats and trim
- Weld-overlay hardfacing on steel substrates
- Cast surgical implant components
- Hot shear and trim blades
Advantages
- Low embodied carbon — 10 kg CO₂/kg, better than 82% of cobalt-chrome alloy grades
- Readily welded — 55/100, better than 80% of cobalt-chrome alloy grades
- Forms and bends easily — 20/100, better than 77% of cobalt-chrome alloy grades
Stellite 21 properties
Typical room-temperature values for Stellite 21-As Cast; bars are the position among cobalt-chrome alloy grades.
Physical3
Stellite 21 has a density of 8.33 g/cm³ (0.301 lb/in³), lighter than 64% of cobalt-chrome alloy grades. It melts at 1,186°C (2,167 °F).
Mechanical16
Stellite 21 has a yield strength of 495 MPa (71.8 ksi) and a tensile strength of 710 MPa (103 ksi) — weaker than 65% of cobalt-chrome alloy grades. Elongation at break is 9% and the elastic modulus is 248 GPa (36 Msi).
Thermal6
Stellite 21 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 conducts electricity at 2 % IACS, better than 79% of cobalt-chrome alloy grades.
Chemical & Environmental3
Corrosion resistance is very good (80/100), better than 63% of cobalt-chrome alloy grades.
Sustainability4
Producing a kilogram of Stellite 21 takes about 145 MJ of energy and emits 10 kg of CO₂ — less than 73% of cobalt-chrome alloy grades. Typical recycled content is 25%.
Manufacturability8
Stellite 21'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.
Strength versus weight in the cobalt-chrome alloy family
Yield strength against density for every cobalt-chrome alloy grade FabDigit runs. Stellite 21 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with Stellite 21
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.
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 |
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.
Equivalent designations
Standards and trade names that resolve to Cobalt-Chrome Alloy Stellite 21 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- R30021
- Trade names
- CoCrMo Stellite
- Similar grades
- F75
How much does Stellite 21 cost?
Stellite 21 is a specialty-cost cobalt-chrome alloy ($$$$$), pricier than about 99% 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.
Stellite 21 — frequently asked
What is Stellite 21 used for?
Stellite 21 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?
Stellite 21 has a typical yield strength of 495 MPa (71.8 ksi) and a tensile strength of 710 MPa (103 ksi) — weaker than 65% of cobalt-chrome alloy grades. Strength varies by condition: see the 5 listed tempers.
Is Stellite 21 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 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?
Not anodizable; passivate or electropolish, and it takes a mirror polish for valve seats and implant surfaces; hard coatings rarely needed.
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 is the maximum service temperature of Stellite 21?
Stellite 21 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.
How much does Stellite 21 cost?
Stellite 21 is a specialty-cost cobalt-chrome alloy ($$$$$), pricier than about 99% 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
- 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; 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.