Cobalt-Chrome Alloys
Cobalt-chrome is the alloy family for surfaces that must stay hard while wet, hot and rubbing. The chromium oxide skin makes it as corrosion-proof as the best stainless; the cobalt matrix work-hardens under sliding contact instead of wearing away; and the carbides hold that hardness to 800 °C where steel has long softened. That combination is why artificial hip joints, valve seats in refinery steam, dental frameworks and jet-engine combustor rings are all Co-Cr — and why the alloy is expensive and among the hardest metals to machine.
Cobalt-chrome by application group
Orthopaedic Co-Cr-Mo28 % Cr, 6 % Mo, low C · F75 (cast), F1537 / F799 (wrought), F907460 – 2,000Hip and knee components, spinal and trauma hardware, dental frameworks — biocompatible, MRI-conditional, harder and more wear resistant than titanium or stainless implants.
Stellite hardfacing alloys25–30 % Cr, 4–15 % W, 1–2.5 % C · Stellite 6, 21, 1215450 – 650Valve seats and trim, pump shafts and sleeves, saw and knife edges, extrusion tooling, hot-forging dies — as solid castings, wrought bar or weld/PTA/laser overlays on steel.
High-temperature Co-Cr-W20 % Cr, 15 % W, 10 % Ni · L605 (Haynes 25), Haynes 1885460 – 1,830Combustor liners, afterburner and exhaust parts, turbine rings and seals, industrial furnace fixtures — oxidation resistant to 1,000 °C with better hot-wear and sulfidation resistance than nickel alloys.
Other cobalt alloysVarious2380 – 1,250MP35N, Elgiloy, Tribaloy, cast dental alloys and proprietary grades outside the groups above.
Choose cobalt-chrome for
Orthopaedic implants — hip and knee bearing surfaces, spinal rods, fracture plates (ASTM F75 cast, F1537 wrought); dental crowns, bridges and partial-denture frameworks; valve seats, pump sleeves, saw teeth, extrusion dies and any wear face that also sees corrosion or heat (Stellite); and combustor, afterburner and turbine components at 800–1,000 °C where a nickel alloy would oxidize or creep (L605, Haynes 188).
Look elsewhere when
Titanium Grade 23 or 316LVM meets the implant requirement at lower cost and easier machining, the wear surface can be a hard coating on a cheaper substrate (Stellite is often deposited as a weld overlay or PTA layer on steel, not bought as a solid part), the part is large and lightly loaded, or the shape demands heavy stock removal — Co-Cr machines at a fraction of the speed of stainless and eats carbide. Cobalt is also a regulated, price-volatile metal; nickel-free grades exist for sensitized patients.
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Cobalt-Chrome Alloy by application
- Implants and dental
- F75 cast for complex joint geometry; F1537 wrought for the highest fatigue strength in stems, rods and plates; F90 for wire and formed devices.
- Wear under corrosion or heat
- Stellite 6 is the general-purpose hardfacing grade (40 HRC, best all-round); Stellite 21 for tougher, more corrosion-resistant applications and steam valve trim; 12 where hardness matters most.
- Sheet and rings at 800–1,000 °C
- Combustor cans, nozzles, exhaust collectors and heat-treating fixtures — L605 stays ductile and oxidation resistant where 310 stainless scales and 625 creeps.
AI suggestions — verify with an engineer before ordering. Estimates are indicative; the quote page prices your exact geometry.
Manufacturing notes
- CNC machining
- Co-Cr work-hardens as fast as any alloy and is abrasive from its carbides: cutting speeds run at 10–20 % of stainless, with rigid setups, sharp coated carbide or ceramic inserts, heavy constant feed and no dwelling. Stellite above 40 HRC is finished by grinding. Expect the machining cost to exceed the material cost; design with radii and generous stock.
- Investment casting and 3D printing
- Complex implant and dental geometry is investment-cast (F75) or laser powder-bed printed (F75 / F1537 chemistry) to near-net shape and then ground and polished — printing is now the standard route for patient-specific implants and dental frameworks.
- Hardfacing overlays
- Stellite is most economically applied as a 1–3 mm weld overlay (TIG, PTA, laser cladding) on a steel or stainless part, then ground to size — a solid Stellite component is reserved for small, fully wetted or fully exposed parts.
- Heat treatment
- Cast F75 is solution-treated or HIPed to close porosity and homogenize carbides; wrought F1537 is used as hot-worked or annealed; L605 is solution-annealed only. Stellite is used as cast or deposited — no hardening treatment is needed or possible.
- Finishing
- Implant bearing surfaces are polished to Ra < 0.05 µm and passivated; dental frameworks are electropolished and porcelain-bonded; wear parts are ground and lapped. No coating is needed for corrosion; nitrogen implantation or DLC can further lower implant wear.
Most-quoted cobalt-chrome alloy grades
| Grade | Application group | Yield, MPa | Tensile, MPa | Density, g/cm³ | Machinability | Weldability | Best for |
|---|---|---|---|---|---|---|---|
| F75 | Orthopaedic Co-Cr-Mo | 510 | 720 | 8.3 | Not recommended | Poor | Cast implants and dental frameworks |
| Stellite 6 | Stellite hardfacing alloys | 541 | 834 | 8.44 | Not recommended | Good | General hardfacing and wear parts |
| Stellite 21 | Stellite hardfacing alloys | 495 | 710 | 8.33 | Poor | Good | Tough, corrosion-resistant wear parts |
| L605 | High-temperature Co-Cr-W | 460 | 1,010 | 9.13 | Poor | Very good | Sheet and rings to 1,000 °C |
| F90 | Orthopaedic Co-Cr-Mo | 460 | 1,000 | 9.13 | Poor | Very good | Wire and formed medical devices |
Finishes for cobalt-chrome alloy
All 111 finishes2 of our 111 surface finishes take cobalt-chrome alloy: 0 recommended outright, 1 with process care, 1 in limited cases. Each finish opens to its datasheet — thickness, hardness, salt-spray hours, spec codes and the cobalt-chrome alloy-specific notes — and the configurator prices it on the grade you pick.
| Finish | Group | On cobalt-chrome alloy | Thickness, µm | Hardness, HV | Salt spray, h | Cost |
|---|---|---|---|---|---|---|
| Electropolishing | Anodizing, conversion & passivation | With care | removes 5–25 | — | — | $$$ |
| Stainless Steel Passivation | Anodizing, conversion & passivation | Limited | 0 | — | — | $ |
Cobalt-Chrome Alloy — frequently asked
Cobalt-chrome or titanium for an implant?
Co-Cr for the bearing surfaces — femoral heads, knee condyles — because it is harder, polishes finer and wears an order of magnitude slower against polyethylene. Titanium Grade 23 for stems, plates and screws that bond to bone, because its modulus is closer to bone (less stress shielding) and it is lighter and easier to machine. Many joint systems use both: a Co-Cr head on a titanium stem.
What is Stellite, and is it a solid part or a coating?
Stellite is the trade name for a family of Co-Cr-W-C hardfacing alloys (Stellite 6 is the best known). It is bought both ways: as cast or wrought solid bar and plate for small wear parts, and — far more often — as welding rod, powder or wire deposited 1–3 mm thick on a steel component and ground to size. The overlay route gives the wear surface where it is needed at a fraction of the cost.
How hard is cobalt-chrome?
Wrought F1537 and cast F75 run 30–45 HRC; Stellite 6 about 40 HRC, Stellite 12 up to 48 HRC, and the alloys work-harden further in service. That is not tool-steel hardness, but Co-Cr keeps it at 800 °C, in steam and in acids, where a 60 HRC tool steel would have softened or rusted — and it resists galling and adhesive wear far better than its hardness number suggests.
Why is Co-Cr so expensive to machine?
The carbides that give it wear resistance abrade cutting tools, the matrix work-hardens the instant it is deformed, and the alloy conducts heat poorly so the edge runs hot. Speeds are a tenth of stainless and tool life is short. The industry answer is near-net-shape casting or 3D printing plus grinding and polishing, with milling only where necessary.
Is cobalt-chrome safe in the body?
Yes — ASTM F75, F799, F1537 and F90 have decades of implant history. The concern is metal-ion release from wearing metal-on-metal bearings, which is why modern designs pair Co-Cr against polyethylene or ceramic. Patients with cobalt or nickel sensitivity may need ceramic or titanium alternatives; nickel-free Co-Cr-Mo grades are also available.