High-Temperature Cobalt Alloys
The high-temperature cobalt alloys are solid-solution Co-Cr-W-Ni sheet and bar alloys: L605 (Co-20Cr-15W-10Ni) and Haynes 188 (Co-22Cr-22Ni-14W with lanthanum). They are not age-hardened, so they stay ductile and weldable, and they resist oxidation and sulfidation to about 980 °C (L605) and 1,095 °C (Haynes 188) — where nickel alloys scale or creep. Annealed L605 yields about 460 MPa with 1,000 MPa tensile and work-hardens strongly.
Popular Co-Cr-W grades
Compare in the explorer| Grade | Yield, MPa | Tensile, MPa | Density, g/cm³ | Machinability | Weldability | Best for |
|---|---|---|---|---|---|---|
| L605 | 460 | 1,010 | 9.13 | Poor | Very good | Combustor and exhaust sheet to 980 °C |
| Haynes 188 | 464 | 960 | 8.98 | Poor | Very good | Longer, hotter service to 1,095 °C |
| MP159 | 1,830 | 1,965 | 8.3 | Not recommended | Poor | Ultra-high-strength fasteners to 595 °C |
| S-816 | 480 | 1,000 | 8.68 | Not recommended | Poor | Legacy turbine blades and bolting |
| Ultimet | 490 | 1,000 | 8.47 | Poor | Very good | Weldable wear and corrosion parts |
All 5 Co-Cr-W grades
Choose Co-Cr-W for
Sheet-metal hot sections — combustor cans, liners, nozzles, exhaust collectors, heat shields — turbine rings and seals, furnace fixtures and muffles at 800–1,100 °C, jet-engine fasteners that must hold full strength at 600 °C (MP159), and hot components that also rub, where the cobalt matrix resists galling better than any nickel alloy.
Look elsewhere when
The part needs high strength at 650–750 °C rather than oxidation resistance above 900 °C (Inconel 718 or Waspaloy), the temperature stays below 800 °C where Inconel 625 or 310S stainless is cheaper and easier to buy, the loads are low enough for Inconel 601 furnace hardware, or the job is wear at moderate temperature where Stellite 6 is harder.
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Co-Cr-W by application
- Combustor and exhaust sheet
- L605 for liners, cans, nozzles and collectors; Haynes 188 where the metal temperature exceeds about 950 °C or the design life is long, for its adherent oxide and retained ductility.
- Furnace fixtures and muffles
- L605 and Haynes 188 for fixtures and heat shields that see sulfur-bearing or carburizing atmospheres, where the cobalt base outlasts Inconel 601.
Working with Co-Cr-W
- Machining
- Work-hardens like an austenitic stainless but harder and more abrasive: coated carbide, rigid setups, moderate speed, heavy constant feed and no dwelling. Expect 20–30 % of the speed used on 304 stainless. MP159 is machined in the solution-annealed condition and aged afterwards.
- Welding
- L605 and Haynes 188 weld readily by TIG and resistance welding with matching filler and no preheat; the joints are as oxidation-resistant as the base metal. Solution-anneal at 1,175–1,230 °C after heavy forming or welding to restore ductility.
- Forming
- Sheet forms well in the annealed condition but work-hardens fast, so deep parts are formed in stages with intermediate anneals. Rapid cooling from the anneal keeps carbides in solution and the sheet ductile.
Other cobalt-chrome alloy series
High-Temperature Cobalt Alloys — frequently asked
What is Co-Cr-W?
The high-temperature cobalt alloys are solid-solution Co-Cr-W-Ni sheet and bar alloys: L605 (Co-20Cr-15W-10Ni) and Haynes 188 (Co-22Cr-22Ni-14W with lanthanum). They are not age-hardened, so they stay ductile and weldable, and they resist oxidation and sulfidation to about 980 °C (L605) and 1,095 °C (Haynes 188) — where nickel alloys scale or creep. Annealed L605 yields about 460 MPa with 1,000 MPa tensile and work-hardens strongly.
Which grade of Co-Cr-W should I use?
L605 for combustor liners, afterburner and exhaust parts, turbine rings and seals up to about 980 °C, and for hot-wear parts where its work-hardened surface resists galling. Haynes 188 when the part runs hotter or longer: the lanthanum makes the oxide scale adhere, oxidation resistance extends to 1,095 °C, and it keeps its ductility after thousands of hours where L605 embrittles from Laves-phase precipitation. MP159 is the cold-worked and aged fastener alloy, holding 1,800 MPa tensile to about 595 °C. S-816 is the older cast and wrought turbine-blade and bolting alloy still found on legacy drawings. Ultimet is the wear-plus-corrosion alloy of the group, weldable and work-hardening, for pump and valve parts rather than for hot gas.
Which grade of Co-Cr-W is the strongest?
MP159 has the highest yield strength in the series at 1,830 MPa; Ultimet follows at 490 MPa. Values are for each grade's default condition.
Which grade of Co-Cr-W is easiest to machine?
L605 (machinability poor, 18/100), then Ultimet (18/100).
L605 or Haynes 188?
L605 (also sold as Haynes 25) for most parts up to about 980 °C: it is cheaper, more widely available in sheet and bar, and has decades of engine history. Haynes 188 for longer or hotter exposure — its lanthanum-doped oxide scale resists spalling to 1,095 °C, and it keeps room-temperature ductility after long ageing, where L605 embrittles from Laves-phase precipitation. They weld and form the same way.
Why choose a cobalt alloy over Inconel for a hot part?
Three reasons: better resistance to sulfidation and to hot-gas corrosion, better hot-wear and galling resistance from the cobalt matrix, and retained strength at 900–1,000 °C in a solid-solution alloy that is still weldable. Nickel alloys win on strength below about 800 °C (Inconel 718 yields over 1,000 MPa at 650 °C, L605 about 250 MPa) and on price, so cobalt is reserved for the hottest sheet-metal parts and rubbing surfaces.