Alloy L-605 / UNS R30605 Forging Parts Cobalt-chromium-tungsten-nickel superalloy for continuous service to 980 °C. Forged rings, discs, shafts, flanges and bars to AMS 5759

01What is Alloy L-605 and why is it used?

Alloy L-605 is the workhorse wrought cobalt superalloy. It was developed for gas-turbine hot-section hardware in the 1950s and remains specified today because it solves a combination of problems that nickel alloys solve only individually: high strength at red heat, resistance to oxidation and sulfidation, exceptional resistance to galling and metal-to-metal wear, and (uniquely among the high-temperature alloys) biocompatibility good enough for permanent surgical implants.

The chemistry does three separate jobs. Chromium at 20% forms the protective Cr₂O₃ scale that gives the alloy its oxidation and sulfidation resistance. Tungsten at 15% is the principal strengthener: it is a large, slow-diffusing atom that distorts the cobalt lattice and resists dislocation motion at temperature, and it also forms the hard M₆C carbides that pin grain boundaries during creep. Nickel at 10% stabilises the face-centred-cubic form of cobalt, preventing the transformation to the brittle hexagonal form that would otherwise occur on cooling and making the alloy formable and weldable.

What Alloy L-605 does not have is a γ′ or γ″ precipitate. It cannot be strengthened by aging, and any attempt to specify an aging cycle for it is a specification error. Its strength at room temperature is modest. The AMS 5759 minimum yield is only 310 MPa, roughly a third of what an aged 17-4PH forging delivers. But that strength falls away far more slowly with temperature than any precipitation-hardened alloy, because there is no precipitate to over-age.

02What are the equivalent designations for Alloy L-605?

Engineers reach this alloy through a dozen different names depending on which standards body, which decade and which industry the drawing came from. Every designation in the table below refers to the same 51Co-20Cr-15W-10Ni chemistry, and Jiangyin Jiangnan Metal Co., Ltd. accepts purchase orders under all of them.

Note on scope: AMS 5759 and AMS 5537 differ only in product form, not chemistry. ASTM F90 applies the same element ranges but tightens silicon. See Section 03.

03What is the chemical composition of Alloy L-605?

The composition below is per AMS 5759, the specification governing L-605 bars, forgings and rings. Cobalt is not given a range. It is the balance, and works out to approximately 51%.

Where AMS 5759 and ASTM F90 differ

Most sources present L-605 chemistry as a single table. In practice the aerospace and surgical-implant specifications are not identical, and ordering to the wrong one causes certificate rejection.

04What are the mechanical properties of Alloy L-605?

Two different sets of numbers circulate for this alloy and they are routinely confused. AMS 5759 minimums are the contractual values a supplier guarantees on the mill certificate. Typical values are what solution-annealed material actually delivers, and are considerably higher. Design to the minimums; expect the typicals.

Values apply to solution heat treated bars, forgings and rings. Heavy sections may show properties at the lower end of the typical band. Cold-worked material is substantially stronger and correspondingly less ductile; L-605 in the cold-worked condition is outside the scope of AMS 5759 in the solution-treated state.

Strength at temperature

This is the reason the alloy exists. The table gives typical short-time tensile properties and 1,000-hour stress-rupture strength for solution-annealed material.

Indicative values only. These are typical published figures for solution-annealed wrought L-605 and are not guaranteed minimums. Elevated-temperature and creep-rupture properties depend on section size, grain size, prior thermal history and test direction. For design purposes, use data from the applicable specification or request lot-specific testing. We can supply elevated-temperature tensile and stress-rupture testing on production coupons.

05What are the physical properties of Alloy L-605?

Two of these numbers change how you buy the part. The density of 9.13 g/cm³ is about 10% higher than a nickel superalloy and 18% higher than steel, so a forging of the same geometry costs more in raw weight than engineers expect. The thermal conductivity of roughly 9.4 W/m·K is very low, which is what makes the alloy so difficult to machine: cutting heat has nowhere to go except into the tool.

06What is the maximum service temperature of Alloy L-605?

Approximately 980 °C (1800 °F) for continuous service. Above that the Cr₂O₃ scale begins to lose adherence during thermal cycling and creep strength falls steeply; brief excursions to 1090 °C (2000 °F) are survivable but the alloy retains only about 10% of its room-temperature strength there.

Bands are approximate and overlap in practice. The middle band is the alloy's normal working range. Carbide precipitation there is expected and does not prevent service, but it does change room-temperature ductility after the part cools. See Section 07.

Oxidation and sulfidation

L-605 resists oxidation in still air to about 980 °C. Its resistance to sulfidation (attack by sulphur-bearing combustion products) is better than most nickel-based alloys, because cobalt sulphides have a higher melting point than nickel sulphides and do not form the low-melting eutectic that destroys nickel alloys in dirty fuel environments. This is why L-605 survives in industrial and marine gas turbines burning heavy or high-sulphur fuel where a nickel alloy would not.

In severely cycled service above 1000 °C, Haynes 230 or a lanthanum-bearing cobalt alloy will hold its scale better, because rare-earth additions improve oxide adherence through thermal cycles. L-605 contains no rare-earth addition.

07Why does Alloy L-605 lose ductility after service?

This is the single most misunderstood property of the alloy, and the most common cause of surprise cracking during maintenance. L-605 leaves the mill solution annealed, with its carbon dissolved in the matrix and room-temperature elongation above 50%. Held anywhere in the range of roughly 650-980 °C, carbon comes back out of solution as M₆C and M₂₃C₆ carbides on grain boundaries. At service temperature this does no harm. It actually helps creep strength by pinning the boundaries. The problem appears when the part cools down.

A component that has run for a few thousand hours at 870 °C may return to the shop with room-temperature elongation in the teens rather than the fifties, and impact toughness reduced by more than half. Nothing has gone wrong with the material; this is normal, expected behaviour for a carbide-strengthened cobalt alloy. It matters because a part that was ductile when installed may crack when handled, straightened or bolted up cold at overhaul.

08How does Alloy L-605 compare with Haynes 188, Hastelloy X and Inconel 617?

These four alloys compete for the same combustor and transition-duct hardware, and the choice usually comes down to three questions: does the part slide against anything, does it cycle above 1000 °C, and how much does weight matter.

* Hastelloy X is often quoted to 1200 °C for oxidation resistance, but its useful load-bearing limit is far lower. Compare creep-rupture strength at your actual design stress, not maximum oxidation temperature. Forgings in every grade in this table are available from Jiangyin Jiangnan Metal Co., Ltd. See the full superalloy index.

09How is Alloy L-605 forged and heat treated?

L-605 is a demanding forging alloy. It is stiff at temperature: press loads run roughly two to three times those needed for an equivalent carbon-steel section, and it has a narrow hot-working window. Getting the temperature control right is the whole job.

Melting

We melt L-605 by EAF + AOD/VOD followed by electroslag remelting (ESR), or by VIM + ESR where the drawing calls for aerospace-level cleanliness. ESR is not optional for this grade: it refines the solidification structure, reduces macro-segregation of tungsten, and removes the oxide and sulphide inclusions that would otherwise open up as laps during upsetting.

Forging window

Start at 1177-1232 °C (2150-2250 °F) and finish above 1010 °C (1850 °F). Below about 980 °C the alloy work-hardens so rapidly that further reduction cracks the workpiece rather than deforming it. Multiple reheats are normal and expected. A large ring may see five or six furnace returns. Reduction should be taken in many light passes rather than a few heavy ones, and the finishing pass must deliver enough strain to recrystallise the structure uniformly, or the part will show a mixed grain size on macroetch.

Solution annealing

The only heat treatment L-605 receives is a solution anneal at 1177-1232 °C followed by rapid quench, usually water. The purpose is to dissolve the carbides formed during forging and cooling and to lock the carbon back into solution. Cooling must be fast: a slow cool through 980-650 °C re-precipitates the carbides the anneal was meant to remove, and the part arrives at the customer already partly embrittled.

1. Raw materialESR ingot
   Heat number traced
   Chemistry verified by OES
2. Ingot break-down1177-1232 °C
   Light multi-pass
   Reheat as needed
3. Forge / ring rollFinish > 1010 °C
   Radial-axial mill
   Grain-flow control
4. Solution anneal1177-1232 °C
   30 min per 25 mm
   Rapid water quench
5. Descale & rough machinePickle or blast
   ±2-3 mm stock
   Pre-UT clean-up
6. NDTUT EN 10228-3
   SEP 1921 / ASTM A388
   PT on machined faces
7. Mechanical testTensile per AMS 5759
   Hardness ≤ 277 HBW
   Grain size ASTM E112
8. Certify & shipEN 10204 3.1 / 3.2
   Multi-designation MTC
   Marked and packed

10How do you machine and weld Alloy L-605?

Machining

L-605 is among the hardest commonly specified alloys to machine, roughly 12-16% of the machinability of free-machining B1112 steel. Two properties conspire: the FCC cobalt matrix work-hardens extremely fast, so any tool that rubs instead of cutting instantly creates a hardened layer the next pass has to break through; and thermal conductivity is only 9.4 W/m·K, so cutting heat stays at the tool edge instead of escaping into the chip.

• Rigidity above all. Short tool overhang, heavy tool holders, minimum workpiece stick-out. Chatter destroys tools on this alloy faster than wrong speeds do.
• Get under the work-hardened layer. Depth of cut must exceed the depth of the previously hardened skin, roughly 0.5 mm minimum. Light finishing passes are counterproductive.
• Never dwell. Feed continuously; a tool stopped in contact will work-harden a spot that then wrecks the edge.
• Flood coolant at high concentration and high pressure, directed at the cutting edge.
• Sharp positive-rake carbide for most operations. Ceramics are used for high-speed roughing on rigid setups only.

Welding

L-605 is readily welded by GTAW and can be welded by GMAW, plasma arc and electron beam. Use matching L-605 filler wire. No preheat is required. Post-weld solution annealing at 1177-1232 °C with rapid quench is recommended for any part that will see load at temperature, because the heat-affected zone will otherwise contain a band of coarse grain-boundary carbide. For thin sheet fabrications where a full anneal is impractical, keep heat input low and interpass temperature below 150 °C.

11What forged product forms are available in Alloy L-605?

Jiangyin Jiangnan Metal Co., Ltd. produces Alloy L-605 by three routes, chosen by geometry: open-die forging for shafts, blocks, discs and tube sheets; seamless ring rolling on a radial-axial mill for rings, flanges and casings; and upset forging for short, large-section hubs and heads. Near-net-shape forging matters more on this grade than on most, because L-605 is both expensive per kilogram and slow to machine. Every kilogram of stock the die profile removes saves twice.

12Production capability for Alloy L-605 forgings

Jiangyin Jiangnan Metal Co., Ltd. has been operating as an open-die forging factory since 2008 and employs approximately 460 people, including 9 senior engineers and 32 intermediate engineers. Our works at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province covers melting through to final machining, testing and certification under one roof.

Equipment qualified for cobalt superalloy production

13Which standards, NDT and certification apply to Alloy L-605 forgings?

Governing material specifications

• AMS 5759
• AMS 5537
• ASTM F90
• ISO 5832-5
• UNS R30605
• W.Nr. 2.4964
• GH5605
• EN 10204 3.1
• EN 10204 3.2
• ISO 9001:2015

Non-destructive testing

All Alloy L-605 forgings are ultrasonically examined. We work to EN 10228-3, SEP 1921 or ASTM A388. State which standard and which acceptance class your drawing requires, because the classes are not interchangeable. Surface examination is by liquid penetrant (ASTM E165 or EN ISO 3452); magnetic-particle inspection is not applicable to L-605, which is non-magnetic.

Certification

Standard supply is an EN 10204 3.1 mill test certificate issued by our own qualified inspection department, listing heat number, full chemical analysis, mechanical test results, heat-treatment chart reference, NDT results and every designation the heat simultaneously satisfies. EN 10204 3.2 certificates with a third-party witness (Lloyd's Register, DNV, Bureau Veritas, ABS or TÜV) are issued on request, with witnessed hold points at melting, heat treatment and mechanical testing.

14How do you specify an Alloy L-605 forging order?

Seven steps. Following them removes almost every ambiguity that later turns into a certificate dispute or a rejected part.

1. State the generic designationWrite UNS R30605 / AMS 5759, not a trademarked brand name, which no independent supplier can legally ship.
2. Name the governing specAMS 5759 for forgings and rings · AMS 5537 for flat product · ASTM F90 or ISO 5832-5 for implants.
3. Specify the conditionSolution heat treated 1177-1232 °C, rapid quench. Never specify an aging cycle.
4. Send the drawingDimensions, machining stock, tolerances, surface finish and grain-flow direction for rotating parts.
5. Define NDT acceptanceUT standard and class (EN 10228-3 / SEP 1921 / ASTM A388) plus PT per ASTM E165. Not MT, because the alloy is non-magnetic.
6. Specify the certificateEN 10204 3.1, or 3.2 naming the witness body. State whether multi-designation cross-certification is needed.
7. Give commercial termsQuantity, target date, Incoterms, destination port. Typical L-605 lead time is 10-16 weeks.

Recommended drawing callout

Copy this block into the material callout box of your drawing. It is accepted by AMS, ASTM, EN and GB practice and eliminates most ordering ambiguity.

15Eight specification errors that delay Alloy L-605 orders

Compiled from our own RFQ history on this grade. Every one of these costs weeks when caught at receipt and nothing at all when caught at the specification stage.

16Where is Alloy L-605 used?

The alloy concentrates in four areas: gas-turbine hot sections, high-temperature wear surfaces, sulphidising process environments, and surgical implants. Its distinctive combination of hot strength, sulfidation resistance and galling resistance is what puts it in each.

17Worked design examples

Three simplified calculations showing how the data on this page feeds a real decision. Production designs require finite-element verification and the safety factors of the applicable code.

19Glossary

Alloy L-605

The original Union Carbide / Stellite trade designation for the 51Co-20Cr-15W-10Ni wrought cobalt superalloy. Still the most common name on engineering drawings.

UNS R30605

The generic Unified Numbering System designation for this chemistry. The correct term to use on a purchase order.

HAYNES® 25

Registered trademark of Haynes International, Inc. for material produced by that company. Generic equivalents are UNS R30605, AMS 5759, ASTM F90, W.Nr. 2.4964.

AMS 5759

SAE Aerospace Material Specification covering L-605 bars, wire, forgings and rings in the solution heat treated condition. The governing specification for our forged product.

AMS 5537

SAE specification covering the same alloy as sheet, strip and plate, solution heat treated.

ASTM F90

Specification for wrought Co-20Cr-15W-10Ni alloy for surgical implant applications. Same element ranges as AMS 5759 but restricts silicon to 0.40% maximum.

ISO 5832-5

International standard for wrought cobalt-chromium-tungsten-nickel alloy used in surgical implants.

W.Nr. 2.4964 / CoCr20W15Ni

European material number and chemical-symbol name for the same alloy.

GH5605

Chinese superalloy designation (formerly GH605) for the same nominal chemistry.

Solution heat treatment

Heating to 1177-1232 °C to dissolve carbides into the matrix, followed by rapid quenching to hold them in solution. The only heat treatment applied to L-605.

M₆C and M₂₃C₆ carbides

Tungsten- and chromium-rich carbides that precipitate on grain boundaries during exposure between roughly 650 and 980 °C. They improve creep strength at temperature and reduce room-temperature ductility after cooling.

Solid-solution strengthening

Strengthening produced by dissolving large atoms (here tungsten and chromium) in the matrix, where they distort the lattice and impede dislocation motion. L-605's principal strengthening mechanism.

FCC / HCP

Face-centred cubic and hexagonal close-packed crystal structures. Pure cobalt transforms from FCC to brittle HCP on cooling; the 10% nickel addition in L-605 suppresses this.

Sulfidation

High-temperature attack by sulphur-bearing combustion products. Cobalt alloys resist it better than nickel alloys because cobalt sulphides melt at higher temperatures.

Radiopacity

The degree to which a material blocks X-rays. L-605's 15% tungsten makes it strongly radiopaque, which is why it is used for coronary stent platforms.

Galling

Adhesive wear between sliding metal surfaces that transfers material and seizes the joint. L-605 resists it better than any commonly forged high-temperature alloy.

ESR, electroslag remelting

A secondary refining process in which a consumable electrode is remelted through a molten slag. Essential for L-605 to control tungsten segregation and inclusion content.

EN 10204 3.1 / 3.2

Inspection document types. 3.1 is certified by the manufacturer's own independent inspection department; 3.2 also requires a third-party or customer witness.

Seamless rolled ring

A ring produced by piercing a forged billet and expanding it on a radial-axial ring mill, giving continuous circumferential grain flow and no weld seam.

21Technical references

Chemistry, property, heat-treatment and fabrication data on this page derive from the published standards and engineering references below. Test results on our mill certificates are independent and traceable to calibrated equipment.

1. AMS 5759, Alloy, Corrosion and Heat-Resistant, Bars, Wire, Forgings, and Rings, 51Co - 20Cr - 15W - 10Ni, Solution Heat Treated, SAE International.
2. AMS 5537, Alloy, Corrosion and Heat-Resistant, Sheet, Strip, and Plate, 51Co - 20Cr - 15W - 10Ni, Solution Heat Treated, SAE International.
3. ASTM F90, Standard Specification for Wrought Cobalt-20Chromium-15Tungsten-10Nickel Alloy for Surgical Implant Applications (UNS R30605), ASTM International.
4. ISO 5832-5, Implants for surgery, Metallic materials, Part 5: Wrought cobalt-chromium-tungsten-nickel alloy, International Organization for Standardization.
5. ASM Handbook, Volume 1: Properties and Selection: Irons, Steels, and High-Performance Alloys, ASM International, sections on cobalt-base heat-resistant alloys.
6. ASM Handbook, Volume 14A: Metalworking: Bulk Forming, ASM International, forging of heat-resistant alloys.
7. ASM Specialty Handbook: Heat-Resistant Materials, J. R. Davis (ed.), ASM International.
8. EN 10228-3, Non-destructive testing of steel forgings, Part 3: Ultrasonic testing of ferritic or martensitic steel forgings, CEN.
9. SEP 1921, Ultrasonic testing of steel forgings, Stahl-Eisen-Prüfblatt.
10. ASTM A388, Standard Practice for Ultrasonic Examination of Steel Forgings, ASTM International.
11. ASTM E165, Standard Practice for Liquid Penetrant Testing for General Industry, ASTM International.
12. ASTM E112, Standard Test Methods for Determining Average Grain Size, ASTM International.
13. ASTM E381, Standard Method of Macroetch Testing Steel Bars, Billets, Blooms, and Forgings, ASTM International.
14. EN 10204, Metallic products, Types of inspection documents, CEN.
15. Haynes International, Inc., published technical data for HAYNES® 25 alloy, referenced for typical property comparison only.

Standards cited are the revisions current at the time of the last page review. For procurement, always reference the revision in force at the contract date. All trademarks are the property of their respective owners.

Related grades we forge

Alloy L-605 is one of more than forty superalloy and stainless grades produced at our works. These are the grades most often compared against it, or specified alongside it on the same assembly.

• Haynes 25
• Haynes 230
• Multimet N-155
• Hastelloy X
• Inconel 617
• Inconel 625
• Inconel 718
• Inconel X-750
• Waspaloy
• Rene 41
• MP35N
• MP159
• Incoloy 800HT
• Hastelloy C-276
• 17-4PH
• PH13-8Mo

Product routes: forged rings · forged discs · forged products index · forged valve seat rings · forged eccentric shafts