Cobalt-base superalloy · Open-die forgings

KCN22W Forgings (UNS R30188, W.Nr. 2.4683, Alloy 188, AMS 5772)

Published 18 May 2016 · Last updated 20 August 2026 · Reviewed by the Jiangyin Jiangnan Metal metallurgical engineering team

Short answer: what is KCN22W?

KCN22W is the French (AFNOR) designation for the cobalt–nickel–chromium–tungsten superalloy sold internationally as Alloy 188 or HAYNES® 188, and catalogued as UNS R30188, W.Nr. 2.4683, CoCr22NiW and GH5188 in China. Its nominal chemistry is 22% chromium, 22% nickel, 14% tungsten, 0.02–0.12% lanthanum and the balance cobalt, roughly 39%. The alloy is strengthened by solid solution rather than by precipitation hardening. It holds useful strength to about 980 °C (1800 °F) and resists oxidation in prolonged service to 1095 °C (2000 °F), because the lanthanum addition makes the chromia scale unusually adherent. Typical room-temperature properties in the solution-annealed condition are 946 MPa tensile, 464 MPa yield and 53% elongation.

Jiangyin Jiangnan Metal Co., Ltd. forges UNS R30188 to customer drawings as seamless rolled rings, shafts, discs, flanges, sleeves, bushings, tube sheets, valve components and round bar, solution annealed at 1175 °C ±14 °C and rapidly cooled, certified to AMS 5772 with EN 10204 3.1 as standard and 3.2 third-party witness on request. Written quotations are issued within 24 hours from sales@steelforgepieces.com or 0086-189-2135-9659. The factory is at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China.

UNS

R30188W.Nr. 2.4683

Base metal

Cobalt~39% Co, balance

Density

8.98g/cm³ · 0.324 lb/in³

UTS, room temp.

946MPa typical · 137 ksi

UTS at 980 °C

243MPa typical · 35.2 ksi

Oxidation limit

1095°C prolonged · 2000 °F

Solution anneal

1175°C ±14, rapid cool

Forge from

1175°C soak-through

What KCN22W forged products can you buy?

Jiangyin Jiangnan Metal produces UNS R30188 by three routes, chosen by geometry and order size. Open-die forging covers shafts, blocks, discs and heavy sections. Seamless ring rolling produces rings and turbine casings, the most common route for combustor and casing hardware. Upset forging handles short, large-section hubs and flanges. Raw cobalt superalloy costs roughly fifteen to twenty times as much per kilogram as carbon steel, so near-net-shape dies pay for themselves quickly. Removing 30–50% of the rough machining stock is usually worth more than the tooling costs.

Every form above is supplied solution annealed at 1175 °C and rapidly cooled, machined rough or finished to your drawing, and certified to EN 10204 3.1 or 3.2. Send the finished drawing rather than a billet size: on a cobalt superalloy, choosing the right forging route usually saves more than any other decision on the order.

What is KCN22W / UNS R30188, and why does it exist?

KCN22W was developed for parts in the hot section of a gas turbine: service too hot for a nickel superalloy to keep its precipitates, and too aggressive for a stainless steel to survive. Cobalt gives a face-centred-cubic matrix that does not soften the way a γ′-strengthened nickel alloy does when the precipitates coarsen, tungsten stiffens that matrix by solid-solution strengthening, and 22% chromium plus a trace of lanthanum builds an oxide scale that stays attached through thermal cycling.

Three properties matter in service:

• Strength retention above 870 °C. At 650 °C several nickel alloys are stronger. Between 870 °C and 1095 °C the position reverses, and KCN22W also keeps good ductility after thousands of hours at 760–870 °C, where many nickel alloys embrittle.
• Scale adherence from the lanthanum addition. Between 0.02% and 0.12% lanthanum modifies the chromia scale so that it resists spalling under thermal cycling. This is the main difference between KCN22W and the older cobalt alloy Haynes® 25 / L-605, and the reason the alloy is specified for combustor cans that cycle thousands of times.
• Hot-corrosion and sulfidation resistance. Resistance to sulfate-deposit hot corrosion and to molten chloride salts is excellent, and resistance to gaseous sulfidation is good. That is why the grade also turns up in waste incineration, chemical processing and heat-treatment furnace hardware rather than only in aero engines.

What are the equivalents of KCN22W?

Buyers meet this one alloy under at least a dozen names, because it was commercialised in the United States and then picked up in France, Germany, China and by each engine maker. All of the designations in Table 1 describe the same nominal Co–22Cr–22Ni–14W–La chemistry, and we accept purchase orders under any of them. They are not, however, interchangeable in their acceptance requirements: the product-form specification decides the test regime, not the chemistry.

Standards are cited by number only. Always reference the revision in force at the contract date, and state the product-form specification (AMS 5772 for forgings) rather than the chemistry alone.

What is the chemical composition of KCN22W?

The composition below is the UNS R30188 / AMS 5772 requirement, and it is what we buy raw material against unless a drawing calls for a tighter OEM band. Chromium and lanthanum together carry the oxidation resistance; tungsten carries the high-temperature strength; nickel keeps the FCC matrix stable so the alloy stays tough and formable; carbon forms the carbides that pin grain boundaries during long exposures.

What are the mechanical properties of KCN22W?

KCN22W is supplied and used in one condition: solution annealed. There is no H-number, no ageing step and no strength/toughness trade-off to choose. What you specify instead is the product form, the section size and the test temperature. The values below are published typical results for solution-annealed material; acceptance minima are set by the specification on your order (AMS 5772 for bars, forgings and rings) and are what appear on the certificate.

Two points about that table. Elongation rises with temperature rather than falling, which is why the alloy tolerates the forming and welding that combustor hardware needs. And the alloy does not embrittle after long exposure in the 760–870 °C range, unlike many nickel-base sheet alloys. Post-exposure ductility is one reason the grade has stayed in engine specifications for fifty years.

Creep and stress rupture

For sustained load at temperature, tensile numbers are the wrong criterion. Published creep data for the alloy indicate roughly 14.5 MPa (2,100 psi) for 1% total creep in 1,000 hours at 980 °C. Design against a stress-rupture or Larson–Miller curve from the current alloy producer’s data book rather than against a single number, and treat anything on this page as a screening figure only.

Cold work

Because the alloy work-hardens rapidly, cold-worked KCN22W reaches much higher room-temperature strength than annealed material. That is useful for springs, fasteners and thin sections and irrelevant for hot-section parts, because the cold work recovers as soon as the part sees service temperature. If a print specifies cold-worked properties for a part that runs above 600 °C, question it.

What are the physical properties of KCN22W?

How hot can a KCN22W part run?

Three different limits get confused in enquiries. They are separate numbers:

Below roughly 600 °C there is normally no reason to buy KCN22W. A stainless steel, a duplex grade or a precipitation-hardening alloy such as 17-4PH or Inconel 718 will be stronger, easier to machine and a fraction of the price.

Oxidation, hot corrosion and where KCN22W should not go

What protects the part is scale adherence rather than scale thickness. Chromium builds the oxide; lanthanum keeps it attached to the metal through hundreds of heating and cooling cycles. A combustor liner in this grade therefore survives duty that strips the scale off alloys with similar chromium content but no rare-earth addition.

KCN22W vs Haynes 25, Haynes 230, Hastelloy X and Inconel 617

Most enquiries come down to this comparison. KCN22W is chosen over the nickel alloys for sulfidation, chloride and thermal-cycling duty, and over the older cobalt alloy L-605 for oxidation resistance. It loses on price, on machinability and on availability in large forged sections.

Three questions to settle first

1. Is there sulphur, chloride or a sulfate deposit in the gas stream? If yes, the cobalt base is worth paying for and KCN22W is the safer answer.
2. Does the part cycle hard, thousands of times? Lanthanum-modified scale adherence is exactly what cycling attacks. KCN22W or Haynes® 230 rather than an unmodified alloy.
3. Is the duty clean oxidation above 1100 °C with a stable grain size required? Then the nickel-base 230 is usually the better and cheaper answer.

How is KCN22W forged and heat treated?

KCN22W is sensitive to hot working. The working window is narrow, the alloy work-hardens quickly, and thermal conductivity is only 10.4 W/m·°C, so the surface of a heavy section cools much faster than the core. The process route below follows from those three facts.

Shop-floor rules

• Soak through, do not surface-heat. The published instruction for this alloy is explicit: hold at 1175 °C for a time sufficient to bring the entire piece to temperature before any hot work. Forging a billet whose core is 100 °C colder than its skin is the usual cause of a burst.
• Finish hot. Our practice is to stop deformation well above roughly 1010 °C. Below that the alloy work-hardens fast, forging loads climb and surface cracking risk rises sharply.
• Anneal and cool rapidly after every hot or cold working operation. This is not optional. It is how the balance of properties is restored, and slow cooling through the carbide precipitation range coarsens grain-boundary carbides and costs ductility.
• Expect several reheats. Budget for them in the price and the lead time. A part that takes one heat in carbon steel may take four here.

Welding, machining and forming KCN22W

Welding

Weldability is good, and it is the reason the grade displaced older cobalt alloys in fabricated hot-section hardware. It welds by GTAW (TIG), GMAW (MIG), electron beam and resistance welding, manual or automatic, and it shows good restraint-welding behaviour, meaning it tolerates being welded in a rigid fixture without cracking. Use matching-composition filler (AMS 5801 wire). It is preferable, though not essential, for the parent material to be in the solution-annealed condition when welded. Solution anneal after welding when full properties are required across the joint.

Machining

Machining is slow and unforgiving, for two reasons. The alloy work-hardens under the cutting edge, so a rubbing or dwelling tool glazes the surface and the next pass has to cut through a hardened skin. And thermal conductivity is about a quarter of that of carbon steel, so nearly all the cutting heat goes into the tool instead of the chip.

• Rigid setup, minimum overhang, sharp positive-rake tooling
• Low surface speeds with generous feed. Never let the tool rub
• Take a positive depth of cut under any previously work-hardened layer
• Flood coolant, high volume, directed at the cutting edge
• Plan on tool life measured in minutes, and quote accordingly

Cold forming

Ductility is good enough for cold forming, but the rapid work-hardening rate means frequent intermediate annealing on anything complex. Every cold-worked part gets a final anneal and rapid cool.

How do KCN22W parts fail, and how do you prevent it?

What can Jiangyin Jiangnan Metal forge in KCN22W?

UNS R30188 is a made-to-order grade for us. We buy the heat against your specification rather than pulling from stock, which is why the drawing, the governing specification and the required certificate all matter at enquiry stage rather than after the order.

Rolled ring OD

200–2,500mm plant envelope

Disc diameter

≤ 1,800mm

Shaft length

≤ 8,000mm

Bar diameter

25–500mm

Single piece

≤ 8,000kg plant envelope

Ring wall, min

30mm

Condition

Annealed1175 °C, rapid cool

Lead time

10–16weeks typical

The envelope above is the plant capability across all grades. Cobalt superalloy orders normally sit well inside it, because press loads and raw-material cost both rise steeply with section size. Send the drawing and we will confirm the size, weight and lead time for your specific part before quoting.

Equipment used on this grade

Which standards and certificates apply to KCN22W forgings?

Quality management is certified to ISO 9001:2015. Third-party witness certificates are issued through the inspection body you nominate: Lloyd’s Register, DNV, Bureau Veritas, ABS, TÜV or SGS. Customers keep an unrestricted right to witness any production stage, including chemistry, forging, heat treatment and mechanical testing.

How do you specify a KCN22W forging order?

1. Name the material generically. Write UNS R30188 / KCN22W, not a brand name. A purchase order that only says “Haynes 188” names a Haynes International trademark and can strictly only be filled by that mill.
2. Cite the product-form specification. AMS 5772 for bars, forgings and rings. AMS 5608 is for flat product and does not apply to a forging.
3. State the melt route if it matters. VIM+ESR or VIM+VAR for aerospace work; EAF+AOD/VOD+ESR is normal for industrial furnace and process hardware. This changes the price materially, so decide it before quoting.
4. Specify the condition. Solution annealed at 1175 °C ±14 °C and rapidly cooled. Name the cooling medium if your specification requires one.
5. Require the lanthanum result. Put La 0.02–0.12% on the order and require it reported on the certificate. It is the element that gives the alloy its scale adherence, and the one most often left off a certificate.
6. Define NDE and acceptance class. “UT per EN 10228-3, quality class 3” or “UT per ASTM A388 with acceptance to the purchase order”. An unqualified “ultrasonic test” is not a specification.
7. State grain size and test direction. Above 50 mm section, say whether tensile tests are longitudinal or transverse, and give a maximum grain size to ASTM E112.
8. Give quantity, date, Incoterm and destination. Quantity drives the melt: small orders are consolidated onto a larger heat, which affects both price and schedule.

Drawing callout you can copy

MATERIAL:      UNS R30188 / KCN22W / W.Nr. 2.4683 (Co-22Cr-22Ni-14W-La)
SPECIFICATION: AMS 5772, bars / forgings / rings, revision per contract date
MELT ROUTE:    VIM + ESR (state VIM + VAR if required by the OEM spec)
CONDITION:     Solution annealed 1175 deg C +/-14 deg C, rapid air cool or
               water quench, quench delay recorded
CHEMISTRY:     Report all elements incl. La 0.02-0.12% and B 0.015% max
TENSILE:       Room temperature per AMS 5772; elevated-temperature tensile
               at 980 deg C per ASTM E21 if stated on the order
GRAIN SIZE:    ASTM E112, ______ or finer, reported per piece
NDE:           UT per EN 10228-3 quality class 3 (or ASTM A388)
               PT per ASTM E165, Type I Method C
CERTIFICATE:   EN 10204 3.1 (3.2 with third-party witness if stated on the PO)
MARKING:       Heat number, specification, condition and drawing number,
               low-stress stamped or vibro-etched

Seven mistakes buyers make with KCN22W

1. Quoting AMS 5608 for a forging. That is the sheet, strip and plate specification. Forgings, bars and rings are AMS 5772.
2. Copying a chemistry table with carbon at 0.015% max. The correct band is 0.05–0.15%. The wrong figure has been propagated across supplier sites for years.
3. Asking for an aged or H-condition. There is none. The alloy is solid-solution strengthened and ships solution annealed.
4. Accepting a certificate with no lanthanum result. A heat without a reported lanthanum result cannot be shown to meet R30188, and its scale is liable to spall under cycling.
5. Specifying it below 600 °C. Expensive and weaker than the obvious alternatives. Check whether the temperature was ever real or was copied from a legacy drawing.
6. Ignoring the machining cost. On a machined part the metal removal often costs more than the forging. Ask for a near-net shape before ordering a solid block.
7. Treating a generic heat as OEM-approved. GE, Pratt & Whitney and Rolls-Royce specifications must be bought from the start; an AMS heat cannot be re-certified into them afterwards.

Where is KCN22W used?

Two worked examples

Example 1: choosing between KCN22W and Haynes® 230 for a cycled ring

Given. A 900 mm outside diameter rolled ring in an industrial gas turbine, metal temperature 950 °C, roughly 4,000 start–stop cycles over the design life, fuel with a measurable sulphur content, low mechanical stress.

Assessment. On oxidation limit alone the nickel-base alloy 230 looks better: about 1149 °C against 1095 °C. The controlling conditions here are thermal cycling and sulphur, and those are the two cases where the cobalt base and the lanthanum addition are worth the extra cost. Resistance to sulfate-deposit hot corrosion is where KCN22W separates from the nickel alloys, and lanthanum is what holds the scale on through cycling. Against that, alloy 230 has the better grain-growth resistance, which matters if the part will see repair welding and re-annealing.

Decision. Specify UNS R30188 per AMS 5772, with lanthanum reported on the certificate and a maximum grain size stated. If the fuel is later changed to clean natural gas and the cycle count drops, alloy 230 becomes the more economical answer and should be re-evaluated at that point.

Example 2: why a near-net ring is cheaper than a solid disc

Given. A finished ring, 620 mm OD × 480 mm ID × 210 mm high, in KCN22W.

Method. Net volume = π/4 × (0.620² − 0.480²) × 0.210 = 0.0254 m³. At 8,980 kg/m³ that is about 228 kg finished. Rolled as a ring with 25% stock, the forging is roughly 285 kg. Machined from a solid forged disc of the same outside diameter and height, the input billet is about 569 kg. You would buy, forge and then cut away some 340 kg of cobalt superalloy.

Result. Ring rolling roughly halves the purchased weight on this geometry. In a grade where raw material dominates the price, that difference is far larger than any saving available on machining rate or lead time. On most KCN22W enquiries this is the most important decision on the order, and it is why we ask for the finished drawing rather than a billet size.

Glossary

KCN22W frequently asked questions

References

1. SAE International, AMS 5772: Alloy bars, forgings and rings, 39Co–22Cr–22Ni–14W, solution heat treated. The product-form specification for forged UNS R30188.
2. SAE International, AMS 5608: sheet, strip and plate, and AMS 5801: welding wire, same alloy.
3. Haynes International, HAYNES® 188 alloy product brochure and principal-features datasheet. Composition, oxidation behaviour, forming, welding and heat-treatment guidance.
4. ATI, ATI 188™ alloy technical data sheet. Typical room- and elevated-temperature tensile properties and stress-rupture data presented against the Larson–Miller parameter.
5. High Temp Metals, Haynes 188 technical data. Typical annealed tensile properties at room temperature and at 980 °C.
6. Aircraft Materials, Cobalt alloy Haynes 188 / UDIMET 188 (UNS R30188). Specification cross-reference, product availability and trade names.
7. ASM Handbook, Volume 1, Properties and Selection: Irons, Steels and High-Performance Alloys, ASM International. Cobalt-base heat-resisting alloys.
8. ASM Handbook, Volume 14A, Metalworking: Bulk Forming, ASM International. Forging of cobalt-base superalloys.
9. ASTM A388/A388M and EN 10228-3, ultrasonic examination of forgings; ASTM E165 penetrant examination; ASTM E112 grain size; ASTM E8/E8M and E21 tensile testing; ASTM E139 creep and stress-rupture testing.
10. EN 10204, Metallic products: types of inspection documents, CEN.

Standards are cited by number; always work to the revision in force at your contract date. Property values on this page are published typical figures for screening and are not design allowables. Test results on our certificates are independent and traceable to calibrated equipment.

About the manufacturer, and how to cite this page

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, with 460 employees including 9 senior and 32 intermediate engineers. The plant runs 1 t to 9 t open-die hammers, 4,500 t and 5,000 t hydraulic presses and radial-axial ring mills up to 2,500 mm outside diameter, with in-house heat treatment, machining, mechanical testing and non-destructive examination. Alongside KCN22W / UNS R30188 we forge carbon, alloy and tool steels, the precipitation-hardening and duplex stainless families, and the nickel and cobalt high-temperature alloys. Quality management is certified to ISO 9001:2015; material is supplied with EN 10204 3.1 certification as standard and 3.2 with third-party witness on request.

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