Hastelloy® C-22® / Alloy C-22 (UNS N06022 / 2.4602) Forgings: Rings, Flanges, Discs, Shafts & Tube Sheets

Published: 18 June 2022 · Last updated: 15 August 2026 · Technically reviewed by the Jiangyin Jiangnan Metal Co., Ltd. Metallurgical Engineering Team

What is Hastelloy C-22 / Alloy C-22 (UNS N06022)?

Alloy C-22 is a solid-solution-strengthened nickel-chromium-molybdenum-tungsten alloy designed to survive process streams whose oxidizing or reducing character is unknown, variable or upset. Its nominal composition is 56% nickel, 21% chromium, 13.5% molybdenum and 3% tungsten, with iron and cobalt held low and carbon capped at 0.015%.

The alloy exists because of a specific engineering problem. Chromium protects metal in oxidizing conditions such as nitric acid, wet chlorine, hypochlorite, ferric and cupric chloride, while molybdenum protects it in reducing conditions such as hydrochloric and dilute sulfuric acid. Most corrosion-resistant alloys are biased toward one side: Alloy 625 is chromium-rich and molybdenum-poor, while C-276 is the reverse. Alloy C-22 raises chromium to 21% without giving up the molybdenum-plus-tungsten content needed on the reducing side, so a single material covers both. That is why it is specified for flue-gas desulfurization, mixed-acid pickling, waste incineration scrubbers and pharmaceutical reactors, where the process fluid is a mixture rather than a single acid.

Two consequences follow from the low carbon and silicon levels. First, the alloy is highly resistant to grain-boundary carbide precipitation in the weld heat-affected zone, so it can be used as welded in most corrosion service without a post-weld solution anneal. Second, it has no precipitation-hardening reaction at all. Alloy C-22 cannot be age hardened, and any specification that calls for ageing is a specification error. The alloy is strengthened only by its dissolved alloying elements and by cold work, and its correct delivery condition is solution annealed.

Alloy C-22 is austenitic and face-centred cubic, so it stays tough down to cryogenic temperatures and is essentially non-magnetic. It also has excellent resistance to chloride-induced stress corrosion cracking, the failure mode that limits austenitic stainless steels such as 304 and 316L in hot chloride service.

Is Hastelloy C-22 the same as Alloy C-22?

Yes. Hastelloy® C-22®, Alloy C-22, Alloy 22, UNS N06022 and W.Nr. 2.4602 all name the same nickel-chromium-molybdenum-tungsten alloy. The chemistry, the ASTM and ASME specifications, the solution-annealing practice and the mechanical minimums are identical. What differs is who owns the name and who melted the metal.

The confusion exists because the alloy was developed and named by one company, and the brand name then became the way the whole industry talks about the grade, in the same way that people say Teflon for PTFE. An engineer writes Hastelloy C-22 on a drawing; a purchasing department orders UNS N06022; a mill certificate says 2.4602. All three are asking for the same material.

What actually differs between branded and generic C-22

Nothing in the chemistry. ASTM B575 sets one composition range and every producer works to it. What you are choosing between is melt source, price and paperwork:

When you genuinely need the branded material: if your project specification, client AVL or nuclear/pressure-code documentation names Haynes International as the producer, then a generic UNS N06022 is not a substitute no matter how good the certificate is. Tell us at enquiry stage. We will say so rather than ship generic material against a branded specification.

When generic UNS N06022 is the correct choice: for most chemical-process, FGD, pulp-bleaching and sour-service forgings the specification calls out ASTM B564 or B462 with UNS N06022 chemistry, EN 10204 3.1 certification and an ASTM G28 Method A result. That is a grade specification, not a brand specification, and it is exactly what we forge and certify.

What to write on the purchase order

Write the generic designation. It is unambiguous, it carries no trademark, and it is what the mill certificate will reference:

MATERIAL : UNS N06022 / W.Nr. 2.4602 / NiCr21Mo14W
SPEC     : ASTM B564 (forgings)  [or B462 for flanges and valve parts]
CONDITION: Solution annealed 1121 C + rapid water quench
           NO ageing or precipitation-hardening treatment
TEST     : ASTM G28 Method A, 24 h, on production material
CERT     : EN 10204 3.1   [3.2 with nominated inspection body]

If the drawing you received says Hastelloy C-22 and the specification does not name a producer, quote and order it as UNS N06022. If the specification does name a producer, that is a different commercial decision and you should raise it before the order is placed.

What are the equivalent designations for Hastelloy C-22 / Alloy C-22?

Engineers meet this alloy under at least eight names. All of them describe the same chemistry, and Jiangyin Jiangnan Metal Co., Ltd. accepts purchase orders written under any of them, certifying the material as UNS N06022 / 2.4602.

Trademark ownership is noted so that specification writers can choose a designation that any qualified producer may legally supply. If your purchase order says only "Hastelloy C-22", strictly speaking only Haynes International can fill it; writing "UNS N06022 / 2.4602" opens the order to competitive quotation.

Which ASTM and ASME specification applies to which product form?

For a forged ring, flange or tube sheet the correct pairing is normally ASTM B564 (or B462 where the part is a flange or valve component) plus ASTM G28 Method A as the corrosion acceptance test. Reference the specification revision in force at contract date.

What is the chemical composition of Hastelloy C-22 / Alloy C-22?

The composition below is the ASTM B575 / B574 limit set for UNS N06022, which is the same chemistry referenced by ASTM B564 for forgings and by W.Nr. 2.4602 in Europe. Nickel is the balance and is not specified as a range; it works out to roughly 56%.

The two numbers that most distinguish this alloy from a stainless steel are the carbon and silicon maxima. At C ≤ 0.015% and Si ≤ 0.08% the alloy resists the grain-boundary precipitation that would otherwise occur in the weld heat-affected zone, which is why C-22 weldments can normally be put into corrosion service without a post-weld solution anneal. Mill certificates issued by Jiangyin Jiangnan Metal report every element in this table.

What are the mechanical properties of Hastelloy C-22 forgings?

Alloy C-22 is supplied solution annealed. Because there is no ageing step, the property spread is narrow and predictable; the main variable is section size, since very heavy sections cool more slowly from the anneal.

Typical values are representative of our production on sections up to roughly 200 mm and are confirmed on test coupons cut from each heat-treatment batch. The alloy retains toughness to cryogenic temperature because it is fully austenitic with no ductile-to-brittle transition.

How does strength fall off with temperature?

Indicative typical values for design orientation only. They are not code allowable stresses. For pressure-retaining design use the allowable stress tables in ASME BPVC Section II Part D for SB-564 / SB-574, or the VdTÜV 479 values for EU pressure equipment. Note that long-term operation above about 600 °C also raises the intermetallic precipitation concern described in the heat-treatment section, which is a separate limit from strength.

What are the physical properties of Hastelloy C-22 / Alloy C-22?

How corrosion-resistant is Hastelloy C-22 / Alloy C-22?

Alloy C-22 is one of very few alloys that performs well on both sides of the redox divide. Its 21% chromium maintains a passive film in oxidizing acids and oxidizing chlorides; its 13.5% molybdenum plus 3% tungsten sustains resistance in reducing acids. That dual capability, rather than a record-setting number in any single medium, is the reason it gets specified.

The pitting resistance equivalent number gives a first-order ranking of localized-corrosion resistance:

PREN = %Cr + 3.3 × %Mo + 1.65 × %W
     = 21.25 + 3.3 × 13.5 + 1.65 × 3.0
     = 21.25 + 44.55 + 4.95
PREN ≈ 70          (316L ≈ 25 · 904L ≈ 35 · super duplex 2507 ≈ 43 · Alloy 625 ≈ 51)

Treat that number as a screening index only. PREN was derived for stainless steels and it weights molybdenum heavily, so it under-rewards chromium. By PREN alone C-276 (≈74) outranks C-22 (≈70), yet C-22 is decisively better in oxidizing chlorides such as ferric chloride and in nitric-acid mixtures, because those environments are governed by chromium rather than molybdenum. Rank alloys by the actual environment, not by PREN.

Where Alloy C-22 performs well, and where it does not

Standard corrosion acceptance tests

ASTM G28 Method A is the single most useful acceptance test for a forging, because it directly detects the one thing a forge shop can get wrong: an incomplete solution anneal or too slow a quench. Put it on the purchase order for any C-22 forging over about 100 mm section. Results shown are typical for correctly solution-annealed material; each order is tested to its own acceptance criterion.

Alloy C-22 vs C-276 vs Alloy 625 vs Alloy 59: which should you specify?

These four alloys cover most corrosion-resistant forging enquiries, and the choice between them is usually decided by the redox character of the process stream rather than by strength or price.

Cost index is relative to Alloy C-22 = 1.0 for comparable forged product and lot size; nickel and molybdenum are LME-linked, so absolute prices move weekly. Yield and tensile minimums are ASTM values for the solution-annealed condition. Alloy 625 is shown in the annealed condition; its Grade 2 solution-annealed variant has lower minimums.

How is Hastelloy C-22 / Alloy C-22 forged and heat treated?

This is where most Alloy C-22 forgings are won or lost. The chemistry is unremarkable to melt, but the alloy has a narrow hot-working window, work-hardens rapidly, and will precipitate damaging intermetallic phases if it dwells in the wrong temperature band on the way down.

The precipitation problem, stated plainly

Between roughly 650 °C and 980 °C UNS N06022 precipitates μ phase, P phase and grain-boundary carbides. These phases do two things: they embrittle the alloy, and, far more seriously, they deplete chromium and molybdenum from the regions next to the grain boundaries, which is precisely where corrosion then initiates. A forging that spends an hour cooling slowly through that band can meet every tensile requirement on the certificate and still fail an ASTM G28 Method A test, and then fail in service.

The countermeasure is simple and non-negotiable: after the final forging operation, re-solution anneal at ≈1121 °C (2050 °F) and quench rapidly in water. Air cooling is acceptable only on thin sections. Heavy sections must go into water fast enough that the core clears 650 °C without a long dwell.

Forging route by part geometry

How do you weld and machine Alloy C-22?

Welding

Alloy C-22 is readily welded by GTAW, GMAW, SMAW and plasma-arc processes. Because carbon and silicon are held so low, the heat-affected zone resists sensitisation, and weldments are normally placed in corrosion service in the as-welded condition without post-weld heat treatment. That is a significant fabrication advantage over stainless steels of comparable resistance.

Machining

Alloy C-22 machines like a tough austenitic superalloy: it work-hardens rapidly and its low thermal conductivity of 10.1 W/m·K sends the heat straight into the tool rather than the chip. The two failure patterns are glazing from dwelling in the cut, and notch wear at the depth-of-cut line.

Starting values only; final parameters depend on machine rigidity, setup stiffness and tooling. Three rules dominate: maintain positive feed at all times so the tool cuts below the previously work-hardened layer, never allow the tool to dwell in the cut, and use enough coolant to carry heat away from a material that will not conduct it itself. Where possible, we supply rough-machined forgings so this burden sits with equipment that is already set up for it.

Alloy C-22 failure modes and how to prevent them

What Hastelloy C-22 / Alloy C-22 forged products are available?

Jiangyin Jiangnan Metal Co., Ltd. produces UNS N06022 through three routes chosen by geometry: open-die forging for shafts, blocks, discs and heavy sections; seamless radial-axial ring rolling for rings, flange blanks and pressure-housing rings; and upset forging for short, large-diameter hubs and tube-sheet blanks. All are delivered solution annealed, water quenched and, where required, rough or finish machined.

• Seamless rolled rings
• Forged flanges
• Forged discs
• Tube sheets
• Forged shafts
• Round & flat bar
• Sleeves & bushings
• Forged blocks
• Valve bodies & bonnets
• Valve seat rings
• Forged pipe & hollows
• Nozzles
• Blind & weld-neck flange blanks
• Spindles
• Near-net-shape forgings

Recent Alloy C-22 forgings

Hastelloy C-22 / Alloy C-22 production capability

The company operates from No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, with 460 employees including 9 senior engineers and 32 intermediate engineers. Nickel-alloy work runs on the same presses as the carbon and stainless production but on segregated tooling and dedicated furnace charges, because iron and sulfur pick-up are the two contaminants that spoil a nickel-alloy forging.

Indicative lead times

Measured from order confirmation to ex-works dispatch. Nickel-alloy lead time is dominated by raw-material procurement, which moves with the nickel and molybdenum markets. Confirm current availability when you enquire.

Which standards and quality documents apply?

Quality assurance on every N06022 order

How to specify a Hastelloy C-22 / UNS N06022 forging order

Ten specification mistakes we see on Alloy C-22 enquiries

1. Calling for an ageing or precipitation-hardening treatment. UNS N06022 has no ageing response; the instruction will either be ignored or, worse, followed. Specify solution annealed only.
2. Writing "Hastelloy C-22" on the purchase order. That is a Haynes International trademark. Strictly read, only Haynes can supply it. Write UNS N06022 / 2.4602 and open the order to competition.
3. Specifying magnetic particle inspection. The alloy is non-magnetic and MT will find nothing. Specify liquid penetrant to ASTM E165 or EN ISO 3452.
4. Omitting ASTM G28 Method A on heavy sections. Tensile tests do not detect intermetallic precipitation from a slow quench. G28 does. On sections above about 100 mm it is the test that matters most.
5. Confusing C-22 with C-276 because both are "Hastelloy C". They are different alloys for different environments. See the comparison table. Substituting one for the other has caused real plant failures.
6. Specifying an intermediate-temperature post-weld heat treatment. Any PWHT in the 650–980 °C band actively damages the alloy. If thermal treatment after welding is contractually required, it must be a full re-solution anneal plus quench.
7. Allowing a stainless or Alloy 625 filler as a substitute. Dilution drops molybdenum in the weld metal and the weld corrodes before the base material does. Specify ERNiCrMo-10.
8. Leaving weld heat tint in place. The oxide is cosmetic; the chromium-depleted layer beneath it is not. Write heat-tint removal into the fabrication specification.
9. Quoting only PREN when selecting between nickel alloys. PREN under-values chromium and will point you to C-276 in an oxidizing service where C-22 is clearly better. Select on the environment.
10. Not stating the mating material. C-22 is noble and will accelerate corrosion of any carbon steel or 316L it is bolted to in an electrolyte. Tell your supplier what the part connects to.

Drawing callout template

Copy this block into the material callout box on your drawing. It removes almost all of the ambiguity that causes requotes and rejected certificates.

MATERIAL   : UNS N06022 / W.Nr. 2.4602 / NiCr21Mo14W
             per ASTM B564 (forgings)
             [use ASTM B462 for flanges, fittings, valve parts]
             [use ASME SB-564 where ASME code applies]

CONDITION  : SOLUTION ANNEALED 1121 °C (2050 °F) + RAPID WATER QUENCH
             NO AGEING. NO INTERMEDIATE-TEMPERATURE HEAT TREATMENT.
             Cooling through 980-650 °C to be as rapid as section permits.

MECHANICAL : UTS >= 690 MPa (100 ksi)
             YS 0.2% >= 310 MPa (45 ksi)
             Elongation >= 45 % in 50 mm
             Hardness <= 100 HRB

CORROSION  : ASTM G28 Method A, 24 h, rate <= [state limit] mm/yr
             [add ASTM G48 Method C, CPT >= [state] °C, where required]

NDE        : UT per EN 10228-3 Class [__]  (or ASTM A388 / SEP 1921)
             PT per ASTM E165 Type I Method [__]
             MAGNETIC PARTICLE NOT APPLICABLE - ALLOY IS NON-MAGNETIC

WELDING    : Filler ERNiCrMo-10 per AWS A5.14 (GTAW/GMAW)
             ENiCrMo-10 per AWS A5.11 (SMAW)
             No preheat. Interpass <= 100 °C. Heat input <= 1.5 kJ/mm.
             All heat tint to be removed by pickling or abrasive cleaning.

CERT       : EN 10204 3.1 mill certificate
             [3.2 with third-party witness where specified]
             [NACE MR0175 / ISO 15156-3 compliance statement for sour service]

MARKING    : Heat number, specification, condition, drawing number
             Low-sulfur, low-halogen marking media only

Where is Hastelloy C-22 / Alloy C-22 used?

UNS N06022 is specified where a corrosion failure would shut down a plant or create a safety event, and where the process chemistry is too variable for a cheaper alloy to be trusted. Six sectors account for most of our forging output in this grade.

Representative project scenarios

Representative scenarios illustrating typical scope. Named customer references and project data are available under a confidentiality agreement on request.

Glossary

Alloy C-22 / Alloy 22

Generic names for the nickel-chromium-molybdenum-tungsten alloy designated UNS N06022 and W.Nr. 2.4602.

UNS N06022

The Unified Numbering System designation. The safest identifier to use on a purchase order because it carries no trademark.

W.Nr. 2.4602 / NiCr21Mo14W

The European material number and chemical-symbol designation for the same alloy, used across EU procurement and in VdTÜV 479.

Hastelloy® C-22®

Registered trademark of Haynes International, Inc. for material they produce. Not a generic term.

Solution annealing

Heating to ≈1121 °C to dissolve all carbides and intermetallic phases into a single-phase austenite, then quenching fast enough that they do not re-form. The only heat treatment applicable to this alloy.

μ phase / P phase / σ phase

Intermetallic compounds that precipitate in UNS N06022 between roughly 650 and 980 °C. They embrittle the alloy and deplete chromium and molybdenum locally, which is what destroys corrosion resistance.

Sensitisation

Chromium depletion adjacent to grain-boundary carbides, leaving those regions vulnerable to intergranular attack. C-22 resists it because carbon is capped at 0.015%.

PREN

Pitting resistance equivalent number, %Cr + 3.3%Mo + 1.65%W + 16%N. A screening index for chloride pitting resistance only. Approximately 70 for C-22.

CPT / CCT

Critical pitting temperature and critical crevice temperature, the lowest temperatures at which pitting or crevice attack initiates in a standard ferric chloride test per ASTM G48. CCT is always the lower and more conservative of the two.

ASTM G28 Method A

A 24-hour boiling ferric-sulfate/sulfuric-acid immersion test that reveals intergranular attack from incorrect heat treatment. The most useful single acceptance test for a C-22 forging.

ERNiCrMo-10

The matching bare welding filler for UNS N06022 per AWS A5.14. The covered-electrode equivalent is ENiCrMo-10 per AWS A5.11.

EN 10204 3.1 / 3.2

Inspection document types. 3.1 is issued by the manufacturer's own independent inspection function; 3.2 is countersigned by an independent third party or the purchaser's representative.

Open-die forging

Hot working between flat or simple dies with the workpiece repositioned between blows. Used for shafts, blocks, discs and heavy sections where tooling cost must stay low.

Seamless rolled ring

A ring produced by piercing a billet and rolling it out between a mandrel and a main roll, giving circumferential grain flow with no weld seam.

Heat tint

The coloured oxide left on the surface after welding. Cosmetically minor, metallurgically serious: the layer beneath it is chromium depleted and pits readily.

Frequently asked questions about Hastelloy C-22 / Alloy C-22

Technical references

1. ASTM B564/B564M, Standard Specification for Nickel Alloy Forgings, ASTM International, West Conshohocken, PA.
2. ASTM B462, Standard Specification for Forged or Rolled UNS N06030, UNS N06022 … Alloy Pipe Flanges, Forged Fittings, and Valves and Parts for Corrosive High-Temperature Service, ASTM International.
3. ASTM B574, Standard Specification for Low-Carbon Nickel-Chromium-Molybdenum … Alloy Rod, ASTM International.
4. ASTM B575, Standard Specification for Low-Carbon Nickel-Chromium-Molybdenum … Alloy Plate, Sheet, and Strip, ASTM International.
5. ASTM B622 and B619, seamless and welded nickel-alloy pipe specifications, ASTM International.
6. ASTM G28, Standard Test Methods for Detecting Susceptibility to Intergranular Corrosion in Wrought, Nickel-Rich, Chromium-Bearing Alloys, ASTM International.
7. ASTM G48, Standard Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride Solution, ASTM International.
8. ASTM A262, Standard Practices for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels, Practice C, ASTM International.
9. ASTM A388/A388M, Standard Practice for Ultrasonic Examination of Steel Forgings, ASTM International.
10. ASTM E165/E165M, Standard Practice for Liquid Penetrant Testing for General Industry, ASTM International.
11. ASME Boiler and Pressure Vessel Code, Section II Part B (SB-564, SB-574, SB-575) and Part D allowable stresses, ASME, latest edition.
12. NACE MR0175 / ISO 15156-3, Petroleum and natural gas industries — Materials for use in H₂S-containing environments in oil and gas production — Part 3: Cracking-resistant CRAs and other alloys, ISO.
13. EN 10228-3, Non-destructive testing of steel forgings — Part 3: Ultrasonic testing of ferritic or martensitic steel forgings, and SEP 1921 for acceptance classes, CEN / VDEh.
14. EN 10204, Metallic products — Types of inspection documents, CEN.
15. DIN 17744, Wrought nickel alloys with molybdenum and chromium, and VdTÜV Werkstoffblatt 479 for material 2.4602.
16. AWS A5.14/A5.14M, Specification for Nickel and Nickel-Alloy Bare Welding Electrodes and Rods (ERNiCrMo-10), and AWS A5.11 (ENiCrMo-10), American Welding Society.
17. VDM Metals International GmbH, VDM® Alloy 22 / Nicrofer 5621 hMoW, Material Data Sheet No. 4121.
18. Haynes International, Inc., HASTELLOY® C-22® alloy product brochure.
19. ASM Handbook, Volume 13B, Corrosion: Materials, ASM International, Materials Park, OH. Chapter on corrosion of nickel and nickel-base alloys.
20. ASM Handbook, Volume 14A, Metalworking: Bulk Forming, ASM International. Forging of nickel-base alloys.

Standards are cited by designation without a revision year because the applicable revision is the one in force at your contract date. Trademarks referenced belong to their respective owners. Property values on this page are typical or specification-minimum values for orientation; the governing figures for any order are those on that order's mill certificate.

Request a quotation for Hastelloy C-22 / Alloy C-22 / UNS N06022 forgings

Related nickel-alloy forging grades

• Alloy C-276 / N10276
• Alloy C-4 / N06455
• Alloy C-2000 / N06200
• Alloy 59 / N06059
• Alloy B-3 / N10675
• Inconel 625 / N06625
• Incoloy 825 / N08825
• Monel 400 / N04400
• 904L / N08904