01 Description and selection
Hastelloy C-4, ordered generically as Alloy C-4, belongs to the nickel-chromium-molybdenum group that also includes C-276, C-22 and C-2000. All of these grades resist hydrochloric acid, sulphuric acid and chloride pitting. C-4 differs mainly in what it excludes. There is no tungsten in the composition, iron is limited to 3 %, silicon to 0.08 % and carbon to 0.015 %, and up to 0.70 % titanium is present to combine with residual carbon.
Those limits remove the conditions that cause grain-boundary precipitation in the other C-grades. Ageing studies on C-4 have not detected mu-phase in the 649 to 1093 °C range. Fine intergranular M6C carbides can still form, but their effect on properties is small. A fabricated C-4 vessel can therefore be welded and placed in hot acid service without a post-weld solution anneal.
C-4 also resists chloride stress-corrosion cracking, which limits the use of austenitic stainless steels in many process streams, and it tolerates oxidising atmospheres to about 1038 °C.
Specify Hastelloy C-4 when
- The part will be welded into an assembly that cannot be solution annealed afterwards, such as a large vessel, a field weld or a repair weld.
- Service temperature sits in the 649 to 1038 °C sensitisation window for extended periods.
- The medium is a hot contaminated mineral acid such as HCl, H2SO4 or H3PO4, an organic acid such as formic or acetic, or a mixed acid such as HCl/HNO3.
- Chloride stress-corrosion cracking has already caused a failure in a 316L or duplex component.
- The design must satisfy NACE MR0175 / ISO 15156 hardness limits for sour service.
Consider C-276 or C-22 instead when
If the assembly will be solution annealed after welding, C-276 usually gives equal or better corrosion performance at lower cost and is easier to source at short notice. C-22 is the better choice where the medium alternates between oxidising and reducing conditions, for example in flue gas desulphurisation. Section 06 sets out the differences.
02 Forged product range
All Hastelloy C-4 items below are open-die forged or ring rolled to the customer drawing. There are no dies and no tooling charge, so the minimum order is one piece. Rough machining, finish machining and heat treatment are carried out on site.
| Forged form | Size range | Typical use |
|---|---|---|
| Seamless rolled rings | OD 150-2500 mm, wall 20-350 mm, height up to 800 mm | Vessel shell courses, bearing races, flange blanks |
| Forged flanges | DN 15 to DN 1200, OD up to 2000 mm | Weld neck, slip on, blind and orifice flanges to ASME B16.5, B16.47 or EN 1092-1 |
| Discs and blanks | Dia 100-1800 mm, thickness 20-500 mm | Valve discs, blind covers, closure heads |
| Shafts and spindles | Dia 60-800 mm, length up to 6000 mm | Agitator and pump shafts, valve stems |
| Round bar and billet | Dia 30-600 mm | Machining stock, fastener stock, valve bodies |
| Sleeves and bushings | OD 100-1200 mm, wall 15 mm and above | Wear sleeves, pump liners, seal housings |
| Hollow forged tube | OD 120-1200 mm, length up to 4000 mm | Heat exchanger nozzles, thick-wall piping |
| Tube sheets | Dia up to 2500 mm, thickness up to 400 mm | Shell and tube heat exchangers, condensers |
| Forged blocks and bodies | Single-piece weight 5-3000 kg | Valve bodies, manifolds, wellhead components |
The limits in this table apply individually. A thin-wall ring at maximum diameter and a solid disc at maximum thickness are different problems, so please send the drawing and we will confirm the capability for the specific part.
03 Chemical composition
Composition limits for UNS N06455 to ASTM B564, B574 and B575, in weight percent. The two entries that define the grade are the absence of tungsten and the 3 % maximum on iron.
| Element | Min | Max | Function |
|---|---|---|---|
| Nickel (Ni) | Balance | – | Austenitic matrix, resistance to chloride stress-corrosion cracking |
| Chromium (Cr) | 14.0 | 18.0 | Passivity in oxidising acids |
| Molybdenum (Mo) | 14.0 | 17.0 | Resistance to reducing acids and pitting |
| Iron (Fe) | – | 3.00 | Held low for thermal stability |
| Cobalt (Co) | – | 2.00 | Residual, restricted for nuclear service |
| Manganese (Mn) | – | 1.00 | Deoxidiser |
| Titanium (Ti) | – | 0.70 | Combines with carbon, suppresses carbides in the heat-affected zone |
| Silicon (Si) | – | 0.08 | Restricted, promotes precipitation if high |
| Phosphorus (P) | – | 0.040 | Residual |
| Sulphur (S) | – | 0.030 | Residual |
| Carbon (C) | – | 0.015 | Very low, prevents grain-boundary carbides |
| Tungsten (W) | – | Not added | Deliberately absent, C-276 contains 3.0 to 4.5 % |
Pitting resistance equivalent calculated from the nominal 16 Cr and 15.5 Mo as PREN = Cr + 3.3 x Mo is approximately 67.
04 Mechanical properties
Room-temperature minimum values in the solution-annealed condition, which is the standard delivery condition for our Hastelloy C-4 forgings unless the order states otherwise. Mill results are usually higher than the minimum. Tensile values of 750 to 800 N/mm² are common on forged sections.
| Condition | Tensile strength Rm | Yield Rp0.2 | Elongation A5 | Hardness |
|---|---|---|---|---|
| Solution annealed 1066 °C and rapid quench |
690 N/mm² (100 ksi) min | 275 N/mm² (40 ksi) min | 40 % min | 35 HRC max NACE MR0175 limit |
Strengthening
Alloy C-4 is solid-solution strengthened and cannot be hardened by heat treatment. The only heat treatment applied is solution annealing at about 1066 °C followed by rapid quenching. Higher strength is available only through cold work, and cold-worked parts should be re-annealed once outer-fibre elongation reaches 7 % or more, otherwise resistance to chloride stress-corrosion cracking falls. Drawings that call for solution treatment and ageing on C-4 have usually been copied from a precipitation-hardening grade such as Inconel 718. Please raise this with us before material is cut.
05 Physical properties
| Property | Metric | Imperial |
|---|---|---|
| Density | 8.64 g/cm³ | 0.312 lb/in³ |
| Melting range | 1350-1400 °C | 2460-2550 °F |
| Modulus of elasticity at 20 °C | 211 GPa | 30.8 x 10³ ksi |
| Modulus of rigidity at 20 °C | 81.0 GPa | 11.8 x 10³ ksi |
| Thermal conductivity at 20 °C | 10.1 W/m·K | 70 Btu·in/ft²·h·°F |
| Mean thermal expansion, 20-300 °C | 12.6 µm/m·°C | 7.0 µin/in·°F |
| Electrical resistivity | 125 µΩ·cm | 49.1 µΩ·in |
| Magnetic response | Non-magnetic, austenitic | |
Temperature ranges
06 Comparison with C-276 and C-22
Buyers most often ask how Hastelloy C-4 compares with C-276 and C-22. All three are forged in the same shop, and the composition differences decide which one suits a given duty.
| Property | Hastelloy C-4 | Hastelloy C-276 | Hastelloy C-22 |
|---|---|---|---|
| Generic name | Alloy C-4 | Alloy C-276 | Alloy 22 |
| UNS / W.Nr. | N06455 / 2.4610 | N10276 / 2.4819 | N06022 / 2.4602 |
| Chromium | 14-18 % | 14.5-16.5 % | 20-22.5 % |
| Molybdenum | 14-17 % | 15-17 % | 12.5-14.5 % |
| Tungsten | None | 3.0-4.5 % | 2.5-3.5 % |
| Iron | 3.0 % max | 4.0-7.0 % | 2.0-6.0 % |
| Resistance to sensitisation | Highest of the three, as-welded service is normal | Good, post-weld anneal advised for severe duty | Very good |
| Oxidising media | Good | Moderate | Highest of the three, from the higher chromium |
| Reducing acids | Very good | Highest of the three, from the tungsten addition | Very good |
| Cost and availability | Higher cost, specialist sourcing | Lowest of the three, widely stocked | Mid range |
| Choose it when | The welded fabrication cannot be re-annealed, or service runs long in the 649 to 1038 C range | General chemical process duty, strong reducing acids | Mixed oxidising and reducing service, flue gas desulphurisation, waste incineration |
If you are unsure which grade fits, send the medium, concentration, temperature and pressure to sales@steelforgepieces.com and we will recommend a grade before you commit to a forging.
07 Equivalent designations and specifications
| System | Designation |
|---|---|
| Generic designation | Alloy C-4 (also written Alloy C4) |
| UNS | N06455 |
| Werkstoff / EN | 2.4610 |
| DIN | NiMo16Cr16Ti |
| AFNOR | NC16D16M |
| Trade names | Hastelloy C-4 (Haynes International, also written Hastelloy C4), Nicrofer 6616 (VDM Metals) |
| Form | ASTM | ASME |
|---|---|---|
| Forgings | B564 | SB-564 |
| Forged flanges and fittings | B462 | SB-462 |
| Rod and bar | B574 | SB-574 |
| Plate, sheet and strip | B575 | SB-575 |
| Seamless pipe and tube | B622 | SB-622 |
| Welded pipe and tube | B619 / B626 | SB-619 / SB-626 |
| Welded fittings | B366 | SB-366 |
08 Manufacturing route
Route for a typical Alloy C-4 seamless rolled ring.
- MeltingEAF plus VOD for the base heat. ESR remelting is added where the drawing calls for tighter cleanliness, or for thick sections that will be ultrasonically tested to a fine acceptance class.
- Ingot inspection and croppingChemical analysis by spectrometer against the ASTM B564 limits. Hot tops and pipe are cropped off before forging.
- HeatingSoak to the hot-working range of 954 to 1107 C. The window is narrow and the alloy work hardens quickly. Under-heating causes cracking and over-heating coarsens the grain.
- Forging and ring rollingUpset and draw on the hydraulic press to break down the cast structure and reach the specified forging ratio, then punch and roll for ring forms, with reheats as required.
- Solution annealing1066 C, held according to section thickness, then rapid quenched, with water quenching used for heavy sections. This step restores corrosion resistance after hot work and is not optional.
- MachiningTurned, bored and faced to the drawing, with machining allowance agreed in advance. Finish machining to final tolerance is available.
- TestingUltrasonic testing plus tensile, hardness and any corrosion tests called up by the specification. See section 09.
- Marking, certification and packingHeat number and part identification hard stamped, EN 10204 3.1 or 3.2 certificate issued, then seaworthy packing for export through Shanghai or Ningbo.
09 Testing and certification
Every Hastelloy C-4 / Alloy C-4 forging leaves the works with the tests below, whichever name the order was placed under. The certificate records the grade as UNS N06455.
Included on every order
- Chemical analysis by optical emission spectrometer, reported against the ASTM B564 limits.
- Room-temperature tensile test giving Rm, Rp0.2, A5 and Z.
- Hardness, Brinell or Rockwell, including the 35 HRC maximum check to NACE MR0175 for sour service.
- Ultrasonic testing to ASTM A388, EN 10228-3 or SEP 1921, acceptance class as stated on the order.
- Dimensional report against the approved drawing.
- EN 10204 3.1 mill certificate, heat number traceable to the individual forging.
Available on request
- EN 10204 3.2 with third-party witness by SGS, Bureau Veritas, TUV, Lloyd's Register or DNV.
- Intergranular corrosion test to ASTM G28 method A or B, the usual proof of correct annealing on C-family alloys.
- Positive material identification on every piece.
- Liquid penetrant testing to ASTM E165 or ASME Section V Article 6.
- Impact testing, including sub-zero, to ASTM E23 or ASTM A370.
- Grain size to ASTM E112 and macro-etch to ASTM E381.
- NACE MR0175 / ISO 15156 compliance statement for sour service.
10 Applications
Where Hastelloy C-4 and Alloy C-4 forgings are specified.
11 Frequently asked questions
What is Hastelloy C-4 / Alloy C-4?
Hastelloy C-4 and Alloy C-4 are two names for one grade, UNS N06455, W.Nr. 2.4610. It is a low-carbon nickel-chromium-molybdenum alloy with nominally 16 % chromium and 16 % molybdenum, balance nickel. It contains no tungsten, iron is limited to 3 % maximum, and titanium up to 0.70 % combines with residual carbon. This composition makes it the most microstructurally stable of the common Ni-Cr-Mo alloys. It does not form mu-phase after long exposure between 649 °C and 1038 °C, so weld heat-affected zones stay ductile and resist intergranular attack.
Is Hastelloy C-4 the same as Alloy C-4?
Yes. They are the same grade under two names, and both are often written without the hyphen as Hastelloy C4 and Alloy C4. Hastelloy is a registered trademark of Haynes International, Inc., and Hastelloy C-4 is that company's brand name for the grade. Alloy C-4 is the generic designation used in ASTM specifications and on mill certificates, where it appears as UNS N06455 or W.Nr. 2.4610. The same material is also sold as Nicrofer 6616 and as NiMo16Cr16Ti.
Composition limits, mechanical minimums and heat treatment are identical whichever name is on the enquiry, so quote either one and we will price the same material.
Can you supply Hastelloy C-4 forgings?
Yes, in the sense that matters to most buyers. We forge UNS N06455 to ASTM B564, the grade sold under the Hastelloy C-4 name, and supply it solution annealed with an EN 10204 3.1 or 3.2 certificate.
The material is melted and forged in China, and the certificate states UNS N06455 and W.Nr. 2.4610 rather than the trademark, so it is not Haynes International branded product. If your purchase specification names Hastelloy C-4 and accepts material to UNS N06455, we can supply against it. If it requires material of Haynes origin, please tell us before the order is placed.
What is the difference between Hastelloy C-4 and Hastelloy C-276?
C-276 contains 3.0 to 4.5 % tungsten and up to 7 % iron. C-4 contains no tungsten, a maximum of 3 % iron and up to 0.70 % titanium. C-276 performs better in aggressive reducing acids and is the more common general-purpose choice. C-4 has higher thermal stability and is preferred where the part sees long exposure between 649 °C and 1038 °C, or where a welded fabrication must enter service without post-weld heat treatment. Jiangyin Jiangnan Metal forges both grades. Section 06 sets out the full comparison.
Which standard covers Hastelloy C-4 / Alloy C-4 forgings?
ASTM B564 (ASME SB-564) is the primary specification for nickel alloy forgings including UNS N06455. ASTM B462 covers forged flanges and fittings for high-temperature service, ASTM B574 covers rod and bar, ASTM B575 covers plate, sheet and strip, and ASTM B622 covers seamless pipe and tube. Jiangyin Jiangnan Metal Co., Ltd. supplies Alloy C-4 forgings to ASTM B564 as standard and can work to DIN, EN, JIS, API 6A or a customer specification on request.
Can Alloy C-4 be hardened by ageing or precipitation heat treatment?
No. Alloy C-4 is solid-solution strengthened and cannot be hardened by heat treatment. The only heat treatment applied is solution annealing at approximately 1066 °C followed by rapid quenching, usually in water. Ageing would work against the purpose of the grade, which depends on remaining free of precipitates. Higher strength is available only through cold work, and cold-worked parts should be re-annealed once outer-fibre elongation reaches 7 % or more.
Does Hastelloy C-4 need post-weld heat treatment?
In most cases no. Hastelloy C-4 was developed to resist sensitisation in the weld heat-affected zone, so most chemical process equipment enters service in the as-welded condition. Post-weld solution annealing is still worth specifying for the most severe acid duty, or where a customer specification requires it. Hot forming must always be followed by re-annealing to restore corrosion resistance.
What size Hastelloy C-4 rings and forgings can you produce?
Jiangyin Jiangnan Metal Co., Ltd. rolls seamless Hastelloy C-4 rings from approximately 150 mm to 2500 mm outside diameter and forges discs, shafts, sleeves, tube sheets and hollow tube in single-piece weights from about 5 kg to 3000 kg. The practical limit depends on the shape, the forging ratio required and the ingot size available. Send the drawing to sales@steelforgepieces.com and we will confirm the capability for the specific part.
What certificates and testing are supplied with Hastelloy C-4 forgings?
Every Hastelloy C-4 forging is supplied with an EN 10204 3.1 mill test certificate showing heat number, chemical analysis and mechanical test results traceable to the part. EN 10204 3.2 certification with third-party witness by SGS, Bureau Veritas, TUV or Lloyd's Register is available on request. Ultrasonic testing is carried out to ASTM A388, EN 10228-3 or SEP 1921 as specified. PMI, dye penetrant, intergranular corrosion testing to ASTM G28 and hardness testing can be added to the order.
What is the minimum order quantity and lead time for Hastelloy C-4 forgings?
These are made-to-drawing open-die forgings, so the minimum order is one piece and there is no tooling cost. Lead time is normally 25 to 45 days from drawing approval, depending on whether suitable Hastelloy C-4 raw material is in stock and on the size, machining and testing required. Shorter deliveries are sometimes possible where bar or billet stock is already on hand.
Where are these Hastelloy C-4 / Alloy C-4 forgings made?
They are forged by Jiangyin Jiangnan Metal Co., Ltd. at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, in the Jiangyin forging and special steel district on the lower Yangtze River, about two hours from Shanghai Port. Telephone +86-189-2135-9659 or email sales@steelforgepieces.com.
12 About the manufacturer
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging works in Jiangyin, Jiangsu Province. We forge to customer drawings in nickel alloys, stainless steel, alloy steel, tool steel and carbon steel, covering seamless rolled rings, flanges, shafts, discs, sleeves, bushings, tube sheets and hollow forged tube.
Because the process is open-die there is no tooling to pay for, so a single prototype ring is as practical as a production batch. Melting, forging, solution annealing, machining, ultrasonic testing and certification are handled at one site, which keeps heat-number traceability intact from ingot to finished part. Export shipments go through Shanghai and Ningbo.
Company Jiangyin Jiangnan Metal Co., Ltd.Works No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Telephone +86-189-2135-9659
Email sales@steelforgepieces.com
Website www.steelforgepieces.com
Languages English, Chinese