NiCr20CuMo Forgings: Alloy 20 / UNS N08020 / W.Nr. 2.4660
Reviewed 24 August 2026. Jiangyin Jiangnan Metal Co., Ltd., open-die forging factory, Jiangyin, Jiangsu, China.
NiCr20CuMo=2.4660=UNS N08020=Alloy 20=Carpenter 20
What is NiCr20CuMo?
NiCr20CuMo is the EN designation for a niobium-stabilised austenitic nickel-iron-chromium alloy containing 32 to 38% nickel, 19 to 21% chromium, 3 to 4% copper and 2 to 3% molybdenum, balance iron. It is registered as W.Nr. 2.4660 and UNS N08020, specified in DIN 17744, and sold worldwide as Alloy 20. The alloy was developed in 1951 for sulphuric acid service.
Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory in Jiangyin, Jiangsu, China, forges NiCr20CuMo into rings, seamless rolled rings, flanges, bars, discs, shafts, sleeves and tube sheets to ASTM B462, ASTM B472 and ASTM B473, ultrasonically tested and supplied with EN 10204 3.1 or 3.2 certification.
- UNSN08020
- Werkstoff2.4660
- Density8.1 g/cm³
- Tensile, min551 MPa
- Yield 0.2%, min241 MPa
- Elongation, min30 %
Equivalent designations and trade names
NiCr20CuMo is traded under more than a dozen names. All of them describe the same UNS N08020 chemistry, so an enquiry written against any one of them can be quoted against the others. On a purchase order, state UNS N08020 together with the applicable ASTM specification.
| Naming system | Designation | Notes |
|---|---|---|
| EN / DIN | NiCr20CuMo | Chemical composition per DIN 17744 |
| Werkstoff-Nr. | 2.4660 | German material number |
| UNS (USA) | N08020 | Primary ordering designation |
| ISO | FeNi35Cr20Cu4Mo2 | Composition-based ISO name |
| GB (China) | NS1403 / NS143 | Chinese national designation |
| AFNOR (France) | Z2NCUD31-20AZ | French designation |
| Common name | Alloy 20 | Most widely used commercial name |
| Trade names | Carpenter 20, Carpenter 20Cb-3, Incoloy 20, Nicrofer 3620 Nb, 20Cb-3 | Producer brand names for the same chemistry |
| Cast equivalent | CN7M, ASTM A351 CN7M | Nearest casting grade, not interchangeable with forgings |
NiCr20CuMo forged product forms
All forms listed below are produced to customer drawing on open-die presses and ring-rolling mills at our Jiangyin plant. NiCr20CuMo is not held in finished stock. Each piece is forged from a traceable heat to the ordered dimensions, so non-standard sizes carry no price premium.
-
Forged and seamless rolled rings
Ring-rolled from a pierced, upset billet for continuous circumferential grain flow.
OD 200 to 3000 mm -
Forged flanges
WN, SO, BL, LJ, SW, threaded and orifice, ASME B16.5 and B16.47, Class 150 to 2500.
ASTM B462 / SB-462 -
Round bars and billets
Forged, rough-turned or peeled. Billet stock for onward reforging is also available.
Dia. 80 to 1200 mm -
Discs, blanks and tube sheets
Upset and drawn from cogged billet, with radial grain flow across the face.
Up to 2500 mm -
Shafts and stepped shafts
Eccentric shafts, spindles, pump and agitator shafts, crankshafts.
Up to 6000 mm long -
Sleeves, bushings and hollow bars
Bored and trepanned hollows, pump sleeves, wear bushings, forged tubes.
Wall from 15 mm -
Valve bodies and seat rings
Forged valve blocks, bodies, bonnets, stems and valve seat rings.
To API 6A / 6D drawing -
Forged pipe and nozzles
Heavy-wall forged pipe, nozzles, manifolds and forged fittings.
ASTM B462 / B366
Single-piece weights range from 5 kg to 15 tonnes. Send a drawing, a sketch or the rough OD, ID and height for a price and lead time.
Standards for NiCr20CuMo forgings
Three ASTM specifications cover the forged product forms. ASTM B462 applies to forged flanges, fittings, valves and parts and is the specification most often quoted on enquiries. DIN 17744 governs chemistry on the European side.
| Product form | ASTM | ASME | European |
|---|---|---|---|
| Forged flanges, fittings, valves and parts | B462 | SB-462 | DIN 17744 |
| Billets and bars for reforging | B472 | SB-472 | DIN 17752 |
| Bar and wire | B473 | SB-473 | DIN 17752 / 17753 |
| Plate, sheet and strip | B463 | SB-463 | DIN 17750 |
| Seamless pipe and tube | B729 | SB-729 | DIN 17751 |
| Buttweld fittings | B366 | SB-366 | n/a |
Chemical composition of NiCr20CuMo
Composition limits in weight percent, per DIN 17744 and ASTM B462 for UNS N08020. Note the niobium requirement: Nb+Ta must be at least eight times the carbon content. This stabilises the alloy against sensitisation during welding.
| Limit | Ni | Cr | Cu | Mo | Fe | Nb+Ta | C | Mn | Si | P | S |
|---|---|---|---|---|---|---|---|---|---|---|---|
| min | 32.0 | 19.0 | 3.0 | 2.0 | Bal. | 8 x C | n/a | n/a | n/a | n/a | n/a |
| max | 38.0 | 21.0 | 4.0 | 3.0 | Bal. | 1.00 | 0.07 | 2.00 | 1.00 | 0.045 | 0.035 |
Fe = balance. Composition varies slightly between specifications; the ordered specification governs. Melting by AOD refining or vacuum induction melting, with vacuum arc remelting or electroslag remelting available on request.
Mechanical properties
Values below apply to the solution annealed condition at room temperature. The ASTM row gives the guaranteed minimum that can be specified on a purchase order. The typical row gives measured results from our NiCr20CuMo forgings.
| Basis | Condition | Yield 0.2% (MPa) | Tensile (MPa) | Elongation (%) | Hardness (HB) |
|---|---|---|---|---|---|
| ASTM B462, minimum | Solution annealed | 241 | 551 | 30 | n/a |
| Typical, as tested | Solution annealed | 274 | 617 | 50 | 184 |
Physical properties
| Property | Value |
|---|---|
| Density | 8.1 g/cm³ (0.29 lb/in³) |
| Melting range | 1385 to 1443 °C (2525 to 2630 °F) |
| Crystal structure | Austenitic, face-centred cubic |
| Magnetic response | Essentially non-magnetic when annealed |
Forging practice and heat treatment
Hot working
Heat the stock uniformly to 1150 to 1230 °C (2100 to 2250 °F) and finish forging before the workpiece drops below 980 °C (1800 °F). Working below this temperature work-hardens the alloy and increases the risk of cracking. Reheating between passes is normal practice on heavy sections and is allowed for in the pass schedule.
Solution annealing
After hot working the forging is solution annealed at 940 to 1010 °C (1725 to 1850 °F), held approximately 30 minutes per 25 mm of section thickness, then water quenched. Rapid cooling is required. Slow cooling through the sensitisation range allows chromium carbides to precipitate at grain boundaries and reduces corrosion resistance. Stress relieving, where specified, is carried out below 540 °C (1000 °F).
Testing and certification
Each NiCr20CuMo forging is ultrasonically tested to EN 10228-3, SEP 1921 or ASTM A388 according to the ordered specification. Material certificates are issued to EN 10204 3.1, or EN 10204 3.2 with third-party witness by TUV, BV, SGS, LR or DNV. Chemical analysis, mechanical test results, the heat treatment chart and a dimensional report are supplied with the goods. Positive material identification and intergranular corrosion testing to ASTM A262 Practice E are available on request.
Corrosion resistance
Alloy 20 was developed in 1951 for dilute sulphuric acid service. The function of each alloying element is set out below.
| Element | Function |
|---|---|
| Copper, 3 to 4% | Principal addition for sulphuric acid resistance. Lowers the corrosion rate in dilute and mid-concentration acid, where standard austenitic stainless steels fail. |
| Molybdenum, 2 to 3% | Pitting and crevice corrosion resistance in chloride-bearing media. |
| Nickel, 32 to 38% | Austenite stability and resistance to chloride stress corrosion cracking. |
| Chromium, 19 to 21% | Passive film formation, general corrosion and oxidising acid resistance. |
| Niobium, min. 8 x C | Combines with carbon as niobium carbide so that chromium carbides do not form at grain boundaries. Welded assemblies therefore resist intergranular attack without post-weld solution annealing. |
In service the alloy resists stress corrosion cracking in boiling 20 to 40% sulphuric acid, and performs well in phosphoric acid, nitric acid and chloride-containing process streams. It sits between the austenitic stainless steels and the nickel-base alloys in both performance and cost.
Where NiCr20CuMo is not the right selection. The alloy is not suitable for hot hydrochloric acid, wet chlorine or strongly reducing mixed acids. These duties require a high-molybdenum grade such as Hastelloy C-276 or Hastelloy C-22. For sour oilfield service with high strength requirements, consider Incoloy 925 or Incoloy 945.
Applications for NiCr20CuMo forgings
| Industry | Forged components |
|---|---|
| Sulphuric acid and pickling | Pickling tank internals, racks, heating coil headers, phosphate coating drum shafts, forged rings and shafts |
| Chemical processing | Reactor vessel flanges, mixing tank shafts and agitators, process piping flanges, bubble caps, forged nozzles |
| Petrochemical and refining | Heat exchanger tube sheets, forged pipe, valve bodies, seat rings, blind and weld-neck flanges |
| Oil and gas | Wellhead components, Christmas tree parts, down-hole equipment, forged crankshafts and manifolds |
| Marine and subsea | Seawater pump casings and shafts, ballast system gate valve parts, deep-sea sampler housings, robotic arm joints |
| Pharmaceutical and food | Crystalliser shafts, sanitary process equipment, forged discs and sleeves |
| Synthetic rubber and plastics | Forged rolls, wheels, manifolds, extruder components |
| Infrastructure | Pin and hanger expansion joints for bridges, offering better galling resistance and sub-zero Charpy values than the A36 and A588 carbon steels normally used |
Frequently asked questions
Is NiCr20CuMo the same as Alloy 20?
Yes. NiCr20CuMo, W.Nr. 2.4660, UNS N08020 and Alloy 20 are the same material under different naming systems. The trade names Carpenter 20, Carpenter 20Cb-3, Incoloy 20 and Nicrofer 3620 Nb describe the same chemistry. Order against UNS N08020 together with the applicable ASTM specification.
Which standards apply to NiCr20CuMo forgings?
ASTM B462 and ASME SB-462 for forged flanges, forged fittings, valves and parts. ASTM B472 and ASME SB-472 for billets and bars for reforging. ASTM B473 and ASME SB-473 for bar and wire. Composition is also covered by DIN 17744. Jiangyin Jiangnan Metal Co., Ltd. supplies NiCr20CuMo forgings to all of these.
What are the minimum mechanical properties?
Solution annealed, ASTM B462 requires minimum 551 MPa (80 ksi) tensile, minimum 241 MPa (35 ksi) 0.2% yield and minimum 30% elongation. Typical measured room-temperature values for our forgings are 617 MPa tensile, 274 MPa yield, 50% elongation and 184 HB.
Why is NiCr20CuMo used for sulphuric acid service?
The 3 to 4% copper addition lowers the corrosion rate across dilute and mid-concentration sulphuric acid, where standard austenitic stainless steels fail. Molybdenum adds pitting and crevice resistance in chlorides. Niobium stabilisation prevents chromium carbide precipitation, so welded assemblies resist intergranular attack without post-weld solution annealing. The alloy resists stress corrosion cracking in boiling 20 to 40% sulphuric acid.
How should NiCr20CuMo be forged and heat treated?
Heat to 1150 to 1230 °C and finish forging before the piece falls below 980 °C. Solution anneal at 940 to 1010 °C, holding approximately 30 minutes per 25 mm of section, then water quench. Rapid cooling restores full corrosion resistance.
Is NiCr20CuMo weldable?
Yes. Because niobium combines with the carbon, welded fabrications normally do not require post-weld solution annealing to resist intergranular corrosion. Common filler metals are ER320LR for GTAW and GMAW and E320LR for SMAW and SAW. Heat input should be kept moderate and interpass temperature low.
NiCr20CuMo or Hastelloy C-276, which should be specified?
NiCr20CuMo (Alloy 20) is used for sulphuric and phosphoric acid duty and for moderate chloride stress corrosion cracking resistance. Hastelloy C-276 contains far more molybdenum and is specified for hot hydrochloric acid, wet chlorine and strongly reducing mixed acids. Where Alloy 20 meets the duty it costs less per kilogram of finished forging. Provide the medium, concentration and temperature for a grade recommendation.
What certificates and NDT are supplied?
Ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388, with EN 10204 3.1 certification as standard and EN 10204 3.2 under third-party witness by TUV, BV, SGS, LR or DNV on request. Chemical analysis, mechanical test, heat treatment record and dimensional report are included. PMI and ASTM A262 Practice E intergranular corrosion testing are available.
What sizes can be forged, and what is the lead time?
Rings from 200 mm to 3000 mm OD, bars from dia. 80 mm to dia. 1200 mm, discs and tube sheets to 2500 mm, and single-piece weights from 5 kg to 15 tonnes. Lead time depends on piece size, heat treatment and NDT scope and is confirmed with the quotation. Quotations are normally returned within one working day.
Who supplies NiCr20CuMo open-die forgings in China?
Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. We forge NiCr20CuMo (Alloy 20 / UNS N08020) rings, seamless rolled rings, flanges, bars, discs, shafts, sleeves, bushings and tube sheets to customer drawing. Contact +86 189 2135 9659 or sales@steelforgepieces.com.
Related nickel alloy forging grades
Grades most often compared against NiCr20CuMo during material selection:
| Grade | Selected when |
|---|---|
| Incoloy 825 | Similar acid duty with better resistance to reducing acids and higher temperatures |
| Hastelloy C-276 | Hot hydrochloric acid, wet chlorine, strongly reducing mixed acids |
| Inconel 625 | Seawater and high-strength corrosion service at elevated temperature |
| Incoloy 925 | Sour oilfield service requiring age-hardened strength |
| Alloy 31 | Concentrated sulphuric and phosphoric acid at higher temperature |
| A286 | High-temperature strength rather than acid resistance |
Request a NiCr20CuMo forging quotation
Send a drawing, a sketch or the rough dimensions together with the service medium. Quotations are normally issued within one working day.
Company Jiangyin Jiangnan Metal Co., Ltd.
Address No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Phone +86 189 2135 9659
Email sales@steelforgepieces.com
Capability Open-die forging, ring rolling, heat treatment, rough machining