UNS N08020 Forgings (Alloy 20 / Carpenter 20Cb-3) to ASTM B462
UNS N08020, sold under the names Alloy 20, Carpenter 20Cb-3 and Werkstoff 2.4660, is an austenitic nickel-iron-chromium alloy. It carries 32 to 38 % nickel, 19 to 21 % chromium, 3 to 4 % copper and 2 to 3 % molybdenum, and is stabilised with niobium. The grade was created for sulfuric acid service. It also holds up well against chloride stress-corrosion cracking, pitting and crevice corrosion. Forged and rolled parts are supplied to ASTM B462 / ASME SB-462: minimum tensile strength 551 MPa (80 ksi), minimum yield 241 MPa (35 ksi) in the annealed condition.
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin, Jiangsu Province, China. We forge UNS N08020 rings, seamless rolled rings, flanges, round bars, discs, shafts, sleeves, bushings, tube sheets and pipes to customer drawings, supplied with EN 10204 3.1 or 3.2 certification. Enquiries go to sales@steelforgepieces.com or +86 189 2135 9659.
What is UNS N08020?
UNS N08020 is a corrosion-resistant austenitic alloy of roughly 35 % nickel, 35 % iron and 20 % chromium, with niobium, copper and molybdenum added. It sits on the line between super-austenitic stainless steel and nickel alloy. ASTM B462 classes it as a nickel alloy.
The grade dates from 1951 and was developed for dilute sulfuric acid. Copper is what gives it that resistance. Molybdenum improves pitting and crevice corrosion behaviour. Niobium ties up carbon as niobium carbide, so welded and forged sections resist intergranular attack without post-weld heat treatment.
Being austenitic, the alloy cannot be hardened by heat treatment. Cold work is the only way to raise its strength. All UNS N08020 forgings we ship are solution annealed and water quenched unless the purchase specification says otherwise.
Designations and equivalent grades
The same chemistry appears on drawings under a dozen different names. Here are the ones that come up most often on enquiries for forged parts.
| System | Designation | Notes |
|---|---|---|
| UNS | N08020 | Primary designation |
| Common name | Alloy 20, Nickel Alloy 20 | Generic industry name |
| Trade name | Carpenter 20Cb-3, Incoloy 20 | Registered mill trade names |
| Werkstoff (DIN) | 2.4660 | German material number |
| EN | NiCr20CuMo | European designation |
| AFNOR | Z2 NCUD 31-20 AZ | French designation |
| ASTM (forgings) | B462 | Forged and rolled flanges, fittings, valves, parts |
| ASTM (bar) | B473 | Bar and wire |
| ASTM (plate) | B463 | Plate, sheet and strip |
| ASTM (pipe) | B729 / B464 | Seamless pipe and tube, welded pipe |
| Cast equivalent | CN7M (ASTM A351 / A743) | Casting grade, not interchangeable with forgings |
Chemical composition of UNS N08020
These are the chemical requirements of ASTM B462 / ASME SB-462 for forged and rolled UNS N08020. ASTM B473 (bar) and ASTM B463 (plate) carry the same limits.
| Element | Symbol | Weight % |
|---|---|---|
| Nickel | Ni | 32.00 to 38.00 |
| Chromium | Cr | 19.00 to 21.00 |
| Iron | Fe | Balance, approx. 30 to 44 |
| Copper | Cu | 3.00 to 4.00 |
| Molybdenum | Mo | 2.00 to 3.00 |
| Niobium (columbium) | Nb (Cb) | 8 × C min, 1.00 max |
| Manganese | Mn | 2.00 max |
| Silicon | Si | 1.00 max |
| Carbon | C | 0.07 max |
| Phosphorus | P | 0.045 max |
| Sulfur | S | 0.035 max |
Melting practice. Billet for forging is produced by AOD refining or vacuum induction melting, followed where required by electroslag or vacuum arc remelting. We can supply UNS N08020 forgings from ESR or VAR remelted material where the application calls for better cleanliness and less segregation.
Mechanical properties of UNS N08020 forgings
Minimum room-temperature values for annealed UNS N08020 forgings under ASTM B462:
| Product form | Tensile strength, min | Yield strength, min (0.2 % offset) | Elongation, min | Reduction of area, min |
|---|---|---|---|---|
| Forgings (ASTM B462) | 551 MPa / 80 ksi | 241 MPa / 35 ksi | 30 % | 50 % |
| Bar (ASTM B473) | 551 MPa / 80 ksi | 241 MPa / 35 ksi | 30 % | 50 % |
Annealed hardness runs to about 217 HB maximum. For oil and gas work the grade is listed in NACE MR0175 / ISO 15156 in the annealed or cold-worked condition at 32 HRC maximum. Impact testing to ASTM A370 at sub-zero temperature can be added to any order.
Physical properties of UNS N08020
| Property | Metric | Imperial |
|---|---|---|
| Density | 8.08 g/cm³ | 0.292 lb/in³ |
| Melting range | 1385 to 1443 °C | 2525 to 2630 °F |
| Modulus of elasticity | approx. 193 GPa | approx. 28 × 10⁶ psi |
| Magnetic response | Non-magnetic in the annealed condition | |
| Crystal structure | Austenitic, face-centred cubic | |
Corrosion resistance
Buyers reach for UNS N08020 when 316L or duplex will not last, but a full nickel alloy such as Hastelloy C-276 costs more than the job can carry. What it does well:
- Sulfuric acid. The 3 to 4 % copper gives useful service across a wide band of concentrations and temperatures. This is the application the alloy was built for.
- Chloride stress-corrosion cracking. High nickel content puts it well ahead of 304 and 316.
- Intergranular attack. Niobium stabilisation stops chromium carbide precipitation, so welded and forged sections need no post-weld heat treatment.
- Phosphoric and nitric acids. Used in phosphate coating drums, nitric acid equipment and mixed-acid pickling lines.
- Pitting and crevice corrosion. The 2 to 3 % molybdenum lifts pitting resistance above the standard austenitic grades.
Where the order calls for it, we run the boiling 65 % nitric acid test and the ferric sulfate / sulfuric acid test on finished forgings before shipment.
Forging and heat treatment
Hot working
Billet goes into the furnace at 1150 to 1230 °C (2100 to 2250 °F) for open-die forging. Watch the temperature: the material should not drop below 980 °C (1800 °F) while under the hammer, or you get cracking and poor grain structure. Reheating between passes is normal on heavy sections.
Annealing
After hot working, forgings are solution annealed at 940 to 1010 °C (1725 to 1850 °F), held at least 30 minutes per 25 mm of section thickness, then water quenched. Fast cooling through the sensitisation range is what preserves the corrosion resistance.
Machining and welding
The alloy work-hardens fast. Use positive-rake tooling, rigid setups, slow speeds and heavy positive feeds, and keep the tool cutting rather than dwelling. It welds readily by GTAW, GMAW and SMAW with matching AWS ERNiCrMo-3 or Alloy 20Cb-3 filler. Niobium stabilisation means no post-weld heat treatment.
UNS N08020 forged products we manufacture
We produce the following open-die and ring-rolled forgings in UNS N08020, to customer drawings or to dimensional standards such as ASME B16.5 and ASME B16.47.
| Product form | Typical size range | Common standards |
|---|---|---|
| Seamless rolled rings | OD 200 to 3000 mm, height to 800 mm | ASTM B462 |
| Forged rings | OD 100 to 3000 mm | ASTM B462 |
| Forged flanges | DN 15 to DN 1500, Class 150 to 2500 | ASME B16.5 / B16.47, EN 1092-1 |
| Round bars | Ø 20 to 800 mm | ASTM B473 |
| Forged discs and blanks | Ø 100 to 2500 mm | ASTM B462 |
| Forged shafts and spindles | Ø 50 to 800 mm, length to 6000 mm | ASTM B462 |
| Sleeves and bushings | OD to 1500 mm | ASTM B462 |
| Forged pipes and hollow bars | OD 100 to 1200 mm | ASTM B462 |
| Tube sheets | Ø to 3000 mm | ASTM B462, ASME VIII |
| Valve bodies, seat rings, stems, blocks | To drawing | ASTM B462, API 6A |
| Forged blocks, nozzles, manifolds | To drawing | ASTM B462 |
Parts ship as-forged, rough-machined with test-piece allowance, or finish-machined to drawing. For corrosion-critical duty we recommend rough machining, so the oxidised and decarburised surface layer comes off before the part goes into service.
Testing, inspection and certification
Every forging leaves the works with documentation traceable to the heat number.
| Test or document | Standard | Status |
|---|---|---|
| Chemical analysis | ASTM E1473, spectrometer | Standard |
| Tensile and yield test | ASTM A370, ISO 6892-1 | Standard |
| Hardness test | ASTM E10 / E18 | Standard |
| Ultrasonic testing | EN 10228-3, SEP 1921, ASTM A388 | Standard on request |
| Dye penetrant testing | ASTM E165 | On request |
| Intergranular corrosion test | ASTM A262, ASTM G28 | On request |
| Impact test, sub-zero | ASTM A370, ISO 148-1 | On request |
| Grain size and microstructure | ASTM E112 | On request |
| Material certificate | EN 10204 3.1 | Standard |
| Third-party certificate | EN 10204 3.2 (BV, SGS, TÜV, LR, DNV) | On request |
| Sour service compliance | NACE MR0175 / ISO 15156 | On request |
Applications of UNS N08020 forgings by industry
| Industry | Typical forged components | Why this grade |
|---|---|---|
| Sulfuric acid production | Rolled rings, shafts, heating-coil parts, pickling tank internals, racks | Copper content handles dilute and mid-concentration sulfuric acid |
| Chemical and petrochemical | Flanges, rings, tube sheets, process piping parts, mixing tank parts, bubble caps | General corrosion resistance plus freedom from intergranular attack |
| Oil and gas | Wellhead and Christmas tree parts, down-hole equipment, valve bodies, seat rings, stems, blocks | NACE MR0175 listed, resists chloride SCC |
| Marine and offshore | Seawater pump parts, ballast system gate valves, forged tubes, deep-sea sampler housings | Pitting and crevice resistance in seawater |
| Pharmaceutical and fine chemicals | Reactor vessel parts, crystalliser components, agitator shafts, nozzles | Clean surfaces, low contamination, holds up in mixed acids |
| Pulp, paper, synthetic rubber | Forged rolls, wheels, manifolds, eccentric shafts | Stands up to process liquors and organic acids |
| Bridges and structures | Pin and hanger expansion joint parts | Better corrosion and galling resistance, better low-temperature toughness than A36 or A588 |
| Phosphate and plating lines | Coating drums, racks, heating coils | Handles phosphoric acid and mixed acid baths |
About the manufacturer
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin, Jiangsu Province, China. We forge carbon steel, alloy steel, tool steel, stainless steel and nickel alloys, UNS N08020 among them, into rings, seamless rolled rings, flanges, bars, discs, shafts, sleeves, bushings, tube sheets and forged pipes. Parts go out worldwide against customer drawings and specifications.
- CompanyJiangyin Jiangnan Metal Co., Ltd.
- BusinessOpen-die forging factory
- AddressNo.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
- Telephone / WeChat+86 189 2135 9659
- Emailsales@steelforgepieces.com
- Websitewww.steelforgepieces.com
Materials forged: nickel alloys (UNS N08020, Inconel, Incoloy, Monel, Hastelloy, Nimonic, Waspaloy), stainless steel (A286, 17-4PH, 15-5PH, PH13-8Mo), tool steel, alloy steel and carbon steel.
How to request a quotation
For a price and lead time on UNS N08020 forgings, send the following to sales@steelforgepieces.com:
- Drawing in PDF, DWG or STEP, or the finished dimensions, and whether you want as-forged, rough-machined or finish-machined parts.
- Quantity and required delivery date.
- Applicable standard: ASTM B462, ASME SB-462, ASME B16.5 or your own specification.
- Testing and certification: EN 10204 3.1 or 3.2, ultrasonic testing class, corrosion testing, NACE MR0175 compliance.
- Destination port for CIF or FOB pricing.
Quotations normally go back within one working day.
Frequently asked questions about UNS N08020
What is UNS N08020?
UNS N08020 is an austenitic nickel-iron-chromium alloy with 32 to 38 % nickel, 19 to 21 % chromium, 3 to 4 % copper and 2 to 3 % molybdenum, stabilised with niobium. Most people know it as Alloy 20 or Carpenter 20Cb-3. It was developed for sulfuric acid service. Forged parts fall under ASTM B462.
Is UNS N08020 the same as Alloy 20 and Carpenter 20Cb-3?
Yes. UNS N08020 is the UNS number. Alloy 20, Nickel Alloy 20, Incoloy 20 and Carpenter 20Cb-3 are trade and common names for the same chemistry. The German material number is Werkstoff 2.4660 and the EN designation is NiCr20CuMo. The cast equivalent, CN7M, has its own specification and does not substitute for forgings.
Which standard covers UNS N08020 forgings?
ASTM B462 / ASME SB-462, covering forged and rolled alloy pipe flanges, forged fittings, valves and parts for corrosive high-temperature service. Related specifications are ASTM B473 for bar, ASTM B463 for plate and ASTM B729 for seamless pipe.
What is the chemical composition of UNS N08020?
Per ASTM B462: nickel 32.00 to 38.00 %, chromium 19.00 to 21.00 %, copper 3.00 to 4.00 %, molybdenum 2.00 to 3.00 %, niobium 8 × carbon minimum to 1.00 % maximum, manganese 2.00 % max, silicon 1.00 % max, carbon 0.07 % max, phosphorus 0.045 % max, sulfur 0.035 % max, iron balance.
What are the minimum mechanical properties of UNS N08020 forgings?
Annealed, ASTM B462 asks for minimum tensile strength 551 MPa (80 ksi), minimum 0.2 % offset yield 241 MPa (35 ksi), minimum elongation 30 % and minimum reduction of area 50 %. Annealed hardness runs to about 217 HB maximum.
At what temperature is UNS N08020 forged and annealed?
Forge from 1150 to 1230 °C (2100 to 2250 °F). Do not work the material below 980 °C (1800 °F). After forging, solution anneal at 940 to 1010 °C (1725 to 1850 °F) for at least 30 minutes per 25 mm of section, then water quench.
Why is Alloy 20 used for sulfuric acid service?
Copper. The 3 to 4 % copper addition is what buys the resistance to dilute and intermediate-concentration sulfuric acid. That is why the grade turns up in pickling tanks, acid pumps, heating coils and mixed-acid process equipment where 304 and 316 corrode too fast to be economic.
What is the difference between UNS N08020 and Incoloy 825?
Both are nickel-iron-chromium alloys with copper and molybdenum. Incoloy 825 (UNS N08825) runs higher nickel at 38 to 46 % and is titanium-stabilised; UNS N08020 has 32 to 38 % nickel and is niobium-stabilised. Alloy 20 usually wins on sulfuric acid, Incoloy 825 on phosphoric acid and sour service. We forge both grades.
Who manufactures UNS N08020 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, manufactures UNS N08020 (Alloy 20) forged rings, seamless rolled rings, flanges, bars, discs, shafts, sleeves, bushings, tube sheets and forged pipes to ASTM B462 and to customer drawings. Contact sales@steelforgepieces.com or +86 189 2135 9659.
What certificates are supplied with UNS N08020 forgings?
Each order carries an EN 10204 3.1 material certificate showing heat number, chemical analysis, mechanical test results and heat treatment record. Third-party EN 10204 3.2 certification by BV, SGS, TÜV, Lloyd's Register or DNV is available on request, as are ultrasonic testing reports to EN 10228-3, SEP 1921 or ASTM A388.
Can UNS N08020 forgings be welded without post-weld heat treatment?
Yes. Niobium stabilisation ties up carbon as niobium carbide and keeps chromium carbide from precipitating at grain boundaries. That is where the "Cb" in 20Cb-3 comes from, and why post-weld heat treatment is normally unnecessary.
UNS N08020 key facts
- UNS number
- N08020
- Also known as
- Alloy 20, Nickel Alloy 20, Carpenter 20Cb-3, Incoloy 20, Werkstoff 2.4660, NiCr20CuMo
- Alloy type
- Austenitic nickel-iron-chromium alloy with copper and molybdenum, niobium stabilised
- Forging standard
- ASTM B462 / ASME SB-462
- Nominal composition
- 35 Ni, 35 Fe, 20 Cr, 3.5 Cu, 2.5 Mo, Nb
- Tensile strength, min
- 551 MPa (80 ksi), annealed
- Yield strength, min
- 241 MPa (35 ksi), annealed
- Elongation, min
- 30 %
- Density
- 8.08 g/cm³
- Forging temperature
- 1150 to 1230 °C (2100 to 2250 °F)
- Annealing
- 940 to 1010 °C (1725 to 1850 °F), water quench
- Primary use
- Sulfuric acid and mixed-acid process equipment
- Manufacturer
- Jiangyin Jiangnan Metal Co., Ltd., Jiangyin, Jiangsu, China
- Contact
- sales@steelforgepieces.com, +86 189 2135 9659
Standards and references
- ASTM B462 / ASME SB-462, forged and rolled alloy pipe flanges, forged fittings, valves and parts for corrosive high-temperature service. Chemical and mechanical requirements for UNS N08020.
- ASTM B473, UNS N08020, UNS N08024 and UNS N08026 nickel alloy bar and wire.
- ASTM B463, UNS N08020 plate, sheet and strip.
- ASTM B729, UNS N08020 seamless pipe and tube.
- ASTM A388, EN 10228-3 and SEP 1921, ultrasonic examination of forgings.
- EN 10204, types of inspection documents (3.1 and 3.2).
- NACE MR0175 / ISO 15156, materials for H₂S-containing environments in oil and gas production.