ASTM A182 F61 / UNS S32550 / 1.4507 Super Duplex Forgings
Open-die forged rings, rolled rings, flanges, shafts, discs, tube sheets, sleeves and bars in copper-bearing 25Cr super duplex stainless steel. Solution treated and liquid quenched to ASTM A182 Table 1, certified to EN 10204 3.1 or 3.2. Forged at our works in Jiangyin, Jiangsu, China.
Grade data sheet. Last reviewed 30 September 2026 by the technical department, Jiangyin Jiangnan Metal Co., Ltd.
- Tensile, min
- 109 ksi [750 MPa]
- Yield 0.2%, min
- 80 ksi [550 MPa]
- Elongation, min
- 25 %
- Reduction of area
- 50 % min
- Solution anneal
- 1050-1125 °C
- Target PREN
- above 40
1. Grade description
ASTM A182 Grade F61 is the forging designation for UNS S32550, a highly alloyed copper-bearing super duplex (ferrite-austenite) solid solution strengthened stainless steel. It gives high strength and wear resistance with corrosion resistance better than 316 stainless steel, and it resists stress corrosion cracking, crevice corrosion and pitting better than lower alloyed materials. In most media it out-performs 22Cr duplex alloy 2205.
The grade is sold commercially as Ferralium 255, a registered trademark of Meighs Ltd, Langley Alloys Division, and generically as Alloy 255. Its European designation is W.Nr. 1.4507 / X2CrNiMoCuN25-6-3. The alloy dates from the 1960s. More than 9 tonnes of it went into the 1980s refurbishment of the Statue of Liberty, replacing corroded internal structural members.
ASTM A182/A182M is the Standard Specification for Forged or Rolled Alloy and Stainless Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service. It covers flanges, fittings, valves and similar pressure parts, with a limit of 10,000 lb [4,540 kg] per piece. Duplex forgings for pressure vessels are also covered by ASTM A1049/A1049M, which lists S32550 as Grade F61.
2. Chemical composition
| Element | Min | Max |
|---|---|---|
| Carbon (C) | - | 0.040 |
| Manganese (Mn) | - | 1.50 |
| Phosphorus (P) | - | 0.040 |
| Sulfur (S) | - | 0.030 |
| Silicon (Si) | - | 1.00 |
| Chromium (Cr) | 24.00 | 27.00 |
| Nickel (Ni) | 4.5 | 6.5 |
| Molybdenum (Mo) | 2.9 | 3.9 |
| Copper (Cu) | 1.50 | 2.50 |
| Nitrogen (N) | 0.10 | 0.25 |
| Iron (Fe) | Balance | |
ASTM A182/A182M Table 2, identification symbol F 61, UNS S32550, described as 26 chromium, 6 nickel, 3.5 molybdenum with nitrogen and copper, 255.
| Element, % | ASTM A182 F61 / UNS S32550 | EN 1.4507 / X2CrNiMoCuN25-6-3 |
|---|---|---|
| C max | 0.04 | 0.03 |
| Mn max | 1.5 | 2.0 |
| Si max | 1.0 | 0.7 |
| P max | 0.040 | 0.035 |
| S max | 0.030 | 0.015 |
| Cr | 24.0 to 27.0 | 24.0 to 26.0 |
| Ni | 4.5 to 6.5 | 6.0 to 8.0 |
| Mo | 2.9 to 3.9 | 3.0 to 4.0 |
| Cu | 1.5 to 2.5 | 1.0 to 2.5 |
| N | 0.10 to 0.25 | 0.20 to 0.30 |
EN 1.4507 limits per EN 10088-1 as published by Virgamet. The EN grade has higher nickel and nitrogen floors. If an order must satisfy both ASTM F61 and EN 1.4507, say so at enquiry stage and we melt to the overlapping window.
3. Mechanical properties
| Property | Requirement |
|---|---|
| Tensile strength, min | 109 ksi [750 MPa] |
| Yield strength, 0.2 % offset, min | 80 ksi [550 MPa] |
| Elongation in 2 in. [50 mm] or 4D, min | 25 % |
| Reduction of area, min | 50 % |
| Brinell hardness | A182 Table 3 carries no Brinell value for F61. A limit of 302 HBW is commonly applied as a project requirement. |
ASTM A182/A182M Table 3. Published A182 duplex references differ on hardness: one gives 302 HBW as the F61 ceiling, while the A182 table itself leaves the entry blank. Both positions are stated here rather than one. Where a hardness cap applies to your project, name it on the order and we test and certify to it.
Typical values in the solution annealed condition, for guidance only and not acceptance criteria: tensile 700 to 900 MPa, yield above 500 MPa, elongation above 25 %, hardness below 270 HB. In bar form, Alloy 255 is the only super duplex stainless steel reported to reach a yield strength above 85 ksi. Charpy impact energy of 33 ft-lb [45 J] or more at minus 50 F [minus 46 C] is quoted as typical for F61 (255) duplex.
4. Physical properties
| Property | Value |
|---|---|
| Modulus of elasticity at 20 C | 200 GPa |
| Modulus of elasticity at 100 / 200 / 300 C | 194 / 186 / 180 GPa |
| Yield Rp0.2 at 100 / 150 / 200 / 250 C | above 450 / 420 / 400 / 380 MPa |
| Thermal conductivity | 15 W/m·K |
| Specific heat capacity | 500 J/kg·K |
| Linear expansion, 20-100 / 200 / 300 C | 13.0 / 13.5 / 14.0 x10-6 per K |
| Electrical resistivity | 0.8 micro-ohm·m |
| Magnetic response | Ferromagnetic, as with all duplex grades |
Typical values for 1.4507 / UNS S32550 published by Virgamet. Indicative only. The mill certificate governs the material you receive.
5. Melting, forging and heat treatment
5.1 Melting route
ASTM A182 clause 6.2 allows stainless steels to be melted in an electric furnace, with optional separate degassing and refining, in a vacuum furnace, or by either of these followed by vacuum or electroslag consumable remelting. Our EAF plus VOD plus ESR route for F61 falls inside those options and gives the cleanliness and chemistry control a 25Cr super duplex needs. Sufficient discard is taken to secure freedom from injurious piping and undue segregation, as required by clause 6.3.
5.2 Hot working
Hot working of the 255 alloy is carried out between 1800 F and 2100 F, followed by annealing at 1950 F with a water quench. Rolling and forging of 1.4507 is commonly quoted between 1200 C and 900 C. Cold work producing more than 10 % deformation calls for the same heat treatment afterwards. Above 20 % deformation, intermediate heat treatments should be used.
5.3 Solution annealing
| Heat treat type | Solutioning temperature | Cooling media | Quench below |
|---|---|---|---|
| Solution treat and quench | 1920-2060 F [1050-1125 C] | Liquid | 500 F [260 C] |
ASTM A182/A182M Table 1, ferritic-austenitic stainless steels. ASTM A1049/A1049M gives the same 1920-2060 F [1050-1125 C] range for S32550 Grade F61. A182 clause 7.1 also requires forgings to be cooled below 1000 F [538 C] after hot working before heat treatment.
5.4 Machining, stress relief and welding
F61 machines with the same methods and equipment used for 300 series stainless steels. Carbide tipped tooling is preferred, and feeds and speeds should allow for the higher strength compared with 316. Heavily machined components can be stress relieved by heating briefly to 675 F followed by rapid cooling. Welding is done by TIG, MIG or SMAW on material in the annealed condition. No preheat is needed, but the surfaces to be welded must be cleaned carefully. Where pickling is used for cleaning, a solution of 15 % HNO3 plus 2 % HF by volume at a minimum of 55 F is cited. Post weld heat treatment is not necessary, though it is preferred on heavy sections to optimise corrosion resistance.
6. Corrosion resistance and PREN
Against austenitic grades such as 304, 316 and 317, F61 shows better corrosion resistance in most media, and it typically out-performs duplex 2205. It performs well in sulphuric, phosphoric and nitric acids and resists organic acids including acetic and formic acid. Highly reducing media should be avoided. The higher copper content compared with other super duplex grades is what gives the 255 alloy its advantage in acids such as sulphuric, which is why it is used in fertiliser and phosphoric acid plants.
Pitting resistance between grades is compared using the pitting resistance equivalent number:
PREN = %Cr + (3.3 x %Mo) + (16 x %N)
NACE MR0175 and NORSOK M-630 require the three main super duplex stainless steels, Ferralium 255, UNS S32750 and UNS S32760, to have a PREN above 40. PREN varies from heat to heat because Cr, Mo and N vary inside their windows. The formula gives no credit for copper, even though copper improves the acid resistance of the 255 alloy, so PREN understates its performance in acids. Treat PREN as a selection guide, not as a guarantee of service performance.
7. Forged product forms
We produce the following in A182 F61 / UNS S32550 / 1.4507, forged as close to the specified shape and size as practicable in line with A182 clause 6.4, and machined to drawing on request.
Rolled rings
Radial and axial rolled rings and forged rings for valve bodies, pumps, swivels and turbine housings.
Flanges
Weld neck, slip-on, blind, socket weld, threaded, lap joint, orifice and long weld neck blanks to ASME B16.5, B16.47 Series A and B, and EN 1092-1.
Shafts and spindles
Pump shafts, eccentric shafts, crankshafts, spindles and stepped shafts for corrosive and marine duty.
Discs and blanks
Forged discs and near net blanks for gears, closure heads and machined components.
Tube sheets
Heat exchanger forged tube sheets and baffle blanks.
Sleeves and bushings
Forged sleeves, bushings and cylinders for subsea and compressor equipment.
Bars and billets
Forged round bars, square bars and rectangular blocks for further machining.
Valve components
Valve bodies, stems, seat rings and blocks for ball, gate, globe, check, plug and strainer duty.
Hollow forgings
Forged tubes, hollow bars, nozzles, manifolds and pressure vessel components.
8. Applications by industry
The combination of strength and wear resistance suits the 255 alloy to offshore oil and gas, pulp and paper, nuclear, marine, chemical processing and flue gas desulphurisation. Documented uses include subsea equipment for oil and gas, chemical process industry equipment, pollution control scrubbers, marine seals, pumps and valves, bolts and fasteners, grain and vegetable processing equipment, pulp and paper bleaching components, water and sewage treatment plant, and desalination equipment. Published application summaries also list pressure vessels, biofluid processing, and mechanical and structural components. The grade is used in the paper, chemical, nitrogen, aviation and power engineering sectors for screws, shafts, sleeves, fittings, pipelines, pump parts, chemical storage tanks and heat exchangers.
| Sector | Typical A182 F61 forgings |
|---|---|
| Offshore and subsea oil and gas | Rolled rings, flanges, shafts, hubs and connector bodies for seawater, firewater and subsea pipework, risers and manifolds |
| Chemical and fertiliser | Pump and valve forgings for sulphuric, phosphoric, nitric, acetic and formic acid service |
| Power and FGD | Scrubber and flue gas desulphurisation components, forged rings and plate blanks |
| Desalination and water | High pressure RO plant forgings, seawater piping components, water and sewage treatment parts |
| Pulp and paper | Bleaching plant components, shafts and sleeves |
| Marine and structural | Marine seals, fasteners, high strength corrosion resistant structural parts |
9. Testing, NDT and certification
Every F61 order is released against a documented test package. Baseline scope and the options you can add:
| Item | Standard or basis | Status |
|---|---|---|
| Chemical heat analysis | ASTM A182 clause 8 and A961 | Standard |
| Tension test, one per heat | ASTM A182 clause 9.5.2, austenitic and ferritic-austenitic grades | Standard |
| Hardness test | ASTM A182 clause 9.6 and A961 | Standard |
| Heat treatment record with temperature and quench medium | ASTM A182 Table 1 | Standard |
| Ultrasonic examination | ASTM A388/A388M, EN 10228-3, SEP 1921 | To order |
| Magnetic particle or liquid penetrant | ASTM A275/A275M, ASTM E165 | To order |
| Ferrite content | Point count to ASTM E562 or calibrated ferritescope. Base metal target 35 to 65 %, 40 to 60 % in practice | To order |
| Intermetallic and sigma phase screening | ASTM A923 Method A etch, Method B Charpy, Method C 500x microstructure. ASTM A1084 electrochemical | To order |
| Pitting corrosion test | ASTM G48 Method A, 6 % ferric chloride at a specified temperature | To order |
| Grain size | ASTM E112 | To order |
| Certification | EN 10204 3.1, or 3.2 countersigned by a third party such as DNV, BV, Lloyd's Register, ABS or TUV | Standard or optional |
| Marking | Manufacturer name or trademark, grade symbol, heat number and specification designation, per ASTM A182 | Standard |
Ferrite banding of 35 to 65 % for base metal and 30 to 70 % for weld metal follows NACE MR0175 / ISO 15156 practice for duplex stainless steels. These are project requirements rather than automatic A182 requirements, so confirm the acceptance criteria on the order.
10. Equivalent grades
| System | Designation |
|---|---|
| ASTM and ASME | A182 Grade F61, SA-182 F61, A1049 Grade S32550 |
| UNS | S32550 |
| EN and DIN | 1.4507, X2CrNiMoCuN25-6-3 |
| JIS, near equivalent | SUS 329J4L |
| Common names | Alloy 255, Super Duplex 255, Grade 255, Ferralium 255 |
| Closely related | UNS S32520 / A182 F59, UNS S39553 |
Where copper is not required, or where warm seawater rather than acid drives the design, the usual alternatives are A182 F53 (UNS S32750, 2507) and A182 F55 (UNS S32760). For 22Cr duplex duty see A182 F51 (UNS S31803), and for 6Mo super austenitic duty see A182 F44 or 904L. The practical difference is that F61 carries 1.50 to 2.50 % copper and is better suited to acidic environments than F53, while F53 and F55 are the conventional answers to chloride and seawater service.
11. Questions we are asked
Is A182 F61 the same as Ferralium 255?
In substance, yes. Alloy 255 is the generic description of the Ferralium 255 super duplex stainless steel, covering DIN 1.4507, UNS S32550 and ASTM F61. Ferralium is a registered trademark of Meighs Ltd, Langley Alloys Division, so a forging we supply is properly described as A182 F61 / UNS S32550 / Alloy 255 rather than by the trademark.
What is the largest F61 forging you can make?
ASTM A182 limits products made to that specification to 10,000 lb [4,540 kg] per piece. Heavier forgings are normally ordered to ASTM A336/A336M or A965/A965M, and duplex pressure vessel forgings to ASTM A1049/A1049M. Send the finished weight and section thickness with the enquiry and we confirm the right specification and our current capacity for that size.
Do you supply to NACE MR0175 and ISO 15156 for sour service?
Duplex stainless steels are accepted by ISO 15156-3 in the solution annealed and liquid quenched condition with 35 to 65 % ferrite, inside temperature and H2S partial pressure envelopes that depend on the PREN band. State the sour service envelope on the enquiry and we confirm whether F61 is compliant for those conditions or whether a nickel alloy is needed. We do not certify to MR0175 without the service data to support it.
Why does an F61 forging need a liquid quench instead of air cooling?
Slow cooling through roughly 1000 F to 1800 F precipitates carbides, nitrides and sigma phase, which destroy toughness and corrosion resistance. A182 Table 1 therefore requires solution treatment at 1920 to 2060 F [1050 to 1125 C] followed by a liquid quench below 500 F [260 C]. Heavy sections need spray or mist assisted quenching to reach the required cooling rate at the core.
Can F61 be used above 300 C?
No. The ASME Boiler and Pressure Vessel Code Section VIII maximum continuous operating temperature for the 255 alloy is 500 F, and duplex grades lose toughness above roughly 600 F. For higher temperatures the answer is a nickel alloy. See our nickel alloy forgings.
What do you need in order to quote?
A drawing or the finished dimensions, the quantity, the specification and revision such as ASTM A182 Grade F61, the delivery condition (as forged, rough machined or finish machined), the NDT and testing scope, the certification level (EN 10204 3.1 or 3.2), and the destination port. With that we can normally return a firm price and lead time quickly.
Request an A182 F61 quotation
Send a drawing or size list and we quote the forging, heat treatment, machining, testing and certification as one package. We forge to customer drawings: rings, flanges, shafts, discs, tube sheets, sleeves, bushings and bars. If another grade suits the service better, we will say so.
Jiangyin Jiangnan Metal Co., Ltd., Open-Die Forging Factory
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province 214423, China
Tel, WhatsApp and WeChat: +86-189-2135-9659
Email: sales@steelforgepieces.com
References
ASTM A182/A182M, Standard Specification for Forged or Rolled Alloy and Stainless Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service, Tables 1, 2 and 3 and clauses 6, 7 and 9. ASTM A1049/A1049M for duplex stainless forgings. Corrosion Materials data sheet, Alloy F255 / UNS S32550 / W.Nr. 1.4507. Langley Alloys technical notes on Alloy 255 and on PREN in super duplex stainless steels. Virgamet data sheet for 1.4507 / X2CrNiMoCuN25-6-3 / UNS S32550. Ferrobend ASTM A182 UNS S32550 specification page. Specialty Steel Supply F61 (255) duplex data. Figures are given for guidance. Order against the current edition of the applicable standard and rely on the mill certificate for the material supplied.
A plain-text version of this data sheet is available at /md/a182-f61.md.