Grade Overview
Duplex stainless steels hold roughly equal fractions of ferrite and austenite. That mixed structure is what gives them about double the yield strength of a standard austenitic grade together with strong resistance to chloride stress-corrosion cracking. UNS S32550 sits in the super duplex band of that family, carrying 25 to 26 % chromium in practice and a deliberate copper addition of 1.50 to 2.50 %, which is the feature that sets it apart from the tungsten-bearing and plain super duplex grades.
Langley Alloys, which maps ASTM A182 F61 to UNS S32550, identifies the grade as an approximation of Ferralium 255, the first super duplex stainless steel, invented by Langley Alloys and launched in 1969. Ferralium is a registered trademark of Langley Alloys Ltd. Jiangyin Jiangnan Metal supplies against the UNS S32550 and ASTM A182 F61 specifications, not the trademarked product.
Some supplier listings describe A182 S32550 as a 13 % chromium 410-type martensitic material. That is wrong. S32550 is ferritic-austenitic, and the chemistry in section 03 reflects the published ASTM A182 limits.
Equivalent Designations
| System | Designation | Note |
|---|---|---|
| UNS | S32550 | Primary designation |
| ASTM / ASME forging | A182 F61, SA182 F61 | Forged flanges, fittings, valves and parts |
| EN / Werkstoff | 1.4507, X2CrNiMoCuN25-6-3 | European equivalent, chemistry differs slightly |
| Generic trade names | Alloy 255, Grade 255, Super Duplex 255, SD50 | Ferralium 255 is a Langley Alloys trademark |
| Related ASTM grade | A182 F59, UNS S32520 | Separate grade in the same family |
| Related JIS grade | SUS 329J4L | Listed alongside S32550 in reference tables |
| Other listings | 52N+, UR52N, X3CrNiMoCuN26-6-3-2 | Proprietary and national variants |
Cross-reference tables show similar grades, not interchangeable ones. EN 1.4507 calls for 6.0 to 8.0 % Ni and 0.20 to 0.30 % N, while UNS S32550 allows 4.5 to 6.5 % Ni and 0.10 to 0.25 % N. If a part has to satisfy both, say so at enquiry stage and we will aim the melt chemistry at the overlap.
Chemical Composition
Below are the ASTM A182 Grade F61 limits for UNS S32550. The grade is melted here through the electric arc furnace and ladle furnace with vacuum oxygen decarburisation, which is the standard route for stainless and duplex steels where low carbon and controlled nitrogen matter. Electroslag remelting is available where a specification calls for it.
| Element | Minimum | Maximum |
|---|---|---|
| Carbon, C | – | 0.040 |
| Manganese, Mn | – | 1.50 |
| Silicon, Si | – | 1.00 |
| Phosphorus, P | – | 0.040 |
| Sulfur, S | – | 0.030 |
| Chromium, Cr | 24.0 | 27.0 |
| 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 | |
Against EN 1.4507
| Element | UNS S32550, A182 F61 | EN 1.4507 |
|---|---|---|
| C | 0.040 max | under 0.03 |
| Mn | 1.50 max | under 2.0 |
| Si | 1.00 max | under 0.7 |
| P | 0.040 max | under 0.035 |
| S | 0.030 max | under 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 | 1.50 to 2.50 | 1.0 to 2.5 |
| N | 0.10 to 0.25 | 0.20 to 0.30 |
Mechanical and Physical Data
Specified minimums, ASTM A182 F61
| Property | Imperial | Metric |
|---|---|---|
| Tensile strength, min | 109 ksi | 750 MPa |
| Yield strength, 0.2 % offset, min | 80 ksi | 550 MPa |
| Elongation in 2 in. or 4D, min | 25 % | 25 % |
| Reduction of area, min | 50 % | 50 % |
Typical achieved values
Published typical values for this chemistry sit above the A182 floor. For bar up to 12 in., typical ultimate tensile is around 114.5 ksi, 789 MPa, with 85 ksi, 586 MPa yield and 25 % elongation; at 12 in. and above, around 110 ksi, 758 MPa, with 83 ksi, 573 MPa yield. Hardness is generally reported between about 220 and 270 HBW. General data for 1.4507 gives 700 to 900 MPa tensile, yield above 500 MPa, elongation above 25 % and hardness below 270 HB.
| Property | Value |
|---|---|
| Modulus of elasticity at 20 C | 200 GPa |
| Modulus at 100 / 200 / 300 C | 194 / 186 / 180 GPa |
| Yield Rp0.2 at 100 / 200 / 250 C | over 450 / 400 / 380 MPa |
| Thermal conductivity | 15 W/m·K |
| Specific heat capacity | 500 J/kg·K |
| Linear expansion, 20 to 100 C | 13.0 x 10-6 /K |
| Electrical resistivity | 0.8 µΩ·m |
This alloy has been evaluated for maximum continuous operation at 500 F, 260 C, under the ASME Boiler and Pressure Vessel Code. Duplex grades should not be held at elevated temperature for long periods, because exposure in the intermetallic precipitation range embrittles the structure.
Corrosion Performance
The pitting resistance equivalent number is the quickest way to rank stainless, duplex and super duplex grades against chloride pitting.
| UNS | Common name | PREN |
|---|---|---|
| S31803 | Duplex 2205 | 36 |
| S32550 | Super duplex, 255 type, A182 F61 | about 40 |
| S32750 | Super duplex, A182 F53 | super duplex class |
| S32760 | Super duplex with tungsten, A182 F55 | 41 |
A PREN of 32 to 35 is widely treated as the practical floor for seawater service. Duplex grades typically land near 35 and super duplex grades clear 40, so S32550 sits inside the super duplex band. Beyond pitting, the grade is noted for superior sulfuric acid resistance and performs in sour service, phosphoric and nitric acid duty, and organic acids such as acetic and formic. Strongly reducing media remain the limiting case for any stainless steel.
The figures above are for comparison. Confirm the final choice against your own process conditions and corrosion data, and against NACE MR0175 / ISO 15156 or NACE MR0103 where sour service applies.
Forging and Heat Treatment
Hot working
Published guidance puts rolling and forging of 1.4507 and S32550 between roughly 1200 and 900 C. Super duplex has a narrow working window: finish too cold and the ferrite cracks, soak too hot and the grain coarsens while the phase balance drifts toward ferrite. Our press and ring mill run this grade on controlled soak, finish and reheat cycles for that reason.
Solution treatment
ASTM A182 requires Grade F61 to be solution treated and quenched, not annealed and air cooled. The solutioning range is 1920 to 2060 F, 1050 to 1125 C, with a liquid quench taking the part below 500 F, 260 C. General data for 1.4507 gives a comparable supersaturation range of 1020 to 1100 C.
Speed through the quench is what matters. Sigma phase, a hard chromium-rich intermetallic, forms in duplex steels held between roughly 600 and 1000 C, and its presence cuts both toughness and corrosion resistance. Heat-treatment practice for duplex products aims to keep ferrite between about 40 and 60 % with rapid quenching. Heavy sections are the hard case, which is where section thickness and quench arrangement have to be planned before forging rather than fixed afterwards.
Welding and machining
Maximum interpass temperature is reported as 100 C for super duplex, against 150 C for 2205; exceeding it slows cooling through the sensitisation range. Matching consumables are covered by UNS W39553 and AWS A5.4 E2553-XX, ASME IX group P10H. For machining, the alloy cuts at satisfactory rates by conventional methods but work-hardens quickly and runs hot. The practical points are a rigid and overpowered machine, rigid workholding with minimal tool overhang, genuinely sharp tooling replaced on schedule, positive-rake carbide for most operations, heavy constant feeds so the tool never dwells in the cut, and soluble-oil lubrication.
Choosing Between The Duplex Forging Grades
ASTM A182 numbers ferritic-austenitic steels between F50 and F71, with ascending numbers roughly tracking the order grades were added.
| Grade | UNS | Type | Position |
|---|---|---|---|
| F51 | S31803 | 22 % Cr duplex | Original 22 % Cr designation |
| F60 | S32205 | 22 % Cr duplex | Tightened composition for better pitting resistance. S32205 can be dual-certified as S31803, not the reverse. Around 80 % of duplex production. |
| F53 | S32750 | 25 % Cr super duplex | Higher chromium than F51; higher yield allows thinner sections |
| F55 | S32760 | 25 % Cr super duplex with tungsten | Traces to Zeron 100 development |
| F61 | S32550 | Super duplex with copper | Langley Alloys states F61 gives increased strength and corrosion performance over F53 and F55, with Ferralium 255 minimum yield above 85 ksi where those grades are held to 80 ksi, plus up to 2.0 % copper aiding pitting resistance |
| F68 / F71 | S32304 / S32808 | Lean and hyper duplex | Specialist grades, limited availability |
That number is Langley's statement for their proprietary Ferralium 255, whose composition is tighter than the generic UNS S32550 band at 24.5 to 26.5 % Cr, 5.50 to 6.50 % Ni, 3.10 to 3.80 % Mo, 1.50 to 2.00 % Cu and 0.20 to 0.25 % N. The generic ASTM A182 F61 minimum yield is 80 ksi. If a design leans on the higher figure, write it into the purchase specification as a supplementary requirement and prove it on test.
UNS S32550 Forged Shapes
Everything below is forged from steel melted on site, to customer drawing or size list. The works runs a 6,300 tonne open-die press and a 6 metre radial-axial ring mill, with a 30 tonne maximum single-piece weight.
Seamless Rolled Rings
Rectangular and contoured sections, gear ring blanks, slewing rings, bearing races.
Forged Rings
Upset and punched rings outside the mill envelope, retaining rings, valve seat rings.
Flanges
Weld neck, blind, slip-on, socket weld, lap joint, orifice and long weld neck to ASME B16.5, B16.47 and API 6A.
Bars and Shafts
Round, flat and square bar, stepped shafts, pinion and eccentric shafts, spindles, rolls.
Discs and Tube Sheets
Solid forged discs, covers and tube sheets, supplied proof-machined for volumetric inspection.
Cylinders and Sleeves
Hollow forged cylinders, sleeves, bushings, couplings and heavy-wall sections bored from solid.
Valve and Wellhead Parts
Bodies, bonnets, blocks, stems, seat rings, spools, nozzles and manifolds to API 6A and NACE MR0175.
Blocks and Specials
Die and mould blocks, wheels, pinions and bespoke open-die profiles.
Related pages: forged disks, forged tube sheets, stainless and duplex grade index, nickel alloy forgings.
Where The Grade Is Used
Published application areas for this alloy cover waste processing, fertilizer production, seawater and marine environments, sour service, chemical processing, pulp and paper, flue gas desulfurisation, and pumps and valves. Reference data for 1.4507 adds paper, chemical, nitrogen, aviation and power engineering, taking in screws, shafts, sleeves, fittings, pipelines, pump parts, chemical storage tanks, heat exchangers and radiator components.
In forged form the enquiries we see most often are seawater and firewater systems, subsea and topside oil and gas pipework with risers and manifolds, pressure vessels and heat exchangers, desalination and high-pressure reverse osmosis plant, FGD scrubber equipment, phosphoric and sulfuric acid service, and pump and valve internals where strength and chloride resistance both matter.
Testing and Certification
UNS S32550 forgings ship with EN 10204 3.1 certification as standard, or third-party EN 10204 3.2 where a project requires independent witness. Because the steel is melted here, the certificate traces back to the melt number rather than stopping at a purchased billet. Ultrasonic examination follows EN 10228-3, SEP 1921 or ASTM A388, with the acceptance class agreed before manufacture. The works holds CCS, BV, DNV, LR and NK approvals.
ASTM A182 supplementary requirements can be invoked on the order. Those most often applied to super duplex are S1 macroetch, S2 heat treatment details, S3 material for optimum resistance to stress-corrosion cracking, S4 corrosion tests, S6 hardness and S12 detection of detrimental phases in austenitic-ferritic stainless steels. Project specifications we work to also include PED 2014/68/EU, AD 2000-Merkblatt W2, W7 and W10, API 20E BSL 1 and BSL 2, NACE MR0175 / ISO 15156 and NACE MR0103.
For super duplex, ferrite content, impact energy at temperature and ASTM A923 type intermetallic screening are usually the clauses that decide whether a forging passes. Quoting them up front lets us set the forging ratio and quench route correctly instead of finding a problem at final test.
Questions We Are Asked
What is UNS S32550?
A copper-bearing super duplex stainless steel with a ferritic-austenitic structure, designated ASTM A182 Grade F61 in forged form and EN 1.4507, X2CrNiMoCuN25-6-3, in Europe. Composition runs 24.0 to 27.0 % Cr, 4.5 to 6.5 % Ni, 2.9 to 3.9 % Mo, 1.50 to 2.50 % Cu and 0.10 to 0.25 % N. It approximates Ferralium 255, the first super duplex stainless steel, launched by Langley Alloys in 1969.
Is UNS S32550 the same as ASTM A182 F61?
F61 is the A182 forging designation for UNS S32550. A182 covers forged alloy and stainless pipe flanges, fittings, valves and parts for high-temperature service. The F prefix marks forged products and duplex grades are numbered F50 to F71.
What are the minimum mechanical properties of A182 F61?
109 ksi, 750 MPa, minimum tensile strength; 80 ksi, 550 MPa, minimum yield; 25 % minimum elongation in 2 in. or 4D; and 50 % minimum reduction of area.
What is the PREN of UNS S32550?
About 40, which places it in the super duplex class. Published comparisons give 36 for S31803, 2205, and 41 for S32760. A PREN of 32 to 35 is widely treated as the minimum for seawater duty.
How is the grade heat treated after forging?
Solution treat and quench, not anneal and air cool. ASTM A182 specifies 1920 to 2060 F, 1050 to 1125 C, with a liquid quench taking the part below 500 F, 260 C. The quench has to be fast because sigma phase forms between roughly 600 and 1000 C.
How does S32550 compare with 2205?
2205, covering S31803 and S32205, is a 22 % chromium duplex with a PREN near 36. S32550 is a 25 to 26 % chromium super duplex with a PREN near 40 and higher strength. Langley Alloys states the F61 type gives increased strength and corrosion performance over F53 and F55, with Ferralium 255 minimum yield above 85 ksi against 80 ksi for those grades.
Can the grade be machined?
Yes, by conventional production methods at satisfactory rates, but it work-hardens quickly, generates high cutting heat and has high shear strength. Rigid setups, sharp positive-rake carbide tooling, heavy constant feeds and soluble-oil coolant are the points that decide tool life.
Who supplies UNS S32550 forgings?
Jiangyin Jiangnan Metal Co., Ltd., an integrated melting works and open-die forge at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, operating since 1997 with 460 staff. Telephone +86 189 2135 9659, email sales@steelforgepieces.com. The plant melts, forges, heat treats, machines and certifies UNS S32550 rings, flanges, bars, discs, shafts, tube sheets and valve parts on one site.
Quote a UNS S32550 Forging
Send a drawing, or just the dimensions: outside diameter, inside diameter, height or length, specification, quantity and the certificate you need. We come back with price, forging route, heat treatment plan and lead time.
Jiangyin Jiangnan Metal Co., Ltd.
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
T +86 189 2135 9659
E sales@steelforgepieces.com
Ferralium is a registered trademark of Langley Alloys Ltd. Zeron is a registered trademark of its respective owner. Jiangyin Jiangnan Metal Co., Ltd. is not affiliated with either company and supplies material to the UNS S32550 and ASTM A182 F61 specifications. Figures on this page are published reference data for engineering comparison; confirm against the current edition of the governing standard and your project specification before ordering.