Ferralium® 255
Also known as Ferralium® 255-SD50, UNS S32550, EN 1.4507
Ferralium® 255 is a proprietary super duplex stainless steel with high proof stress, PREN over 40 and excellent sub-zero toughness.
Ferralium® 255 is Langley Alloys' proprietary super duplex stainless steel, originally developed in the 1960s as the first super duplex to incorporate nitrogen as a strengthening element. It is supplied in the hot worked and annealed condition.
As a 25% chromium alloy with significant copper additions, it achieves a Pitting Resistance Equivalent Number (PREN) exceeding 40 and outstanding resistance to sulphuric, nitric and phosphoric acid. It is the first super duplex to achieve 586 N/mm² minimum 0.2% proof stress at section sizes up to 12" (300mm), and maintains excellent ductility and impact strength at sub-zero temperatures. Listed in NACE MR0175 for sour service and carrying ASME Pressure Vessel approval.
We stock bar in the UK and USA, and plate in the USA, with pipe, tube and fittings also in stock; forgings and castings to order.
- First super duplex stainless steel to achieve 586 N/mm² minimum 0.2% proof stress up to 12" (300mm) section
- PREN >40 - outstanding resistance to pitting and crevice corrosion in seawater and chloride environments
- Critical Pitting Temperature exceeding 50°C
- Higher Copper content provides a self-healing effect at pitting sites to inhibit further growth
- Excellent ductility and impact strength at both ambient and sub-zero temperatures
- High resistance to abrasion, erosion and cavitation erosion
- Very low Sulphur content minimises inclusions as pitting initiation sites
- Particularly resistant to sigma phase formation at larger section sizes
- Listed in NACE MR0175 for sour service; ASME Pressure Vessel approval
- Available as bar, plate, tube and fittings with complementary weld wire
| Element | Min | Max |
|---|---|---|
| Chromium (Cr) | 24.50 | 26.50 |
| Nickel (Ni) | 5.50 | 6.50 |
| Molybdenum (Mo) | 3.10 | 3.80 |
| Copper (Cu) | 1.50 | 2.00 |
| Iron (Fe) | Bal | |
| Manganese (Mn) | 0.80 | 1.20 |
| Nitrogen (N) | 0.20 | 0.25 |
| Silicon (Si) | - | 0.70 |
| Carbon (C) | - | 0.025 |
| Phosphorus (P) | - | 0.025 |
| Sulphur (S) | - | 0.005 |
Work out the PREN for this composition with our PREN calculator.
| Property | Imperial | Metric |
|---|---|---|
| 0.2% Proof stress (min) | 85 ksi | 586 N/mm² |
| Tensile strength (min) | 114.5 ksi | 790 N/mm² |
| Elongation (5.65√S0 and 4D) | 25% | 25% |
| Reduction of area | 50% | 50% |
| Hardness (Brinell) | 220-270 HB | 220-270 HB |
| Impact strength (room temp) | 59 ft.lb | 80 J |
| Impact strength (-46°C) | 33 ft.lb av (25.8 ft.lb min) | 45 J av (35 J min) |
| Property | Imperial | Metric |
|---|---|---|
| 0.2% Proof stress (min) | 85 ksi | 586 N/mm² |
| Tensile strength (min) | 114.5 ksi | 790 N/mm² |
| Elongation (5.65√S0 and 4D) | 25% | 25% |
| Reduction of area | 50% | 50% |
| Hardness (Brinell) | 220-270 HB | 220-270 HB |
| Impact strength (room temp) | 59 ft.lb | 80 J |
| Impact strength (-46°C) | 33 ft.lb av (25.8 ft.lb min) | 45 J av (35 J min) |
| Property | Imperial | Metric |
|---|---|---|
| 0.2% Proof stress (min) | 83 ksi | 570 N/mm² |
| Tensile strength (min) | 110 ksi | 760 N/mm² |
| Elongation (5.65√S0 and 4D) | 25% | 25% |
| Reduction of area | 50% | 50% |
| Hardness (Brinell) | 220-270 HB | 220-270 HB |
| Impact strength (room temp) | 59 ft.lb | 80 J |
| Impact strength (-46°C) | 33 ft.lb av (25.8 ft.lb min) | 45 J av (35 J min) |
| Property | Imperial | Metric |
|---|---|---|
| 0.2% Proof stress (min) | 79.8 ksi | 550 N/mm² |
| Tensile strength (min) | 114.5 ksi | 790 N/mm² |
| Elongation (5.65√S0 and 4D) | 25% | 25% |
| Reduction of area | 50% | 50% |
| Hardness (Brinell) | 220-270 HB | 220-270 HB |
| Impact strength (room temp) | 59 ft.lb | 80 J |
| Property | Imperial | Metric |
|---|---|---|
| 0.2% Proof stress (min) | 80 ksi | 550 N/mm² |
| Tensile strength (min) | 110 ksi | 760 N/mm² |
| Elongation (5.65√S0 and 4D) | 15% | 15% |
| Hardness (Rockwell C) | 28 HRC max | 28 HRC max |
| Property | Value |
|---|---|
| Density (kg/m³) | 7810 |
| Mean coefficient of thermal expansion, 20-100°C (m/m/°C) | 11.1 x 10⁻⁶ |
| Mean coefficient of thermal expansion, 20-200°C (m/m/°C) | 11.5 x 10⁻⁶ |
| Mean coefficient of thermal expansion, 20-300°C (m/m/°C) | 12.0 x 10⁻⁶ |
| Thermal conductivity, 20°C (W/m.K) | 14.2 |
| Thermal conductivity, 100°C (W/m.K) | 16.3 |
| Thermal conductivity, 200°C (W/m.K) | 18.4 |
| Specific electrical resistance, 20°C (µΩ.m) | 0.80 |
| Specific electrical resistance, 100°C (µΩ.m) | 0.88 |
| Specific electrical resistance, 200°C (µΩ.m) | 0.93 |
| Specific heat, 20°C (J/kg.K) | 475 |
| Specific heat, 100°C (J/kg.K) | 500 |
| Specific heat, 200°C (J/kg.K) | 532 |
| Magnetic permeability | 33 |
| Young's modulus (kN/mm²) | 199 |
| Compression modulus (N/mm²) | 150 x 10³ |
| Torsional modulus (N/mm²) | 75 x 10³ |
| Fracture toughness, KQ (N/mm² · m½) | 98 |
| Poisson's ratio | 0.32 |
| Property | Minimum | Typical |
|---|---|---|
| Yield strength (0.2%) | 550 N/mm² | 760 N/mm² |
| Tensile strength | 750 N/mm² | 940 N/mm² |
| Elongation | 20% | 24% |
| Hardness | 300 HV | |
| Impact at -46°C | 45 J | 70 J |
| Diameters available | 1.2 / 1.6 / 2.4 / 3.2 mm |
Equivalents & cross-references
Standard designations
- UNS
- S32550Unified Numbering System
- EN
- 1.4507European harmonised standard
- ASTM
- A182 Grade F61Forgings and fittings A240Plate, sheet and strip A479Bar and shapes
- NORSOK
- MDS D54Material data sheet MDS D57Material data sheet
- NACE
- MR0175 / ISO 15156Sour service
- API
- 6AWellhead and tree equipment
Ferralium® 255 is also designated UNS S32550, EN 1.4507, ASTM A182 Grade F61, ASTM A240, ASTM A479, NORSOK MDS D54, NORSOK MDS D57, NACE MR0175 / ISO 15156 and API 6A.
Trade name equivalents
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Ferralium 255-SD50
Ferralium 255-SD50 is an alternate designation for Ferralium® 255.
Common questions
What is Ferralium 255?
Ferralium 255-SD50 is a super duplex stainless steel supplied in the hot worked and annealed condition, covered by UNS S32550 (also S32520), ASTM A182 Grade F61, ASTM A479, ASTM A276 Condition A and EN 10088-3 1.4507. It is a 25% chromium alloy with significant copper additions and a Pitting Resistance Equivalent Number (PREN) above 40. It is listed in NACE MR0175/ISO 15156 for sour service and holds ASME pressure vessel approval. Langley Alloys stocks it as bar, plate, tube and fittings, with complementary weld wire; forgings and castings are to order.
What is Ferralium 255 used for?
Ferralium 255 is used for oil and gas pumps, valves, wellhead and subsea equipment; marine propellers, shafts, rudders, seals, pumps and valves; and bolts and fasteners. It is also used in pollution control scrubbers and fans, process equipment for sulphuric, nitric and phosphoric acid, pulp and paper digester components, and desalination, water and sewage treatment plant. Its high strength lets designers reduce section size, weight and cost.
Is Ferralium 255 suitable for seawater and sour service?
Yes. In seawater and other chloride-containing environments Ferralium 255 provides outstanding resistance to pitting and crevice corrosion, with a Critical Pitting Temperature exceeding 50°C and a seawater corrosion rate below 0.01 mm/year. It is listed in NACE MR0175/ISO 15156 for sour service, with hardness controlled to a maximum of 28 HRC (270 HB). Its higher copper content also gives a self-healing effect at pitting sites to inhibit further growth.
Why choose Ferralium 255 for large sections?
Ferralium 255 is the first super duplex stainless steel to achieve a minimum 0.2% proof stress of 586 N/mm² (85 ksi) in sections up to 12" (300mm) diameter. It is particularly suited to larger components because the formation of sigma phase is much less likely than with other super duplex stainless steels, and its microstructure is certified free from grain boundary carbides, sigma, chi and laves phases.
What is the UNS number for Ferralium 255?
The UNS number for Ferralium® 255 is S32550. It is a 25% chromium, 5% nickel, 3% molybdenum super duplex stainless steel with a PREN greater than 40, listed in NACE MR0175/ISO 15156 for sour service and approved by ASME for pressure vessel applications.
What is Ferralium 255 equivalent to?
Ferralium® 255 is Langley Alloys' registered trade name for UNS S32550, a super duplex stainless steel also designated EN 1.4507, ASTM A479 and ASTM A182 Grade F61. It meets Norsok MDS D54 and D57, NACE MR0175/ISO 15156, API 6A, and ASME UHA-23.
What is EN 1.4507 stainless steel?
EN 1.4507 is the European harmonised designation for UNS S32550, a super duplex stainless steel stocked by Langley Alloys as Ferralium® 255-SD50. It offers a PREN exceeding 40 and is listed in NACE MR0175/ISO 15156 for sour service environments.
What is ASTM A182 F61?
ASTM A182 Grade F61 is the forged fitting and flange designation for UNS S32550, the super duplex stainless steel stocked by Langley Alloys as Ferralium® 255. Bar and shapes are supplied to ASTM A479 and A276.
What is the density of Ferralium 255?
Ferralium 255 has a density of approximately 7.81 g/cm³ (7810 kg/m³).
Is Ferralium 255 magnetic?
Yes. Ferralium 255 is a super duplex stainless steel with a part-ferritic structure, so it is ferromagnetic (magnetic).
Datasheets
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SD50 (annealed bar)
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3AF (age hardened)
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SD50 HS110 (high strength)
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FG46 (fastener grade)
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Plate
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Pipe & tube
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3SF (forgings)
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3SC (castings)
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Welding wire (AWS E2553)
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The original super duplex
In this Technical Corner, Rodney tells the story of Ferralium 255, the world's first commercial super duplex stainless steel, patented by Langley Alloys in 1968.
With 25% chromium plus nitrogen and copper, it delivers high strength, excellent corrosion resistance and real cost-effectiveness, and 50 years on it still performs in the most aggressive subsea and industrial environments.
Visit our YouTube channelSolution-treated, water-quenched and ultrasonically tested as standard.
Processing capability
Cutting
Automated band sawing to 650mm section. CNC sawing at all sites.
Cutting servicesFirst-stage processing
Water jet cutting, turning, boring and grinding undertaken in-house.
Processing servicesInspection & testing
Each bar ultrasonically tested and visually inspected. ASTM G48A corrosion test at 50°C and ferrite content certification available.
Inspection & testing
Tools for this grade
Pitting & crevice resistance
Pitting & Crevice Resistance
Rank alloys by PREN and get an indicative pitting temperature for a chloride service. Pick a grade and a service temperature to see whether it has margin against pitting, or compare the range in the table below. A first-pass screen for chloride and seawater service.
| Grade | UNS | PREN | Indicative CPT | Relative pitting resistance |
|---|
Indicative screen, not a certified result. PREN ranks pitting resistance; the pitting temperature here is estimated from PREN (CPT ≈ 2.5 × PREN - 50), consistent with Langley's "PREN >40, CPT exceeding 50°C" for super duplex. Real critical pitting/crevice temperature depends on test method, product form, surface finish and service chemistry. Crevice corrosion starts well below the pitting temperature - allow a margin at gaskets, deposits and flange faces. Use certified data for design.
Sour-service screen (NACE MR0175)
Sour-Service Screen
Work out whether a service is sour from the H2S partial pressure, and see each alloy's NACE MR0175 / ISO 15156 status and hardness limit. A first-pass screen for oil & gas material selection - the full environmental envelope for a grade is set in ISO 15156-3 Annex A.
Candidate grade
| Grade | Family | NACE status | Hardness limit |
|---|
First-pass screen only. This shows whether the service is sour (from H2S partial pressure) and each material group's NACE MR0175 hardness limit and general suitability. It does not reproduce the full environmental windows (maximum H2S partial pressure, temperature, chloride, in-situ pH per grade) - those are in ISO 15156-3 Annex A and must be checked there for the specific grade, product form and condition. Qualification also depends on heat treatment, cold work and welding.
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