• Alloy 255
  • 1.4507
  • X2CrNiMoCuN 25-6-3
  • Z3 CNDU 25-07 Az
  • Norsok MDS D57
  • ASTM A276 / A476
  • UNS S32550
  • ASME A182 F61
View Data Tables For This Product

Ferralium 255 – 3AF Aged Grade (UNS S32550)

Ferralium® 255 – 3AF is a super duplex stainless steel which is supplied in either a hot worked condition, annealed or aged condition.

By subjecting the product to an additional ageing process, it is possible to further increase the tensile strength of the product whilst retaining the products high levels of ductility.

As a variant of our unique Ferralium® 255 – SD50 product, it is a 25% Cr alloy with significant additions of Cu, offering excellent corrosion resistance in a wide variety of corrosive chemicals including sulphuric, nitric and phosphoric acid.  When exposed to seawater and other chloride containing environments, it also provides outstanding resistance to pitting and crevice corrosion, with a critical pitting temperature exceeding 50°C.

Excellent ductility and impact strength are retained at both ambient and sub-zero temperatures, despite the elevated strength levels. These are also combined with a high resistance to abrasion, erosion and cavitation erosion. Listed in NACE MR 01 75 for sour service and having gained ASME Approval for Pressure Vessel applications, Ferralium® 255-3AF is tested to the highest degree using tests designed to guarantee that the trade-marked product possesses high integrity, a correct phase balance and the absence of sigma and other deleterious phases.

stainless steels


  • Alloy 255
  • 1.4507
  • X2CrNiMoCuN 25-6-3
  • Z3 CNDU 25-07 Az
  • Norsok MDS D57
  • ASTM A276 / A476
  • UNS S32550
  • ASME A182 F61
View Data Tables For This Product

Data Tables

Chemical Composition:


Mechanical Properties:

0.2% Proof Stress600 N/mm287 ksi
Tensile Strength840 N/mm2121.8 ksi
Elongation, 5.65√S0 and 4D23%
Reduction of Area
Hardness (Brinell)250-330
Impact Strength (Room Temp)70J51.6 ft.lb


  1. Testing shall be carried out in accordance with ASTM A370 or EN ISO 6892-1 (tensile), EN ISO 6506-1 (hardness)
  2. Minimum properties quoted (tested at room temperature in a longitudinal direction)
  3. Testing performed on each melt of material per heat treatment batch
  4. Hardness shall be in accordance with NACE MR 1075 with a maximum HRC value of 28 (270HB)
  5. ASTM A262 corrosion test (Practice B) no pitting and < 0.54g/m2hr weight loss
  6. Ferrite content 35-55%
  7. Microstructure certified free from grain boundary carbides, sigma, chi and laves phases





Physical Properties:

Density (Kg/m3)7810
Magnetic Permeability (20°C)33
Young’s Modulus (kN/mm2)200
Specific Electrical Resistance, 20°C (µΩ-m)0.8
Mean coefficient of thermal expansion, 20-100°C (m/m/degC)11.1 x 10-6
Specific Heat, 20°C (J/kg.K)475
Thermal conductivity, 20°C (W/m.K)14.2

Product Features

Key Features:

  • The aged product achieves even higher tensile strength, > 840N/mm2 (121.8 ksi), whilst retaining high ductility
  • Ferralium® was developed in the 1960’s, pioneering the addition of nitrogen, to create the first super duplex stainless steel
  • The product was then further developed throughout the 1990’s to extend PREN > 40, and more recently to increase its mechanical properties
  • Pitting Resistance Equivalent (PREN) >40, indicating outstanding resistance to pitting and crevice corrosion
  • Very low levels of sulphur minimise the likelihood of inclusions as sites for potential pitting corrosion
  • Higher copper content provides self-healing effect at sites of pitting to inhibit further growth
  • Available as bars, plate, pipe and fittings with complementary weld wire
  • Particularly suitable for larger components as the formation of sigma phase is much less likely than it is for other Super Duplexes


  • Oil & Gas industry pumps, valves, wellhead and subsea equipment
  • Pollution control scrubbers, precipitators, fans and pumps
  • Marine propellers, shafts, rudders, seals, pumps, valves
  • Bolts and fasteners
  • Process industry equipment in sulphuric acid, nitric acid, phosphoric acid, PP / PVC/TiOx production, agrochemicals
  • Grain and vegetable processing plant, sugar cane centrifuges
  • Pulp and paper digester blow vales, feed valves, washers, black liquor heater tubes, bleaching components
  • Copper smelting fans, tuyere bars, wet scrubbers, leaching area precipitators
  • Water and sewage treatment, desalination, swimming pools
Datasheet SD Ferralium 255 3AF Aged Brochure Ferralium 255 SD50 detailed product information (rev2)
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