• Alloy 255 (Super Duplex 255)
  • 1.4507
  • Norsok MDS D55
  • X2CrNiMoCuN 25-6-3
  • Z3 CNDU 25-07 Az
  • ASTM A240
  • UNS S32550
  • UNS S32520
  • ASME (Table UHA23, code case 1883)
View Data Tables For This Product

Ferralium 255 (Plate) (UNS S32550)

Ferralium® 255 is a super duplex stainless steel supplied in the hot worked, annealed and pickled condition. It achieves higher strengths than other alternative corrosion resistant alloys, offering the potential to reduce section size and therefore weight and cost.

As a 25% Cr alloy, with significant additions of Cu, it offers excellent corrosion resistance in a wide variety of corrosive chemicals including sulphuric, nitric and phosphoric acid.  In seawater and other chloride containing environments it also provides outstanding resistance to pitting and crevice corrosion, with Critical Pitting Temperature exceeding 50°C. Excellent ductility and impact strength at both ambient and sub-zero temperatures combine with a high resistance to abrasion, erosion and cavitation erosion.

Listed in NACE MR 0175 for sour service and having gained ASME Approval for Pressure Vessel applications, Ferralium® 255 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.

ferralium 255 plate


  • Alloy 255 (Super Duplex 255)
  • 1.4507
  • Norsok MDS D55
  • X2CrNiMoCuN 25-6-3
  • Z3 CNDU 25-07 Az
  • ASTM A240
  • UNS S32550
  • UNS S32520
  • ASME (Table UHA23, code case 1883)
View Data Tables For This Product

Data Tables

Chemical Composition:


Mechanical Properties:

For plates up to 3” in thickness
0.2% Proof Stress550 N/mm279.8 ksi
Tensile Strength790 N/mm2114.5ksi
Elongation, 5.65√S0 and 4D25%
Reduction of Area50%
Hardness (Brinell)220-270
Impact Strength (Room Temp)80J59 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 G48A corrosion test (at 40°C)  no pitting and < 0.8g/m2 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)199
Specific Electrical Resistance, 20°C (Ω-m)0.80 x 10-6
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:

  • Originally developed in 1960’s, pioneering the addition of nitrogen, to create the first super duplex stainless steel
  • Continuously developed through 1990’s to extend PREN > 40, and more recently to increase 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 Duplex grades


  • 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 Plate Brochure Ferralium 255 SD50 detailed product information (rev2) Article Ferralium 255 for FGD Brochure Ferralium 255 SD50 Machining Guidelines Brochure Ferralium 255 SD50 Welding Guidelines
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