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UNS - S32550

Alloy 255 is a super duplex stainless steel which includes 25% chromium. Alloy 255 consists of copper expansion, which provides it with greater resistance to sulfuric acid than other super duplex grades. Due to its duplex structure alloy 255 also offers magnificent strength attributes and resistance to chloride ion stress corrosion cracking.

Ferralium 255 sets a new standard for Super Duplex as the first to state 570N/mm² as the minimum 0.2% Proof Stress. It offers magnificent corrosion resistance in a wide variety of corrosive chemicals, including phosphoric, sulphuric and nitric acids. In seawater and other chloride consists of environments Ferralium 255 also gives outstanding resistance to pitting and crevice corrosion, with Critical Pitting Temperature exceeding 50°C. Magnificent ductility and effect of strength at both ambient and sub-zero temperatures join with a high resistance to abrasion, erosion and cavitation erosion. Ferralium 255 is tested to the highest degree, utilizing tests intended to ensure that the trademarked product possesses high integrity, a correct phase balance and the absence of sigma and other deleterious phases. Ferralium 255 is especially applicable for large forgings, as the development of sigma phase is much less likely than it is for other Super Duplexes.

  • Superior Corrosion Resistance
  • Pitting
  • Crevice Corrosion
  • Chloride Stress Corrosion Cracking
  • General Corrosion In Many Environments
  • Good Ductility
  • High Strength-To-Weight Ratio
  • High Fatigue Strength In Marine Environments
  • Superior Abrasion and Cavitation Erosion Resistance
  • High Mechanical Strength - (over twice the yield strength of austenitic stainless steels)
  • Good Fabricability

  • Chemical Process Industry
  • Marine Industry and Shipbuilding
  • Oil and Gas Industry
  • Pollution Control
  • Copper Smelting
  • Pulp and Paper Industry
  • Food Industry
  • Agrochemicals
  • Civil Engineering


Albeit generously harder than most different stainless steels, Alloy 255 can be effectively machined utilizing most common techniques. Slow speeds and heavy, steady feeds are required to overcome this alloy’s tendency to work harden.


Alloy 255 can be effectively formed utilizing each and every technique of hot or cold working.


Alloy 255 can be effectively welded utilizing most common technique, including GTAW, GMAW and SMAW process. At the point when this filler metal is required, for joining with a disparate of higher alloy content, select the filler relating to the higher alloy material for best results.

Heat Treatment

The alloy reacts to annealing, yet is not age-hardenable.

Hot Working

Forging might be done within the scope of 2220 F to 1700 F. A re-anneal must be done following forging in order to regain optimum corrosion resistance.

Cold Working

This is a ductile alloy, like the stainless steels yet stiffer and it is promptly cold worked by standard means. Annealing must be done after cold work to restore corrosion resistance.


Anneal at 1900°F and fast cool.


Hardens are done by cold work only, but should be utilized in annealed condition for corrosion resistance.

Chemical Composition %

0.040.10 - - 27.01.50 max4.5 - 6.51.50 - 2.502.9 - 3.9

Mechanical Properties

Tensile Strength (ksi)0.2% Yield Strength (ksi)Elongation% in 2 inches

Physical Properties

UnitsTemperature in °C
Density7.81 g/cm³Room
Specific Heat0.113 Kcal/kg.C 20°
Melting Range1385 - 1443.3 °C-
Modulus of Elasticity 199 KN/mm²20°
Electrical Resistivity78.6 µΩ.cm20°
Coefficient of Expansion11.1 µm/m °C20 - 100°
Thermal Conductivity14.2 W/m -°K20°

ASTM Specifications

Pipe / Tube (SMLS) Tube WeldedSheet / PlateBarFitting
A 790A 789A 240 A 479 A 815


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