Characteristics of Super-Duplex Stainless Steel

Duplex stainless steels were initially created in Sweden for the sulfite paper industry over 70 years ago.

Duplex alloys were developed to prevent corrosion caused by chloride-containing cooling waters and other harsh chemical process fluids. 

Duplex stainless steels have a mixed microstructure with equal quantities of ferrite and austenite. Their corrosion performance varies according on the alloy composition. The name “Super-Duplex” was used in the 1980s to describe high-performance Duplex steel with a pitting resistance equivalent of more than 40 (based on Cr% + 3.3Mo% + 16N%).

Super-Duplex steel’s high chromium content makes it resistant to acids, acid chlorides, caustic solutions, and other environments in the chemical, petrochemical, pulp, and paper industries. It can replace 300 series stainless steel, high nickel superaustenitic steels, and nickel-based alloys.

High chromium, nickel, and molybdenum concentration increases corrosion resistance between granules and pits. Nitrogen additions enhance structural hardening by an interstitial solid solution process, increasing yield strength and ultimate strength while maintaining toughness.

Furthermore, the two-phase microstructure provides superior resistance to pitting and stress corrosion cracking compared to typical stainless steels.

Duplex steel has been more popular since its initial generation. High-strength, corrosion-resistant super-duplex coils are now widely used in several sectors, including maritime and chemical, architecture, mast rigging, wire lines, hoisting and pulley equipment, and well service strands. Advancements in wire processing processes now allow for the fabrication of steel wires as small as 1mm in diameter.

The various Alloys

Super-Duplex is categorized as Duplex stainless steel.

Duplex stainless steels are rated for corrosion resistance based on their alloy composition. Modern Duplex stainless steel may be classified into four groups:

There are four types of duplex steel:

  1. lean (2304), 
  2. work-horse (2205),
  3. 25 Cr (Alloy 255 and DP-3),
  4. Super-Duplex (25-26 Cr and increased Mo and N compared to 25 Cr grades, including 2507, Zeron 100, UR 52N+, and DP-3W).

Chemical Composition of Supex Duplex Stainless Steel

The chemical composition of the stainless steel grade of Super Duplex is shown in the table below.

ElementContent (%)
Chromium, Cr24 – 26
Nickel, Ni6 – 8
Molybdenum, Mo3 – 5
Manganese, Mn1.20 max
Silicon, Si0.80 max
Copper, Cu0.50 max
Nitrogen, N0.24 – 0.32
Phosphorous, P0.035 max
Carbon, C0.030 max
Sulfur, S0.020 max
Iron, FeBalance

Physical Properties of Supex Duplex Stainless Steel

The physical parameters of stainless steel grade Super Duplex are listed below.

Density7.8 g/cm30.281 lb/in3
Melting point1350°C2460°F

Applications of Super Duplex Stainless Steel

Super Duplex SS is widely used in the following sectors:




Pulp and paper


Water desalinization

Oil and gas production

Products made using Super Duplex include:


Wire fittings

Cargo tanks

Water heaters

Storage vessels

Hydraulic piping

Heat exchangers

Hot water tanks.

Spiral wound gaskets

Lifting and pulleying equipment

Propellers, Rotors, and Shafts

Newzel Industries is a Manufacturer & Worldwide Exporter of Super Duplex Steel Products

Super Duplex Flanges

Super Duplex Flanges

Super Duplex Fittings

Super Duplex Fittings

Super Duplex Pipes

Super Duplex Pipes

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