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:
- lean (2304),
- work-horse (2205),
- 25 Cr (Alloy 255 and DP-3),
- 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.
| Element | Content (%) |
| Chromium, Cr | 24 – 26 |
| Nickel, Ni | 6 – 8 |
| Molybdenum, Mo | 3 – 5 |
| Manganese, Mn | 1.20 max |
| Silicon, Si | 0.80 max |
| Copper, Cu | 0.50 max |
| Nitrogen, N | 0.24 – 0.32 |
| Phosphorous, P | 0.035 max |
| Carbon, C | 0.030 max |
| Sulfur, S | 0.020 max |
| Iron, Fe | Balance |
Physical Properties of Supex Duplex Stainless Steel
The physical parameters of stainless steel grade Super Duplex are listed below.
| Properties | Metric | Imperial |
| Density | 7.8 g/cm3 | 0.281 lb/in3 |
| Melting point | 1350°C | 2460°F |
Applications of Super Duplex Stainless Steel
Super Duplex SS is widely used in the following sectors:
Power
Marine
Chemical
Pulp and paper
Petrochemical
Water desalinization
Oil and gas production
Products made using Super Duplex include:
Fans
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 Fittings
Super Duplex Pipes
