Duplex Stainless Steel (DSS) is a high-performance stainless steel family characterized by a dual-phase microstructure consisting of approximately 50% austenite and 50% ferrite. This balanced structure combines the corrosion resistance and toughness of austenitic stainless steel with the high strength and stress corrosion cracking resistance of ferritic stainless steel.
Duplex stainless steels were developed to overcome the limitations of conventional austenitic grades such as lower yield strength and susceptibility to chloride stress corrosion cracking, while maintaining excellent resistance to localized corrosion in harsh environments.
Typical Chemical Composition
| Element | Typical Range (%) | Role |
|---|---|---|
| Chromium (Cr) | 21 – 26 | Corrosion & oxidation resistance |
| Nickel (Ni) | 4.5 – 8.0 | Austenite stabilization |
| Molybdenum (Mo) | 2.5 – 4.0 | Pitting & crevice resistance |
| Nitrogen (N) | 0.10 – 0.30 | Strength & phase balance |
| Carbon (C) | ≤ 0.03 | Prevents carbide precipitation |
| Manganese (Mn) | ≤ 2.0 | Deoxidation |
| Iron (Fe) | Balance | Base metal |
Microstructure & Metallurgy
• ~50% Austenite (FCC): Toughness, ductility, corrosion resistance
• ~50% Ferrite (BCC): High strength, SCC resistance
This dual-phase structure provides nearly twice the yield strength of austenitic stainless steels while significantly improving resistance to chloride-induced stress corrosion cracking.
Typical Mechanical Properties
| Property | Typical Range |
|---|---|
| Tensile Strength | 620 – 900 MPa |
| Yield Strength (0.2%) | 450 – 550 MPa |
| Elongation | 20 – 30% |
| Hardness | 250 – 300 HB |
| Impact Toughness | High (excellent at low temperatures) |
| Density | ~7.8 g/cm³ |
| Modulus of Elasticity | ~200 GPa |
Corrosion Resistance Performance
✔ Excellent resistance to pitting and crevice corrosion
✔ Outstanding resistance to stress corrosion cracking
✔ Suitable for seawater and chloride-rich environments
✔ High resistance to intergranular corrosion
Pitting Resistance Equivalent Number (PREN):
• Duplex 2205: ~34 – 36
• Super Duplex 2507: ~40 – 45
Key Characteristics
✔ High mechanical strength
✔ Excellent fatigue and impact performance
✔ Good weldability with controlled heat input
✔ Reduced material thickness and weight
✔ Long service life in aggressive environments
Refining & Processing Properties
• Produced using EAF with AOD / VOD refining
• Supplied in solution-annealed condition
• Not heat-treatable for hardening
• Higher forming forces required than austenitic grades
• Moderate machinability with rigid tooling
Available Forms
✔ Plates & sheets
✔ Coils
✔ Pipes & tubes (seamless & welded)
✔ Bars (round, square, hex)
✔ Angles, channels & fittings
✔ Forged components
✔ Wires & rods
Applications
Oil & Gas: Offshore platforms, subsea pipelines, pressure vessels
Marine: Seawater piping, desalination plants, marine hardware
Chemical: Reactors, storage tanks, process piping
Infrastructure: Bridges, structural supports in corrosive zones
Water Treatment: RO plants, sludge handling systems
Food & Pharma: Hygienic piping, processing equipment
Advantages
✔ High strength and corrosion resistance
✔ Excellent resistance to stress corrosion cracking
✔ Weight and cost optimization through thinner sections
✔ Long-term reliability in harsh environments
Limitations
⚠ Higher initial cost than carbon steel
⚠ Requires skilled welding and fabrication control
⚠ Not suitable for prolonged high-temperature exposure above ~300–350°C
Why Choose Duplex Stainless Steel
Duplex stainless steel is the preferred choice for severe operating environments where strength, corrosion resistance, and long service life are critical. Its ability to outperform conventional stainless steels while reducing material thickness makes it a cost-effective and reliable solution for oil & gas, marine, chemical, infrastructure, and desalination industries.