Last verified 19 August 2026.
The comparison
| Property | Duplex 2205 | 2304 | Evidence |
|---|---|---|---|
| Proof strength Rp0.2, minimum (EN) | 500 MPa | 450 MPa | E3 E3 |
| PREN | 35 — | 26 — | E3 E3 |
| Modulus of elasticity | 200 GPa | 200 GPa | E3 E3 |
| Density | 7.8 g/cm³ | 7.8 g/cm³ | E3 E3 |
| Thermal conductivity | 15 W/(m·K) | 15 W/(m·K) | E3 E3 |
| Tensile strength Rm, minimum | 700 MPa | 650 MPa | E3 E3 |
| Elongation A80, minimum | 20 % | 20 % | E3 E3 |
| Proof strength Rp0.2, minimum (ASTM) | 450 MPa | not established here | E3 / — |
All shared rows compare like for like.
The trap on this comparison
Proof strength Rp0.2 is specified twice: 450 MPa (ASTM A240/A240M, plate, 20 °C) and 500 MPa (EN 10088-2, cold rolled strip, 20 °C) — 11% apart. Both correct. Which one governs is a question about your drawing and your product form, not about the material.
Where each side’s numbers come from
See Duplex 2205 and 2304 — each page lists every source, every demotion and every gap. Nothing on this page is derived from anything not on those two, and our coverage limits are stated separately.
Where a PREN appears above, read it as a ranking number rather than a qualification: what PREN can and cannot tell you.
When to choose which
Duplex 2205. Where strength sets the section or chlorides set the material. At the 450 MPa ASTM A240 minimum against 170 for 316L, a strength-driven part in 2205 is dramatically thinner, and for a plate in bending that compounds. The higher PREN also moves you out of the range where 316L is marginal in warm chloride service.
2304. Structural work in moderate chlorides where the alternative is thick 316L. At roughly double the proof strength, a section designed to yield can be materially thinner, and the material saving usually outruns the price premium. Tanks, bridges, reinforcement and process vessels in brackish rather than sea water are the recurring uses.
Against Duplex 2205: Fabrication and supply, not properties. Duplex has a narrower heat-input window, needs procedures qualified for it, and is not on every stockist’s shelf in every thickness. A shop with qualified duplex procedures treats 2205 as ordinary; a shop without them faces a new PQR and an eight-week lead time, and that is frequently decisive regardless of what the property table says.
Against 2304: Fabrication discipline and temperature ceiling. Duplex needs a controlled heat input window to keep its phase balance, so procedures have to be qualified and welders have to follow them. And like every duplex it has an upper temperature limit that austenitics do not, which rules it out of hot service entirely.
What this comparison does not cover
- Crevice corrosion, the usual failure mode in seawater service, which PREN does not predict.
- Elevated temperature: 2205 has a service ceiling that 316L does not share, driven by 475 °C embrittlement and sigma-phase formation. Not sourced here.
- Cryogenic behaviour.
- Fatigue, fracture toughness and stress corrosion cracking.
- Cost, which moves with alloy surcharges and is not a fixed ratio.
- Composition limits, not established.
- The temperature ceiling is real but not established here as a number.
- Impact toughness and the transition temperature.
- Welding procedure guidance, heat input windows and filler selection.
- Crevice corrosion, which the pitting ranking number does not predict.
Generated from data/materials/2205.yaml and 2304.yaml.