Duplex 2205 (UNS S31803 / S32205, EN 1.4462) is the most-specified standard duplex stainless steel grade. Super Duplex 2507 (UNS S32750, EN 1.4410) is one tier above Duplex 2205 in the duplex / super duplex stainless steel family. The two are not direct substitutes, Duplex 2205 sits at PREN ~35 (standard duplex), Super Duplex 2507 at PREN ~42 (super duplex). The Duplex 2205 vs Super Duplex 2507 question is typically an upgrade decision: when do service conditions exceed Duplex 2205 limits and require super duplex?
| Element | Duplex 2205 (S31803/S32205) | Super Duplex 2507 (S32750) |
|---|---|---|
| Carbon (C), max. | 0.030 | 0.030 |
| Chromium (Cr) | 21.0–23.0 | 24.0–26.0 |
| Nickel (Ni) | 4.5–6.5 | 6.0–8.0 |
| Molybdenum (Mo) | 2.5–3.5 | 3.0–5.0 |
| Nitrogen (N) | 0.08–0.20 | 0.24–0.32 |
| Copper (Cu) | none | max 0.5 (not specified) |
Composition jump from Duplex 2205 to Super Duplex 2507: +3% Cr, +1% Mo, +0.12% N. Both grades have no Cu addition (for Cu-bearing super duplex, see Ferralium 255).
Duplex 2205 PREN = 22 + 3.3 × 3 + 16 × 0.15 ≈ 34.3 minimum, ~35 typical. Super Duplex 2507 PREN = 25 + 3.3 × 4 + 16 × 0.27 ≈ 42.5 typical. The 7+ PREN unit gap reflects the substantially better chloride pitting resistance of Super Duplex 2507. Critical Pitting Temperature (ASTM G48 method A): Duplex 2205 ~25 °C; Super Duplex 2507 ~40 °C, a ~15 °C extension of the chloride pitting service envelope.
| Property | Duplex 2205 | Super Duplex 2507 |
|---|---|---|
| Yield strength (Rp0.2), min | 450 MPa | 550 MPa |
| Tensile strength (Rm), min | 620 MPa | 795 MPa |
| Elongation (A5), min | 25% | 15% |
| Hardness (NACE MR0175), max | 32 HRC | 32 HRC |
| Charpy at −46 °C, min (NORSOK) | 45 J | 45 J |
| Density | 7.80 g/cm³ | 7.80 g/cm³ |
Among super-duplex grades, Super Duplex 2507 and Ferralium 255 are interchangeable for chloride-pitting-dominated service (seawater, NORSOK offshore). The differentiator: Ferralium 255's 2% Cu addition gives improved performance in reducing-acid environments (HCl, dilute H2SO4, brines), making it preferred for chemical processing service combining chloride and reducing acids. See Ferralium 255 vs Super Duplex 2507 comparison and Ferralium 255 vs Duplex 2205 upgrade guide.
Both Duplex 2205 (UNS S31803, S32205) and Super Duplex 2507 (UNS S32750) are covered by the same ASTM specification family across product forms: ASTM A479 (bar), A789 (tube), A790 (pipe), A815 (fittings), A182 (forgings, F51/F60 for 2205, F55 for 2507), A240 (plate / sheet). EN equivalents: EN 10088-3 (1.4462 / 1.4410), EN 10222-5 (forgings), EN 10272 (pressure-rated bar).
