Ferralium 255 (UNS S32550) is a super duplex stainless steel (PREN ≥ 40); Duplex 2205 (UNS S31803 / S32205) is the standard duplex grade one tier below (PREN ~35). The two are not direct substitutes, they sit at different tiers of the duplex / super duplex stainless steel family. The Ferralium 255 vs Duplex 2205 question is typically an upgrade decision: when do service conditions exceed Duplex 2205 limits and require super duplex?
| Element | Ferralium 255 (S32550) | Duplex 2205 (S31803 / S32205) |
|---|---|---|
| Carbon (C), max. | 0.04 | 0.030 |
| Chromium (Cr) | 24.0–27.0 | 21.0–23.0 |
| Nickel (Ni) | 4.5–6.5 | 4.5–6.5 |
| Molybdenum (Mo) | 2.9–3.9 | 2.5–3.5 |
| Copper (Cu) | 1.5–2.5 | not specified |
| Nitrogen (N) | 0.10–0.25 | 0.08–0.20 |
Full element-by-element table on the Duplex 2205 chemical composition page.
Ferralium 255 PREN = 25 + 3.3×3 + 16×0.2 = 38.1 minimum, ~41 typical per heat. Duplex 2205 PREN = 22 + 3.3×3 + 16×0.15 = 34.3 minimum, ~35 typical per heat. The 5+ PREN unit increase is the defining benefit of upgrading from Duplex 2205 to Ferralium 255, it extends Critical Pitting Temperature from ~25 °C (Duplex 2205) to ≥ 35 °C (Ferralium 255) per ASTM G48 method A.
| Property | Ferralium 255 | Duplex 2205 |
|---|---|---|
| Yield strength (Rp0.2), min | 550 MPa | 450 MPa |
| Tensile strength (Rm), min | 760 MPa | 620 MPa |
| Elongation (A5), min | 15% | 25% |
| Hardness (NACE MR0175), max | 32 HRC | 32 HRC |
Standard upgrade triggers from Duplex 2205 to super duplex (Ferralium 255 / 2507 / Zeron 100):
Ferralium 255 typically commands a 30–50% material premium over Duplex 2205 due to higher Cr / Mo / Ni / Cu loading and tighter manufacturing controls. For applications within Duplex 2205 service limits, the super-duplex upgrade is unjustified. For applications at or beyond those limits, the upgrade prevents in-service pitting failures whose lifecycle cost vastly exceeds the material premium. Both grades available from TorqBolt, see Ferralium 255 grade page or Duplex 2205 reference for details.
