Ferralium 255 (UNS S32550) and Zeron 100 (UNS S32760) are both super duplex stainless steel grades meeting the PREN ≥ 40 threshold, but with distinct alloying chemistries that suit different service environments. Ferralium 255 is the Cu-bearing variant (~2% Cu) developed by Langley Alloys (UK); Zeron 100 is the W-bearing variant (~0.7% W) originally developed by Weir Materials. For full Zeron 100 grade reference, see the manufacturer-specialist site at zeron100.com (UNS S32760).
| Element | Ferralium 255 (S32550) | Zeron 100 (S32760) |
|---|---|---|
| Chromium (Cr) | 24.0–27.0 | 24.0–26.0 |
| Nickel (Ni) | 4.5–6.5 | 6.0–8.0 |
| Molybdenum (Mo) | 2.9–3.9 | 3.0–4.0 |
| Nitrogen (N) | 0.10–0.25 | 0.20–0.30 |
| Copper (Cu) | 1.5–2.5 | 0.5–1.0 |
| Tungsten (W) | none | 0.5–1.0 |
Ferralium 255 PREN = %Cr + 3.3·%Mo + 16·%N ≈ 40–42 typical per heat. Zeron 100 uses the modified PREW formula adding W weighted at 1.65: PREW = %Cr + 3.3(%Mo + 0.5·%W) + 16·%N ≈ 41–42 typical. Both grades comfortably exceed the PREN ≥ 40 super duplex threshold.
| Property | Ferralium 255 (S32550) | Zeron 100 (S32760) |
|---|---|---|
| Yield strength (Rp0.2), min | 550 MPa | 550 MPa |
| Tensile strength (Rm), min | 760 MPa | 750 MPa |
| Elongation (A5), min | 15% | 25% |
| Hardness (NACE MR0175), max | 32 HRC | 32 HRC |
| Charpy impact at −46 °C, min (NORSOK) | 45 J | 45 J |
Choose Ferralium 255 when service involves reducing acids (dilute H2SO4, HCl, brines), chemical processing applications, or when the project specification requires a Cu-bearing super duplex grade.
Choose Zeron 100 when service involves the most aggressive seawater environments (warm seawater > 40 °C, high-velocity flow), or when the project specification (often UK / North Sea offshore) calls for the W-bearing variant. Both grades are interchangeable for standard NACE MR0175 sour-service applications and most marine seawater service.
Both grades are covered by the same ASTM specifications: ASTM A479 (bar), ASTM A789 (tube), ASTM A790 (pipe), ASTM A815 (fittings), ASTM A182 (forgings/flanges). Both qualify under NORSOK M-650 with QTR per MDS D55, and NACE MR0175 / ISO 15156-3 for sour service. TorqBolt manufactures Ferralium 255 in Mumbai & Rajkot, India.
