Duplex 2205 is the most-specified standard duplex stainless steel grade, designated UNS S31803 (original 1980s composition) and UNS S32205 (modern narrowed composition introduced 1996). European designation: EN 1.4462 / X2CrNiMoN22-5-3. Nominal composition: 22 Cr – 5 Ni – 3 Mo – 0.15 N, balanced austenite-ferrite microstructure (35–55% ferrite per NORSOK M-630), PREN ~35 (below the super duplex PREN ≥ 40 threshold).
| Element | UNS S31803 (1980s) | UNS S32205 (1996+, narrowed) | EN 1.4462 |
|---|---|---|---|
| Carbon (C), max. | 0.030 | 0.030 | 0.030 |
| Manganese (Mn), max. | 2.00 | 2.00 | 2.00 |
| Phosphorus (P), max. | 0.030 | 0.030 | 0.035 |
| Sulphur (S), max. | 0.020 | 0.020 | 0.015 |
| Silicon (Si), max. | 1.00 | 1.00 | 1.00 |
| Chromium (Cr) | 21.0–23.0 | 22.0–23.0 | 21.0–23.0 |
| Nickel (Ni) | 4.5–6.5 | 4.5–6.5 | 4.5–6.5 |
| Molybdenum (Mo) | 2.5–3.5 | 3.0–3.5 | 2.5–3.5 |
| Nitrogen (N) | 0.08–0.20 | 0.14–0.20 | 0.10–0.22 |
| Copper (Cu) | not specified | not specified | not specified |
The original UNS S31803 specification permitted a wider Cr (21–23%), Mo (2.5–3.5%), and N (0.08–0.20%) range, which allowed mills to produce heats at the LOW end, some heats hit PREN as low as 31. To guarantee PREN ≥ 35, the narrower UNS S32205 chemistry was introduced (Cr 22–23%, Mo 3.0–3.5%, N 0.14–0.20%). Most modern mill heats are dual-certified S31803 / S32205 by hitting the narrower S32205 ranges.
Ferralium 255 chemistry sits one tier above Duplex 2205 in the duplex / super duplex stainless steel family. The differences pushing PREN from ~35 (Duplex 2205) to ~40 (Ferralium 255) are: higher Cr (24–27 vs 21–23%), higher Mo (2.9–3.9 vs 2.5–3.5%), higher N (0.10–0.25 vs 0.08–0.20%), plus a 2% Cu addition that Duplex 2205 lacks. See Ferralium 255 vs Duplex 2205 upgrade guide for full selection criteria.
PREN = %Cr + 3.3 · %Mo + 16 · %N. With nominal Duplex 2205 composition (22 Cr, 3 Mo, 0.15 N): PREN = 22 + 9.9 + 2.4 = 34.3 minimum. Typical per-heat values 35–38. PREN < 40 places Duplex 2205 in the standard-duplex tier; super duplex grades (Ferralium 255, Super Duplex 2507, Zeron 100) sit above the PREN ≥ 40 threshold.
