North American Unified Numbering System designation, equivalents, composition, and qualifying standards
UNS S32550 is the North American Unified Numbering System designation maintained jointly by ASTM International and SAE International for the Cu-bearing super duplex stainless steel commercially known as Ferralium 255. The designation appears across the ASTM family of standards (A479 for bar, A789 for tube, A790 for pipe, A815 for fittings, A182 grade F61 for forgings, A276 for shapes, A240 for plate / sheet) and is cross-referenced to the corresponding EN designation 1.4507 (X2CrNiMoCuN25-6-3) in the European EN 10088-3 / EN 10222-5 standards. The composition envelope is 25Cr-5Ni-3Mo-2Cu-0.2N, with the 2 percent copper addition being the metallurgical differentiator from Cu-free super duplex grades like 2507 (UNS S32750) and Zeron 100 (UNS S32760).
| Designation system | Code |
|---|---|
| UNS (USA) | S32550 |
| EN steel name | X2CrNiMoCuN25-6-3 |
| EN steel number | 1.4507 |
| Trade name (Langley Alloys) | Ferralium 255 |
| NORSOK MDS | D55 |
| ASTM A182 grade | F61 |
| ASTM A815 fitting grade | WP-S32550 |
| ASTM A193 bolt supplementary | S6 |
| ASTM A194 nut supplementary | S7 (inch), S7M (metric) |
| NACE MR0175 / ISO 15156-3 table reference | Table A.10 |
| AWS welding consumable family | 25.10.4.L (E2594, ER2594) |
| Element | Min % | Max % |
|---|---|---|
| Carbon (C) | none | 0.040 |
| Manganese (Mn) | none | 1.50 |
| Phosphorus (P) | none | 0.040 |
| Sulphur (S) | none | 0.030 |
| Silicon (Si) | none | 1.00 |
| Chromium (Cr) | 24.0 | 27.0 |
| Nickel (Ni) | 4.5 | 6.5 |
| Molybdenum (Mo) | 2.9 | 3.9 |
| Copper (Cu) | 1.5 | 2.5 |
| Nitrogen (N) | 0.10 | 0.25 |
| Iron (Fe) | Balance | |
| PREN, calculated, min | 40 | |
