Specifications
| Super Duplex 255 | Alloy 255 | 1.4507 |
| X2 CrNiMoCuN 25-6-3 | Z3 CNDU 25-07 Az | Norsok MDS D57 |
| Uranus 52N+ | ASTM A276/A476 | UNS S32550 |
| ASME A182 F61 | UNS S32520 | CD4MCuN (Cast grade) |
UNS S32550
Alloy 255, belonging to the Ferralium family, is a super duplex stainless steel and the first of its kind. Developed by Langley Alloys specifically for the oil, gas, and chemical industries, it surpasses other stainless steel varieties and corrosion-resistant alloys in terms of strength. It exhibits exceptional resistance to chloride stress corrosion cracking, as well as crevice corrosion and pitting. Moreover, it boasts twice the yield strength of Alloy 20. With its composition of 25% chromium and significant copper additions, Alloy 255 provides outstanding corrosion resistance across a wide range of aggressive chemical environments. This includes corrosive substances such as sulphuric, nitric, and phosphoric acid. Alloy 255 is a super duplex stainless steel designed for the oil, gas, and chemical industries, offering exceptional corrosion resistance and twice the yield strength of Alloy 20.
Chemical Composition Limits
| Cr | Ni | Mo | Co | Nb (+Ta) | Ti | V | W | Cu | C | Mn | N | Si | P | S | Fe | Al | |
| Min | 24.50 | 5.50 | 3.10 | – | – | – | – | – | 1.50 | – | 0.80 | 0.20 | – | – | – | – | – |
| Max | 26.50 | 6.50 | 3.80 | – | – | – | – | – | 2.00 | 0.025 | 1.20 | 0.25 | 0.70 | 0.025 | 0.005 | Bal | – |
Mechanical Properties
| Bars up to and including 4.0” (100mm) diameter or section | Bars greater than 4.0” (100mm) and up to 12.0” (300mm) diameter or section | Bars greater than 12.0” (300mm) diameter or section | ||||
| 0.2% Proof Stress | 586 N/mm2 | 85ksi | 586 N/mm2 | 85ksi | 570 N/mm2 | 83ksi |
| Tensile Strength | 790 N/mm2 | 114.5ksi | 790 N/mm2 | 114.5ksi | 760 N/mm2 | 110ksi |
| Elongation, 5.65√S0 and 4D | 25% | – | 25% | – | 25% | – |
| Reduction of Area | 50% | – | 50% | – | 50% | – |
| Hardness (Brinell) | 220-270 | – | 220-270 | – | 220-270 | – |
| Impact Strength (Room Temp) | 80J | 59 ft.lb | 80J | 59 ft.lb | 80J | 59 ft.lb |
| Impact Strength (-46degC) | 45J av (35J min) | 33 ft.lb av (25.8 ft.lb min) | 45J av (35J min) | 33 ft.lb av (25.8 ft.lb min) | 45J av (35J min) | 33 ft.lb av (25.8 ft.lb min) |
Physical Properties
| Density (Kg/m3) | 7810 |
| Magnetic Permeability (20°C) | 33 |
| Young’s Modulus (kN/mm2) | 199 |
| Specific Electrical Resistance, 20°C (Ω-m) | 0.80 x 10-6 |
| Mean coefficient of thermal expansion, 20-100°C (m/m/degC) | 11.1 x 10-6 |
| Specific Heat, 20°C (J/kg.K) | 475 |
| Thermal conductivity, 20°C (W/m.K) | 14.2 |
| Fracture Toughness, KQ (MPa/m2) | 98 |
Key Features
- Originally developed in the 1960s, Ferralium 255 pioneered the addition of nitrogen to create the first super duplex stainless steel.
- Continuously developed through the 1990s to extend PREN > 40 and more recently to increase mechanical properties.
- First super duplex stainless steel to achieve 586N/mm2 as a minimum 0.2% Proof Stress, up to 12” (300mm) section sizes.
- Pitting Resistance Equivalent (PREN) >40, indicating outstanding resistance to pitting and crevice corrosion.
- Very low levels of sulphur minimise the likelihood of inclusions as sites for potential pitting corrosion.
- Higher copper content provides a self-healing effect at sites of pitting to inhibit further growth.
- Available as bars, plate, pipe and fittings with complementary weld wire.
- Particularly suitable for larger components as the formation of the sigma phase is much less likely than it is for other Super Duplex grades.
Applications
- Oil & Gas industry pumps, valves, wellheads and subsea equipment.
- Pollution control scrubbers, precipitators, fans and pumps.
- Marine propellers, shafts, rudders, seals, pumps, valves.
- Bolts and fasteners.
- Process industry equipment in sulphuric acid, nitric acid, phosphoric acid, PP / PVC/TiOx production, agrochemicals.
- Grain and vegetable processing plant, sugar cane centrifuges.
- Pulp and paper digester blow vales, feed valves, washers, black liquor heater tubes, bleaching components.
- Copper smelting fans, tuyere bars, wet scrubbers, leaching area precipitators.
- Water and sewage treatment, desalination, swimming pools.