Super Duplex 32550
Super Duplex 255 – SD50 (super duplex 255) is a super duplex stainless steel supplied in the hot worked and annealed condition. It achieves higher strengths than most stainless steels and alternative corrosion resistant alloys, offering the potential to reduce section size and therefore weight and cost.
As a 25% Cr alloy, with significant additions of copper, Ferralium® 255 offers excellent corrosion resistance in a wide variety of corrosive chemicals including sulphuric, nitric and phosphoric acid. In seawater and other chloride containing environments it also provides outstanding resistance to pitting and crevice corrosion, with Critical Pitting Temperature exceeding 50°C. Excellent ductility and impact strength at both ambient and sub-zero temperatures combine with a high resistance to abrasion, erosion and cavitation erosion.
Listed in NACE MR 01 75 for sour service and having gained ASME Approval for Pressure Vessel applications, Super Duplex 255-SD50 is tested to the highest degree using tests designed to guarantee that the trade-marked product possesses high integrity, a correct phase balance and the absence of sigma and other deleterious phases.
Chemical Composition
| Cr | Ni | Mo | Co | Nb (+Ta) | Ti | V | W | Cu | C | Mn | N | Si | P | S | Fe | Al | |
| Min | 24.50 | 6.00 | 3.00 | 0.50 | 0.24 | 0.10 | |||||||||||
| Max | 26.00 | 8.00 | 5.00 | 0.50 | 0.03 | 1.20 | 0.32 | 0.80 | 0.035 | 0.020 | Bal |
Mechanical Properties:
| 0.2% Proof Stress | 550 N/mm2 | 79.8 ksi |
| Tensile Strength | 800 N/mm2 | 116 ksi |
| Elongation, 5.65√S0 | 25% | |
| Reduction of area | 45% | |
| Hardness (Brinell) | <270 | |
| Impact Strength (Room Temp) | 80J | |
| Impact Strength (-46oC) | Longitidinal 45J (35J min) | |
| Transverse 45J (35J min) | ||
Notes:
- Testing shall be carried out in accordance with ASTM A370 or EN ISO 6892-1 (tensile), EN ISO 6506-1 (hardness)
- Minimum properties quoted (tested at room temperature in a longitudinal direction)
- Testing performed on each melt of material per heat treatment batch
- Hardness shall be in accordance with NACE MR 1075 with a maximum HRC of 25
- ASTM G48A corrosion test (at 50°C) No pitting and < 3.0g/m2 weight loss (ASTM specification < 4.0g/m2)
- Ferrite content 35-55%
- Microstructure certified free from grain boundary carbides, sigma, chi and laves phases
Physical Properties:
| Density (Kg/m3) | 7810 |
| Magnetic Permeability (20°C) | 33 |
| Young’s Modulus (kN/mm2) | 199 |
| Specific Electrical Resistance, 20°C (µΩ.m) | 0.8 |
| Mean coefficient of thermal expansion, 20-300°C (m/m/oC) | 11.1 x 10-6 |
| Specific Heat, 20°C (J/kg.K) | 475 |
| Thermal conductivity, 20°C (W/m.K) | 14.2 |