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Super Duplex Steel F61 Overview
Super Duplex F61, also known by its UNS designation S32550, is a high-performance stainless steel known for its exceptional corrosion resistance, high strength, and durability. This alloy is part of the super duplex family, which combines the best attributes of both austenitic and ferritic stainless steels. Duplex F61 is particularly well-suited for demanding applications in harsh environments, such as those found in the oil and gas, petrochemical, and marine industries.
Duplex F61 Corrosion Resistance
- Pitting and Crevice Corrosion: Excellent resistance due to high chromium, molybdenum, and nitrogen content.
- Stress Corrosion Cracking: Superior resistance to stress corrosion cracking in chloride-containing environments.
- General Corrosion: High resistance to both acidic and alkaline environments, making it suitable for a wide range of industrial applications.
Super Duplex F61 (UNS S32550) Chemical Composition
| Element | Percentage (%) |
|---|---|
| Chromium (Cr) | 24-27 |
| Nickel (Ni) | 4.5-6.5 |
| Molybdenum (Mo) | 2.9-3.9 |
| Copper (Cu) | 1.5-2.5 |
| Nitrogen (N) | 0.10-0.25 |
| Manganese (Mn) | 1.0 max |
| Silicon (Si) | 1.0 max |
| Carbon (C) | 0.03 max |
| Phosphorus (P) | 0.040 max |
| Sulfur (S) | 0.020 max |
| Iron (Fe) | Balance |
F61 (255) Duplex Stainless Steel Mechanical Properties
| Property | Value |
|---|---|
| Tensile Strength | 690-930 MPa (100-135 ksi) |
| Yield Strength (0.2% offset) | 450 MPa (65 ksi) min |
| Elongation | 25% minimum |
| Hardness | 28 HRC max |
UNS S32550 / 1.4507 / F61 Physical Properties
| Property | Value |
|---|---|
| Density | 7.8 g/cm³ |
| Melting Range | 1350-1400°C (2462-2552°F) |
| Thermal Conductivity | 14 W/m·K at 20°C |
| Specific Heat Capacity | 500 J/kg·K at 20°C |
| Electrical Resistivity | 0.85 µΩ·m at 20°C |
1.4507, UNS S32550, Super Duplex F61 Product Forms:
Steel Pipes (Tubing)
ASTM A790: Standard Specification for Seamless and Welded Ferritic/Austenitic S32550 Stainless Steel Pipe.
ASTM A928: Standard Specification for Ferritic/Austenitic (Duplex) Stainless Steel Electric Fusion Welded Pipe.
Steel Plates (Sheets)
ASTM A240: Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for Pressure Vessels and for General Applications.
Flanges
ASTM A182: Standard Specification for Forged or Rolled Alloy and Stainless Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service.
Pipe Fittings
ASTM A815: Standard Specification for Wrought Ferritic, Ferritic/Austenitic, and Martensitic Stainless Steel Piping Fittings.
Frequently Asked Questions (FAQ)
Q: What is the PREN of Super Duplex F61?
A: F61 typically has a PREN (Pitting Resistance Equivalent Number) of >40. This ensures it remains immune to pitting in seawater and most industrial brines.
Q: Is F61 the same as Ferralium 255?
A: Yes. UNS S32550 is the technical designation, F61 is the ASTM A182 forging grade name, and Ferralium 255 is the original brand name.
Q: How does the copper in F61 help?
A: The 1.5% - 2.5% Copper addition increases the alloy's resistance to corrosion in reducing acids (like sulfuric and phosphoric acid) and improves its wear resistance in slurry applications.
Q: What is the typical heat treatment for F61?
A: It must be solution annealed at temperatures between 1025℃ and 1125℃ (1875℃ to 2050℃), followed by a rapid water quench to prevent the formation of brittle intermetallic phases.
