AISI F55
AISI F55 Super Duplex Stainless Steel: Technical Properties, Application Areas and Industrial Importance
Technical Description
AISI F55 is one of the super duplex stainless steel classes offering high mechanical strength and superior corrosion resistance. Chemically it contains 25% Cr, 7% Ni, 3.5% Mo, 0.7% W, 0.2% N and 0.5% Cu. This composition provides a balanced distribution of approximately 50% ferrite and 50% austenite phases in its structure. This microstructure makes it possible for F55 to show excellent resistance to both stress corrosion cracking (SCC) and localised corrosion types such as pitting.
The typical tensile strength of AISI F55 is in the range of 750–880 MPa, while its yield strength is at a minimum level of 550 MPa. These values make F55 a superior candidate in applications exposed to both corrosion and high loads. In addition, its mechanical properties such as ductility and impact strength are at satisfactory levels even at low temperatures. For this reason it can be used in cryogenic conditions down to -50°C.
Super duplex F55 stands out particularly through its PREN (Pitting Resistance Equivalent Number) value. For F55 this value is generally above 40 (typically 42–45), which makes it ideal in sea water, in chlorine-containing environments and in high temperature acidic solutions.
Standards Relating to AISI F55
The AISI F55 alloy has been defined by various international norms. Among the most frequently encountered specifications:
- ASTM A182: Use in forged or machined parts.
- ASTM A240: Products in plate, sheet and strip form.
- ASTM A276: Products in bar and section form.
- ASTM A790 / A928: Seamless and welded pipes.
- ASTM A995 Gr. 6A: Designation for cast parts.
- NACE MR0175 / ISO 15156: Usability in sour gas environments.
- ASME SA-240 and SA-790: These are the standards accepted for pressure vessel applications.
Although there is no special standard corresponding directly to F55 in the AMS (Aerospace Material Specifications) system, and F55 is defined instead by ASTM, ASME and NORSOK standards.
AISI F55 Trade Names and Equivalents
AISI F55 is commercially known generally by the name Zeron 100. This trade name refers to a variant whose hot forming, welding and heat treatment processes have been specially optimised. Among the other equivalent names are UNS S32760, 1.4501 (EN standard) and F55 (EN 10283).
This alloy is designated as Zeron 100 particularly in the European and Asian markets, and in the USA more often as UNS S32760. Both designations have the same technical content and should be assessed together in terms of the supply chain.
AISI F55 Application Areas
AISI F55 super duplex stainless steel is used in a very wide range of industrial applications. It is preferred especially in sectors requiring high mechanical strength and resistance to aggressive environments:
- Oil and Gas Industry: F55 is widely used in subsea equipment, wellheads, piping systems and platform constructions. It is preferred in sulphur-containing environments thanks to its compliance with the NACE MR0175 standard.
- Chemical and Petrochemical Plants: Because it shows high resistance to sulphuric acid, phosphoric acid and chlorine-based chemicals, it is used in reactors, exchangers and storage tanks.
- Marine and Shipyard Sector: It provides long-life corrosion resistance in marine environments with a high salt content. It is considered for critical components such as ship propellers, underwater pipes and salt water pumps.
- Paper and Pulp Industry: It is preferred in areas where corrosion-causing chemicals such as chlorine dioxide and hypochlorite are used.
- Power Generation Plants: It provides high performance in steam boilers, exchangers and flue gas cleaning systems.
- Desalination Plants: Its use is widespread in desalination systems, especially in membrane systems and high pressure pipelines.
Advantages of AISI F55
- High Corrosion Resistance: Being resistant to halogen-containing and acidic environments makes it unique in aggressive chemical environments.
- High Strength / Weight Ratio: Since it offers higher strength than carbon steel and austenitic stainless steels, similar structural strength can be obtained with thinner sections.
- Cost Advantage: Although it is more economical than titanium or nickel-based super alloys, it offers a similar performance level.
- Weldability: It can be welded successfully with suitable welding procedures (for example with low heat input).
- Strength at High Temperature: It can be used up to 250°C without losing its mechanical properties.
Disadvantages of AISI F55
- Low High Temperature Strength: At temperatures above 300°C there is a risk of phase separation and embrittlement.
- Machinability Issues: Because of its high strength, tool wear may be experienced in machining. It is necessary to work with hard cutting tips and suitable feed rates.
- Risk of Phase Imbalance in Welding: In the case of unsuitable welding procedures the ferrite/austenite balance may be disturbed, which adversely affects corrosion resistance.
- Complex Supply Chain: F55 is generally supplied to special order and has longer delivery times than standard commercial products.
Conclusion and Industrial Evaluation
AISI F55 is a high performance super duplex stainless steel class preferred especially in applications where high mechanical strength is also required in aggressive corrosion environments. The superior performance it shows both on subsea oil platforms and in chemical process plants increases the strategic importance of F55 in the industrial material portfolio.
Its high PREN value, NACE compliance, mechanical strength and chemical durability have made it a serious alternative to austenitic stainless steels. Especially in fields where titanium or nickel-based super alloys create difficulty in terms of cost and machinability, F55 is an economically and technically applicable solution.
Key Factors in Purchasing and Project Selection
In purchasing processes it is recommended that AISI F55 be assessed against the following criteria:
- Whether the service environment contains corrosive components such as chlorine, H₂S or CO₂.
- Whether NACE MR0175 or ISO 15156 compliance is required.
- The forming, weldability and heat treatment conditions of the material.
- Availability in stock and delivery times.
- Process temperature and expected behaviour under mechanical load.
#1.4501
#UNSS32760
#X2CrNiMoCuWN25-7-4
#ASTMA182 F55
#ASTMA276 F55
#ASTMA479 F55
| Chemical Properties | Min. | Max. | | Mechanical Properties | Value |
|---|---|---|---|---|---|
| C | - | 0.030 | | Tensile Strength (MPa) | 860 |
| Mn | - | 1.00 | | Proof Stress (MPa) | - |
| Si | - | 1.00 | | Elongation A50 mm | 16 |
| P | - | 0.030 | | Hardness Brinell | 270 Max HB |
| S | - | 0.010 | | Density | 7.90 g/cm3 |
| Cr | 24.00 | 26.00 | | Melting Point | - °C |
| Ni | 6.00 | 8.00 | | Modulus of Elasticity | 200 Gpa |
| N | 0.20 | 0.30 | | Electrical Resistivity | 2,2 x10^-6 Ω .m |
| Mo | 3.00 | 4.00 | | Thermal Conductivity | 15.0 W/m.K |
| Cu | 0.50 | 1.00 | | Thermal Expansion | 13.0 x10^-6 /K |
| W | 0.50 | 1.00 | | |
We supply this material
We supply AISI F55 (1.4501) — in the dimensions and forms required. For stock availability and pricing:
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