It is an alloy characterized by a ferritic-austenitic microstructure, containing approximately 40–50% ferrite in the annealed condition. As such, it effectively combines the high mechanical strength of ferritic steels with the corrosion resistance typical of austenitic grades.

General Properties

It is an alloy characterized by a ferritic-austenitic microstructure, containing approximately 40–50% ferrite in the annealed condition. As such, it effectively combines the high mechanical strength of ferritic steels with the corrosion resistance typical of austenitic grades. this alloy is characterized by a ferritic-austenitic microstructure, containing approximately 40–50% ferrite in the annealed condition. As such, it effectively combines the high mechanical strength of ferritic steels with the corrosion resistance typical of austenitic grades.
In addition, this alloy is recognized as a practical solution for applications where chloride-induced stress corrosion cracking (SCC) is a concern. It also demonstrates superior resistance to pitting and crevice corrosion compared to 317L stainless steel.

Moreover, Duplex F51 delivers remarkable performance in marine environments and in contact with most concentrations of sulfuric acid. It also exhibits resistance to stress corrosion cracking in sour (H₂S-containing) environments.

Corrosion resistance:

UNS S31803 is resistant to intergranular corrosion and offers superior performance compared to austenitic stainless steels such as Type 316. In particular, its resistance to stress corrosion cracking is significantly better than that of 304 and 316 grades, making it ideal for corrosive service where durability and reliability are essential.

Physical Properties:

• Melting temperature: 1420 – 1465 °C
• Density: 7.8 g/cm³
• Specific gravity: 7.8
• Tensile modulus of elasticity: 200 GPa

Mechanical Properties:

Welding

UNS S31803 (1.4462, F51) has good weldability, comparable to other stainless steels. A major advantage is its low thermal expansion coefficient, which helps minimize residual stress after welding.
For optimal results:

• Use matching duplex filler metals
• Suitable for electric arc welding processes
• Oxy-acetylene welding should be avoided due to the risk of carbon contamination
• Post-weld annealing is not mandatory, but may significantly enhance corrosion resistance in demanding applications

Heat Treatment

Although Duplex F51 cannot be hardened by conventional heat treatment, it can be solution-annealed at 1020–1100°C, followed by rapid water quenching. This process ensures an optimal microstructure and enhanced performance in corrosive environments.