Duplex stainless steels have a two-phase microstructure with approximately 50% austenite and 50% ferrite. Chemical composition is typically 21 – 25% chromium, 1 – 7% nickel, 0.10 – 0.27% nitrogen and, if used, 1.5 – 4% molybdenum.
Hyperduplex stainless steels are even higher alloyed with up to 32% chromium and 9% nickel. The most common duplex steel is 2205 (1.4462 / S32205, S31803).
Due to the high content of chromium, nitrogen and additions of molybdenum, duplex stainless steels are characterized by their high resistance to pitting and crevice corrosion. For example, the pitting resistance of 2205 is significantly higher than that of 316L.
All modern types of duplex stainless steels are produced with low carbon content. This and the favorable microstructure, make them resistant to sensitization to intergranular corrosion. The duplex microstructure also contributes to high resistance to stress corrosion cracking.
Duplex stainless steels combine the properties of ferritic and austenitic steels. The yield strength is up to twice as high as for austenitic steels with similar pitting corrosion resistance and the ductility is higher as compared to ferritic steels.
For more information about the weldability, take a look at our Stainless Steel Handbook.