DUPLEX/ SUPER DUPLEX

Duplex stainless steels have a mixed structure of austenite and ferrite, the aim generally being to produce a 50/50 mix, although in commercial alloys the ratio can be 40/60.
Duplex steels have improved strength over stainless steels and also in terms of resistance to localized corrosion, mainly from pitting and stress corrosion cracking.
Duplex alloys are categorized into groups based on their alloy content and corrosion resistance. Known as Duplex Lean, it refers to series such as the UNS S32101 (LDX 2101), S32304 and S32003. The standard duplex is 22% chromium, with 2205 S31803/S32205 known to be the most commonly used. Super duplex refers to 25% chromium grades such as S32760 (ZERON 100), S32750 (2507), and S32550 (Ferralium).
Hyper Duplex refers to higher grades of chromium as S32906. The properties of duplex stainless steels are obtained with an overall lower alloy content similar to super-austenitic performance grades, making their use economical for many applications.