Super Duplex Stainless Steel

Super duplex stainless steel is a subgroup of duplex stainless steels that has a higher alloy content, especially in chromium, molybdenum, and nitrogen. It has a microstructure made up of both austenitic and ferritic grains of steel.

Super Duplex Stainless Steel is more corrosion resistant and has higher mechanical strength than other stainless steels. It’s also known for its high strength and excellent corrosion resistance

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Category: Duplex & Super Duplex Steel Tag: Super Duplex Stainless Steel

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Super-Duplex Stainless Steels and their characteristics

The first-generation Duplex stainless steels were developed more than 70 years ago in Sweden for use in the sulfite paper industry. Duplex alloys were originally created to combat corrosion problems caused by chloride-bearing cooling waters and other aggressive chemical process fluids. Called Duplex because of its mixed microstructure with about equal proportions of ferrite and austenite, Duplex stainless steels are a family of grades, which range in corrosion performance depending on their alloy content. The term “Super-Duplex” was first used in the 1980’s to denote highly alloyed, high-performance Duplex steel with a pitting resistance equivalent of >40 (based on Cr% + 3.3Mo% + 16N%). With its high level of chromium, Super-Duplex steel provides outstanding resistance to acids, acid chlorides, caustic solutions and other environments in the chemical/petrochemical, pulp and paper industries, often replacing 300 series stainless steel, high nickel superaustenitic steels and nickel-based alloys.

The chemical composition based on high contents of chromium, nickel and molybdenum improves intergranular and pitting corrosion resistance. Additions of nitrogen promote structural hardening by interstitial solid solution mechanism, which raises the yield strength and ultimate
strength values without impairing toughness. Moreover, the two-phase microstructure guarantees higher resistance to pitting and stress corrosion cracking in comparison with conventional stainless steels.