Duplex stainless steel is composed of grains of two types of stainless steel material, austenitic and ferritic. The word "duplex" is said because they have a two-phase microstructure consisting of grains of ferritic and austenitic stainless steel. The stainless steel grades have approximately equal proportions (i.e. 50%) in each duplex stainless steel. Duplex alloys have higher strength and better stress corrosion cracking resistance than most austenitic alloys and greater toughness than ferritic alloys, especially at low temperatures. It is a type of steel that has two separate but equal carbon sheets of steel. When duplex stainless steel is melted, it solidifies from the liquid phase to a completely ferritic structure. 

As the material cools to room temperature, about half of the ferritic grains transform to austenitic grains. Duplex steel was developed to exploit the desirable properties of both austenitic and stainless steel. Duplex steels also exhibit better flexibility and toughness compared to ferritic stainless steels, but both the steel does not provide these properties as successfully as austenitic stainless steels do. Due to duplex steel's lower molybdenum and nickel contents, its rates are lower than the austenitic and ferritic grades.

Some benefits of duplex stainless steel include:

  • Duplex stainless steel is two times stronger than ferritic or austenitic stainless steel grades.
  • Higher toughness and ductility.
  • It shows very good resistance from stress corrosion cracking.
  • Cheaper than the austenitic stainless steel material because the nickel and molybdenum alloy content is less in duplex stainless steel than austenitic stainless steel.

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