Duplex stainless steel is composed of approximately the same amount of ferrite and austenite stainless steels. Combining both steels into one metal joins the most attractive properties of each one to form a stainless steel family with outstanding characteristics.

Composition

Advances in steelmaking over the last 30 years have led to increased interest in duplex stainless steel. Its microstructure contains grains of both austenitic and ferritic steels which each have a one-phase composition. When the two are combined, a two-phase structure forms the metal to have an austenite-ferrite phase balance.

Properties

The combination of austenitic and ferritic steels forms a steel with very favorable properties.  Duplex stainless steel offers the following properties as compared with austenitic and ferritic stainless steels:

• Higher strength: Twice as strong as austenitic or ferritic stainless steels.
• Ductility and toughness: Better values than ferritic but not as high as austenitic.
• Corrosion resistance: Excellent resistance in most environments and especially resistant to chloride pitting and corrosion. Range is similar to austenitic stainless steel.
• Weldability: Good in thick sections and better than ferritic.
• Stress corrosion cracking: Very good resistance and better than austenitic when exposed to chlorides, high temperatures, or humidity.
• Cost: lower nickel and molybdenum contents reduce the cost of duplex as compared to austenitic and ferritic steels.

Benefits

Because of Duplex’s increased yield strength over austenitic stainless steel, it is possible to reduce section walls of components. This can lead to reduced material costs and weights. In structural applications or in pressure vessels and storage tanks, requiring less material is very cost effective.

Excellent chloride corrosion resistance and resistance to stress corrosion cracking make duplex ideal for applications such as hot water or brewing tanks, process plant tanks and piping, oil and gas piping, and swimming pool structures.

The favorable properties of duplex stainless steel made it a candidate for use in a wide variety of industries and applications. Fabricating duplex is similar to other stainless steels and it is currently being used in industries such as desalination, food, pulp and paper, oil and gas, and building and construction.