The duplex stainless steels have a microstructure, when heat treated properly, of nearly equal proportions of austenite and ferrite. This microstructure ensures that the duplexes are much more resistant to stress corrosion cracking (SCC) than austenitic stainless steels. The specification 0.2% Proof Stress of the duplexes is more than double that of austenitic stainless steels such as the 304 types andu316L types. This often allows down gauging in the design, depending on Young's Modulus and buckling limitations.

The microstructures inside duplex stainless steels are approximately 50 per cent austenite and 50 per cent ferrite, and consequently duplex products share the physical properties of both ferritic and austenitic grades. Duplex stainless steels are resistant to the cracking caused by chloride stress corrosion in austenitic grades, and have improved resistance to localised corrosion. This family of stainless steels has roughly twice the yield strength of their counterpart austenitic grades which means we can use it to design thinner gauge tubing. Higher hardness values provide better wear resistance for high precision tubes.
Duplex steels are easily welded and formed, similar to austenitic grades. Depending on chromium, nickel and molybdenum content, duplex stainless steels are divided into four main categories: lean duplex, duplex, super duplex and hyper duplex. This family of alloys has great advantages in both material and engineered fabrication costs.

Typical applications for this alloy group include heat exchanger tubes, umbilicals, structural tanks, pulp and paper making equipment, pipes and fittings, and seawater handling systems.