Duplex stainless steels have a ferritic-austenitic microstructure, in roughly equal proportions 50% ferrite and 50% austenite. Duplex combines many of the attractive properties of ferritic and austenitic stainless steels into one. They are designed to provide better corrosion resistance, in particular to stress corrosion and pitting corrosion. The microstructure leads to higher strength than standard austenitic stainless steels such as Type 304 or 316. Duplex stainless steels have become more and more popular in recent years.