Duplex stainless steel includes mixed microstructure with about equal proportions of ferrite and austenite. After its first generation, duplex Stainless steel pipe has become more and more popular. Nowadays, high-strength and corrosion resistant super-duplex coil has been produced to apply in the marine and chemical industries, architecture, wire lines, lifting and pulley equipment and so on.

Today, modern duplex stainless steel can be divided into four groups:
Lean Duplex such as 2304, which contains no deliberate Mo addition;
2205, the work-horse grade accounting for more than 80% of duplex usage;
25 Cr duplex such as Alloy 255;
Super-Duplex, with 25-26 Cr and increased Mo and N compared with 25 Cr grades.