This chapter is devoted to duplex stainless steels (DSSs). This chapter begins with an introduction to the different types of DSSs (ordinary, lean, superduplex and hyperduplex), their applications and compositions of the commonly used grades. Their typical microstructures and methods for phase prediction via different constitution diagrams are discussed. The precipitate phases that may form in DSSs and their implications on mechanical/corrosion properties are presented (a more in-depth discussion on these precipitates is presented in Chapter 8). The superplasticity of DSSs is discussed in detail. Both the conventional method and a new one for producing the microduplex structure are introduced. Recent developments in explaining the underlying mechanisms leading to the superplastic behaviour in DSSs are discussed.
Keywords: Duplex stainless steel, wrought duplex stainless steel, cast duplex stainless steel, superduplex stainless steel, hyperduplex stainless steel, lean duplex stainless steel, microduplex microstructure, superplasticity, phase prediction, constitution diagram, ferrite potential, ferrite factor.