Duplex stainless steel refers to a stainless steel in which the ferrite phase and the austenite phase account for about half of the solid solution structure. 

Through reasonable composition managing and heat treatment process control, the coexistence of ferrite phase and austenite phase is realized, and the advantages of the two phases are combined, such as the excellent toughness and weldability of austenitic stainless steel, and the difference between ferritic stainless steel and ferritic stainless steel. High strength and resistance to chloride stress corrosion. 

Compared with austenite of the same performance level, it significantly reduces the content of the precious metal elemental of nickle, which is the perfect unity of low cost and high performance. 

Therefore, in recent years, as a weldable structural material, it has been rapidly developed. 

It has become an important part of stainless steel and has been successfully and widely used in many fields such as petroleum, chemical industry, ship building, paper making, seawater desalination, transportation, nuclear power, bridges, building curtain walls, etc.