Duplex stainless steel is a kind of stainless steel material. They are called biphasic (or austenite-ferrite) because their metallurgical structure consists of two phases, with almost equal proportions of austenite and ferrite. These materials have improved corrosion resistance, particularly chloride stress corrosion and chloride pitting, and have higher strength than standard austenitic stainless steels such as SS304 or SS316. Compared with austenitic stainless steel, the main difference in composition of duplex steel is the chromium content of 20-28% higher; Molybdenum content is high, up to 5%; The nickel content was reduced to 9% and the nitrogen content was reduced to 0.05-0.50%. Both low nickel content and high strength are significantly cost effective.