Duplex stainless steel is a kind of stainless steel in which ferrite and austenite account for about half of the solid solution structure, or the content of less phases at least needs to reach 30%. On the basis of austenitic stainless steel, duplex stainless steel increases the content of ferrite forming elements Cr, Si, Nb, etc., and reduces the content of austenite forming elements Ni, C, Mn, thus obtaining austenite ferrite duplex structure, which is a nickel saving stainless steel. It has the performance characteristics of both ferrite and austenitic steel, that is, compared with ferrite, it has higher plasticity and toughness, no room temperature brittleness, significantly improved intergranular corrosion resistance and welding performance, while maintaining the 475 ℃ brittleness of ferrite stainless steel, high thermal conductivity, superplasticity and other characteristics; Compared with austenitic stainless steel, it has high strength and is resistant to intergranular corrosion, pitting corrosion and chloride stress corrosion. It has excellent performance in seawater corrosion environment, agricultural production acid and other special medium corrosion environment. In order to further improve the performance of duplex stainless steel, a super duplex stainless steel with better local corrosion resistance to harsh media and welding performance was developed.