Duplex stainless steel organization ferrite and austenite phase each accounted for 50%, were generally is least a youthful appearance also need to be as high as 30%. The development of duplex stainless steel in the 1930 s, when is to solve high carbon austenitic stainless steel intergranular corrosion problems. So far, duplex stainless steel have been developed to the third generation:
1, the first generation: in the United States in the 1940 s the development of type 329 stainless steel, heat exchanger pipe is widely used in nitric acid unit. In the mid - 1960 - s, the Swedish developed specifically for improve the resistance to chloride corrosion fracture of 3 re60 type dual phase steel (00 cr18ni5mo3n), but because the carbon content is higher, generally used for castings and forgings.
2, the second generation: since the 1970 s, as the secondary refining technology (AOD), vacuum refining technology (VOD) and the widespread development of continuous casting technology, ultra-low carbon (C) 0.03% or less (w) of steel production is easy to implement, 00 cr22ni5mo3n is representative of the second generation of duplex stainless steel. The steel grade in the 1970 s, is developed by the Swedish material grades for SAF 2205, corresponding to the American brand for UNS S31803.
3, the third generation: in the late 1980 s, developed the third generation of duplex stainless steel, the main brands have SAF2507 etc. Characterized by low carbon, high molybdenum, high nitrogen (w (C) = 0.01% ~ 0.02%, w (Mo) = 4.0%, w (N) = 0.3%), excellent resistance to pitting corrosion performance, pitting resistance equivalent PREN more than 40.
In the 21st century, duplex stainless steel is mainly in two directions: one is the section nickel, such as S32101, S32003 steel, the steel has good corrosion resistance, but also has lower production cost, substitute for 304, 316 stainless steel. Second, more corrosion resistance, such as 2507, 2906 super duplex stainless steel and so on, with good resistance to pitting corrosion, stress corrosion resistance, alternative 904 l austenitic stainless steel, nickel base alloy, etc.
