Super duplex stainless steel(SDSS) refers to the duplex stainless steel with prEN > 40, 25% Cr and high molybdenum (> 3.5%) and high nitrogen (0.22% ～ 0.30%). The main brands are UNS S32550 (ur52n +), S32750 (SAF 2507) and S32760 (zeron 100). They were developed by cli in France, Sandvik in Sweden and mater + Platt in England. The composition of these three steels is similar.