Duplex Stainless Steel

1, The composition of duplex stainless steel
Duplex Stainless Steel (Duplex Stainless Steel, referred to as DSS), refers to the ferritic and austenitic each accounted for about 50%, the general content of the lesser phase of the stainless steel needs to reach a minimum of 30%. In the case of low C content, Cr content of 18% to 28%, Ni content of 3% to 10%. Some steel also contains Mo, Cu, Nb, Ti, N and other alloying elements.
2、Classification of duplex stainless steel
The first category is low alloy type, representative grade UNS S32304 (23Cr-4Ni-0.1N), the steel does not contain molybdenum, PREN value of 24-25, in terms of stress corrosion resistance can be used instead of AISI304 or 316.
The second category is medium alloy type, the representative grade is UNS S31803 (22Cr-5Ni-3Mo-0.15N), PREN value of 32-33, its corrosion resistance between AISI 316L and 6% Mo + N austenitic stainless steel.
The third type of high alloy type, generally containing 25% Cr, also contains molybdenum and nitrogen, some also contain copper and tungsten, standard grade UNSS32550 (25Cr-6Ni-3Mo-2Cu-0.2N), PREN value of 38-39, the corrosion resistance of this type of steel is higher than that of the duplex stainless steel 22% Cr.
The fourth category is super duplex stainless steel type, containing high molybdenum and nitrogen, standard grade UNS S32750 (25Cr-7Ni-3.7Mo-0.3N), some also contain tungsten and copper, PREN value is greater than 40, can be applied to harsh media conditions, has a good corrosion resistance and mechanical properties, can be compared with the super austenitic stainless steel.