The main feature is that the yield strength can reach 400-550mpa, which is 2 times of ordinary stainless steel, so it can save material and reduce the cost of equipment manufacturing. In terms of corrosion resistance, especially in the harsh medium environment (such as seawater, high content of chloride), the pitting corrosion resistance, gap corrosion, stress corrosion and corrosion fatigue performance of duplex stainless steel is obviously better than ordinary austenitic stainless steel, can be comparable to high alloy austenitic stainless steel.

Steel gradeC≤Mn≤Si≤S≤P≤Cr≤NiMoCu≤N

Steel grade


Duplex stainless steel

The first type is the low alloy type, representing the UNS S32304(23cr-4ni-0.1n). It contains no molybdenum in steel, has a PREN of 24-25, and can be used in place of AISI304 or 316 in stress corrosion resistance.

The second type is medium alloy, representing UNS S31803(22Cr-5Ni-3Mo-0.15N) with a PREN value of 32-33. Its corrosion resistance is between AISI 316L and 6%Mo+N austenitic stainless steel.

The third category is high alloy type, generally containing 25%Cr, but also contains molybdenum and nitrogen, some also contain copper and tungsten, the standard brand UNSS32550(25Cr-6Ni-3Mo-2Cu-0.2N), PREN value is 38-39, the corrosion resistance of this kind of steel is higher than 22%Cr duplex stainless steel.

The fourth category is super duplex stainless steel, containing high molybdenum and nitrogen, standard 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 medium conditions, has good corrosion resistance and mechanical synthesis, can be comparable to super austenitic stainless steel.