Duplex Stainless Steel Grades

Duplex stainless steel(DSS) has a higher chromium content of 20–28%; higher molybdenum up to 5%, lower nickel up to 9%, and 0.05–0.50% nitrogen in compare with austenitic stainless steel. Duplex stainless steel material is an ideal selection in the aspect of resistance against pitting corrosion. The resistance against pitting corrosion is characterized by the pitting resistance equivalence number, or PREN Number defined as follows:

PREN = %Cr + 3.3 %Mo + 16 %N

Accroding to the PREN Number values, duplex stainless steel is categorized into four grades:

1. Lean duplex stainless steel (PREN range: 22–27): No deliberate Molybdenum addition. Mainly used in the building and construction industry for bridges, pressure vessels, or tie bars. Example: S32001, S32101, S32304, S32202.

2. Standard duplex stainless steel (PREN range: 28–38): The most widely used (More than 80%) duplex stainless steel material with mid-range properties. Eg: S32003, S31803, S32205

3. Super duplex stainless steel (PREN range: 38-45): Higher contents of Cr, Ni, Mo, N, and even W.  Specifically designed for highly corrosive oil&gas and chemical industries. Such as S32750, S32760, S32950, S32808.

4. Hyper duplex stainless steel (PREN >45): These are highly alloyed duplex stainless steel. For example: S32707, S33207

Common Duplex Stainless Steel Material Grades