Duplex stainless steel was first created in order to address corrosion problems stemming from chloride bearing cooling waters or other chemical process fluids.

Duplex stainless steel is a family of grades which are ranged in accordance to their corrosion performance, as well as their content of alloy; Duplex’s alloy content being almost equal proportions of ferrite and austenite.

Super Duplex was a term phrased in order to indicate its highly alloyed composition of which provides a pitting resistance of >40.  The chemical composition is based on Cr% + 3.3Mo% + 16N%.

Super Duplex contains very high levels of chromium which provides above average resistance to acids, caustic solutions and acid chlorides.  It also provides high levels of corrosion resistance to any environment which uses chemicals or petrochemical solutions.  It is fast replacing 300 series stainless steel or high nickel super-austenitic steels.

Based on a chemical composition which has high contents of nickel, chromium and molybdenum, Super Duplex improves intergranular and pitting corrosion resistance.  With the addition of nitrogen to promote structural hardening it not only raises yield strength but also strength values without impairing its toughness.

The Various Alloys

Super Duplex stainless steel resides in the group of Duplex stainless steel.  It is graded for its corrosion performance and for its content of alloy.  Duplex can be divided into four groups:

1.    Super Duplex, which contains 25-26Cr and increased Mo and N.  This grade is comparable to 25 Cr and 2507
2.    Lean Duplex stainless steel such a 2304 which contains no added Mo
3.    2205, which is a grade considered the work horse as it accounts for over 80% duplex use
4.    25 Cr duplex.

All of these materials are available from us here at Chemipetro.