Duplex Stainless Steel

Duplex stainless steel mean that mixed micro structure of about equal portion of austenite and ferrite. Duplex are family of grade combining good corrosion resistance with high strength and easy fabrication.

Modern duplex steels can be divided into five groups:

• Lean duplex such as 2304, which contains no deliberate Mo additions;

• Standard duplex such as 2205, the workhorse grade accounting for more that 80% of duplex use

• Super duplex by definition is a duplex stainless steel has 25% chromium or more and have pitting corrosion equivalent (PRE) > 40, PRE = %Cr + 3.3(%Mo+0.5%W) + 16(%N). Common examples are S32760 (Zeron 100), S32750 (2507) and S32550 (Ferralium), but not all ferralium are super duplex grade.

• Hyper duplex, defined as a highly alloyed duplex stainless steel  with PREN in excess of 45

Base on microstructure view, by adding nickel the crystallographic structure change from ferritic body-center cubic (BCC) to austenitic face-center cubic  (FCC) at least 6% nickel.

Increasing the nickel content change the microstructure of stainless steel from feritic to duplex to austenite.

Especially for super duplex stainless steel below a video which will help to understand its materials was made.

Some  application of duplex are fitting, steel pipe, marine chemical tank.

For more in detail explanation regarding duplex stainless steel may find in link below:

Practical Guidelines for the Fabrication of Duplex stainless steel