Advantages and disadvantages of Duplex Stainless Steels

Duplex stainless steels are becoming more common. They are being offered by all the major stainless steel mills for a number of reasons: Higher strength leading to weight saving, Lower price, Better price stability, and Greater corrosion resistance particularly stress corrosion cracking

The basic idea of duplex is to produce a chemical composition that leads to an approximately equal mixture of ferrite and austenite. This balance of phases provides the following: Higher strength – The range of 0.2% PS for the current duplex grades is from 400 – 550 MPa. This can lead to reduced section thicknesses and therefore to reduced weight. Good weldability in thick sections – Not as straightforward as austenitics but much better than ferritics. Good toughness – Much better than ferritics particularly at low temperature, typically down to minus 50 deg C, stretching to minus 80 deg C. Resistance to stress corrosion cracking – Standard austenitic steels produced by duplex steel fittings manufacturers are particularly prone to this type of corrosion.

The attractive combination of high strength, wide range of corrosion resistance, moderate weldability would seem to offer great potential for increasing the market share of duplex stainless steels. However, it is important to understand the limitations of duplex steel flange supplies and why they are always likely to be “niche players”.

The advantage of high strength immediately becomes a disadvantage when considering formability and machinability. The high strength also comes with lower ductility than austenitic grades. Therefore, any application requiring a high degree of formability, for example, a sink, is ruled out for duplex grades. Even when the ductility is adequate, higher forces are required to form the material, for example in tube bending. There is one exception to the normal rule of poorer machinability, grade 1.4162. Stainless steel forged flanges Wholesale