The two phase microstructure led to the name Duplex.  The microstructure consists of grains of ferritic and austenitic stainless steels.  When Duplex stainless steel melts it hardens from this liquid phase into a completely ferritic structure.  As it cools to room temperature approximately half of these ferritic grains change into austenitic grains.  The result is that Duplex stainless steel contains about half of each material, ferrite and austenite.

This Duplex structure gives this particular family of stainless steel its much applauded properties.  For one it provides about twice the strength of regular ferritic or austenitic stainless steels.  Duplex stainless steels also provide much higher levels of toughness and ductility over ferritic grades. They don’t, however, match these superior properties provided in austenitic grades of stainless steel.

Superior Qualities

While all stainless steels offer resistance to corrosion, the levels depend on their individual compositions.  If chloride pitting or crevice resistance is required then they must contain in their composition a mixture of chromium, molybdenum and nitrogen.  Duplex stainless steel has corrosion resistance levels that are similar to austenitic stainless steels.  For instance from types 304 or 316 grades to 6% molybdenum stainless steels.

Duplex grades have excellent resistance to stress corrosion cracking.  This is a property that has been inherited from their ferritic makeup.  While austenitic stainless steels provide superior corrosion resistance, ferritic stainless steel provides superior stress cracking resistance.

Due to the lower nickel and molybdenum composition, Duplex stainless steels can be lower in cost.  Apart from this and due to their yield strength, it is often possible to reduce the thickness.  The combination of these two factors offers not only cost savings, but also savings in relation to weight – especially when compared to austenitic stainless steels.

Duplex stainless steel can be found here at Chemipetro, one of the UK’s leading manufacturers of pipe fittings and flanges, for reasonable prices.