What is the difference between stainless steel and super duplex stainless steel?

A stainless steel is a type of steel that resists corrosion. The composition of a steel product is based upon iron, and a stainless steel needs at least 11.5% chromium in order to resist general corrosion. Therefore, steels with more than 11.5% chromium content are known as stainless steels.

There are several families of different stainless steels, categorised by their microstructure and properties. For instance, there are austenitic, ferritic and martensitic (precipitation hardened) stainless steels defined by their internal microstructure – which largely defines their physical properties.

Austenitic stainless steels generally provide excellent corrosion resistance, good mechanical properties over a wide range of operating temperatures, including low temperature toughness, and are non-magnetic. Ferritic stainless steels are generally of lower corrosion resistance, and lower cost, but do resist stress corrosion cracking. Martensitic stainless steels are generally very high strength.

Duplex stainless steels have a balance of austenitic and ferritic microstructures, which gives them a favourable combination of mechanical and physical properties. The first duplex stainless steels were developed around a content of 22% chromium. However, to increase strength and corrosion resistance the chromium level was increased to 25%. Duplex stainless steels with a chromium level of 25% are referred to as super duplex stainless steels. It is possible to increase their strength and corrosion resistance further by increasing their chromium content as high as 32%, in which case they are referred to as hyper duplex stainless steels.

Langley Alloys carries an extensive range of duplex stainless steels, super duplex stainless steels and high performance austenitic stainless steels.


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