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Special Piping Materials is well known for the high-quality Duplex products that we source and stock for our discerning clients around the world. We can provide a whole range of different products in duplex, including specialist fittings & flanges, pipe, plate, sheet, tube and bar.
For more information about our Duplex Stainless Steel range of products, please contact your local Special Piping Materials sales adviser today.
Duplex stainless steel is a very useful metal that is used the world over. It gets its name from the fact that it consists of two different grades of metal.
Essentially, Duplex is a Fe-Ni-Cr alloy that has a two-phase ferritic-austenitic stainless-steel microstructure when it is at room temperature.
Duplex steels are characterised by high chromium (19–28%) and molybdenum (up to 5%) and lower nickel contents than austenitic stainless steels. The most used duplex stainless steels are the 2205 (22% Chromium, 5% Nickel) and the 2507 (25% Chromium, 7% Nickel); 2507 is known as “super duplex” due to its higher resistance to corrosion.
The advantage of combining ferritic and austenitic grades is that the resultant metal has a metallurgical structure that consists of two phases and therefore benefits from the properties of both microstructures.
These properties make duplex steel highly sought after in heavy industries, like oil and gas nuclear and chemical processing.
The origin of Duplex steels can be traced back to the 1920s, with the first cast being made in Sweden in 1930. However, the popularity of using duplex only started to rise around 30 years ago when steelmaking technology became more advanced.
The two types of metals used to make Duplex – austenitic and ferritic – are both fit for purpose in many types of scenarios but they both have weaknesses that prevent them from being used more widely.
Austenitic has a low strength and a low resistance to stress corrosion cracking, while ferritic also has a low strength, poor weldability and poor low temperature toughness.
Producing a chemical composition that combines austenitic and ferritic results in a metal that has a higher strength, good weldability, good toughness and resistance to stress corrosion cracking.
The high strength of duplex stainless steel means that The range of 0.2% PS for current duplex grades is from 400 – 550 MPa. This can lead to reduced section thicknesses and, subsequently, reduced weight. This advantage is particularly significant for applications such as pressure vessels, storage tanks and structural Applications like bridges.
However, one of the negatives is that Duplex is brittle at extreme temperatures which means that its use is normally restricted to a maximum temperature of 300 degrees and minimum temperature of –50 degrees.
When creating duplex stainless steels, the aim is to produce a 50/50 mixed microstructure of austenite and ferrite metals, although, in commercial alloys, the mix may be 40/60 respectively.
Interestingly, it is considered that we are still very much in the development phase of duplex steels, as different ratios of austenitic vs ferritic metals are still being tested.
Duplex stainless steel has an array of various benefits such as:
The extensive benefits of Duplex stainless steel mean that it can be used in many different are used in:
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