Duplex and Super Duplex
Duplex is a material that has approximately equal amounts of austenite and ferrite. These combine excellent corrosion resistance with high strength. Mechanical properties are approximately double those of singular austenitic steel and resistance to stress corrosion cracking is superior to type 316 stainless steel in chloride solutions. Duplex material has ductile or brittle transition at approximately -50 degrees. High Temperature use is usually restricted to a maximum temperature of 300 degrees for indefinite use due to embrittlement.
Duplex stainless steels have a mixed microstructure of austenite and ferrite, the aim being to produce a 50/50 mix, although in commercial alloys, the mix may be 40/60 respectively. Duplex steels have improved strength over austenitic stainless steels and also improved resistance to localised corrosion, particularly pitting, crevice corrosion and stress corrosion cracking. They 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 Steel are the 2205 (22% Chromium, 5% Nickel) and 2507 (25% Chromium, 7% Nickel); the 2507 is also known as “Super Duplex” due to its higher corrosion resistance.
Super duplex pipe is known to have better stress corrosion, cracking resistance and mechanical properties. The high corrosion resistance of super duplex pipeline supplies makes them ideal for onshore and offshore environments in oil and gas applications. Please see our industry pages for more information regarding the implications of Super Duplex piping. Super Duplex is an Austenitic Ferritic Iron Chromium – Nickel Alloys with Molybdenum addition. It has good resistance to pitting and a very high tensile strength and high resistance too stress corrosion cracking at moderate temperatures compared to that of conventional austenitic stainless steels.
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