The 3rd generation DSS is super duplex stainless steel (SDSS) of an ultra-low carbon, high molybdenum and high nitrogen content which developed in the late 1980s. Its representative grades are 2507, 2906, 2707, etc. The PRE value is large today, we mainly talk about the largest and most common 2205 duplex steel (international grades are UNS S31803 and UNS S32205). Generally, duplex steel refers to the 2205 grade without special instructions.
Advantages of austenite + ferrite two-phase duplex steel
Duplex steel is formed on the basis of 18-8 austenitic stainless steel, which increases the Cr content or adds other ferrite elements, so that the steel has austenite and ferrite biphasic structure, and saves nickel.
The theoretical ratio is 1:1, which is approximately 50%. Generally, a certain phase is 40~60%.
Under low stress, chromium-containing dual-phase steel has good resistance to chloride stress corrosion and good pitting corrosion resistance. In general, the pitting and crevice corrosion resistance of duplex steels exceeds 316L. Due to the excellent corrosion resistance and strength required. According to the statistics, the amount of 2205 has increased by at least 15 times in the past ten years.
The comprehensive mechanical properties are good, with high strength and fatigue strength, and the yield strength is twice that of 18-8 austenitic stainless steel. Therefore, the thickness of the material can be reduced in design.
About the application market of duplex 2205 pipe
Duplex pipe is widely used in various fields due to its unique advantages. It is summarized as follows:
Pulp and paper industry: The pulp and paper industry is the first processing industry to duplex steel. The use of dual-phase steel instead of 304 and 316 austenitic stainless steel sulphuric acid and sulphuric acid cooking pots improves the corrosion resistance and strength of the steamer, while reducing the wall thickness and reducing the total weight of the steamer. This is also an important market for the inventor of 2205 duplex steel, Outokumpu, Sweden.
Chemical processing industry: The chemical processing industry has a wide range of applications and complicated working conditions. Storage tanks for the preservation of industrial wet process phosphoric acid are usually made of 316L or 317L type austenitic stainless steel, but the walls are thick. With duplex steel 2205, the strength is almost double that of 316L and 317L, and the wall thickness can be reduced, thereby reducing the importance and cost of the tank. At the same time, in the industrial sulfuric acid environment, especially in the presence of chloride ions, 2205 has better local corrosion resistance than ordinary austenitic stainless steel.
Refining industry: The refining industry is one of the fields that use more duplex steels. It is mainly used in atmospheric and vacuum distillation.