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Modern Duplex Steels

By adding Ni to a ferritic chromium steel the structure will change and become a mixture of ferrite and austenite. With increasing Ni, the proportion of austenite increases. The content of Cr is 18 – 28% and Ni 4 – 7%. This results in 20 – 75% austenite, depending on the amount of other alloying elements. Duplex steels are not hardenable. They are magnetic in the proportion to the ferrite content.


The modern duplex steels are all ELC grades, and they have excellent corrosion properties. Their yield strength is at least twice as high as for austenitic steels in the annealed condition, while the difference is smaller in the cold-worked condition. They have good weldability. The physical properties offer design advantages. Based on the best characteristics of austenite and ferrite, duplex stainless steels combine mechanical strength with extremely high corrosion resistance. In fact, duplex’s yield strength is considerably superior to that of conventional stainless steels, allowing for lighter constructions, more compact system designs and less welding. In tube applications, for example, duplex’s higher strength lends itself to thinner walls that withstand the same pressure levels as those of conventional steels. Equally important, duplex’s high corrosion resistance ensures signifi cantly more uptime than carbon steels and conventional stainless steels. Taking into account duplex stainless steels’ favorable long-term life-cycle costs, duplex costs less, sometimes much less, than competing materials. That’s why duplex stainless steels also make financial sense.


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