The main advantage of duplex stainless steel is its ability to provide extremely cost-effective performance compared with a wider range of alloys. At its typical pricing point, there are no obvious alternatives that can match its high strength and excellent corrosion resistance.
Duplex stainless steels are based upon a mixed microstructure of austenite and ferrite. They combine the most favourable properties of austenitic stainless steels (good corrosion resistance, good impact toughness, ready fabrication) and ferritic stainless steels (high strength, resistance to stress corrosion cracking) whilst limiting the content of expensive alloying elements such as nickel and molybdenum.
As duplex stainless steels provide high-strengths, you can usually do more with less. This means that a thinner section of duplex stainless steel can meet the same demands as a thicker section of austenitic stainless steel.
Duplex stainless steels also tend to have good weldability with all standard welding processes usable although they are not as easily welded as the austenitic grades.
For many applications, duplex stainless steel is the optimum choice for corrosion resistance, strength and cost. However, there are two main disadvantages of these alloys. Firstly, their impact toughness is worse at very low temperatures, so they are not specified for applications below -50degC. Similarly, their use is limited in applications > 250degC, due to the potential formation of deleterious intermetallic phases if exposed for extended periods. These seem phases can form during welding, but well-developed welding procedures are able to avoid such issues.
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