The main advantage of duplex stainless steel is its cost-effective performance. At its typical pricing point, no obvious alternative matches its combination of high strength and excellent corrosion resistance. Its main limitations are at temperature extremes.
Advantages
Duplex stainless steels are based on a mixed microstructure of austenite and ferrite. They combine the most favourable properties of austenitic grades (good corrosion resistance, good impact toughness, ready fabrication) and ferritic grades (high strength, resistance to stress corrosion cracking), while limiting the content of expensive alloying elements such as nickel and molybdenum.
Their high strength means you can usually do more with less: a thinner section of duplex stainless steel can meet the same demands as a thicker section of austenitic stainless steel.
Duplex grades also have good weldability with all standard welding processes, although they are not as easily welded as the austenitic grades.
Disadvantages
For many applications, duplex stainless steel is the optimum choice for corrosion resistance, strength and cost. There are two main disadvantages:
- Impact toughness is worse at very low temperatures, so duplex grades are not specified for applications below -50°C.
- Their use is limited above 250°C, due to the potential formation of deleterious intermetallic phases during extended exposure. These phases can also form during welding, but well-developed welding procedures avoid the issue.