Duplex Stainless Steels
Duplex stainless steels have high chromium and low nickel contents. This gives duplex stainless steels microstructures that include both austenitic and ferritic phases. They include alloys like 2304 and 2205. These alloys are so named due to their respective compositions - 23% chromium, 4% nickel and 22% chromium, 5% nickel.
By having both austenite and ferrite in the microstructure, duplex stainless steels feature properties of both classes. Although a compromise between the two ‘pure’ types, duplex grades can offer some unique property solutions. Duplex grades are resistant to stress corrosion cracking, but not to the same level as ferritic grades. The toughness of duplex grades is superior to that of the ferritic grades – but inferior to that of the austenitic grades.
Most importantly, the corrosion resistance of duplex steels is equal, or superior to 304 and 316 stainless steel. This is particularly so for chloride attack.
Duplex grades are readily welded. They also have high tensile strengths.
Duplex Stainless Steel Applications
Duplex stainless steels typically find application in areas like:
- Heat exchangers
- Marine applications
- Desalination plants
- Food pickling plants
- Off-shore oil & gas installations
- Chemical & petrochemical plant