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These are stainless steels containing relatively high chromium (between 18 and 28%) and moderate amounts of nickel (between 4.5 and 8%). The nickel content is insufficient to generate a fully austenitic structure and the resulting combination of ferritic and austenitic structures is called duplex. Most duplex steels contain molybdenum in a range of 2.5 - 4%. Basic properties - high resistance to stress corrosion cracking
- increased resistance to chloride ion attack
- higher tensile and yield strength than austenitic or ferritic steels
- good weldability and formability
Common uses - marine applications, particularly at slightly elevated temperatures
- desalination plant
- heat exchangers
- petrochemical plant
Common duplex grades and their applications Common Name | UNS No | Forms Available* | Typical Compositions (%) | Typical Applications | | | | C | Cr | Ni | Mo | N | Cu | W | | + | S32304 | Sheet, Plate, Pipe, Fittings | 0.03 | 23.0 | 4.0 | - | 0.1 | - | - | Similar corrosion resistance to 316L. Higher yield strength and stress-corrosion cracking resistance. Used where high corrosion resistance is required in marine, mining, chemical, food and power industries. Particularly useful in nitric acid. | 2205 | S31803 S32205 | Plate, Pipe, Bar, Fittings | 0.03 | 22.0 | 5.5 | 3.0 | 0.14 | - | - | Superior corrosion resistance to 316L and 317L, combined with high strength. Excellent stress corrosion and abrasion resistance. Typically used in heat exchangers, gas scrubbers, fans, chemical tanks, flowlines, marine and refinery applications. | + | S32550 | Plate, Sheet, Pipe, Bar, Fittings | 0.03 | 25.0 | 5.5 | 3.0 | 0.15 | 2.0 | - | Excellent resistance to corrosion by seawater, acids and salts combined with high strength, abrasion resistance and weldability. | + | S32750 | Plate, Pipe, Bar, Fittings | 0.03 | 25.0 | 7.0 | 4.0 | 0.3 | - | - | Extremely high resistance to corrosion in severe marine, chloride and acid environments. Suitable for heat exchangers, reactors, pipework etc. | + | S32760 | Plate, Pipe, Bar, Fittings | 0.02 | 25.0 | 7.0 | 3.5 | 0.25 | 0.7 | 0.7 | + | S32520 | Plate, Pipe, Bar, Fittings | 0.02 | 25.0 | 6.5 | 3.5 | 0.25 | 1.6 | - | * Compatible or equivalent grades also available in castings.
+ Proprietary alloy names apply. |
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