Duplex steel has a two-phase microstructure, which consists of ferrite and austenite. The steel belongs to the group of rust and acid-resistant steels. This steel has two particularly good properties. That steel grade has a higher strength than rustproof chrome-nickel steel and a higher ductility or malleability than rust-proof chromium steel.
The distinctive properties of Duplex steel are its high resistance to surface corrosion, local corrosion and stress corrosion cracking. The structure of this steel has a very high resistance to corrosion fatigue, energy absorption, erosion and attrition, it has low thermal expansion and has good weldability properties. Due to its high resistance to corrosion in general and surface corrosion, Duplex steel is mainly used in the chemical industry, the petrochemical industry, for seawater desalination plants and in offshore engineering.
Duplex steel can be welded with any standard type of welding. However, one exception is gas welding (oxy-acetylene welding). The workpieces to be welded should not have any signs of stresses or dirt and must be bright. They are welded with the least possible introduction of heat.
As Duplex steel has a high strength, machining work also set higher tool requirements. The best method for cutting is to use laser or plasma cutting machines. If the steel is to be sawn, attention must be paid to strong guiding of the saw blade, low cutting speed, strong feed and high flow of coolant. Cutting with shears is also only possible with very high forces.
There are different grades of Duplex steel, which are divided into different groups. These include, among other things:
is not alloyed with molybdenum and is available in steel grades 1.4482, 1.4162, 1.4062, 1.4362 and 1.4655.
has excellent resistance to corrosion and is the most die commonly usable variant. This steel is designated 1.4462, Duplex with 25% chromium is designated 1.4507.
is available in grades 1.4410, 1.4501 and 1.4477. The very high corrosion resistance is achieved by adding molybdenum. Its high strength and chloride resistance enables it to be used in diverse seawater applications.