Duplex
What is duplex stainless steel?
Duplex stainless steel is a type of stainless steel whose microstructure is made up of both austenitic and ferritic phases, typically in a 50/50 ratio. This combination gives the steel excellent strength and corrosion resistance, making it a popular material for demanding machine workshop applications.
Duplex stainless steel composition and microstructure
The main alloying elements in duplex stainless steel are chromium (about 22–25%) and nickel (about 4–7%), and it often also contains molybdenum, nitrogen, and copper to improve corrosion resistance and mechanical properties. This alloy structure enables the combination of austenitic and ferritic microstructures, which gives the steel its unique properties.
Strength and corrosion resistance of duplex stainless steel
Duplex stainless steels have a high yield strength, which is about twice that of conventional austenitic stainless steels. In addition, their corrosion resistance, especially against stress corrosion cracking, is significantly better—making them suitable for challenging environments, such as structures in contact with seawater.
Use of duplex stainless steel in the machine workshop industry
Duplex stainless steels are widely used in the machine workshop industry due to their excellent strength and corrosion resistance. They are particularly well suited for the needs of the pulp and paper industry, as well as chemical processing equipment where high resistance to corrosive substances is required.
Machinability of duplex stainless steel
The machinability of duplex stainless steel differs somewhat from that of conventional austenitic steels. Its high strength and toughness present challenges for chip control, so it is important to optimize machining parameters and select the right tools to achieve the best results.
Weldability of duplex stainless steel
Duplex stainless steels are very weldable as long as their special characteristics are taken into account in the welding process. It is important to avoid excessively high temperatures and rapid cooling to prevent the formation of unwanted phases that could weaken the steel's properties.
Different types of duplex stainless steel
There are several types of duplex stainless steels, such as lean duplex, standard duplex, super duplex, and hyper duplex, which differ in alloy content and corrosion resistance. For example, super duplex steels offer even better corrosion resistance and strength but are also more challenging to machine due to their higher alloy content.
Summary
Duplex stainless steel combines the best features of austenitic and ferritic microstructures, offering excellent strength and corrosion resistance. Thanks to these properties, it is a popular material in the machine workshop industry, especially for applications where high durability and reliability are required in demanding conditions.
