Duplex stainless steel

Duplex stainless steel (Duplex steel) is a stainless steel produced by the duplex process. By adding nickel to ferritic chromium steel, a fine-grained microstructure is formed with a base containing ferrite and austenite in almost equal proportions. Duplex steel typically contains chromium and nickel.

Super Duplex steel is a stainless steel that belongs to the group of super steels. It is suitable even for use in outer space. The main difference that characterizes super duplex steel is a large percentage of chromium and molybdenum in its chemical composition. Therefore, acids and alkalis have practically no effect on it. Such steel is completely immune to chlorides. Due to the increased content of alloying elements, super duplex steel is endowed with a number of super characteristics:
- increased resistance to corrosion;
- high mechanical strength;
- better wear resistance, etc.

The main reason for the development of austenitic-ferritic (duplex) stainless steels is the insufficient resistance of austenitic steels to intercrystalline corrosion caused by cooling chloride waters and other aggressive industrial liquids.
The idea of ​​creating such steels originated in the 1920s in France and Sweden. The first smelting was carried out in the Swiss city of Avesta in 1930. The first brand of duplex steel was patented in 1936.
The main reasons for the emergence and increased production of duplex and superduplex steels also include:
- improvement of technology for regulating nitrogen content in steels;
- nickel deficiency;
- rising cost of austenitic steels;
- increased demand as a result of the active construction of oil platforms and rigs, which require steels with increased resistance to corrosion in sea salt water.

The main advantage of duplex and super duplex steels is their increased yield strength compared to simple austenitic steel grades. In addition, austenitic-ferritic steel has the following characteristics:
- increased resistance to pitting and crevice corrosion;
- increased resistance to stress corrosion cracking;
- good corrosion resistance to sulfide stress;
- high mechanical strength;
- good weldability;
- ease of processing;
- low thermal expansion;
- high energy absorption and thermal conductivity;
- increased resistance to corrosion fatigue;
- wear resistance.
Due to the low content of expensive nickel in the composition, the price of duplex is more affordable, which is very important for modern industry.

Duplex and super duplex grades of stainless steel are quite actively and widely used in:
- in the oil and gas industry;
- in the chemical and food industries;
- in pulp and paper production;
- in energy;
- in shipbuilding;
- in mechanical engineering;
- in aviation;
- in the production of equipment and apparatus for working in sulfuric and hydrochloric acids;
- in the production of equipment for seawater desalination;
- in the production of heat exchangers, water heaters, rotors and pressure vessels;
- in the production of tanks for the transportation of chemical products;
- in the production of fire protection partitions on oil platforms;
- it is used to produce reinforcement for metal structures, sheets, strips, angles, wire, etc.

The welding process of material made of two-phase stainless steel is not particularly complicated. However, the temperature during welding must be strictly controlled. Moreover, ignoring this feature, you can miss all the benefits of using this excellent material.
The application of rolling or bending technologies to two-phase duplex steel with a thickness of 7.5 to 10 cm and more may be ineffective, since many grades of duplex steels have a shape memory effect.