What are duplex stainless steels?

At the beginning of the 20th century, metallurgists discovered that they could prevent the rusting of steel by adding chromium in a percentage close to 10%. That’s how stainless steel was born.

Today, stainless steel is one of the most widely used metal compounds in the world, not only because of its high resistance to atmospheric corrosion, but also because it is easily shaped, aesthetically pleasing and very durable.

Within the family of stainless steels, there are various categories that differ in composition. Thus we find austenite, ferrite, martensite or duplex stainless steel. Today we will focus our attention on this last category, duplex.

Duplex steel

Duplex is one of the most resistant steels, resisting corrosion as well as traction and compression. Its chrome content is between 18 and 26%, while nickel makes up between 4.5 and 6.5%. The incorporation in the mixture of elements such as nitrogen, silicon, tungsten, molybdenum or copper makes its durability even greater.

Duplex steel is so called because of its equal proportions of ferrite and austenite.

  • Ferrite is one of the crystalline structures of iron, specifically those crystallized in cubic systems. It is also known as “iron-α” (alpha). One of its main uses is in the manufacture of magnets, due to its marked magnetic properties.
  • On the other hand, austenite, also known as “gamma iron” (γ), is a specific arrangement of the carbon and iron atoms that allows the iron to accept more dissolved carbon. Austenite is not ferromagnetic at any temperature, unlike ferrite.

Properties of Duplex Steel

Thanks to this composition, duplex stainless steel has the following characteristics:

  • High resistance to both genreal surface and crack corrosion, the types that usually occur in contact areas between parts
  • Great strength, being one of the strongest steels; it is very difficult to fracture, either by fatigue or by corrosion under stress.
  • Magnetism
  • Great tensile strength, in a measure far superior to standard steels
  • An elastic limit twice that of other types of steel, such as austenitic
  • Very high mechanical strength
  • Great tenacity, higher than that of ferritic steels
  • Low thermal expansion
  • Hardness that cannot be increased by heat treatment
  • Excellent workability and weldability, much more than ferritic steels, although less than austenitic steels

 Uses of Duplex Steel

Because of these qualities, duplex steel is a very adaptable material, allowing it to be transformed in ways that meet specific needs. This fact, coupled with its resistance and hardness, makes it one of the most commonly used raw materials for manufacturing parts in industry.

Duplex Steel, an Industry Leader

Due to its high corrosion resistance, duplex steel is used in many industries, such as the manufacture of industrial fans, rotors, shafts and drives. It is also used in refineries, chemical tanks and gas treatment plants.

On the other hand, its high elasticity makes it a perfect material for the construction of infrastructure elements such as bridges, while its ease of cleaning and excellent sanitizability have led to its widespread use in the food industry.

In short, duplex steel is a very versatile material, without which many industries would have to reinvent themselves.