What is Duplex Stainless Steel? Properties and Composition

What is Duplex Stainless Steel?

While traditional carbon steel has been used for millennia, one of its main drawbacks is corrosion. Developing steel that could withstand the elements and resist rust became something of a Holy Grail. Major advances were made throughout the nineteenth century with the addition of chromium. Finally, scientists developed a stable, commercially viable form of stainless steel in the early 1900s, which was initially marketed under the brand name Staybrite.

Today’s manufacturers and producers have many stainless steel options, including several popular duplex options. Working with an experienced metal supplier who is dedicated to assisting its customers in finding the best material for each application is the best option.

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What is Duplex Stainless Steel?

Duplex stainless steel is a stainless steel grade that combines austenitic and ferritic properties. The metallurgical structure of duplex stainless steel is divided into two distinct phases. They are composed of an equal number of austenitic stainless face-centered cubic lattices and ferritic stainless body-centered lattices.

This gives duplex stainless steel several advantages. To begin with, this stainless steel family has excellent corrosion resistance. This is particularly true for chloride pitting and chloride stress corrosion.

At once, duplex stainless steels have greater strength than traditional austenitic grades such as 304 or 316. To achieve these advancements, duplex steels have a higher chromium content, typically ranging between 20% and 28%. Additionally, there is more molybdenum, up to 5%, and less nickel, typically less than 9%. Nitrogen levels are typically between 0.05% and 0.50%.

In terms of yield strength, duplex stainless steels outperform standard austenitic and ferritic stainless grades. They contain less nickel and are significantly less expensive than traditional stainless steel grades. Type 304 stainless steel, for example, has a typical yield strength of 36 KSI. In comparison, the yield strength of standard duplex stainless steel type 2205 is 74 KSI. Meanwhile, the yield strength of a super duplex grade like 2507 is 84 KSI.

Properties of Duplex Stainless Steel

Duplex stainless steel has excellent corrosion resistance:

The increased addition of chromium and molybdenum improves Duplex Stainless Steel’s corrosion resistance. Molybdenum repels corrosive media naturally, whereas chromium forms a passivation layer to protect Duplex Stainless Steel components.

Does not corrode due to cracks:

Several grades of stainless steel frequently fail when exposed to chloride-containing environments for extended periods. In contrast, Duplex Stainless Steel is extremely dependable in situations where other grades of SS fail to perform well. Even when continuously exposed to chloride environments, stainless steel remains strong and does not corrode.

Strength & Reliability:

Duplex Stainless Steel has superior mechanical properties when compared to regular austenitic stainless steel grades. Even when beaten into thin and flat sheets, Duplex Stainless Steel retains its strength and physical properties, delivering consistently high performance.


Duplex stainless steel is more difficult to weld and machine than austenitic stainless steel grades like Stainless Steel 316 Seamless Pipes. Post-weld annealing and rapid cooling are required to avoid precipitation formation.

Why Duplex Stainless Steel is Most Popular ?

Duplex stainless steel remains a relatively small segment of the overall stainless steel market for the reasons stated above. Alloys are generally divided into four types. The first of these is known as a lean duplex.

The molybdenum and nickel content of lean duplex stainless steels is low to none. Type 2304 is an example of a common grade used in storage tanks and other similar applications.

The levels of nickel and molybdenum in the regular duplex are typically 3-6% and 2-3%, respectively. This category includes 2205, the most commonly used duplex stainless steel, which is widely used in the pharmaceutical industry.

The high molybdenum (3.5-4%) and chromium (25%) content of super duplex stainless steels distinguish them. This makes them especially strong and resistant to corrosion, and their superior performance justifies investment in the oil, gas, and chemical industries.

Finally, hyper duplex stainless steels have even higher levels of molybdenum and chromium, at 4.8% and 27%, respectively. S32707 is a good example, and it is used in the energy and oil industries, particularly in deep-sea applications.


Duplex stainless steel is a versatile and durable material that has many advantages over other stainless steel grades. It is widely used in industries from energy to construction due to its strength, ductility, resistance to corrosion, and high temperature properties. Its composition also provides excellent weldability which makes it particularly suitable for the fabrication of complex structures. The combination of strength, resistance, and weldability gives duplex stainless steel an edge over other stainless steel grades and makes it a cost-effective solution for various projects. Ultimately, duplex stainless steel stands out as a reliable material choice with longevity and proven performance. From industrial infrastructure to household appliances, this grade lends itself perfectly to a wide range of applications.

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