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It Is Important To Understand The Properties Of Duplex Stainless Steel

Approximately 50% of duplex stainless steels consist of ferrite (a face-centered cubic structure) and 50% of austenite (a body-centered cubic structure). In contrast to two-phase alloys, where one phase precipitates, both of these phases coexist as a stable mixture. Due to the alloying elements in duplex stainless steels, ferritic and austenitic phases are more likely to form. The alloying elements are either chromium, silicon, molybdenum, or carbon, nickel, nitrogen.

Duplex steels become less corrosion-resistant and less strong at high temperatures because the relatively unstable ferrite phase is converted into the undesirable beta prime phase. Embrittlement is the term used to describe this phenomenon.

Duplex Stainless Steel

This is due to the fact that embrittlement occurs primarily at temperatures of 475 oC, however, there are an increasing number of occasions when the production of the alpha prime phase begins to occur at temperatures as low as 300 oC, which limits the maximum service temperature of duplex steels used in this industry.

Duplex stainless steels typically exhibit a higher yield strength than martensitic, austenitic and ferritic grades. Due to the precipitation of intermetallic phases at higher temperatures and the onset of brittleness as they approach cryogenic temperatures, they have a narrow working temperature range. Some common grades of duplex stainless steel are listed below with their selected properties. 

With its two-phased microstructure of equal amounts of austenite and ferrite, Duplex stainless steel is the preferred choice for storage tanks, pressure vessels, heat exchangers, bridges, railings, aquaculture, desalination systems, and various other applications. Duplex is a cost-effective and reliable alternative to standard austenitic stainless steels, such as 304 and 316L because of its excellent strength, corrosion resistance, and low maintenance requirements. Particularly in coastal or offshore areas. 

It is less costly to use Duplex stainless steel than carbon steel and ordinary stainless steel due to weight savings from reducing the thickness. In addition, it requires less handling, fabrication, and welding, thereby saving you time and money. Duplex stainless steel is also renowned for its well balanced chromium, molybdenum, and nitrogen chemistry, which results in less duplex nickel content, thus contributing to better price stability over time. It is not without reason that Duplex material outperforms traditional stainless steels, the most common of which is its imperviousness to corrosion. can supply you with Duplex material of the highest quality, in the shape and quantity you desire, regardless of what you will build, enforce or repair - whether it's a construction project, petrochemical industry, paper production or offshore oil platform. 

Duplex stainless steel fasteners

Advantages Of Duplex Stainless Steel

  • The highest level of strength
  • Stress corrosion cracking and corrosion resistance are good
  • The level of prices is more predictable
  • Fatigue resistance is good
  • In most applications, weight savings of over 30% are achieved
  • As a result of the fact that no regular painting is required, there is a low life cycle cost
  • Made from more than 85 % recycled materials and 100% recyclable

Standards And Grades Of Duplex Stainless Steel

You can choose from a wide range of Duplex stainless steel at in different grades and alloys. Our company offers a wide selection of austenitic-ferritic steels, suitable for all types of applications and industries. Depending on your project, you may need a duplex steel with the right pitting resistance equivalent number (PREN). For this reason, we offer a variety of duplex alloys such as Lean Duplex, Standard Duplex, and SuperDuplex.

lean duplex
  • Lean Duplex

Compared with the normal duplex steel, Lean Duplex is an extremely new design that was designed specifically for the building and construction industry, where the need for a very high corrosion resistance is not necessary as in other areas. 

However, it still has all the other benefits of duplex steel, such as higher strength, lighter weight, and lower maintenance requirements (compared to austenitic alloys). The lean duplex steel we offer is available in three different alloys, each with its own distinct characteristics. 

With a PREN of 24, this Low Alloyed Lean Duplex stainless steel is a low alloyed low alloyed stainless steel with an added Cr, Mo, and N content that results in an improved performance. This lean Duplex stainless steel grades possesses a 50/50 balance between ferrite and austenite and can be fabricated to provide much higher yield strength than ordinary austenitic steel. It is also extremely formable and corrosion resistant. 

A low Ni-alloyed duplex steel, called LDX 2101 or UNS S32101, has a chemical composition of CH, MO, and Ni that gives the steel excellent corrosion resistance and good weldability, resulting in a steel that is both resistant to localized and uniform corrosion. In addition to being a price stabilizing metal, it also boasts a high strength, making it the ideal choice for a wide variety of industries and applications. 

A PREN of 28, along with a mechanical strength of 125, is the result of EDX 2304 / UNS S32304's improved balanced composition of Ch, Mo and Ni, compared with the standard UNS 32304. It is worth noting that UNS S32304 is the best choice if you are looking for a lean duplex ss that is resistant to pitting corrosion with unmatched strength. 

  • Standard Duplex

A century and a half ago, the process of producing superstrong and corrosion-resistant Duplex steel involved mixing ferritic and austenitic components. Fortunately, thanks to modern technology and methods, we are now able to produce duplex stainless steel with a higher quality with lower environmental impact, and up to 85 % of it can be recycled.  

There are two duplex grades in the market today: UNS S31803 / S32205 are the most common duplex grades. They are widely known for being resistant to localized corrosion and stress corrosion cracking, as well as having a great deal of mechanical strength and weldability. There are several applications for standard duplex stainless steels that are widely used in the oil, gas and paper industries, such as hydropower, pressure vessels, structural components and chemical tankers. In cases where it is not desired to choose between high strength and high corrosion resistance, then Standard Duplex is the perfect answer for you. 

  • Super Duplex

In the oil, gas and chemical industries, super duplex steel is a special type of duplex stainless steel developed specifically for meeting the very high standards they set for themselves. It is the type of stainless steel that you need in order to protect against chloride-rich and halide-rich environments, and the grade is the right choice for everything from pressure vessels to chemical tankers and paper and pulp equipment. It is made of heavy duty stainless steel.

There are two types of super duplex grades in the world that are frequently used, and that are UNS S32750 and UNS S32760. These grades are very resistant to localized corrosion as well as stress corrosion cracking, and they also have good mechanical strength. Unlike UNS S32750, UNS S32760 also contains a significant amount of Wolfram and Copper, which helps it resist heat damage.

Duplex Stainless Steel Applications

The lack of formability and machinability of duplex stainless steels, along with the highly complicated metallurgical process of production, makes duplex steels mostly used for niche applications, as they have many limitations. As such, they are mostly used for niche applications, despite the fact that duplex stainless steels are highly durable and highly formable stainless steels.

A duplex stainless steel can be applied in a wide variety of applications based on its limitations and advantages, but most of the applications require corrosion resistance, such as pitting corrosion, crevice corrosion resistance, stress corrosion, fatigue corrosion, abrasion corrosion, or resistance to acidic or caustic environments, and so on. In this section, we will explore some of the most common industrial applications.

  • Paper production

For fabrication of vessels that contain bleach and other corrosive liquids in the paper processing industry, stainless steels that are duplex in composition are preferred to austenitic or ferritic stainless steels.

  • Desalination

A corrosion-resistant material will need to stand up to a test that is performed in a high-temperature environment, such as the desalination of seawater, a process that exposes the material to highly corrosive chlorine. Duplex stainless steel has become the most commonly used material to fabricate evaporators because of its high strength and corrosion resistance. It can also be made with thinner cross-sections since duplex stainless steel is a higher-performance material.

  • Oil and Gas

With the introduction of new duplex stainless steels with PRE numbers above 40, it has been possible to manufacture products such as valves, piping, and manifolds, which have to withstand extreme temperatures, pitting, crevice corrosion, and other corrosion processes which are vital to the oil and gas industry.

  • Construction

It is commonly used in the construction of bridges over seawater and structures that are close to the sea since duplex stainless steel is corrosion-resistant.

  • Food and Drink Storage

As a result of their relatively low cost and excellent corrosion resistance, lean duplex steels offer a great deal of promise as metals for commercially storing food and drinks during the processing process.