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Duplex Stainless Steels – a comparison and selection guidelines

Duplex stainless steels are a family of stainless steels known for their excellent combination of mechanical properties and corrosion resistance. They are called ‘duplex’ because their microstructure consists of roughly equal amounts of austenite and ferrite. This balanced structure provides superior strength and resistance to stress corrosion cracking compared to conventional austenitic or ferritic stainless steels.

 


The enhanced corrosion resistance of duplex steels is primarily due to their higher chromium, molybdenum and nitrogen content. Duplex stainless steels were developed to overcome some limitations of traditional stainless steel grades, such as the popular 304 and 316 types, and they offer better price stability as they have lower nickel content than austenitic grades, making them less sensitive to market fluctuations in nickel prices.

 

Within the duplex steel family, there are several sub-categories: standard duplex, super duplex and lean duplex. Each has distinct characteristics, making them suitable for different applications:

 

Standard Duplex

Standard duplex stainless steels, such as grade 2205 (UNS S31803/S32205), are the most commonly used within the duplex family. They offer a balanced composition of chromium, nickel, molybdenum and nitrogen, which imparts excellent corrosion resistance and mechanical strength. These steels exhibit higher yield strength compared to traditional austenitic stainless steels, making them ideal for applications in chemical processing, oil and gas, and marine environments.

 

Super Duplex

Super duplex stainless steels, including grades like UNS S32750 and UNS S32760, are characterised by their superior strength and exceptional resistance to corrosion. These grades contain higher levels of chromium, molybdenum and nitrogen, which enhance their ability to withstand highly corrosive environments. Super duplex steels are ideal for applications in harsh conditions, such as offshore oil and gas platforms, subsea equipment and chemical processing plants.

 

Lean Duplex

Lean duplex stainless steels, such as grades 2101 and 2304, are designed to offer a cost-effective alternative to standard duplex and austenitic stainless steels while still providing good corrosion resistance and mechanical properties. These grades have lower nickel and molybdenum content, with the term ‘lean’ reflecting this streamlined, cost-conscious approach to alloy composition, which reduces their overall cost. Lean duplex steels uses include structural components, storage tanks and pressure vessels in less aggressive environments.

 

Conclusion

The duplex family of stainless steels offer exceptional corrosion resistance and high tensile strength, making them an ideal choice in applications that traditional stainless steel grades cannot handle. From the extremes of offshore oil and gas processing, to the heat and chemical bombardment of pulp and paper processing, duplex stainless steel benefits service life and maintenance requirements. By carefully selecting the appropriate grade based on specific requirements, industries can optimise both performance and cost-efficiency

 

If you're considering duplex steel for your next project, the experts at P&P Non-Ferrous are ready to help. Call us today to speak with one of our knowledgeable sales team. As a leading provider of stainless steel and other non-ferrous metals throughout the UK for more than 40 years, we can help you source the perfect materials, grades, parts or components for projects of any size.



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