What is Duplex Stainless Steel? Comparing Duplex Stainless Steel with Other Stainless Steels
Dubbed as the “material of the future”, Duplex stainless steel offers outstanding advantages that meet application requirements in various specialized conditions. So, what exactly is Duplex stainless steel? What types of Duplex stainless steel are available? And what are the differences between this type of stainless steel and others? Let’s explore these questions with Son Ha SSP in the article below.
What is Duplex Stainless Steel?
Duplex stainless steel, also known simply as Duplex, is a type of stainless steel with a dual microstructure, combining both Ferritic and Austenitic structures in a 1:1 ratio. This blend allows Duplex stainless steel to inherit the properties of both Ferritic and Austenitic types, creating a material that is significantly stronger and more durable than standard stainless steels.
Duplex Stainless Steel Inherits the Properties of Both Ferritic and Austenitic Types
Duplex stainless steel contains a relatively high amount of chromium and nitrogen, giving it high inertness and enabling it to resist corrosive environmental conditions. Advances in manufacturing technology have resulted in modern Duplex types with lower nickel content, while still maintaining excellent mechanical properties and superior corrosion resistance. Super Duplex and Hyper Duplex varieties have been developed, offering even greater corrosion resistance and durability in harsh environments. Duplex stainless steel has become increasingly popular and is gradually replacing conventional stainless steels such as SUS 304, 304L, 316, 316L, and 310s.
Types of Duplex Stainless Steel
Duplex stainless steel is categorized based on the alloying elements, such as nickel and molybdenum. Depending on the percentage of these elements, various grades of Duplex stainless steel are produced. Here are the main types:
2.1. Inox Lean Duplex SS
Lean Duplex SS is a “reduced” version of standard Duplex stainless steel, with lower nickel content and often without molybdenum, such as in grades 2101, 2102, 2202, and 2304. The goal of this type is to reduce production costs while maintaining the essential characteristics of Duplex stainless steel, such as high strength and lower susceptibility to pitting and crevice corrosion compared to 316L stainless steel.
- Characteristics: Lower cost compared to standard Duplex due to reduced nickel content. It withstands moderate corrosive environments but is less corrosion-resistant than higher-alloyed Duplex types.
- Applications: Commonly used in moderately corrosive environments, such as in the construction industry and mechanical applications.
2.2. Inox Duplex SS
Standard Duplex SS has a balanced microstructure between austenitic and ferritic phases, with a 50/50 ratio. It has higher nickel and molybdenum content, seen in grades like 2205, 2003, and 2404. Duplex SS provides better corrosion resistance and higher mechanical strength than conventional stainless steels.
- Characteristics: Suitable for medium-corrosive environments, with excellent localized and pitting corrosion resistance compared to 304 and 316 stainless steel.
- Applications: Widely used in the oil and gas industry, chemical processing, shipbuilding, and coastal construction projects.
Applications of Duplex Stainless Steel in the Oil and Gas Industry
2.3. Inox Super Duplex
Super Duplex has higher levels of chromium, molybdenum, and nickel than standard Duplex, resulting in outstanding corrosion resistance, especially in high-salinity or chemically aggressive environments.
- Characteristics: Superior resistance to corrosive environments, such as marine, humid, and salty climates, as well as areas exposed to industrial chemicals like acids. It also offers very high mechanical strength.
- Applications: Commonly used in pipelines, heat exchangers in processing plants, chemical processing tanks, and maritime applications.
2.4. Inox Hyper Duplex
Hyper Duplex is the most advanced version of Duplex stainless steel, with the highest alloy content in the series, containing 26-30% chromium, 3.5-5.0% molybdenum, and 0.30-0.50% nitrogen. This stainless steel type is specifically manufactured for extremely corrosive environments with high acid and chloride levels. Produced in limited quantities, it is mainly available in seamless pipe form. Compared to Super Duplex, Hyper Duplex offers even higher load capacity and superior corrosion resistance.
- Characteristics: The highest strength and corrosion resistance among all Duplex types. It is especially useful in environments with extreme chloride concentrations and highly aggressive corrosion conditions.
- Applications: Used in applications requiring the highest resistance, such as chemical plants, offshore oil rigs, and seawater treatment systems, where environmental conditions are extremely harsh.
Comparison of Duplex Stainless Steel with Other Types of Stainless Steel
Below is a comparison table of Duplex Stainless Steel and other types based on factors such as Strength, Corrosion Resistance, Machinability, and Applications:
| Criteria | Inox Duplex | Inox Austenitic | Inox Ferritic | Inox Martensitic |
| Durability | Very high, excellent load-bearing capacity | Medium | Low | High, but dependent on heat treatment |
| Corrosion Resistance | Excellent, especially in chloride environments | Good, but less than Duplex | Low, susceptible to corrosion | Low, requires protection in corrosive environments |
| Machinability | Difficult due to high hardness | Easy, highly ductile | Easy to machine | Difficult, brittle, requires careful machining |
| Applications | Chemical, oil & gas, maritime industries | Industry, construction, household appliances | Household items, decorative applications | Cutting tools, blades, wear-resistant components |
Through this article, Son Ha SSP has shared fundamental knowledge about duplex stainless steel. If you are looking for a trusted provider specializing in custom stainless steel pipes, contact Son Ha SSP via our hotline at 1900 6566 for consultation and a detailed quotation as soon as possible!
