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From Standard to Super Duplex Stainless Steels: How Do They Make an Amazing Leap in Corrosion Resistance?
With the advancement of science and technology, the demand for materials has become higher and higher. Especially in industries such as petroleum, chemicals and construction, the durability and adaptability of stainless steel have become key factors. Duplex stainless steel, due to its unique metal structure and excellent properties, has become an indispensable material in these applications. This article takes an in-depth look at the properties of duplex stainless steels and the amazing advances in corrosion resistance.
The metallic structure of duplex stainless steels consists of two phases: austenite and ferrite, which makes them superior to standard austenitic stainless steels in strength and corrosion resistance.
Structure and properties of duplex stainless steel
Duplex stainless steel is called "duplex" not only because of its microstructure, but also its chemical composition. Duplex stainless steels have higher chromium content and lower nickel content than standard austenitic stainless steels, making them extremely resistant to chloride-induced stress corrosion cracking and pitting corrosion. resistance.
Specifically, the chromium content of duplex stainless steel is usually between 20% and 28%, the molybdenum content can reach 5%, and the nickel content is reduced to less than 9%. In addition, 0.05% to 0.50% nitrogen is often added to duplex stainless steel to further enhance its strength and corrosion resistance.
Due to their low nickel content and high strength, duplex stainless steels can offer similar strength properties in a thinner form, giving them significant material cost advantages.
Corrosion resistance standards and grades
Based on corrosion resistance, duplex stainless steels can be divided into three main grades, which are characterized by their corrosion resistance equivalent number (PREN):
- Standard biphase (PREN range: 28–38) is usually EN 1.4462 (type 2205), which is the most commonly used grade on the market.
- Superduplex (PREN range: 38–45) Typically EN 1.4410, these materials have been developed for the specific needs of the petroleum and chemical industries, where they offer superior corrosion resistance and strength.
- Cheap biphase (PREN range: 22–27) such as EN 1.4362, more suitable for less demanding applications such as construction.
Although superduplex stainless steels outperform standard products in terms of performance, they are more difficult to process because high chromium and molybdenum content can lead to the formation of intermetallic compounds that are harmful to the material's properties.
Application Scope
Duplex stainless steel has been widely used in many industries due to its excellent mechanical properties and corrosion resistance, covering the following fields:
- Oil and natural gas: used in various equipment, such as flow lines, manifolds, risers, etc.
- Construction engineering: used for the design of building exteriors, bridges, seawalls, etc.
- Chemical engineering: pressure vessels, heat exchangers, distillation towers, etc.
- Water treatment: desalination plants, large water storage tanks, etc.
Duplex stainless steel not only plays an important role in the petroleum and chemical industries, but also shows strong adaptability in many fields such as construction and environmental protection.
Heat treatment and its challenges
During the heat treatment process, duplex stainless steel needs to be rapidly cooled to room temperature to avoid the precipitation of intermetallic compounds. This is also a key step to ensure material performance. Improper heat treatment can result in reduced strength and corrosion resistance, so correct treatment processes are critical.
With technological advancement, superduplex stainless steel is gradually overcoming challenges in the processing process and making breakthroughs in many scientific researches.
With the continuous changes in market demand, the development of duplex stainless steel has attracted more and more attention. Advances in materials not only improve the safety and reliability of industry production, but also contribute to environmental protection and sustainability. In the future, can duplex stainless steel continue to lead the innovation trend of stainless steel materials?
