Duplex Steel

Duplex steel is a type of stainless steel known for its two-phase microstructure, consisting of both austenitic and ferritic phases. This unique structure gives duplex steel a combination of high strength, excellent corrosion resistance, and superior toughness. Duplex steels are used in industries like chemical processing, oil and gas, marine applications, and construction where resistance to stress corrosion cracking and pitting is crucial. Its ability to withstand extreme environments, coupled with good weldability, makes it a preferred choice for high-performance applications.

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Duplex Steel Grades

Ductile iron, also known as spheroidal graphite iron, has several grades, each with distinct properties.

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Duplex 2205 (UNS S31803/S32205)

  • Composition: 22% chromium, 5-6% nickel, 3% molybdenum
  • Properties: This is the most commonly used duplex grade, known for excellent resistance to pitting, crevice corrosion, and stress corrosion cracking. It offers high strength, good weldability, and exceptional toughness.
  • Yield Strength: 65,000 psi (450 MPa)
  • Tensile Strength: 90,000 psi (620 MPa)
  • Elongation: 25%
  • Hardness: 293 HB (Brinell Hardness)
  • Uses: Ideal for pressure vessels, storage tanks, heat exchangers, and pipelines in the chemical, petrochemical, and oil industries.

Super Duplex 2507 (UNS S32750/S32760)

  • Composition: 25% chromium, 7% nickel, 4% molybdenum
  • Properties: Offers superior resistance to chloride stress corrosion cracking, pitting, and crevice corrosion. It also has higher strength and toughness compared to standard duplex grades, making it suitable for extremely harsh environments.
  • Yield Strength: 80,000 psi (550 MPa)
  • Tensile Strength: 116,000 psi (800 MPa)
  • Elongation: 15%
  • Hardness: 310 HB
  • Uses: Offshore oil rigs, subsea equipment, desalination plants, and high-pressure chemical processing.

Lean Duplex 2101 (UNS S32101)

  • Composition: 21% chromium, 1.5% nickel, 0.3% molybdenum
  • Properties: A cost-effective duplex steel with lower nickel content while maintaining good corrosion resistance, fatigue resistance, and strength. This grade offers a good balance between performance and price.
  • Yield Strength: 65,000 psi (450 MPa)
  • Tensile Strength: 94,000 psi (650 MPa)
  • Elongation: 30%
  • Hardness: 260 HB
  • Uses: Ideal for structural components, storage tanks, and bridges.

Duplex 2304 (UNS S32304)

  • Composition: 23% chromium, 4% nickel, 0.1% molybdenum
  • Properties: Offers similar corrosion resistance and strength to 316 stainless steel but with lower nickel content, making it more economical. It is also known for good stress corrosion cracking resistance.
  • Yield Strength: 65,000 psi (450 MPa)
  • Tensile Strength: 87,000 psi (600 MPa)
  • Elongation: 25%
  • Hardness: 270 HB
  • Uses: Suitable for water treatment systems, food processing equipment, and heat exchangers.

Manufacturing Processes for Duplex Steel

Hot Rolling

Hot Rolling

Duplex steel is often subjected to hot rolling, where the material is heated above its recrystallization temperature and passed through rollers to create sheets, plates, or bars. This process enhances the mechanical properties of duplex steel, improving its strength and toughness. Hot rolling allows for the effective shaping of components that are critical for applications requiring high strength, such as pressure vessels, pipelines, and structural elements in construction and marine environments. The hot-rolled products typically exhibit improved ductility and better surface finish, making them suitable for further processing or direct use in demanding applications.

Cold Working

Cold Working

Cold working involves deforming duplex steel at room temperature, which increases its strength and hardness through strain hardening without significantly compromising its corrosion resistance. This method is particularly effective for producing smaller components that require precise dimensions and enhanced mechanical properties, such as fasteners, valves, and precision parts. Cold working can include processes like cold rolling, drawing, or bending, and it is often used to produce components that must endure high stress while maintaining their structural integrity in various applications, including oil and gas and chemical processing industries.

Welding

Welding

Duplex steel is known for its good weldability, making it suitable for various welding techniques. Processes like Gas Tungsten Arc Welding (GTAW) and Gas Metal Arc Welding (GMAW) are commonly employed to join duplex steel components. During welding, it is crucial to control the heat input to maintain the desired balance between the austenitic and ferritic phases of the steel. Proper welding procedures help prevent issues such as sigma phase formation and ensure that the welds retain the excellent mechanical and corrosion-resistant properties of the base material. Welding duplex steel is widely used in the construction of pressure vessels, heat exchangers, and marine structures where reliability and durability are essential.

Investment Casting

Investment Casting

Casting is a process used to shape duplex steel into complex forms by pouring molten metal into molds. Duplex steel is cast into components such as pump bodies, valve housings, and impellers, commonly utilized in the chemical and oil industries. This method allows for the creation of intricate shapes that would be difficult or uneconomical to achieve with other forming techniques. The casting process not only ensures strength and durability but also maintains the corrosion resistance properties of duplex steel, making it suitable for components exposed to harsh environments, including seawater and corrosive chemicals. Various casting techniques, including sand casting and investment casting, can be utilized based on the desired shape, size, and production volume.

If you're seeking high-performance duplex steel solutions customized to your manufacturing needs, contact Align Manufacturing for expert support.

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At Align Manufacturing, we pride ourselves on our commitment to producing quality metal parts. Our experienced team utilizes equipment and processes to ensure each component meets the highest standards of precision and reliability.

We continuously strive to innovate and improve our methods, ensuring that our clients receive parts that not only meet but exceed their expectations in performance and durability. With a focus on excellence and customer satisfaction, Align MFG remains a trusted partner for all your metal needs.

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