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Duplex Stainless Steel

Duplex stainless steel is a unique type of stainless steel that combines the beneficial properties of both austenitic and ferritic stainless steels. Known for its high strength and excellent corrosion resistance, duplex stainless steel is increasingly used in various industries, particularly in challenging environments. This article will cover the composition, grades, magnetic properties, uses, and microstructure of duplex stainless steel.

Duplex Stainless Steel Composition

Duplex stainless steel typically contains a balanced mix of austenitic and ferritic phases, generally consisting of about 22% chromium and 5-7% nickel. This unique composition gives duplex stainless steel its strength and enhanced resistance to stress corrosion cracking.

Here is a typical composition table for common duplex stainless steel grades:

Grade	Chromium (Cr) %	Nickel (Ni) %	Molybdenum (Mo) %	Nitrogen (N) %
2205	22.0 – 23.0	4.5 – 6.5	3.0 – 3.5	0.08 – 0.2
2507	24.0 – 26.0	6.0 – 8.0	3.5 – 4.0	0.2 – 0.3

Duplex Stainless Steel Grades

2101

1.4162

X2CrMnNiN21-5-1

UNS S32101

—

2205

1.4462

X2CrNiMoN22-5-3

08X22H6M2T

03X22H5AM2

2507

1.4410

X2CrNiMoN25-7-4

02X25H7M3

07X25H7M2

2304

1.4362

X2CrNiN23-4

03X23H4

—

Alloy 255

1.4507

X2CrNiMoCuN25-6-3

UNS S32550

—

Zeron 100

1.4501

X2CrNiMoCuWN25-7-4

UNS S32760

—

Duplex Stainless Steel Magnetic

Duplex stainless steel is generally magnetic due to its ferritic content. This characteristic can be beneficial in applications where magnetic properties are required. However, the degree of magnetism can vary depending on the specific grade and the processing it has undergone. In comparison to austenitic stainless steels, which are typically non-magnetic, duplex stainless steels exhibit moderate magnetism.

Duplex Stainless Steel Uses

Duplex stainless steels are widely used in applications that require high strength and excellent corrosion resistance. Common uses include:

Oil and Gas Industry: Pipelines, risers, and pressure vessels.
Marine Applications: Shipbuilding, offshore platforms, and seawater systems.
Chemical Processing: Reactors, heat exchangers, and storage tanks.
Pulp and Paper Industry: Chemical handling equipment and pulp digesters.

Duplex Stainless Steel Microstructure

Duplex stainless steel features a unique microstructure that consists of approximately equal proportions of austenite and ferrite. This balanced microstructure contributes to its excellent mechanical properties and corrosion resistance. Here’s a simplified diagram illustrating the microstructure of duplex stainless steel:

    *   *   *   *   *    (Austenite)
  *   *   *   *   *   *
    *   *   *   *   *    (Ferrite)
  *   *   *   *   *   *