Material Grades – Duplex Steel Fasteners

Duplex steel fasteners are known for their excellent combination of strength and corrosion resistance, making them ideal for demanding industrial environments. Duplex stainless steels are a family of stainless steels that contain a balanced mixture of austenitic and ferritic microstructures, offering enhanced mechanical and chemical properties compared to standard stainless steel grades.

What is Duplex Steel?

Duplex stainless steel contains approximately 50% austenite and 50% ferrite. This dual-phase structure provides:

  • High strength (twice that of 304 or 316 stainless steel)
  • Outstanding resistance to stress corrosion cracking (SCC)
  • Excellent resistance to pitting and crevice corrosion
  • Good weldability and fatigue strength

Common Duplex Steel Grades for Fasteners

1. UNS S31803 / S32205 (Duplex 2205)

  • Description: The most widely used duplex stainless steel grade.
  • Corrosion Resistance: Excellent resistance to chloride stress corrosion and pitting.
  • Mechanical Strength: About twice the yield strength of 304 and 316 stainless steels.
  • Applications: Offshore oil & gas, marine, chemical processing, desalination, and pressure vessels.
  • Standards: ASTM A479 / ASTM A182

2. UNS S32750 / S32760 (Super Duplex)

  • Description: Known as Super Duplex Stainless Steel, these grades offer even higher strength and corrosion resistance than 2205.
  • Corrosion Resistance: Superior resistance to seawater, acidic, and chloride-rich environments.
  • Applications: Subsea equipment, heat exchangers, pulp & paper industries, and chemical plants.
  • Standards: ASTM A479 / ASTM A182

Mechanical Properties (Typical for Duplex 2205 Fasteners)

Property Value (approximate)
Tensile Strength 620 – 880 MPa
Yield Strength ≥ 450 MPa
Elongation ≥ 25%
Hardness ≤ 290 HB

Super Duplex grades exhibit even higher values for strength and corrosion resistance.

Key Benefits of Duplex Steel Fasteners

  • High strength-to-weight ratio
  • Superior resistance to corrosion, especially in aggressive environments
  • Excellent performance in saltwater and chloride-rich atmospheres
  • Long service life with minimal maintenance
  • Cost-effective for heavy-duty applications due to reduced material thickness needs

Applications of Duplex Fasteners

  • Oil & Gas exploration and pipelines
  • Offshore platforms and marine structures
  • Desalination plants
  • Chemical and petrochemical industries
  • Heat exchangers and pressure vessels
  • Paper and pulp industries