The primary goal of heat-treating steel wire is to restore its microstructure to a state suitable for further cold drawing.

In simple terms, after cold drawing, the molecular structure of the wire changes—its strength increases, but it becomes more brittle. Beyond a certain point, the wire may fracture during drawing instead of being smoothly elongated.

Heat treatment helps revert the internal structure of the wire, making it more ductile for subsequent cold drawing while maintaining the desired strength.

​Objectives of Steel Wire Heat Treatment:

1. ​Eliminate work hardening from previous cold drawing, enabling further processing.
2. ​Optimize the microstructure of hot-rolled wire rods for smooth drawing.
3. ​Develop specific microstructures to enhance mechanical properties after cold drawing.
4. ​Achieve the required structure and performance as specified by end users.

​Types of Steel Wire Heat Treatment

(1) Patenting (Lead Quenching / Isothermal Transformation)

Commonly known as ​lead patenting, this is a widely used method for producing high-strength, high-toughness steel wire. After lead bath treatment, the wire’s strength and hardness typically increase by about ​10%.

​(2) Annealing

Annealing involves slow cooling and serves the following purposes:

• ​Homogenize microstructure
• ​Remove work hardening and brittleness
• ​Soften finished wire
• ​Adjust toughness, ductility, tensile strength, yield point, elongation, and other properties

Types of Annealing:

• ​Full Annealing: Heating above the critical temperature, holding, then slow cooling.
• ​Recrystallization Annealing (Intermediate Annealing): Used to eliminate work hardening by heating above the recrystallization temperature but below the critical point.
• ​Spheroidizing Annealing: Forms spherical carbides distributed in a ferrite matrix, improving machinability.
• ​Normalizing: Heating ~30°C above the upper critical point, followed by rapid cooling in air or a protective atmosphere (typically an intermediate treatment).

​(3) Quenching & Tempering (Oil Tempering)

Applied ​after cold drawing to final dimensions, mainly for medium/high-carbon wires used in ​springs and card clothing needles.

• ​Process: Heat 30–50°C above the upper critical point, hold, quench in oil, then reheat in molten lead.
• ​Features vs. Cold-Drawn Wire:
  • Higher strength (for diameters >2mm) and elasticity
  • More uniform physical properties
  • Longer service life
  • Reduced deformation

​(4) Stress Relieving (Tempering)

Used for ​cold-drawn medium/high-carbon wires to eliminate internal stresses. Common in ​prestressed concrete wires and ​tire bead wires.

• ​Effects:
  • ↑ Elongation
  • ↓ Stress relaxation
  • ↑ Yield-to-tensile ratio
  • ↓ Tensile strength & bendability

​(5) Stabilization Treatment

A ​low-temperature thermomechanical process where drawn wire is heated under load to enhance deformation resistance. Used for ​prestressed steel strands and cables.

​(6) Solution Treatment

Essentially a ​high-temperature annealing to dissolve alloying elements into the matrix. Primarily for ​stainless & heat-resistant wires.

​(7) Thermomechanical Treatment

Combines ​deformation and phase transformation to synergistically improve strength, ductility, and toughness.