What factors affect tensile strength of galvanized wire?

Release time:

2026-06-05

Tensile strength mainly depends on raw steel composition, cold drawing, heat treatment, galvanizing technology, wire diameter, and service environment as listed below：

Key Factors Affecting Tensile Strength of Galvanized Wire

Tensile strength mainly depends on raw steel composition, cold drawing, heat treatment, galvanizing technology, wire diameter, and service environment as listed below：

1. Raw Steel Chemical Composition (Base Material)

Carbon content: The most decisive factor. Higher carbon percentage increases tensile strength significantly; low-carbon steel (Q195, ~0.06%–0.16% C) produces soft wire of 350–550 MPa, while high-carbon steel (0.6%–1.2% C) makes high-tensile wire over 1000 MPa.
Alloy trace elements: Mn improves base strength and hardness; Si enhances structural stability; Cr, V, Nb refine grains and inhibit strength drop during hot-dip galvanizing; excessive S & P impurities reduce tensile performance sharply.

2. Cold Drawing Process

Total drawing reduction rate and pass schedule control internal grain deformation:

Larger cumulative cold reduction refines steel grains and raises tensile strength greatly (hard-drawn wire).
Insufficient drawing leads to low strength; over-drawing causes hidden micro-cracks to downgrade final tensile property.

3. Pre-galvanizing Annealing Heat Treatment

Full annealing: Softens wire by grain recrystallization, lowers tensile strength for flexible binding wire (300–500 MPa).
Patenting (lead quenching): Forms fine sorbite microstructure, the core pretreatment for ultra-high tensile galvanized wire (for bridge cable, ≥1770 MPa).
No annealing keeps high tensile from cold drawing deformation hardening.

4. Galvanizing Method & Thermal Impact

(1) Hot-dip galvanizing (440–480℃ molten zinc bath)

High-temperature heating triggers partial temper softening, grain coarsening and Fe-Zn alloy diffusion; tensile strength normally drops 5%–10%, especially obvious on high-carbon wire with high pre-drawing strength. Longer immersion time in zinc liquid aggravates strength loss.

(2) Electro-galvanizing (room-temperature electroplating)

No thermal input to steel substrate; original tensile strength of bare wire is almost fully retained, preferred for high-tensile finished wire.

Zinc coating thickness has nearly no direct influence on tensile strength, as zinc layer is much softer than steel core.

5. Wire Diameter

Under identical raw material and production flow: thinner finished wire gets higher tensile strength after multi-pass cold drawing; thicker wire features relatively lower tensile value.

6. Post-production Storage & Service Environment

Long-term high-temperature exposure (>120℃) slowly causes substrate structure relaxation and strength degradation.
Corrosion (rust pits, zinc coating failure): surface corrosion pits turn into stress concentration points, drastically reduce actual breaking tensile strength of in-service wire.