1. Wire Rod Pre-treatment
Hot-rolled high-carbon steel wire rods (typically 5.5–9 mm in diameter) are first passed through a mechanical descaler (using bending and straightening rollers) to crack and remove surface iron oxide scale. They are then immersed in hydrochloric or sulfuric acid baths to completely eliminate residual scale, rust, and oil. After pickling, the rods undergo multi-stage water rinsing followed by drying.
2. Initial Phosphating Treatment
The pickled and dried wire rods enter a phosphating bath, where a zinc-based phosphate conversion coating forms on the surface. This phosphate coating acts as a lubricant carrier during the drawing process, effectively reducing die wear and preventing surface scratches on the steel wire. After phosphating, the wire undergoes rinsing and drying again.
3. First Drawing
The phosphated wire rods undergo 1 to 3 passes of rough drawing using a straight-line wire drawing machine. Significant work hardening occurs during this stage; while the wire's strength increases, its ductility decreases, necessitating subsequent heat treatment to restore the microstructure.
4. Heat Treatment (Sorbitizing / Quenching and Tempering)
This is the core process for wire rope steel, determining the final balance between strength and toughness. The wire enters a continuous heat treatment furnace, where the heating zone temperature is approximately 930–970°C. It is then immersed in a lead bath (at approx. 570°C) for isothermal quenching, transforming the austenite into a sorbite microstructure. Mechanical properties are further adjusted through tempering. Sorbite combines high strength with high toughness, making it the ideal microstructure for wire rope steel.
5. Secondary Phosphating Treatment
Oxidation occurs on the wire surface during heat treatment, so the wire must undergo pickling, rinsing, zinc-based phosphating, rinsing, and drying again to prepare for fine drawing.
6. Surface Treatment (based on application)
Depending on the intended operating environment of the wire rope, the steel wire undergoes specific surface protection treatments prior to final drawing:
Bright wire: subjected only to phosphating and soaping treatments. Hot-dip galvanized wire: galvanized by passing the steel wire through a bath of molten zinc (at a temperature of approximately 460°C).
Electro-galvanized wire: galvanized via electrolytic deposition.
7. Secondary Drawing (Multi-pass cold drawing)
The wire undergoes multiple consecutive cold-drawing passes (typically 10–12 passes) to progressively reduce its diameter until the target size is achieved. After precision drawing, the tensile strength of the wire can reach 1,570–2,160 MPa or higher, depending on the final diameter and intended application.
8. Finished Steel Wire Inspection
Rope-making wire undergoes 100% inspection; key testing items include:
Diameter measurement: Using a micrometer or laser diameter gauge, with precision controlled to within ±0.01 mm.
Tensile strength test: Tensile testing on samples to verify the strength grade.
Repeated bending test: To assess wire toughness.
Torsion test: To assess the wire's plastic deformation capability.
Coating adhesion test (for coated wire): Checking for coating detachment via a wrapping test.
Surface quality inspection: Visual or instrumental inspection for defects such as cracks, scratches, or corrosion.
Wire that passes inspection is coiled according to specifications and serves as raw material for the strand-forming process.