Influence of Carbon Content on the Mechanical Properties of Ultra-high Strength of Coated Steel Wire

Ultra-high strength of steel wire for offshore mooring lines can be achieved by increasing carbon content, addition of alloying elements and increasing cold work. The influence of carbon content and zinc coating on the tensile strength and torsion deformation have been investigated for drawn and hot dip galvanized steel wires at various drawing strain. In this work, experiments were conducted to increase the tensile strength of hyper-eutectoid steel wires by increasing carbon content from 0.87%wt to 0.98%wt. The samples with various diameter was drawn to their final diameter, then hot dip galvanized at 460ᵒC in a zinc bath to improve the anti-corrosion property. Torsion deformation has been investigated by twisting the drawn steel wires to different number of revolutions. Fractured samples after torsion test were analysed by optical and Field Emision Scaning Electron Microscope. The results showed that by increasing carbon content up to 0.98%wt (sample D) at drawing strain of 1.97 greatly increased the tensile strength up to 2338 MPa. However, delamination occurred at the zinc coating layer at strength exceeding 2250 MPa and the maximum limit of tensile strength of 0.92% C (sample D) is 2026 MPa without delamination. The effect of zinc coating layer on torsion degradation also revealed that the zinc alloy layer had a significant effect on delamination in the hot dip coating which associated with the higher carbon and silicon content (sample B) in the steel wires.