High strength galvanized wire for bridge cables

To accomplish the strengthening of galvanized steel wires, it is important to prevent the occurrence of delamination in torsion and to suppress the loss of strength during hot-dip galvanization. The enhancement of the patented wire strength by solid solution hardening and refinement of the pearlite lamellar spacing is more effective than increasing the total amount of drawing reduction to depress delamination. The decrease of strength during the galvanization process is mainly caused by the spheroidization of severely deformed cementite, resulting in the collapse of the lamellar structure. An increase in the Si content or the addition of Cr reduces the loss in strength. It is considered that Si and Cr decrease the rate of cementite spheroidization. Si and Cr additions are also advantageous for strengthening of the patented wire, resulting in the prevention of delamination. Based on these findings, 1770 and 1960 MPa wires have been successfully developed, and found to show mechanical properties equal to or better than those of conventional wires. The new wires have been used in the main cables and catwalk ropes of Akashi Kaikyo Bridge and Kurushima Bridge.