Study On Preparation Technique Of High Strength Hot-dip Galvanized Steel Wires For Bridge Cables

In this paper, based on the research of 6.20-1960 high strength hot-dip galvanized steel wire used in long-span bridge cable, Import Ф14.0mm S87 A and domestic Ф14.0mm S90 B wire rods were chosen parallel to trial. Experiment results show that the domestic wire rod can be produced to meet the requirements of long-span bridge cable.In the development process of the steel wire, the chemical composition, metallographic structure of two wire rods were analyzed, the work hardening behaviors of cold drawn steel wire and the influence of different hot dip galvanizing process parameters on the properties of steel wire were researched. The evolution process of steel wire with different drawing deformation, the influence of different line speed on the hot galvanized coating and the wire structure difference between the before and after hot dip galvanized were observed by SEM.Wire rod comparison results show the performance index of the domestic rod is similar to the import wire rod. The average pearlite spacing are 153.4nm and 142.5nm separately. For the 6.10 mm diameter cold drawn steel wires with the same production process, the domestic contrasts with the imported, about 70 MPa higher tensile strength, 0.5% lower elongation, 10.5% lower section shrinkage rate, the same turns, more than 30 rings. SEM results show that in the cross section cementite always keep axis distribution, but size and spacing are constantly changing, cementite layer curved with the increase of deformation; In the longitudinal section, the cementite is elongated and spacing becomes smaller along with the increase of deformation. And the proportion of pearlite in steel wire turning to drawing direction becomes larger.Alkaline pretreatment has no obvious effect on the properties of steel wire. Because of the short time of heat recovery effect, after lead bath pretreatment, the tensile strength decreased by about 30 MPa and the Turn rings dropped to an average of 22 from an average of 31. After hot dip galvanizing, these differences have been assimilated. Two kinds of different pre treatment process had no significant effect on galvanized steel wire performance.The thickness of zinc iron alloy layer in steel wire coating was thinner with the increase of the line velocity. Speed increase also will increase the pure zinc layer thickness, so in a given speed range, coating weight remained stable. For the tensile test of wire coating before and after, it is found that the maximum force without obvious difference indicates that the deformation contribution of coating on wire in the tensile test of wire resistance is very small and decrease in tensile strength is actually caused by the different calculation of cross-sectional area. By scanning electron microscope observation of the steel wire microstructure before and after hot dip galvanized, the granular and short rodshaped cementite microstructure appeared in local area after hot dip galvanizing, indicating part of cementite was broken in hot dip galvanizing process.