Study On Microstructure Of SWRS82B For Long-span Bridges And Torsion Performance Of Steel Wire

SWRS82B wire was the raw material of hot-dip strand for long-span bridges. At present, the strength of hot-dip strand's could reach acceptance criterion, which produced by homemade WRS82B wire. Nevertheless, it's torsion capability couldn't.The torsion fractures are classified as three types: even fracture, sidestep fracture and fastigiated fracture. Even fracture belongs to normal rupture. The strand ruptures when cut-stress reaches its critical value. The reason of sidestep fracture is that zonary structure decreases the cut-stress of hot-dip steel strand. The disfigurements on the steel strand surface will cause fastigiated fracture easily. The form of crack on steel strand surface, as well as the depth of the crack, affects the torsion capability critically. Transverse crack is worse than the other two types of crack.The torsion value of steel strand decreased markedly after galvanization. It was shown that the pre-processes of galvanization didn't affect it. The differential scanning calorimeter(DSC) experiments indicated that there was a exothermic reaction at 450℃, Which was almost equal to the temperature of galvanization. SEM results show that Fe3C transforms into spherical structure after drawing and galvanization.The grain of wire refined when alloy Vanadium was appended, and interlamellar spacing of pearlite was reduced from 0.14μm to 0.12μm by cooling quickly. Performance of wire was promoted evidently. DSC experiments indicated that temperature rang, during which cementite laminate transformed into spherical structure, increased from 400~500℃to 450~550℃after SWRS82B wire was advanced in quality. the critical depth of the transverse crack increased from 0.05mm to 0.15mm. Mostly the torsion value increased from 22 to 25.When the quality of SWRS82B wire was improved, the production results showed that hot-dip steel strand could meet the use requirement, especially for torsion performance.