Effect of cold drawing on microstructure and mechanical properties of Nb microalloyed steel wire for bridge cable
Utilizing Nb microalloying in steel can enhance precipitation strengthening and grain refinement strengthening.Additionally,employing cold drawing techniques can improve the microstructure and mechanical properties of steel wire,thereby optimizing its comprehensive performance.In order to study the effect of cold drawing on the properties of Nb microalloyed steel wires,the torsional properties and tensile strength of steel wires with different cold drawn strains were compared using torsional testing machines and slow strain tensile machines.Additionally,the microstructure and fracture morphology of steel wires with varying strain rates were examined and analyzed by using scanning electron microscope(SEM),electron backscatter diffraction(EBSD)and transmission electron microscope(TEM).The findings demonstrate that cold drawing substantially enhances the yield strength and tensile strength of high-strength pearlite steel,albeit with a minor decrease in its plasticity.During the cold drawing process,the pearlite lamellae of steel wire undergo bending,curling,and rotating to the drawing direction due to physical compression and interaction between the lamellae.This process also leads to the breaking of larger clusters,resulting in grain refinement.Simultaneously,the augmentation of remaining tensile stress resulted in a significant accumulation of dislocation entanglements and the formation of dislocation cells.The analysis of the strengthening mechanism demonstrates that the decrease in dislocation cells leads to an increment in the strength of the steel wire and a reduction in its plasticity.Additionally,the residual stress induced during the cold drawing process can lead to the expansion of cracks on the fracture surface of the steel wire.However,by stress releasing treatment,the torsional performance and crack propagation of the steel wire can be enhanced.
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