Microstructure Evolution and Its Effects on the Mechanical Behavior of Cold Drawn Pearlite Steel Wires for Bridge Cables

The microstructure evolution and its effects on the mechanical performance of 2000 MPa bridge cable steel wires were investigated by transmission electron microscope (TEM), electron backscatter diffraction (EBSD), X-ray diffractometer (XRD) and mechanical tests. Experimental results reveal that, with the increasing strain from 0 to 1.42, a fiber structure and a fiber texture aligned with the wire axis are gradually developed accompanied by cementite decomposition and the formation of sub-grains; the tensile strength increases linearly from 1 510 to 2 025 MPa, and the reduction of the area is stable with a slight decline from 44% to 36%. After annealing at 450 degrees C for different times, pronounced changes in the microstructure occur. Cementite lamella fragment into coarser globules corresponding to a remarkable spheroidization process, while ferrite domains recover and recrystallize, and this process is associated to modifications in the mechanical properties. Furthermore, based on the observations on dislocation lines crossing through cementite lamellae, a possible mechanism of cementite decomposition is discussed.