Microstructure and mechanical properties of cold drawn pearlitic steel wires: effects of drawing-induced heating

Abstract

To investigate the effects of drawing-generated heating on the microstructural and mechanical properties of cold drawn pearlitic steel wires, cryogenic and room temperature (RT) drawing were carried out. Microstructure evolution of the steel wires was examined by scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD) analysis. Experimental results show that with the increase of cold drawing strain interlamellar spacing of pearlite was reduced, while the crystalline cementite was gradually transformed into amorphous state. Only slight difference in the microstructure and mechanical properties was identified between the RT and cryogenic drawings. Specifically, as the drawing strain increased, the cryogenic drawn wires have lower strength but better ductility. For example, the tensile strength of cryogenic drawn wires (ε = 2.2) is about 2050 MPa, about 90 MPa lower than that of RT drawn wires. On the other hand, cryogenic drawing wires have produced a lower volume fraction of nano-crystalline cementite particles. As the nano-crystalline cementite particles could hinder the movement of dislocations, a lower fraction of nano-crystalline cementite in cryogenic drawn wires is believed to be responsible for observed lower strength and better ductility.