Evolution of microstructure and tensile properties of cold-drawn hyper-eutectoid steel wires during post-deformation annealing

Manufacturing temperatures of severely cold-drawn hyper-eutectoid steel wires are sufficiently high to influence the mobility of dislocations and alloy elements, thereby affecting the materials’ mechanical properties. Herein, we describe the evolution of microstructure and tensile strength of the as-drawn 3.45 GPa steel wire during post-deformation annealing for 30 min at 150−450 °C. Annealing at 150 °C raised the strength to 3.77 GPa by age-hardening through activation of dislocations pinning by carbon, while further temperature rising up to 450 °C caused a severe loss of strength. It was proved that annealing at 300 and 450 °C destabilizes the lamellar microstructure, promoting the formation of carbon-deficient (Fe,Mn,Cr)3C-type cementite particles with preferentially rounded and partially faceted hetero-interfaces. Annealing at 450 °C yielded the accumulation of Mn and Cr at the ferrite/particle interfaces, and their concentrations at the interfaces were dependent on the interface structure; i.e., lower concentrations at rounded interfaces (formed through capillarity–driven coarsening of the spheroidized cementite), and higher concentrations at faceted interfaces (that are initially existing in the as-drawn state). Our proof-of-principle observations, supported by thermodynamic calculations and kinetic assessments, provide a pathway for understanding the changes in microstructural and tensile properties during manufacturing of the hyper-eutectoid steel wires.