Correlative study on spheroidisation-induced changes in mechanical strength and corrosion resistance of eutectoid steel wire rods

Eutectoid steel wire rods are widely used in industrial applications where mechanical performance and corrosion durability are governed by microstructural state. In the present study, spheroidisation of eutectoid steel was achieved through controlled cyclic heat treatment involving repeated heating above Ac3 (780 °C) and cooling below Ac1 (670 °C) for 3, 5, 7, and 9 cycles. Microstructural evolution was characterised using scanning electron microscopy and dilatometric analysis, while mechanical and corrosion responses were evaluated through uniaxial tensile testing and potentiodynamic polarisation measurements. Cyclic processing progressively transformed lamellar pearlite into spheroidised cementite with increasing ferrite fraction. Tensile results showed a monotonic reduction in yield and ultimate tensile strength with increasing cycle number, accompanied by enhanced ductility; elongation increased by 28%, whereas ultimate tensile strength decreased by 30% after 9 cycles compared with the as-received condition. Corrosion resistance generally deteriorated with increasing spheroidisation due to ferrite enrichment; however, specimens processed for 7 cycles exhibited the lowest corrosion current density, attributed to the formation of a uniform spheroidised cementite barrier. The study establishes quantitative processing–structure–property–corrosion correlations and identifies an optimum cyclic heat-treatment window for wire rod applications.