Aging behavior and delamination in cold drawn and post-deformation annealed hyper-eutectoid steel wires

The effects of drawing strains and post-deformation annealing conditions on the aging behavior and the occurrence of delamination in cold drawn hyper-eutectoid steel wires were studied. At low annealing temperatures the increased tensile strength for a short annealing time would be attributed to age hardening, which came from the decomposition of the unstable cementite in deformed pearlite. The decrease of tensile strength at the high annealing temperature was due to age softening, which would be attributed to the decreased carbon content in lamellar ferrite through the spheroidization or the re-precipitation of cementite, and recovery or recrystallization of ferrite. The extent for the occurrence of delamination during annealing expanded to the high temperature region with the increased amount of deformation in steel wires. At high annealing temperatures, the decreased carbon content dissolved in lamellar ferrite due to age softening would result in the decrease of tensile strength and suppress the occurrence of delamination. The total magnitude of carbon content dissolved in lamellar ferrite either by the partial dissolution of lamellar cementite during wire drawing or by the partial decomposition of lamellar cementite during post-deformation annealing would control the occurrence of delamination in cold drawn steel wires.