Effects of drawing strain and annealing on the mechanical properties for heavily cold drawn hyper-eutectoid steel wires

In this study, the effects of drawing strain and annealing at low temperature on the mechanical properties have been investigated. The mechanical properties, such as hardness and strength and fatigue, were performed. The fatigue tests of hyper eutectoid steel wires were performed by the Hunter-type tester, specially designed for ultra thin wires (< 0.2mm phi), under the bending stress. The mechanical properties of the steel wires increased with increase of annealing temperature, and the increase was more significant with higher drawing strain. Also, as annealing temperature increased, the hardness and tensile strength gradually increased up to 200 degrees C and then dramatically decreased at above temperature. However, bending fatigue limit, including fatigue life, showed the some different phenomena with increase of annealing temperature. These different behaviors depending on annealing temperature were discussed in terms of microstructural parameter changes such as pearlite morphology, rearrangement and coalescence of the dislocations.