Atomic force microscopy: a powerful tool to study the radial gradients in mechanical properties of hard-drawn pearlitic steel wire

摘要

Hard-drawn pearlitic steel wire (total true strain ε=4) is characterized by its nano-sized microstructural features of alternating ferrite and cementite plates. This extremely fine structure is of great technical importance: as the interlamellar distance determines the onset of plastic flow, the tensile strength of such wires exceeds 4000 MPa while maintaining a sound fatigue behavior and an acceptable level of ductility. The excellent mechanical behavior is realized by the wiredrawing technique where the wire passes through a series of conical converging dies and the pearlite strengthens exponentially. Inevitably, this deformation process induces a significant amount of inhomogeneity aspects in the material, resulting in radial gradients of the wire properties. Analysis of the drawing process has pointed out several significant factors acting upon this inhomogeneity phenomenon, but until now there is no fundamental knowledge explaining the contribution of each parameter to the (in)homogeneous drawing deformation.