Impact of mechanical anisotropy on the geometry of flat-rolled fully pearlitic steel wires

The aim of the paper is to emphasize the role of anisotropy on metal flow in a bulk forming process, namely on lateral spread in pearlitic steel flat wire cold rolling. A precise final geometry of flat-rolled drawn wires is required in view of their industrial applications. Numerical modelling is undertaken to optimize the process and product properties. However, in the first part of the present study, the comparison between experimental and computed cross-sections shows a 10% discrepancy. It is shown first that temperature and friction are not the reasons for this underestimation, then that anisotropy may explain it. Indeed, ovalization of radially cut compression samples is observed at the end of wire-drawing, highlighting the appearance of wire-drawing-induced plastic anisotropy. Coefficients of Hill's quadratic anisotropic constitutive model have been identified at several stages of the wire-drawing and rolling process, using compression and shear tests, in order to study the sensitivity of the process to anisotropy and its influence on lateral spread. Then, the Finite Element Method (FEM) has been used to simulate rolling passes. Taking into account plastic anisotropy significantly improves the estimation of the final width; yet the underestimation is still 5% (instead of 10%). On the one hand, these results unambiguously prove that plastic anisotropy has an impact on flow during cold metal forming processes, provided free surfaces are present. On the other hand, they show further improvement is needed; it is suggested to use more sophisticated anisotropy models, as it has been done in sheet metal forming.