Non-monotonic radial distribution of tensile yielding strength in cold-drawn pearlitic wire

It is commonly accepted that the surface layer in the cold-drawn pearlitic steel wire has a higher strength than the centre. In the present work, via testing the cold-drawn wire after removing the surface layer by an electrochemical method, it is discovered that the tensile yielding strength distributes non-monotonically from the surface to the centre. A valley is observed at the sub-surface. It is found that the maximum accumulative strain during drawing occurs at the sub-surface which leads to more hardening. The presence of residual stress after drawing reduces the tensile yielding stress. With increasing thickness of the removed layer, the tensile yielding stress increases monotonically. Finally, the only reason for the non-monotonic distribution of the tensile yielding stress is the strain path which the material at the sub-surface experiences in drawing and subsequent tension. It actually belongs to a reverse and a cross loading, which result in softening.