Strain and strain rate hardening effects on the macroscopic shear bands and deformation shape of a caliber-rolled wire

Abstract

The effect of the strain hardening exponent (n) and strain rate sensitivity (m) on the strain distribution and surface profile of a workpiece during the caliber rolling process has been investigated to fully understand the influence of material properties on shape change and strain distribution of the caliber-rolled wire. Twinning-induced plasticity (TWIP) steel with high n and low m values and low carbon ferritic steel with low n and high m values were mainly compared using both experimental test and finite element analysis. The macroscopic shear bands were clearly observed in the caliber-rolled wire, indicating that the deformation is highly inhomogeneous during the caliber rolling process. The homogeneity of the strain distribution in caliber-rolled wire increased with increasing n and m values due to the fast propagation of the plastic region to other areas from the first hardened area in a material. The effect of the n value was higher than that of the m value. Consequently, TWIP steel had weaker macroscopic shear bands compared to plain carbon steel. The length of the maximum spread of caliber-rolled wire in the free surface increased with decreasing n and m values because the dead metal zone can be easily formed with decreasing n and m values. Therefore, the caliber roll design applied to plain carbon steel cannot be applied to TWIP steel because the roundness of caliber-rolled TWIP steel was poor in such a case. A roll gap thus needs to be modified with the n and m values of a material to fabricate the desired shape of a product.