Significantly Enhanced Strength of a Drawn Twinning-Induced Plasticity Steel Wire and its Deformation Twinning Dependency

This study describes a higher strength of drawn twinning-induced plasticity (TWIP) steel wire compared with its strain hardening exponent (n) and reveals that the outstanding strain hardening rate of TWIP steel was strongly related to the twinning behavior rather than dynamic strain aging based on a comparison of deformation behaviors between the tension and wire drawing in pearlitic, ferritic, and TWIP steels. The ratio of a hardening rate (h) of a drawn wire to the n in a tensile test, referred to as h/n, of ferritic, pearlitic, and stainless steels was approximately 1371 MPa, whereas that of the TWIP steel was approximately 2620 MPa. This means that the high strength of the drawn TWIP steel wire cannot be explained by n value alone. Compared with the tensile-strained specimen, the drawn wire exhibited a higher twinning rate, indicating that the high h/n value of the TWIP steel was related to the twinning behavior. The higher twinning rate of the drawn wire was attributed to the combined effects of the complex stress states owing to the die geometry and the directional nature of the deformation twinning. This means that the strength of TWIP steel can be easily improved using the general bulk forming processes, particularly complex forming processes.