Microstructure and strength–ductility balance of pure titanium processed by cryogenic rolling at various rolling reductions

In this study, we examined the microstructure and strength–ductility balance of pure Ti processed by cryogenic-temperature rolling (CTR) at various rolling reductions (RRs). The strength–ductility balance of the processed materials was evaluated by multiplying the yield strength by the fracture elongation, which were measured by tensile testing. Generally, the strength–ductility balance deteriorates as metallic materials are strengthened, but remarkably, CTR enhanced the strength–ductility balance while significantly strengthening pure Ti by adjusting the amount of RR. CTR formed numerous thin twins in the grains of the material with suppressed dislocation generation due to the increased twinning activity and relatively decreased slip activity at a low temperature, which cannot be achieved in typical processes performed at or above room temperature. This unique microstructure enhanced the strength–ductility balance of the processed material by intensifying grain refinement and improving resistance to necking instability. However, the strength–ductility balance deteriorated when a large RR was imposed due to the significant changes in the microstructure as the deformation proceeded. Therefore, it is important to adjust the amount of RR for CTR to impart its exceptional ability. We discuss the effects of microstructural factors on the strength–ductility balance in terms of possible strengthening mechanisms and strain-hardening capacity. The present findings could guide the design of optimized CTR for the production of pure Ti plates or sheets with excellent tensile properties and extend their use in industrial applications.