Deformation Resistance in Plate Rolling of Commercially Pure Titanium and Ti-6Al-4V Alloy

Abstract

Hot deformation resistance of commercially pure (C.P.) titanium and Ti-6 Al-4 V alloy was investigated by uni-axial compression and plain strain compression tests. For both titanium plates, mill load and rolling temperatures during hot rolling in a wide plate mill were measured, and mean hot deformation resistance was calculated based on the rolling theory and heat transfer model. Reheating temperatures of C.P.Ti and Ti-6Al-4V alloy were 850°C and 950°C respectively, and the finish-rolling temperature of Ti-6Al-4V alloy was aimed to be reduced below 750°C. The true stress-true strain curve of C.P.Ti was that of dynamic recovery type, which was characterized by work hardening with straining, followed by steady state flow stress. On the other hand, the S-S curve of Ti-6Al-4V alloy exhibited high temperature yielding at a small strain, followed by softening and steady state flow behavior. The mean deformation resistance obtained by plain strain compression testing was higher by 1.5 to 3 times than that from uniaxial compression testing. Hot deformation resistance equations established by analysis of mill load and rolling temperature were well consistent to that from plain strain compression testing in which residual strain was taken into consideration. The residual strain in C.P.Ti and Ti-6Al-4V alloy started to take place at the rolling temperatures of 750°C and 850°C respectively, and hot deformation resistance in both titanium plates markedly increased below these temperatures due to strain accumulation.