Abstract:In order to establish the rolling process parameters of grade-2 commercially pure titanium (CP-Ti), it is necessary to understand the transformation mechanism and mechanical properties of this material. The β→α transformation kinetics of the grade-2 CP-Ti during continuous cooling was measured and its hot compression behavior was investigated using Gleeble-1500 thermal mechanical simulator. Dynamic CCT diagram confirms that cooling rate has an obvious effect on the start and finishing transformation and microstructures at room temperature. The critical cooling rate for β-phase transforms to α phase is about 15 °C/s. When the cooling rate is higher than 15 °C/s, some β phases with fine granular shape remain residually into plate-like structure. The plate-like α phase forms at cooling rate lower than 2 °C/s, serrate α phase forms at medium cooling rates, about 5−15 °C/s. The flow stress behavior of grade-2 CP-Ti was investigated in a temperature range of 700−900 °C and strain rate of 3.6−40 mm/min. The results show that dynamic recrystallization, dynamic recovery and work-hardening obviously occur during hot deformation. Constitutive equation of grade-2 CP-Ti was established by analyzing the relationship of the deformation temperature, strain rate, deformation degree and deformation resistance.

Key words: commercially pure titanium; phase transition; mechanical properties; flow stress