Effect of hot rolling on the structure of TC21 alloy with acicular alpha

The modification of acicular alpha of TC21 titanium alloy during hot rolling was investigated for finer grains under the condition of optimized preheating time. Two different preheating schedules were used to roll TC21 alloy plates at strains of 0.36, 0.69, and 1.2. The results show that preheating time has a great effect on microstructure evolution. By and large, under a given set of deformation conditions, the materials with shorter preheating time more rapidly formed finer equiaxed grains compared to the materials with longer preheating time. The nature of the modification of acicular alpha to equiaxed morphology was identified to be a two-step process: the formation of the necklace-like structure by geometric dynamic recrystallization, and then the separation of alpha lamellae by boundary splitting along subboundaries and the subsequent globularization by migration of interfaces.