β Grain Evolution and Static Recrystallization Mechanism during Hot Rolling and Annealing of Ti-35421 Titanium Alloy

Ti-35421 titanium alloy is a new near-β titanium alloy with low cost, and its size and distribution of β grain are important microstructural parameters to influence the mechanical properties. To provide a guideline for the fabrication of uniformly fine β grains, Ti-35421 alloy was hot rolled and subsequently annealed at different temperatures and different time in β region, and the combined effect of rolling and annealing on the β grain evolution and static recrystallization (SRX) was investigated. The results show that, during rolling, the initial coarse equiaxed β grain is elongated, and the dynamic recovery dominates the microstructure evolution. During annealing, a middle rolling temperature of 850 °C induces the most intense SRX. The increasing annealing temperature or annealing time promote the SRX. The SRX occurs by the grain boundary bulge nucleation and makes the elongated β grains transform into equiaxed grains, but not all equiaxed grains belong to SRXed grains. The effect of annealing parameters on grain morphology evolution is well interpreted based on the SRX mechanism. Conclusively, an annealing temperature of 850 °C and annealing time of 15 min are appropriate to produce uniformly fine β grains for the hot-rolled Ti-35421 titanium alloy.