Microstructure Evolution and Recrystallized Behavior of Friction Stir Welding Twin-Induced Plasticity Steel

The restoration mechanism of twin-induced plasticity (TWIP) steel during friction stir welding (FSW) changed with the degree of the deformation, and the microstructure evolution and dynamic recrystallization are complex and unclear. In this paper, the electron backscattered diffraction and transmission electron microscopy techniques were used to evaluate the dynamic grain structure of FSW joint of TWIP steel. The results showed that the dynamic recrystallization mechanisms in TWIP steel during FSW contained discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX). The recrystallization mechanism transitioned from DDRX at the initial deformation stage to DDRX and CDRX at the middle deformation stage, eventually becoming primarily CDRX at the end deformation stage. Numerous annealing twin boundaries (ATBs) were formed within the joint, and the straight ATBs primarily resulted from grain growth accidents, while cluster-shaped ATBs were formed through re-excitations and decomposition of specific grain boundaries.