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To explain the intrinsic mechanism of the yield plateau phenomenon in commercially pure titanium,the tensile behaviors of commercially pure titanium specimens after 91.6％cryorolling and subsequent annealing at 280℃,335℃,450℃and 600℃have been studied.The results show that the yield plateau phenomenon is a result of dislocation behaviors controlled by grain size and thus only exists within a given range of mean grain size.α grain boundaries are the main dislocation mul-tiplication sources of commercially pure titanium.Fine-grained microstructure could offer numerous dislocation multiplica-tion locations during deformation.Once the applied stress is above the yielding strength,dislocations multiply rapidly and the mobile dislocation density is high.To retrieve the imposed strain rate,the mean dislocation velocity is bound to be low.Therefore,it takes time for them to interact with each other.As a result,the movement of dislocations is hardly blocked and the deformation could continue at a nearly constant applied stress.Consequently,the so-called yield plateau behavior presents in the tensile curves.The disappearance of yield plateau phenomenon in coarse-grained and ultrafine-grained microstructures is attributed to the quick realization of the mutual interactions among dislocations at the initial stage of tensile test.