The effects of ausforming procedure and subsequent annealing treatments on microstructures of cobalt (Co) samples are investigated by electron channeling contrast and electron backscatter diffraction techniques.Results show that the ausformed Co samples consist of coarsen blocky laths (single ε phase) with the irregular morphology and the ultra-fine acicular laths (dual phase:γ and ε) with the slender and rectangular morphologies.As compared to the slight reduction sample,the much denser acicular laths are observed in the heavily ausformed sample.In addition,recrystallization behavior and annealing-induced γ → ε transformation have occurred in ausformed Co samples during the annealing treatment.