The formation of the microstructure of the AK8 alloy with different initial grain sizes upon hot deformation has been investigated by optical and electron microscopy. It is shown that the processes of formation of the structure depend not only on the regimes of deformation (temperature and strain rate) but also on the initial grain size. The deformation of the AK8 alloy with a grain size of 16.2 μm and less in the temperature range of 400-500°C is accompanied by dynamic recrystallization. The hot deformation of the AK8 alloy with a grain size of more than 16.2 μm leads to the formation of a polygonized structure in the material. A diagram of the structural state of the AK8 alloy depending on the initial grain size was constructed from the results of this work.