With the electron backscattered diffraction (EBSD) technique the non-uniform microstructure forming under conditions of inhomogeneous dynamic deformation were investigated by the example of explosively bonded steel plates. The layers with fine-grained recrystallized structure as well as deformation-induced fragmented structure are distinguished within the narrow interface zone undergone intense deformation. The study was focused on the mechanism of the fragmented structure formation. Within the layers subjected to mediate deformation, the deformation-induced branching boundaries, along which the misorientation gradually changes from the angles above 30° to the ones below a tolerance angle of 2°, have been examined. The development of such boundaries was shown to demonstrate early stage of the fragmentation process.