The main features of plastic strain macrolocalization and structure of low-carbon steel after hot rolling and electrolytic hydrogen saturation in a thermostatted three-electrode electrochemical cell at a controlled constant cathode potential have been studied. Using the method of double-exposure speckle photography at different stages of strain hardening the main types and parameters of plastic flow macrolocalization (propagation rate and wavelength) have been identified. The effect of interstitial impurity of hydrogen on the change of the substructure and cementite morphology has been determined using methods of optical and electron microscopy. Attention has been given to the formation of dislocation substructures; bending-torsion of the α-phase lattice has been revealed, as evidenced by the presence of bend extinction contours. The main sources of stress field have been found to be grain and fragment boundaries.