Study of Dislocation Structure, Internal Stresses, and Redistribution of Carbon Atoms in the Zone of Localized Deformation in Structural Steel 20

The paper presents the results of investigation of the dislocation structure, the magnitude of the curvature–torsion of the crystal lattice, the amplitudes of the internal stress fields, as well as the redistribution of carbon atoms in zones of stable localization of deformations depending on the state of samples made of structural steel 20. Samples were studied without operation, after operation without destruction, and with destruction. The samples were stretched at the same speed until a stable deformation localization zone appeared, after which the loading was stopped. To study the dislocation structure, we used the method of transmission electron microscopy on thin foils. It has been shown that deformation of samples made of structural steel 20 in the direction “initial” → “not destroyed” → “destroyed” sample in all morphological components of the structure, as well as in the material as a whole, gradually leads to a fragmentation of the structure down to a nanocrystalline structure in individual areas of the material. Dislocations move to fragment boundaries, and the scalar dislocation density ρ decreases. At the same time, internal shear stresses σ_s decrease. The change in local stresses σ_l is of a different nature, namely, the plastic component of local stresses \(\sigma _{{\text{l}}}^{{{\text{pl}}}}\) decreases, and the elastic component \(\sigma _{{\text{l}}}^{{{\text{el}}}}\) increases sharply. It has been established that deformation of steel 20 leads to the destruction of cementite particles located at the boundaries of dislocation fragments (the volume fraction decreases) and the formation of carbides inside the fragments (their volume fraction increases). Carbon from destroyed cementite particles at the boundaries of fragments is spent on the formation of cementite particles inside the fragments, of crystal lattice defects, and the formation of carbides in new morphological structures (micro- and nanograins).