OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 2 2025 layer, strain localization occurs at the initial stages of plastic strain, but the more ductile rod core prevents further strain localization in subsurface layers, which changes the stress distribution. Such deformation behavior causes the generation and accumulation of geometrically necessary dislocations (GND) at the boundary of layers with different structures. In turn, GND interact with mobile dislocations and fix them in this area, which provokes additional strain strengthening. In addition, such a stress condition can be accompanied by the activation of additional slip systems [35]. Based on the results of load-unload tests, it is shown that the material with a heterogeneous structure exhibits the highest value of back stresses (Fig. 8). The difference in the value of back stresses is comparable to the difference in the yield strength (Table). Fig. 8. Back stress levels obtained for specimens with different microstructures, subjected to 95 % CRF, followed by annealing at 700 °C Thus, based on the results of mechanical tests as a function of the temperature of post-deformation heat treatment for the steel under study, three areas can be distinguished with different strength and ductility ratios, which is graphically shown in Fig. 9. It is obvious that changing the structure type significantly affects mechanical properties. Specifically, the material with a cold-deformed structure is characterized by high strength and low ductility. Steel with a homogeneous structure obtained during post-deformation heat treatment has high ductility and low strength. Whereas, the material with a heterogeneous structure possesses a good balance between strength and ductility. Fig. 9. Relationship between yield strength (σ0.2) and proportional elongation (δu) of the steel under study in various microstructural conditions Conclusion The effect of a heterogeneous structure obtained during to a 95 % area reduction and subsequent heat treatment at 600‑700 °C on mechanical properties of the AISI 316Ti steel was studied. The following conclusions are drawn: 1. The proposed thermomechanical treatment forms a heterogeneous structure in the studied steel. The microstructure of the cold-deformed workpiece is changed from a twin-matrix structure in the rod center to a UFG structure in the subsurface layer. Heat treatment at 600‑700 °C is accompanied by polygonization over the cross section of the rod. Additionally, heat treatment at 700 °C activates the formation of recrystallization nuclei in the subsurface layer. Furthermore, from the center to the edge of the rod, texture
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