OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 2 2025 bilizes. Due to the saturation of mechanical twinning, the strain hardening rate decreases at the third stage (Fig. 7, b2). In the present study, the stage-like strain hardening is ascribed to the heterogeneous microstructure (Fig. 7). On the curves for all three types of samples obtained from a rod after heat treatment at 700 °C, two stages of strain hardening can be distinguished (Fig. 7, b2-4). The first stage is also characterized by a sharp decrease in strain hardening. At the second stage, the slope of the curve changes, and the decrease in strain hardening rate becomes less intense. Table presents that all three types of samples after 95 % CRF have high strength and low ductility. The ultimate tensile strength (σu) is 1,240‑1,300 MPa, and the yield strength (s0.2) is 1,150‑1,210 MPa. Fig. 7. Stress-strain curves (a1, b1, c1) and work hardening behavior of the center (a2, b2, c2), edge (a3, b3, c3) and heterogeneous (a4, b4, c4) material after different modes of thermo-mechanical treatment
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