OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 2 2025 Mechanical properties of Fe-21Mn-6Al-1C steel samples in the initial state and steel samples cut from the center and edge of rods after various CRF reductions ε 0 % 20 % 40 % 60 % 80 % Position Center Edge Center Edge Center Edge Center Edge σu, MPa 818 1,009 1,133 1,505 1,381 1,853 1,621 2,062 1,741 σ0.2, MPa 459 705 1,028 1,499 1,303 1,838 1,531 2,062 1,626 δ, % 55.6 51.4 32.7 18.6 20.3 10 16.9 5.7 15.4 δu, % 47.9 37.9 10 0.3 1.8 0.3 1.4 0.2 1.2 the same time, an increase in the yield strength to 705 MPa and ultimate tensile strength to 1,009 MPa is observed (Table). The ductility of the edge of the rod is noticeably lower (δ = 32.7%; δu = 10%), while the strength characteristics are higher (σu = 1,133 MPa; σ0.2 = 1,028 MPa). Further CRF is accompanied by a change in the above-mentioned ratio of strength and plasticity between the center and the edge of the rod to the opposite: the strength becomes higher at the central part of the rod, and plasticity ‑ at the edge. For example, after 80 % CRF, the uniform elongation (δu) of the center and edge material decreases to 0.2 % and 1.2 %, respectively. In this case, the elongation to failure of the center material is 5.7 %, and of the edge material – 15.4 %, which is mainly determined by concentrated deformation. The strength properties, in turn, of the center in the rod (σu = 2,062 MPa; σ0.2 = 2,062 MPa) exceed these characteristics of the edge (σu = 1,741 MPa; σ0.2 = 1,626 MPa) by 18-27 %. With an increase in the degree of CRF, the strain-hardening rate decreases (Fig. 7). a b с Fig. 7. True stress and strain-hardening coefficient (SHC) as a function of true strain during uniaxial tensile testing of samples cut from the center and edge of the rod after CRF with ε = 20% (a), ε = 40% (b), and ε = 80% (c) Previously, using finite element modeling, it was predicted that in CRF, moderate tensile/compressive stresses act at the center of the rod, and high compressive stresses operate at the edge of the rod [16, 17]. Such a non-uniform stress condition leads to the accumulation of greater plastic deformation at the rod edge compared to the core. TEM methods have shown that in the studied steel, during CRF, various deformation mechanisms are activated, resulting in a whole spectrum of structural states along the rod radius. Thus, in the Fe-21Mn-6Al-1C steel, the following stages of microstructure formation are observed (Fig. 2): after low degrees of deformation (ε = 20 %) – formation of deformation microbands along various systems in the center and parallel deformation microbands at the rod edge; after medium degrees of deformation (ε = 40-60 %) – formation of single mechanical twins of various systems in the center and parallel packets of twins at the edge; after high degrees of deformation (ε = 80 %) – twinning according to various systems in the center and formation of a fragmented microstructure at the edge. The results of EBSD analysis show
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