Structure and mechanical properties of low-carbon ferrite-pearlite steel after severe plastic deformation and subsequent high-temperature annealing

In the work, we studied the structure and mechanical properties of low-carbon ferrite-pearlite steel (Fe-l.12Mn-0.08V-0.07Ti-0.1C, wt %) after severe plastic deformation and subsequent high-temperature annealing. The ferrite-pearlite steel was subjected to equal-channel angular pressing at T = 200 °C (Bc mode, 4 passes) and to high-pressure torsion at room temperature (5 revolutions at 6 GPa). It is shown that severe plastic deformation under these conditions gives rise to fragmented structures with an average fragment size of 260 nm after equal-channel angular pressing and 90 nm after high-pressure torsion. Quasi-hydrostatic pressure increases the steel microhardness to 6.4 GPa, which is much higher than the steel microhardness in the initial state and after equal-channel angular pressing (1.6 and 2.9 GPa, respectively). The formed structures feature high thermal stability: up to 400 °C after high-pressure torsion and up to 500 °C after equal-channel angular pressing. The contributions of dispersion and substractural hardening to the high strength properties of Fe-Mn-V-Ti-C steel under severe plastic deformation and to the high thermal stability of its submicro- and nanocrystalline structures in high-temperature annealing are discussed.