Gradient of strength and microstructure after deformation by free torsion of metal bar

Abstract

The article presents the results of the study and analysis of the structure, properties and deformation parameters of a longlength bar of a circular cross-section from grade 10 steel obtained using severe plastic deformation (SPD) by free torsion at a temperature of 600°C. Using computer simulations with Deform 3D software, the stress-strain state of the samples, including the distribution of accumulated strain, average stresses, and thermal field, are investigated. A physical experiment was carried out, the structure parameters and microhardness in the longitudinal section of the samples after deformation were investigated. It was shown that the free-torsion SPD method provided a non-uniform accumulation of ultrahigh strains up to 6 in long-length metal bars of a circular cross-section, the formation of a gradient type structure with a mean grain size from 1 to 7 μm and with a gradient in mechanical properties. The effect of localization of deformation during uniform torsion of the workpiece was revealed, at the same time, the temperature of the bar during severe plastic deformation increased up to 230°C. EBSD analysis revealed a gradient structure of steel specimens with a mean grain size of about 1 µm near the surface area and ~5 µm near the central area.