Tatiana Yu. Kin

This study conducts a preliminary FE simulation of screw piercing and screw rolling processes for producing bimetallic pipes with variable inner and outer positioning and thickness of the corrosion-resistant steel CL (13Cr and 18Cr10Ni grades) as a rational first step before experimental testing. The results demonstrate that a favorable stress–strain state is formed in both processes under the selected deformation parameters (there are no high tensile stresses in the area of high strains and low temperatures). Shape change analysis confirmed that the pipe geometric dimensions according to simulation are sufficiently close to the target values, with only minor deviations in wall thickness and ovality. The change in CL thickness during piercing ranges from 34% to 51% and increases with the elongation ratio. In the rolling process, it reaches approximately 55–56%. The CL position, its thickness and the material choice significantly influence the deformation heating intensity within the bonding of base and clad materials, as well as the magnitude of the forces acting on the tool in contact with the CL. The obtained results can serve as a methodology that lays the groundwork for experimental verification and the further technology implementation, while minimizing risks and costs.

Numerical simulation of metal forming processes is finding increasingly wide applications in advanced industry for the optimization of material processing conditions and prediction of process parameters, finally delivering a reduction of production costs. This work presents a comparison between simulation results of radial shear rolling (RSR) of VT3-1 titanium alloy (Ti-Al-Mo-Cr-Fe-Si) and results of experimental RSR at 1060 °C, 980 °C, and 900 °C in one, three, and five passes, respectively. The digital model (DM) demonstrates a high convergence of the calculation results (calculation error of less than 5%) with the actual geometric parameters of the experimental bars, their surface temperature, and rolling time during the experiment, which indicates a good potential for its application in the selection of deformation modes. Based on the simulation and experimental data, the conditions providing for the formation of differently sized grains in the bar cross-section have been identified. All of the as-rolled bars exhibit a gradient distribution of macrostructure grain size number (GSN), from the smallest one at the bar surface (2–4) to the greatest one in the center (4–6). The macrostructure GSN correlates with the workpiece temperature, which is the highest in the axial zone of the bars, and with the experimentally observed high plastic strain figures in the surface layers. It was found that, depending on the temperature conditions and reduction ratio per pass, any minor change in the values of process parameters can lead to the formation of macrostructures with different grain size numbers.

Co-Cr-Mo alloys are in high demand as materials for medical implants. However, hot processing of these alloys is quite difficult due to the need to maintain narrow temperature range of deformation to achieve the required mechanical properties and structure of the products. The features of formation of structure, phase composition and mechanical properties of Co-Cr-Mo alloy at the main stages of thermomechanical treatment were considered in this study. The results demonstrated a significant enhancement in the strength characteristics of the alloy during processing in both forging and radial shear rolling (RSR). At the same time, radial shear rolling processing simultaneously increased the strength and ductility of the alloy. According to the XRD analysis data, the phase composition changes from single-phase structure (FCC-phase) after forging to a mixture of FCC-phase and HCP-phase after RSR during processing. The structure gradient characteristic of RSR decreased as the total elongation ratio increased, maintaining a tendency towards a finer-grained structure near the surface of the bars and a coarser one in the center. This tendency was reflected in the average grain size and the level of mechanical properties. Combined thermomechanical treatment, including the RSR process, made it possible to achieve a unique formation of microstructure and phase composition in the Co-Cr-Mo alloy, ensuring high strength while maintaining ductility.

Radial-shear rolling technology (RSR) is a modern, effective technique for obtaining structured semi-finished and final bar products from various metals and alloys, including hard-to-deform ones. Due to design features (feed angle 18–20 °, rolling angle 0–12 °, taper angle of roll 10 ± 2,5 °) implemented in the RSR equipment (mini-mills) and unique trajectory-deformation conditions, the possibility of obtaining ultrafine-grained functional-gradient structure is realized. At the same time, mini-mills are characterized by compactness and versatility of working tools, which allows to reduce labor costs and follow the concept of lean production. This article reviews the industrial application of technology and equipment of RSR and scientific and applied research in this direction by various scientific groups, outlines the elements of theory, as well as the main stages of development and implementation. The reviewed publications indicate the demand for and prospects of application of RSR technology for obtaining products with a unique combination of properties. The study was supported by a grant from the Russian Science Foundation (Project No. 23-19-00477), https://rscf.ru/project/23-19-00477/.

Effect of radial shear rolling on the morphology of intermetallic particles, and the mechanical properties of 7075 alloy at different processing temperatures and heat treatment after deformation was investigated. The results were consistent with data on metallographic investigation of phase particle shape, counts, and distribution. It was found that the formation, quantitative distribution, and circularity of particles at the surface and in the centre of the bar depended on the processing temperature and temperature gradient between surface and centre and were defined with a scheme of stresses in the deformation zone. The values of strength properties for all bars obtained by RSR depended on the processing regimes, while plasticity (elongation to failure δ = 14%–20%) increased with the growth of processing temperature. Article highlights Radial shear rolling makes it possible to obtain aluminium alloy bars with a gradient structure and a combination of high strength and ductility. The influence of the RSR method is reflected in the nature of the distribution of dispersive particles in the matrix of alloy. Mechanical properties of bars subjected to the RSR method depend on the initial processing regimes, while the level of plasticity increases with the growth of processing temperature.

An experimental testing of the technology for obtaining a deformed Co-28Cr-6Mo alloy using radial shear rolling is presented. Mechanical peeled and homogenized ingots of vacuum induction melting with a diameter of 57 mm were subjected to radial shear rolling in 4-5 passes to bars with a diameter of 18 and 29 mm at a temperature of 1200 °C with quenching of the final profile in water or cooling in air. A study of the microstructure, mechanical properties in the cast and deformed state was carried out. The requirements of GOST ISO 5832-12-2009 in terms of normalized indicators - tensile strength, yield strength and relative elongation are fully satisfied. At the same time, there is an increase in relative elongation by 1.4-1.6 times compared with the initial cast state and an excess of regulatory requirements by 3.0-3.3 times. The experimental technology has been implemented at NUST MISIS radial shear rolling mills and has the prospect of industrial scaling. The very significant advantages of the proposed technology include a small total elongation ratio (μ = 3.86), which ensures that the requirements of GOST on mechanical properties for the deformed Co-Cr-Mo alloy are met.The study was supported by the Russian Science Foundation grant No. 23-19-00477, https://rscf.ru/project/23-19-00477/.