The new developing technologies of metal formation, based on simple shear, are known as severe plastic deformation (SPD) technologies. They are actively used for improving the mechanical properties of metals. Even complex systems such as steels have not been adequately investigated for SPD process. However, studies are in progress as is reflected from the publications in the literature. Due to insufficient knowledge of the structural changes, occurring in low-carbon steels during SPD, there is a need for a more detailed consideration by modern methods. This paper discusses the characteristics of the formation of structure and texture of low-carbon steels subjected to warm twist extrusion (TE). A relatively new method, which makes possible a detailed study of the structure of metals, is electron backscattered diffraction (EBSD). EBSD has shown that warm TE increases the structure isotropy, thus leading to significant fragmentation and activation of the mechanisms of dynamic polygonization, recrystallization and grain-boundary sliding. These structural features lead to hardening of the material by 1·5 times, while maintaining a high level of plasticity.

The mechanisms of structure formation in low-carbon steel deformed by warm twist extrusion (Tdef = 400°C) are considered. The analysis of electron backscattering diffraction shows that dynamic recrystallization and grain boundary sliding play an active role in structure formation in the process of severe plastic deformation. It was shown that severe plastic deformations induce dissolution of carbon.

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Shear deformation is one of the effective ways for grain boundary engineering. In the current contribution, the effect of the shear deformation incorporated into the conventional drawing process is shown. A specific feature of this experimental technology is a reduction of the structural anisotropy. This effect is related to the application of dies with shear that makes the metal flow to change its direction. In particular the grain refinement is stronger. The experimental drawing technology results in an extensive increase in the fraction of small grains (less than 3 μm in size) and a decrease in the fraction of large grains. A large amount of small grains with high-angle boundaries in this case is registered. The formation of this kind of grains is explained by progress in competing processes of large grain fragmentation and continuous dynamic recrystallization. The result is the change of the type of the grain boundaries from smooth to serrated ones and the formation of unclosed high-angle grain boundaries. Besides, it has been demonstrated that a certain part of small grains provides grain boundary sliding. The comparative analysis of the hardness tests has demonstrated increasing hardness with deformation accumulation, but after the classical drawing, the hardness grows linearly and stepwise after the experimental shear drawing. The physical reasons of such behaviour are explained by microstructural features which are discussed in current contribution.

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