Shear impact during steel wire drawing on grain boundaries and mechanical properties
Résumé
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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