Abstract
Abstract Results of the electron backscatter diffraction (EBSD) study on structural changes in Armco iron subjected to severe plastic deformation by differential speed rolling (DSR) with different values of roll speed mismatch (R = 1, 2, 3, and 4) are shown in the present article. Results of the EBSD microstructure evaluation reveal that a differentiation of roll speeds results in an effect of structure refinement—iron samples processed with high roll speed mismatch are characterized by a high fraction of grains with submicron size. A microtexture examination shows that the DSR process leads to an overall texture weakening effect and a displacement (a shifting to different “stable” positions) of the basic rolling texture components, due to an additional presence of a simple shear component in the deformation gradient imposed to the material. Despite the higher hardness of the DSR-processed samples, results of the EBSD strain analysis indicate that some part of the stored deformation energy is released during rolling with an additional presence of shear strain. This finding points toward the possibility of activating a dynamic transformation of the material structure into some more stable state. However, since the observed structural changes take place inside deformation bands and do not lead directly to the formation of a fully equiaxed grain structure, it seems to be more reasonable to call the observed structure transformation a subgrain structure evolution through accumulated shear deformation, which may be related to the dynamic recovery process.
Highlights
THE processing and properties of ultrafine-grained (UFG) materials have generated considerable interest recently from both an industrial and a scientific standpoint
According to the results shown by Megantoro et al.,[27] an application of differential speed rolling (DSR) processing leads to a prominent temperature rise in an IF steel sample
Since the observed structural changes take place inside deformation bands, and do not lead directly to the formation of a fully equiaxed grain structure, it may be stated that a high fraction of submicron grains in the material subjected to the high ratio DSR method is an effect of both the strain-induced grain subdivision and the temperature rise, which supports activation of the continuous dynamic recovery and shear-assisted substructure rearrangement
Summary
THE processing and properties of ultrafine-grained (UFG) materials have generated considerable interest recently from both an industrial and a scientific standpoint. There are a few hydrostatic SPD methods that have been successfully used to fabricate UFG metals and alloys (e.g., equal channel angular pressing, cyclic extrusion compression, or high pressure torsion) These and other methods were described recently in a comprehensive review article by Estrin and Vinogradov.[7] despite positive results in terms of structure and properties control, hydrostatic SPD techniques have rather poor industrial potential due to the small size of processed samples and low manufacturing efficiency. The DSR process was successfully applied in the field of controlling the crystallographic texture of engineering materials This issue is especially important for aluminum and magnesium alloys, which, due to formation of unfavorable rolling and recrystallization textures, possess a worse susceptibility to deep drawing than widely applied low carbon steels. In the present article, existing experimental data are supplemented with the results of our electron backscatter diffraction (EBSD) examination of the microstructure, the texture, and the internal lattice strain evolution of Armco iron during DSR processing
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