Electron Backscatter Diffraction Study on Microstructure, Texture, and Strain Evolution in Armco Iron Severely Deformed by the Differential Speed Rolling Method

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. (C) The Minerals, Metals & Materials Society and ASM International 2015