Nanostructural Evolution and Deformation Mechanisms of Severely Deformed Pure Fe

Microstructural evolution and mechanical behavior of commercially pure Fe during severe deformation by cold caliber rolling followed by wire drawing were investigated using transmission electron microscopy and electron backscatter diffraction. Following by a drastic increment of strength in the early stage of deformation, shear banding as a softening mechanism leads to decreasing of work hardening rate and finally a steady state situation at medium strains, creating a bimodal microstructure. Increasing strain beyond 3 is associated with increasing the rate of work hardening and refinement of the material. Severely deformed Fe after cold caliber rolling to equivalent strain of 4.5 evolves from lamellar ultrafine-grained structure. Additional deformation by drawing results in more homogeneous structure and activates new mechanisms. A dynamic recovery appears at severe strains through mechanically assisted triple junction motion. It is found that suppression of triple junction motion enhances the refinement of microstructure and the strength, such that the highly deformed Fe after equivalent strain of 7 has a nano/ultrafine-grained structure combined with a high tensile strength of 1115 MPa.