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Characterization of fragmented structure developed during necking of iron tensile specimen

The microstructure fragmentation during necking of the iron tensile specimen was investigated by the electron backscatter diffraction technique. The material under study was the commercially pure iron containing particles of manganese sulfides and oxides. The undeformed mean grain size was ≈54 μm. The aim of the research was the characterization of the structural state preceding ductile rupture. The deformation microstructure was examined on the longitudinal section of the specimen in the locations corresponding to various true strains from ≈1 up to 1.8, which allowed studying the structure evolution in a single specimen. Special attention was paid to the deformation-induced high-angle boundaries, which are known to be preferable sites of microcracks nucleation. It was shown that a considerable number of high-angle boundaries appear already at a strain of ≈1, and their fraction rises with further straining. Large-scale fragmentation peculiarities of different kinds associated with the formation of high angle boundaries were found and discussed in terms of the effect of the neighborhood of grains on their fragmentation. Besides, multiple shear microbands of submicron width inclined to the tensile direction by angles ≈35° and larger were observed in the longitudinal section, which intersect the previously formed deformation substructure. The boundaries of these microbands were shown to make significant contribution to the accumulation of high angle boundaries.