shear band formation during warm rolling of iron
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Shear bands formed during both cold and hot plastic deformation have been linked with several proposed mechanisms for the formation of
ultrafine grains. The aim of the present work was to undertake a detailed investigation of the microstructural and crystallographic characteristics
of the shear bands formed during hot deformation of a 22Cr-19Ni-3Mo (mass%) austenitic stainless steel and a Fe-30 mass%Ni based austenitic
model alloy. These alloys were subjected to deformation in torsion and plane strain compression (PSC), respectively, at temperatures of 900C
and 950C and strain rates of 0.7 s-
1 and 10 s-
1, respectively. Transmission electron microscopy and electron backscatter diffraction in
conjunction with scanning electron microscopy were employed in the investigation. It has been observed that shear bands already started to form
at moderate strains in a matrix of pre-existing microbands and were composed of fine, slightly elongated subgrains (fragments). These bands
propagated along a similar macroscopic path and the subgrains, present within their substructure, were rotated relative to the surrounding matrix
about axes approximately parallel to the sample radial and transverse directions for deformation in torsion and PSC, respectively. The subgrain
boundaries were largely observed to be non-crystallographic, suggesting that the subgrains generally formed via multiple slip processes. Shear
bands appeared to form through a co-operative nucleation of originally isolated subgrains that gradually interconnected with the others to form
long, thin bands that subsequently thickened via the formation of new subgrains. The observed small dimensions of the subgrains present within
shear bands and their large misorientations clearly indicate that these subgrains can serve as potent nucleation sites for the formation of ultrafine
grain structures during both subsequent recrystallisation, as observed during the present PSC experient
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ultrafine grains. The aim of the present work was to undertake a detailed investigation of the microstructural and crystallographic characteristics
of the shear bands formed during hot deformation of a 22Cr-19Ni-3Mo (mass%) austenitic stainless steel and a Fe-30 mass%Ni based austenitic
model alloy. These alloys were subjected to deformation in torsion and plane strain compression (PSC), respectively, at temperatures of 900C
and 950C and strain rates of 0.7 s-
1 and 10 s-
1, respectively. Transmission electron microscopy and electron backscatter diffraction in
conjunction with scanning electron microscopy were employed in the investigation. It has been observed that shear bands already started to form
at moderate strains in a matrix of pre-existing microbands and were composed of fine, slightly elongated subgrains (fragments). These bands
propagated along a similar macroscopic path and the subgrains, present within their substructure, were rotated relative to the surrounding matrix
about axes approximately parallel to the sample radial and transverse directions for deformation in torsion and PSC, respectively. The subgrain
boundaries were largely observed to be non-crystallographic, suggesting that the subgrains generally formed via multiple slip processes. Shear
bands appeared to form through a co-operative nucleation of originally isolated subgrains that gradually interconnected with the others to form
long, thin bands that subsequently thickened via the formation of new subgrains. The observed small dimensions of the subgrains present within
shear bands and their large misorientations clearly indicate that these subgrains can serve as potent nucleation sites for the formation of ultrafine
grain structures during both subsequent recrystallisation, as observed during the present PSC experient
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