Characteristics of shear bands formed in an austenitic stainless steel during hot deformation

A detailed investigation of the substructural characteristics of shear bands, formed in an austenitic stainless steel during deformation in torsion at 900°C, with particular emphasis on their nucleation stages, has been undertaken. Shear bands forming at large strains in a matrix of pre-existing microbands are composed of well-recovered, slightly elongated cells. These bands propagate along a similar macroscopic path and the cells, present within their substructure, are rotated relative to the surrounding matrix about axes close to a common macroscopic direction. The cell boundaries are frequently non-crystallographic, suggesting that the cells might often form through the operation of multiple slip. Shear bands appear to form through a cooperative nucleation of originally isolated cells that gradually interconnect with each other to form long, thin bands that subsequently thicken via the formation of new cells. When crossing a shear band, cumulative misorientations across consecutive cell boundaries display a typical sigmoidal profile, characterised by a gradual increase of misorientation angles to a peak value followed by a subsequent gradual decrease towards the matrix orientation. The formation of new cells thus appears to be assisted by the stress fields generated by lattice rotations of the previously formed cells.