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 900degreesC, 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. (C) 2002 Elsevier Science B.V. All rights reserved.