The Strain Dependent Accommodation Behaviour of Extrinsic Grain Boundary Dislocations

Abstract

Previous work on a fully austenitic stainless steel has shown that the nucleation and growth of Niobium Carbide (NbC) particles at grain boundaries can be substantially affected by deformation introduced prior to ageing (1). The present investigation which is, in part, an extension of the above work was instigated to examine the accommodation behaviour of extrinsic grain boundary dislocations as a function of deformation and temperature. The alloy investigated contained 20% chromium, 25% nickel, 0.6% niobium, 0.02% carbon + nitrogen, balance iron. Solution treated specimen material was cold rolled by 2%, 5% and 13% prior to annealing for times between 5 and 15 minutes at temperatures ranging from 650°C to 1000°C.Figures la and b show typical grain boundaries in the as-worked 2% and 5% materials; extrinsic dislocations appearing as linear features in the grain boundaries. However, grain boundaries in specimen material deformed by 13% contained such large numbers of these defects that the clear resolution of the individual dislocations was frequently impossible.