Spreading of extrinsic grain boundary dislocations in austenitic steel

The dependence of the spreading process of extrinsic grain boundary dislocations (EGBD's) on grain boundary state and misorientation, and spreading kinetics in austenitic steel is investigated. Spreading of EGBD's at non-equilibrium grain boundaries obtained by successive cold rolling and annealing treatments at a temperature much lower than 0.8Tm is found to occur at approximately 450 °C. EGBD's in specimens annealed at 0.8Tm however spread at about 550 to 600 °C. This observation seems therefore to indicate that at approximately 0.8Tm an irreversible change in grain boundary structure takes place. It is also found that EGBD's lying at special and incoherent twin boundaries spread at 700 °C compared with 550 to 600 °C for equilibrium, random boundaries in the same material. Observations of spreading kinetics indicate that the latter is not solely controlled by grain boundary diffusion.