A study of the dislocation core structure in high nitrogen austenitic stainless steel by weak beam EM

Abstract

The large strengthening effect of nitrogen interstitials and its strong influence on the dislocation distribution of Fe-Cr-Ni austenite have been rationalized by Owen et al. using a short-range-order-based model. However, the model cannot explain the high population of screw dislocations resulted from a small amount of plastic deformation. Grujicic suggested that nitrogen addition to Fe-Cr-Ni austenitic stainless steels causes spreading of the screw dislocation core into two or more non-parallel planes which results in low dislocation mobility. Higher stress and higher temperature are thus required to overcome the energy barrier for the movement of dislocations. The core structure of dislocations in nitrogen-containing stainless steels is of fundamental importance for understanding the strengthening mechanism of this material. The weak beam dark field imaging technique allows the direct observation of partial dislocations and stacking faults bonded by the partials. When the optimum imaging condition is satisfied, relatively intense, narrow images of less than 2 nm wide can be obtained.