Influence of Nitrogen Content and Deformation Temperatures on Dislocation Structures in Austenitic Stainless Steels

Nitrogen-added austenitic stainless steels exhibit excellent work-hardenability due to planar slips of dislocations. Two mechanisms of the planar slip have been proposed so far: glide plane softening mechanism and stacking-fault energy (SFE) reduction mechanism, which are thought to be dependent on nitrogen content and deformation temperature. In this study, conventional TEM, STEM-EDS and HR-STEM characterizations were carried out to clarify the influences of deformation temperature and nitrogen content on the dislocation characteristics of austenitic stainless steels. In the case of the nitrogen-added steel, the dislocation configurations became planar at a high temperature, 973 K. HR-STEM analysis revealed that SFE decreased with N addition and increased with temperature increase. Weak-beam TEM and HR-STEM analyses revealed that the planar dislocations were composed of 60 degrees mixed-dislocations and SFs at room temperature, and edge-dislocation and SFs at 973 K. These results suggested that the edge components of defects interacted elastically with N and N-Cr pairs and contributed to the origin of the planar slips.