Grain boundary structural changes during annealing and high temperature deformation of ferritic stainless steel

Abstract

Grain boundary structure and energy have an influence on the formation of the annealing texture as well as the material ability to continue the steady state deformation at high temperatures. Texture measurements together with the statistical distribution of grain boundary rotation parameters show changes during high temperature deformation. Annealed structure contains grain boundaries having rotation parameters in certain favoured groups. Such groups do not necessarily belong to any low indexed coincidence orientation relationship, even though periodic contrast of grain boundary dislocations in numerous boundaries is resolved in the transmission electron micrographs. The texture becomes stronger during the high temperature deformation with increasing strain compared with the annealed texture. The rotation parameters of grain boundaries in deformed structure include often few degrees rotations from certain coincidence orientation relationship, but they do not, however, show such a grouping of rotation parameters as in the annealed structure. Furthermore, rotation angles of small angle boundaries were found to increase with increasing deformation strain at high temperature. Several mechanisms of grain boundary sliding are interpreted based on the structural observations. Finally, based on the existence of orientation relationship groups, estimates for low energy grain boundaries are presented.