Grain boundary segregation in an oxide-dispersion-strengthened ferritic steel

In order to enhance the creep ductility of oxide-dispersion-strengthened (ODS) ferritic steels, zone annealing is carried out which results in recrystallization. In extruded bars of the ODS material MA957, a significant curvature of the recrystallization interface has been observed in longitudinal sections. MA957 is a superalloy of nominal composition Fe-14Gr-1Ti-0.3Mo-0.27 Y2O3 wt% which contains a fine yttria dispersion in a fully ferritic 14% Cr matrix. It has been suggested earlier that the curvature of the recrystallization interface is a consequence of gradients in solute segregation which influence grain boundary mobility. An accurate analysis of grain boundary microchemistry in MA957 was carried out using a field-emission gun scanning transmission electron microscope in order to provide more information on this topic. Highly localized segregation of titanium to grain boundaries was observed which is likely. (UK)