Grain growth on reheating for an as-cast Al-Nb-containing steel with segregated composition

Reheating treatments for as-cast Al-Nb-containing steel were examined at temperatures correlating to the predicted dissolution temperatures of the precipitates present in the interdendritic and dendritic regions. Bimodal grain growth was observed in this steel when reheated in the range 1160–1200°C as Nb-rich particles remaining in the interdendritic region prevented further growth of grains originating from the dendritic region when the pinning precipitates of AlN dissolved. The isolated abnormally large grain structure seen for the homogenised condition from previous work was not observed in the as-cast Al-Nb steel under any conditions. It is suggested that elemental segregation (particularly for Nb) plays a role in providing a spatially distributed (banded) pinning effect on the large grains growing from the dendritic regions.