Rapid solidification is regarded as being an effective method to refine the microstructure and reduce or eliminate the segregation of alloying elements.In this study the microstructures of rapid solidified carbon steel droplets (cooled in silicone oil) with different C contents by drop tube processing were observed.The volumes of droplets were set to be 2 mm × 2 mm × 2 mm (TM) and 5 mm × 5 mm × 5 mm (FM).For most samples,the microstructures are nearly the same from the surface to the center region.The microstructures of the FM samples with higher C content are much finer than those of the TM samples,which is the opposite of the situation with the lower C content samples.The distribution of C along the diameter of each sample was detected.The segregation of C was observed in TM samples with higher C contents while not in FM samples.This is regarded as relating to recalescence and the diffusion of C atoms during the solidification process.