Abstract: The discoloration was found below the risers of the ductile iron castings after the processing of the products. The discoloration reasons of ductile iron castings were searched through metallographic examination, mechanical property testing, chemical composition analysis and so on. The results show that: the color below the risers of ductile iron castings changed, and it had the morphology of poor spheroidization, flocculent graphite, aggregation and cluster distribution of graphite nodules; the poor spheroidization and flocculent graphite were produced mainly because of less or exhausted spheroidal elements and less graphite nodules; while the aggregation and cluster distribution of graphite nodules were the graphite floating phenomenon due to the high carbon equivalent.