某些球铁铸件产品加工后，发现冒口下方变色。对其进行金相检验、力学性能测试、化学成分分析等，以确定球铁铸件变色原因。结果表明：球铁铸件冒口下方发生变色，主要有球化不良、絮状石墨和石墨球聚集、成串分布的形态；球化不良、絮状石墨主要是由球化元素少或已被消耗、石墨球数量少等造成，而石墨球聚集、成串分布是由碳当量偏高造成的石墨漂浮现象。

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.