Abstract
The quantity and morphology of spheroidal graphite have an important effect on the properties of ductile iron, and the characteristics of spheroidal graphite are determined by the solidification process. The aim of this work is to explore the precipitation and evolution of graphite nodules in hypoeutectic, eutectic, and hypereutectic ductile irons by thermal analysis, liquid quenching and metallographic technique. Results show that hypoeutectic ductile iron has the longest solidification time and the lowest eutectic temperature; eutectic ductile iron has the shortest solidification time; hypereutectic ductile iron has the highest eutectic temperature. After solidification is completed, hypoeutectic ductile iron has the lowest nodule count, nodularity and graphite fraction; eutectic ductile iron has the highest nodule count, nodularity and the smallest nodule diameter; hypereutectic has the highest nodule diameter and graphite fraction. The nucleation and growth of graphite nodules in hypereutectic ductile iron starts before bulk eutectic crystallization stage, however, the precipitation and evolution of graphite nodules of hypoeutectic and eutectic ductile irons mainly occur in the eutectic crystallization stage. The graphite precipitated in eutectic crystallization of hypoeutectic, eutectic, and hypereutectic ductile irons, are 61%, 68% and 43% of total graphite volume fraction, respectively. Simultaneously, there are plenty of austenite dendrites in hypoeutectic and hypereutectic ductile irons, which are prone to shrinkage defects. Therefore, the eutectic ductile iron has the smallest shrinkage tendency.
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Acknowledgments
This work was financially supported by the National Natural Science Foundation of China (NSFC) under Grant Nos. 51601054 and 51775006, the Natural Science Foundation of Hebei Province of China under Grant Nos. E2017202095 and E2016202100, the Scientific and Technological Transformative Project of Tianjin Supporting Beijing-Tianjin-Hebei under Grant No. 18YFCZZC00030, and the Central Government Guides Local Science and Technology Development Fund Projects under Grant No. 206Z1005G.
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Bin-guo Fu Male, born in 1984, Ph.D. His research interests mainly focus on the cast iron melt quality online measurement and control.
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Liu, Jh., Yan, Js., Zhao, Xb. et al. Precipitation and evolution of nodular graphite during solidification process of ductile iron. China Foundry 17, 260–271 (2020). https://doi.org/10.1007/s41230-020-0042-2
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DOI: https://doi.org/10.1007/s41230-020-0042-2