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Solidification, Macrostructure and Shrinkage Formation of Ductile and Compacted Irons
International Journal of Metalcasting ( IF 2.6 ) Pub Date : 2020-04-02 , DOI: 10.1007/s40962-020-00444-z
Roberto E. Boeri , Marcos G. López , Nicolás E. Tenaglia , Juan M. Massone

This manuscript summarizes recent investigation of the authors into the solidification and shrinkage defect formation of ductile and compacted graphite cast irons. The study makes use of the DAAS (direct austempering after solidification) technique, developed earlier by some of the authors, to reveal the solidification grains. In addition, color metallography is used to reveal the microsegregation pattern. The formation of shrinkage defects is related to both the solidification macrostructure and the microsegregation pattern. The examination of the macrostructure shows that large solidification grains, composed by dendritic austenite and graphite, characterize the solidification of compacted graphite irons of carbon equivalent values ranging from hypoeutectic to hypereutectic. Similar results are observed for ductile iron, but in this case, the hypereutectic irons display a finer macrostructure. The characteristics of the primary austenite dendrites are revealed by the microsegregation pattern, which is exposed by the color etching reagent. This pattern also clarifies the nature of the interaction between the growing austenite and the compact and spheroidal graphite particles. The microshrinkage cavities in both ductile and compacted graphite irons form at the interior of the austenite grains, where fluid feeding cannot compensate the contraction of the last-to-freeze portions of the melt. Schematics of the solidification of ductile and compacted irons are proposed, accounting for the experimental observations.



中文翻译:

球墨铸铁的凝固,宏观组织和收缩形成

该手稿总结了作者最近对球墨铸铁和压实石墨铸铁的凝固和收缩缺陷形成的研究。该研究利用了一些作者较早开发的DAAS(凝固后直接奥氏体化)技术来揭示凝固晶粒。另外,彩色金相学用于揭示微偏析图案。收缩缺陷的形成与凝固宏观结构和微观偏析模式有关。宏观结构检查表明,由树枝状奥氏体和石墨组成的大凝固晶粒表征了碳当量值从次共晶到过共晶的压实石墨铁的凝固。对于球墨铸铁,观察到类似的结果,但在这种情况下,过共晶铁表现出更好的宏观结构。奥氏体原始枝晶的特征通过微偏析图案得以揭示,该微偏析图案由彩色蚀刻剂暴露。该图案还阐明了正在生长的奥氏体与致密且球形的石墨颗粒之间相互作用的性质。球墨铸铁和压实石墨铁中的微缩腔均在奥氏体晶粒内部形成,在此处流体进料无法补偿熔体最后凝固的部分的收缩。考虑到实验观察结果,提出了球墨铸铁和压缩铁的凝固示意图。它被彩色蚀刻剂曝光。该图案还阐明了正在生长的奥氏体与致密且球形的石墨颗粒之间相互作用的性质。球墨铸铁和压实石墨铁中的微缩腔均在奥氏体晶粒内部形成,在此处流体进料无法补偿熔体最后凝固的部分的收缩。考虑到实验观察结果,提出了球墨铸铁和压缩铁的凝固示意图。它被彩色蚀刻剂曝光。该图案还阐明了正在生长的奥氏体与致密和球形石墨颗粒之间相互作用的性质。球墨铸铁和压实石墨铁中的微缩腔均在奥氏体晶粒内部形成,在此处流体进料无法补偿熔体最后凝固的部分的收缩。考虑到实验观察结果,提出了球墨铸铁和压缩铁的凝固示意图。进料不能补偿熔体最后凝固部分的收缩的场合。考虑到实验观察结果,提出了球墨铸铁和压缩铁的凝固示意图。进料不能补偿熔体最后凝固部分的收缩的场合。考虑到实验观察结果,提出了球墨铸铁和压缩铁的凝固示意图。

更新日期:2020-04-18
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