Microstructure Evolution of Cast Iron Alloys during Solidification

Author of the article:YANG Guichun1,2, ZHANG Shuyong2 , LIANG Xingyu2

Author's Workplace：(1. State Key Laboratory of Engines, Tianjin Ulniversity, Tianjin 300072, China; 2. China North Engine Research Institute, Tianjin 300400, China

Key Words：cast iron alloy; solidification curve; quenching temperature; graphite morphology

Abstract：Cast iron (HT300, Rut300, QT600) for diesel engine cylinder head was used as the research object. The solidification process of cast iron samples in different solidification stages was analyzed by liquid quenching. The microstructure and phase composition of cast iron were studied, and the evolution mechanism of microstructure was analyzed. The growth process of graphite was also studied. The results show that the heat release of vermicular cast iron is more during the eutectic reaction stage, followed by nodular cast iron and gray cast iron. The graphite of cast iron alloy is spheroidal in its initial morphology, and the graphite spheroidal grows independently. During the eutectic reaction stage, the graphite spheroidal or vermicular shape changes. The internal and external elements of graphite are very different, the internal carbon content is very high, and the enrichment phenomenon of O, S, Si, Mg and other alloying elements appears around the graphite. The atomic percentage of carbon element in graphite core is 91.72%. The percentage of carbon atom in the outer part of graphite decreases to 77.95%, the percentage of S element atom increases by 4.74%, and the percentage of Mg element atom increases by 5.09%.