Formation Mechanism of Chunky Graphite and Its Preventive Measures

作     者：Hideo Nakae Sanghoon Jung Ho-Chul Shin 

作者机构：Department of Materials Science and EngineeringWaseda University National Institute of AIST Corporate Res.and Dev.Div.Hyundai.Kia Motors 

出 版 物：《Journal of Materials Science & Technology》 (材料科学技术（英文版）)

年 卷 期：2008年第24卷第3期

页      面：289-295页

核心收录：

学科分类：08[工学] 0805[工学-材料科学与工程（可授工学、理学学位）] 080502[工学-材料学] 

主　　题：Chunky graphite Spheroidal graphite Solidification Cooling curve 

摘      要：The formation mechanism of chunky graphite has been reviewed and studied. The study consisted of a unidirectional solidification method, a small droplet method and a furnace cooling method. Four kinds of iron samples were prepared, namely, the pure Fe-C, Fe-C-S, Fe-C-Ce and Fe-C-Si-Ce alloys, and three kinds of nickel samples, namely the Ni-C, Ni-C-S and Ni-C-Mg alloys. The results of the unidirectional solidification of the Ni-C alloys showed that spheroidal graphite is not observed in the continuous solidified region, in which only flake-like graphite is observed, while spheroidal graphite is usually observed in the quenched liquid region. The existence of spheroidal graphite in the solidified phase is recognized only in the discontinuous growth mode of the Ni-C-Mg alloy solidified at 150 mm/h. This means that the spheroidal graphite is directly crystallized from the melt and entrapped by the flake-like chunky graphite that is formed by the continuous growth mode. In the small droplet method, a small piece of the Fe-C or Fe-C-Ce sample was melted on a pure graphite plate then cooled at a different cooling rate in a He-3%H2 atmosphere. The graphite in the Fe-C-Ce alloy is usually spherical. Nevertheless, the graphite morphology of the final solidified area changed from spherical to chunky and chunky to ledeburite with an increase in the cooling rate. This means that the chunky graphite is formed in the residual liquid region by the solidification into Fe-graphite system. The sample was cooled in a furnace, and the graphite morphology changes from spherical to chunky and chunky to ledeburite with the decrease in the Si content. These phenomena can be confirmed by the cooling curves of these samples.