Thermal Microstructural Multiscale Simulation of Solidification and Eutectoid Transformation of Hypereutectic Gray Cast
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CASTINGS made from cast iron account for 72 pct of all castings produced globally and almost two-thirds of these are gray cast iron (GCI)[1] due to its good castability, machinability, damping capacity, thermal shock resistance and competitive pricing.[2] Gray iron castings are nowadays used in a very wide variety of applications including machinery, structures, and automotive components.[3] Depending on the need, physical and mechanical properties of castings may be altered by adding certain elements which change the graphite morphology from lamellar (i.e., flake) to nodular (i.e., spheroidal).[4–7] In addition, in lamellar graphite castings, different shapes of the lamellae may be obtained by increasing the carbon equivalent (CE) sufficiently (>4.26 pct wt) to change the composition from hypoeutectic to hypereutectic.[8] Some benefits of the hypereutectic composition are improved damping capacity and thermal diffusivity since these properties are enhanced by longer and thicker graphite lamellae.[9] Moreover, the shrinkage effect is significantly reduced when using this composition[10] and surface finish is diminished on machined surfaces.[11] Hardness and elastic modulus also reduce,[12] as the stress raising effect of lamellar graphite ends worsens.[13] ALEJANDRO URRUTIA, M.Sc. Student, and DIEGO J. CELENTANO, Professor, are with the Departamento de Ingenierı´ a Meca´nica y Metalu´rgica, Pontificia Universidad Cato´lica de Chile, Santiago, Chile. Contact e-mail: [email protected] DAYALAN R. GUNASEGARAM, Senior Research Scientist, and NATALIA DEEVA, Research Project Officer, are with the Commonwealth Scientific and Industrial Research Organization (CSIRO), Melbourne, VIC, Australia. Manuscript submitted July 1, 2013. Article published online May 20, 2014 3954—VOLUME 45A, AUGUST 2014
GCI solidification has been the subject of several modeling studies which were aimed at recreating the process. For instance, Kermanpur et al.[14] simulated the mold filling and solidification with a commercial software package to obtain the zones where porosity was produced; Shaha et al.[15] predicted heat flows during solidification using the finite element method (FEM); Kumar and Kumar[16] used a commercial software package to simulate fluid flow, heat transfer, and solidification to obtain the cooling rates. Microstructural models for the solidification analysis of gray iron have also been developed.[17–20] The gray eutectic crystallization corresponds to a stable transformation that has a lamellar structure. It is classified as an irregular eutectic where the two phases present are the austenite and graphite that grow cooperatively. Graphite can nucleate in liquid[10] or on complex oxides and sulfides.[21,22] Because of the temperature difference in the front of the two phases, graphite is the leading phase and austenite nucleates and grows afterward attached to graphite.[23] Jackson and Hunt[24] developed a growth model for regular lamellar eutectics which is the basis for the works on irregular eutectics such as, for instance, that by Magnin and
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