Stable Eutectoid Transformation in Nodular Cast Iron: Modeling and Validation
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TRODUCTION
CAST irons are Fe-C-Si alloys in which graphite, ferrite, and pearlite are the microconstituents at ambient temperature. Ferrite is a solid solution of carbon in BCC iron, cementite is the chemical compound Fe3C, and pearlite is a laminar microconstituent formed by ferrite and cementite. The mechanical properties of cast irons largely depend on their microstructure, i.e., type, fractions, size, and size distribution of its microconstituents.[1,2] Nucleation and growth processes of graphite are of great importance in predicting the final graphite fraction and quantity and size distribution of graphite spheroids, and this greatly influences the final mechanical properties of the alloy at ambient temperature.[3] Regarding-ferrite, a common assumption is that graphite spheroids are surrounded
FERNANDO D. CARAZO, Professor and Researcher, is with Instituto de Meca´nica Aplicada, Universidad Nacional de San Juan, Av. Libertador Gral. San Martı´ n 1109 (Oeste), C.P. J5400ARL, San Juan, Argentina, and also with CONICET, C1425FQB, Godoy Cruz 2290, C.A.B.A., Argentina. Contact e-mail: [email protected] PATRICIA M. DARDATI, Professor, is with GIDMA and Departamento de Ingenierı´ a Meca´nica, Universidad Tecnolo´gica Nacional Facultad Regional Co´rdoba, Maestro M. Lo´pez esq. Cruz Roja Argentina s/n, Ciudad Universitaria, Co´rdoba, Argentina. DIEGO J. CELENTANO, Professor, is with Departamento de Ingenierı´ a Meca´nica y Metalu´rgica, Research Center for Nanotechnology and Advanced Materials (CIEN-UC), Pontificia Universidad Cato´lica de Chile, Av. Vicun˜a Mackenna 4860, Macul, Santiago, Chile. LUIS A. GODOY, Plenary Professor, is with the Institute for Advanced Studies in Engineering and Technology, FCEFyN, National University of Co´rdoba and CONICET, Av. Ve´lez Sarsfield 1601, Co´rdoba, Argentina, and also with CONICET, C1425FQB, Godoy Cruz 2290, C.A.B.A., Argentina. Manuscript submitted March 16, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
by ferrite shells. To illustrate the nature of ferrite, the micrograph in Figure 1 shows that shells are formed by large ferrite grains without a texture, which in most cases completely surround the spheroids. However, depending on the composition of the alloy and the cooling characteristics of the process, the spheroids may be partially covered by ferrite or even have no ferrite on their surface. Testing is of course the main source of information with regard to the cooling process and transformations that take place in a cast iron part. However, there are cost limitations and also difficulties in visualizing all parts of a process without causing interference with the same process which is being observed. This has motivated a growing interest in modeling the thermal and metallurgical process by means of computational mechanics. The successful application of such models largely depends on qualitative as well as quantitative aspects, i.e., a correct understanding of the nature of the process under consideration, and an accurate evaluation of parameters and variables involved.
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