Thermo-metallurgical modeling of nodular cast iron cooling process

FERNANDO D. CARAZO ; PATRICIA M. DARDATI ; DIEGO J. CELENTANO ; LUIS A. GODOY

METALLURGICAL AND MATERIALS TRANSACTIONS B

TMS

Lugar: Warrendale, Pennsylvania; Año: 2012 vol. 43 p. 1579 - 1595

0360-2141

A new numerical model to describe the microstructural evolution of a slightly hypereutectic nodular cast iron during its cooling is presented. In particular, equiaxial solidification assuming the independent nucleation of austenite and graphite nodules is considered. In this context, the austenite has dendritic growth whereas the graphite grows with a spherical shape. After the solidification, the graphite nodules present in the cast iron continue growing since the carbon content in austenite decreases. Once the stable (equilibrium) eutectoid temperature is reached, the alloy experiences the austenite-ferrite transformation. The nucleation of the ferrite basically takes place at the contour of the spherical graphite nodules with low carbon concentration. A ferrite shell surrounding the graphite nodules is formed afterwards by means of a carbon diffusion-governed process. Then, a ferrite-pearlite competitive transformation occurs when the temperature is below the metastable temperature. This thermo-microstructural model is discretized and solved in the context of the finite element method. The model allows the computation of cooling curves, fraction evolution for each component and, in addition, size and distribution of graphite nodules. The obtained numerical results are compared with experiments using standardized Quick-cup type cups where satisfactory numerical predictions of the final microstructure and cooling curves were achieved.