Thermo-metallurgical modeling of nodular cast iron cooling process. http://dx.doi.org/10.1007/s11663-012-9710-y

Abstract

A new numerical model to describe the microstructural evolution of a eutectic nodular cast ironduring its cooling is presented. In particular, equiaxial solidification assuming an independentnucleation of austenite and graphite nodules is considered. In this context, the austenite hasdendritic growth whereas the graphite grows with a spherical shape. After solidification occurs,the model assumes that the graphite nodules present in the cast iron continue growing since thecarbon content in austenite decreases. Once the stable eutectoid temperature is reached, thealloy undergoes the austenite-ferrite transformation. The nucleation of the ferrite takes place atthe contour of the spherical graphite nodules where austenite has low carbon concentration. Aferrite shell surrounding the graphite nodules is formed afterward by means of a process governedby carbon diffusion. Then, a ferrite-pearlite competitive transformation occurs when thetemperature is below the metastable temperature. This thermo-metallurgical model is discretizedand solved by means of the finite element method. The model allows the computation of coolingcurves, fraction evolution for each component, and size and distribution of graphite nodules.The present numerical results are compared with experiments using standardized Quick-cuptypecups, and satisfactory numerical predictions of the final microstructure and cooling curvesare achieved.