Metastable Eutectoid Transformation in Spheroidal Graphite Cast Iron: Modeling and Validation

Abstract

This paper presents a new microstructural model of the metastable eutectoidtransformation in spheroidal graphite cast irons. The model takes into account the nucleation andgrowth of pearlite nodules. The nucleation is assumed to be continuous and dependent on themetastable undercooling associated with the upper limit of the three-phase field, while the growthrate is considered to be ruled by the silicon partitioning between ferrite and cementite at thepearlite/austenite front. The initial conditions for the metastable transformation are obtained froma microstructural simulation of solidification, graphite growth, and stable eutectoidtransformation. These microstructural models are coupled with the thermal balance solved at amacroscopic level via the finite element method. The experimental validation of the metastableeutectoid model achieved by comparison with measured values of ferrite, graphite, and pearlitefractions at the end of the cooling process demonstrates the sound predictive capabilities of theproposed model.