3D Phase-field Simulations of Spheroidal Cast Irons and Evaluation of Homogenized Elastic Mechanical Properties

The Volumetric Multicomponent Multiphase Field model implemented in MICRESS® enables microstructure simulation of spheroidal graphite cast iron in 3D space. In this work, it is combined with the homogenization tool HOMAT to study the correlation between graphite characteristics and effective elastic mechanical properties. In a first step, the microstructure evolution of near-eutectic Fe-C-Si-(Mg) grades is simulated from the pure melt to the as-cast structure. The required thermodynamic and diffusion data are evaluated by run-time coupling to CALPHAD data. Temperature evolution is simulated by balancing latent heat release and heat extraction, considering the casting modulus and the mould diffusivity. During the initial solidification, dendritic austenite and spheroidal graphite nucleate and grow independently in the melt. After encapsulation by austenite, the graphite nodules continue to grow by interstitial diffusion of carbon. The eutectoid decomposition of primary austenite to ferrite and graphite is modelled under assumption of para-equilibrium conditions. The final as-cast structure is characterized by graphite nodules of varying size and morphology distributed in a polycrystalline, fully ferritic matrix. To generate representative volume elements (RVE) with different characteristics of graphite precipitates, a series of simulations are performed under independent variation of chemical composition, casting modulus and nucleation conditions. From each RVE, the graphite fraction, the nodule number, the mean nodule size and the mean sphericity are evaluated. In a second step, the RVEs are transferred to the HOMAT software and homogenized values for the Young's modulus, the shear modulus, and the Poisson's ratio are evaluated and discussed in correlation with the characteristic graphite properties and classic mean field approaches.