Kinetics of Nucleation and Growth of Graphite at Different Stages of Solidification for Spheroidal Graphite Iron

The importance of the nucleation and growth phenomena that controls the solidification of castings on the mechanical properties and soundness of cast iron cannot be overemphasized. The graphite nucleation mechanism is directly related to the carbon content of the iron and the inoculation treatment. To further understand these phenomena, interrupted solidification experiments were conducted on spheroidal graphite irons at three different levels of carbon equivalent (4.0, 4.2, 4.4), with and without the addition of a commercial inoculant. A detailed scanning electron microscopy investigation was carried out to analyze and quantify the possible nucleation sites at different solid fractions, as well as the influence of the inoculant in their formation. Thermodynamic software was used to evaluate the probability of formation of the compounds. A detailed discussion on the differences in nucleation of graphite between the beginning and end of solidification is provided.