LAUSR

Nonmetallic inclusions play a vital role for graphite nodule nucleation in cast iron with spheroidal graphite (SGI). Therefore, knowledge about composition of heterogeneous nuclei is practically important and can be used to control solidification in SGI castings. Thermodynamic simulations were performed to predict types of nonmetallic precipitates formed in the entire SGI processing, including melt nodularization and inoculation as well as followed melt cooling and casting solidification. To verify simulation results, the experimental SGI heats were performed with variations in nodularization and inoculation practices. Two types of specimens were collected. The first one was direct-quenched from the inoculated melt, and the second one was taken from the castings. An automated SEM/EDX inclusion analysis was used for evaluation of families of nonmetallic inclusions located in the matrix and inside graphite nodules. Nucleation activity of different precipitates was determined from the partitioning of active elements (Mg, Al, Si, Ca, Ce, La, Ti, Zr) between the graphite nuclei and the matrix. Simulation and experimental data were used to discuss a nucleation mechanism of graphite nodules in inoculated SGI. Engineering of nonmetallic inclusions can be used to control SGI solidification.