EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

SiMoCr spheroidal graphite cast irons contain a high silicon content (>3.8%) as well as molybdenum and chromium. Silicon provides a solid solution strengthened ferritic matrix while chromium and molybdenum contribute to the formation of carbides and influence the amount and properties of perlite. These alloying elements thus increase strength indicators at the expense of ductility and impact strength. Furthermore, the ductility of these cast irons degrades as the solidification time increases. This degradation is often associated in the literature with a degeneration of nodular graphite to chunky graphite.
The objective of this study is to predict by simulation the risks of chunky graphite formation of an SiMoCrNi spheroidal graphite cast iron as a function of the solidification conditions. Three standard Y-block specimen molds were manufactured in ALPHASET type chemically-bonded sand under industrial conditions and each mold had 4 Y-block cavities of sizes I to IV. The moulds were instrumented with thermocouples inserted in the Y-blocks of sizes I and IV to record thermal analysis curves representative of different solidification conditions during three castings. The characteristic solidification temperatures were determined to estimate the solidification times for each curve. In parallel, the Novaflow&Solid software was used to simulate the thermal analysis curves at any point of each Y-block and compare them with those recorded experimentally. To reinforce the agreement between simulations and experiments, the curves of the evolution of thermal conductivity and heat capacity of sand and cast iron as a function of temperature obtained experimentally by Laser Flash tests were integrated into the simulation parameters. The simulation results were then combined with microstructural observations to predict the risk of chunky graphite formation as a function of solidification conditions.