Influence of Graphite-Phase Parameters on the Mechanical Properties of High-Silicon Ductile Iron

High silicon solid solution-strengthened ductile iron exhibits advantageous combinations of static strength and ductility due to elevated silicon contents. However, the Charpy impact toughness decreases rapidly with increasing silicon content. In particular, the transition temperature between ductile and brittle fracture behaviour is shifted significantly to higher temperatures. Therefore, the optimum adjustment of the graphite phase is of major importance in order to achieve sufficient toughness properties. So far, little is known about the influence of the graphite phase on the toughness properties of high-silicon ductile iron. In the present study, the graphite particle distribution was therefore systematically varied for ductile iron grade EN-GJS-500-14. The effect of the graphite nodule count in the range from 77 to 273 1/mm(2), and the influence of the average particle size and particle distance on the Charpy impact energy and the characteristics of the resulting transition curves were investigated by means of statistical analyses. The results that were obtained indicate that the ductile-to-brittle transition temperature in Charpy impact tests can be reduced by about 22 degrees C by increasing the average nodule count by 100 1/mm(2). Additionally, both the lower and upper shelf energies are raised by increasing the nodule count by 100 1/mm(2). Based on these results, it becomes apparent to producers that the inoculation technology for toughness-stressed components needs to be specifically considered and adapted.