Structure Characteristics of Silicon Alloyed Ductile Cast Iron

Abstract

Experiments deal with the solidification pattern of FeSiCaMgRE-treated and un-inoculated and inoculated [Ca,Ce,S,O-FeSi] three ductile iron compositions [2.5%Si; 4%Si and 4%Si-1.6%Mo (Si:Mo = 2.5)]. Structure analysis is performed in 20mm diameter bar, resin sand mould solidification. Increasing of the Si content leads to increasing the graphite amount. Mo addition in high Si-iron limits the graphitizing effect of Si, but the graphite amount remains higher compared with conventional iron. A similar evolution is registered for graphite nodule count, while Si-Mo iron has lower nodule count compared with referred iron. For the same production conditions, graphite nodularity [according to ISO 945 evaluation] is negatively affected by Si and Si-Mo: it decreases from 95% up to 80% value, but remains at the accepted level, which means that the selected inoculant seems to be effective in these irons. For high Si-ductile irons, the nodularity evaluation must be more carefully considered, by including a minimum limit of the accepted sphericity shape factor. Increasing of the Si content leads to a prevalent ferritic matrix. Supplementary addition of Mo at the upper limit in Si-Mo affects the ferritic effect of Si, resulting an intermediary ferrite and pearlite mixture. It is found that inoculation is important for high-Si, and particularly for Si-Mo alloyed irons, requiring a high efficiency inoculation procedure.