2014 Volume 86 Issue 6 Pages 471-475
Generally, thin-walled ductile cast iron (TWDI) is produced with a high carbon equivalent (CE), which is decided by the contents of silicon and carbon used, in order to control chilling. In this study, a TWDI plate with a thickness of 2mm was made with various CEs adjusted by varying the silicon and carbon contents. Casting was melted in a 15kg high frequency induction furnace. Before the melt was treated with graphite spheroidizing agent and inoculation, the CE value was measured using a CE meter. The specimens were divided into groups A and B according to the chemical composition. for group A, the silicon content was kept unchanged at 2.4mass% while the CE value was changed by only the addition of carbon. For group B, the silicon content was increased while keeping carbon content constant at 3.6mass%. Graphite nodule count and Vickers hardness were measured and the microstructure was also observed. As a result, microstructures with free-carbides were obtained when the silicon content exceeded 2.4mass% and CE was over 4.2. The peariite area ratio increased when the carbon content exceeded 3.7mass%. The ferrite area ratio and graphite nodule count increased with increasing silicon content. Moreover, the graphite nodule count exceeded 3000nod/mm2 and peariite ratio dropped below 30% when the silicon content was over 2.7mass%. The graphite nodule count of the sample with hypereutectic composition varied in the range of 1700～2400nod/mm2 as carbon content increased.
