Abstract
The differences in the characteristic of cast iron melt according to the types of melting furnaces, such as cupola and low frequency induction furnace, may be mainly due to the difference in melting speed. The authors conducted model experiments by melting at rapid and slow heating speeds with various maximum superheat temperatures. In rapid melting, graphite nucleation became gradually inactive as superheat temperature rose. In slow melting, especially, irons superheated to higher than 1,500°C, showed a rapid increase in chill depth which indicates a harder nucleation of graphite. The cause of these phenomena is ascribed to the difference in the quantity of carbon microsegregation in the melt. Thus a low carbon steel rod was dipped in the melt under a constant condition, and the rate of carbon diffusion was examined. In slow heating and high superheat melting, the rod diameter decreased rapidly. This signified higher effective carbon concentration in the melt. On the other hand, rapid heated and low superheated melt was considered to be a colloidal liquid containing carbon microsegregation as a dispersed phase. This carbon microsegregation may effectively act on graphite nucleation in eutectic solidification.
