Abstract
When a molten metal is solidified at an undercooled temperature below the equilibrium liquidus, the nucleation rate dN/dt and the growth rate dR/dt are given by dN/dt=A·θ·dθ and dR/dt=B·θ2 where A and B are constants. On the assumption that the above theory can be applied to all sections of the casting, the author compiled a digital computer program in using a differential method for simulating the solidification of the casting. Furthermore, using this program, the influence of the nucleation rate and the growth rate on the width of mushy zone was studied. The results indicated that the width of mushy zone increased when the nucleation rate was higher, or when the growth rate was lower. It was considered from these results that the width of mushy zone in spheroidal graphite cast iron is longer than gray cast iron by reason of its slow growth rate, and the width of mushy zone in inoculated cast iron is longer than that in uninoculated cast iron because the nucleation rate is higher.
