Solidification of spheroidal graphite cast irons - I. Physical modelling

It is well known that eutectic and slightly hypereutectic cast iron may present austenite dendrites which should appear only in hypoeutectic alloys according to the phase diagram. Such an experimental fact was difficult to explain within the framework of the currently available quantitative models of the solidification of these alloys. The aim of this work is thus to present a physical model of the solidification of SG cast irons which quantitatively accounts for the formation of non-eutectic austenite during cooling and solidification of hypereutectic as well as hypoeutectic cast irons. Amongst other features, this model includes the description of the nucleation and growth of the proeutectic graphite in hypereutectic alloys. However, the most important part of the model is the quantitative description of the so-called eutectic stage of the solidification of SGI. Numerical simulations based on the present model are presented and discussed in Part II. (C) 1998 Acta Metallurgica Inc.