Abstract
The solidification of cast iron has been studied by means of remelting small amounts of high purity cast iron in a specially designed high vacuum and high frequency inducation furnace. The meltings were closely controlled to minimize possible influence of impurities and gases. The results show that as the holding temperature of melt raised and the cooling rate of melt increased the spheroidal graphite was formed in Fe-C-Si alloys containing a large amount of silicon, and mottle iron structure (inverse chill) emerging from a two-step eutectic reaction was observed in hypoeutectic alloys. The objective of this study was to investigate the solidification behavior of these two alloys.
The following conclusions were drawn :
(1) Eutectic solidification starts with gray in high purity cast iron remelted and solidified in a vacuum with a cooling rate of 10-143°C/min (average cooling rate at a temperature range of 1,170∼1,200°C ).
(2) In a certain range of cooling rate decided by the composition and the holding temperature of melt the eutectic may solidify with either white or gray. Eutectic solidification which was initially gray transformed to white. The cooling curve indicates two eutectic reactions and inverse chill is formd.
(3) This range shifts to the high cooling rate side and becomes narrower with either the increase in carbon equivalent or the decrease in the holding temperature of melt.
(4) In vacuum-melted high purity cast iron, the spheroidal graphite is formed without the usual treatments. The conditions for the formation of spheroidal graphite are similar to that for the inverse chill in relation to the holding temperature and cooling rate of melt.
(5) The main factor responsible for these phenomena is purity of cast iron.
