1994 Volume 58 Issue 1 Pages 30-36
Unidirectional solidification experiments were conducted on high purity iron-carbon alloys containing various amounts of sulphur or cerium in order to clarify the mechanism of spheroidization of graphite in cast iron. A self sealing method was used to prevent decarburization and oxidation of cerium. In the alloys containing 0.003 mass% sulphur or 0.2 mass% cerium, the graphite flakes at the interface were completely covered with austenite. At this time, the intergraphite spacing decreased suddenly at a critical solidification rate of 4 mm/h. In the alloys containing more sulphur (>0.006 mass%), the graphite flakes at the interface protruded into the liquid phase. In this case, there was a sudden increase in the intergraphite spacing at a solidification rate of 4 mm/h. It is considered that the change in the morphology at the interface was caused by lowering the graphite/liquid interfacial energy. The sudden increase in the intergraphite spacing was caused by the limiting effect of the adsorbed sulphur on the branching of graphite flakes. In addition, an equilibrium interface morphology was achieved by holding the furnace stationary for 5 h.
