Effect of Rare Earth/Sulfur Ratio on Graphite Morphology and Chill Depth in Flake Graphite Cast Iron

Abstract

  A series of cast irons was produced to determine the effect of Rare Earth additions on the graphite morphology and chilling tendency of low (0.01∼0.03%S) and high (0.03∼0.1 %S) sulfur level content flake graphite cast iron. This paper also presents solidification cooling curves and microstructures of base iron and RE-added flake graphite cast iron. In this study, various ratios of RE/S were used to find the stoichiometric balance of RE/S for the optimum condition of type A graphite forming range and maximum chill depth. To clearly identify the chilling tendencies, two types of pig iron (generally known as high quality pig iron and ordinary pig iron) were used. All experiments were conducted without post inoculation in order to clarify the effects of Rare Earth in the cast iron. The results clarified that about 2.5 RE/S ratio formed type A graphite and chill depth was of the minimum level. The recalescence of cooling curve indicates that type A graphite can be achieved at 3K or less. In the 3 to 6K range, the graphite structure tends to change from type A to type A+D graphite.