Experimental Investigation of Chunky Graphite Formation in Small-Section Ductile Iron Castings

摘要

The formation of chunky graphite has generally beenrnrelated to the thermal centre of heavy - section ironrncastings. Previous works carried out on large blocks withrncooling rate in the liquid state of about 6. 3 ～ 6. 5 Klminrnallowed highlighting some of the factors related to thernextent of chunky graphite. In the present study, attemptsrnto obtain chunky graphite in small-section castings werernmade by enhancing the factors found to promote itsrnappearance. Degenerate graphite was observed inrnstandard keel-block castings with cooling rates above 100rnKlmin in the liquid period. Well-formed graphiternspheroids were always observed in the bottom parts of thernkeel-blocks where chunky graphite was not detected. Onrnthe other hand, all the upper parts of castings werernaffected by chunky graphite. The effect of postrninoculation, of Si content in the melt, of Ce or Mg-Cerntreatment and oxygen activity will be discussed. The totalrnoxygen content has been compared with some other valuesrnobtained from ductile, compact and grey iron samples.