Effects of Trace Elements on Solidification Morphology of Spheroidal Graphite Cast Iron

Abstract

  Molten spheroidal graphite cast iron was melted as raw materials using steel can scrap (S.C.S), of which the Al cap portion was removed, and cast into several kinds of molds to examine spheroidal graphite cast iron characteristics (chilling tendency, nodule count, graphite spheroidization), mechanical properties (tensile strength, brinell hardness, elongation) and chemical composition. In this study, a standard sample was first melted, and then samples containing 10, 20, 30, 40, 50, 55, 60, 70% S.C.S. in raw materials were melted. Since it is known that the generation of chill is influenced by the critical nodule count for graphitization/stabilization (P.c. ), chilling tendency was investigated by P.c. rather than the total chill depth.
  In this experiment, Sn contents increased with increasing S.C.S. Cr, Ti, and Mn contents also increased, though slightly. The total chill depth increased when the compounding ratio of S.C.S. exceeded 50%. Although the percentage of graphite spheroidization did not change in the specimens, that of pearlite increased with increasing compounding ratio of S.C.S. P.c. increased in samples with 40% and 50% S.C.S., and decreased in samples with 60% and 70% S.C.S.. Moreover, the nodule count reached its maximum when the compounding ratio of S.C.S. was 50% at the same cooling rate (3.5 K/s). Therefore, 50% compounding ratio of S.C.S. is thought to be optimum from the viewpoint of spheroidal graphite nucleation.