Influence of Mg Content on Graphite Growth in Hypereutectic Cast Iron and Crystallographic Feature of Graphite

Abstract

  In-situ and time-resolve X-ray imaging was performed to observe the solidification of hypereutectic Fe-C-Si alloys containing 0.05 and 0.002mass%Mg. The crystallographic orientations of spherical graphite particles in conventional spheroidal graphite cast iron and specimen after the in-situ observation were measured by the EBSD technique. Mg concentration influenced nucleation frequency and the temperature range in which the primary graphite particles independently grew. The spherical graphite particles became approximately 40μm in diameter for 2-5s and then were engulfed in the eutectic of γ-Fe and graphite in the 0.05mass%Mg specimen. In the 0.002mass%Mg specimen, the nucleation frequency of primary graphite particles became lower. Most of the graphite particles exhibited spherical shape until diameter reached 40μm and then changed shape from spherical to a flake-like shape. The graphite particles grew for 20s until the engulfment by the eutectic solidification. EBSD analysis showed that the c-axis of graphite crystals tended to be parallel to the normal direction of spherical surface for both conventional alloys and the in-situ specimens. The results proved that the same growth mechanism operated in both specimens.