X-Ray Imaging of Formation and Growth of Spheroidal Graphite in Ductile Cast Iron

Hideyuki Yasuda,Kentaro Uesugi,A Sugiyama,Kohei Morishita,C Kiattisaksri,Tomoya Nagira,Masato Yoshiya,Akihisa Takeuchi

doi:10.4028/www.scientific.net/msf.925.104

Abstract

Time-resolved and in-situ observations using synchrotron radiation X-rays were performed to observe solidification of cast iron (CE=4.5, 0.02mass%Mg). Morphology of graphite particles was influenced by specimen holder material. In the Al2O3 holder, graphite particles were spheroidal at the beginning and then deviated from the spheroidal shape. In addition, the coupled eutectic solidification of austenite and graphite occurred at the final stage. In contrast, the divorced eutectic solidification, in which graphite particles and austenite dendrites independently grew, was selected until the end of solidification in MgO holder. Spheroidal graphite particles were engulfed by austenite. Consequently, typical microstructure observed in ductile cast iron was reproduced in the in-situ observation. The results suggested that oxygen potential, which was determined by Al2O3 or MgO (specimen holder) in the observations, could be an important factor for the selection of eutectic growth mode and graphite morphology.

Highlights

It is known that small addition of Ce or Mg to cast iron changed the graphite morphology from a flake shape to a more compacted or spheroidal shape [1, 2]
Summary The time-resolved and in-situ observations allowed to observe the evolution of spheroidal graphite particles and shape transformation from spheroidal shape to compacted and flake-like shape
The coupled eutectic solidification occurred at the final stage of solidification

Summary

Introduction

It is known that small addition of Ce or Mg to cast iron changed the graphite morphology from a flake shape to a more compacted or spheroidal shape [1, 2]. The solidification sequence in the ductile cast iron is rather complicated [3, 4]. The divorced eutectic growth is normally selected in the melt which contains sufficient Mg or Ce, leading to spheroidal or compacted graphite particles in the matrix. S solved in the melt can degradation graphite shape [14]. It is still not clear how the spheroidal graphite particles form during solidification

Methods

Results

Conclusion