It is well known that controlling the graphite shape in cast iron is a critical issue to achieve appropriate properties. It is of interest to know how the microstructure in cast iron evolves during solidification. So far, time-evolution of the microstructure has not been observed in-situ. This paper presents the in-situ observation results of cast iron solidification using X-ray imaging of synchrotron radiation. Transmission X-ray images with a spatial resolution of as small as 5μm were obtained by an X-ray detector SATICON in an imaging beam line 20B2 at SPring-8. A 10 × 10 × 0.1mm specimen was melted and solidified in a mold made of Al2O3 placed in a vacuum chamber. The observation showed that the solidification started with austenite dendrites, after which the eutectic structure was formed. Graphite clusters of about 100μm in diameter were formed in the remaining liquid surrounded by the eutectic structure at a cooling rate of less than 10K/min. At a cooling rate of 10K/min, the primary dendrite and the eutectic grains moved up and down, respectively, due to the bouncy force.
