Observation of Flake Graphite Nucleation and Growth in Gray Iron through Interrupted Solidification and Inclusion Analysis

Solidification and cooling of a hypoeutectic gray cast iron were interrupted at various stages by quenching the iron sampled with custom-made quartz molds in an iced brine. Microstructure evolution of the gray iron was interrupted and retained by quenching. A scanning electron microscope equipped with energy-dispersive X-ray spectrometry and automated feature analysis software was used to characterize the flake graphite and nonmetallic inclusions. Based on the area and perimeter information obtained, the length and thickness of flake graphite in various stages of solidification and cooling were achieved. Growth rates of Type A graphite along the prismatic and basal directions during eutectic reaction were determined as 1.4 µm/s and 0.02 µm/s, respectively. Inclusion analysis indicated the significant role of manganese containing sulfide and oxysulfide inclusions on nucleating graphite in gray iron.