Continuously cast ductile iron: Processing, structures, and properties

Ductile iron billets were continuously cast using a horizontal casting machine. The billets were cast successfully, and the overall quality of the billets was acceptable. The as-cast microstructure consisted of eutectic carbide, chunky carbide and graphite nodules in a pearlite matrix. The amount of carbide was relatively large compared with that in traditional sand castings. Graphite nodularity decreased as the melt was held for longer periods of time before casting after inoculation and nodularisation treatments. The fading effect was significant when the melt was held for 6 min and longer. Graphite nodularity was found to affect the tensile strength and elongation, but not hardness, of the billets. The surface quality of the billets was fair, although light waves and drawal marks were clearly visible. The billets had good roundness. The tensile strength was found to be between 410 and 550 MPa; the elongation was 2.5–4.0%; and the hardness was 520–550 HB. Possible approaches to improving the as-cast structure and the implications of this research are discussed.