Observation of structures, chemical analysis, mechanical testing and ultrasonic measurement were carried out for the evaluation of spheroidal graphite cast iron containing chunky graphite. In the observation of the macro-structure and micro-structure of thick-walled spheroidal graphite cast iron, a region containing a spheroidal graphite structure showed metallic luster and that containing a chunky graphite structure of distributed minute graphite showed pitch-dark. In the chunky graphite region, the carbon content took higher values than that of the spheroidal graphite region. Results of mechanical testing indicated elongation of the test piece containing the chunky graphite to be about 1/5 of the test piece of the spheroidal graphite structure, and the tensile strength of the chunky graphite to be about 70 N/mm² lower than that of the spheroidal graphite structure. In the ultrasonic measurement, the attenuation in the chunky graphite was larger than that of the spheroidal graphite structure and the ultrasonic velocity of the chunky graphite was lower than that of the spheroidal graphite structure region.

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  Spheroidal graphite cast iron ingots containing chunky graphite were made, and ultrasonic measurement was carried out in the spheroidal graphite region and chunky graphite region. The sound velocity was measured at high precision by the sing-around method. The intensity of the bottom echo and scattered wave were analyzed. The sound velocity in the chunky graphite region was about 0.7% lower than that in the spheroidal graphite region, and the bottom echo intensity was about 50% lower. The change in the bottom echo intensity was simulated under simple assumptions to obtain good agreement with the measurement. There were considerable differences in the scattered wave distribution of both regions. These results suggest possibility to detect the chunky graphite region existing in spheroidal graphite cast iron and to evaluate the size of the chunky graphite region nondestructively.

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  The nucleation and growth behaviour of chunky graphite in heavy section ductile cast irons were studied. The microstructure in quenched samples during solidification was observed using optical microscopy and EPMA. Only spheroidal graphite was observed as the initial form of graphite at the early stage of the solidification. When the growth of the graphite nodules stopped during solidification, chunky graphite began to nucleate at the interfacial sites around the solidification front of the austenite and grow at the thin liquid channel in austenite. During this growth, the advancing end came into contact with the residual liquid iron through the thin liquid channel. Spheroidal graphite is not directly related to the nucleation and growth of chunky graphite. In this study, the Site Theory was used as one explanation of the nucleation and growth mechanism.

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  A high performance continuous aluminum melting and holding crucible furnace was developed. The furnace has a compact single-body combining the features of a bath melting/holding crucible furnace and non-crucible continuous rapid tower melting/holding furnace. Continuous melting at minimum temperature in a crucible contributes to less generation of aluminum oxide and less metal loss. Ideal temperature for casting is achieved. Higher metal quality with less hard spots and gas absorption increases productivity. Utilization of exhaust heat improves energy saving. This furnace also provides better work environment and other benefits for the realization of efficient in-house continuous melting and holding of aluminum ingots and returns.

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