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Prediction of Chunky Graphite in Nodular Cast Iron on the Base of Numerical Simulation and Experimental Data

Bauer B., Mihalic Pokopec I., Petrič M., Mrvar P.

Archives of Metallurgy and Materials

2020

Vol. 65, iss. 1

343--347

Chunky graphite has been recognized for a long time as one of the major problems in production of heavy section nodular cast iron. A great number of studies have been conducted to describe the chunky graphite formation, but a clear understanding of its appearance and a safe mastering of the melt preparation to avoid chunky graphite are not yet available. In the present work the cooling curves were recorded in large cone blocks and standard TA cup. According to measured data from the cone block, melt characteristics and heat transfer coefficient between casting and mould were adjusted in the ProCAST® simulation software. For a near-eutectic nodular cast iron test melt with 0.7 wt.% Ni, relationship between the area of the cone block affected by chunky graphite and simulation software results has been observed, i.e., thermal modulus and time to solidus.

Elimination of Chunky Graphite in Castings with Large Thermal Points

Futas P.

Archives of Foundry Engineering

2016

Vol. 16, iss. 4

57--60

The presence of the chunky graphite is unwanted in the cast iron with the spheroidal graphite for this significantly lowers the properties of the ductile iron. This shape of the graphite is formed as the result of the slow cooling rate of the castings with large thermal point and also due to the presence of the elements which suppress the formation of the spheroidal graphite and support formation of the chunky graphite. The spheroidal graphite present in the ductile iron assures the excellent mechanical properties, while the chunky graphite significantly reduces those properties of the ductile iron. Therefore it is of importance to assume conditions under which prevented is the formation of the chunky graphite. The casts were carried out under the conditions of the regular operation of the foundry and tested were various types of modifiers and inoculators and also pre-inoculators containing the elements suppressing the formation of the chunky graphite (Al, Sb a Ba). Applied were also the chromium breaker core to suppress the formation chunky graphite which was present in the structure in the places after the feeders elimination. As whole, executed were eight casts with various types of the modifiers and inoculators.