Kinetics Of Graphite Expansion During the Solidification of Lamellar and Spheroidal Graphite Iron

Wednesday, April 9, 2014: 2:40 PM
Room: Utopia D (Renaissance Hotel )
Gorka Alonso , Azterlan, Durango, Spain
Doru M. Stefanescu , The Ohio State University, Columbus, OH
Ramon Suarez , Veigalan Estudio, Durango, Spain
Aitor Loizaga , Azterlan, Durango, Spain
Gorka Zarrabeitia , Azterlan, Durango, Spain
A newly developed Linear Displacement Analysis (LDA) - Thermal Analysis (TA) experimental apparatus was used to measure linear displacement during the solidification of spheroidal graphite (SG) and lamellar graphite (LG) irons with carbon equivalent in the range of 3.7 to 4.4%. As the apparatus includes a sand mold encased in a steel shell that prevents mold wall movements, the thermal expansion of the mold is eliminated, and only the displacement caused by the shrinkage or expansion of the metal is recorded by the transducers. The linear displacement is measured through quartz rods introduced directly into the liquid metal and connected to transducers. The temperature is measured by thermocouples positioned in the mold at the same height with the quartz rods. The concomitant TA and LDA enables the direct correlation between expansion /contraction and the temperature change during solidification events such as graphite formation, and thus the understanding of the kinetics of graphite expansion.

Graphite expansion increased considerably as the graphite shape changed from lamellar to spheroidal. The most important process variable other than magnesium was the carbon content. Graphite expansion increased with both carbon and carbon equivalent. It also increased for all data with the time interval over which graphite expansion occurred. The time for graphite expansion increased noticeably with the carbon content of the iron. It did not depend on the graphite shape, as hypereutectic irons, both lamellar and spheroidal, had similar expansion times.

To understand the kinetics of graphite expansion the evolution of graphite expansion was plotted as a function of the fraction solid. Thus, it was possible to calculate the amount of expansion available at the end of solidification. Such data, when correlated with process variables, are expected to be useful in developing melting/inoculation processes that guarantee lower microshrinkage, and processes for producing riserless spheroidal graphite irons.