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