Austenitizing of Spheroidal Graphite Cast Iron

Abstract

An investigation has been carried out on the process and the mechanism of austenitizing of spheroidal graphite cast iron by dilatometric and metallurgical methods.
The austenitizing is affected remarkably by the microstructure, and the rate of the transformation reduces in the order of pearlitic, Bull's-eye, and ferritic structures.
In ferritic spheroidal graphite cast iron, austenite phase forms mainly around the graphite nodules at high temperature and along the ferrite grain boundary at low temperature.
The transformation is retarded by increasing silicon contcnt, due to the elevation of A_c1 temperature and reduction of austenite.
Exponent, n, in the rate equation of the austenitizing (Johnson-Mehl equation) takes considerably lower values than 3.
The experimental results fairly coincide with the calculated one by a diffusional model.
It is assumed that the austenitizing of ferritic spheroidal graphite cast iron is controlled by carbon diffusion, and there exists a steady state reacion except for the early stage.