Growth Mechanism of Graphite Spheroids from Nano- to Micro-Scale

Investigation on the graphite nucleation and growth mechanism of the compacted graphite iron

Much effort has been put in the past for describing the structure of graphite spheroids and for suggesting a growth mechanism from these observations. Many theories have emerged, but none of them is yet fully established and accepted 70 years after the patent on manufacturing spheroidal graphite cast irons. In the meantime, observations with optical microscopy have become more and more challenged by electron microscopy, either in scanning or in transmission mode. However, conclusions drawn from these various types of observations sometimes appear conflicting. This unsatisfactory situation is here investigated for three special features of spheroidal graphite, namely: (i) the crystalline quality of graphite in the spheroids; (ii) the curved leaf-like overgrowth at the outer surface of spheroids; (iii) the radial structure that is evidenced with optical microscopy. The present results lead to sustain that the mechanism of graphite growth remains the same during the whole solidification process of spheroidal cast irons.