Morphological changes of graphite spheroids during heat treatment of ductile cast irons

Abstract The partial dissolution of graphite spheroids in ductile cast iron during two heat treatments was investigated. The dissolution takes place along crystalline defects of the spheroid regularly spaced out around it. A growing matrix intrusion forms at these locations, spheroidizes and then detaches itself from the matrix, creating an enclosed matrix particle in the graphite. An estimation made with an existing model (Rayleigh instability) of globulization kinetics is in good agreement with the observations. The role of the silicon present in the matrix on the dissolution rate and on the resulting graphite–matrix interface is discussed at the end.