ABSTRACT
In order to study the thermal stability of the lamellar eutectioid structure, spheroidization of two kinds of lamellar pearlite(the pearlite in a Fe-C system and delta-pearlite in a Fe-Cr system obtained by carburization) by annealing at temperatures between 500-700 ℃ and 1100-1200 ℃ has been investigated by a quantitative microscopy. The rate of spheroidization could be described by a cubic law ; (1/S)³-(1/S_0)³=κt, where S is the total area of the interface between the ferrite and cementite per unit volume and So is the initial value. The rate constant κis approximated by κ=k₃/(3f)³, where k₃is the rate constant in the Ostwald ripening of cementite particles and f is the volume fraction of cementite. Small addition of Cr remarkably retarded the spheroidization. This effect was mainly due to the large distribution coefficient between the ferrite and cementite.
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