The graphitization of white cast iron during annealing assumes a very complex character, and is accompanied by a change in mechanisms and factors responsible for growth of the graphite phase: preferential diffusion of carbon toward graphitization centers through eutectic cementite occurs in the first stage, and through austenite in the second.
The new explanation for the familiar phenomenon of the growth of the graphite phase in contact with ledeburitic cementite during annealing of white cast iron disproves the theory of "in-situ" decomposition of cementite.
The irregular diffusion of carbon in cementite along the (001) planes obviously assumes the character of preferentially grain-boundary transfer (along the boundaries of blocks assuming the shape of thin plates); in this case, the carbon should exhibit increased mobility in this direction as a result of both the reduced value of the factor before the exponent and the comparatively low energy of activation of diffusion.
Carbon may "swing" from the surrounding layer of high-silicon solid solution into the eutectic cementite; this significantly accelerates the first stage of graphitizing annealing.
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Il'inskii, V.A., Zhukov, A.A., Kostyleva, L.V. et al. Certain laws of geometric thermodynamics of the graphitization of white cast irons. Met Sci Heat Treat 28, 415–419 (1986). https://doi.org/10.1007/BF00836888
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