Certain laws of geometric thermodynamics of the graphitization of white cast irons

Conclusions

• 1. 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.

• 2. 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.

• 3. 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.

• 4. 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.