| The effects of stress on the first stage graphitization have heen studied by using nodular cast irons solidified under three levels of stress of approximately 1.38×10^6, 2.45×10^6, and 4.83×10^6 dyne/㎠ The results obtained ara as follows. (1) The first stage graphitization of the cast iron is accelerated with stress level, and the higher the annealing temperature, the greater the effect of stress on the graphitization. (2) The activation energies for graphite nucleation and graphite growth decrease from 33,000 to 22,000 ㎈/㏖ and from 29,000 to 20,000 ㎈/㏖ respectively as the stress level is increased up to 4.83×10^6 dyne/㎠. (3) As-cast hardness of the cast iron increases with increasing stress level. (4) Free cementite particles distributed in the as-cast structure and the pearlite lamella spacing in the matrix become smaller at the higher stress level. |
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