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The application of the additivity principle to recrystallization Magee, Kenneth Howard


This research is part of an ongoing program at the University of British Columbia to mathematically model industrial annealing processes. To enable one to predict the final mechanical properties of a cold rolled steel sheet after being subjected to an industrial annealing cycle, the progress of recrystallization must be predicted with temperature increase during annealing. This is accomplished by applying the additivity principle to isothermal recrystallization kinetic data. To determine whether additivity is applicable to recrystallization, isothermal recrystallization kinetic data for a low carbon, rimmed, cold rolled steel sheet, was determined over a temperature range of 440°C-560°C, using molten salt annealing and diamond pyramid microhardness evaluation methods. The data was characterized using the Avrami equation. Continuous heating recrystallization trials were carried out using resistance heated strip specimens. The progress of recrystallization was monitored using an x-ray procedure based on examining the increased Ka doublet peak resolution of the {211} plane, experienced during the formation of recrystallized material. Diamond pyramid microhardness evaluation was also applied to the continuously heated specimens. Applying the Additivity principle to the isothermal kinetic data resulted in computer predictions which displayed reasonably good agreement with the kinetics obtained experimentally. The difference between the predicted and the experimental recrystallization behaviour was related to recovery effects. The degree of recovery, which is thermal history dependent, determines the amount of stored strain energy available for recrystallization. Once the recovery effect was eliminated by applying suitable heat treatments prior to the continuous heating cycle, the computer predictions displayed excellent correlation with the experimentally obtained continuous heating recrystallization kinetics. The x-ray procedure used to monitor recrystallization was found to be effective. However, modifications to the procedure will be necessary to enable it's use for the insitu monitoring of specimens subjected to the high heating rates typical of continuous annealing conditions.

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