Recrystallization kinetics of low and ultra low carbon steels during high-rate annealing

Annealing experiments were carried out to study the effect of rapid heating rates on the recrystallization kinetics and grain size of steels with a ra nge of carbon levels (0.003-0.05 % C). The steels were cold-rolled to 70 % reduction and subsequently annealed at heating rates from 50 to 1 000 degre esC/s to peak temperatures (T-p) in the range 600 to 800 degreesC and held at T-p for various times and cooled to ambient temperature at a rates up to 2 000 degreesC/s. For the steels investigated, the rate of anisothermal re crystallization and the final grain size decreases with increasing heating rate. These results do not support previous work in which it was concluded that ultra-rapid softening (which was associated with an observed decrease in recrystallization temperature at high heating rate and a concomitant inc rease in grain size) occurs at heating rates in excess of 500 degreesC/s. A n annealing model, based on JMAK transformation kinetics, is presented, whi ch predicts the kinetics of recrystallization for any combination of input parameters: heating rate, peak temperature, holding time and cooling rate. The model is shown to predict the strong effect of holding time and cooling rate on the rate of recrystallization at high heating rates.