Influence of heating rate on anisothermal recrystallization in low and ultra-low carbon steels

High-rate annealing experiments were carried out to study the effect of heating rate on the recrystallization kinetics, grain size and texture of steels with a range 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 1000°C s−1 to peak temperatures (Tp) in the range 600 to 900°C. To minimise masking effects associated with rapid isothermal recrystallization at high temperature, all samples were water-quenched within 0.05 s of reaching Tp. For the steels investigated, the rate of anisothermal recrystallization and the final grain size decrease 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 increase in grain size) occurs at heating rates in excess of 500°C s−1. The present results, together with simulation using an anisothermal annealing model, indicate that ‘ultra-rapid softening’ is likely to be an artefact of these earlier experiments.