Effect of Continuous Annealing on Microstructure and Bake Hardening Behavior of Low Carbon Steel

The influences of the heating rate, annealing temperature and soaking time during continuous annealing on the microstructure evolution and bake hardening behavior of the low carbon steel were investigated. After 2% pres-training, bake treatment (180 °C × 20 min) was carried out to measure BH (bake hardening) values. The results showed that, with the increase of the annealing temperature, the grain size increased except for annealing in the intercritical region. Furthermore, the BH value increased and the mean grain size reduced with increasing the heating rate from 5 to 80 °C/s. The BH value was very low before complete recrystallization. After a significant decrease from 630 to 720 °C, the BH value enhanced when the steel was annealed at 750 °C. With the increase of the soaking time from 20 to 100 s, the BH value reduced linearly due to the segregation of solute C atoms.