The interaction between Nb(CN) precipitation and recrystallization during the hot rolling of Nb-containing HSLA steels has been investigated. In this research, the progress of precipitation was first followed using a stress relaxation procedure performed on a Gleeble 1500 machine. The rolling temperature at which recrystallization is no longer complete (T_(nr)) was then measured by means of the rolling simulations conducted on a servo-hydraulic hot torsion testing system. Based on these experimental data and the classical theory of nucleation, kinetic models were developed for predicting the precipitation start time (P_s) under isothermal conditions, as well as the precipitation start temperature (T_(Ps)) during continuous cooling. Comparison between the model predictions and T_(nr) measurements indicates that the interaction between precipitation and recrystallization during the hot rolling of Nb-containing HSLA steels can be classified into three categories: (I) when the interstand time, t_I is short, the kinetics of recrystallization are solely solute-controlled and the T_(nr) decreases with increasing t_I; (II) when t_I adopts intermediate values, precipitation is rate-limiting and the T_(nr) increases as t_I is increased; (III) finally, when t_I is relatively long, the retarding effects of precipitation are weakened due to particle coarsening and thus the T_(nr) behavior is that described under the first category.
展开▼
