Softening and microstructural change following the dynamic recrystallization of austenite

To characterize the dynamic recrystallization behavior of austenite, continuous-torsion tests were carried out on a Mo steel over the temperature range 950 ‡C to {dy1000} ‡C, and at strain rates of 0.02, 0.2, and 2 s^-1. Interrupted-torsion tests also were performed to study the characteristics of postdynamic recrystallization. Quenches were performed after increasing holding times to follow the development of the postdynamic microstructure. Finally, torsion simulations were carried out to assess the importance of metadynamic recrystallization in hot-strip mills. The postdynamic microstructure shows that the growth of dynamically recrystallized grains is the first change that takes place. Then metadynamically recrystallized grains appear and contribute to the softening of the material. The rate of metadynamic recrystallization and the meta-dynamically recrystallized grain size depend on strain rate and temperature and are relatively independent of strain, in contrast to the observations for static recrystallization. True dynamic recrystallization-controlled rolling (DRCR) is shown to require such short interpass times that it does not occur in isolation in hot-strip mills. As these schedules involve 20 to 80 pct softening by metadynamic recrystallization, a new concept known as metadynamic recrystallization-controlled rolling (MDRCR) is introduced to describe this type of situation. 1 C. ROUCOULES, formerly with the Department of Mining and Metallurgical Engineering, McGill University, Montreal, PQ, Canada