SOFTENING AND MICROSTRUCTURAL CHANGE FOLLOWING THE DYNAMIC RECRYSTALLIZATION OF AUSTENITE

To characterize the dynamic recrystallization behavior of austenite, c ontinuous-torsion tests were carried out on a Mo steel over the temper ature range 950-degrees-C to 1000-degrees-C, and at-strain rates of 0. 02, 0.2, and 2 s-1. Interrupted-torsion tests also were performed to s tudy the characteristics of postdynamic recrystallization. Quenches we re performed after increasing holding times to follow the development of the postdynamic microstructure. Finally, torsion simulations were c arried out to assess the importance of metadynamic recrystallization i n hot-strip mills. The postdynamic microstructure shows that the growt h of dynamically recrystallized grains is the first change that takes place. Then metadynamically recrystallized grains appear and contribut e to the softening of the material. The rate of metadynamic recrystall ization and the meta-dynamically recrystallized grain size depend on s train rate and temperature and are relatively independent of strain, i n contrast to the observations for static recrystallization. True dyna mic recrystallization-controlled rolling (DRCR) is shown to require su ch short interpass times that it does not occur in isolation in hot-st rip mills. As these schedules involve 20 to 80 pct softening by metady namic recrystallization, a new concept known as metadynamic recrystall ization-controlled rolling (MDRCR) is introduced to describe this type of situation.