The dynamic, static and metadynamic recrystallization of a Nb-microalloyedsteel

Using hot torsion tests, the dynamic (DRX), static (SRX) and metadynamic (M DRX) recrystallization characteristics of a Nb-microalloyed steel were stud ied. The torsion tests were carried out at temperatures in the range 850 to 1 050 degreesC with strain rates ranging from 0.5 to 5/sec. At the higher temperatures, the Nb remained in solution, while precipitation was underway in the lower temperature range. The results indicate that Nh precipitation has little influence on the value of the critical strain (epsilon (c)) for dynamic recrystallization. The peak strain/Zener-Hollomon parameter equati on is derived and the effect of austenite grain size on the peak strain is considered. The times for 50 % recrystallization for static and metadynamic recrystallization were established by means of interrupted torsion tests a nd are compared. The rate of metadynamic recrystallization increases With S train rate and temperature and is observed to be independent of the pass st rain; this contrasts sharply with the observations for static recrystalliza tion. Finally, an example is given of an industrial rolling process in whic h DRX/MDRX can play important roles. Here, the occurrence of dynamic/metady namic recrystallization causes the load to drop or else to increase less ra pidly than in the case of pure strain accumulation in the absence of SRX.