Static Recrystallization in Austenite and its Influence on Microstructural Changes in C-Mn Steel and Vanadium Microalloyed Steel at the Hot Strip Mill

By using torsional test, microstructural changes in commercially available C-Mnand vanadium microalloyed steel were studied and changes in austenite on rolling through roughing and finishing mills were estimated on the basis of preliminary static recrystallization determinations. Amethodfor determining the temperature at which recrvstaflization starts to be inhibited in microalloyed steel involving experimenta] measurementsof the activation energy wasdeveloped. The influenoe of the activation energy on changes in austenite brought about by rolling at an ordinary hot strip mill wasestablished by torsional simulation of various thermal cycles, both at a roughing and at a finishing mill, Austenite in C-Mnsteel wasfound to be impossible to harden under these conditions-not even on rolling at a finishing mill at temperatures close to Ar3-as a result of its activation energy being constant at all temperatures. Onthe other hand. hardening of austenite in microalloyed steel wasreadily accomplished at a finishing mill at temperatures belbw the critical recrystallization temperature (915 ºC) as the activation energy increases sharply below such a temperatute.The authors are grateful for the financiai support of the DGICYT-Spain(Project PB89-0022).Peer reviewe