STATIC RECRYSTALLIZATION IN AUSTENITE AND ITS INFLUENCE ON MICRO-STRUCTURAL CHANGES IN C-MN STEEL AND VANADIUM MICROALLOYED STEEL AT THE HOT STRIP MILL

By using torsional test, microstructural changes in commercially avail able C-Mn and vanadium microalloyed steel were studied and changes in austenite on rolling through roughing and finishing mills were estimat ed on the basis of preliminary static recrystallization determinations . A method for determining the temperature at which recrystallization starts to be inhibited in microalloyed steel involving experimental me asurements of the activation energy was developed. The influence of th e activation energy on changes in austenite brought about by rolling a t an ordinary hot strip mill was established by torsional simulation o f various thermal cycles, both at a roughing and at a finishing mill. Austenite in C-Mn steel was found to be impossible to harden under the se conditions-not even on rolling at a finishing mill at temperatures close to Ar3-as a result of its activation energy being constant at al l temperatures. On the other hand, hardening of austenite in microallo yed steel was readily accomplished at a finishing mill at temperatures below the critical recrystallization temperature (915-degrees-C) as t he activation energy increases sharply below such a temperature.