Austenite Softening in the Finishing Stage of T.M.C.P. Of High Niobium-Low Manganese Microalloyed Steels

Abstract

Recently several studies have been developed on the use of microalloyed steels with low Mn content (below 1%) in the controlled rolling of heavy plates for the manufacture of pipes. However, lower Mn contents should lead to the acceleration of NbCN precipitation kinetics during rolling, reducing the soluble Nb content in austenite. This fact, plus the heavy and fast passes applied under virtually isothermal conditions in a heavy plate rolling mill, increases the risk of partial recrystallization during the finishing stage of the controlled rolling, since strain hardening of austenite becomes significant and the interaction between precipitation and recrystallization is increasingly delayed. The objective of this study was to analyze the evolution of mean flow stress during the finishing stage of controlled rolling in these low Mn, high Nb microalloyed steels to better understand the metallurgical mechanisms acting during this process.