Continuous cooling transformation behaviour of microalloyed steels containing Ti, Nb, Mn and Mo

Abstract

Continuous cooling transformation diagrams are determined for microalloyed steels containing Ti, Nb, Mn and Mo in undeformed as well as in thermomechanically processed conditions using dilatometry. Effects of thermomechanical processing, cooling rate and Nb content on γ/α transformation kinetics are presented. Thermomechanical processing is found to accelerate the onset of γ/α transformation (γ transformation start temperature, Ar3, is raised). However, the progress of γ/α transformation is retarded considerably in deformed samples. Increase in cooling rate lowers Ar3 significantly and accelerates the progress of transformation. Nb lowers Ar3 undeformed austenite but raises Ar3 of thermomechanically processed austenite.