Improvement of hot ductility in the Nb-microalloyed steel by high temperature deformation

Abstract

Loss of hot ductility at the straightening stage of the continuous casting of HSLA steel is attributed to different microalloying elements, in particular Nb. However, such elements are essential for the desired mechanical characteristics of final product. Since the chemistry cannot be altered to alleviate the problem, thermomechanical processing was studied in order to improve the hot ductility. A Nb-microalloyed steel was examined. The thermal history occurring in the continuous casting process was taken into account as well. Firstly, it was noticed that the steel has a low hot ductility after being subjected to in situ melting followed by the thermal schedule. Then, the effect of deformation applied in the vicinity of the δ→γ transformation, while the thermal schedule was being executed, was investigated. Such deformation appeared to improve the hot ductility considerably. Finally, the mechanism of such improvement in the hot ductility was discussed. © 2005 ISIJ.