Ultra-Fine Ferrite Grain Refinement by Static Re-Crystallization of Hot Rolled Vanadium Micro-Alloyed Steels

Abstract

The phenomenon of ultrafine-grain refinement of ferrite during transformational grain refinement (TGR) followed by static re-crystallization of vanadium micro-alloyed steels was studied. A substantial grain refinement (2.8m) was attained during TGR process by rolling at 900°C. Cold rolling with 70% of reduction introduced strain, utilized for re-crystallization during annealing at different temperatures. Electron Backscattered Diffraction (EBSD) technique was employed to quantify the low angle grain boundaries (LAGB) and high angle grain boundaries (HAGB) spacings and results were correlated with hardness drops during annealing process. At higher annealing times and temperatures the vanadium precipitates restricted the process of grain growth probably due to effective dispersion strengthenening. The abnormal grain growth during annealing, predicted previously for niobium steels, found absent in the present vanadium microalloyed steels.