Abstract

The present work studied the recrystallization kinetics of a Nb-bearing high strength low alloy (HSLA) steel using a fully-computer controlled laboratory batch annealing (BA) process. This work was designed to study the effect of thermo-mechanical processing (TMP), transformation products, and the amount of cold deformation on the kinetics of recrystallization. The amount of deformation above and below the non-recrystallization (Tnr) temperature of the steel used in this study was investigated in terms of the grain boundary character distribution (GBCD) assessed in the hot band condition. The hot band condition was then subjected to 60 % cold deformation prior to the BA studies. The cold rolled samples were placed in the laboratory BA furnace using the simulated cold spot temperature (CST) annealing process. The selected annealing temperature was 650°C and the holding times varied between 15 minutes and 12 h. The central focus of this work was to understand how the TMP schedule affects the GBCD of the hot band; how the frequency of this initial GBCD changes with the amount of cold deformation; and how the steel composition, stored energy, GBCD, and annealing processing parameters influence the annealing behavior of the steel used in this study. Advanced microstructural techniques including orientation imaging microscopy and electron back-scattered diffraction (EBSD) provided the evolution of the GBCD, the changes in stored energy with annealing times. The results of this investigation clearly showed that when the TMP is conducted in a temperature range where the deformation of austenite favors twin formation, leading to higher levels of high angles grain boundaries (HAGB) and special coincidence site lattice (CSL) boundaries, the kinetics of recrystallization are increased. The results of this work were presented and discussed.

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