Abstract
Data required for calculation the static re-crystallization kinetics have been evaluated from laboratory simulations. In this work series of two hit isothermal tests were conducted for low carbon Nb/Ti microalloyed steel containing (0.074 wt.% C, 1.15 wt.% Mn, 0.035 wt.% Nb and 0.016 wt.% Ti) on high temperature torsion machine. These tests were conducted on four different temperatures and using inter-pass times between 0.5 and 5s with aim to investigate the influence of thermal activation on static re-crystallization. All tests were conducted on temperatures over Tnr temperature, i.e. in temperature range in which all niobium is present only in solid solution. Method of evaluation of recrystallized fraction was mechanical metallography, i.e. evaluation based on shape of each stress-strain curve. Results have provided following solutions: - On all temperatures, X vs. time dependences have "S" shape, confirming nucleation and growth mechanism of static recrystallization - Increase of test temperature shortens time required for full recrystallization, confirming thermal activation of static recrystallization - Activation energy for static recrystallization estimated in this work of 281kJ/mol is in excellent agreement with previously reported data (both experimental and modeled) and indicates that diffusion of Nb in austenite is most probably the rate controlling process; - Value of Avrami exponent estimated in this work, n=1, implies that static recrystallization occurs at interfaces, i.e. on grain boundaries, twins, deformation bands. - Full description of Avrami type kinetics of static recrystallization is estimated, the results obtained will be used for optimization of present model for prediction of roll forces for Hot Strip Mill in SARTID Company for Steel Manufacturing.