Analysis of the Effect of Al on the Static Softening Kinetics of C-Mn Steels Using a Physically Based Model
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IN the past decades, extensive research on the effect of processing parameters on the microstructures and mechanical properties of hot rolled steels has been carried out and several models based on semi-empirical equations have been developed.[1–3] However, recently there has been a trend to develop more physically based models. The latter present several advantages compared to empirical equations: they are not limited to the conditions they were developed for, and in addition, they can provide valuable insight into the processes that occur during hot rolling. Nevertheless, there are also some limitations related to physical models, such as uncertainty in the values of some of the parameters involved in the equations employed or how alloying elements can affect softening processes. Several authors have investigated the application of physical models to the microstructural evolution of steels during and after hot deformation. During deformation, the internal energy of the austenite is increased through the storage of dislocations. After deformation, the energy stored in the material can decrease due to two different mechanisms: recovery, defined as the continuous rearrangement and annihilation of dislocations, or through recrystallization, which consists of the nucleation and growth of new grains free of dislocations into the deformed matrix. Since the driving force for both mechanisms is the stored energy of deformation, the ZALOA ARETXABALETA, Ph.D. Student, BEATRIZ PEREDA, Researcher, and BEATRIZ LO´PEZ, Professor, are with the CEIT and TECNUN, University of Navarra, P de Manuel Lardizabal, 15, 20018 Donostia-San Sebastia´n, Basque Country, Spain. Contact e-mail: [email protected] Manuscript submitted March 15, 2013. Article published online October 1, 2013 934—VOLUME 45A, FEBRUARY 2014
progression of recovery may reduce the driving force available for recrystallization, leading to retardation in recrystallization progression.[4] As a result, in order to model microstructural evolution of austenite, physical models must consider the coupled effect of these two processes. In addition to the effect of deformation and annealing parameters, the effect of microalloying elements on recovery and recrystallization must be taken into account. The effect of conventional microalloying elements, such as Nb, Ti, V or Mo in solid solution on the static softening kinetics of the austenite has been widely studied and it has been shown that they lead to a significant retardation on static softening processes.[5,6] Retardation on recrystallization kinetics has usually been attributed to a reduction in grain boundary mobility due to the solute drag effect. Although less studied, works which indicate that elements in solid solution can also retard recovery kinetics are as well found in the literature.[7] However, most of these studies have been carried out from an empirical point of view, and as a result, it is difficult to extrapolate the results to different conditions. Moreover, these studies all concentrated on conventional microalloyi
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