Controversies in Development of Parabolic Grain Growth Kinetics Formulae

The kinetics of grain growth basically depends on the time and temperature of annealing as well as metallurgical factors such as pinning of precipitates and solute drag effects. Because of the influence of grain size on determining the properties of materials, especially mechanical properties, several attempts have been made to propose a precise theoretical/empirical grain growth kinetics model [1-3]. The empirical observations and the theoretical treatments generally support a parabolic equation of the form, where D is the average grain size, D0 is the average initial grain size, t is the annealing time, T is the absolute annealing temperature, and R is the universal gas constant. Additionally, n, K0, and QGG are the grain growth exponent, the proportionally constant, and the activation energy of grain growth, respectively [4-6]. Theoretically, n should be equal to 2 [7] but empirical investigations resulted to higher n values, where n has been determined between 5 and10 for austenite [7]. Since the grain growth process occurs by grain boundary migration and this happens by diffusion of atoms across the boundary [5], QGG should be close to the activation energy for lattice self-diffusion (QSD) [8]. However, in many of the reported works, QGG is quite different from QSDdue to the deviation of the n values from the theoretical one The present study is intended to give a better insight about the kinetics of grain growth by consideration of theoretical backgrounds. Therefore, the parabolic kinetics of grain growth was critically discussed. For this purpose, The grain growth kinetics of AISI 304L stainless steel has been investigated to verify the consistency of the experiment with the theory