Grains That Grow, and Secondary Recrystallization

Grain growth and its secondary recrystallization are discussed. The chemical free-energy difference associated with recrystallization is easy to understand because the new grain is relatively free of the defects produced by cold working. The term normal grain growth is used to describe the phenomenon associated with an increase in average grain size during the annealing process. Larger grains have a larger than average number of grain faces, which have a center of curvature that lies outside grain. Growth of grains during secondary and tertiary recrystallization usually is associated with thin sheet materials where the surface grains represent a large fraction of the total number of grains. The grains that grow are those having a crystal orientation where the free surface has an atomic plane parallel to the surface that minimizes surface energy.