A study on the annealing behavior of Cu-added bake-hardenable steel using an in situ EBSD technique

A combination of electron backscatter diffraction and in situ heating was used to study the annealing behavior of Cu-added bake-hardenable (BH) steel. The annealing behavior of cold-rolled, Cu-added BH steel was strongly dependent on the type and number of average orientations developed in the deformed grains. If deformed grains (type I) had a single γ-fiber component as the average orientation of a unique grain (UG), the density of the nuclei was very low and recrystallization began at a later stage of the in situ annealing. However, the average grain size of the recrystallized grains was drastically increased regardless of the deformed grain as soon as recrystallization had begun. If deformed grains (type II) had multiple γ-fiber components as the average orientation of a UG, the density of the nuclei steadily increased as the elapsed time of in situ annealing increased. The area fraction of the recrystallized grains in the partially recrystallized specimens gradually increased, but the kinetics depended on the deformed matrix. However, the average grain size of the recrystallized grains gradually increased in all deformed grains from the beginning of in situ annealing. If deformed grains (type III) had texture components which could not be assigned to either γ-fiber or α-fiber components as the average orientation of a UG, the number of the recrystallized grains was maximized, but the recrystallization kinetics based on a normalized number of recrystallized grains was similar to that of type II. Since type III was a minor deformed grain in the as-rolled Cu-added BH steel, the recrystallization in types I and II was identified as the principal feature determining the overall recrystallization phenomena of Cu-added BH steel.