The role of coincident site lattice boundaries during selective growth in interstitial-free steels

The development of textures in interstitial-free (IF) steels as a result of annealing after cold rolling is described with the help of a combined nucleation and growth model. Nucleation is simulated by assuming that high stored energy nucleation occurs preferentially in high Taylor factor regions in the 75 to 85 pct cold reduced materials. Growth of the nuclei then takes place by means of Σ (110) type as well as by Σ 7 (111) type coincident site lattice (CSL) transformations. Of the six symmetrically equivalent (110) transformation axes, only the ones near the maximum shear stress poles are assumed to operate. The effects of the migration of individual Σ 9, Σ 11, Σ 17c, Σ 19a, Σ 33a, and Σ 33c (110) boundaries are analyzed. Their relative mobilities and contributions to the final texture are deduced by matching the simulated and experimental preferred orientations using a /ldleast-squares” method. On the basis of experimental results for two steels, the various boundary types are observed to have the following mobility ratios: Σ 33a: 12, Σ 19a:4, Σ 9:1, Σ 33c:l, and Σ 17c: 2.