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 resu lt of annealing after cold rolling is described with the help of a com bined nucleation and growth model. Nucleation is simulated by assuming that high stored energy nucleation occurs preferentially in high Tayl or factor regions in the 75 to 85 pet cold reduced materials. Growth o f the nuclei then takes place by means of Sigma [110] type as well as by Sigma 7 [111] type coincident site lattice (CSL) transformations. O f 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 Sigma 9, Sigma 11, Sigma 17c, S igma 19a, Sigma 33a, and Sigma 33c [110] boundaries are analyzed. Thei r relative mobilities and contributions to the final texture are deduc ed by matching the simulated and experimental preferred orientations u sing a ''least-squares'' method. On the basis of experimental results for two steels, the various boundary types are observed to have the fo llowing mobility ratios: Sigma 33a:12, Sigma 19a:4, Sigma 9:1, Sigma 3 3c:1, and Sigma 17c: 2.