Orientation selective recrystallization of nonoriented electrical steels

A nonoriented electrical steel that was commercially hot rolled and then given a 70 pet cold reduction on a laboratory mill was annealed at 680 degrees C for 6 minutes. The sheet was then submitted to a second rolling reduction of 5.2 pet, followed in turn by a second annealing at 730 degrees C for various times. The textures were measured after the first and second recrystallization treatments and analyzed using a nucleation and growth model. In the model, the nucleus orientation distribution function is first calculated by assessing the nucleation probability for each deformed matrix orientation. The nucleation texture is then transformed into the recrystallization texture by means of an appropriate growth criterion. The calculations indicate that the annealing texture of the conventionally rolled (70 pet reduction) sheet can be accounted for on the basis of random nucleation followed by selective growth. The latter is characterized by the following physical features: (a) the low mobility of low angle grain boundaries, (b) the enhanced mobility of {110} plane matching boundaries, and (c) variant selection of the {110} plane that carries the largest amount of slip during deformation. The computer simulations also show that low stored energy nucleation is favored in the lightly rolled sheet. These nuclei grow into the matrix by a selection mechanism that involves the increased mobility of Sigma 19a and Sigma 33a [110] coincident site lattice (CSL) boundaries.