Influence of ferrite rolling temperature on grain size and texture in annealed low C and IF steels

Single pass rolling experiments were carried out on two low carbon steels and an IF grade at temperatures between ambient and 700 degrees C. These were followed by salt bath annealing treatments. The main aim was to investigate the effect of the transition from cold to warm rolling on annealing behavior. Three aspects of annealing were examined: the kinetics of recrystallization; the final grain size; and the resulting texture. The sensitivity of these to the deformation temperature was markedly greater in the low C grades than in the IF grade. In the low C material, changing the rolling temperature from cold to warm resulted in an increase in time to 50% recrystallization of about 1 1/2 orders of magnitude, a two-fold increase in final grain size and a remarkably different texture (i.e. one composed of a partial RD fibre instead of the typical ND fibre). By comparison, recrystallization was only slightly influenced by deformation temperature in the IF steel. These observations are explained in terms of the influence on nucleation of the stored energy and the degree of in-grain banding. In particular, the present results suggest that in-grain shear bands play a larger role in the formation of ND fibre grains than previously thought. From an industrial standpoint, IF steels clearly lend themselves more readily to the replacement of cold by warm rolled material than do low C grades.