Effects of shear band formation on texture development in warm-rolled IF steels

Warm, or ferritic, rolling is gaining in popularity amongst steelmakers as a means of cutting the cost of steel production and opening up the window of hot band properties. Some of the more unique, but important, metallurgical aspects of the process are reviewed. In particular, it is shown that the effect of changing the rolling temperature from the cold to the warm range on the properties of rolled and annealed sheet is far greater in low carbon (LC) than in interstitial-free (IF) steels. The former contain much lower densities of shear bands than the latter when warm rolled (WR) under the same conditions. This is attributed to the higher rate sensitivities and other physical properties of the low carbon (LC) grades, which arise in turn from the additional dynamic strain ageing (DSA) that accompanies an increase in strain rate. The IF grades have finer grain sizes when annealed after rolling above 500°C than the LC grades, apparently because of the much higher incidence of shear bands in the former materials in this temperature range. The conventional {1 1 1}⊥ ND “deep drawing” textures of cold-rolled and annealed IF grades are also present after WR and annealing. By contrast, the ND texture is absent in WR and annealed LC steels. This is attributed to the absence of shear bands in WR LC steels and therefore to the absence of the {1 1 1} nuclei that appear to be formed in the vicinity of these bands. Conversely, it is the presence of shear bands in WR IF steels that makes possible the replacement of cold rolling in these materials.