Modeling of flow stress and rolling load of a hot strip mill by torsion testing.

Abstract

In order to characterize the Lake Erie Works hot strip mill, Stelco Steel, two grades of steel (C-Mn and Nb) were subject to torsional simulation. The flow stresses and rolling loads are considered in this report. The microstructural behaviours of the two grades are compared in a separate publication. As anticipated, for long interpass times, the Tnr temperature (temperature of no-recrystallization) can be clearly established only for the Nb steel, the other grade under-going nearly full softening, i.e. recrystallization, at all temperatures. By contrast, for short interpass times of the order of 2 s, typical of the strip mill, there is little pass-to-pass strain accumulation in either steel. In the temperature range 1 020 to 920°C, static recrystallization is largely responsible for the hight degree of interpass softening in the C-Mn steel. In the case of the Nb steel, because of solute effects, the short interpass times do not permit much conventional recystallization. Instead, softening is brought about mostly by dynamic and post-dynamic recrystallization. This is possible because there is considerably less Nb(CN) precipitation during the short interpass times than under reversing (plate) mill conditions. The decreased level of precipitation in the Nb steel, followed by the initiation of dynamic recrystallization, leads to lower rolling loads in the strip mill for this grade than in the plate mill at the same rolling temperatures.