The problems associated with the use of conventional rolling mill models are described. These include the unavoidable variations in temperature and strain rate (rolling speed) during rolling. They are exacerbated by the wide variety of mill types and configurations found in industry and their correspondingly broad ranges of interpass time. Finally, a major limitation arises from the approach currently employed to model the "strain accumulation" attributable to incomplete softening between passes, particularly during the processing of microalloyed steels.