Shorter process times in the controlled rolling of plate

Abstract

The controlled rolling of plate in reversible one-stand rolling mills is often carried out with two or more plates at the same time. The rolling schedule involves two rolling periods, one at high temperature and the other at low temperature. Between these rolling periods there is a holding period to allow the plate to cool before the finishing reductions. In single plate rolling the holding period must be minimized to obtain high production rate. In tandem plate rolling one plate, and in triple plate rolling two plates, are rolled during the holding period. In these cases the time for the rolling stages, the holding period, and the time for transport, must be controlled to optimize production. An investigation on Nb-, V- and NbV-steels was made in a 5-MN pilot-plant rolling mill at the Metal Working Research Plant in Luleå. Strength and toughness were examined as a function of the rolling schedules to investigate how to optimize the production in single, tandem and triple plate controlled rolling. Nb- and NbV-steels seem to offer greater opportunities than V-steels, when short process times are required. In the NbV-steels the same mechanical properties can be obtained by using either high slab-reheating temperature (1250°C) and low finish-rolling temperature (750°C) or low slab-reheating temperature (1125°C) and high finish-rolling temperature (850°C) or linear combinations between these two schedules. This gives the opportunity to control the total rolling timeand the length of the holding time to optimize production in single, tandem and triple plate controlled rolling.