Optimization of run-out table cooling parameters to control coil collapse in carbon-manganese steels

Abstract

In the production of carbon-manganese hot rolled steel strips, less than 6 mm thickness, the wound coil had a shape defect associated with coil collapse. The defect was overcome by the assessment of physical simulation of the associated phase transformations in the run out table using Gleeble. It was found that when the steel strips had a lower Ar₁ temperature than the coiling temperature, the occurrence of coil collapse was common. The coil collapse is due to the secondary phase transformation taking place during coiling and coil holding, where the liberation of the transformation heat softens the coil that leads to the coil collapse. Hence, by optimization of the hot rolling conditions such that the phase transformation is completed at the ROT before coiling, it is possible to avoid the coil collapse. Gleeble based physical simulation of the cooling pattern was correlated with the theoretical Ar₁ temperature to enable prediction of the coil collapse possibility. Based on the physical simulation of the different cooling conditions, imposition of the correct cooling condition at the industrial ROT enabled elimination of coil collapse. In addition to avoiding coil collapse, the production loss associated with 4 to 5 min holding at the down coiler was overcome.