Hot Rolled Coil Property Heterogeneities due to Coil Cooling: Impact and Prediction

The importance of coil cooling conditions on mechanical properties uniformity of HSLA and AHSS steel grades is discussed. It is namely shown that hot rolled coil under conventional industrial production can be cooled non-uniformly. That is why to predict correctly the final steel microstructure and mechanical properties of hot-rolled products an accurate description of not only run-out table condition but also of coil cooling should be done. Two solutions to provide accurate description of coil cooling were tested. First one is to use 2D finite element (FE) thermal model. When coupled with the ArcelorMittal metallurgical model to predict hot-rolled microstructure and properties (TACSI) it matches well the industrial data within +/-15-20MPa both for the tensile and yield strength. However, this approach is recognized to be heavy and time consuming. A second solution, a new 2D coil cooling simplified model incorporated in TACSI model, proved to be quite efficient, as it leads to performances similar to the more detailed first solution. Moreover, it is able to compute the coupling between the thermal evolution of the hot band and the kinetics of phase transformation during coil coiling and cooling, and will enable a better evaluation of the final mechanical properties especially for the grades for which the phase transformation is not completed before hot band coiling.