Mathematical Modeling for the Simultaneous Prediction of Rolling Force and Microstructure Evolution in the Tandem Hot Rolling of Fine Grain Steel Sheets and Plates

A new mathematical model to predict rolling force and microstructure evolution in tandem hot strip rolling of fine grain steel sheets and plates has been proposed. This model is composed by combining Orowan's theory for plastic deformation, FDM analysis temperature and incremental modeling for the evolution of microstructure. This model enables us to predict rolling force, rolling torque and microstructure simultaneously from finishing train to the run out table with quite short computing time, although flow stress is directly calculated by dislocation density and the residual dislocation of austenite is reflected to phase transformation. Proposed model has been used to characterize tandem hot rolling of fine grain steel sheets and plates. In order to manufacture fine grain steel sheets and plates, heavy reduction tandem hot rolling under low temperature is needed. As rolling force and rolling torque in finishing stands are higher than conventional rolling schedules, it is strongly requested to know whether rolling can be done within the capacity of rolling mill. The proposed model is helpful to design the best schedule to roll fine grain steel sheet and plate considering rolling reduction, rolling speed and rolling temperature. Also, there is good relationship between ferrite grain size of the hot rolled steel sheets and plates and residual dislocation density of austenite phase at the onset of phase transformation. Then, regressive equation to describe relation between them is newly proposed. This equation could be applicable to other rolling sequence such as bar rolling, because it is given by general analytical scheme for the evolution of microstructure.