Optimization of mechanical properties of high strength dual phase steel through thermo-mechanical simulation

JSW Steel has been producing a number of high strength dual phase steels for automotive applications. These steels are processed through the state-of-the-art continuous annealing lines. The cold rolled steel sheets are passed through different zones including preheating, heating, soaking, slow cooling, rapid cooling, overaging and final cooling in a very short time. The strengthening mechanisms in these processes such as phase transformation, precipitation etc. are a strong function of line speed and strip temperatures. Minor change in any of these parameters causes significant variations in mechanical properties. Optimization of these process parameters becomes challenging due to the associated costs involved in plant scale experimentation. The same can be effectively carried out on a lab scale using thermo-mechanical simulator “Gleeble”. Processing routes for the different annealing cycles can be converted into time-temperature plots and programmed in Gleeble for lab scale continuous annealing line (CAL) simulations. In the present work, an offline simulation methodology was established for CAL process through Gleeble. The mechanical properties in Gleeble simulated samples were found to be in close agreement with the actual plant trials. Furthermore, the established methodology was successfully utilized to investigate the effects of different CAL parameters on the mechanical properties of a high strength dual phase steel grade. Consequently, on the basis of physical simulations, the optimum processing conditions were identified to achieve desired mechanical properties during plant processing.