Sometimes it is necessary to change the steel grade while the changing the ladle in the steel continuous casting process. The continuous casting mechanism causes mixing the two steel melts with different chemical compositions. Steel producers need to know the nearly accurate place of the mixed slab and the length of the mixed slab should be minimizing from the economical view point. In this study, the steel grade transition during the ladle change in a continuous casting process is simulated by presenting a new mathematical model. First, the mixing process for both isothermal and non-isotherm tundish are investigated by residence time distribution models. These models led to a set of ordinary differential equations that were solved with a four order Runge-Kutta algorithm by the finite difference numerical method. Steady state water modeling was carried out under isothermal and non-isothermal conditions. Experimental data obtained from the water model were used to calibrate the mixing models. Then, heat transfer mechanisms and solidification process are simulated for a continuous casting machine and the geometric shape of the liquid pool is predicted considering different conditions. This model involves a two-dimensional (2-D) transient energy equation. The governing equation was solved using QUICK algorithm by the finite-volume procedure. The modeling results were verified by the measured slab surface temperatures and others researcher's results for the different cooling regions of slab. The mixing process in the liquid pool of strand is also investigated by a mixing model. Then, mixing in the strand is investigated by residence time distribution models and the governing equations solved by numerical methods. Finally, when the solidification process in the strand is completed, the variations of chemical composition in the final product are calculated. To verify the results of the intermix model, several samples are taken from the different positions of the slab and chemical composition of several elements are measured using a spectrometry technique in Mobarakeh Steel Company. Comparison shows that a reasonable agreement was achieved. The model results show that the weight of mixed grade steel are affected by parameters such as molten steel volume in the tundish at the time of new ladle opening, slab dimensions, rate of casting and non-isothermal effect on the tundish. The obtained results also show that the effect of difference temperature between two mixing grade both decreasing mixed grade in the tundish and decreasing mixed grade in the slab especially under certain conditions.
