Cellular Automata Simulation And Experimental Research On Solidification Structure Of Twin-roll Vibration Cast-rolling Strip

The twin-roll strip vibration cast-rolling technology is a new near-net shape technology that introduces vibration into the traditional cast-rolling.At present,the theoretical research on vibration cast-rolling is limited to the macroscopic physical field in the molten pool.The understanding of the mechanism of vibration affecting the solidification structure of the cast-rolling strip is not deep enough,and it has a large blindness when formulating cast-rolling process parameters.This paper combined numerical simulation and cellular automata method to achieve the prediction of solidification structure of vibrating cast-rolling strip,so as to provide effective guidance for the rapid determination of process parameters in the actual production process,and greatly reduce time and economic costs,which is of great significance to improve the production efficiency of the vibration cast-rolling process and the quality of the cast-rolling strip.A thermo-fluid coupling numerical simulation model of twin-roll strip vibration cast-rolling molten pool was established,and the distribution characteristics of macro physical fields such as temperature and flow fields in the non-vibration cast-rolling during the unsteady phase and the stable phase were analyzed.Through comparison,the specific influence of vibration on the macroscopic physical field in the molten pool was studied,which provided a theoretical basis for the later analysis of the solidification structure formation process of the vibration cast-rolling strip.A shearing model of dendrite at the solidification front of vibration cast-rolling was established,which proved that vibration can break the dendrite and refine the grain.Based on the characteristics of the process,the grain refining mechanism in the vibration cast-rolling was preliminarily analyzed.The results shown that the refining effect of the vibration on the grains in the strip was the comprehensive result of multiple factors such as dendrite fracture and the release of chilled crystal.To this end,a nucleation rate model that couples shear flow and vibration was used,in which theeffect of vibration on the solidified structure was equivalent to the change of nucleation energy and diffusion coefficient,to provide a reliable nucleation rate model for the simulation and research of the solidification structure of the strip.Based on the temperature field data provided by the thermal-fluid coupling numerical simulation of the molten pool and the nucleation rate model couples with shear flow and vibration,the cellular automaton method was used to write a simulation program for solidification structure of vibration cast-rolling strip.With this program,the evolution of solidification structure of non-vibration and vibration castrolling strips was simulated respectively.By comparison,it was concluded that vibration can inhibit the growth of columnar crystals,increase the ratio of equiaxed crystals,and refine the strip grains.By comparing the simulated solidification structure of cast-rolled strip under different vibration conditions,it was found that with the increase of vibration frequency and amplitude,the effect of vibration on the solidification structure of cast-rolling strip is gradually improved.The vibration cast-rolling experiment of 20 CrMn steel was completed.The temperature of the strip exit was collected in the experiment,which was compared with the results obtained by numerical simulation,so as to verify the accuracy of the simulation model.The mechanical properties of the thin strips obtained from the experiments were tested,and the effect of vibration on improving the mechanical properties of the thin strips was verified.The metallographic structure of the strips were observed,the mechanism of vibration to improve the mechanical properties of the strip was analyzed,and the reliability of the simulation program for the solidification structure of the vibration cast-rolling strip constructed in this paper was verified.