| Continuous casting technology is an important way of steel production at present.The quality of slab is directly related to the quality of subsequent products.The existence of oscillation marks not only affects the flatness of the surface of the slab,but also seriously affects the quality of the subsequent rolling material due to the existence of a large number of microcracks,coarse grains,component segregation and other defects in the bottom of oscillation marks.Many scholars have put forward their own views on the mechanism of oscillation marks,but there is still controversy.The negative strip time in the oscillation process parameters is the most important process parameter,at the same time,negative strip stage is also a very important time in the formation process of oscillation marks,the effect of negative strip time on oscillation marks and slag is not clear,and the idea that reducing negative strip time can reduce oscillation marks is still relatively rare.Therefore,it is of great significance to research on the formation mechanism of oscillation marks and the influence of negative strip time on solid slag,liquid slag and the depth of oscillation marks.Firstly,in the process of studying the formation of oscillation marks,due to the high temperature environment of the mold,it is difficult to monitor all physical quantities,and the two-dimensional and three-dimensional thermal-fluid-solid coupling models are established by numerical simulation.Dynamic mesh,multiphase flow model and turbulence model are introduced according to the mold oscillation,the flow characteristics of steel and slag.The heat transfer in mold and secondary cold zone was analyzed,and the boundary conditions of heat transfer were determined.According to the viscosity curve of slag and the physical properties of molten steel in the literature,the material parameters were determined.Secondly,at the key time points in the oscillation cycle,especially the negative strip stage,the flow law of molten steel and slag in the meniscus and gap were analyzed,and the changes of temperature and pressure at the meniscus in the mold were also analyzed,and the point of starting the initial solidification movement caused by temperature change was combined with the pressure change of meniscus and slag to explain the formation process of oscillation marks.Finally,the negative strip time of oscillation process parameters is changed by changing the oscillation frequency,casting speed and the modification ratio(α)of nonsinusoidal waveform,and the changes of liquid slag,solid slag,slag consumption and the depth of marks are monitored,and the results of single factor changing negative strip time on slag and oscillation marks,and multi-factor changing negative strip time affecting oscillation marks were summarized.The results show that reducing the negative strip time by changing the oscillation frequency and deflection modification ratio can increase the consumption of slag,while changing the casting speed is opposite.By reducing the negative strip time through the oscillation frequency and deflection modification ratio within a certain range,the oscillation marks can be reduced,the negative strip time can be increased by increasing the casting speed,and the oscillation marks can also be reduced by changing above three factors to reduce the negative strip time. |
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