Study On The Mold Flux Of High Casting Speed Thin Slab Continuous Casting Based On The Mechanism Of Performance Coordination

In recent years,high casting speed thin slab continuous casting technology has developed rapidly in iron and steel enterprises at home and abroad with the advantages of less construction investment,low equipment consumption and labor cost and high production efficiency.However,the high casting speed has brought about the increased risk of slag entrainment,the frequent occurrence of longitudinal cracks and bonding on the surface of thin slab in the process of thin slab continuous casting,which has brought challenges to the smooth production.Therefore,based on the performance coordination mechanism of“anti slag entrainment,low heat transfer and high lubrication”,the research and development of high casting speed thin slab mold flux system are carried out.The main contents are as follows:Based on the process parameters of high casting speed thin slab continuous casting,the multiphase coupling model in the mold was established and calculated.It was found that when the casting speed is 6.0m/min,under the action of thin slab mold flux on site,the phenomenon of shear slag curling is obvious at 500～600mm from the steel liquid level of the mold to the nozzle.At the same time,it is calculated that the shear rate in the surface area of the mold steel liquid level is between 10～90s^-1,and the shear rate in the meniscus and below of the mold can reach 120～1600s^-1;Through the calculation of three-dimensional heat transfer model of slab in mold,it was found that with the increase of casting speed,the surface temperature of slab shell increases,and the tendency of longitudinal crack on slab surface intensifies.At the casting speed of 6.0m/min,the cooling rate of slag film in the mold can reach 75℃/s.In order to realize that the mold flux has the whole process liquid slag film in the mold,the break temperature of the mold flux should be controlled below 1145℃.Based on the performance requirements of mold flux,the shear thinning behavior,low heat transfer behavior and high lubrication behavior of mold flux were studied respectively,and its action mechanism was mastered.It is proposed that in order to achieve the anti slag entrainment performance（shear thinning property）,the Al₂O₃content in slag is controlled between 6.96%～8.61%,and the fluidity index n is controlled between 0.74～0.77;In order to achieve low heat transfer performance,the basicity of mold flux is controlled between 1.70～1.80,and the crystallization rate of slag film is controlled between 35%～45%;In order to achieve high lubrication performance,the content of Li₂O in slag should be controlled between 0.86%～4.33%.Based on the above optimum chemical composition range for realizing anti slag entrainment,low heat transfer and high lubrication performance of mold flux,the interaction relationship between them was studied through orthogonal test,and the cross region that can meet the above three properties at the same time was found,that is,the basicity is controlled between 1.74～1.80,the Al₂O₃content is controlled between 7%～8%,and the Li₂O content is controlled between 1%～2%.The mold flux for thin slab with high casting speed was prepared.Through the test of various properties of the high casting speed thin slab mold flux,it was found that the performance parameters of the mold flux are within the reasonable range of the above performance requirements,that is,the synergy of“anti slag entrainment,low heat transfer and high lubrication”performance was realized.The slag entrainment behavior,liquid-solid slag film thickness and slag consumption under the action of basic mold flux and high casting speed thin slab mold flux were simulated.It was found that compared with basic mold flux,the use of high casting speed thin slab mold flux can not only effectively reduce the occurrence of slag entrainment,but also better control the heat transfer in the meniscus area of the mold;At the same time,the whole process liquid lubrication is realized,the lubrication ability is improved,and the performance coordination mechanism of“anti slag entrainment,low heat transfer and high lubrication”is further revealed.Based on the research on the synergistic mechanism of“anti slag entrainment,low heat transfer and high lubrication”,combined with the solidification characteristics of medium carbon steel and on-site process parameters,the mold flux for medium carbon steel continuous casting with high casting speed was prepared and produced.Through the field hot test,it was found that compared with the original mold flux,the number of longitudinal cracks and bonding on the slab surface with the new mold flux is significantly reduced,the slab surface is smooth,there is no slag inclusion,and the vibration marks are evenly distributed,indicating that the new mold flux realizes the synergy of“anti slag entrainment,low heat transfer and high lubrication”performance,and can meet the technical requirements of stable production of thin slab continuous casting with high casting speed.Figure 105;Table 45;Reference 160...