Study On Liquid Steel Flow Behavior And Submerged Nozzle Optimization In 300 Mm × 150 Mm Rectangular Billet Continuous Casting Mould

During continuous casting,the flow behavior of molten steel in the mold directly affects the melting of mold slag,the fluctuation of liquid level,the floating of inclusions,etc.Unreasonable distribution of liquid steel flow field in the mould can easily induce surface quality defects such as surface cracks and subcutaneous bubbles of continuous casting billet and affect the final rolling quality.In this paper,the continuous casting process of 300 mm X 150 mm rectangular billet in Tangshan Guofeng Iron and Steel Co.,Ltd is taken as the research object.In order to effectively solve the normal longitudinal cracks and bubble quality defects on the surface of the rectangular billet.A mathematical model of liquid steel flow in rectangular billet crystallizer is developed with the help of the commercial finite element software FLUENT.The influence of dip angle,immersion depth and drawing speed of the submerged nozzle of the crystallizer on the flow and heat transfer behavior of the liquid steel in mould were systematically investigated with this mathematical model.The main contents and results of this paper are as follows:1)Based on the commercial finite element software FLUENT,the mathematical coupling model of liquid steel flow and its temperature field in rectangular billet crystallizer was established.The liquid steel flow behavior and temperature field distribution in mould under different process conditions were systematically studied with this model.The reasonable process parameters suitable for the current rectangular billet continuous casting process were preliminarily explored.The results showed that the temperature and velocity of molten steel surface decrease with the increase of dip angle of submerged nozzle.When the dip angle of immersion nozzle was 15°,the temperature of free liquid level in the mold was higher,which was propitious to the melting of mold slag.Therefore,the optimum dip angle of immersion nozzle for the studied billet continuous casting machine is 15°.The liquid surface velocity and temperature of the crystallizer increase rapidly with the increase of the casting speed.The reasonable casting speed range of the rectangular billet continuous casting process is 1.4 m/min-1.6 m/min.With the increase of the depth of the nozzle,the temperature and velocity of molten steel surface in the mold decreased continuously,and the reasonable submerged depth of the mold nozzle in the continuous casting process of rectangular billet is about 170 mm.2)Based on the reasonable process parameters determined by the mathematical model,the corresponding orthogonal test scheme was carried out for determining the final suitable process for the industrial production.The experimental results showed that the final optimum dip angle of submerged nozzle was 20°,the depth of immersion 170 mm,the casting speed 1.6m/min.Plant results indicated that the bubble grade of casting billet of 300 mm section size is reduced from 2-3 level to 0 level,and the ratio of longitudinal surface cracks decreased from 6.25%to 0%after the application of the optimized technology.