Mathematical Simulation Of Flow Field Optimization In Four Strand Bloom Mold

The flow behavior of molten steel in the mold affects mold flux melting,liquid slag layer distribution,liquid level fluctuations and slag entrainment,lubrication at the meniscus,formation of the primary shell,floating and separation of bubbles and inclusions,temperature distribution in the mold,and casting slab Central segregation,slab surface and subcutaneous quality all have an impact.This paper analyzes the source of macro inclusions,nozzle nodules,and cast slab corner cracks in the billet corner cracks and macro inclusion defects in a steel plant,and uses simulation experiments to analyze the mold flow field under the original working conditions Based on this evaluation,the correlation between macroscopic inclusions and slab corner cracks and the mold flow field is studied,and the method of combining physical simulation and numerical simulation is used to influence the flow field of the mold under the casting conditions.The structural size and insertion depth of the immersion nozzle have been optimized,and the optimization results have been industrially applied.The research results are as follows:(1)Using the raw nozzle to evaluate the flow field of the mold,it is found that the liquid level of the mold fluctuates greatly.At the corner of the mold,the 1/10 wave value reaches 3-5 times the target control value,and there is periodic exposure of the liquid surface;The slag layer is unevenly distributed,and the maximum thickness difference ?max reaches 3 times the target control value;there is obvious slag entrapment on the liquid level of the crystallizer.(2)The corner cracks of the cast slab are formed by cracks along the coarse austenite grain boundaries.In the original working condition,the liquid level in the mold fluctuates greatly,the distribution of the mold slag liquid slag layer is uneven,and the corners of the mold appear periodic liquid surface exposure,which causes the mold slag to not normally flow in the corners of the mold,and the casting slab passes through the corners.The thermal resistance is large,resulting in coarse austenite grains,and internal arc corner cracks appear under the action of straightening stress.(3)The main sources of macroscopic inclusions in the steel sample include two aspects: one is that the liquid level in the mold under the original working condition fluctuates greatly,which leads to the entrapment of the mold powder;the other is that the nodules that fall off the nozzle float up to the liquid level with the flow field.Due to the exposure of the periodic liquid surface near the corners of the mold,the nodules cannot be absorbed by the liquid mold powder,and are drawn into the molten steel by the strong circulating flow,staying in the steel,and becoming macroscopic inclusions.(4)Due to the limitation of steel plant equipment,the maximum insertion depth of the nozzle is 150 mm,and a reasonable mold flow field cannot be achieved by optimizing the insertion depth of the nozzle;under the condition of a fixed nozzle insertion depth of 150 mm,as the inner diameter of the nozzle increases,the mold liquid level tends to be stable.The degree of nozzle nodules increases;when the diameter of the middle hole is 50 mm,the elliptical nozzle controls the uniformity of the crystallizer liquid surface speed better than the square nozzle,and the nozzle nodules and impact depth are smaller than the square nozzle.(5)Industrial application results show that the use of an elliptical nozzle with a diameter of 50 mm can control the macroscopic inclusions and corner cracks of the cast slab,and improve the quality of the cast slab.