Study On Behavior Of Bubbles And Liquid Slag Distribution In Mold For Slab Caster

With the development of continuous casting process of high efficiency and wide use of blowing argon, the metallurgical effects of mold become more and more important. It is a key to process running smoothly and improvement of strand quality to thoroughly study the behaviors of molten steel, slag and gas bubbles in mold.The slab mold at No.2 slab caster of MeiSteel was the object for investigation in the dissertation. According to similitude principle, a 0.6:1 mold model was established. Associate with the condition in plant and the defect of slab quality, the influence of casting speed,immersion depth of nozzle and blowing argon flowrate on the liquid surface level fluctuation, the distribution of liquid slag, slag entrapment, bubble distributions, impact depth and flow flied in the mold was investigated by using water model. The parameter of blowing Ar flowrate was optimized. At the same time, the harmful influence of SEN bias and clogging on pouring liquid steel has been studied. In addition, the SEN of high speed casting was optimized by considering the behavior of liquid steel and slag. Finally, the trials were carried out in plant according to the results of physical simulation.The study shows that the casting speed has the most important influence to the flow in the mold, then blowing Ar flowrate. The effect of blowing Ar flowrate on the behavior of liquid steel and slag in the mold are different, the biggest influence is near the nozzle. At high casting speed, the slag entrapment caused by the shearing flow in the mold would happen easily. When the casting speed is low but hight Ar flowrate, the slag entrapment was mainly caused by the large bubbles. The slag with shallow impacting depth would float to the surface. And the slag with largely impacting would be brought to the bottom of the mold, which result in the defects of the slab and break out accident.The casting speed has the most important influence to bubbles distribution in the mold. The number of bubble in mold narrow zone will be more when casting speed is higher. When the casting speed is low, the bubbles mainly get together near the nozzle. Along with impacting depth increasing, the number of bubble will become less and the bubble's diameter will be larger firstly and then smaller. The Ar flow rate was optimized according to reducing the number of gas bubble which enter into solidifying front and avoiding gas bubble aggregating around the nozzle which results in slag entrapment. A quantitative relation between the flowrate of blowing Ar and the flowrate of the casting liquid steel through mold was obtained. After the optimum Ar flowrate was used at No.2 slab caster, the evaluation grade of the slabs with pinhole by the sulfur pint test decreases from 1.0 to 0.5,and the ratio of the slabs with pinhole reduces 12.7% by the sulfur pint test and 61.8% by the macroscopic test, respectively.