| IF Steel used in auto sheet is a kind of indispensable metal material to the development of modern automobile industry. Through the research on the production technology and inclusions of IF Steel used in auto sheet produced by a steel plant, it is found that the contents of FeO and MnO in converter finishing slag are relatively high. The content of inclusions in the steel, especially the large inclusion which is over 100μm, is also high. To solve these problems, the converter finishing slag is optimized by means of using converter slag modification agent. In the research, the flow fields in tundish are tested before and after the tundish is installed a tunnel type filter. Meanwhile, after the installment of tunnel type filter, the influences of the location of dam and retaining wall, and the hight of dam, on the flow field in tundish are studied. All of these are carried by means of physical simulation. Then, industrial tests are carried. The following are the results:The slag basicity during tapping on converters id 3.25. The quality fraction of FeO and MnO is 23.64%, and the oxidability is high. The average content of inclusion is 2.8mg/10kg.80 percent of inclusions are smaller than 180μm. The average diameter is 1.50-4.68μm and the average area is 2.91-13.13μm2. The average index number is 19.03-58.28A/mm2. The average area percentage is 0.009～0.068%.60～80 percent of large inclusions are Al2O3 and Ti-Al inclusions.For the production of IF Steel in a steel plant, an Al-CaCO3-CaF2 converter slag modification agent is devised. Compared with current slag-making balls, this kind of new modification agent decrease 20% of FeO and MnO to less than 2%. The oxidability of top slag decreases dramatically. Thus Al2O3 inclusions can be controlled. The basicity of converter finishing slag is over 5. After reaction, CaO-Al2O3-SiO2 is formed and melting point is below 1500℃. The recovery rate of Al is about 70%. To adjust the ratio of Ca/Al, without adding Al2O3, no extra inclusions are brought in. This can improve the cleanness of IF Steel.The results of physical simulation show that tunnel type filter can effectively improve the flow field. Plan 3 shows the best optimization (the distance between retaining wall and long nozzle is 544mm; the distance between dam and retaining wall is 112mm; the height of dam is 84mm). The duration of tracer peak increases to 238.6s from 238.6s of previous tundish. The average duration of stay increase to 412.57s from 348.22s of previous tundish. The dead zone volume fraction decreases to 5.57% from 22.49 of previous tundish. The plug zone volume fraction increases to 36.21% from 28.67% of previous tundish.The results of industrial test show that before and after optimization, the changes of inclusions’ average diameters in casting blank are not obvious. After the optimization, the average area of inclusions is relative larger. The amount of inclusions and the area percentage of inclusions decrease significantly. These mean that the optimized "turbulence inhibitor+tunnel type filter+retaining wall+dam" tundish combination control device can effectively improve the flow field in tundish, optimize the conditions of inclusions floatation removal, decrease the content of inclusions in casting blank, and improve the cleanness of molten steel.
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