Study On The Surface Quality Of Billet At Nanjing Iron And Steel Group Corp

During the process of continuous casting, the existing surface defect increases the workload of finishing, which does not achieve that the billet can be transported and rolled directly, then the cost of production is increased. Even the shell of billet could be pull crack, the breakout could be caused. So the rate of no surface finishing of billet increased is always the aim that metallurgist work for.In this paper, the surface quality problem of Nanjing iron and steel Co. is studied. On the condition of using the present producing technics and mold slag, the characteristic of the surface quality of its billet is that the oscillation mark is not faultiness, abnormity, and sunken; the mark is shallow when the casting speed is slow, while the mark is protruding when the casting speed is fast, even the oscillation scar and oscillation hook appears; the surface cockles and adheres slag; the micro crack appears in the subsurface. Because the technical route is the low slag consumption and shallow oscillation mark, the above-mentioned shallow surface defect can be burned off in following process, but the serious including slag, crack, and air hole in the subsurface caused by oscillation scar, cockles, and oscillation hook cannot be burned off. It can induced the plating of thin slab crusting, the bar forming scar with root, even the phenomena of dropping block appears. In order to eliminating the surface defect of billet and improving the surface quality of billet, the following aspects have been studied and analyzed by using the method of laboratory study and industry experiment. 1) The reason which cause the surface quality problem of billet is studied; 2) The numerical and physical simulation is used for studying the liquid steel flowing behavior in the mold; 3) The numerical simulation is used for studying the liquid slag flowing on meniscus field; 4) The mold oscillation parameters have been studied and analyzed; 5) The seriation of mold slag is studied.Though the laboratory study, the industry experiment, and the systematically study for the correlation factor which influence the behavior of solidification in the meniscus field, the mostly factor which influence the surface quality of billet is gained. They are mold oscillation parameters and the chemical and physical characteristic of mold slag. The optimizing project of mold oscillation parameters is put forward, and mold slag is classify by the steel type which is presently produced in Nanjing electric cooker factory. Though the examination of industry produce application, it is indicated that afteradopting the optimized mold oscillation parameters and the matching mold slag series, the surface quality is improved greatly. The oscillation mark is equality, regular, and there is no including slag and crack below the mark; the surface quality of cold rolling slab can meet the need of the user's quality request; there is no scrap which caused by the surface defect among the hot rolling bar.This paper make use of the large business software FLUENT for the numerical simulation of the mold slag flowing in the meniscus field. It provide theoretic base for the systematically analysis of the factor which influence the slag flowing behavior in the meniscus field.