The quality of the final product is determined by the quality of the slab supplied. In a broad sense, the so-called continuous casting slab quality refers to the severity of slab defects allowed to obtain qualified products.
Its meaning is:
– Billet purity (number of inclusions, morphology, distribution, gases, etc.).
– Slab surface defects (cracks, slag inclusions, pores, etc.).
– Internal defects of the slab (cracks, segregation, inclusions, etc.).
The purity of the slab is mainly determined by the treatment process before the molten steel enters the mold. That is to say, to make the molten steel “cleaner”, efforts must be made in each process before the molten steel enters the mold, such as selecting the appropriate out-of-furnace refining, tundish metallurgy, and protective pouring. The surface defects of the slab are mainly determined by the solidification process of molten steel in the mold. It is related to the formation of the mold shell, the fluctuation of the liquid level of the mold, the design of the submerged nozzle, and the performance of the mold slag. The parameters affecting the surface quality must be controlled within the target value to produce defect-free slabs, which is the premise of hot transfer and direct rolling. The internal defects of the slab are mainly determined by the cooling process of the slab in the secondary cooling zone and the slab support system. Reasonable secondary cooling water distribution, centering of backup rolls, and prevention of billet bulging are the prerequisites for improving the internal quality of billets. Therefore, in order to obtain good billet quality, different process technologies can be used in different stages of continuous casting such as ladle, tundish, mold and secondary cooling area according to the different requirements of steel grades and products. effective control.