Effect of Ladle Bottom Optimization on the Slab Cleanliness of Continuous Casting Slabs

To investigate the mechanism by which optimizing the ladle bottom structure improves steel cleanliness， this study focuses on slag entrapment behavior and adopts the critical vortex height as the key indicator for evaluating the tendency of slag entrainment. By analyzing the water model data， three parameters including step volume， steel throughput and the distance from the nozzle to the step， were selected to establish empirical formulas correlating them with the critical vortex height. Additionally， a formula was fitted to describe the relationship between step volume and the remaining molten steel volume in the ladle， providing a theoretical basis for structural optimization design. Based on this foundation， a novel sloped step-type ladle bottom structure was designed. The ladle bottom was optimized into an inclined plane sloping toward the nozzle， with the sloped section ranging in height from 260 mm to 220 mm， a gradient of 2°， and a total slope height of 70 mm. This optimized bottom structure is primarily applicable to ladles with capacities between 150 tons and 300 tons. At the same time， industrial trials were conducted to verify the effectiveness of the design. An automatic scanning electron microscope was used to analyze inclusions in both the tundish and slab before and after optimization. The results show that after optimization， the total oxygen content （w［T.O］） in the tundish steel sample decreased from 40×10⁻⁶ to 27×10⁻⁶， and the total nitrogen content （w［T.N］） dropped from 87×10⁻⁶ to 61×10⁻⁶. The number density of inclusions larger than 2 μm decreased from 28/mm² to 5/mm².In the slab， the number of 10 μm–14 μm inclusions was significantly reduced， with the maximum size decreasing from 53 μm to24 μm. The area fraction and number density of inclusions showed the most notable reduction at the slab thickness center.The optimization of the ladle bottom structure can effectively enhance molten steel cleanliness by controlling slag entrapment at the end of casting and suppressing the migration and accumulation of inclusions， demonstrating significant engineering application value.