Progress in cleaning and purification of liquid steel technology based on fine heterogeneous phases

The production of high purity steel is a major issue for iron and steel enterprises. Obtaining bubbles with controllable size and dispersed distribution in liquid steel is an important method for removing fine inclusions and producing high-quality steel. Microheterogeneous purification of molten steel technology is a carbonate decomposition reaction-based process that generates fine bubbles and slag droplets to eradicate small inclusions. On this basis, composite spheres (powders) with various metallurgical functions are designed, and industrial field tests are carried out at ANSTEEL. The results show that the microheterogeneous purification of molten steel is a low-cost, high-efficiency, simple, and easy molten steel purification technology. The carbonate composite sphere (powder) can cause dispersion, microbubbles, and slag droplets in the molten steel. Its size is 0.02–0.2 mm, and the size distribution and slag droplet composition can be controlled. Rapid dephosphorization and slag-forward movement can be achieved by feeding composite balls during converter tapping. For low phosphorus steel, the minimum phosphorus content can reach 0.002% (in mass, the same below) and the dephosphorization efficiency is >50%. The slag-forward movement process can reduce the temperature drop during molten steel transmission, promote rapid slag formation in ladle furnace (LF) refining, increase the LF heating rate by 2 °C·min^–1, and shorten the refining LF treatment cycle by 3–5 min. The addition of composite spheres in the Rheinstahl–Heraeus (RH) refining process can remove fine inclusions and provide deep desulfurization. The inclusion of free molten steel in the interstitial can be effectively removed. Compared to conventional inclusion removal technology, the number of the oxide inclusions can be reduced, and the inclusion size becomes finer. The total oxygen (mass fraction) in the as-cast slab can approach 5×10⁻⁶ using this novel technology, and the steel production cost per ton can be reduced by 5–12 RMB. The sulfur content of ultralow carbon nonoriented silicon steel can be consistently controlled below 0.002%, and the desulfurization efficiency is >50%. Recently, the advancement of this process has piqued the attention of metallurgical workers, and some new technologies have emerged and matured. Based on the principle of microheterogeneous purification of molten steel process, this paper introduces the latest progress of microheterogeneous purification of molten steel technology in detail, summarizes the characteristics and mechanism of microheterogeneous removal of fine inclusions, desulfurization, dephosphorization, slag migration, and RH rapid decarbonization, and looks forward to the problems to be solved in the engineering field and the future developments.