The Origin of Inclusions in Continuous Casting Billet
Inclusions in continuous casting billet can cause serious economic losses and even serious safety accidents. Thus, it is inevitable and important to identify the origin of inclusions. This paper mainly aims to discuss the origin of inclusions in continuous casting billet and to clarify their mechanism of entry.
There are two main source of inclusions in continuous casting billet: internal and external source. The internal source includes raw materials, flux and inclusions generated by reactions in molten steel during the casting process and the external source include slag and ladle tuning inclusions generated in the process of ladle refining and ladle addition.
The internal source of inclusions in continuous casting billet mainly includes the raw material inclusions, flux inclusions and inclusions generated by reactions in molten steel during the casting process. The raw materials mainly include slag, refractory materials and refractory linings from the oxidation of elements in steel and metal. These inclusions, if not removed during the casting process, enter the molten steel and cause inclusions in the continuous casting billet. In addition, flux often contains a large amount of refractory materials and slag-forming elements that are not only beneficial for desulphurization, but also can generate inclusions in the molten steel during operation. In the process of smelting, some fluxes react with the elements in steel to form inclusions, which enter the continuous casting billet and cause inclusions.
The external source of inclusions in continuous casting billet mainly includes slag and ladle tuning inclusions generated in the process of ladle refining and ladle addition. In the process of ladle refining and ladle addition, the molten steel contacts different kinds of slag, including basic slag, high-alumina slag and silicate slag. All kinds of slags contain a large number of inclusions, including silicates or other refractories as well as oxides, sulfur and P-based compounds. When the molten steel contacts with different kinds of slag, these inclusions can be transferred to the molten steel and enter the continuous casting billet, thus causing inclusions in the continuous casting billet. In the process of ladle refining, the ladle slag can be incompletely removed, which leads to the inclusions entering the molten steel. Moreover, some other inclusions can also be generated in the slag layer during the operation of ladle refinement or addition, such as Al-Si or Al-Ca-Mg inclusions caused by the reaction between slag materials and ladle atmosphere. These inclusions will enter the molten steel and enter the billet.
In summary, inclusions in continuous casting billet mainly include two sources, internal and external source. The internal source mainly comes from raw materials, flux and inclusions generated by reactions in molten steel during the casting process; The external source mainly comes from slag and ladle tuning inclusions generated in the process of ladle refining and ladle addition. In order to reduce the generation of inclusions in continuous casting billet, it is important to control and reduce the external sources by controlling and selecting raw materials, selecting suitable flux and properly using ladle refining.
