Introduction
Continuous casting protection slag is a kind of powder slag produced by steelmaking process. It is composed of a mixture of iron oxide, calcium oxide, silicon oxide and aluminum oxide. Generally, the slag produced in the steelmaking process can be divided into two kinds, one is molten slag which is directly discharged from the steelmaking furnace, and the other is protection slag produced by the continuous casting process to protect the surface of the material from oxidization. The protection slag also called dross or slag, is a by-product of continuous casting, which refers to the solidification generated by the oxidation of the protective flux and the combination of the slag and the molten steel surface in the continuous casting process.
Physical Properties
Continuous casting protection slag has the characteristics of semi-solid state, good heat conduction, strong dissolution ability and high expansion coefficient. The main components of protection slag are SiO2、Al2O3、MgO、CaO、MgO and FeO etc. The particle size of protection slag is larger than that of molten steel and the specific surface area is smaller than that of molten steel. The composition and phase composition of protection slag also has certain differences, which are affected by the raw materials, process parameters and cooling conditions of steelmaking.
Chemical Properties
Due to the strong alkalinity and insolubility of protection slag in acid, its ability to dissolve in acid is greatly improved under high temperature. The corrosion rate of oxygen to the molten steel decrease when the temperature is higher than 1400℃. The dissolved oxygen rate in the protection slag can be as high as 100%, while the dissolved oxygen rate in the steel is only 2%. Therefore, the formation of protection slag can prevent the oxidation of steel to a certain extent, but it can also corrode the surface of steel due to its strong alkalinity.
Conclusion
In conclusion, continuous casting protection slag has many physical and chemical properties. Its particle size is larger than that of molten steel, the specific surface area of protection slag is smaller than that of molten steel, and its composition and phase composition are affected by steelmaking raw materials, processes, and cooling conditions. Furthermore, continuous casting protection slag has a strong alkalinity and insolubility in acid and its ability to dissolve in acid increases with temperature. It can protect the steel surface from oxidation and prevent the oxidation of steel to some extent, while at the same time it can also corrode the surface of steel due to its strong alkalinity.
