Protecting Slag: A Brief Introduction to Continuous Casting Protective Slag
Release time:
2020-07-02
During steelmaking and ingot casting, when the molten steel is poured and allowed to settle, the preparation method of protective slag is usually placed or suspended at or near the bottom of the mold. When the molten steel enters the bottom of the ingot mold through the flow channel and contacts the preparation method of the mold protective slag, the preparation method of the protective slag floats on the surface of the steel. Because the melting point of the mold protective slag preparation method is much lower than the temperature of the molten steel, a liquid slag layer is formed on the surface of the steel. As the molten steel continuously enters the ingot mold and the surface of the steel continues to rise, the protective slag preparation method continues to melt, covering the surface of the ingot with a slag film.
The mold protective slag has the following functions: (1) The slag layer isolates the air and prevents the secondary oxidation of the molten steel; the slag absorbs the floating inclusions in the molten steel; the slag film between the mold wall and the ingot promotes the smoothness of the ingot surface; the powder slag can also maintain the temperature of the molten steel. The preparation method of the mold protective slag usually consists of three parts: a basic slag containing oxides such as calcium oxide, silicon dioxide, and aluminum oxide; a flux preparation method that adjusts the melting point, viscosity, and components such as Na2O and F; and a carbon material that adjusts the melting speed of the continuous casting protective slag.
Graphite, carbon black, and coke powder, etc. are used as carbon materials in the preparation method of mold powder, with an addition amount of 10%-30%. It can not only adjust the melting speed and prevent the sintering of the continuous casting protective slag preparation method, but also improve the spreadability of the continuous casting protective slag preparation method and enhance the heat preservation effect. However, in the preparation method of mold mold powder, carbon materials often cause local carburization of the ingot. The preparation method of non-melting continuous casting protective slag is in direct contact with the molten steel at the bottom of the mold. Carbon dissolves in the molten steel, causing carburization. When the molten steel rises to the joint between the ingot body and the cap, the powder slag accumulates and remains here. The contact between the powder slag and the molten steel and the red-hot ingot body causes carburization, and carbon transfer causes central carburization in the cap-shaped area where the molten steel solidifies.
Therefore, for low-carbon steel die casting, the local carburization defects in the ingot caused by the preparation method of continuous casting protective slag are often unavoidable. For steel grades with a carbon content of less than 1%, special continuous casting protective slag preparation methods must be used.
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