What are the factors that affect the absorption of inclusions in molten steel by mold flux?

Briefly explain how to make the inclusions floating on the steel slag interface quickly transfer to the liquid slag, so that it can be quickly absorbed and dissolved

The immersion nozzle injection causes the convective movement of the molten steel in the mould, and the inclusions floating on the slag interface of the mold may be involved in the solidification shell due to the fluctuation of the mold liquid level, resulting in inclusions under the skin of the cast slab or surface inclusions Slag affects the surface quality. Therefore, it is hoped that the inclusions floating up to the steel slag interface will be quickly absorbed and dissolved by the liquid slag layer.

To make the inclusions floating up to the steel slag interface quickly transfer to the liquid slag, this process is determined by:

1) Contact area of ​​steel slag interface;

(2) The viscosity of the liquid slag;

(3) The ability of slag to dissolve inclusions.

In other words, the better the fluidity of the slag, the larger the contact area of ​​steel slag, and the easier it is for inclusions to enter the slag. As long as the inclusions enter the slag, the slag can quickly absorb and dissolve, and the ability of the slag to dissolve the inclusions is mainly determined by the chemical composition of the slag, that is, the content of CaO and SiO2 (CaO%/SiO2% is called alkalinity) and the slag The original Al2O3 content.

The production test indicated that the alkalinity increases, the slag dissolves Al2O3 inclusions. When the alkalinity is greater than 1.1, the Al2O3 dissolving ability decreases; the original Al2O3 content in the slag is greater than 10%, and the slag dissolves Al2O3 rapidly. Therefore, when preparing mold flux, the ratio of CaO% to SiO2% of the slag should be 0.9-1.0, and the original Al2O3 content should be as low as possible, generally less than 10%.

How much is the ability of the liquid slag layer on the molten steel surface of the mold to dissolve Al2O3 inclusions? Studies have pointed out: when CaO%/SiO2%=0.9~1.0, the content of Al2O3 in the slag is greater than 20%, and high melting point compounds will be precipitated, causing the slag As the melting point increases, the viscosity increases, and the floating inclusions can no longer be absorbed.

However, during the pouring process, the mold powder is continuously consumed and the floating inclusions are continuously absorbed, so that the slag is enriched by Al2O3. In order to keep the slag having a good ability to absorb Al2O3 without changing the slag performance, the following measures can be taken:

(1) When preparing slag powder, choose suitable raw materials and reduce the content of Al2O3 in the original slag as much as possible;

(2) Appropriately increase the consumption of slag powder and the content of Al2O3 in the diluted slag;

(3) Al2O3 is enriched in the slag during the pouring process, and the crystallizer can be used to replace the slag.

 

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