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Oxygen control in steel during continuous casting-to prevent re-contamination of molten steel(1)

[12/31/2021]


After the molten steel is refined outside the furnace, the T[O] of the molten steel can reach (10~30)×10-6, or even lower. Most of the inclusions (more than 85%) produced by the deoxidation of molten steel are floated and removed. It can be said that molten steel is "clean". Keep T[O] in the slab at the same level as T[O] in the molten steel after refining outside the furnace, otherwise the effect of refining outside the furnace will be lost. The tasks in the continuous casting process are: ①to prevent re-contamination of molten steel; ②to try to further eliminate inclusions.

For this reason, the technical measures adopted in the continuous casting process include:
(1) Prevent secondary oxidation

① Protective pouring (△[N]<(3~5)×10-6);
②Alkaline lining;
③Alkaline covering agent;
④ The tundish is sealed and filled with argon gas.
(2) Prevent slagging during pouring

The tracer test traced the source of inclusions in the cast slab: foreign inclusions accounted for 41%, secondary oxidation accounted for 39%, and deoxidized products accounted for 20%.
It can be seen that preventing secondary oxidation and slag entrapment during the casting process is an effective measure to improve the cleanliness of the cast slab. Measures to prevent slagging during the pouring process include:
①Reduce tapping slag (ladder slag layer <50mm);
②Ladle slag detector;
③Tundish constant weight operation.
(3) Prevent mold slag from entrapment

① Crystallizer liquid level control (3mm);
② Stability of molten steel flow in the mold (reasonable SEN design);
③ Suitable protective slag.
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