ferro silicon and ferro manganese deoxidation

In the initial stage of molten steel entering the deoxidation operation, the oxygen content in the molten steel is high, and the temperature is also suitable for precipitation deoxidation. Under such conditions, adding a bulk deoxidizer to the molten steel can rapidly reduce the amount of dissolved oxygen in the molten steel, thereby significantly shortening the process of deoxidizing operations. After that, the deoxidation products formed by the deoxidation elements in the molten steel have a long time to float and discharge.This deoxygenation process is usually called pre-deoxygenation. It always uses manganese and silicon as deoxidation elements, which is already a routine in steelmaking operations, following introduce some tips for the using of manganese and silicon.

(1)Why should manganese and silicon be used for pre-deoxidation? Among the commonly used deoxidizing elements, both manganese and silicon have relatively low deoxidizing capacity,however, under the condition of high oxygen content in molten steel, the deoxidizing effect is very good. Manganese and silicon can not only enhance the deoxidizing ability of silicon, but also, when the ratio of the two elements is proper, the deoxidized product can become MnO·SiO2 with low melting point, which is easy to float.　

(2)The ratio of manganese and silicon in the pre-deoxidizer has been studied and tested, the results show that no matter whether it is MnO-SiO2 compound or MnO-FeO-SiO2 compound, only when the SiO2 content is less than 47%, Liquid silicates may form at the steelmaking temperature. The pre-deoxidizer used in steelmaking can be ferro manganese and ferro silicon, or manganese-silicon alloy, only if ratio of the amount of manganese added to the amount of silicon (Mn/Si ratio)>3, can form liquid silicate,Mn/Si ratio> 4.5, non-metallic inclusions in steel can be further reduced.

(3)Adding order of ferro manganese and ferro silicon. If pre-deoxidation is not using silicon manganese alloy, but ferro manganese and ferro silicon, there is a problem of adding sequence. When pre-deoxidizing, the oxygen content in the molten steel is quite high, if ferro silicon is added first, a large amount of SiO2 will soon be formed, then add ferro manganese,the deoxidizing ability of manganese is lower than that of silicon,even if the ratio of Mn/Si is high, it is impossible to reduce SiO2.Therefore, the content of SiO2 in the pre-deoxidized product is very high, and it is not easy to form liquid manganese silicate, which is not conducive to the floating of inclusions, and the content of non-metallic inclusions in steel is correspondingly high.If the ferro manganese is added first, so that a large amount of MnO is formed in the molten steel, and then the ferro silicon is added,the MnO is dominant in the inclusions, and the liquid manganese silicate is easy to form and it is easy to float. In summary, in order to ensure the metallurgical quality of steel, ferro manganese should be added first, and followed is ferro silicon.

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