Electric Arc Furnace Steelmaking Slag

Slag is an important result of participating in various metallurgical reactions, and has the function of removing impurities in steel and protecting molten steel. 

Keeping the slag in good condition at each stage of electric furnaces steelmaking is one of the important conditions for producing high-quality steel.

Source

Sources of Electric Arc Furnaces Steelmaking Slag

The surface of molten steel in each stage of electric arc furnace steelmaking is covered with slag, and its main sources include the following four aspects:

1) Deliberately adding slagging materials for the purpose of smelting, such as lime, limestone, silica sand, fluorspar, iron ore, carbon powder, ferrosilicon powder, refractory brick fragments, etc.

2) The products in the smelting process are mainly oxides or sulfides of various elements contained in steel, such as FeO, MnO, SiO2, Cr2O3, etc.

3) The lining is eroded and enters the refractory material in the slag, such as MgO in the basic slag and SiO2 in the acidic slag.

4) Impurities brought in by various raw materials.

The Role Of Electric Arc Furnace Steelmaking Slag

In the process of steelmaking, slag has the following functions.

1) Oxidation and reduction of molten steel are controlled by slag. The main links in the steelmaking process are oxidation and reduction. 

In the oxidation period, some elements in the molten steel must be oxidized; In the reduction period, the residual oxygen in the molten steel must be removed. To control the oxygen content in the molten steel, the FeO content in the slag must be controlled.

2) Phosphorus and sulfur are harmful impurities in steel. To remove P and S, it is necessary to rely on slag with appropriate composition and strong binding ability with phosphorus oxide or sulfide to transfer it from molten steel to slag.

3) The temperature of the arc column is very high, which can dissociate the gas into an ion state and be absorbed by the molten steel. The slag covering the surface of the molten steel has a good protective effect on the molten steel and can reduce the intrusion of gas. The temperature of the slag is high, and the thermal conductivity is low, so that the heat loss of the molten steel is small and the temperature is stable.

4) Protect the furnace lining.

The slag layer can surround the arc to reduce its radiation erosion to the furnace lining, and the effect is better when foaming slag.

5) Remove non-metallic inclusions.

The furnace charge for steelmaking is often mixed with impurities such as sand and soil, oxides generated by oxidation of various elements, damaged and peeled furnace lining refractory materials, etc., if mixed into steel, they all become non-metallic inclusions. 

These non-metallic inclusions have very high melting points, such as SiO2 at 1710°C and A12O3 at 2050°C, which cannot be melted at the steelmaking temperature, but the compound compound formed by combining with slag has a much lower melting point and is in a liquid state, which is easy to melt. Aggregate and separate from molten steel.

Conductivity of Slag

Slag has the ability to conduct electricity because charged ions and free electrons can flow under a certain voltage, which plays an important role in electric arc furnace steelmaking.

There are two main factors affecting the conductivity of slag.

1) The higher the content of basic oxides in the slag, the stronger the conductivity; the higher the content of acid oxides, the weaker the conductivity. Therefore, the conductivity of acidic slag is not as good as that of alkaline slag.

In addition, the low-valent oxides (such as FeO) in the slag will enhance its electrical conductivity, so the electrical conductivity of the oxidized slag is better than that of the reduced slag. CaO can also improve the conductivity of slag. In acidic slag, CaO can reduce the viscosity of slag and affect the conductivity more obviously.

2) As the temperature of the slag increases, the activation energy of charged ions and free electrons increases, and the conductivity increases with the increase of temperature.

The above is part of the relevant knowledge about electric arc furnace steelmaking slag. If you want to know more, or have any needs, please feel free to contact us.

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