Methods of Deoxidation in Steelmaking
In the steelmaking process, it is necessary to remove harmful impurities such as carbon and sulfur from the molten iron. This is achieved by blowing oxygen or adding oxidizers to introduce oxygen molecules into the molten iron. The role of blowing oxygen in steelmaking is to react with carbon, silicon, manganese, phosphorus, sulfur, and other elements in the molten iron, forming gases or higher melting point oxides. This reduces the harmful impurities of these five elements in the steel composition and utilizes the chemical heat released during the oxidation reaction to increase the temperature of the molten iron.
However, in the later stages, excessive oxygen can lead to an increase in oxides within the molten steel. If these oxides remain in the steel, they will degrade the performance of the cast steel. Deoxidation requires the addition of elements that combine with oxygen and can easily be removed from the molten steel into the slag. According to the binding strength of various elements with oxygen in the molten steel, the order from weak to strong is as follows: chromium, manganese, carbon, silicon, vanadium, titanium, boron, aluminum, zirconium, and calcium. Therefore, ferro alloys composed of silicon, manganese, aluminum, and calcium are commonly used for deoxidation in steelmaking.
Currently, the main methods of deoxidation in the industry are precipitative deoxidation and diffusive deoxidation. Precipitative deoxidation involves directly adding solid deoxidizers (like ferro silicon ) to the molten steel, where the deoxidizers react with FeO to achieve deoxidation. This method is also known as forced deoxidation. The removal of deoxidation products in precipitative deoxidation affects its effectiveness.
Diffusive deoxidation relies on the diffusion behavior of oxygen in the molten steel to transfer oxygen into the slag, thus reducing the oxygen content in the steel. The specific process involves scattering powdered deoxidizers onto the surface of a thin slag after the melting and reduction period, first lowering the oxygen content in the slag. This disrupts the equilibrium of solubility between oxygen in the slag and the molten steel, causing the oxygen in the molten steel to diffuse into the slag. As the oxygen in the slag continuously decreases, the oxygen in the molten steel will keep diffusing into the slag, thereby reducing the oxygen content in the steel.
