13 steps of electric arc furnace steelmaking-part 2

Oxidation period and decarburization period in electric arc furnace

The oxidation period of ordinary power electric arc furnace steelmaking usually refers to the process stage from the dissolution of the charge, sampling and analysis to the completion of the oxidation slag. Some think it started from blowing oxygen or adding ore to decarbonize. The main task of the oxidation period is to oxidize the carbon and phosphorus in the molten steel; remove the gas and inclusions; make the molten steel uniformly heated. Decarburization is an important process in the oxidation period. In order to ensure the purity of steel, the amount of decarburization is required to be greater than about 0.2%. With the development of refining technology outside the furnace, most of the oxidation refining of the electric arc furnace is moved to the ladle or refining furnace.

Refining period

The steelmaking process uses slagging and other methods to select some elements and compounds that are harmful to the quality of steel into the gas phase or discharge or float into the slag through a chemical reaction to remove them from the molten steel. The continuous caster discharges the billet. The continuous caster discharges the billet.

Restoration period

In ordinary power electric arc furnace steelmaking operations, the period from the completion of slagging at the end of oxidation to tapping is usually called the reduction period. Its main task is to create reduced slag for diffusion, deoxidation, desulfurization, control of chemical composition and temperature adjustment. High-power and ultra-power electric arc furnace steelmaking operations have cancelled the reduction period.

Out of electric furnace refining

The steelmaking process in which the molten steel initially made in a steelmaking furnace (converter, electric furnace, etc.) is transferred to another vessel for refining is also called secondary metallurgy. Therefore, the steelmaking process is divided into two steps: primary smelting and refining. Primary refining: The charge is melted, dephosphorized, decarburized and main alloyed in a furnace with an oxidizing atmosphere. Refining: Degas, deoxidize, desulfurize, remove inclusions and fine-tune the composition in a container of vacuum, inert gas or reducing atmosphere. The advantages of splitting steelmaking into two steps are: it can improve the quality of steel, the steelmaking workshop can shorten the smelting time, simplify the process and reduce the production cost. There are many types of out-of-furnace refining, which can be roughly divided into two types: out-of-furnace refining under normal pressure and out-of-furnace refining under vacuum. According to different treatment methods, it can be divided into ladle processing type furnace refining and ladle refining type furnace refining.

Mixing of molten steel

The stirring of molten steel during the refining process outside the furnace. It homogenizes the composition and temperature of molten steel, and can promote metallurgical reactions. Most metallurgical reaction processes are phase-interface reactions, and the diffusion rate of reactants and products is the limiting link of these reactions. When molten steel is at rest, its metallurgical reaction speed is very slow. For example, it takes 30 to 60 minutes to desulfurize molten steel in an electric furnace; while it takes only 3 to 5 minutes to stir molten steel in furnace refining. When molten steel is in a static state, the inclusions float up and remove, and the removal speed is slow; when the molten steel is stirred, the removal speed of the inclusions increases exponentially, and is related to the stirring strength, type, and characteristics and concentration of the inclusions.

Ladle wire feeding

Feed the steel ladle with deoxidizing, desulfurizing and fine-tuned powders, such as Ca-Si powder, or directly fed to aluminum wire, carbon wire, etc., to deep desulfurize, calcium and fine-tune the molten steel into the steel ladle through the wire feeder The method of carbon and aluminum and other ingredients. It also has the function of cleaning molten steel and improving the morphology of non-metallic inclusions.