The operation of adding raw materials such as molten iron or scrap steel to the electric furnace is the first step of the steelmaking operation of the electric arc furnace.
2. Slagging
Slag making is an operation to adjust the composition, basicity, viscosity and reaction ability of slag in steel and iron production. For example, the purpose of oxygen blowing operation is to generate slag with enough fluidity and basicity, which can transfer enough oxygen to the metal surface, so as to reduce the sulfur and phosphorus below the upper limit of planned steel grade, and minimize the amount of splashing and slag overflowing during oxygen blowing.
3. Slag out
According to different smelting conditions and purposes, the operation of slag discharging or raking is adopted in the process of EAF steelmaking. For example, when smelting with the single slag method, the oxidation slag must be removed at the end of oxidation; when reducing slag is made with the double slag method, the original oxidation slag must be completely discharged to prevent phosphorus return, etc.
4. Pool stirring
Energy is supplied to the molten metal pool to make the molten metal and slag move, so as to improve the dynamic conditions of the metallurgical reaction. Pool stirring can be realized by means of gas, mechanical, electromagnetic induction and other methods.
5. Dephosphorization
Chemical reaction to reduce phosphorus content in molten steel. Phosphorus is one of the harmful impurities in the steel. The steel with more phosphorus is easy to crack when it is used at room temperature or lower, which is called "cold brittleness". The higher the carbon content in steel, the more serious the brittleness caused by phosphorus. Generally, the phosphorus content of ordinary steel is not more than 0.045%, and the phosphorus content of high-quality steel is less.
6. Bottom blowing
N2, Ar, CO2, Co, CH4, O2 and other gases are blown into the molten pool of the furnace through the nozzle at the bottom of the furnace according to the process requirements to accelerate the melting and promote the metallurgical reaction process. The bottom blowing process can shorten the smelting time, reduce the power consumption, improve the dephosphorization and desulfurization operation, increase the amount of residual manganese in the steel, and improve the metal and alloy yield. It can make the composition and temperature of molten steel more uniform, so as to improve the quality of steel, reduce the cost and improve productivity.
7、 Melting period
The melting period of steelmaking is mainly for open-hearth and electric furnace steelmaking. The melting period of EAF steelmaking is from the beginning of power on to the end of the melting of all the trace materials in the furnace, and from the end of molten iron blending to the end of the melting of all the materials in the open hearth steelmaking. The task of the melting period is to melt and heat up the charge as soon as possible, and make the slag in the melting period.
8. Oxidation and decarbonization
The oxidation period of EAF steel-making usually refers to the process stage from the melting and cleaning of furnace burden, sampling and analysis to the completion of slag removal. It is also believed that it starts from blowing oxygen or adding ore to decarbonize. The main tasks of the oxidation period are to oxidize the carbon and phosphorus in the molten steel, to remove the gas and inclusions, and to heat the molten steel uniformly. Decarburization is an important process in the oxidation stage. In order to ensure the purity of steel, the amount of decarburization is required to be more than 0.2%. With the development of off furnace refining technology, the oxidation refining of EAF mostly moves to ladle or refining furnace.
9. Refining period
In the process of steelmaking, some elements and compounds harmful to the quality of steel are selected into the gas phase or discharged or floated into the slag through chemical reaction through slagging and other methods, so that they can be excluded from the molten steel.
10. Reduction period
In the operation of EAF, the period from the end of oxidation to the end of tapping is usually called reduction period. Its main task is to make reducing slag for diffusion, deoxidization, desulfurization, chemical composition control and temperature adjustment. The reduction period has been canceled in high power and superpower EAF steelmaking operations.
11. Off furnace refining
The steelmaking process in which the primary molten steel in a steelmaking furnace (converter, electric furnace, etc.) is transferred to another vessel for refining, also called secondary metallurgy. Therefore, the steelmaking process is divided into two steps: primary refining and refining. Primary smelting: the charge is melted, dephosphorized, decarburized and main alloyed in an oxidizing atmosphere. Refining: degassing, deoxidizing, desulfuration, removal of inclusions and fine-tuning of the composition of primary molten steel in vacuum, inert gas or reducing atmosphere. The advantages of steelmaking in two steps are: improving the quality of steel, shortening the smelting time in steelmaking workshop, simplifying the process and reducing the production cost. There are many kinds of off furnace refining, which can be roughly divided into two categories: off furnace refining under atmospheric pressure and off furnace refining under vacuum. According to the different treatment methods, it can be divided into ladle treatment and ladle refining.
12. Liquid steel mixing
The stirring of molten steel in the refining process outside the furnace. It can homogenize the composition and temperature of molten steel and promote the metallurgical reaction. Most metallurgical reactions are phase interface reactions, and the diffusion rate of reactants and products is the limiting link of these reactions. In the static state, the metallurgical reaction speed of molten steel is very slow, for example, it takes 30-60 minutes to desulfurize the static molten steel in the electric furnace, while it only takes 3-5 minutes to desulfurize the molten steel by stirring the molten steel in the furnace refining. When the molten steel is in static state, the removal rate of inclusions floats upward and is slow; when the molten steel is stirred, the removal rate of inclusions increases exponentially and is related to the stirring strength, type, characteristics and concentration of inclusions.
13. Ladle wire feeding
By feeding deoxidizing, desulfurizing and fine-tuning powder wrapped with iron sheet, such as Ca Si powder, or directly feeding aluminum wire, carbon wire, etc. into the ladle through wire feeder, the method of deep desulfurizing, calcium treatment and fine-tuning of carbon and aluminum in the steel can be carried out. It also has the functions of cleaning molten steel and improving the morphology of non-metallic inclusions.
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