What is an electric arc furnace?
The development of an electric arc furnace
After the middle of the 19th century, various large-scale smelting devices that realized electric-heat conversion have appeared one after another. In 1879, William Siemens first conducted research on the use of electric energy to melt steel charges. In 1889, an ordinary induction steelmaking furnace appeared. In 1900, the first steelmaking electric arc furnace designed by the French P.L.T.Heroult was put into production. Since then, the electric arc furnace steelmaking has made considerable progress in the past 100 years and has become one of the most important steelmaking methods.
1. Electric furnace steel accounted for a very low percentage before the 1950s, and it was a special type of steelmaking method.
2. After the 1950s, electric furnace steel has developed rapidly. Between 1950 and 1990, the total output of electric furnace steel in the world increased by nearly 17 times. The percentage of electric furnace steel has also increased from 6.5% to 27.5%.
3. Since the 1990s, the world's electric furnace steel has maintained rapid development. Between 1990 and 1998, the world's annual output of electric furnace steel increased by 51.23 million tons, and the percentage of electric furnace steel increased to 33.9%.
In the development process of electric arc furnace steelmaking, it has experienced ordinary power electric arc furnace → high power electric arc furnace → ultra-high power electric arc furnace
How are electric arc furnaces classified?
Electric arc furnaces can be divided into three-phase electric arc furnaces, consumable electric arc furnaces, single-phase electric arc furnaces, and resistance electric arc furnaces according to the arc form.
Electric arc steelmaking furnaces are divided into ordinary power electric arc furnaces, high power electric arc furnaces, and ultra-high power electric arc furnaces according to the transformer capacity per ton of furnace capacity.
The main structure of the electric arc furnace
How does the electric arc furnace make steel?
The advantages of electric arc furnace steelmaking
· High temperature and easy to control
· Can create a reducing atmosphere, which is conducive to desulfurization
· High thermal efficiency, up to 65% or more
· Simple smelting equipment and low investment
3 items that need to be paid attention to in electric arc furnace steelmaking
1. Selection of steelmaking process
The process flow of the third phase:
Furnace repair → charging → melting period (divided into four stages: arc starting period → well penetration period → main melting period → melting end heating period) → oxidation period → reduction period → tapping.
Loading: scrap steel, a small amount of molten iron can also be loaded, called hot charging molten iron.
Melting period: mainly the melting of scrap steel.
Oxidation period: Removal of impurities, N, H, etc. in molten steel through ore oxidation or oxygen blowing
Reduction period: slagging, etc.
Now commonly used: scrap preheating → oxygen melting period → tapping → refining
Now generally the reduction period is taken to LF for operation, which can shorten the smelting cycle and the operation is more convenient.
The choice of the production process should be selected and used according to the actual situation of the furnace to achieve the best production efficiency and tapping quality.
2. Selection of operation methods for electric arc furnace steelmaking
Electric arc furnace steelmaking is divided into alkaline operation methods and acid operation methods.
Alkaline operation method: The electric arc furnace uses alkaline refractory materials as the lining, and alkaline slag is produced during the smelting process. Its characteristic is that the sulfur and phosphorus in the raw materials can be removed so that the sulfur and phosphorus content in the finished steel can reach (100～10)× 10-4% or less.
This operation process has no limit in principle to the sulfur and phosphorus content in scrap steel, but considering the furnace productivity and steel cost, the sulfur and phosphorus content should not be higher than 0.05%.
Acid operation method: The electric arc furnace is lined with acidic refractory materials, and the smelting process produces acidic slag saturated with SiO2. The slag does not have the ability of desulfurization and dephosphorization, and it is required that the sulfur and phosphorus in the scrap steel be below the specifications of the steel grade. Therefore, there are few sources of scrap steel and high price, which limits the development of the acid operation.
Nowadays, the most commonly used in the world is the alkaline operation method. Compared with the acidic method, the alkaline method has the characteristics of low cost and low requirements for steelmaking materials.
3. The choice of graphite electrode
The graphite electrodes mainly produced by the Rongxing Group are UHP, HP, RP, three graphite electrodes with different power.
The resistivity of an ultra-high power graphite electrode (UHP) is 4.6~5.8.
The resistivity of high-power graphite electrodes (HP) is 5.8~6.6.
The resistivity of regular power graphite electrodes (RP) is 7.0~10.0.
Graphite electrode is an indispensable energy supply material in electric arc furnace steelmaking. When choosing a graphite electrode, it should be selected according to the actual power and conditions of the furnace.
More importantly, it is necessary to choose a strong graphite electrode supplier to ensure the production efficiency of steelmaking and the quality of steel tapping.
13 steps of electric arc furnace steelmaking
1. Feeding: The operation of adding raw materials such as molten iron or scrap steel to the electric furnace is the first step of the electric furnace steelmaking operation.
2. Slagging: the operation of adjusting the composition, alkalinity, viscosity, and reaction ability of slag in the production of steel and iron. For example, the oxygen blowing operation is to generate slag with sufficient fluidity and alkalinity, which can transfer enough oxygen to the metal surface, so as to reduce the sulfur and phosphorus below the upper limit of the planned steel grade and make the oxygen spray splash The amount of slag and spillage is minimized.
3. Slagging: The slagging or slagging operation adopted in the smelting process according to different smelting conditions and purposes during electric arc furnace steelmaking. For example, when smelting with a single slag method, oxidation slag must be stripped off at the end of oxidation; when using the double slag method to make reduction slag, the original oxidation slag must be completely released to prevent phosphorus from returning.
4. Molten pool stirring: Supply energy to the molten metal pool to make the molten metal and slag move to improve the kinetic conditions of the metallurgical reaction. The stirring of the molten pool can be achieved by means of gas, mechanical, electromagnetic induction, and other methods.
5. Dephosphorization: a chemical reaction to reduce the phosphorus content in molten steel. Phosphorus is one of the harmful impurities in the steel. Steel with a lot of phosphorus, when used at room temperature or lower, is prone to brittleness, which is called "cold brittleness". The higher the carbon content in steel, the more serious the embrittlement caused by phosphorus. Generally, it is stipulated that the phosphorus content of ordinary steel does not exceed 0.045%, and high-quality steel requires less phosphorus.
6. Electric furnace bottom blowing: N2, Ar, CO2, CO, CH4, O2, and other gases are blown into the molten pool in the furnace according to the process requirements through the nozzle placed at the bottom of the furnace to achieve the purpose of accelerating the melting and promoting the metallurgical reaction process. . The use of bottom blowing technology can shorten smelting time, reduce power consumption, improve dephosphorization and desulfurization operations, increase the amount of residual manganese in steel, and increase the yield of metals and alloys. And it can make the composition and temperature of the molten steel more uniform, thereby improving the quality of steel, reducing costs, and increasing productivity.
7. Melting period: The melting period of steelmaking is mainly for open-hearth and electric furnace steelmaking. The melting period of electric arc furnace steelmaking is called the melting period from the start of electrification to the complete melting of the furnace steel spikes, and the open-hearth steelmaking from the completion of the molten iron to the completion of the charge. 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 period and decarburization period: The oxidation period of ordinary power electric arc furnace steelmaking usually refers to the process stage from the dissolution of the furnace charge, the 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.
9. Refining period: the steelmaking process uses slagging and other methods to select some elements and compounds harmful to the quality of steel into the gas phase or discharge or float into the slag through chemical reactions to remove them from the molten steel. period. The continuous caster discharges the billet. The continuous caster discharges the billet.
10. Reduction 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, chemical composition control, and temperature adjustment. High-power and ultra-power electric arc furnace steelmaking operations have canceled the reduction period.
11. Out-of-furnace refining: the steelmaking process in which the molten steel that has been smelted in a steelmaking furnace (converter, electric furnace, etc.) is moved to another vessel for refining, 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 of the molten steel in a vacuum, inert gas, or reducing atmosphere container. The advantages of dividing 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 atmospheric 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.
12. Molten steel stirring: 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 in a static state, its metallurgical reaction speed is very slow. For example, it takes 30 to 60 minutes to desulfurize the molten steel in an electric furnace; while it takes only 3 to 5 minutes to stir the molten steel in the furnace refining. When molten steel is in a static state, the inclusions are removed by floating upwards, 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.
13. Wire feeding to the ladle: The wire feeder is used to feed deoxidation, desulfurization, and fine-tuned powders, such as Ca-Si powder, into the ladle wrapped in iron sheets, or directly fed into aluminum wire, carbon wire, etc. Calcium treatment and methods to fine-tune the composition of carbon and aluminum in steel. It also has the function of cleaning molten steel and improving the morphology of non-metallic inclusions.
At present, more than 95% of the world's electric furnace steel output is produced by electric arc furnaces, so electric furnace steelmaking mainly refers to electric arc furnaces.
The equipment and production technology of the electric arc furnace are still under development. . .