Eaf steelmaking is mainly divided into five stages: raw materials, ingredients, melting, oxidation and reduction.
How is steel made in an electric arc furnace?
13 steps of EAF steelmaking
1. Add furnace burden
The operation of adding raw materials such as molten iron or scrap steel to an arc furnace.
Adjust the composition, alkalinity and viscosity of slag in steel and iron production. Oxygen blowing, for example, is used to produce slag with sufficient fluidity and alkalinity. Can transfer enough oxygen to the liquid level of the metal. Reduce sulfur and phosphorus to below steelmaking requirements. And reduce the amount of slag ejected and spilled when oxygen is blown.
3. Slag discharge
Slag discharge or slag scraping operation in the process of eAF steelmaking according to different smelting conditions and purposes. In the case of single slag smelting, oxidizing slag must be scraped at the end of oxidation. When using double slag method to make reducing slag, the original oxidizing slag must be thoroughly released to prevent the return of phosphorus.
4. Stir in the melting furnace
The kinetic condition of metallurgical reaction is improved by supplying energy to the metal melting furnace to make the molten metal liquid and slag move. Melting furnace agitation can be achieved by means of gas, mechanical, electromagnetic induction and other methods.
Phosphorus is a harmful impurity in steel. Steel with a lot of phosphorus is prone to fracture when used in normal conditions or at lower temperatures. The higher the carbon content is, the more serious the fracture caused by phosphorus content is. The phosphorus content of ordinary steel is <0.045%, and the phosphorus content of high-quality steel is even less. So steelmaking requires reducing chemical reactions that contain phosphorus.
6. Electric furnace bottom blowing
N2, Ar, CO2, CO, CH4, O2 and other gases are blown into the furnace through the nozzle placed at the bottom of the furnace according to the process requirements. In order to achieve the purpose of accelerating melting and promoting metallurgical reaction process. The bottom blowing technology can shorten the smelting time, reduce the power consumption and improve the dephosphorization and desulfurization operation. The residual manganese content in steel and the yield of metal and alloy were increased. It can also make the composition and temperature of molten steel more even, so as to improve steel quality, reduce cost and increase productivity.
7. Melting period
The melting period of steelmaking is mainly for open hearth furnace and electric arc furnace. Furnace furnace steelmaking process will be melted from electrification to furnace burden completely. Furnace furnace steelmaking process will be melted from molten iron to furnace burden completely. The mission of the melting stage is to melt and heat the furnace burden as soon as possible and form the furnace slag in the melting stage.
8. Oxidation period and decarburization period
The oxidation period of ordinary power eAF steel making usually refers to the process stage of furnace burden melting, sampling and analysis to scrape the oxidized slag. There are also believed to be from the oxygen or add ore decarburization. The main task of oxidation period is to oxidize carbon and phosphorus in molten steel. Remove gas and inclusions. Heat the molten steel uniformly. Decarburization is an important operation process in oxidation period. In order to ensure the purity of steel, it is required to decarbonize more than 0.2%. With the development of refining technology, most of the oxidation refining of eAF is carried out in ladle or refining furnace.
9. Refining period
The steelmaking process USES slagging and other methods to remove elements and compounds that are harmful to steel. It's discharged by chemical reaction. The process operation period that is removed from the molten steel.
10. Reduction stage
In ordinary power eAF steelmaking operation, the period from slagging at the end of oxidation to steel output is usually called reduction period. Its main tasks are to make reduction slag for diffusion, deoxidation, desulfurization, control of chemical composition and temperature adjustment. Reduction periods for high power and ultra power eAF steelmaking operations have been cancelled.
11. Refining outside the furnace
The process of transferring molten steel from a steelmaking furnace (converter, electric furnace, etc.) to another vessel for refining. Also known as secondary metallurgy.
The steelmaking process is therefore divided into two steps: initial refining and refining.
Primary refining: the charge is melted, dephosphorized, decarbonized and alloyed in an oxidizing atmosphere furnace.
Refining: degassing, deoxidizing, desulphurizing, removing inclusions and fine-tuning the composition of the steel in a vacuum, inert gas or reductive atmosphere container.
The advantages of making steel in two steps are that the quality of steel can be improved, the smelting time can be shortened, the process can be simplified and the production cost can be reduced.
There are many kinds of refining outside furnace, which can be divided into two kinds: under atmospheric pressure and under vacuum.
According to the different treatment methods, it can be divided into ladle treatment furnace refining and ladle refining furnace refining.
12. Stir the liquid steel
The stirring of molten steel in the refining process outside the furnace. It homogenizes the composition and temperature of molten steel and promotes metallurgical reactions. Most metallurgical reactions are phase interface reactions, the diffusion rate of reactants and products is the limiting link of these reactions. In the static state, the metallurgical reaction rate of liquid steel is very slow. For example, desulfurization of liquid steel in the static furnace takes 30~60 minutes. It takes only 3~5 minutes to desulphurize by stirring molten steel in furnace refining. When the molten steel is at rest, the inclusions float up and are removed at a slower speed. The removal rate of inclusions increases exponentially when stirring molten steel, and is related to the stirring strength, type and the characteristics and concentration of inclusions.
13. Ladle thread feeding
The method of deep desulfurization and calcium treatment of molten steel and fine adjustment of carbon and aluminum in steel by feeding wire feeding machine into ladle with powder of deoxidization, desulfurization and fine adjustment of composition of steel, such as CA-SI powder, or directly feeding aluminum wire and carbon wire into steel. It also has the function of cleaning molten steel and improving the shape of nonmetallic inclusion.
Electric arc furnace working
Arc furnace is an electric furnace that USES arc energy to smelting metal.
There are three types of arc furnaces for industrial use:
The first type is the direct heating type. The arc occurs between the special electrode rod and the smelted charge, which is directly heated by the arc. Mainly used for steelmaking, followed by smelting iron, copper, refractory materials, refined steelmaking liquid, etc.
The second type is indirect heating type. The arc occurs between two special electrode bars. The charge is radiated by the arc and used for smelting copper and copper alloy. This kind of furnace is noisy, melting quality is poor, has been gradually replaced by other furnaces.
The third type, called the ore furnace, is made of ore with high resistivity. The lower part of the electrode is usually buried in the charge during the working process. The heating principle is that the heat generated by the resistance of the charge and the electric arc between the electrode and the charge is not only used when the current passes through the charge. So it is also called arc resistance furnace.
Electric arc furnace in steel making
1. Preparation before smelting:
Check whether the mechanical, electrical, water cooling, hydraulic, feeding and other equipment and systems are normal, and prepare all kinds of tools and materials before opening the furnace.
2. Plug the steel outlet: first clean the slag steel stuck on the inside and outside of the steel outlet, close the tray of the steel outlet, and then fill the steel outlet with the steel outlet filler, and require the steel outlet to be filled and compacting.
3. Furnace repair: Furnace repair requires quick repair, thin repair, temperature drop fast repair first.
4. Charging: After the steel outlet is filled and sealed, the back support of the furnace body is put in place, the furnace body is lifted, the electrode is lifted, the lock of the rotating frame is lifted, the furnace cap and the rotating furnace cap are lifted in place, and the prepared steel and iron materials are added into the furnace. Special personnel should be assigned to direct the rest of the train to stay away from the furnace. When feeding, the bottom of the basket should be within 200mm from the edge of the furnace wall. The material basket is located in the middle of the furnace body slightly away from the position of the transformer.
5. Press: after adding the material, when the material exceeds the upper edge of the furnace body, press the material. It is required to use a heavy hammer to press the burden lower than the upper edge of the body, and it is required to remove the material supported on the upper edge of the body.
6. Close the furnace cover: after the material is pressed, turn the furnace cover back. After it is in place, close the furnace cover to ensure that the furnace cover is inside the plug and the lock pin of the rotating big frame is properly locked.
7. Power transmission: Assign an electrician to ring the bell three times after receiving the power transmission instruction and carefully observe the situation on and around the furnace body to make sure that there is no one on the furnace and turn off the power transmission.
8. Power supply system: The sixth voltage (760V) is used in the melting period, and the current is 35 ~ 45KA. The specific power supply system is determined by mastering the equipment performance and smelting conditions.
10. Oxygen combustion-supporting melting: oxygen combustion-supporting melting starts immediately when electricity is sent. Operate in strict accordance with the operating procedures required by the oxygen combustion aid equipment.
11. Oxygen blowing assisted melting: after power transmission, switch to oxygen blowing assisted melting when oxygen burning assisted melting reaches a certain degree. It is required that oxygen flow should be converted gradually from low oxygen to medium oxygen to high oxygen when oxygen blowing for melting. It is strictly prohibited to directly open to medium oxygen and high oxygen operation.
12. Hot metal mixing: at the same time, the electric furnace can send electricity and add hot metal into the furnace through the hot metal mixing device. The molten iron should be mixed evenly and stably with moderate speed.
13. Secondary feeding: When the first feeding is melted by about 85%, the second feeding can be arranged. First, the power is cut off, the oxygen gun gas of the furnace wall is switched to the protective state, the horizontal support is well done, the electrode is lifted to the limit position, the revolving frame is unlocked, the furnace cap is lifted, the furnace cap is unscrewed to the maximum position, and the second batch of material is loaded. When the charge is higher than the furnace edge, the material is pressed as required. Press the material to cover the furnace.
14. The requirements of the second batch of materials, such as electricity transmission, oxygen-combustion-assisted melting, oxygen-blown melting and power supply system, are the same as those of the first batch of materials.
15. Advance slagging and dephosphorization: when the charge melts more than 90%, lime is added into the furnace. The amount of lime is controlled by 3% of the total weight of the charge and added in 2 to 3 times to realize the fast material, fast slag, fast temperature rise and low temperature dephosphorization.
16. Toner spray: when the furnace slag can't bury arc effectively, toner is sprayed into the furnace. The amount of toner sprayed into the furnace is controlled at about 15Kg/min, subject to the stable burying arc of furnace slag and good fluidity of furnace slag.
17. Oxidation refining: When the temperature is greater than 1520 ° C, sampling analysis will be carried out at 1560 ~ 1580 ° C to remove most of the molten slag, and the amount of slag added, oxygen supply intensity and oxygen supply will be determined according to the composition analysis results and target control composition. When adding slag, stop spraying toner into the furnace to ensure the rapid melting of slag. After the slagging is opened, spray toner into the furnace and take samples for analysis.
18. Steel outlet operation:
1) Open the horizontal support after the furnace and push the tilting furnace operation button to the operation position behind the furnace.
2) Open the outlet. When the outlet packing fails to flow spontaneously, burn oxygen and drain immediately.
3) After the steel flows down, control the speed of tilting furnace according to the speed of discharging steel. It is strictly prohibited that the speed of tilting furnace is too fast, resulting in eccentric cap burning and leakage or more serious accidents.
4) Realize the operation of retaining steel and slag. Ensure that the amount of steel remaining in each furnace is controlled within 10 ~ 15T.
5) When returning to the furnace after the discharge of steel, start slowly, go fast in the middle, and turn to the slow gear when no slag is left, so as to avoid shaking off the electrode and slag during the process of returning to the furnace after the discharge of steel. It is forbidden to drop a lot of slag in the process of steel production.
6) Stirring in the process of steel discharging: argon gas is switched on before steel discharging, and the pressure of argon gas is 0.4 ~ 0.6mpa. The pressure of argon gas is adjusted according to the effect of steel liquid stirring to ensure good mixing of steel liquid.