In terms of today’s actual steelmaking situation, converter steelmaking is used more frequently. The automation level of this steelmaking method is generally higher than other technologies, and its production effect is relatively significant. However, this steelmaking method has specific requirements. During the application period, attention must be paid to the good application of deoxidation technology, because the quality of the deoxidation operation can determine the effect of the steelmaking operation to a certain extent. Generally speaking, during the steelmaking operation, the application of converter steelmaking requires attention to the operation of deoxidation technology, so discussion and research on it is of great significance to the development of the steelmaking industry.
Keywords: converter steelmaking; deoxidation process; countermeasure analysis
Overview of converter steelmaking and deoxidation processes
Principles of converter steelmaking
The equipment used in the converter steelmaking operation is the converter. The shape of the converter is similar to that of a pear. The interior is a furnace wall made of refractory bricks. The furnace body can rotate 360 degrees at any angle. The raw materials required for steelmaking are molten iron and scrap steel. The entire blowing process of converter steelmaking is an oxidation reaction. The basic tasks of steelmaking include: decarburization, dephosphorization, desulfurization, and deoxidation to remove harmful gases and impurities, increase temperature, and adjust ingredients. . During the blowing process, according to the temperature and composition of the molten iron, the operator uses the heat balance formula and the formula of adding white ash and light burning to form the appropriate alkalinity and magnesium oxide in the steelmaking slag system to effectively remove C, P, and S, and achieve the appropriate level at the end of smelting. Tapping temperature and composition requirements. Since the top-blown oxygen reacts strongly with the molten iron and scrap steel in the furnace during the blowing process, the oxygen content of the final molten steel cannot meet the quality requirements of the steel type. Therefore, deoxidation and alloying operations must be carried out during the tapping process. Improve the quality of steel to meet steel grade requirements.
The important role of deoxidation process in the steelmaking process
The deoxidation technology during converter steelmaking is mainly to reduce the amount of oxygen in the steel and prevent the high oxygen content from reacting with other substances that is not conducive to production quality requirements. After the deoxidation process of steelmaking is completed, the proportion of oxygen is about 5 parts per thousand, and the amount of oxygen in boiling steel is about 0.25 to 0.3 parts per thousand. Deoxidation alloying can be good. Improve the quality of steel and reduce capital investment in steelmaking. Nowadays, there are many methods of deoxidation operation, but the scientific content is low. The methods of deoxidation technology application need to be continuously optimized to maximize the technical operation effect. The improvement of deoxidation technology can improve the quality of steel to a certain extent and increase the number of steel market transactions in my country. It can be seen that deoxidation technology is very critical for steelmaking.
Oxygen generation and hazard analysis in steelmaking
Oxygen in molten steel often occurs in the form of non-metallic inclusions or dissolved oxygen. Oxygen may appear during the material and oxygen blowing steelmaking process. However, no matter which method is used for steelmaking, other components in the steel can be eliminated in this way. When substances are decomposed, especially during the treatment of substances such as manganese, silicon, phosphorus and carbon, oxygen is basically used, and chemical reactions occur with oxygen, causing other substances to fuse with oxygen to generate new substances and decompose at the same time out of other substances. The molten steel must contain oxygen to a greater or lesser extent. Therefore, during oxygen blowing steelmaking, due to the oxidation of the molten steel and the continuous reduction of the amount of other substances, the amount of oxygen in the molten steel also continues to decrease. There is no measurement of the oxygen in the molten steel. With good management, the oxygen content in the molten steel is high. After it is completely condensed, it can change with the molten steel to form crystalline substances and ferrous oxide. The presence of ferrous oxide in the molten steel can cause damage to the cast slab, thereby reducing the quality of the finished steel. In severe cases, it can cause deformation, produce hot brittleness, cold brittleness, hydrogen embrittlement, or lead to oxidation problems in the steel. ‘s appearance. If the oxygen content in the molten steel exceeds the standard, it will easily aggravate the damage of sulfur, and at the same time, chemical phenomena will continue to occur. When changes occur, it will also lead to the emergence of various oxidizing substances, which will be doped into the steel products, reducing the quality of the finished steel and affecting the steel products. various performances. The carbon contained in the molten steel in the condensation process also undergoes chemical changes with dissolved oxygen, causing boiling. Especially when the oxygen content is high, the boiling phenomenon is more significant, because various deoxidation phenomena will occur in the liquid steel, resulting in differences in the actual boiling conditions. According to various boiling conditions, various steel materials will appear, such as For boiling steel, killed steel and semi-killed steel, if carbon monoxide bubbles are contained in the molten steel, it will easily cause the concentration in the slab to decrease and damage the hardness of the steel. Because of the above situation, it is necessary to use the usual methods to develop the solution, improve the deoxidation quality of the molten steel, and reduce the amount of oxygen in the molten steel.
Current status of deoxygenation technology
In recent years, aluminum is still a frequently used deoxidizing substance in converter steelmaking deoxidation technology during steelmaking operations. However, the recycling and reuse rate of aluminum is between 10% and 25%, and the probability of application is low. Therefore, To a certain extent, it has intensified the capital investment of steelmaking-related companies. If individual steelmaking units want to handle the related situations well, they need to continuously study aluminum-related deoxidizing substances, such as ferro-silicon aluminum and ferro-aluminum manganese. Under normal conditions, the density of this deoxidizing material is higher than that of aluminum. Adding the deoxidizing material to the molten steel allows sufficient reaction time, so the recycling application effect can be improved. After the deoxidation operation, composite oxidized substances with lower melting points are produced, so the desired deoxidation efficiency can be achieved. After aluminum is deoxidized, a large amount of aluminum oxide can appear. The appearance of this substance can affect the performance of the finished steel to a certain extent, especially the fatigue resistance of the steel.
Analysis of converter steelmaking deoxidation process
Precipitation deoxidation and diffusion deoxidation are the most frequently used deoxidation methods during converter steelmaking. They both require the use of deoxidizers to carry out deoxidation production. The precipitation deoxidation method is direct deoxidation, while diffusion deoxidation is indirect deoxidation. In addition, the vacuum deoxidation method is also used more frequently during specific operations. This deoxidation method does not require the use of a deoxidizer, ensuring that the molten steel is in a vacuum state, destroying the state of carbon and oxygen, catalyzing the chemical change of carbon and oxygen, forming carbon monoxide and then reacting with it. Separation of molten steel. The selection of deoxidation technology and deoxidation materials during actual production must be determined based on the company’s specific status and product type.
Precipitation deoxidation method
During the precipitation deoxidation method, the selection and application of the deoxidizer affects the quality of the deoxidation operation to a certain extent. Because the research and application of deoxidation in converter steelmaking continues to increase, deoxidation technology has been well improved during specific operations, especially the calcium-based deoxidation substances used in basic precipitation deoxidation technology, whose deoxidation effects are relatively significant.
(1) Study the composition of calcium-based deoxygenated substances. Calcium-based deoxidizing substances include calcium, carbon, silicon, barium, rhenium, aluminum, etc. According to the type of steel, scientific configuration of the composition of calcium-based deoxidizing substances can effectively improve the fusion of deoxidizing substances and oxygen, thereby achieving good results. The quality of deoxidation operations.
(2) Research on the production principle of calcium-based deoxygenated substances. Calcium is a key element, and its fusion is higher compared with other elements. Barium is similar to calcium and has a high deoxidizing ability. Doping barium into silicon-aluminum ferro can produce silicon-aluminum barium, which can effectively improve the deoxidizing ability of barium. When barium and calcium were compared, it was found that calcium has a higher deoxidation performance. The molar mass ratio of calcium to barium is 1 to 3.43. It can be seen that if you want to decompose the same amount of oxygen, you need to add 1 kilogram of calcium, and add The barium quantity should be 3.43kg. However, the solubility of calcium in molten steel is weak. Even if the temperature of the molten steel is as high as 1,600 degrees Celsius, the solubility of calcium only reaches 0.3 parts per thousand. At the same time, calcium basically cannot dissolve in solid iron. And under such conditions, the vapor pressure of calcium is about twice as high as the atmospheric pressure, so the vapor pressure of calcium is high. If calcium is simply used as a deoxidizing substance, a lot of calcium will be wasted, which will increase capital investment and reduce production. economy. Therefore, if you want to improve the application effect of deoxidation substances, you must ensure the deoxidation operation effect, and you need to use various methods to improve the solubility of calcium substances in molten steel. According to the specific situation, the addition amount of other elements in the calcium substance should be studied to improve its solubility.
Optimization of deoxidation process of plain carbon steel
During the application of ordinary carbon steel deoxidation technology for steelmaking, attention must be paid to the following operations:
(1) In the early stage of deoxidation operation, low-priced carburizing substances should be reasonably added to the converter.
(2) Gradually carry out deoxidation operations and deoxidation alloying operations in the use of ferrosilicon and silicon-manganese alloys.
(3) Carry out deep deoxygenation operation through argon blowing station. During actual operation, during converter steelmaking, if the end point of the converter is greater than or equal to 0.5 thousandths, you can add carburizing substances when the molten steel fills the bottom of the furnace, and at the same time carefully check the dissolution of the carburizing substances and the rolling conditions of the ladle. Ferrosilicon and silicon-manganese alloy are added when it is determined to meet the standards to complete the deoxidation alloying operation; if the end point of the converter is less than or equal to 0.5 thousandths, it can be added when the steelmaking process is 20% complete. Appropriate amounts of aluminum-iron and silicon-manganese alloys are added to the furnace body in sequence after the pre-deoxidation operation is completed to complete the deoxidation alloying operation. During the argon blowing process, it is necessary to ensure its integrity, and at the same time, the intensity and time of the operation need to be controlled in accordance with standards. Compared with before, the deoxidation technology in the optimization measures is more economical. If the W (C) in the molten steel is too high, carburizing substances can be used to carry out pre-deoxidation operations. If the W (O) in the molten steel is too high, it needs to be applied. Deoxidizing low-cost aluminum and iron can not only improve the safety performance of ordinary carbon steel deoxidation technology, but also reduce investment capital, and its application and promotion value are high.
Vacuum deoxidation method
The vacuum deoxidation method uses vacuuming. The treated molten steel is placed under vacuum conditions to destroy the state of carbon and oxygen, catalyze the chemical changes of carbon and oxygen, and separate carbon monoxide from the molten steel to complete the deoxidation operation. Adding an appropriate amount of inert gas during the deoxidation operation can promote the agitation of the molten steel and play a catalytic effect during the occurrence of chemical standards for carbon and oxygen. It causes carbon monoxide to separate from the molten steel, thereby reducing the damage to the molten steel. Non-metallic substances can be separated during the rising process of carbon monoxide, and decarburization operations can be performed during the deoxidation operation. This method is applied during the production of low carbon steel. Relatively extensive. The separation of carbon monoxide can promote the stirring of molten steel, implement good chemical phenomena, ensure the quality of deoxidation operations, and reduce the use of deoxidation substances and lime, reducing the investment in deoxidation operations. During the specific production period, the applied technology is relatively simple and can well ensure the quality of steel. The external operation links of the converter and electric furnace are used as a good method to improve the quality of steel.
Diffusion deoxidation process
Diffusion deoxidation technology mainly uses deoxidation substances to control the amount of oxygen during steelmaking. This method can reduce the degree of damage to the steel and ensure the quality of the steel produced. Its shortcomings are low diffusion efficiency, long application time of deoxidation operation, which will cause time loss, and at the same time, phosphorus reversion may occur. If the deoxidation technology is relatively sophisticated, it can reduce the time required for the deoxidation operation. This shows that the diffusion deoxidation method has higher application value.
Conclusion
In summary, the quality of steelmaking is closely related to the control of oxygen content during the steelmaking process. Therefore, in steelmaking practice, specific control of oxygen content must be based on the hazards of oxygen. This article clarifies the quality control factors in the steelmaking process, conducts a detailed analysis of the generation of oxygen and the hazards of oxygen in the converter steelmaking process, and explains the deoxidation methods and specific operations in the converter steelmaking process. Purpose It is to provide scientific guidance and assistance for the utilization of deoxidation process in converter steelmaking practice, so as to achieve an overall improvement of the quality of converter steelmaking.