This article combines the author’s practical experience to explain the steelmaking deoxidation process, and also describes the inclusion control to ensure the excellence of each steelmaking process. We also put forward targeted strategies for the control of inclusions in each process, improve the quality of steelmaking and reduce the content of inclusions in steelmaking during the steelmaking process.
Keywords: steelmaking; deoxidation process; inclusions; control
Steelmaking deoxidation is an important process in steelmaking. If steelmaking deoxidation cannot be carried out efficiently, it will directly affect the control of steelmaking inclusions. If steelmaking deoxidation is not complete, there will be room for the oxidation of inclusions. Under oxygen, the cast slab will easily Problems such as bubbles under the skin, nodules at the nozzle, and an increase in inclusions in the billet. Therefore, thorough deoxidation of molten steel can reduce the number of oxidized inclusions in the steel, change the form of sulfide inclusions, enhance the stability of the steel, and stabilize the mechanical properties. Incomplete deoxidation of steelmaking is the key to cleaning inclusions. At the same time, converter blowing is a steelmaking process. During the furnace blowing process, the oxygen supply to the molten pool needs to meet a certain amount to ensure the stability of the refractory materials and the molten steel can also play its role. The role of dissolved oxygen, and molten steel contains dissolved oxygen, which increases the hazards of molten steel. Blowing in the furnace will increase the physical quality. Deoxidation that does not meet the standard will cause serious harm. At the end of blowing, it must be ensured that the level of removal is sufficient to promote pouring. Orderly and efficient, it has a better effect on the structural rationality of the slab. Therefore, the entire steelmaking process must select the correct deoxidizer and control the amount of deoxidizer added. The oxygen content of the molten steel must also be controlled to ensure the degree of deoxidation.
Factors affecting the oxidation of molten steel
The oxygen content of molten steel at the end of blowing is a quantitative indicator of oxidation. The greater the oxygen content, the stronger the oxidation. The factors that affect the oxygen content of molten steel are as follows. The first is the end-point carbon content, which is inversely proportional to the oxygen content of the molten steel; the second is the residual manganese content in the molten steel, which is inversely proportional to the oxygen content. The residual manganese content directly affects the carbon content of the molten steel, and indirectly affects the carbon content of the molten steel. The third is the temperature of the molten steel. The higher the temperature of the molten steel, the more abundant the oxygen content of the molten steel. The fourth is the operation process. The operation process is subjective, and the exquisiteness of the process directly affects the oxygen content of the molten steel. High The operation of the gun position and the degree of stirring of the molten pool directly affect the oxygen content of the molten steel; the fifth is the slag removal process during tapping, and the degree of slag removal affects the oxygen content of the molten steel.
Purpose of deoxidation
Converter steelmaking must be deoxidized to ensure the effectiveness of steelmaking. During oxidation refining, molten steel needs to be deoxidized. The oxygen content in the steel at the end of smelting must be completely removed to facilitate the smooth pouring in the next step. Of course, deoxidation does not completely remove all oxygen content in molten steel. It only removes the required range of steel types, avoids the generation of deoxidation products and non-metallic inclusions, and controls the shape and quantity of inclusions.
Deoxidation principles and deoxidizers
The selection of deoxidizing agent for steelmaking requires suitable deoxidizing metals. The deoxidizing agent must also be combined with the alloy to ensure the alloying of the argon blown wire for deoxidation. Common deoxidizing agents include calcium silicon and barium. The calcium silicon and barium alloys are Ca and Ba in steel. The oxidation alloy, the alloy and the deoxidizer can be completely dissolved when added to the molten steel at the same time, and the two are completely miscible in the liquid state. The vaporization of barium in the molten steel can accelerate the solubility of calcium, and the application effect of calcium is improved; the oxidation of barium and sulfur in the molten steel The degree of solubility is small, so the deoxidizer added to the silicon-calcium-barium alloy can achieve a good deoxidation effect and reduce the oxidation of molten steel. At the same time, the deoxidizer must not only have deoxidation effect but also have adsorption capacity to adsorb deoxidation products and effectively discharge them. In addition, the deoxidizer must be added in an orderly manner. Low-strength deoxidizer must be put in before high-strength deoxidizer is added to ensure that the degree of deoxidation increases from weak to strong. The deoxidation process also needs to increase the fusion of elements. The alloying elements can increase the stability of deoxidation and avoid alloy burning loss.
The deoxidation process directly determines the deoxidation effect, and the total oxygen content of molten steel will also be different under different deoxidation processes. First of all, pre-deoxidation is required when tapping steel from the converter. The process at this stage is to alloy silicon, manganese and other elements in the furnace, blow argon and feed wire, then heat and refine, and then perform vacuum casting. However, different types of steel have different requirements for deoxidation processes. In particular, the barium substance in molten steel can not only form surface active substances with inclusions to discharge the molten steel, but also can refine the grains. When using aluminum-iron deoxidizer, the amount of precipitation deoxidation must be controlled. As a strong metal deoxidizer, aluminum-iron must precipitate low-carbon aluminum. During precipitation deoxidation, the steel increases the metal aluminum and silicon in the molten steel and reduces the oxygen and silicon in the molten steel. Nitrogen can be used to reduce electrolytic inclusions in the slab, and the acid-soluble aluminum produced can be used for continuous casting, which can significantly reduce the oxygen content of molten steel.
Inclusion control strategies
Sources of inclusions
Inclusions usually appear in both the smelting and pouring stages. Therefore, the control of inclusions requires different methods in the two stages. Non-metallic phases are put into deoxidation, and compounds are generated during the process. When encountering non-metallic inclusions in steel, they directly reduce the physical properties of the steel. Inclusions in steel are mainly substances produced during the deoxidation process of steel or secondary oxidation products produced by elements and oxygen during the deoxidation process. They are also accompanied by slag and steelmaking materials mixed into the steel. Foreign inclusions have large particles and are easily visible to the naked eye floating in molten steel, while endogenous inclusions are accidental and irregular and difficult to detect.
Control of inclusions in converter smelting
In order to reduce the number of inclusions generated in the converter, the following points should be controlled. The first is to control the oxygen content at the end of the converter, and control the end point content through supplementary blowing and deep blowing; the second is to increase the final MgO content and alkali content of the converter. degree, controlling the content and alkalinity through tapping slag blocking, slag modification, etc.; the third is to reduce the sulfur content of molten steel, which is achieved by suppressing sulfides; the fourth is to reduce the density difference between high alkalinity desulfurization slag and molten steel, The difference in density causes the molten slag to be unable to be integrated into the molten steel, and the molten slag precipitates from the molten steel, thereby achieving the purpose of detaching the inclusions.
Control of inclusions during casting
First, protect the pouring of molten steel. After refining, the molten steel needs to be isolated from reacting with air, refractory materials and slag. Protective pouring is required for the molten steel, which has a significant effect on isolating the contact between the molten steel and the atmosphere. It also controls the absorption of oxygen and nitrogen by the molten steel under high temperature conditions, while ensuring that the tundish is To ensure the airtightness of the crystallizer, the tundish uses a covering agent that can adsorb and dissolve floating inclusions in the crystallizer. Second, tundish metallurgy. The removal of inclusions in the tundish requires enhancing the floating ability of the inclusions. The flow direction of the tundish steel liquid in the flowing steel is controlled and optimized through retaining walls, dams, and chokes, and the eddy current formed by the impact of the retaining walls on the ladle is used to limit the flow. , when the flow of molten steel at the tundish nozzle stabilizes, the inclusions will float up and be discharged.
In steelmaking enterprises, the deoxidation process is a very important process technology, which will be related to the subsequent production quality. In the actual production process, workers are required to pay full attention to and scientifically apply the deoxidation process, and to take effective measures to control its inclusions to ensure that product performance meets standards.