LF refining white slag control method

Abstract

The invention belongs to the technical field of steelmaking processes, and relates to an LF (ladle furnace) refining white slag control method, which realizes rapid formation and stable maintenance of white slag by accurately controlling refining slag components and process parameters. In the converter smelting process, table aluminum is added for deoxidation according to the oxygen determination result; adding metallurgical lime to make white slag in advance during tapping; in the LF refining stage, electric smelting refining slag and metallurgical lime are added, deoxidizing materials such as aluminum particles and silicon carbide are added in batches, it is ensured that white slag is rapidly formed, and the refining time is kept to be longer than or equal to 15 minutes. According to the method, the white slag making time is effectively shortened, the cost is reduced, meanwhile, the refining desulfurization rate is remarkably increased, the oxygen content of the molten steel is reduced, and the purity of the molten steel is improved. The method is suitable for various steelmaking process routes, and an efficient and environment-friendly white slag control solution is provided for the steelmaking industry.

Description

Technical Field

[0001] The invention belongs to the technical field of steelmaking process and relates to a method for controlling LF refining white slag. Background Art

[0002] LF refining is an important part of the steelmaking process. It is mainly used for secondary refining of molten steel to further reduce the impurity content in the steel and improve the cleanliness and quality of the molten steel. During the LF refining process, the composition control of the refining slag has an important influence on the removal of inclusions, deoxidation, desulfurization and other processes in the steel. The refining slag usually adopts the low melting point slag system of the CaO-SiO2-Al2O3 ternary phase diagram, and its composition and basicity have a significant effect on the refining effect.

[0003] In the LF refining process, the main function of the refining slag is to adsorb inclusions in the steel. The composition and basicity of the slag have a direct impact on the deoxidation, desulfurization and adsorption of inclusions. As the Al2O3 content in the slag increases, the Al2O3 content of inclusions in the steel will also increase significantly, resulting in an increase in the size of the inclusions and an increase in the number density, thereby reducing the cleanliness of the molten steel. Studies have shown that when the Al2O3 content in the slag is about 20%, the number density of inclusions is the smallest and the cleanliness of the molten steel is the highest.

[0004] At present, flaw detection steel usually adopts the LF+RH double refining process path. The composition control of LF refining slag has an important influence on the inclusion content in steel. In order to reduce the inclusion content in steel and improve the cleanliness of molten steel, the LF refining slag system must be controlled within a reasonable range. However, the existing LF refining slag control method has problems such as long slag making time, short white slag duration, and high cost. An efficient and low-cost white slag control method is urgently needed.

[0005] Therefore, developing a LF refining white slag control method that can quickly form white slag and maintain the white slag refining time is of great significance for improving the cleanliness of molten steel and reducing production costs. Summary of the invention

[0006] In view of this, the object of the present invention is to provide a method for controlling white slag in LF refining, which can optimize the composition control of LF refining slag, shorten the slag making time, and prolong the duration of white slag, thereby effectively improving the LF refining effect.

[0007] To achieve the above object, the present invention provides the following technical solution: a method for controlling white slag from LF refining, comprising the following steps:

[0008] A. During the converter smelting process, according to the oxygen determination results at the end of smelting, Taiwan aluminum is added for deoxidation to reduce the oxygen content of molten steel. The Al content of Taiwan aluminum is ≥99.5%, Si ≤0.15%, and S ≤0.01%;

[0009] B. After the alloy is added to the converter, metallurgical lime is added to make white slag in advance. The amount of metallurgical lime added is 800kg / furnace. The metallurgical lime particle size requirement is: ≤5mm ratio ≯5%, and the metallurgical lime activity requirement is: 300ml~350ml;

[0010] C, from the converter tapping to the LF refining process, add 600kg / furnace of molten refining slag and 600kg / furnace of metallurgical lime;

[0011] D. During the LF refining process, 60kg / furnace of aluminum particles and 80kg / furnace of silicon carbide were intermittently added to quickly form white slag, and the white slag refining time was maintained ≥15 minutes.

[0012] Optionally, the composition control range of the LF refining slag system is: CaO=45-50%, SiO2=8-10%, Al2O3=20-30%, MgO=5%, (MnO+FeO)≤1%, and basicity R=4-5.

[0013] Optionally, during the converter smelting process, the total charge amount is 235t, the iron-steel ratio is controlled at 830-900kg / furnace, the converter smelting time is 7 minutes, and all auxiliary materials such as metallurgical lime, magnesium balls, and limestone are added.

[0014] Optionally, after 7 minutes of converter smelting, the temperature in the furnace is adjusted with a slag-removing agent, the amount of slag-removing agent added is ≤1000kg, and other auxiliary materials are ≤500kg.

[0015] Optionally, the amount of metallurgical lime added during the steel-making process is controlled at 800 kg / furnace.

[0016] Optionally, argon is blown into the CAS after steel is tapped to make the temperature and composition of the molten steel uniform.

[0017] Optionally, during the LF refining process, 600 kg / furnace of metallurgical lime and 600 kg / furnace of molten refining slag are added, and 60 kg / furnace of aluminum particles and 80 kg / furnace of silicon carbide are intermittently added to quickly form white slag, and the white slag refining is maintained for more than 15 minutes.

[0018] Optionally, after the LF treatment, the molten steel is transported to the RH vacuum treatment, and after the RH treatment, it is transported to the continuous casting to be cast into steel billets. The baking time of the continuous casting tundish is ≥2 hours, the moisture content of the crystallizer protective slag is ≤0.5, a long shroud is used for protective casting between the large ladle and the tundish, and protective casting is used between the tundish and the crystallizer.

[0019] Optionally, calcium fluoride is not used as a slag-forming material during the LF refining process.

[0020] Optionally, during the LF refining process, aluminum particles and silicon carbide are added to maintain the white slag refining effect and continuously keep the white slag, so as to achieve the requirement of controlling the white slag refining time ≥15 minutes.

[0021] The beneficial effects of the present invention are:

[0022] 1) The present invention adds metallurgical lime in advance during the converter steelmaking process to perform pre-slag making, and utilizes the heat and impact stirring of molten steel to quickly form slag, thereby significantly shortening the formation time of white slag during LF refining and improving production efficiency.

[0023] 2) In the LF refining process, the present invention can effectively maintain the refining effect of white slag by adding deoxidizing materials such as aluminum particles and silicon carbide in batches, and adding metallurgical lime and molten refining slag in combination, ensuring that the white slag lasts for ≥15 minutes, thereby improving the cleanliness of molten steel.

[0024] 3) The present invention avoids the use of expensive slag-making materials such as calcium fluoride by optimizing the control of slag composition, reduces environmental pollution, and reduces slag-making costs, thus having significant economic benefits.

[0025] 4) The present invention can effectively adsorb inclusions in steel, reduce the inclusion content in steel, and improve the cleanliness of molten steel by controlling the composition range of LF refining slag (CaO=45-50%, SiO2=8-10%, Al2O3=20-30%, MgO=5%, (MnO+FeO)≤1%, basicity R=4-5).

[0026] 5) The present invention adopts the process route of converter steelmaking, LF refining, RH vacuum refining and continuous casting, combined with the technology of steel slag washing and white slag making in advance of electric melting refined slag, which improves the slag making efficiency, shortens the LF white slag slag forming time, and further improves the refining effect of LF refined white slag.

[0027] 6) The present invention does not use calcium fluoride as a slag-making material during the LF refining process, thereby avoiding the environmental pollution caused by calcium fluoride and meeting the requirements of green and environmentally friendly modern metallurgical processes.

[0028] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. DETAILED DESCRIPTION

[0029] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0030] In this embodiment, a method for controlling white slag from LF refining is provided. The method adopts a process route of 210t combined blowing converter → CAS → LF → RH → continuous casting, and adopts the following smelting process, specifically:

[0031] 1. Converter smelting stage:

[0032] The molten iron and scrap steel are loaded into the converter for converter oxygen blowing smelting to obtain converter smelting molten steel. The total loading amount is 235t, the iron-steel ratio is controlled at 830-900kg / furnace, and the converter smelting time is 7 minutes. During the smelting process, metallurgical lime, magnesium balls, limestone and other auxiliary materials are added to ensure that all auxiliary materials are added within 7 minutes.

[0033] 2. Adjustment in the later stage of converter smelting:

[0034] After 7 minutes of converter smelting, the slag-removing agent is used to adjust the temperature in the furnace. According to the TSC (converter end point oxygen determination) measurement results, the amount of slag-removing agent added is ≤1000kg, and the amount of other auxiliary materials added is ≤500kg.

[0035] 3. Steel-making process:

[0036] During the process of tapping the converter, metallurgical lime is added for pre-slag making. The amount of metallurgical lime added is controlled at 800kg / furnace. The particle size requirement of metallurgical lime is: ≤5mm, the proportion is ≯5%, and the activity requirement is: 300ml~350ml. The heat and impact stirring of molten steel are used, and argon blowing and stirring at the bottom of the ladle are used to quickly melt the metallurgical lime to form slag.

[0037] 4. CAS argon blowing treatment:

[0038] After tapping, the molten steel is sent to CAS (ladle argon blowing station) for argon blowing treatment to even out the temperature and composition of the molten steel.

[0039] 5. LF refining stage:

[0040] The molten steel is hoisted to the LF (ladle furnace) for refining. During the LF refining process, 600kg of metallurgical lime and 600kg of molten refining slag are added per furnace, and 60kg of aluminum particles and 80kg of silicon carbide are added intermittently to quickly form white slag. By controlling the amount of deoxidizing material and slag-making material added, the white slag refining time is maintained at ≥15 minutes.

[0041] 6. RH vacuum treatment:

[0042] After LF refining, the molten steel is transported to the RH (vacuum cycle degassing device) for vacuum treatment to further remove gas and inclusions in the steel.

[0043] 7. Continuous casting stage:

[0044] After the RH treatment, the molten steel is transported to the continuous casting machine for casting. During the continuous casting process, ensure that the baking time of the tundish is ≥2 hours and the moisture content of the mold protection slag is ≤0.5%. Long nozzle protection casting is used between the large ladle and the tundish, and protection casting is also used between the tundish and the crystallizer to ensure the quality of the steel billet.

[0045] The invention discloses a method for controlling white slag in LF refining. The method adopts a process route of converter steelmaking, LF refining, RH vacuum refining and continuous casting. Compared with the existing process, the method adopts steel slag washing and electric melting refining slag to make white slag in advance, thereby improving the slag making efficiency, shortening the LF white slag slag forming time and improving the refining effect of the LF refining white slag.

[0046] The invention provides a method for controlling white slag in LF refining. In the LF refining process, aluminum balls and silicon carbide are used to maintain the white slag refining effect, and the white slag is continuously kept to meet the requirement of controlling the white slag refining time to be ≥15 minutes.

[0047] Patent No.: CN113502372A provides a method for making white slag using 8%-10% aluminum powder, 50%-60% ferrosilicon powder, 25%-30% carbon powder and 5%-10% calcium fluoride. Calcium fluoride can reduce the melting point of slag and adjust the fluidity of slag. The addition of aluminum powder can achieve rapid deoxidation and white slag. The addition of carbon powder can promote the formation of long arc foam slag. Ferrosilicon powder can promote the stable maintenance of white slag. The present invention does not use calcium fluoride and is environmentally friendly.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A method for controlling LF refining white slag, characterized in that: The following steps are involved: A. During the converter smelting process, according to the oxygen determination results at the end of smelting, Taiwan aluminum is added for deoxidation to reduce the oxygen content of molten steel. The Al content of Taiwan aluminum is ≥99.5%, Si ≤0.15%, and S ≤0.01%; B. After the alloy is added to the converter, metallurgical lime is added to make white slag in advance. The amount of metallurgical lime added is 800kg / furnace. The metallurgical lime particle size requirement is: ≤5mm ratio ≯5%, and the metallurgical lime activity requirement is: 300ml~350ml; C, from the converter tapping to the LF refining process, add 600kg / furnace of molten refining slag and 600kg / furnace of metallurgical lime; D. During the LF refining process, 60kg / furnace of aluminum particles and 80kg / furnace of silicon carbide were intermittently added to quickly form white slag, and the white slag refining time was maintained ≥15 minutes.

2. The method for controlling LF refining white slag according to claim 1, characterized in that: The control range of LF refining slag composition is: CaO=45~50%, SiO2=8~10%, Al2O3=20~30%, MgO=5%, MnO+FeO≤1%, basicity R=4~5.

3. The method for controlling LF refining white slag according to claim 1, characterized in that: During the converter smelting process, the total loading amount is 235t, the iron-steel ratio is controlled at 830-900kg / furnace, the converter smelting time is 7 minutes, and all auxiliary materials such as metallurgical lime, magnesium balls, and limestone are added.

4. The method for controlling LF refining white slag according to claim 1, characterized in that: After 7 minutes of converter smelting, use slag-removing agent to adjust the temperature in the furnace. The amount of slag-removing agent added is ≤1000kg, and other auxiliary materials are ≤500kg.

5. The method for controlling LF refining white slag according to claim 1, characterized in that: The amount of metallurgical lime added during the steel-making process is controlled at 800kg / furnace.

6. The method for controlling LF refining white slag according to claim 1, characterized in that: After steel is tapped, argon is blown into the CAS to even out the temperature and composition of the molten steel.

7. The method for controlling LF refining white slag according to claim 1, characterized in that: During the LF refining process, 600 kg of metallurgical lime and 600 kg of molten refining slag are added per furnace, and 60 kg of aluminum particles and 80 kg of silicon carbide are added intermittently to quickly form white slag, and the white slag is refined for more than 15 minutes.

8. The method for controlling LF refining white slag according to claim 1, characterized in that: After the LF treatment, the molten steel is transported to the RH vacuum treatment. After the RH treatment, it is transported to the continuous casting to be cast into steel billets. The baking time of the continuous casting tundish is ≥2 hours, the moisture content of the crystallizer protective slag is ≤0.5, a long nozzle is used for protective casting between the large ladle and the tundish, and protective casting is used between the tundish and the crystallizer.

9. The method for controlling LF refining white slag according to claim 1, characterized in that: In the LF refining process, calcium fluoride is not used as a slag-forming material.

10. The method for controlling LF refining white slag according to claim 1, characterized in that: During the LF refining process, the addition of aluminum particles and silicon carbide can maintain the white slag refining effect and keep the white slag continuously, so as to achieve the requirement of controlling the white slag refining time ≥15 minutes.