A method for cleaning an rh vacuum tank

Abstract

The application discloses an RH vacuum tank cleaning method and belongs to the technical field of metallurgy. The method comprises the following steps: smelting steel materials by a converter to obtain molten steel, adding aluminum blocks in the steel material deoxidization process during tapping of the converter; performing LF smelting on the molten steel, and controlling the content of C, Mn and Si at the upper limit of the process target value at the end of the LF smelting; and using a to-be-cleaned RH vacuum tank to perform RH vacuum degassing on the molten steel after the LF smelting. The application uses the pure molten steel obtained by smelting the steel materials by the converter to flush the residual steel in the RH vacuum tank, so that the RH vacuum tank is cleaned. In the RH vacuum degassing process, the excessive Al, Si, Mn and C in the molten steel can react with oxygen in the residual steel, so that the oxygen content in the molten steel is reduced, and the purity of the molten steel is improved. Through the above steps, the cleaned molten steel can be directly cast on a continuous casting machine, the refining capacity of the LF furnace is released, the waste of energy and time cost caused by the molten steel returning to the treatment is avoided, and the production efficiency and economic benefits are significantly improved.

Description

Technical Field

[0001] This application relates to the field of metallurgical technology, and in particular to a method for cleaning an RH vacuum tank. Background Technology

[0002] After the RH vacuum tank is filled with new steel and cooled, there are still impurities and residual steel with strong oxidizing properties inside the vacuum tank. It is necessary to clean the RH vacuum tank with ordinary steel to prevent it from affecting the quality of subsequent specialty steel production.

[0003] In related technologies, when steel mills use molten steel to deeply clean the RH vacuum tank, the residual steel in the vacuum tank contains a large amount of oxygen. The molten steel after cleaning the RH furnace vacuum tank needs to be returned to the LF refining furnace for slag formation and deoxidation, which takes more than an hour. This increases the refining pressure of the LF furnace and results in a waste of energy and time costs. Summary of the Invention

[0004] The purpose of this application is to provide a method for cleaning RH vacuum tanks, which can shorten the production process of cleaning RH vacuum tank molten steel while ensuring the quality of the cleaned RH vacuum tank molten steel.

[0005] To solve the above-mentioned technical problems, this application adopts the following technical solution:

[0006] This application provides a method for cleaning an RH vacuum tank, including:

[0007] S1, steel is smelted in a converter to obtain molten steel. During the tapping process of the converter, aluminum blocks are added to the steel based on the deoxidation process of the steel.

[0008] S2, the molten steel is subjected to LF smelting, and the C, Mn and Si contents at the end of LF smelting are controlled according to the upper limit of the process target value composition.

[0009] S3, using the RH vacuum tank to be cleaned to perform RH vacuum degassing on the molten steel after LF smelting.

[0010] In this scheme, purified molten steel is obtained by smelting steel in a converter. This purified molten steel is then used to flush the residual steel in the RH vacuum tank, thus cleaning the RH vacuum tank. Specifically, during the converter tapping process, aluminum blocks are added to the steel deoxidation process to accelerate deep deoxidation and reduce the oxygen content of the molten steel. During LF smelting, the C, Mn, and Si contents at the LF smelting endpoint are controlled according to the upper limit of the process target values. During RH vacuum degassing, excess Al, Si, Mn, and C in the molten steel react with the oxygen in the residual steel. The resulting oxidation products are carried away by the RH vacuum degassing, thereby reducing the oxygen content in the molten steel and improving its purity and castability. Through these steps, the cleaned molten steel in the RH vacuum tank can be directly cast in continuous casting, resulting in a stable casting curve, no billet drops, and controllable quality. This not only releases the refining capacity of the LF furnace but also avoids the energy and time waste caused by steel reprocessing, significantly improving production efficiency and economic benefits.

[0011] Optionally, the steel material is No. 60 steel strip.

[0012] Optionally, the steel grade is SA-210C.

[0013] Optionally, in step S1, the weight of the aluminum block added is 40kg-60kg.

[0014] Optionally, in step S2, the aluminum content is controlled to be 0.01%-0.03% during LF hoisting.

[0015] Optionally, in step S2, the superheat of the ballast is 110℃-130℃.

[0016] In this scheme, the liquidus temperature of the molten steel ladle increases by 110℃-130℃. During the RH vacuum degassing process, the molten steel temperature drops by approximately 2.5℃ / min. Therefore, the RH treatment process may result in a temperature drop of 40-50℃. Furthermore, after the RH treatment, the soft blowing of the molten steel will cause a further temperature drop of 0.3-0.5℃ / min. If the pre-reserved superheat at the RH ladle temperature is insufficient, the molten steel may approach the liquidus line during casting, resulting in solidification and inability to be poured.

[0017] Optionally, in the RH vacuum degassing process, the vacuum holding time is ≥15 min.

[0018] Optionally, during the RH vacuum degassing process, after the vacuum holding period ends, pure calcium rod cored wire is fed in. The length of the pure calcium rod cored wire fed in is 100m-150m, and the Ca content is 96%-98%.

[0019] This solution alters the morphology and composition of inclusions through calcium treatment. Untreated aluminum-killed steel contains numerous high-melting-point corundum-like Al2O3 inclusions. These inclusions are sharp and polygonal, easily adhering and accumulating at the nozzle, leading to blockage. By adding calcium, these Al2O3 inclusions partially react with Ca to form low-melting-point calcium aluminates (such as 12CaO·7Al2O3, melting point approximately 1400℃). Calcium aluminate inclusions are liquid or semi-liquid spherical, with high surface tension, making them less prone to adhesion to the nozzle and more easily floated and removed in the molten steel. This effectively prevents nozzle blockage and nodule formation during continuous casting, improving casting smoothness. Simultaneously, calcium has a strong affinity for existing sulfide inclusions (mainly MnS) in the steel, preferentially combining with sulfur to form CaS inclusions. CaS has a high melting point and exists in the steel as small solid particles. More commonly, however, complex calcium aluminate-sulfide inclusions are formed (i.e., calcium reacts with both oxygen and sulfur simultaneously). These inclusions form spherical bodies composed of both soft and hard phases during cooling. For example, the phenomenon of "inclusion spheroidization" is often observed in high-sulfur steel after calcium treatment: MnS inclusions that were originally elongated or chain-like after rolling become discontinuous spherical Ca-containing sulfur inclusions. This transformation greatly improves the isotropy and toughness of the steel, because the adverse effects of spherical inclusions on the mechanical properties of the material are far less than those of sharp-angled or elongated inclusions. In addition, calcium treatment also reduces the total amount of inclusions: on the one hand, Ca can assist in deoxidation and desulfurization, removing some oxygen and sulfur into the slag in the form of inclusions; on the other hand, calcium-modified inclusions are less likely to agglomerate into large sizes and are more likely to float and be absorbed by the refining slag or intercepted by the slag-blocking system during continuous casting, thereby further reducing the total oxygen and total sulfur content of the molten steel and achieving a comprehensive improvement in the cleanliness of the molten steel.

[0020] Optionally, after step S3, the method further includes:

[0021] The molten steel after RH vacuum degassing is continuously cast.

[0022] Compared with existing technologies, the beneficial effects achieved by this application are as follows: In this application, pure molten steel is obtained by smelting steel in a converter, and this pure molten steel is used to flush the residual steel in the RH vacuum tank, thereby cleaning the RH vacuum tank. Specifically, during the converter tapping process, aluminum blocks are added to the steel deoxidation process to accelerate deep deoxidation of the molten steel and reduce its oxygen content. During LF smelting of the molten steel, the C, Mn, and Si contents at the LF smelting endpoint are controlled according to the upper limit of the process target values. During the RH vacuum degassing process, excess Al, Si, Mn, and C in the molten steel can react with the oxygen in the residual steel. The resulting oxidation products are carried away by the RH vacuum degassing, thereby reducing the oxygen content in the molten steel and improving its purity and castability. Through the above steps, the molten steel after cleaning the RH vacuum tank can be directly cast into the continuous casting system. The continuous casting curve is stable, there is no billet drop, and the quality is controllable. This not only releases the refining capacity of the LF furnace, but also avoids the waste of energy and time costs caused by the reprocessing of molten steel, significantly improving production efficiency and economic benefits. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments or related technologies of this disclosure, the accompanying drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic flowchart of an RH vacuum tank cleaning method provided in an embodiment of this application;

[0025] Figure 2 This is a schematic diagram of the continuous casting liquid level control provided in Embodiment 1 of this application;

[0026] Figure 3 This is a schematic diagram of the continuous casting liquid level control provided in Embodiment 2 of this application. Detailed Implementation

[0027] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure / application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its application or use.

[0028] Given the technical problems existing in related technologies, namely, when using molten steel to deeply clean the RH vacuum tank, the residual steel in the vacuum tank contains a large amount of oxygen. Therefore, the molten steel after cleaning the RH furnace vacuum tank needs to be returned to the LF refining furnace for slagging and deoxidation, which increases the refining pressure of the LF furnace and leads to a waste of energy and time costs. This application introduces a method for cleaning the RH vacuum tank, which can shorten the production process of cleaning the RH vacuum tank steel while ensuring the quality of the cleaned RH vacuum tank steel. (Reference) Figure 1 The RH vacuum tank cleaning method in this application includes:

[0029] S1, steel is smelted in a converter to obtain molten steel. During the tapping process, aluminum blocks are added to the steel based on the deoxidation process.

[0030] This application obtains pure molten steel through converter smelting, and uses this pure molten steel to flush away residual steel in the RH vacuum tank, thereby cleaning the RH vacuum tank. During the converter tapping process, an excessive amount of aluminum blocks is added to the steel deoxidation process to accelerate deep deoxidation of the molten steel and reduce its oxygen content.

[0031] The weight of the aluminum block added can be 40kg-60kg. For example, in some specific embodiments, the weight of the aluminum block added can be 40kg, 45kg, 50kg, 55kg, and 60kg, etc.

[0032] S2 involves LF smelting of molten steel, with the C, Mn, and Si contents at the end of the LF smelting process controlled at the upper limit of the target composition.

[0033] In LF smelting of molten steel, the C, Mn, and Si contents at the LF smelting endpoint are controlled according to the upper limit of the internal process target values. During LF ladle removal, the aluminum content can be controlled to 0.01%-0.03%, for example, in some specific embodiments, the aluminum content can be controlled to 0.01%, 0.02%, and 0.03%, respectively. During RH vacuum degassing, excess Al, Si, Mn, and C in the molten steel can react with oxygen in the residual steel. The resulting oxidation products are carried away by subsequent RH vacuum degassing, thereby reducing the oxygen content in the molten steel and improving its purity and castability. Through the above steps, the molten steel after cleaning the RH vacuum tank can be directly cast in continuous casting, resulting in a stable casting curve, no billet drops, and controllable quality. This not only releases the refining capacity of the LF furnace but also avoids the energy and time cost waste caused by steel reprocessing, significantly improving production efficiency and economic benefits.

[0034] Furthermore, during the RH vacuum degassing process, the molten steel temperature drops by approximately 2.5℃ / min. Therefore, the RH treatment process may result in a temperature drop of 40-50℃. Additionally, after the RH treatment, the soft blowing of the molten steel will cause a further temperature drop of 0.3-0.5℃ / min. If the superheat reserved at the RH ladle temperature is insufficient, the molten steel may approach the liquidus line during casting, leading to solidification and inability to be poured. Therefore, the liquidus line temperature can be increased by 110℃-130℃ during ladle pouring, i.e., the ladle superheat is 110℃-130℃. For example, in some specific embodiments, the ladle superheat can be 110℃, 115℃, 120℃, 125℃, and 130℃, etc.

[0035] S3, using the RH vacuum tank to be cleaned to perform RH vacuum degassing on the molten steel after LF smelting.

[0036] During RH vacuum degassing, the vacuum holding time is ≥15 min. After vacuum holding, pure calcium rod cored wire can be fed in. The feeding length of the pure calcium rod cored wire can be 100m-150m, and the Ca content can be 96%-98%. For example, in some specific embodiments, the feeding length of the pure calcium rod cored wire can be 100m, 110m, 120m, 130m, 140m, and 150m, etc. The Ca content in the pure calcium rod cored wire can be 96%, 97%, and 98%, etc.

[0037] Calcium treatment alters the morphology and composition of inclusions. Untreated aluminum-killed steel contains numerous high-melting-point corundum-like Al2O3 inclusions. These inclusions are sharp and polygonal, easily adhering and accumulating at the nozzle, leading to blockage. By adding calcium, these Al2O3 inclusions partially react with Ca to form low-melting-point calcium aluminates (such as 12CaO·7Al2O3, melting point approximately 1400℃). Calcium aluminate inclusions are liquid or semi-liquid spherical, with high surface tension, making them less prone to adhesion to the nozzle and more easily floated and removed in the molten steel. This effectively prevents nozzle blockage and nodule formation during continuous casting, improving casting smoothness. Simultaneously, calcium has a strong affinity for existing sulfide inclusions (mainly MnS) in the steel, preferentially combining with sulfur to form CaS inclusions. CaS has a high melting point and exists in the steel as small solid particles. More commonly, however, complex calcium aluminate-sulfide inclusions are formed (i.e., calcium reacts with both oxygen and sulfur simultaneously). These inclusions form spherical bodies composed of both soft and hard phases during cooling. For example, the phenomenon of "inclusion spheroidization" is often observed in high-sulfur steel after calcium treatment: MnS inclusions that were originally elongated or chain-like after rolling become discontinuous spherical Ca-containing sulfur inclusions. This transformation greatly improves the isotropy and toughness of the steel, because the adverse effects of spherical inclusions on the mechanical properties of the material are far less than those of sharp-angled or elongated inclusions. In addition, calcium treatment also reduces the total amount of inclusions: on the one hand, Ca can assist in deoxidation and desulfurization, removing some oxygen and sulfur into the slag in the form of inclusions; on the other hand, calcium-modified inclusions are less likely to agglomerate into large sizes and are more likely to float and be absorbed by the refining slag or intercepted by the slag-blocking system during continuous casting, thereby further reducing the total oxygen and total sulfur content of the molten steel and achieving a comprehensive improvement in the cleanliness of the molten steel.

[0038] The method of the present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0039] Example 1

[0040] S1, 60# steel strip is smelted in a converter to obtain molten steel. During the tapping process of the converter, 60kg of aluminum blocks are added on the basis of the steel deoxidation process.

[0041] S2, the molten steel is subjected to LF smelting, and the final LF smelting content is 0.6243% C, 0.3206% Mn, 0.6603% Si, 0.1175% Cr, and 0.0139% Alt.

[0042] The temperature of the molten steel ladle increased by 110℃-130℃ from the liquidus, and the ladle temperature reached 1621℃.

[0043] S3. The molten steel after LF smelting is degassed using an RH vacuum tank to be cleaned. The vacuum holding time during RH vacuum degassed is 16 minutes. After the vacuum holding period, 120m of pure calcium rod cored wire with a Ca content of 97% is fed in.

[0044] After RH vacuum degassing is completed, the molten steel after RH vacuum degassing is continuously cast.

[0045] refer to Figure 1 The continuous casting pouring liquid surface curve is stable, and there is no billet drop.

[0046] Example 2

[0047] S1, SA-210C is smelted in a converter to obtain molten steel. During the tapping process of the converter, 40 kg of aluminum blocks are added to the steel based on the deoxidation process of the steel.

[0048] S2, the molten steel is subjected to LF smelting, and the final LF smelting content is 0.1851% C, 0.8206% Mn, 0.2587% Si, 0.0351% Cr, and 0.0113% Alt.

[0049] The temperature of the molten steel ladle increased by 110℃-130℃ from the liquidus, and the ladle temperature reached 1621℃.

[0050] S3. The molten steel after LF smelting is degassed using an RH vacuum tank to be cleaned. The vacuum holding time during RH vacuum degassed is 15 minutes. After the vacuum holding period, 120m of pure calcium rod cored wire with a Ca content of 97% is fed in.

[0051] After RH vacuum degassing is completed, the molten steel after RH vacuum degassing is continuously cast.

[0052] refer to Figure 2 The continuous casting pouring liquid surface curve is stable, and there is no billet drop.

[0053] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of this disclosure / application, and these improvements and modifications should also be considered within the protection scope of this disclosure / application.

Claims

1. A method for cleaning an RH vacuum tank, characterized in that, include: S1, steel is smelted in a converter to obtain molten steel. During the tapping process of the converter, aluminum blocks are added to the steel based on the deoxidation process of the steel. S2, the molten steel is subjected to LF smelting, and the C, Mn and Si contents at the end of LF smelting are controlled according to the upper limit of the process target value composition. S3, using the RH vacuum tank to be cleaned to perform RH vacuum degassing on the molten steel after LF smelting.

2. The RH vacuum tank cleaning method according to claim 1, characterized in that, The steel material is No. 60 steel strip.

3. The RH vacuum tank cleaning method according to claim 1, characterized in that, The steel grade of the material is SA-210C.

4. The RH vacuum tank cleaning method according to claim 1, characterized in that, In step S1, the weight of the aluminum block added is 40kg-60kg.

5. The RH vacuum tank cleaning method according to claim 1, characterized in that, In step S2, during LF hoisting, the aluminum content is controlled to be 0.01%-0.03%.

6. The RH vacuum tank cleaning method according to claim 1, characterized in that, In step S2, the superheat of the ballast is 110℃-130℃.

7. The RH vacuum tank cleaning method according to claim 1, characterized in that, During the RH vacuum degassing process, the vacuum holding time is ≥15 min.

8. The RH vacuum tank cleaning method according to claim 5, characterized in that, During the RH vacuum degassing process, after the vacuum is maintained, pure calcium rod cored wire is fed in. The length of the pure calcium rod cored wire fed in is 100m-150m, and the Ca content is 96%-98%.

9. The RH vacuum tank cleaning method according to claim 1, characterized in that, Following step S3, the method further includes: The molten steel after RH vacuum degassing is continuously cast.

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