A method for improving the service life of RH immersion tube

Abstract

The present application belongs to the technical field of steel metallurgy, and particularly relates to a method for prolonging the service life of RH immersion tube, comprising the following steps: S1, baking the RH vacuum chamber to make the temperature of the RH vacuum chamber reach the production operation temperature; S2, first performing slag folding treatment on the ladle, then placing the RH immersion tube at the lower end of the RH vacuum chamber in the RH ladle containing liquid steel slag and molten steel to perform soaking treatment, so that the liquid steel slag is hung on the inner wall of the RH immersion tube; S3, removing the RH ladle, and performing gunning treatment on the inner wall of the RH immersion tube by using a gunning system, and drying for 10-20s after gunning; S4, putting the RH immersion tube treated in step S3 into production, and sequentially performing slag hanging treatment and gunning treatment on the RH immersion tube according to the method of steps S2 and S3 after each treatment of 1 furnace of molten steel, until the RH immersion tube is scrapped. The method can prolong the service life of the RH immersion tube to more than 150 furnaces.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, and specifically to a method for improving the service life of RH-impregnated pipes. Background Technology

[0002] Since its introduction in the late 1960s, the RH vacuum refining equipment has undergone 50 years of functional improvement. Currently, the metallurgical functions of RH vacuum refining technology include dehydrogenation, decarburization, deoxidation, desulfurization, precise control of steel composition and temperature, inclusion control and removal, etc. The range of steel varieties suitable for smelting has greatly increased, making it an indispensable refining equipment for smelting high-grade pipeline steel, ultra-low carbon steel, silicon steel and other high-value-added steels. Therefore, increasingly higher requirements are being placed on the performance of refractory materials used in RH.

[0003] RH-impregnated tubes are an important refractory material in RH vacuum refining equipment. Located at the bottom of the vacuum tank, they come into direct contact with high-temperature molten steel during smelting and are directly exposed to the atmosphere when not in production. Their working conditions are extremely harsh, making them a critical component affecting normal RH production. Furthermore, there is a lack of experience in maintaining RH vacuum refining furnaces, resulting in a relatively short service life for RH-impregnated tubes. Currently, RH-impregnated tubes contribute approximately 25% to the total cost per ton of steel in RH refining (excluding alloy costs). Moreover, the lifespan of the vacuum chamber tank bricks is related to the lifespan of the RH-impregnated tubes; for example, replacing the RH-impregnated tubes twice requires replacing the lower tank once. Therefore, extending the lifespan of the impregnated tubes is crucial for reducing RH refining costs.

[0004] Existing technologies primarily rely on spraying to extend the service life of RH-impregnated tubes. However, the effect of spraying alone on improving the service life of RH-impregnated tubes is limited. To address this issue, patent document CN114574664A discloses a method for repairing RH-impregnated tubes. This method mainly extends the service life of RH-impregnated tubes by spraying damaged areas on the inner wall and treating the outer wall for slag adhesion. However, high-temperature erosion and air blowing primarily occur on the inner wall of the RH-impregnated tube. Spraying only damaged areas on the inner wall consumes a large amount of spraying material, and the effect on extending the service life of RH-impregnated tubes is not ideal; the service life of tubes repaired using this method is only 8-9 heats. Therefore, it is necessary to further research new methods to further improve the service life of RH-impregnated tubes. Summary of the Invention

[0005] To address the shortcomings of the prior art, this invention discloses a method for improving the service life of RH-impregnated tubes, employing the following technical solution:

[0006] A method for improving the service life of RH-impregnated tubes includes the following steps:

[0007] S1. The RH vacuum chamber is baked to bring its temperature up to the production operating temperature.

[0008] S2. Place the RH immersion tube at the lower end of the RH vacuum chamber into an RH ladle containing liquid steel slag and molten steel for immersion treatment, so that the liquid steel slag hangs on the inner wall of the RH immersion tube.

[0009] S3. Move the RH ladle to the soft-blowing position and blow argon. Using a spraying system, such as a spraying trolley, immediately spray the inner wall of the RH impregnation tube. The purpose is to use the temperature of the liquid steel slag to make the liquid steel slag and the spraying material tightly bond. After spraying, dry for 10-20 seconds. Drying can be done directly using the temperature of the liquid steel slag. When the RH impregnation tube is used ≤50 heats, the spraying thickness should be controlled at 20-30 mm. When the RH impregnation tube is used >50 heats, the total thickness of the RH impregnation tube after spraying should be controlled at 200-240 mm. At the same time, the outer wall of the RH impregnation tube should also be sprayed, and the spraying thickness of the outer wall of the RH impregnation tube should be controlled at 20-30 mm.

[0010] S4. Put the RH-impregnated tube after step S3 into production. After each heat of molten steel is processed, the RH-impregnated tube is subjected to slag treatment and spraying treatment in sequence according to the methods of steps S2 and S3 until the RH-impregnated tube is scrapped.

[0011] The lifespan of an untreated RH-impregnated tube is around 80 heats. After treating the RH-impregnated tube with the repair method of this invention, the lifespan can be extended by about 70 heats, bringing the lifespan of the RH-impregnated tube to about 150 heats, which significantly reduces production costs.

[0012] Furthermore, step S1 specifically includes:

[0013] The RH vacuum chamber is first baked in the drying position. Once it meets the conditions for production, i.e., the vacuum chamber temperature is ≥850℃, the RH vacuum chamber is then transferred from the drying position to the production position for a second baking, so that the temperature of the RH vacuum chamber reaches the production operating temperature, i.e., the vacuum chamber temperature is ≥1000℃.

[0014] Furthermore, step S2 specifically involves:

[0015] The RH ladle containing liquid steel slag and molten steel is transferred to the bottom of the RH immersion tube. The RH ladle is raised so that the RH immersion tube is inserted into the liquid steel slag to a depth of 200-300 mm. The thickness of the steel slag on top of the molten steel is 150-300 mm. At this time, the lower end of the RH immersion tube is immersed in the steel slag. The RH ladle is lowered to the bottom of the RH immersion tube and waited for 10-20 seconds.

[0016] The RH ladle is raised a second time to insert the RH immersion pipe into the liquid steel slag to a depth of 300-400 mm. The RH ladle is then lowered below the RH immersion pipe, and the process is allowed to proceed for 10-20 seconds.

[0017] The RH ladle is raised a third time to insert the RH immersion pipe into the liquid steel slag to a depth of 400-500 mm. The RH ladle is then lowered below the RH immersion pipe, and the process is allowed to proceed for 10-20 seconds.

[0018] The RH ladle is raised for the fourth time so that the RH immersion pipe is inserted into the liquid steel slag to a depth of 500-600 mm, and then the RH ladle is lowered below the RH immersion pipe.

[0019] The insertion depth refers to the distance from the top of the molten steel slag to the bottom of the RH immersion tube. The inner wall of the RH immersion tube is slag-coated from bottom to top. Slag is first applied to the lower part of the RH immersion tube, and then the insertion depth is gradually increased. This allows the RH immersion tube to come into contact with the molten steel below the slag layer after slag coating, reducing the corrosion of the refractory material of the RH immersion tube body by the molten steel.

[0020] Applying slag to the entire interior of the RH immersion tube causes steel slag to adhere to the argon blowing holes and the blowing pipe, affecting the argon blowing process during production. This invention addresses this problem by introducing oxygen into the argon blowing holes and the blowing pipe, utilizing the oxygen to oxidize the steel slag, melting it, and blowing it out. For details, please refer to patent document CN1128775071A. By solving this technical problem, this invention can achieve complete slag adhesion inside the RH immersion tube, further extending its lifespan.

[0021] Furthermore, after the soaking treatment in step S2, the thickness of the slag coating on the inner wall of the RH-impregnated tube is ≤80mm.

[0022] Furthermore, step S2 also includes the following steps:

[0023] Before the soaking treatment, the RH ladle is first disassembled to pour the liquid steel slag from the continuously cast ladle into the RH ladle, thereby increasing the amount of liquid steel slag.

[0024] Currently, liquid steel slag cannot be utilized effectively, resulting in significant labor requirements for cleaning, poor working conditions, and difficulties in sanitation. This invention addresses this issue by performing a ladle-breaking operation on the RH ladle, thereby rationally utilizing the liquid steel slag after continuous casting. This reduces refining slag consumption, stabilizes the slag composition, and improves slag utilization. Simultaneously, the steel slag adhering to the inner wall of the RH immersion tube can remove inclusions during production, improving the cleanliness of the molten steel and reducing refractory material consumption and production costs. Furthermore, the ladle-breaking operation allows for a slag thickness of 150–300 mm within the RH ladle. Further, step S2 includes the following steps:

[0025] After immersion treatment, the temperature of the RH immersion tube is raised to 850-1000℃. The RH immersion tube is not immediately lifted off the surface of the molten steel. Instead, the RH equipment lifting system is used to move the RH immersion tube up and down repeatedly on the surface of the molten steel more than twice.

[0026] Raising the temperature of the RH immersion tube to 850-1000℃ aims to ensure the slag is in a liquid state, facilitating smooth slag adhesion and ensuring even coverage of the inner and outer walls of the RH immersion tube. The RH immersion tube temperature can be further increased by raising the RH vacuum chamber temperature, for example, by baking it to 1100℃. Instead of immediately lifting the RH immersion tube off the molten steel surface, the RH equipment's lifting system is used to repeatedly move the tube up and down above the molten steel surface more than twice. This allows more slag above the molten steel surface to adhere to the inner and outer walls of the tube, increasing its wall thickness.

[0027] Furthermore, during step S3 of the spraying process, the angle between the spraying nozzle and the spraying tube body is controlled at 120-130 degrees to improve the top spraying effect. Preferably, wet spraying is used.

[0028] Furthermore, in step S4, the criterion for determining whether an RH-impregnated pipe is scrapped is: the thickness of the thinnest part of the RH-impregnated pipe body wall is ≤60mm. The RH-impregnated pipe body refers to the refractory material of the RH-impregnated pipe itself, excluding steel slag and sprayed layer.

[0029] Furthermore, the composition of the liquid steel slag in step S2 is: CaO 50%–60%, Al2O3 15%–20%, SiO2 7%–20%, and MgO 8%–13%.

[0030] Furthermore, the composition of the spraying material used in step S3 is: 80%–90% MgO, 2.5%–10% CaO, and 35%–10% Al2O3.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] Existing technologies primarily employ spraying to repair the inner wall of RH immersion tubes, extending their service life. However, these technologies only treat the outer wall of the RH immersion tube with slag. This invention, by treating the inner wall of the RH immersion tube with slag, offers several advantages: firstly, it reduces the amount of spraying material used, lowering production costs; secondly, it improves the adhesion of the spraying material; and thirdly, since high-temperature erosion and air blowing occur on the inner wall of the RH immersion tube, which is subject to severe corrosion, the slag treatment increases the inner wall thickness, causing corrosion to occur first on the sprayed layer and the adhered slag layer, reducing material loss and even perforation after the RH immersion tube body is corroded. Simultaneously, during production, the eroded slag can also absorb harmful substances from the molten steel. Using the method of this invention, the service life of RH immersion tubes can be extended to over 150 heats, significantly reducing production costs. Detailed Implementation

[0033] Example 1

[0034] This embodiment discloses a method for improving the service life of RH-impregnated tubes, including the following steps:

[0035] S1. The RH vacuum chamber is baked to bring its temperature up to the production operating temperature.

[0036] Specifically, the RH vacuum chamber is first baked in the drying position to reach a temperature of 850°C. Then, the RH vacuum chamber is transferred from the drying position to the production position for a second baking, which brings the temperature of the RH vacuum chamber to 1000°C.

[0037] S2. Hanging liquid steel slag on the inner wall of the RH immersion pipe, specifically including the following sub-steps:

[0038] S21. Perform a ladle-breaking operation on the RH ladle, pouring the liquid steel slag from the continuously cast ladle into the RH ladle to increase the amount of liquid steel slag.

[0039] S22. Transfer the RH ladle to the bottom of the RH immersion pipe, raise the RH ladle so that the RH immersion pipe is inserted into the liquid steel slag to a depth of 200mm, lower the RH ladle to the bottom of the RH immersion pipe, and wait for 10s.

[0040] The RH ladle is raised a second time to insert the RH immersion tube into the liquid steel slag to a depth of 400 mm. The RH ladle is then lowered below the RH immersion tube, and 10 seconds are waited.

[0041] The RH ladle is raised a third time to insert the RH immersion pipe into the liquid steel slag to a depth of 500mm. The RH ladle is then lowered below the RH immersion pipe, and 10 seconds are waited.

[0042] The RH ladle is raised for the fourth time to insert the RH immersion tube into the liquid steel slag to a depth of 600 mm. The RH ladle is then lowered below the RH immersion tube. The insertion depth refers to the distance from the liquid surface of the liquid steel slag to the bottom of the RH immersion tube.

[0043] S23. Raise the temperature of the RH immersion tube to 1000℃. Do not immediately lift the RH immersion tube off the molten steel surface. Use the RH equipment lifting system to move the RH immersion tube up and down twice on the molten steel surface.

[0044] S3. Move the RH ladle to the soft blowing position and blow argon. Use the spraying trolley to spray the inner wall of the RH impregnated tube. Dry for 10 seconds after spraying. When the RH impregnated tube is used ≤50 heats, the spraying thickness is controlled at 30mm. When the RH impregnated tube is used >50 heats, the total thickness of the RH impregnated tube after spraying is controlled at 240mm.

[0045] S4. Put the RH-impregnated tubes processed in step S3 into production. After each heat of molten steel is processed, the RH-impregnated tubes are subjected to slag treatment and spraying treatment in sequence according to the methods of steps S2 and S3 until the thickness of the thinnest part of the RH-impregnated tube body is ≤60mm. At this point, the RH-impregnated tubes are scrapped and no longer put into production.

[0046] The RH-impregnated tube in this embodiment has a service life of 153 furnaces.

[0047] Comparative Example 1

[0048] The only difference between this comparative example and Example 1 is that the slag treatment on the inner wall of the RH impregnation tube is not performed, i.e., step S2 is not performed. The other steps are exactly the same as in Example 1. The service life of the RH impregnation tube in this comparative example is 75 furnaces.

Claims

1. A method for improving the service life of RH-impregnated tubes, characterized in that, Includes the following steps: S1. The RH vacuum chamber is baked to bring its temperature up to the production operating temperature. S2. Place the RH immersion tube at the lower end of the RH vacuum chamber into an RH ladle containing liquid steel slag and molten steel for immersion treatment, so that the liquid steel slag hangs on the inner wall of the RH immersion tube. S3. Remove the RH ladle and immediately apply a spraying system to the inner wall of the RH impregnation tube. After spraying, dry for 10-20 seconds. When the RH impregnation tube is used for ≤50 heats, the spraying thickness should be controlled at 20-30 mm. When the RH impregnation tube is used for >50 heats, the total thickness of the RH impregnation tube after spraying should be controlled at 200-240 mm. S4. Put the RH-impregnated tube after step S3 into production. After each heat of molten steel is processed, the RH-impregnated tube is subjected to slag treatment and spraying treatment in sequence according to the methods of steps S2 and S3 until the RH-impregnated tube is scrapped. Step S2 is as follows: The RH ladle containing liquid steel slag and molten steel is transferred to the bottom of the RH immersion tube. The RH ladle is raised so that the RH immersion tube is inserted into the liquid steel slag to a depth of 200~300mm. The RH ladle is then lowered to the bottom of the RH immersion tube and waited for 10~20s. The RH ladle is raised a second time to insert the RH immersion tube into the liquid steel slag to a depth of 300-400 mm. The RH ladle is then lowered below the RH immersion tube, and the process is allowed to proceed for 10-20 seconds. The RH ladle is raised a third time to insert the RH immersion pipe into the liquid steel slag to a depth of 400-500 mm. The RH ladle is then lowered below the RH immersion pipe, and the process is allowed to proceed for 10-20 seconds. The fourth lifting of the RH ladle causes the RH immersion pipe to be inserted into the liquid steel slag to a depth of 500-600 mm. The RH ladle is then lowered below the RH immersion pipe. The insertion depth refers to the distance from the surface of the liquid steel slag to the bottom of the RH immersion tube.

2. The method for improving the service life of RH-impregnated tubes according to claim 1, characterized in that, Step S1 is as follows: The RH vacuum chamber is first baked in the drying position. Once it meets the conditions for production, i.e., the vacuum chamber temperature is ≥850°C, the RH vacuum chamber is then transferred from the drying position to the production position for a second baking, so that the temperature of the RH vacuum chamber reaches the production operating temperature, i.e., the vacuum chamber temperature is ≥1000°C.

3. The method for improving the service life of RH-impregnated tubes according to claim 1, characterized in that, After the soaking treatment in step S2, the thickness of the slag coating on the inner wall of the RH-impregnated tube is ≤80mm.

4. The method for improving the service life of RH-impregnated tubes according to claim 1, characterized in that, Step S2 also includes the following steps: Before the soaking treatment, the RH ladle is first disassembled to pour the liquid steel slag from the continuously cast ladle into the RH ladle, thereby increasing the amount of liquid steel slag.

5. The method for improving the service life of RH-impregnated tubes according to claim 1, characterized in that, Step S2 also includes the following steps: After immersion treatment, the temperature of the RH immersion tube is raised to 850-1000°C. The RH immersion tube is not immediately lifted off the surface of the molten steel. Instead, the RH equipment lifting system is used to move the RH immersion tube up and down repeatedly on the surface of the molten steel more than twice.

6. The method for improving the service life of RH-impregnated tubes according to claim 1, characterized in that, During step S3 spraying, the angle between the spraying nozzle and the RH impregnation tube body should be controlled at 120~130 degrees.

7. The method for improving the service life of RH-impregnated tubes according to claim 1, characterized in that, In step S4, the criterion for scrapping the RH-impregnated pipe is: the thickness of the thinnest part of the RH-impregnated pipe body wall is ≤60mm.

8. The method for improving the service life of RH-impregnated tubes according to claim 1, characterized in that, The composition of the liquid steel slag in step S2 is: CaO 50%~60%, Al2O3 15%~20%, SiO2 7%~20% and MgO 8%-13%.

9. The method for improving the service life of RH-impregnated tubes according to claim 1, characterized in that, The composition of the spraying material used in step S3 is: MgO 80%~90%, CaO 2.5%~10% and Al2O 35%~10%.