A method of improving the internal cleanliness of a steel rail

Abstract

The application provides a method for improving the internal cleanliness of a steel rail, and belongs to the technical field of steel metallurgy. The method comprises a converter smelting process, an RH smelting process and a continuous casting process. In the converter smelting process, the end-point oxygen content is controlled to be below 200 ppm after converter blowing, the superheat degree of the molten steel after tapping is controlled to be between 100-120 DEG C above the liquidus, no slag is added during the tapping process, no alloy deoxidation operation is performed, and the molten steel is directly transferred to a sealed ladle after tapping. In the RH smelting process, vacuum treatment is performed, the vacuum pressure is controlled to be below 67 Pa, after vacuum treatment for 5-10 minutes, the gas in the steel is fully released, then alloying operation is performed according to the steel grade requirement, and after the alloying operation is completed, the vacuum degree is continuously maintained below 67 Pa for 10-15 minutes. The application can improve the internal cleanliness of the steel rail, can be applied to the steelmaking process on a large scale, and is simple to operate and stable in effect.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, and specifically relates to a method for improving the cleanliness of the inside of steel rails. Background Technology

[0002] As the world's fastest operating trains at 350 km / h, heavy-haul trains face stringent requirements for safety and comfort. Extending the service life of these trains is a crucial indicator, and safety, comfort, and service life are all closely related to the internal quality of the rails. As the primary load-bearing component of the train, the cleanliness of the rails directly impacts its safe operation. In the actual rail production process, all factors affecting the internal cleanliness of the rails occur during the smelting stage. Therefore, how to systematically analyze the factors influencing cleanliness during the smelting process and formulate corresponding process improvement measures to enhance cleanliness is a pressing technical challenge for the rail industry.

[0003] Patent CN201810834438.8 provides a smelting method to improve the cleanliness of heavy rail steel. This invention mainly improves rail cleanliness by adding calcium treatment during LF refining, but it has the problem of subsequently generating other calcium-containing inclusions. Patent CN202410198063.6 provides a smelting method to achieve the cleanliness of rails exported according to European standards. This invention mainly meets the cleanliness requirements of rails under European standards by strictly controlling the process parameters of each process, but its effect on improving the internal cleanliness of the rail is very limited. Both of these patents are aimed at improving rail cleanliness by optimizing or strengthening certain process parameters, but their improvement on the internal cleanliness of the rail is limited. Overall, they are not the best choice. On the other hand, correspondingly stricter process control or the addition of new processes will affect the overall efficiency of the steel plant. In summary, neither of these two methods is the best choice. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for improving the internal cleanliness of rails, thereby ensuring the safe and long-term operation of rails in online service.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for improving the internal cleanliness of steel rails, the method comprising converter smelting, RH smelting, and continuous casting processes; in the converter smelting process, after the converter blowing is completed, the final oxygen content is controlled below 200ppm, and the superheat of the molten steel after tapping is controlled between 100-120°C above the liquidus line. No slag is added during the tapping process, no alloy deoxidation operation is performed, and the entire process is slag-free. Furthermore, after tapping, the steel is directly placed into a sealed ladle to avoid contact with the outside world, thereby minimizing the formation of a large number of inclusions. In the RH smelting process, a vacuum treatment operation is performed, with the vacuum pressure controlled below 67 Pa. After vacuum treatment for 5-10 minutes, the gas in the steel is fully released. Then, alloying is carried out according to the steel grade requirements. After alloying, the vacuum degree is maintained below 67 Pa for another 10-15 minutes to ensure the full removal of inclusions and gases.

[0006] In the RH smelting process described in this invention, after the RH vacuum treatment is completed and before continuous casting, the ladle is kept airtight and left to stand for 15-30 minutes to allow inclusions to float to the surface further.

[0007] The continuous casting process described in this invention employs full argon sealing protection to prevent molten steel from contacting air and generating inclusions, which in turn affects the improvement of rail cleanliness.

[0008] The method described in this invention establishes a monitoring mechanism for the cleanliness of molten steel based on the lifespan and quality changes of refractory equipment such as ladles and tundishes. The system is labeled with three states: red, yellow, and green. In the green state, the equipment can be used normally. In the yellow state, the ladle wall thickness must be measured after use. In the red state, use is prohibited. Specifically, a ladle wall thickness loss of 10-30mm is in the green state, 31-70mm is in the yellow state, and above 71mm is in the red state.

[0009] The oxygen content of the rails obtained by the method described in this invention is ≤4×10⁻⁶. -4 %.

[0010] After the cast billet obtained by the method of the present invention is rolled into rail, the pass rate of non-metallic inclusions with a Class A rating of ≤2.0 and Class B, C and D ratings of ≤1.0 is 100%, and the pass rate of NDT flaw detection is 100%.

[0011] The design concept of this invention is as follows: The rail smelting process is relatively long, from molten iron pretreatment to converter primary smelting, LF refining, RH / VD vacuum refining, and finally to large billet continuous casting. The main factors affecting cleanliness are all raw and auxiliary materials, refractory materials, equipment, and process control that come into contact with the molten steel. In actual production, a large amount of excess oxygen exists after converter blowing. During the deoxidation process using alloys, including slag removal during tapping, a large number of inclusions are generated. In the LF process, creating a reducing slag with a certain alkalinity can partially float these inclusions. Subsequent RH vacuum refining can further float and remove these inclusions. Finally, protective casting during continuous casting achieves high-cleanliness rail production. However, in the above traditional smelting processes, under large-scale production conditions, smelting time is limited, and the equilibrium time required for some reactions cannot be reached. Fluctuations in the lifespan and quality of refractory materials in the ladle and tundish also have a certain impact on the internal cleanliness of the rail. Therefore, from the perspective of traditional processes, improving rail cleanliness is also somewhat constrained.

[0012] To further improve the cleanliness of the steel rails, the project team conducted extensive experimental research and found that cleanliness improvement can be achieved in two ways: first, by controlling the generation of inclusions at the source; and second, by suppressing the influence of external factors such as air on the quality of molten steel during the casting process. The converter tapping process is a significant source of large inclusions, primarily because the tapping process is open, allowing alloyed slag to enter the ladle during tapping. The refining furnace heating process disrupts the steel-slag balance, and argon blowing further increases the contact between molten steel and air, leading to a large number of inclusions. Vacuum treatment is a crucial means of reducing inclusions. Compared to traditional processes that optimize certain parameters, this invention takes a unique approach, creatively reducing the sources of inclusions in steel through slag-free steelmaking operations and vacuum degassing.

[0013] The beneficial effects of adopting the above technical solution are as follows: This invention can improve the internal cleanliness of steel rails, can be applied on a large scale in the steelmaking process, and is simple to operate and has stable results. Compared with traditional steelmaking processes, the smelting of this invention can effectively reduce the adverse effects on cleanliness caused by steel pollution and refractory corrosion due to process control. After the billet is rolled into steel rails, the pass rate for non-metallic inclusions of Class A rating ≤2.0 and Class B, C, and D ratings ≤1.0 is 100%, and the pass rate for NDT flaw detection is 100%, thus improving product quality and social and economic benefits. Detailed Implementation

[0014] The present invention will be further described in detail below with reference to specific embodiments. Example 1

[0015] A method for improving the internal cleanliness of steel rails includes converter smelting, RH smelting, and continuous casting processes; 1) Converter smelting process: On the top and bottom blown converter, the steel grade is U71Mn rail steel, the final oxygen content is controlled at 150ppm, the superheat of the molten steel is controlled at 110℃ above the liquidus line after tapping, no slag is added during the tapping process, no alloy deoxidation operation is performed, the whole process adopts slag-free operation, and the steel is directly put into the sealed ladle after tapping; after the converter tapping is completed, it directly enters the RH smelting process.

[0016] 2) RH smelting process: Vacuum treatment is performed, with the vacuum pressure controlled at 42 Pa. After vacuum treatment for 8 minutes, ensure that the gas in the steel is fully released. Then, alloying is carried out according to the steel grade requirements. After alloying, the vacuum degree is maintained below 42 Pa for 12 minutes. After RH vacuum treatment, before continuous casting, the ladle is kept sealed and left to stand for 18 minutes to allow the inclusions to float to the surface.

[0017] 3) Continuous casting process: The continuous casting process is protected by argon sealing throughout; the ladle of this furnace is in green condition and can be used normally.

[0018] After the cast billet obtained by the method is rolled into a rail, the oxygen content of the rail is 3.4 × 10⁻⁶. -4 The pass rate for non-metallic inclusions with a Class A rating of ≤2.0 and Class B, C, and D ratings of ≤1.0 was 100%, and the pass rate for NDT flaw detection was 100%. Example 2

[0019] A method for improving the internal cleanliness of steel rails includes converter smelting, RH smelting, and continuous casting processes; 1) Converter smelting process: On the top and bottom blown converter, the steel grade is U71Mn rail steel, the final oxygen content is controlled at 180ppm, the superheat of the molten steel is controlled at 120℃ above the liquidus line after tapping, no slag is added during the tapping process, no alloy deoxidation operation is performed, the whole process adopts slag-free operation, and the steel is directly put into the sealed ladle after tapping; after the converter tapping is completed, it directly enters the RH smelting process.

[0020] 2) RH smelting process: Vacuum treatment is performed, with the vacuum pressure controlled at 50 Pa. After vacuum treatment for 10 minutes, ensure that the gas in the steel is fully released. Then, alloying is carried out according to the steel grade requirements. After alloying, the vacuum degree is maintained below 50 Pa for another 15 minutes. After the RH vacuum treatment is completed, before continuous casting, keep the ladle sealed and let it stand for another 30 minutes to allow the inclusions to float to the surface.

[0021] 3) Continuous casting process: The continuous casting process is protected by argon sealing throughout; the ladle of this furnace is in green condition and can be used normally.

[0022] After the cast billet obtained by the method is rolled into a rail, the oxygen content of the rail is 4.0 × 10⁻⁶. -4 The pass rate for non-metallic inclusions with a Class A rating of ≤2.0 and Class B, C, and D ratings of ≤1.0 was 100%, and the pass rate for NDT flaw detection was 100%. Example 3

[0023] A method for improving the internal cleanliness of steel rails includes converter smelting, RH smelting, and continuous casting processes; 1) Converter smelting process: On the top and bottom blown converter, the steel grade is U71Mn rail steel, the final oxygen content is controlled at 200ppm, the superheat of the molten steel is controlled at 100℃ above the liquidus line after tapping, no slag is added during the tapping process, no alloy deoxidation operation is performed, the whole process adopts slag-free operation, and the steel is directly put into the sealed ladle after tapping; after the converter tapping is completed, it directly enters the RH smelting process.

[0024] 2) RH smelting process: Vacuum treatment is performed, with the vacuum pressure controlled at 67 Pa. After vacuum treatment for 5 minutes, ensure that the gas in the steel is fully released. Then, alloying is carried out according to the steel grade requirements. After alloying, the vacuum degree is maintained below 67 Pa for 10 minutes. After RH vacuum treatment, before continuous casting, keep the ladle sealed and let it stand for 15 minutes to allow the inclusions to float to the surface.

[0025] 3) Continuous casting process: The continuous casting process is protected by argon sealing throughout; the ladle of this furnace is yellow in color. After the ladle is taken off the line, the wall thickness of the ladle is checked and the loss is 65mm, which means it can be used normally.

[0026] After the cast billet obtained by the method is rolled into a rail, the oxygen content of the rail is 3.6 × 10⁻⁶. -4 The pass rate for non-metallic inclusions with a Class A rating of ≤2.0 and Class B, C, and D ratings of ≤1.0 was 100%, and the pass rate for NDT flaw detection was 100%. Example 4

[0027] A method for improving the internal cleanliness of steel rails includes converter smelting, RH smelting, and continuous casting processes; 1) Converter smelting process: On the top and bottom blown converter, the steel grade is U75V rail steel, the final oxygen content is controlled at 100ppm, the superheat of the molten steel is controlled at 120℃ above the liquidus line after tapping, no slag is added during the tapping process, no alloy deoxidation operation is performed, the whole process adopts slag-free operation, and the steel is directly put into the sealed ladle after tapping; after the converter tapping is completed, it directly enters the RH smelting process.

[0028] 2) RH smelting process: Vacuum treatment is performed, with the vacuum pressure controlled at 60 Pa. After vacuum treatment for 10 minutes, ensure that the gas in the steel is fully released. Then, alloying is carried out according to the steel grade requirements. After alloying, the vacuum degree is maintained below 60 Pa for another 15 minutes. After the RH vacuum treatment is completed, before continuous casting, keep the ladle sealed and let it stand for another 20 minutes to allow the inclusions to float to the surface.

[0029] 3) Continuous casting process: The continuous casting process is protected by argon sealing throughout; the ladle of this furnace is in green condition and can be used normally.

[0030] After the cast billet obtained by the method is rolled into a rail, the oxygen content of the rail is 2.8 × 10⁻⁶. -4 The pass rate for non-metallic inclusions with a Class A rating of ≤2.0 and Class B, C, and D ratings of ≤1.0 was 100%, and the pass rate for NDT flaw detection was 100%. Example 5

[0031] A method for improving the internal cleanliness of steel rails includes converter smelting, RH smelting, and continuous casting processes; 1) Converter smelting process: On the top and bottom blown converter, the steel grade is U75V rail steel, the final oxygen content is controlled at 130ppm, the superheat of the molten steel is controlled at 100℃ above the liquidus line after tapping, no slag is added during the tapping process, no alloy deoxidation operation is performed, the whole process adopts slag-free operation, and the steel is directly put into the sealed ladle after tapping; after the converter tapping is completed, it directly enters the RH smelting process.

[0032] 2) RH smelting process: Vacuum treatment is performed, with the vacuum pressure controlled at 28 Pa. After vacuum treatment for 6 minutes, ensure that the gas in the steel is fully released. Then, alloying is carried out according to the steel grade requirements. After alloying, the vacuum degree is maintained below 28 Pa for 15 minutes. After RH vacuum treatment, before continuous casting, the ladle is kept sealed and left to stand for 25 minutes to allow the inclusions to float to the surface.

[0033] 3) Continuous casting process: The continuous casting process is protected by argon sealing throughout; the ladle of this furnace is in green condition and can be used normally.

[0034] After the cast billet obtained by the method is rolled into a rail, the oxygen content of the rail is 4.0 × 10⁻⁶. -4 The pass rate for non-metallic inclusions with a Class A rating of ≤2.0 and Class B, C, and D ratings of ≤1.0 was 100%, and the pass rate for NDT flaw detection was 100%. Example 6

[0035] A method for improving the internal cleanliness of steel rails includes converter smelting, RH smelting, and continuous casting processes; 1) Converter smelting process: On the top and bottom blown converter, the steel grade is U75V rail steel, the final oxygen content is controlled at 200ppm, the superheat of the molten steel is controlled at 120℃ above the liquidus line after tapping, no slag is added during the tapping process, no alloy deoxidation operation is performed, the whole process adopts slag-free operation, and the steel is directly put into the sealed ladle after tapping; after the converter tapping is completed, it directly enters the RH smelting process.

[0036] 2) RH smelting process: Vacuum treatment is performed, with the vacuum pressure controlled at 60 Pa. After vacuum treatment for 10 minutes, ensure that the gas in the steel is fully released. Then, alloying is carried out according to the steel grade requirements. After alloying, the vacuum degree is maintained below 60 Pa for another 15 minutes. After the RH vacuum treatment is completed, before continuous casting, keep the ladle sealed and let it stand for another 25 minutes to allow the inclusions to float to the surface.

[0037] 3) Continuous casting process: The continuous casting process is protected by argon sealing throughout; the ladle of this furnace is in green condition and can be used normally.

[0038] After the cast billet obtained by the method is rolled into a rail, the oxygen content of the rail is 3.8 × 10⁻⁶. -4The pass rate for non-metallic inclusions with a Class A rating of ≤2.0 and Class B, C, and D ratings of ≤1.0 was 100%, and the pass rate for NDT flaw detection was 100%. Example 7

[0039] A method for improving the internal cleanliness of steel rails includes converter smelting, RH smelting, and continuous casting processes; 1) Converter smelting process: On the top and bottom blown converter, the steel grade is U75V rail steel, the final oxygen content is controlled at 100ppm, the superheat of the molten steel is controlled at 100℃ above the liquidus line after tapping, no slag is added during the tapping process, no alloy deoxidation operation is performed, the whole process adopts slag-free operation, and the steel is directly put into the sealed ladle after tapping; after the converter tapping is completed, it directly enters the RH smelting process.

[0040] 2) RH smelting process: Vacuum treatment is performed, with the vacuum pressure controlled at 40 Pa. After vacuum treatment for 5 minutes, ensure that the gas in the steel is fully released. Then, alloying is carried out according to the steel grade requirements. After alloying, the vacuum degree is maintained below 40 Pa for 10 minutes. After RH vacuum treatment, before continuous casting, the ladle is kept sealed and left to stand for 15 minutes to allow the inclusions to float to the surface.

[0041] 3) Continuous casting process: The continuous casting process is protected by argon sealing throughout; the ladle of this furnace is in green condition and can be used normally.

[0042] After the cast billet obtained by the method is rolled into a rail, the oxygen content of the rail is 3.5 × 10⁻⁶. -4 The pass rate for non-metallic inclusions with a Class A rating of ≤2.0 and Class B, C, and D ratings of ≤1.0 was 100%, and the pass rate for NDT flaw detection was 100%. Example 8

[0043] A method for improving the internal cleanliness of steel rails includes converter smelting, RH smelting, and continuous casting processes; 1) Converter smelting process: On the top and bottom blown converter, the steel grade is U75V rail steel, the final oxygen content is controlled at 120ppm, the superheat of the molten steel is controlled at 120℃ above the liquidus line after tapping, no slag is added during the tapping process, no alloy deoxidation operation is performed, the whole process adopts slag-free operation, and the steel is directly put into the sealed ladle after tapping; after the converter tapping is completed, it directly enters the RH smelting process.

[0044] 2) RH smelting process: Vacuum treatment is performed, with the vacuum pressure controlled at 30 Pa. After vacuum treatment for 10 minutes, ensure that the gas in the steel is fully released. Then, alloying is carried out according to the steel grade requirements. After alloying, the vacuum degree is maintained below 30 Pa for 12 minutes. After RH vacuum treatment, before continuous casting, the ladle is kept sealed and left to stand for 20 minutes to allow the inclusions to float to the surface.

[0045] 3) Continuous casting process: The continuous casting process is protected by argon sealing throughout; the ladle of this furnace is yellow in color, and the ladle wall thickness is measured after the line is inspected. The loss is 70mm, which means it can be used normally.

[0046] After the cast billet obtained by the method is rolled into a rail, the oxygen content of the rail is 3.0 × 10⁻⁶. -4 The pass rate for non-metallic inclusions with a Class A rating of ≤2.0 and Class B, C, and D ratings of ≤1.0 was 100%, and the pass rate for NDT flaw detection was 100%.

[0047] The above embodiments are only used to illustrate and not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention without departing from the spirit and scope of the present invention. Any modifications or partial substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for improving the internal cleanliness of steel rails, characterized in that, The method includes converter smelting, RH smelting, and continuous casting processes; The converter smelting process includes controlling the final oxygen content below 200ppm after the converter blowing is completed, controlling the superheat of the molten steel between 100-120°C above the liquidus line after tapping, adding no slag during the tapping process, not performing alloy deoxidation, adopting slag-free operation throughout the process, and directly transferring the tapped steel to a sealed ladle. The RH smelting process includes vacuum treatment, with the vacuum pressure controlled below 67 Pa. After vacuum treatment for 5-10 minutes, the gas in the steel is fully released. Then, alloying is carried out according to the steel grade requirements. After alloying, the vacuum degree is maintained below 67 Pa for another 10-15 minutes. The process also includes maintaining the ladle's airtightness and allowing it to stand for another 15-30 minutes after the RH vacuum treatment is completed and before continuous casting. The continuous casting process is protected by argon sealing throughout the entire casting process. The method establishes a monitoring mechanism for the cleanliness of molten steel based on the lifespan and quality changes of the refractory equipment in the ladle and tundish. Three states are marked: red, yellow, and green. In the green state, the equipment can be used normally; in the yellow state, the ladle wall thickness must be measured after use; and in the red state, use is prohibited. Specifically, a ladle wall thickness erosion of 10-30mm is considered green, 31-70mm is yellow, and above 71mm is red. The oxygen content of the rails obtained by the method is ≤4×10⁻⁶. -4 %.

2. The method for improving the internal cleanliness of rails according to claim 1, characterized in that, After the billet obtained by the method is rolled into rails, the non-metallic inclusions have a Class A rating of ≤2.0 and Class B, C, and D ratings of ≤1.0, with a pass rate of 100% and an NDT flaw detection pass rate of 100%.