Method for improving internal cleanliness of steel rail

Abstract

The invention provides a method for improving internal cleanliness of a steel rail, and belongs to the technical field of ferrous metallurgy. The method comprises the procedures of converter smelting, RH smelting and continuous casting. In the converter smelting process, after converter blowing is finished, the end-point oxygen content is controlled to be below 200 ppm, the superheat degree after molten steel tapping is controlled to be 100-120 DEG C on a liquidus line, no slag charge is added in the tapping process, alloy deoxidation operation is not carried out, and the molten steel is directly fed into a closed steel ladle after tapping; and in the RH smelting procedure, vacuum treatment operation is carried out, the vacuum pressure is controlled to be 67 pa or below, after vacuum treatment is carried out for 5-10 minutes, it is guaranteed that gas in steel is fully escaped, then alloying operation is carried out according to the steel grade requirement, and after alloying is completed, the vacuum degree continues to be kept to be 67 pa or below for 10-15 minutes. The method can achieve the purpose of improving the internal cleanliness of the steel rail, can be applied to the steelmaking process on a large scale, and is easy and convenient to operate and stable in effect.

Description

Technical Field

[0001] The invention belongs to the technical field of steel metallurgy, and in particular relates to a method for improving the cleanliness of the interior of a rail. Background Art

[0002] In recent years, with the implementation of China's railway strategy to strengthen its railway industry, high-speed and heavy-haul rails have become two major trends in the railway industry. As the world's fastest operating train at 350 km / h, heavy-haul trains have stringent safety and comfort requirements. Improving the service life of heavy-haul trains is a crucial indicator, and these factors, in turn, are closely linked to the internal quality of the rails. As the train's primary load-bearing component, the internal cleanliness of the rails directly impacts their safe operation. In the actual rail production process, the smelting stage is the only stage that has a significant impact on internal rail cleanliness. Therefore, systematically analyzing the factors influencing cleanliness during the smelting process and developing corresponding process improvements to improve cleanliness is a pressing technical challenge for the rail industry.

[0003] Patent CN201810834438.8 provides a smelting method for improving the cleanliness of heavy rail steel. This invention mainly improves the cleanliness of the rail by adding calcium treatment to LF refining, but there is a problem of subsequent generation of other calcium-containing inclusions; Patent CN202410198063.6 provides a smelting method for exporting rails with cleanliness in accordance with European standards. This invention mainly meets the rail cleanliness requirements under European standards by strictly controlling the process parameters of each process, but the effect of improving the internal cleanliness of the rail is very limited. The above two patents are both aimed at improving the cleanliness of the rails, which is achieved by optimizing or strengthening certain process parameters. The improvement of the internal cleanliness of the rails is limited. Overall, they are not the best choice. On the other hand, the corresponding strict control of the process or the addition of new processes will affect the overall efficiency of the steel plant. Overall, the above two methods are not 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 cleanliness of the interior of a rail, which ensures the safe and long-life operation of the rail in on-line service.

[0005] To solve the above technical problems, the present invention adopts the following technical solution: a method for improving the internal cleanliness of a rail, 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 200 ppm, the superheat of the molten steel after tapping is controlled between 100-120°C above the liquidus, no slag is added during the tapping process, no alloy deoxidation operation is performed, and a slag-free operation is adopted throughout the tapping process. After tapping, the steel is directly poured into a sealed ladle to avoid contact with the outside world and minimize the formation of a large number of inclusions; The RH smelting process is to perform vacuum treatment, and the vacuum pressure is controlled below 67 Pa. After vacuum treatment for 5-10 minutes, the gas in the steel is ensured to escape fully. Then, alloying operation is performed according to the requirements of the steel grade. After the alloying is completed, the vacuum degree is continued to be maintained below 67 Pa for 10-15 minutes to ensure that inclusions and gas are fully removed.

[0006] In the RH smelting process of the present invention, after the RH vacuum treatment is completed and before continuous casting, the ladle is kept airtight and allowed to stand for 15-30 minutes to keep the inclusions further floating.

[0007] In the continuous casting process of the present invention, argon sealing protection is adopted throughout the continuous casting process to prevent the molten steel from contacting with air and generating inclusions, which in turn affects the cleanliness of the rails.

[0008] The method of the present invention establishes a mechanism for monitoring the cleanliness of molten steel based on the life and quality changes of refractory equipment such as ladles and tundishes, and marks three states: red, yellow, and green. In the green state, the steel ladle can be used normally. In the yellow state, the wall thickness of the steel ladle must be measured after it is offline. In the red state, it is prohibited to use the steel ladle. Among them, the steel ladle wall thickness loss of 10-30mm is green state, 31-70mm is yellow state, and above 71mm is red state.

[0009] The oxygen content of the rail obtained by the method of the present invention is ≤4×10 -4 %.

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

[0011] The design concept of the present invention is as follows: The rail smelting process is long. From molten iron pretreatment to primary refining in the converter, LF refining, RH / VD vacuum refining, and finally to continuous casting of large square billets, the main factors affecting cleanliness are all raw 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. The deoxidation process using the alloy, including slagging during the tapping process, produces a large number of inclusions. In the LF process, a reducing slag with a certain basicity can partially float these inclusions. Subsequently, RH vacuum refining can further float and remove these inclusions. Finally, protected casting during the continuous casting process can achieve high-cleanliness rail production. However, in the above traditional smelting process, under large-scale production conditions, the smelting time is limited, the equilibrium time required for some reactions cannot be achieved, and the lifespan and quality fluctuations of the refractory materials in the ladle and tundish also have a certain impact on the internal cleanliness of the rail. Therefore, from the perspective of the traditional process flow, improving rail cleanliness is also subject to certain constraints.

[0012] To further improve the internal cleanliness of the rails, the project team conducted a large number of experimental studies and found that cleanliness can be improved from two aspects: first, controlling the generation of inclusions at the source, and second, suppressing the influence of air and other external factors on the quality of the molten steel during the casting process. The converter tapping process is one of the important sources of large inclusions. The main reason is that the tapping process is open, and the slag after alloying may enter the ladle during the tapping process; the heating process in the refining furnace will destroy the balance of the slag, and the argon blowing and stirring will further cause the molten steel to come into contact with a large amount of air, thereby generating a large number of inclusions. Vacuum treatment is an important means to reduce inclusions. Compared with the traditional process of optimizing certain parameters, the present invention takes a unique approach and creatively reduces the source of inclusions in steel through technical innovations such as slag-free steelmaking operation and vacuum degassing.

[0013] The beneficial effects of the above technical solution are: the present invention can achieve the goal of improving the internal cleanliness of rails, can be applied on a large scale in the steelmaking process, is simple to operate, and has stable results. Compared with traditional steelmaking processes, the present invention effectively reduces the adverse effects of process control on cleanliness, such as molten steel contamination and refractory erosion. After the ingot is rolled into rail, the pass rate for non-metallic inclusions is ≤2.0 for Class A and ≤1.0 for Classes B, C, and D, with a 100% pass rate. The NDT inspection pass rate is also 100%, improving product quality and social and economic benefits. DETAILED DESCRIPTION

[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 a rail, comprising converter smelting, RH smelting, and continuous casting processes; 1) Converter smelting process: In the top and bottom double-blown converter, the steel grade smelted is U71Mn rail steel. The final oxygen content is controlled at 150ppm, and the superheat of the molten steel after tapping is controlled at 110℃ on the liquidus line. No slag is added during the tapping process, and no alloy deoxidation operation is performed. The whole process adopts slag-free operation. After tapping, the steel is directly discharged into a closed ladle. After the converter tapping is completed, it directly enters the RH smelting process.

[0016] 2) RH smelting process: vacuum treatment operation is carried out, and the vacuum pressure is controlled at 42Pa. After vacuum treatment for 8 minutes, ensure that the gas in the steel is fully escaped, and then alloying operation is carried out according to the requirements of the steel grade. After the alloying is completed, the vacuum degree is continued to be maintained below 42Pa for 12 minutes; after the RH vacuum treatment is completed, before continuous casting, the ladle is kept airtight and allowed to stand for 18 minutes to keep the inclusions further floating.

[0017] 3) Continuous casting process: the continuous casting process adopts argon sealing protection throughout the process; the ladle of the furnace is in green state and can be used normally.

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

[0019] A method for improving the internal cleanliness of a rail, comprising converter smelting, RH smelting, and continuous casting processes; 1) Converter smelting process: In the top and bottom double-blown converter, the steel grade smelted is U71Mn rail steel. The final oxygen content is controlled at 180ppm, and the superheat of the molten steel after tapping is controlled at 120℃ on the liquidus line. No slag is added during the tapping process, and no alloy deoxidation operation is performed. The whole process adopts slag-free operation. After tapping, the steel is directly discharged into a closed ladle. After the converter tapping is completed, it directly enters the RH smelting process.

[0020] 2) RH smelting process: vacuum treatment is carried out, and the vacuum pressure is controlled at 50Pa. After 10 minutes of vacuum treatment, ensure that the gas in the steel is fully released, and then carry out alloying operations according to the requirements of the steel grade. After the alloying is completed, continue to maintain the vacuum degree below 50Pa for 15 minutes; after the RH vacuum treatment is completed, before continuous casting, keep the ladle airtight and continue to stand for 30 minutes to keep the inclusions further floating.

[0021] 3) Continuous casting process: the continuous casting process adopts argon sealing protection throughout the process; the ladle of the furnace is in green state and can be used normally.

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

[0023] A method for improving the internal cleanliness of a rail, comprising converter smelting, RH smelting, and continuous casting processes; 1) Converter smelting process: In the top and bottom double-blown converter, the steel grade smelted is U71Mn rail steel. The final oxygen content is controlled at 200ppm, and the superheat of the molten steel after tapping is controlled at 100℃ on the liquidus line. No slag is added during the tapping process, and no alloy deoxidation operation is performed. The whole process adopts slag-free operation. After tapping, the steel is directly poured into a closed ladle. After the converter tapping is completed, it directly enters the RH smelting process.

[0024] 2) RH smelting process: vacuum treatment is carried out, and the vacuum pressure is controlled at 67Pa. After 5 minutes of vacuum treatment, ensure that the gas in the steel is fully released, and then carry out alloying operations according to the requirements of the steel grade. After the alloying is completed, continue to maintain the vacuum degree below 67Pa for 10 minutes; after the RH vacuum treatment is completed, before continuous casting, keep the ladle airtight and continue to stand for 15 minutes to keep the inclusions further floating.

[0025] 3) Continuous casting process: the continuous casting process adopts argon sealing protection throughout; the status of the ladle of the furnace is yellow. After it is offline, the thickness of the ladle wall is tested and the loss is 65mm, which means it can be used normally.

[0026] After the slab obtained by the method is rolled into rail, the oxygen content of the rail is 3.6×10 -4 %, non-metallic inclusions, Class A rating ≤ 2.0, Class B, C, D rating ≤ 1.0, the pass rate is 100%, and the NDT flaw detection pass rate is 100%. Example 4

[0027] A method for improving the internal cleanliness of a rail, comprising converter smelting, RH smelting, and continuous casting processes; 1) Converter smelting process: In the top and bottom double-blown converter, the steel grade smelted is U75V rail steel, the final oxygen content is controlled at 100ppm, and the superheat of the molten steel after tapping is controlled at 120℃ on the liquidus line. No slag is added during the tapping process, and no alloy deoxidation operation is performed. The whole process adopts slag-free operation. After tapping, the steel is directly poured into a closed ladle. After the converter tapping is completed, it directly enters the RH smelting process.

[0028] 2) RH smelting process: vacuum treatment is carried out, and the vacuum pressure is controlled at 60Pa. After 10 minutes of vacuum treatment, ensure that the gas in the steel is fully released, and then carry out alloying operations according to the requirements of the steel grade. After the alloying is completed, continue to maintain the vacuum degree below 60Pa for 15 minutes; after the RH vacuum treatment is completed, before continuous casting, keep the ladle airtight and continue to stand for 20 minutes to keep the inclusions further floating.

[0029] 3) Continuous casting process: the continuous casting process adopts argon sealing protection throughout the process; the ladle of the furnace is in green state and can be used normally.

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

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

[0032] 2) RH smelting process: vacuum treatment operation is carried out, and the vacuum pressure is controlled at 28Pa. After 6 minutes of vacuum treatment, ensure that the gas in the steel is fully released, and then carry out alloying operation according to the requirements of the steel grade. After the alloying is completed, continue to maintain the vacuum degree below 28Pa for 15 minutes; after the RH vacuum treatment is completed, before continuous casting, keep the ladle airtight and continue to stand for 25 minutes to keep the inclusions further floating.

[0033] 3) Continuous casting process: the continuous casting process adopts argon sealing protection throughout the process; the ladle of the furnace is in green state and can be used normally.

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

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

[0036] 2) RH smelting process: vacuum treatment is carried out, and the vacuum pressure is controlled at 60Pa. After 10 minutes of vacuum treatment, ensure that the gas in the steel is fully released, and then carry out alloying operations according to the requirements of the steel grade. After the alloying is completed, continue to maintain the vacuum degree below 60Pa for 15 minutes; after the RH vacuum treatment is completed, before continuous casting, keep the ladle airtight and continue to stand for 25 minutes to keep the inclusions further floating.

[0037] 3) Continuous casting process: the continuous casting process adopts argon sealing protection throughout the process; the ladle of the furnace is in green state and can be used normally.

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

[0039] A method for improving the internal cleanliness of a rail, comprising converter smelting, RH smelting, and continuous casting processes; 1) Converter smelting process: In the top and bottom double-blown converter, the steel grade smelted is U75V rail steel, the final oxygen content is controlled at 100ppm, and the superheat of the molten steel after tapping is controlled at 100℃ on the liquidus line. No slag is added during the tapping process, and no alloy deoxidation operation is performed. The whole process adopts slag-free operation. After tapping, the steel is directly poured into a closed ladle. After the converter tapping is completed, it directly enters the RH smelting process.

[0040] 2) RH smelting process: vacuum treatment is carried out, and the vacuum pressure is controlled at 40Pa. After 5 minutes of vacuum treatment, ensure that the gas in the steel is fully released, and then carry out alloying operations according to the requirements of the steel grade. After the alloying is completed, continue to maintain the vacuum degree below 40Pa for 10 minutes; after the RH vacuum treatment is completed, before continuous casting, keep the ladle airtight and continue to stand for 15 minutes to keep the inclusions further floating.

[0041] 3) Continuous casting process: the continuous casting process adopts argon sealing protection throughout the process; the ladle of the furnace is in green state and can be used normally.

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

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

[0044] 2) RH smelting process: vacuum treatment is carried out, and the vacuum pressure is controlled at 30Pa. After 10 minutes of vacuum treatment, ensure that the gas in the steel is fully released, and then carry out alloying operations according to the requirements of the steel grade. After the alloying is completed, continue to maintain the vacuum degree below 30Pa for 12 minutes; after the RH vacuum treatment is completed, before continuous casting, keep the ladle airtight and continue to stand for 20 minutes to keep the inclusions further floating.

[0045] 3) Continuous casting process: the continuous casting process adopts argon sealing protection throughout; the status of the ladle of the furnace is yellow, and the thickness of the ladle wall is detected after the line, and the loss is 70mm, which can be used normally.

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

[0047] The above embodiments are only used to illustrate rather than 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 the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for improving the internal cleanliness of a rail, characterized in that: The method includes 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 on the liquidus line. No slag is added during the tapping process, and no alloy deoxidation operation is performed. The whole process adopts a slag-free operation, and the steel is directly poured into a closed ladle after tapping. The RH smelting process is to carry out vacuum treatment operation, and the vacuum pressure is controlled below 67Pa. After vacuum treatment for 5-10 minutes, it is ensured that the gas in the steel is fully escaped, and then alloying operation is carried out according to the requirements of the steel grade. After the alloying is completed, the vacuum degree is continued to be maintained below 67Pa for 10-15 minutes.

2. A method for improving the internal cleanliness of a rail according to claim 1, characterized in that: In the RH smelting process, after the RH vacuum treatment is completed and before continuous casting, the ladle is kept airtight and allowed to stand for 15-30 minutes.

3. The method for improving the internal cleanliness of a rail according to claim 1, characterized in that: In the continuous casting process, the entire continuous casting process is protected by argon sealing.

4. A method for improving the internal cleanliness of a rail according to any one of claims 1 to 3, characterized in that: The method establishes a monitoring mechanism for the cleanliness of molten steel based on the life and quality changes of refractory equipment such as ladles and tundishes, and marks three states: red, yellow, and green. In the green state, the steel ladle can be used normally. In the yellow state, the wall thickness of the steel ladle must be measured after it is offline. In the red state, the steel ladle is prohibited from being used. Among them, the green state is when the wall thickness of the steel ladle is damaged by 10-30 mm, the yellow state is when it is 31-70 mm, and the red state is when it is 71 mm or more.

5. A method for improving the internal cleanliness of a rail according to any one of claims 1 to 3, characterized in that: The oxygen content of the rail obtained by the method is ≤4×10 -4 %.

6. A method for improving the internal cleanliness of a rail according to any one of claims 1 to 3, characterized in that: After the cast slab obtained by the method is rolled into a rail, the non-metallic inclusions of category A rating ≤2.0, category B, C, and D rating ≤1.0 have a pass rate of 100%, and the NDT flaw detection pass rate is 100%.