Process for large-section round billet quick-change middle ladle of different steel grades

Abstract

The application discloses a large-section round billet different-steel-grade quick-change tundish process, which comprises the following steps: taking a low-cost phi 390 cylindrical steel pier and a 45mm-thick steel plate as raw materials, welding three steel plates on the circumferential surface of the cylindrical steel pier at an angle of 120 DEG to form a partition; when pouring of a first steel grade tundish is stopped, the partition is put into a crystallizer and accurately sinks to a position 1000mm below the molten steel surface in the crystallizer, and then pouring of a second steel grade tundish is started to complete the different-steel-grade quick-change tundish operation. The application can realize continuous production through the quick-change tundish mode between large-section different steel grades, significantly improves production efficiency, and achieves the purposes of mutual non-influence of billet compositions during the different-steel-grade quick-change tundish, no need to cut off the composition abnormal billet, low production spare part cost, and simple and efficient operation method.

Description

Technical Field

[0001] This invention relates to a process for quick tundish replacement of large-section round billets of different steel grades, belonging to the field of metallurgical engineering. Background Technology

[0002] Currently, the quick-change tundish process without connectors developed for large cross-section round billets has certain limitations. Taking the production of φ800 cross-section S355NL and 40Cr as an example, the steel grade currently being produced is S355NL, and the next steel grade planned to be produced is 40Cr. The following problems exist: (1) There is no problem of mutual influence of composition when using the traditional quick-change tundish process for the same steel grade, but when using quick-change tundish for different steel grades, according to the solidification theory, the liquid phase cavity in the middle of the continuously cast steel billet is connected. The molten steel in the liquid phase cavity of 40Cr will continuously replenish the liquid phase cavity of S355NL, causing abnormal composition of S355NL steel billet. (2) If the tundish mixed casting process is used to continuously produce S355NL and 40Cr, it is necessary to use the method of cutting off the billet with abnormal composition for disposal. It is necessary to cut off about 30m of scrap, with a total weight of 115t, which has a significant impact on the overall metal yield of continuous casting. (3) If S355NL and 40Cr do not adopt the quick-change tundish and intermediate tundish mixed casting process and are organized for production separately, the continuous casting machine will need to increase the casting interval by 1 casting interval, which is about 5.5 hours, reducing the continuous casting machine's operating rate and affecting the efficiency improvement of the continuous casting machine.

[0003] Therefore, there is an urgent need to develop a process for quick tundish replacement of large-section round billets with different steel grades. By using an isolation component, the flow of molten steel in the liquid phase cavity can be blocked, thereby ensuring that the billet composition meets the requirements during quick tundish replacement of different steel grades. Summary of the Invention

[0004] The present invention aims to provide a quick-change tundish process for large cross-section round billets of different steel grades, which overcomes the limitations of the traditional quick-change tundish process, greatly shortens the waiting time between castings of the continuous casting machine, improves the operating efficiency of the continuous casting machine, and fully releases the production capacity potential of the continuous casting machine.

[0005] The large-section round billet quick-change tundish process for different steel grades provided by this invention is based on the traditional quick-change tundish process. It addresses the difficulty of steel grade incompatibility caused by the flow and feeding of molten steel in the liquid phase cavity during quick-change of different steel grades. It uses an inexpensive and simple-to-manufacture isolation component, which is placed below the molten steel surface in the crystallizer during the quick-change tundish operation. This effectively blocks the flow channel of the liquid phase cavity in the billet, ensuring that the composition of the two steel grades does not affect each other during quick-change of different steel grades.

[0006] This invention provides a quick-change tundish process for large-section round billets of different steel grades, comprising the following steps: Using low-cost φ390 cylindrical steel blocks and 45mm thick steel plates as raw materials, a separator is fabricated. Based on solidification theory calculations, the dimensions of the welded steel plate are adjusted. When the first steel grade is stopped pouring in the tundish, the separator is placed in the crystallizer, precisely sinking to 1000mm below the molten steel surface. Then, the second steel grade is poured in the tundish, completing the quick-change tundish operation for different steel grades. The function of the separator is to block the flow of molten steel in the liquid phase cavity of the billet, preventing the molten steel of the second steel grade from replenishing the first steel grade through the liquid phase cavity, thus preventing a deviation in the composition of the first steel grade.

[0007] The specific steps of the above-mentioned quick-change tundish process for large-section round billets of different steel grades are as follows:

[0008] (1) Use φ390 cylindrical steel blocks (diameter 390mm, length 300-350mm) and 150*80-150*45mm steel plates (length 150mm, width 80-150mm, thickness 45mm) to make isolation parts;

[0009] (2) Based on the solidification theory calculation and the on-site test of the sinking depth of the isolation component, adjust the size of the isolation component so that it sinks to 1000mm below the meniscus of the crystallizer; the function of the isolation component is to block the flow of molten steel in the liquid phase cavity of adjacent steel billets of different steel grades, prevent the composition of molten steel from being affected, and ensure that the composition of the steel billet meets the requirements.

[0010] (3) After the isolation component placement operation is completed, the traditional process of quick-change tundish without connecting parts is adopted. That is, after the tundish is opened for pouring, the submerged nozzle is inserted below the steel liquid surface of the crystallizer by lowering the height of the tundish.

[0011] In the above process, the operation of placing the isolation component below the molten steel in the crystallizer is as follows: The isolation component is welded with lifting lugs on top, and steel bars are used as lifting tools. The isolation component is slowly placed into the molten steel in the crystallizer by means of overhead crane hoisting. After the steel bar lifting tool melts, the isolation component sinks precisely to 1000mm below the surface of the molten steel in the crystallizer, which plays the role of blocking the liquid phase cavity channel and preventing the molten steel in the liquid phase cavity from flowing and compensating.

[0012] In the above process, the specific manufacturing method of the isolation component is as follows: it is made by welding using φ390 cylindrical steel block and 45mm thick steel plate as raw materials. The height of the φ390 cylindrical steel block is 350mm. Three 150*45*(80~150)mm steel plates are welded on the circumference at an angle of 120°, so that the effective size of the isolation component reaches 390+(80~150)mm.

[0013] This invention enables the quick-change ladle process for large-section round billets without connectors to be stably and efficiently applied in production practice under both the same steel grade and different steel grades by using isolation components and improved on-site operation methods.

[0014] The beneficial effects of this invention are:

[0015] (1) Before the implementation of this invention, the traditional quick-change ladle process for large cross-section steel could only be carried out between steel of the same grade, which had certain limitations. The proposed process can still achieve continuous production between steel of different grades in large cross-section steel by quick-change ladle, which significantly improves production efficiency and achieves the purpose of ensuring that the steel billet composition does not affect each other when quick-change ladle between steel grades, eliminating the need to remove billets with abnormal composition, reducing the cost of production spare parts, and making the operation simple and efficient.

[0016] (2) Reduce the cost per ton of steel in the continuous casting process. The implementation of the quick change of tundish process for different steel grades has achieved the goal of reducing the cost per ton of steel in the continuous casting process by increasing production.

[0017] (3) Compared with other quick-change intermediate packaging processes, the method of the present invention has low cost, simple overall operation process, high success rate and high safety. In the quick-change operation of different steel types, the crane is the main body to carry out related operations, and personnel only perform command, hoisting and auxiliary work.

[0018] (4) The cost of the isolation component is low. The raw materials for the isolation component are φ390 cylindrical steel blocks and 45mm thick steel plates. The raw materials are abundant and inexpensive. The cutting and welding processes can be made by ourselves, resulting in low cost of the isolation component. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the isolation component.

[0020] Figure 2 for Figure 1 Top view.

[0021] In the diagram: 1 is a cylindrical steel pier, and 2 is a steel plate. Detailed Implementation

[0022] The present invention will be further illustrated by the following embodiments, but is not limited to the following embodiments.

[0023] The specific implementation of the method of the present invention will be described in detail below with reference to the embodiments, but the specific implementation of the present invention is not limited to the following embodiments.

[0024] The quick-change tundish process for large-section round billets of different steel grades provided by this invention specifically includes the following sequential steps (taking a φ800 section as an example):

[0025] 1. Theoretical calculation: based on Calculations show that if the isolator is to be precisely lowered to 1000mm below the surface of the molten steel in the crystallizer to achieve the purpose of blocking the flow of molten steel in the liquid phase cavity for feeding, the diameter of the isolator should be 520mm.

[0026] 2. Separator fabrication: The separator is fabricated by welding using φ390 cylindrical steel blocks and 45mm thick steel plates as raw materials. The length of the φ390 cylindrical steel block is 350mm. Three 150*45*130mm steel plates are welded on the circumference at a 120° angle, so that the effective size of the separator is 390+130=520mm.

[0027] 3. Isolator Test: This test involves placing the prepared isolator into the molten steel in the crystallizer by overhead crane after the tundish pouring is stopped. The main purposes are threefold: first, to calculate the overall production operation time; second, to measure the depth of the isolator in the molten steel in the crystallizer; and third, to calculate the sinking speed of the isolator.

[0028] 4. Size correction of the isolation component: Based on the test results of the isolation component, correct the size of the isolation component.

[0029] 5. Production test: During the three-machine three-flow production, only the first flow is tested. Before and after the quick change of the billet joint, the billet is dissected section by section. Samples are taken from the core, 1 / 2 and edge of the cross section for composition analysis. All samples meet the requirements.

[0030] 6. Organize production in batches, gradually optimize and solidify on-site operations, and develop work instructions.

[0031] The process of the present invention will be described below through specific embodiments 1 to 19:

[0032] 1. The implementation case data is shown in Table 1:

[0033] Table 1. Statistics on quick-change of large-section steel with different grades

[0034]

[0035] The following parameters were used in Examples 1-4: Isolation component fabrication: Isolation components were fabricated using φ390 cylindrical steel blocks and 45mm thick steel plates as raw materials through welding. The length of the φ390 cylindrical steel block was 350mm. Three 150*45*130mm steel plates were welded at 120° angles on the circumference, making the effective size of the isolation component 390+130=520mm (see...). Figure 2After setting up this isolator, the following problem arose: the sinking depth of the isolator in the crystallizer did not meet expectations, exceeding 1000mm, indicating that the effective size of the isolator was too small. The size of the isolator steel plate was adjusted from 150*45*130mm to 150*45*150mm (corresponding to "Adjustment 1" in the table, i.e., from the 130mm wide steel plate in Example 4 to the 150mm wide steel plate in Example 5). After modifying the size, the application effect achieved the expected result.

[0036] In Examples 5-7, the three flow operations have a specific sequence. The sinking depth of the isolator in the first flow is as expected, while the sinking depth of the isolator in the second and third flows is less than 1000mm. Therefore, the size of the isolator steel plate was adjusted again. In Examples 5-7, the steel plate sizes are 150*45*150mm, 150*45*140mm, and 150*45*130mm respectively, according to the order of the flow operations, and the sinking depths of all three flows meet the expectations.

[0037] After the operation of Example 7 was completed, the width of the steel plate was adjusted, corresponding to "Adjustment 2" in the table, that is: the size of the isolation steel plate used in Example 8 is 150*45*130mm.

[0038] Examples 8-19: Using the adjusted size of the isolation component, the sinking depth of the isolation component meets the expectations, and the relevant dimensions, parameters and operations are solidified.

[0039] In the above Examples 1 to 19, a total of 19 quick-change castings of different steel grades were organized, with a success rate of 100%. The billet composition inspection showed no abnormalities, the process was stable, and it entered the normalized production stage.

[0040] 2. Implementation method for quick change of tundish for different steel types:

[0041] (1) Prepare a long sprue on the spare intermediate tundish. The spare intermediate tundish should be baked strictly according to the baking curve. When baking the immersion sprue, the baking temperature of the intermediate tundish should be ≥1100℃ and the baking end temperature of the intermediate tundish should be ≥1230℃.

[0042] (2) After the last batch of the old intermediate ladle is stopped, the automatic slag feeder is stopped and the manual slag feeder is adopted to ensure the effect of black slag in the crystallizer.

[0043] (3) When the old tundish has 15t of remaining steel, activate the quick tundish change program.

[0044] (4) When the old tundish has 8t of remaining steel, all flow cycles should be stopped by closing the stopper rods and stopping the casting process. At the same time, the new tundish should be shut off and the stopper rod wear should be checked.

[0045] (5) After the old tundish is moved, the molten steel surface in the crystallizer is moved downward by 150mm, and then the slag ring is quickly removed. Note that the slag surface in the crystallizer should not be disturbed in a large area during the slag ring removal process. When the liquid surface turns red, add protective slag to keep it warm.

[0046] (6) After the slag removal operation is completed, the crane is directed to hoist the prepared isolation piece and slowly place it into the crystallizer. After the steel reinforcement lifting device is burned off, it is pulled out, and the isolation piece sinks to 1000mm below the surface of the molten steel in the crystallizer. The placement of the isolation piece is completed one flow at a time. After the isolation piece is placed, 6-8kg of crystallizer protective slag is added to the crystallizer to clean the copper plate of the crystallizer and prevent slag entrapment and steel leakage. Then, the surface of the molten steel in the crystallizer is moved downward by 100mm to provide sufficient space for pouring.

[0047] (7) Position the new intermediate ladle, align the nozzle with the crystallizer, and drop the intermediate ladle until the bottom of the nozzle is 10-20 mm away from the slag surface of the crystallizer. Set the liquid level, release the quick intermediate ladle change procedure, and start pouring from the main ladle.

[0048] (8) When the molten steel volume of the new ladle reaches 20t, all flows are poured at the same time. After the steel flow stabilizes, the ladle is quickly lowered to the lowest position and the submerged nozzle is quickly inserted into the molten steel in the crystallizer.

[0049] (9) For casting length ≥ 600 mm, adjust the casting speed to 0.15 m / min. For casting length ≥ 800 mm, adjust to the normal casting speed according to the procedure.

[0050] According to the above implementation process, if six quick changes of different steel grades are carried out within a month, the continuous casting machine can save approximately 28 hours of waiting time and increase the machine's hourly operating rate by 0.93%. Through the implementation and promotion of the quick change of different steel grades ladle process, the production efficiency of the continuous casting machine has been further improved.

Claims

1. A quick-change ladle process for large-section round billets of different steel grades, characterized in that... Includes the following steps: Using low-cost φ390 cylindrical steel piers and 45mm thick steel plates as raw materials, three steel plates are welded at 120° angles on the circumference of the cylindrical steel piers to form a separator. When the first steel grade is stopped pouring in the tundish, the separator is placed in the crystallizer and precisely sunk to 1000mm below the surface of the molten steel in the crystallizer. Then the second steel grade is poured in the tundish to complete the quick change of steel grade tundish operation. The specific steps of the large-section round billet quick-change tundish process for different steel grades are as follows: (1) Use cylindrical steel blocks with a diameter of 390mm and a height of 300~350mm and steel plates with a length of 150mm, a width of 80~150mm and a thickness of 45mm to make isolation parts; the steel plates are vertically distributed on the outer circumferential surface of the cylindrical steel blocks, and the included angle between two adjacent steel plates is 120°. (2) Based on the solidification theory calculation and the on-site test of the sinking depth of the isolation component, adjust the size of the isolation component so that it sinks to 1000mm below the surface of the molten steel in the crystallizer; the function of the isolation component is to block the flow of molten steel in the liquid phase cavity of adjacent steel billets of different steel grades, prevent the composition of molten steel from being affected, and ensure that the composition of the steel billet meets the requirements. The specific operation of placing the isolation component below the molten steel in the crystallizer is as follows: The isolation component is welded with lifting lugs on the top. Using steel bars as lifting tools, the isolation component is slowly placed into the molten steel in the crystallizer by using an overhead crane. After the steel bar lifting tool melts, the isolation component is precisely lowered to 1000mm below the surface of the molten steel in the crystallizer, which plays the role of blocking the liquid phase cavity channel and preventing the molten steel in the liquid phase cavity from flowing and compensating. After the tundish pouring is stopped, the prepared isolators are placed into the molten steel in the crystallizer by means of overhead crane. There are three main purposes: first, to calculate the overall production operation time; second, to measure the depth of the isolators in the molten steel in the crystallizer; and third, to calculate the sinking speed of the isolators. (3) After the isolation component placement operation is completed, the process of quick-change tundish without connecting parts is adopted. That is, after the tundish is opened for casting, the submerged nozzle is inserted below the steel liquid surface of the crystallizer by lowering the height of the tundish.

2. The quick-change tundish process for large-section round billets of different steel grades according to claim 1, characterized in that: The function of the isolator is to block the flow of molten steel in the liquid phase cavity of the billet, and to prevent the molten steel of the second steel grade from feeding into the first steel grade through the liquid phase cavity, thus preventing the composition of the first steel grade from deviating.

3. The quick-change tundish process for large-section round billets of different steel grades according to claim 1, characterized in that: The specific manufacturing method of the isolation component is as follows: it is made by welding using φ390 cylindrical steel block and 45mm thick steel plate as raw materials. Three 150*45*(80~150)mm steel plates are welded at an angle of 120° on the outer circumference of the cylindrical steel block, so that the effective size of the isolation component reaches 390+(80~150)mm; the width of the steel plate can be adjusted.

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