Method for improving flaw detection qualification rate of plate blank and tail blank
By combining a high-pressure reduction process with a finely controlled tail billet production method, the quality problem of tail billets in medium and heavy plate continuous casting was solved, the pass rate of tail billet flaw detection was significantly improved, the metal yield was increased, and the production cost was reduced.
Patent Information
- Application Number
- CN202511153436.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-18
- Publication Date
- 2025-11-21
AI Technical Summary
In the continuous casting process of medium and heavy plates, quality problems of the tail billet, such as central porosity and shrinkage cavities, lead to failure of flaw detection. The existing light reduction process is difficult to effectively improve the internal quality of the billet, which affects the metal yield and production efficiency.
The tail billet production method adopts a combination of large reduction process and precise control, including steps such as limiting rolling specifications, extending refining time, precise slag removal and pulling speed control, local large reduction, slow cooling and segmented heating, to ensure the improvement of tail billet quality.
It significantly improves the pass rate of tail billet flaw detection from 70% to over 99%, increases metal yield, and reduces production costs.
Abstract
Description
Technical Field
[0001] This application relates to the field of iron and steel metallurgy technology, and in particular to a method for improving the pass rate of flaw detection in slab tail billets. Background Technology
[0002] As market demands for steel plate quality increase, the flaw detection of continuously cast tail billets is becoming increasingly stringent. Tail billet quality accounts for a significant portion of metal yield, and substandard tail billet quality can severely negatively impact the overall profitability of the steel mill. In the continuous casting process of medium and heavy plates, tail billets often exhibit a series of quality problems leading to non-compliance with flaw detection due to factors such as casting speed during the shutdown process, the liquid level in the crystallizer, protective casting, and the effectiveness of the protective slag. These problems include central porosity, shrinkage cavities, and low cleanliness.
[0003] Currently, in medium and heavy plate continuous casting, dynamic light reduction is usually used to force the molten steel rich in solute elements at the end to be discharged from the solidification end, thereby improving the center segregation and center porosity. However, as the billet gradually transitions to the tail billet, the pressing effect of light reduction is difficult to be transmitted to the core, so the effect on improving the internal quality of the billet is limited. Summary of the Invention
[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a method to improve the flaw detection pass rate of slab tail billet. Based on light reduction, a large reduction process for tail billet has been developed, which can achieve greater reduction amount and reduction efficiency at the end of solidification. At the same time, the details of tail billet continuous casting production are precisely controlled, thereby comprehensively improving the flaw detection pass rate of tail billet.
[0005] Specifically, the first aspect of this application provides a method for improving the pass rate of flaw detection in slab tail billets, including the following steps:
[0006] (a) Limit the rolling specifications of the tail billet to ensure that the rolling compression ratio is >8;
[0007] (b) For furnaces that have been shut down, increase the refining soft blowing time to ≥20 min, control the superheat to 15-25 °C, and limit the content of Mn, S and P to reduce segregation;
[0008] (c) Perform slag removal operation, precise control of liquid level in tundish, step-by-step descent of casting speed and manual flow stabilization with stopper rod at the end of casting;
[0009] (d) Implement localized large reduction in the fan-shaped section of the billet before it is completely solidified, with a reduction amount > 8 mm;
[0010] (e) Increase the length of the tail blank and adopt slow cooling and segmented heating processes.
[0011] Furthermore, in step (b):
[0012] The Mn content is <1.5%, the S content is <0.001%, and the P content is <0.015%.
[0013] Argon gas is used for soft blowing, and the soft blowing time is ≥25 min.
[0014] Further, step (c) includes:
[0015] During the second-to-last heat of the casting process, slag removal from the tundish and the addition of covering agent should be completed within ≤1 minute.
[0016] The insertion depth of the slag discharge port of the final furnace ladle is 130-170mm, and the slag discharge sensing sensitivity is adjusted to ≥90%.
[0017] Furthermore, in step (c):
[0018] When the tundish tonnage is ≤30 tons, stop the crystallizer slag addition operation and maintain the black slag surface condition;
[0019] When the tonnage drops to 14 tons or the liquid level reaches 650-700mm, the automatic step-down descent program is activated, with a descent rate of 0.05m / min every 30 seconds.
[0020] Furthermore, in step (c):
[0021] When the tonnage is ≤6 tons or the liquid level is 250-300mm, the pulling speed is reduced to 0.15m / min and the machine is stopped. The stopper rod is closed and the blind flange is pushed in simultaneously.
[0022] The downtime must be at least 2 minutes, and top stirring is prohibited.
[0023] Furthermore, in step (d):
[0024] The location of the large pressure was determined by a nail-shooting experiment, and was selected in a fan-shaped section with a central liquid phase cavity thickness > 10 mm.
[0025] The pressing operation begins when the last 3 billets reach the 13th section and ends 800mm from the end of the billet.
[0026] Furthermore, the maximum reduction is 10mm, while the remaining sections maintain dynamic light reduction; before implementing the maximum reduction, it is confirmed that the top of the billet has been sealed.
[0027] Furthermore, in step (e):
[0028] After the billet exits the fan-shaped section, the tail is not cut off, the offline time is ≤40min, and a heat insulation cover is used for slow cooling for >48h.
[0029] Furthermore, in step (e):
[0030] The weak cooling mode reduces the secondary cooling water volume to 2 / 3 of the normal pouring volume;
[0031] After rolling, the steel plates are quickly removed from the production line using a hot slitting shear and cooled for ≤24 hours, with the ends of the steel plates covered with insulation cloth.
[0032] Furthermore, during the tail blank finishing and cutting, the end portion ≥800mm is removed;
[0033] Heating is done in stages, with a total time of ≤4 hours.
[0034] The present invention has the following beneficial effects:
[0035] This invention provides a comprehensive method for improving the pass rate of flaw detection in thick plate tail billets. The comprehensive control measures cover planned allocation, steel composition control, refining time control, slag removal and flushing control in the continuous casting tundish, mold flux thickness control, mold cooling and stopping methods control, casting speed control, high-reduction process control, and rolling process control. In particular, by combining the determination of the liquid core location range through nail-shooting experiments, implementing a high-reduction process on the tail batch can significantly improve the central porosity of the tail billet and enhance the quality of the plate. The method provided by this invention can increase the pass rate of flaw detection in tail billets from 70% to over 99%, bringing significant practical benefits to the plant, increasing the yield of continuously cast metal, and reducing production costs. Detailed Implementation
[0036] To make the objectives, technical solutions, and advantages of this application clearer, the following description and illustration are provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.
[0037] Obviously, the following description is merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios without any inventive effort. Furthermore, it is understood that although the effort involved in such development may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.
[0038] A method for improving the pass rate of flaw detection in slab tail billets includes the following steps:
[0039] (a) Limit the rolling specifications of the tail billet to ensure that the rolling compression ratio is >8;
[0040] (b) For furnaces that have been shut down, increase the refining soft blowing time to ≥20 min, control the superheat to 15-25 °C, and limit the content of Mn, S and P to reduce segregation;
[0041] (c) Perform slag removal operation, precise control of liquid level in tundish, step-by-step descent of casting speed and manual flow stabilization with stopper rod at the end of casting;
[0042] (d) Implement localized large reduction in the fan-shaped section of the billet before it is completely solidified, with a reduction amount > 8 mm;
[0043] (e) Increase the length of the tail blank and adopt slow cooling and segmented heating processes.
[0044] This invention provides a comprehensive method for improving the pass rate of flaw detection in thick plate tail billets. Its integrated control measures encompass planned allocation, steel composition control, refining time control, slag removal and flushing control in the continuous casting tundish, mold flux thickness control, mold cooling and stopping methods control, casting speed control, high-reduction process control, and rolling process control. In particular, by combining the determination of the liquid core location range through nail-shooting experiments, implementing a high-reduction process on the tail batch can significantly improve the central porosity of the tail billet and enhance plate quality. The method provided by this invention can increase the pass rate of flaw detection in tail billets from 70% to over 99%, bringing significant practical benefits to the plant, increasing continuous casting metal yield, and reducing production costs.
[0045] In this embodiment, in step (a), the present invention prioritizes adjustments to the production plan, with the tail billet rolling specification being 20-30mm, the rolling compression ratio being >8, and the rolling reduction rate being controlled at around 1 / 10, so as to minimize the impact of the tail billet core quality on product flaw detection.
[0046] In this embodiment, in step (b) for the shut-down furnace, the soft argon blowing time at the refining station is appropriately increased to ≥20 minutes, preferably 25-30 minutes, to allow inclusions to float sufficiently. The superheat is controlled at 15-25°C. In terms of composition, the shut-down furnace is controlled to have Mn% <1.5%, S% <0.001%, and P% <0.015% to reduce segregation.
[0047] In this embodiment, step (c) includes: in the middle of the second to last heat of casting, slag removal operation is performed. The molten steel level in the tundish is brought to the slag removal port at a speed of 0.05t / s and kept stable. The slag removal port is cleaned in advance to ensure that the slag removal port is smooth and the tundish slag is completely removed. The slag removal time is controlled within 1 minute, and a covering agent is added in time to prevent the molten steel from oxidizing.
[0048] The liquid level velocity in the tundish should not be too high to prevent unstable flow control by the stopper rod, which could cause liquid level fluctuations and quality problems. For the final pour, the insertion depth of the drain nozzle should be controlled at 130-170mm. The slag discharge sensitivity of the ladle should be increased from 30% to 10% to achieve slag-detection shut-off operation, strictly preventing slag discharge from the ladle and significantly reducing the probability of slag entrapment at the end of the tundish pouring stop.
[0049] In this embodiment, in step (c): when the ladle tonnage in the furnace is 30 tons, a large amount of slag is no longer added to the crystallizer. The exposed slag bars are picked out to maintain the black slag surface condition. A small amount of protective slag is added to the exposed red slag area. The operation time is controlled to be <30s.
[0050] When the tonnage drops to 14 tons or the liquid level reaches 650-700 mm, activate the automatic step-down descent program to reduce the pulling speed by 0.05 m / min every 30 seconds. Prepare several oxygen tubes in advance to measure the liquid level in the intermediate drum. When measuring, insert the oxygen tube into the bottom of the intermediate drum for about 5 seconds and then remove it promptly to prevent the oxygen tube from melting.
[0051] In this embodiment, when the tundish tonnage is reduced to 10 tons or the liquid level in the tundish is reduced to 500-550mm, the tundish stopper rod is switched from automatic to manual to stabilize the liquid level, with the liquid level fluctuation controlled within ±3mm. The powder slag layer of the crystallizer is removed with a slag shovel, while the liquid slag layer remains stationary to prevent stirring of the liquid level from causing slag entrapment. The time is controlled within 30-50 seconds.
[0052] When the tonnage is ≤6 tons or the liquid level is 250-300mm, the pouring speed should be reduced to 0.15m / min and the machine stopped. Simultaneously, the stopper rod should be closed and the blind flange pushed in. Strictly prevent slag from falling into the crystallizer. The machine should be stopped for 2 minutes. The tundish car should be moved away promptly, and the top cooling status should be observed. If cooling is slow, appropriate water cooling should be applied. Top stirring is strictly prohibited, as it will cause turbulence and inhibit the floating of inclusions. The optimal tonnage for stopping pouring from the tundish is 8 tons, with a liquid level of 300mm.
[0053] After confirming that the capping is normal, increase the speed by 0.05 m / min every 30 seconds, and increase the pulling speed to 0.95 m / min.
[0054] According to the casting flow tracking system, the tail billet is cooled in a weak cooling mode to prevent the billet from solidifying prematurely and being unable to undergo large reduction. The secondary cooling water volume in each section is reduced to 2 / 3 of the normal pouring volume.
[0055] In this embodiment, the location of the large pressing in step (d) is determined by a nail-shooting experiment, and is selected in a fan-shaped section with a central liquid phase cavity thickness > 10 mm; the pressing operation starts when the last 3 billets reach the 13th section and ends at 800 mm from the end of the billet.
[0056] Specifically, at stage 13, the interior of the billet is in a partially solidified state, with a central liquid cavity thickness >10mm (including the pasty area). Therefore, when the last three billets reach stage 13 of the fan-shaped section, the large reduction stage is manually activated, lowering the stage 13 fan-shaped section by 10mm until it reaches 800mm from the end of the billet. Then, the large reduction stage is restored to normal. Throughout the process, all other stages maintain dynamic light reduction. During the large reduction at the last three stages, ensure the top of the billet is sealed to prevent roof collapse or steel leakage accidents caused by compression.
[0057] In this embodiment, step (e) increases the fixed length of the tail blank, and the modified fixed length is 260 / 250 of the original fixed length, thereby ensuring that the blank can be rolled into the target product.
[0058] After the billet exits the fan-shaped section, the tail is not cut off, and the unloading time is ≤40min. It is then slowly cooled with an insulation cover for >48h. After the billet exits the 15th section, the tail is not cut off. The last billet is then quickly unloaded, with the unloading time controlled within 40min. At the same time, the billet is slowly cooled with an insulation cover for >48h to allow hydrogen to diffuse fully.
[0059] In this embodiment, the tail blank is ground and cut to a length of ≥800mm. It is then heated in a furnace using a segmented heating method, with the heating time controlled within 4 hours.
[0060] After rolling, the steel plate is quickly removed from the production line and cooled using a hot slitting shear. The cooling time is within 24 hours. At the same time, the beginning and end of the steel plate are insulated with insulating cloth.
[0061] Example
[0062] The following examples describe the disclosure of this invention in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight. Unless otherwise stated, all reagents used in the examples are available commercially or synthesized using conventional methods and are ready for use without further processing. Unless otherwise stated, all instruments used in the examples are available commercially.
[0063] Example 1
[0064] A method for improving the pass rate of flaw detection in slab tail billets includes the following steps:
[0065] (a) Limit the rolling specifications of the tail billet to ensure a rolling compression ratio of 9;
[0066] (b) For the shutdown furnace, increase the refining soft blowing time to 22 min, control the superheat to 15-25℃, and control Mn% < 1.5%, S% < 0.001%, P% < 0.015% to reduce segregation;
[0067] (c) In the middle of the second to last heat of casting, slag removal operation is carried out. The molten steel in the tundish is brought to the slag removal port at a rate of 0.05t / s and kept stable. The slag removal port is cleaned in advance to ensure that the slag removal port is smooth and the slag in the tundish is completely removed. The slag removal time is controlled within 50s, and a covering agent is added in time to prevent the molten steel from oxidizing.
[0068] For the last batch of casting, the insertion depth of the water outlet is controlled at 140mm to improve the slag inlet sensing sensitivity of the ladle to ≥90% and achieve the slag-seeking shut-off operation.
[0069] When the ladle capacity of the furnace is 30 tons, no more large-scale slag addition is carried out in the crystallizer. The exposed slag bars are picked out to maintain the black slag surface condition. A small amount of protective slag is added to the exposed red slag areas. The operation time is controlled at 28 seconds.
[0070] When the tonnage drops to 14 tons or the liquid level reaches 680mm, the automatic step-down descent program is activated to reduce the descent speed by 0.05m / min every 30 seconds.
[0071] When the tundish tonnage is reduced to 10 tons or the liquid level in the tundish is reduced to 520mm, the tundish stopper rod is switched from automatic to manual to stabilize the liquid level. The liquid level fluctuation is controlled within ±3mm. The powder slag layer of the crystallizer is removed with a slag shovel, while the liquid slag layer remains stationary to prevent stirring of the liquid surface from causing slag roll-up. The time is controlled within 40 seconds.
[0072] When the tonnage is ≤6 tons or the liquid level is 250-300mm, the pulling speed should be reduced to 0.15m / min and the machine should be stopped. At the same time, the stopper rod should be closed and the blind plate should be pushed in. Strictly prevent slag from falling into the crystallizer. The machine should be stopped for 2 minutes.
[0073] After confirming that the capping is normal, increase the speed by 0.05 m / min every 30 seconds, and increase the pulling speed to 0.95 m / min;
[0074] According to the casting flow tracking system, the tail billet is cooled in a weak cooling mode to prevent the billet from solidifying prematurely and being unable to undergo large reduction. The secondary cooling water volume of each section is reduced to 2 / 3 of the normal pouring volume.
[0075] (d) The location of the large reduction was determined by the nail shooting test and selected in the fan-shaped section with a thickness of 10-12mm in the central liquid phase cavity; the reduction operation started from the end of the 3rd billet to the 13th section and ended at 800mm from the end of the billet, with a reduction of 10mm.
[0076] (e) Increase the fixed length of the tail billet. The modified fixed length = 260 / 250 * the original fixed length. After the tail billet exits the fan-shaped section, the tail is not cut off. The off-line time is 38 minutes, and it is slowly cooled with an insulation cover for 50 hours. After the tail billet exits the 15th section, the tail is not cut off. The tail billet is quickly removed from the line. The off-line time is controlled within 40 minutes. At the same time, the tail billet is slowly cooled with an insulation cover for 50 hours to allow hydrogen to diffuse fully.
[0077] The tail blanks are ground and cut to a length of ≥800mm before being put into the furnace for heating. The heating is done in stages and the heating time is controlled at 3.5 hours.
[0078] After rolling, the steel plate is quickly removed from the production line and cooled using a hot slitting shear. The cooling time is within 24 hours. At the same time, the beginning and end of the steel plate are insulated with insulating cloth.
[0079] Example 2
[0080] This embodiment is basically the same as the previous embodiment, except that the soft blowing time of argon gas in step (b) is 25 minutes.
[0081] Example 3
[0082] This embodiment is basically the same as the previous embodiment, except that the slag discharge time in step (c) is controlled at 55 seconds.
[0083] Example 4
[0084] This embodiment is basically the same as the previous embodiment, except that in step (c), when the tonnage drops to a liquid level of 650mm, the automatic step-down program for pulling speed is started to reduce the pulling speed by 0.05m / min every 30s.
[0085] Example 5
[0086] This embodiment is basically the same as the previous one, except that in step (c), when the tundish tonnage is reduced to 10 tons or the liquid level in the tundish is reduced to 530 mm, the tundish stopper rod is switched from automatic to manual to stabilize the liquid level. The liquid level fluctuation is controlled within ±3 mm. The powder slag layer of the crystallizer is removed with a slag shovel, while the liquid slag layer remains stationary to prevent stirring of the liquid level from causing slag roll-up. The time is controlled within 45 seconds.
[0087] Example 6
[0088] This embodiment is basically the same as the previous embodiment, except that in step (e), the tail billet is not cut off after exiting the fan-shaped section, the offline time is 35 minutes, and a heat insulation cover is used for slow cooling for 49 hours.
[0089] Comparative Example 1
[0090] The conventional continuous casting process is adopted, with no specification restrictions, no large reduction, and no slow cooling measures. The rolling specification is 40-50mm (compression ratio ≈6). The refining soft blowing time is 10min. The stop casting control is not precise liquid level control. The casting speed is directly reduced to 0. The post-treatment is natural cooling without heat preservation.
[0091] Comparative Example 2
[0092] This comparative example is basically the same as Example 1, except that Mn / S / P composition control and soft blowing ≥20min are performed, but there is no slag discharge, no large reduction, no slow cooling during the continuous casting process, the stopper rod is directly closed when the machine is stopped, there is no blind plate protection, and the stack cooling is carried out for 24 hours (without heat insulation cloth).
[0093] Comparative Example 3
[0094] This comparative example is basically the same as Example 1, except that a large pressure of 10 mm is applied in the 13th segment, but Mn = 1.8% and P = 0.020%, natural cooling is used, the tail is cut off by only 300 mm, and the heating time is 6 hours.
[0095] Comparative Example 4
[0096] This comparative example is basically the same as Example 1, except that the continuous casting process has no large reduction and the light reduction is only 3mm.
[0097] Comparative Example 5
[0098] This comparative example is basically the same as Example 1, except that slow cooling is omitted, the length is not increased, the tail is only cut off by 300mm, and the heating time is 6h.
[0099] The tail blanks in Examples 1-6 and Comparative Examples 1-5 were subjected to flaw detection and qualified testing. The results are shown in Table 1.
[0100] Table 1. Results of Flaw Detection of Tail Billet
[0101] Group Number of billets inspected (pieces) Quantity of defective items (pieces) Flaw detection pass rate (%) Example 1 112 2 98.2 Example 2 214 12 94.4 Example 3 170 1 99.4 Example 4 167 9 94.6 Example 5 189 7 96.3 Example 6 119 7 94.1 Comparative Example 1 145 36 75.2 Comparative Example 2 128 26 79.7 Comparative Example 3 137 21 84.7 Comparative Example 4 113 15 86.7 Comparative Example 5 176 23 86.9
[0102] As shown in the table above, the comprehensive method of this invention significantly improves the pass rate of tail billet flaw detection. Compared with the examples, the pass rates of tail billet flaw detection in Comparative Examples 1-5 are generally lower, which further proves the effectiveness of the method provided by this invention in improving the quality of tail billets.
[0103] Comparative Example 1 uses a conventional continuous casting process with no size restrictions, no large reduction, and no slow cooling measures. Its flaw detection pass rate is low because the tail billet has many internal quality defects, such as central porosity and inclusions. These defects are easily detected during flaw detection, leading to a higher failure rate. Furthermore, due to the lack of size restrictions, the rolling compression ratio of the tail billet may be insufficient, failing to effectively compact internal defects and further reducing the flaw detection pass rate.
[0104] Although Comparative Example 2 implemented Mn / S / P composition control and extended soft blowing time, there was no slag removal, no large reduction, and no slow cooling measures during continuous casting. Furthermore, the stopper rod was directly closed without blind plate protection when the machine was shut down. The lack of these factors resulted in the internal quality of the tail billet not being fully improved, and the flaw detection pass rate was low.
[0105] Although Comparative Example 3 was subjected to a 10mm high compression in the 13th section, the Mn and P contents exceeded the standard. In addition, natural cooling and a short tail length were used, and the heating time was also long. The combined effect of these factors led to unstable internal quality of the tail billet and a low pass rate for flaw detection.
[0106] In the comparative example 4, there was no large reduction during continuous casting, and the amount of light reduction was insufficient, which could not effectively compact the internal defects of the tail billet, resulting in a low pass rate for flaw detection.
[0107] Comparative Example 5 eliminated the slow cooling measure, did not increase the fixed length, had a shorter tail length, and a longer heating time. These factors together resulted in the inability of harmful elements such as hydrogen inside the tail billet to diffuse fully and the internal stress to be effectively released, thus affecting the quality of the tail billet and reducing the pass rate of flaw detection.
[0108] In summary, the method for improving the flaw detection pass rate of slab tail billets provided by this invention has significant technical effects and practical application value. By comprehensively controlling key steps such as plan allocation, steel composition, refining time, continuous casting slag removal and discharge, mold mold flux thickness, cooling methods during casting stoppage, casting speed, high-reduction process, and rolling process, the flaw detection pass rate of tail billets can be significantly improved, bringing significant economic and social benefits to steel enterprises.
[0109] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.
Claims
1. A method for improving the pass rate of flaw detection in slab tail billets, characterized in that, Includes the following steps: (a) Limit the rolling specifications of the tail billet to ensure that the rolling compression ratio is >8; (b) For furnaces that have been shut down, increase the refining soft blowing time to ≥20 min, control the superheat to 15-25 °C, and limit the content of Mn, S and P to reduce segregation; (c) Perform slag removal operation, precise control of liquid level in tundish, step-by-step descent of casting speed and manual flow stabilization with stopper rod at the end of casting; (d) Implement localized large reduction in the fan-shaped section of the billet before it is completely solidified, with a reduction amount > 8 mm; (e) Increase the length of the tail blank and adopt slow cooling and segmented heating processes.
2. The method for improving the pass rate of flaw detection in slab tail billets according to claim 1, characterized in that, In step (b): The Mn content is <1.5%, the S content is <0.001%, and the P content is <0.015%. Argon gas is used for soft blowing, and the soft blowing time is ≥25 min.
3. The method for improving the pass rate of flaw detection in slab tail billets according to claim 1, characterized in that, Step (c) includes: During the second-to-last heat of the casting process, slag removal from the tundish and the addition of covering agent should be completed within ≤1 minute. The insertion depth of the slag discharge port of the final furnace ladle is 130-170mm, and the slag discharge sensing sensitivity is adjusted to ≥90%.
4. The method for improving the pass rate of flaw detection in slab tail billets according to claim 1, characterized in that, In step (c): When the tundish tonnage is ≤30 tons, stop the crystallizer slag addition operation and maintain the black slag surface condition; When the tonnage drops to 14 tons or the liquid level reaches 650-700mm, the automatic step-down descent program is activated, with a descent rate of 0.05m / min every 30 seconds.
5. The method for improving the pass rate of flaw detection in slab tail billets according to claim 1, characterized in that, In step (c): When the tonnage is ≤6 tons or the liquid level is 250-300mm, the pulling speed is reduced to 0.15m / min and the machine is stopped. The stopper rod is closed and the blind flange is pushed in simultaneously. The downtime must be at least 2 minutes, and top stirring is prohibited.
6. The method for improving the pass rate of flaw detection in slab tail billets according to claim 1, characterized in that, In step (d): The location of the large pressure was determined by a nail-shooting experiment, and was selected in a fan-shaped section with a central liquid phase cavity thickness > 10 mm. The pressing operation begins when the last 3 billets reach the 13th section and ends 800mm from the end of the billet.
7. The method for improving the pass rate of flaw detection of slab tail billets according to claim 6, characterized in that: The maximum reduction is 10mm, and the remaining sections are kept under dynamic light reduction; before implementing the maximum reduction, it is confirmed that the top of the billet has been sealed.
8. The method for improving the pass rate of flaw detection in slab tail billets according to claim 1, characterized in that, In step (e): after the tail billet exits the fan-shaped section, the tail is not cut off, the offline time is ≤40min, and a heat insulation cover is used for slow cooling for >48h.
9. The method for improving the pass rate of flaw detection in slab tail billets according to claim 1, characterized in that, In step (e): the weak cooling mode is to reduce the secondary cooling water volume to 2 / 3 of the normal pouring volume; After rolling, the steel plates are quickly removed from the production line using a hot slitting shear and cooled for ≤24 hours, with the ends of the steel plates covered with insulation cloth.
10. The method for improving the pass rate of flaw detection of slab tail billets according to claim 1, characterized in that: When grinding and cutting the tail blank, remove the end portion ≥800mm; Heating is done in stages, with a total time of ≤4 hours.