Method for preventing breakout of high alloy steel during continuous casting of extra large round billets

Abstract

The present application relates to steel metallurgy continuous casting technical field, disclose a kind of method for preventing extra-large round billet high alloy steel continuous casting open pouring leakage steel, comprising the following steps: dummy head is sent into crystallizer and completes dummy operation;Put into cooling frame;U-shaped cold charge is placed on cooling frame and straight cold charge is placed in dovetail groove;Setting open pouring stopper opening step program parameters;After starting open pouring, stopper is controlled according to step program to molten steel injection crystallizer;Molten steel overflows cooling frame, then add Li-containing covering slag;Control starting speed V0 to start billet drawing, monitor the length of the billet, when the head of the billet is completely out of the crystallizer, adjust the speed to the crystallizer speed V1, wherein V0≤V1.The present application effectively prevents the occurrence of extra-large round billet high alloy steel continuous casting open pouring leakage steel accident through cooling frame design, cold charge addition optimization, step stopper opening control, starting time planning, Li-containing covering slag development and speed section control.

Description

Technical Field

[0001] This invention relates to the field of continuous casting technology in iron and steel metallurgy, specifically to a method for preventing leakage during the continuous casting of extra-large round billets of high alloy steel. Background Technology

[0002] High-alloy steels, such as P91 for high-pressure boiler tubes and H13 for tooling, possess excellent high-temperature strength, corrosion resistance, and wear resistance, and have broad market prospects in energy, chemical, and mold manufacturing industries. However, the continuous casting of high-alloy steels such as P91 and H13 with a diameter of φ900mm and above differs from that of ordinary carbon steel and low-alloy steel. The continuous casting of high-alloy steels is extremely difficult, facing the following main challenges: 1. High alloy steel has a high content of alloying elements such as Cr, Mo, and Ni, resulting in high hardness and high resistance during continuous casting. If the thickness and strength of the billet shell exiting the crystallizer are not properly controlled, it is very easy to cause steel leakage during casting. 2. High alloy steel has a high alloy content, and the billet shell is not easy to weld. During the casting process, the molten steel in the crystallizer is very easy to separate into layers. If the billet cooling method and the opening of the casting stopper are not designed properly, the molten steel in the crystallizer will be difficult to weld together during the solidification process after separation, which will easily cause steel leakage from the crystallizer. 3. High-alloy steel has a wide temperature range from the liquid phase to the solid phase, poor molten steel fluidity, slow heat transfer, and poor high-temperature strength of the initial billet shell. The requirements for the heat transfer and lubrication performance of the protective slag are much higher than those for ordinary carbon steel. At the same time, the protective slag of high-alloy steel easily absorbs oxide inclusions in the molten steel, forming a thick slag ring in the crystallizer, which deteriorates the heat transfer and lubrication performance of the protective slag and further increases the risk of steel leakage.

[0003] The combination of the above factors makes it extremely easy for leakage accidents to occur during the initial casting of extra-large round high-alloy steel billets. Leakage during the initial casting of extra-large round billets can lead to the following hazards: 1. It affects the production rhythm; the insufficient flow casting causes the furnace and machine to be unable to match, and the daily plan cannot be fulfilled. 2. Large-section crystallizers have a large volume of molten steel and extremely high enthalpy. If molten steel leakage occurs, it will cause great damage to the equipment. If molten steel leakage occurs, the continuous casting equipment will be almost scrapped, increasing equipment maintenance costs and reducing product profits. 3. Large cross-section steel leakage generates a lot of scrap steel, which takes a long time to process and affects subsequent planning and scheduling. 4. Due to the long refining cycle, high alloy steel is prone to spontaneous combustion during ladle casting, requiring oxygen combustion. When steel leakage occurs during the initial casting of extra-large circular continuous casting, the single-furnace casting time is extended, increasing the refining cycle and the probability of spontaneous combustion during ladle casting. One furnace of spontaneous combustion during ladle casting results in a loss of at least 2 million yuan.

[0004] Chinese Patent CN114799100A (publication date: July 29, 2022) discloses a method for starting the casting of large round billets in continuous casting. First, the dummy bar is inserted into the casting position in the crystallizer, and then material is added to the crystallizer. Casting begins when the tundish liquid level reaches the casting level. During the stopper rod casting process, the first rod is pressed into the stopper rod mechanism to 3 / 4 of its stroke. Once the molten steel fills the hook, the flow is stopped, and the stopper rod mechanism stroke is controlled to 1 / 4 until the crystallizer liquid level reaches the casting level. Then, protective slag is added. Press the start-up button to vibrate for 1030 seconds; begin pulling, starting at 0 m / min and increasing the speed by 0.02 m / min every 30 seconds; simultaneously, monitor whether the billet has successfully detached from its shell and descends normally until the pulling speed reaches 0.08 m / min, then maintain this speed for 120 seconds. After the outer arc of the billet shell exits the crystallizer, continue increasing the pulling speed by 0.02 m / min every 20 seconds until the liquid level rises to 150-200 mm from the crystallizer opening, then increase the pulling speed to an appropriate level. This method for starting the casting of large round billets in continuous casting can effectively improve the success rate of starting casting and ensure efficient and smooth continuous casting production. However, this method is only suitable for the production of medium-sized large round billets of conventional steel grades, and is not suitable for the continuous casting of extra-large round high-alloy steel. High-alloy steel has a high content of elements such as Cr, Mo, and Ni, resulting in high hardness and high resistance during billet pulling. If the billet shell is not properly controlled when exiting the crystallizer, it is very easy to cause steel leakage during billet pulling. The high alloy content makes it difficult to weld, and the molten steel in the crystallizer is very prone to stratification during the casting process. If the design of the billet head cooling and the opening of the casting stopper is not reasonable, the molten steel in the crystallizer will stratify, which can easily cause steel leakage when exiting the crystallizer. The combination of these two factors makes it easy for steel leakage to occur during the continuous casting of extra-large round high-alloy steel billets.

[0005] Chinese Patent CN115055655A (Publication Date: September 16, 2022, Publication No.: CN115055655A) discloses a casting device and method for ultra-large continuous casting round billets. The casting device includes a tundish and a crystallizer. A stopper rod for controlling the opening degree is installed in the tundish. The tundish is connected to the crystallizer through an immersion nozzle. A dummy bar is installed at the bottom of the crystallizer, and a casting plug is installed above the dummy bar. The casting plug and the dummy bar are detachably connected vertically. An isolation layer is provided between the upper and lower opposing surfaces of the dummy bar and the casting plug to prevent them from sticking together. An annular gap is left between the casting plug and the peripheral wall of the crystallizer, and a seal is installed in the annular gap to prevent molten steel from flowing through. A condenser is installed above the casting plug to accelerate the solidification of molten steel. This invention achieves safe and stable production of large-size continuous casting round billets. However, this patent only applies to the initial casting of low-carbon and medium-carbon steel with a cross section of φ1200mm, and is not applicable to high-alloy steel. For the initial casting of extra-large round billets of high-alloy steel, it is necessary to combine the characteristics of the hot steel and formulate a separate initial casting method and special protective slag in order to effectively prevent the occurrence of steel leakage accidents during initial casting. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of the above-mentioned technologies by providing a method to prevent leakage during the continuous casting of extra-large round billets of high alloy steel. This method achieves comprehensive control over the casting process of extra-large round billets of high alloy steel by optimizing the cooling frame design, cold material addition, step stopper rod opening control, start-up and calming time planning, development of Li-containing protective slag, and segmented casting speed control, thereby effectively preventing leakage accidents.

[0007] To achieve the above objectives, the method for preventing leaks during continuous casting of extra-large round billets of high-alloy steel according to the present invention includes the following steps: S1) Send the siphon head into the crystallizer to the pouring position, seal the gap between the siphon head and the crystallizer wall with asbestos rope, and lay iron pellets above the siphon head to complete the siphon sealing operation. S2) Place the cooling frame into the crystallizer, and place the hook at the bottom of the cooling frame into the dovetail groove of the ingot head. The cooling frame includes at least three rings of circular ribs and parallel straight tie bars welded to the ring ribs. S3) Weld U-shaped cold material with the opening facing upwards onto the circular rib of the cooling frame, place U-shaped cold material with the opening facing downwards onto the straight tie rod, and put straight cold material into the dovetail grooves on both sides of the hook of the cooling frame. S4) Set the step program parameters for the opening stopper bar opening in the continuous casting machine HMI. The step program includes: the first bar large flow stage, the flow reduction and calming stage, the slightly larger flow filling dovetail stage, the bar stage, the continued flow stage, and the completion start-up stage. The stopper bar opening and duration of each stage are preset according to the billet cross-section specifications and the superheat of the molten steel. S5) When the molten steel in the tundish reaches the casting tonnage, casting is started. The stopper rod automatically executes the stopper rod opening degree and duration of each stage according to the set step program. The molten steel is injected into the crystallizer through the submerged entry nozzle. S6) After observing that the molten steel has overflowed the upper surface of the cooling frame, add Li-containing protective slag into the crystallizer. The addition of protective slag should be completed before the casting machine starts to draw speed. This is to avoid adding too early, which may cause slag entrapment and steel leakage under unsteady casting, and to avoid adding too late, which may cause sticking and steel leakage due to lack of lubrication of the billet shell in the crystallizer. S7) Control the starting speed V0 to start casting, monitor the billet travel length, and adjust the casting speed to the exit speed V1 after the billet head has completely exited the crystallizer, where V0≤V1.

[0008] Preferably, in step S1), the ingot head is inserted into the crystallizer at a distance of 350-400mm from the upper surface of the crystallizer, the gap sealed by the asbestos rope extends ≤3mm beyond the surface of the ingot head, the thickness of the iron particles is 8-12mm, and the area covered by the iron particles is greater than or equal to the area covered by the asbestos rope. This method of sealing the ingot head can effectively isolate the direct contact area between the molten steel and the ingot head, reduce the initial thermal shock, and at the same time, the uniform laying of the iron particle layer provides a stable initial cooling interface, which helps to form a uniform billet shell bottom layer.

[0009] Preferably, in step S1), the asbestos rope composition by weight percentage satisfies the following: MgO: 40.0%~45.0%, SiO2: 43%~46%, H2O: 8%~12%, and density = 2.5~2.53 g / cm³. 3 This asbestos rope can withstand temperatures above 1610℃ and maintains good sealing performance under the impact of high-temperature molten steel, preventing molten steel from leaking from the gaps in the ingot head and ensuring the safety of the initial casting.

[0010] Preferably, in step S2), the outer dimensions of the cooling frame are 40-60mm smaller than the inner wall dimensions of the copper tube of the crystallizer, and the straight tie rods are made of φ18-22mm steel bars, which are arranged in a dense manner.

[0011] Preferably, in step S3), the U-shaped cold material has a size of φ10mm, and the direct cold material has a size of φ20mm; the amount of cold material added for different billet cross-sectional specifications is determined as follows: There are 145-165 U-shaped cold-cooled materials with a cross-section of φ900mm, and 40-50 straight-cooled materials. There are 190-210 U-shaped cold-cooled materials with a cross-section of φ1000mm, and 50-60 straight-cooled materials. There are 215-235 U-shaped cold-cooled materials with a cross-section of φ1100mm, and 55-65 straight-cooled materials. There are 250-270 U-shaped cold-cooled materials with a cross-section of φ1200mm, and 60-70 straight-cooled materials. By rationally determining the amount of cold material added for different cross-sectional specifications, sufficient cooling intensity is ensured in the head area where molten steel contacts the ingot head, allowing the billet head to solidify quickly and form a billet shell of sufficient thickness, effectively preventing steel leakage in the early stages of casting.

[0012] Preferably, in step S4), after the start-up is completed, the stopper opening is reduced or increased, and after the liquid level in the crystallizer stabilizes, the stopper is switched to automatic control following the liquid level in the crystallizer.

[0013] Preferably, in step S5), the initial calming time is controlled according to the billet cross-sectional specifications and the superheat of the molten steel: For a φ900mm cross section, the initial calming time is 130~170s when the superheat is ≤40℃, 150~190s when the superheat is 40~60℃, and 170~210s when the superheat is ≥60℃. For a φ1000mm cross section, the initial calming time is 150~210s when the superheat is ≤40℃, 160~220s when the superheat is 40~60℃, and 180~240s when the superheat is ≥60℃. For a φ1100mm cross section, the initial calming time is 190~230s when the superheat is ≤40℃, 200~240s when the superheat is 40~60℃, and 220~260s when the superheat is ≥60℃. For a φ1200mm cross section, the initial calming time is 210~250s when the superheat is ≤40℃, 220~260s when the superheat is 40~60℃, and 230~290s when the superheat is ≥60℃. A reasonable initial calming time ensures that the billet shell grows uniformly and has sufficient strength in the crystallizer. If the initial calming time is too short, the billet shell will be thin and the box body will be weak, making it easy for steel to leak out of the crystallizer. If the initial calming time is too long, the steel flow will be too small, and the high alloy steel will be difficult to weld due to delamination during casting, which will also easily lead to steel leakage.

[0014] Preferably, in step S6), the physicochemical properties of the Li-containing protective slag, by weight percentage, meet the following: for the P91 series, SiO2: 23.5%~33.5%, CaO: 25%~35%, Al2O3: 0.5%~7.5%, F: 5.5%~10.5%, C: 2.0%~10.0%, Li2O: 0.15%~0.45%, R: 0.90%~1.20%, melting point: 1020℃~1120℃, viscosity: 0.15Pa.s~0.25Pa.s; For the H13 series, SiO2: 22.0%~30.0%, CaO: 25.2%~33.2%, Al2O3: 5.0%~12.0%, F: ≤4.0%, C: 11.0%~19.0%, Li2O: 0.10%~0.20%, R: 1.00%~1.20%, melting point: 1100℃~1200℃, viscosity: 0.50Pa.s~1.00Pa.s; This Li-containing protective slag effectively reduces the melting point and viscosity by adding Li without affecting the crystallization performance of high alloy steel protective slag. It not only meets the strict requirements of high alloy steel for protective slag lubrication and heat transfer, but also inhibits the formation of protective slag crust and slag ring, preventing the risk of steel leakage caused by the deterioration of protective slag performance.

[0015] Preferably, in step S7), the initial casting speed V0 and the casting speed V1 exiting the crystallizer are controlled according to the billet cross-sectional specifications and the superheat of the molten steel in the following manner: For a φ900mm cross-section, V0 is 0.05m / min and V1 is 0.08m / min when the superheat is ≤40℃; V0 is 0.05m / min and V1 is 0.07m / min when the superheat is 40~60℃; and V0 is 0.05m / min and V1 is 0.06m / min when the superheat is ≥60℃. For a φ1000mm cross-section, V0 is 0.05m / min and V1 is 0.07m / min when the superheat is ≤40℃; V0 is 0.05m / min and V1 is 0.06m / min when the superheat is 40~60℃; and V0 is 0.05m / min and V1 is 0.05m / min when the superheat is ≥60℃. For a φ1100mm cross-section, V0 is 0.04m / min and V1 is 0.06m / min when the superheat is ≤40℃; V0 is 0.04m / min and V1 is 0.05m / min when the superheat is 40~60℃; and V0 is 0.04m / min and V1 is 0.04m / min when the superheat is ≥60℃. For a φ1200mm cross-section, V0 is 0.04m / min and V1 is 0.05m / min when the superheat is ≤40℃; V0 is 0.04m / min and V1 is 0.04m / min when the superheat is 40~60℃; and V0 is 0.04m / min and V1 is 0.04m / min when the superheat is ≥60℃. Control V0≤V1 to avoid premature and large increases in drawing speed, which would cause the billet shell to become thinner and the box body to be weak. At the same time, avoid drawing speed lag, which would cause high alloy steel to accumulate due to high viscosity.

[0016] Preferably, in step S7), the billet travel length L is calculated as follows: L = L0 + L t Where L0 is the initial length, which is the length of the crystallizer copper tube minus the distance from the ingot head insertion position to the upper surface of the crystallizer. t This refers to the distance the billet travels after the casting machine starts.

[0017] In this invention, for the initial casting of extra-large round high-alloy steel, when the liquid level in the crystallizer reaches a certain value, the casting speed is automatically activated, the molten steel in the crystallizer starts to vibrate automatically, and the stopper opening is strictly calculated based on a reasonable initial calming time. Under a specific stopper opening setting, sufficient and reasonable initial calming time is ensured for the initial casting of high-alloy steel in each section, ensuring uniform growth of the billet shell in the crystallizer and sufficient strength. If the initial calming time is too short, the billet shell in the crystallizer is thin, the box body strength is insufficient, and steel leakage is easy to occur when exiting the crystallizer; if the initial calming time is too long, the steel flow is too small, the initial casting of high-alloy steel will result in stratification, which is difficult to weld, and steel leakage is easy to occur when exiting the crystallizer.

[0018] High-alloy steel, with its high Cr content in molten steel, produces abundant ferrite. During the L+δ→γ peritectic reaction stage, the large shrinkage of the cast billet significantly exacerbates cracking, placing high demands on the heat transfer control of the protective slag. Simultaneously, high-alloy steel has a wide liquid to solid phase range, resulting in poor molten steel fluidity, slow heat transfer, and low high-temperature strength of the initial billet shell. Compared to ordinary carbon steel, high-alloy steel requires higher lubrication performance from the protective slag. The protective slag should not form a crust. However, high-alloy steel protective slag easily absorbs oxide inclusions within the high-alloy steel, leading to deformation and the formation of a thick slag ring within the crystallizer. This severely deteriorates the heat transfer and lubrication performance of the protective slag, greatly increasing the risk of leaks. Therefore, without affecting the crystallization performance of the high-alloy steel protective slag, Li is added to lower the melting point and viscosity to meet lubrication and heat transfer requirements. This ensures necessary lubrication and heat transfer while inhibiting slag ring formation and preventing slag deterioration.

[0019] Compared with the prior art, the present invention has the following advantages: 1. By designing a cooling frame with a specific structure, which is 40-60mm smaller than copper tubes and has densely arranged φ18-22mm steel reinforcement bars, combined with layered U-shaped cold material (φ10mm) and direct cold material (φ20mm), the cooling intensity of the billet head area in the crystallizer is significantly enhanced, so that the head of the molten steel in contact with the ingot head is cooled quickly, forming a billet shell of sufficient thickness and sufficient box strength, effectively preventing steel leakage in the early stage of casting of extra-large circular cross-section high alloy steel; 2. By designing a stepped stopper opening program and setting specific control times for each stage for different cross-sectional specifications and superheat, the molten steel is ensured to fill the crystallizer with a reasonable flow rate, effectively avoiding the problem of molten steel layering and difficulty in welding in the crystallizer during the casting of high alloy steel, while ensuring uniform growth of the billet shell. 3. By setting corresponding starting and calming times for different cross-sectional specifications and superheat conditions, the billet shell in the crystallizer has sufficient growth time and sufficient strength. This avoids the problem of thin billet shell and insufficient strength of the box body caused by too short calming time, and also avoids the problem of too small steel flow and difficulty in welding high alloy steel layers caused by too long calming time. 4. By developing a special protective slag containing Li, the melting point and viscosity were reduced without affecting the crystallization performance. This not only met the strict requirements of high alloy steel for lubrication and heat transfer, but also effectively inhibited the formation of protective slag crust and slag ring, preventing the risk of steel leakage caused by the deterioration of protective slag performance. 5. By strictly limiting the timing of adding protective slag, it avoids both the unsteady casting and slag leakage caused by adding it too early, and the billet shell sticking and leakage caused by adding it too late. 6. By planning the initial casting speed and the casting speed after exiting the crystallizer, and setting specific casting speed values ​​for different cross-sectional specifications and superheat conditions, and in conjunction with the real-time calculation and monitoring of the billet travel length, operators can accurately grasp the position of the billet head and adjust the casting speed in a timely manner, ensuring uniform cooling of the billet head, sufficient strength of the box, and preventing steel leakage during the exit of the crystallizer. 7. The various technical means in the method of this invention cooperate and work together to form a complete technical solution for preventing leakage during continuous casting of extra-large round billets of high alloy steel. There are clear parameter guidelines for each cross-sectional specification and under superheat conditions. It is highly operable and has significant practical application effects. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the cooling frame structure in the method for preventing leakage during continuous casting of extra-large round billets of high alloy steel according to the present invention. Figure 2 for Figure 1 A longitudinally sectional view; Figure 3 This is a schematic diagram of the U-shaped cold material in this invention; Figure 4 This is a schematic diagram of the structure of the direct-cooling material in this invention; Figure 5 This is a schematic diagram of the ingot head inside the crystallizer; Figures 6-9 Schematic diagrams showing the opening settings of the stopper rod for sections with cross-sections of Φ900mm, Φ1000mm, Φ1100mm, and Φ1200mm respectively (the vertical axis represents the opening of the stopper rod, and the horizontal axis represents time). Figures 10-13 The diagrams show the billet length and casting speed control for cross-sections of Φ900mm, Φ1000mm, Φ1100mm, and Φ1200mm, respectively (the left vertical axis represents the billet travel distance, the right vertical axis represents the casting speed, and the horizontal axis represents time).

[0021] The components in the diagram are labeled as follows: Cooling frame 1, circular rib 2, straight tie rib 3, U-shaped cold material 4. Detailed Implementation

[0022] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] In the description of this invention, it should be noted that the terms center, up, down, left, right, vertical, horizontal, inner, and outer, indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms first, second, and third are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0024] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms installation, connection, and linking should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0025] Example 1 This embodiment takes the production of extra-large round billets of high-alloy steel (H13) with a cross-section of φ900mm as an example. The specific steps are as follows: S1) such as Figure 5 As shown, the siphon head is inserted into the crystallizer at a position 360mm from the upper surface of the crystallizer. The gap between the siphon head and the crystallizer wall is sealed with asbestos rope, with the asbestos rope extending ≤3mm beyond the surface of the siphon head. The asbestos rope composition by weight percentage meets the following requirements: MgO: 42.5%, SiO2: 44.9%, H2O: 10%, density = 2.5g / cm³. 3 Iron pellets are laid above the ingot head, with a thickness of 10mm. The area covered by the iron pellets is larger than the area covered by the asbestos rope, thus completing the ingot sealing operation. S2) Place cooling frame 1 into the crystallizer, and combine... Figure 1 and Figure 2 As shown, the outer dimensions of the cooling frame 1 are 50mm smaller than the inner wall dimensions of the copper tube of the crystallizer. The straight tie rods 3 are made of φ20mm steel bars and are densely arranged. The hook at the bottom of the cooling frame 1 is placed into the dovetail groove of the ingot head. The cooling frame 1 includes three rings of circular ribs 2 and parallel straight tie rods 3 welded on the ring ribs 2. Due to the extremely high heat melting amount inside the extra-large cross-section crystallizer, in this embodiment, the material used for the straight tie rods 3 must be resistant to melting. S3) combination Figure 3 and Figure 4As shown, U-shaped cold material 4 with the opening facing upwards is welded onto the annular rib 2 of the cooling frame 1, and U-shaped cold material 4 with the opening facing downwards is placed on the straight tie rib 3. Straight cold material is placed in the dovetail grooves on both sides of the hook of the cooling frame 1. The U-shaped cold material 4 has a size of φ10mm, and the straight cold material has a size of φ20mm. In this embodiment, the number of cold materials added is as follows: 60 for the outer ring, 40 for the middle ring, 15 for the inner ring, and 40 for the tie rib, for a total of 155. A total of 45 straight cold materials are added. S4) Set the step program parameters for the opening stopper rod in the continuous casting machine HMI. The step program includes: the first rod large flow stage, the flow reduction and calming stage, the slightly larger flow filling dovetail stage, the rod-carrying stage, the continued flow stage, and the completion of the start-up stage. The stopper rod opening and duration of each stage are preset according to the billet cross-section specifications and the superheat of the molten steel. After the start-up is completed, the stopper rod opening is reduced or increased. After the liquid level in the crystallizer stabilizes, the system switches to automatic control of the stopper rod following the crystallizer liquid level. In this embodiment, the following is adopted: Figure 6 The diagram shows the step size of the stopper rod opening for a φ900mm cross-section. The first stage of the large flow lasts for T0 cycles (16s), followed by a calming stage for T1 cycles, then a slightly larger flow stage to fill the dovetail for T2 cycles, filling the entire dovetail and completing the box structure with sufficient strength. The next stage is the rod stage for T3 cycles, followed by a continued flow stage for T4 cycles. The stopper rod opening continues through T5 to T6 cycles, and the start-up is completed in T6 cycles. After the start-up, the stopper rod opening needs to be slightly reduced. After T7 cycles, the liquid level in the crystallizer stabilizes, and the stopper rod is automatically controlled according to the liquid level in the crystallizer. S5) When the molten steel in the tundish reaches the casting tonnage, casting is started. The stopper rod automatically executes the opening degree and duration of each stage according to the set step program. The molten steel is injected into the crystallizer through the submerged entry nozzle. Specifically, in this embodiment, the starting calming time is 140s when the superheat is ≤40℃, 170s when the superheat is 40~60℃, and 190s when the superheat is ≥60℃. S6) After observing that the molten steel has overflowed the upper surface of the cooling frame 1, add a Li-containing protective slag into the crystallizer. The addition of the protective slag should be completed before the casting machine starts to draw speed. In this embodiment, the physicochemical properties of the Li-containing protective slag meet the following weight percentages: SiO2: 26.7%, CaO: 29.8%, Al2O3: 7.4%, F: 2.4%, C: 16.8%, Li2O: 0.15%, R: 1.11%, melting point: 1150℃, viscosity: 0.78 Pa.s; S7) Control the starting speed V0 to start casting, and monitor the billet travel length L, where L = L0 + L t Where L0 is the initial length, which is the length of the crystallizer copper tube minus the distance from the ingot head insertion position to the upper surface of the crystallizer. tThis refers to the distance the billet travels after the casting machine starts. Once the billet head has completely exited the crystallizer, the casting speed is adjusted to the crystallizer exit speed V1, where V0 ≤ V1. In this embodiment, the starting speed V0 and the crystallizer exit speed V1 are controlled as follows: when the superheat is ≤40℃, V0 is 0.05 m / min and V1 is 0.08 m / min; when the superheat is 40~60℃, combined with... Figure 10 As shown, V0 is 0.05 m / min and V1 is 0.07 m / min. When the superheat is ≥60℃, V0 is 0.05 m / min and V1 is 0.06 m / min.

[0026] Example 2 This embodiment takes the production of extra-large round billets of high-alloy steel (P91) with a cross-section of φ1000mm as an example. The specific steps are as follows: S1) Insert the siphon head into the crystallizer at a position 350mm from the upper surface of the crystallizer. Seal the gap between the siphon head and the crystallizer wall with asbestos rope. The gap sealed by the asbestos rope should extend ≤3mm beyond the surface of the siphon head. The asbestos rope composition by weight percentage should meet the following requirements: MgO: 40.0%, SiO2: 46%, H2O: 8%, density = 2.53g / cm³. 3 Iron pellets are laid above the ingot head, with a thickness of 8mm. The area covered by the iron pellets is larger than the area covered by the asbestos rope, thus completing the ingot sealing operation. S2) Place the cooling frame 1 into the crystallizer. The outer dimensions of the cooling frame 1 are 40mm smaller than the inner wall dimensions of the copper tube of the crystallizer. The straight tie rods 3 are made of φ18mm steel bars and are arranged in a dense manner. The hook at the bottom of the cooling frame 1 is placed into the dovetail groove of the ingot head. The cooling frame 1 includes three rings of circular ribs 2 and parallel straight tie rods 3 welded on the ring ribs 2. S3) Weld U-shaped cold material 4 with the opening facing upwards onto the annular rib 2 of the cooling frame 1, place U-shaped cold material 4 with the opening facing downwards onto the straight tie rib 3, and put straight cold material into the dovetail grooves on both sides of the hook of the cooling frame 1. The U-shaped cold material 4 has a size of φ10mm, and the straight cold material has a size of φ20mm. In this embodiment, the number of cold materials added is as follows: 70 for the outer ring, 48 for the middle ring, 16 for the inner ring, 66 for the tie rib, for a total of 200, and a total of 55 straight cold materials are added. S4) Set the step program parameters for the opening stopper rod in the continuous casting machine HMI. The step program includes: the first rod large flow stage, the flow reduction and calming stage, the slightly larger flow filling dovetail stage, the rod-carrying stage, the continued flow stage, and the completion of the start-up stage. The stopper rod opening and duration of each stage are preset according to the billet cross-section specifications and the superheat of the molten steel. After the start-up is completed, the stopper rod opening is reduced or increased. After the liquid level in the crystallizer stabilizes, the system switches to automatic control of the stopper rod following the crystallizer liquid level. In this embodiment, the following is adopted: Figure 7The diagram shows the step size of the stopper rod opening for a φ1000mm cross-section. The first stage of the large flow lasts for T0 cycles (18s), followed by a calming stage for T1 cycles, then a slightly larger flow stage to fill the dovetail for T2 cycles, filling the entire dovetail and completing the box structure with sufficient strength. The next stage is the rod-carrying stage for T3 cycles, followed by a continued flow stage for T4 cycles. The stopper rod opening continues through T5 to T6 cycles, and the start-up is completed in T6 cycles. After the start-up, the stopper rod opening needs to be slightly reduced. After T7 cycles, the liquid level in the crystallizer stabilizes, and the stopper rod is automatically controlled according to the liquid level in the crystallizer. S5) When the molten steel in the tundish reaches the casting tonnage, casting is started. The stopper rod automatically executes the opening degree and duration of each stage according to the set step program. The molten steel is injected into the crystallizer through the submerged entry nozzle. Specifically, in this embodiment, for a φ1000mm cross section, the starting calming time is 170s when the superheat is ≤40℃, 190s when the superheat is 40~60℃, and 210s when the superheat is ≥60℃. S6) After observing that the molten steel has overflowed the upper surface of the cooling frame 1, add a Li-containing protective slag into the crystallizer. The addition of the protective slag should be completed before the casting machine starts to draw speed. In this embodiment, the physicochemical properties of the Li-containing protective slag meet the following weight percentages: SiO2: 33.0%, CaO: 33.8%, Al2O3: 7.2%, F: 10.2%, C: 9.5%, Li2O: 0.42%, R: 1.16%, melting point: 1120℃, viscosity: 0.25 Pa·s; S7) Control the starting speed V0 to start casting, and monitor the billet travel length L, where L = L0 + L t Where L0 is the initial length, which is the length of the crystallizer copper tube minus the distance from the ingot head insertion position to the upper surface of the crystallizer. t This refers to the distance the billet travels after the casting machine starts. Once the billet head has completely exited the crystallizer, the casting speed is adjusted to the crystallizer exit speed V1, where V0 ≤ V1. In this embodiment, the starting speed V0 and the crystallizer exit speed V1 are controlled as follows: when the superheat is ≤40℃, V0 is 0.05 m / min and V1 is 0.07 m / min; when the superheat is 40~60℃, combined with... Figure 11 As shown, V0 is 0.05 m / min and V1 is 0.06 m / min. When the superheat is ≥60℃, V0 is 0.05 m / min and V1 is 0.05 m / min.

[0027] Example 3 This embodiment takes the production of extra-large round billets of high-alloy steel (P91) with a cross-section of φ1100mm as an example. The specific steps are as follows: S1) Insert the siphon head into the crystallizer at a position 400mm from the upper surface of the crystallizer. Seal the gap between the siphon head and the crystallizer wall with asbestos rope. The gap sealed by the asbestos rope should extend ≤3mm beyond the surface of the siphon head. The asbestos rope composition by weight percentage should meet the following requirements: MgO: 45.0%, SiO2: 43%, H2O: 12%, density = 2.52g / cm³. 3 Iron pellets are laid above the ingot head, with a thickness of 12mm. The area covered by the iron pellets is larger than the area covered by the asbestos rope, thus completing the ingot sealing operation. S2) Place the cooling frame 1 into the crystallizer. The outer dimensions of the cooling frame 1 are 60mm smaller than the inner wall dimensions of the copper tube of the crystallizer. The straight tie rods 3 are made of φ22mm steel bars and are arranged in a dense manner. The hook at the bottom of the cooling frame 1 is placed into the dovetail groove of the ingot head. The cooling frame 1 includes three rings of circular ribs 2 and parallel straight tie rods 3 welded on the ring ribs 2. S3) Weld U-shaped cold material 4 with the opening facing upwards onto the annular rib 2 of the cooling frame 1, place U-shaped cold material 4 with the opening facing downwards onto the straight tie rib 3, and put straight cold material into the dovetail grooves on both sides of the hook of the cooling frame 1. The U-shaped cold material 4 has a size of φ10mm, and the straight cold material has a size of φ20mm. In this embodiment, the number of cold materials added is as follows: 75 for the outer ring, 52 for the middle ring, 18 for the inner ring, and 80 for the tie rib, for a total of 225, and a total of 60 straight cold materials are added. S4) Set the step program parameters for the opening stopper rod in the continuous casting machine HMI. The step program includes: the first rod large flow stage, the flow reduction and calming stage, the slightly larger flow filling dovetail stage, the rod-carrying stage, the continued flow stage, and the completion of the start-up stage. The stopper rod opening and duration of each stage are preset according to the billet cross-section specifications and the superheat of the molten steel. After the start-up is completed, the stopper rod opening is reduced or increased. After the liquid level in the crystallizer stabilizes, the system switches to automatic control of the stopper rod following the crystallizer liquid level. In this embodiment, the following is adopted: Figure 8 The diagram shows the step size of the stopper rod opening for a φ1100mm cross-section. The first stage of the large flow lasts for T0 cycles (22s), followed by a calming stage for T1 cycles, then a slightly larger flow stage to fill the dovetail for T2 cycles, filling the entire dovetail and completing the box structure with sufficient strength. The next stage is the rod stage for T3 cycles, followed by a continued flow stage for T4 cycles. The stopper rod opening continues through T5 to T6 cycles, and the start-up is completed in T6 cycles. After the start-up, the stopper rod opening needs to be slightly reduced. After T7 cycles, the liquid level in the crystallizer stabilizes, and the stopper rod is automatically controlled according to the liquid level in the crystallizer. S5) When the molten steel in the tundish reaches the casting tonnage, casting is started. The stopper rod automatically executes the opening degree and duration of each stage according to the set step program. The molten steel is injected into the crystallizer through the submerged entry nozzle. Specifically, in this embodiment, the starting calming time is 210s when the superheat is ≤40℃, 220s when the superheat is 40~60℃, and 240s when the superheat is ≥60℃. S6) After observing that the molten steel has overflowed the upper surface of the cooling frame 1, add a Li-containing protective slag into the crystallizer. The addition of the protective slag should be completed before the casting machine starts to draw speed. In this embodiment, the physicochemical properties of the Li-containing protective slag, by weight percentage, meet the following requirements: SiO2: 33.4%, CaO: 34.5%, Al2O3: 7.4%, F: 10.4%, C: 9.8%, Li2O: 0.44%, R: 1.18%, melting point: 1100℃, viscosity: 0.2 Pa·s. S7) Control the starting speed V0 to start casting, and monitor the billet travel length L, where L = L0 + L t Where L0 is the initial length, which is the length of the crystallizer copper tube minus the distance from the ingot head insertion position to the upper surface of the crystallizer. t This refers to the distance the billet travels after the casting machine starts. Once the billet head has completely exited the crystallizer, the casting speed is adjusted to the crystallizer exit speed V1, where V0 ≤ V1. In this embodiment, the starting casting speed V0 and the crystallizer exit speed V1 are controlled as follows: when the superheat is ≤40℃, combined with... Figure 12 As shown, V0 is 0.04 m / min and V1 is 0.06 m / min. When the superheat is 40~60℃, V0 is 0.04 m / min and V1 is 0.05 m / min. When the superheat is ≥60℃, V0 is 0.04 m / min and V1 is 0.04 m / min.

[0028] Example 4 This embodiment takes the production of extra-large round billets of high-alloy steel (P91) with a cross-section of φ1200mm as an example. The specific steps are as follows: S1) Insert the siphon head into the crystallizer at a position 370mm from the upper surface of the crystallizer. Seal the gap between the siphon head and the crystallizer wall with asbestos rope. The gap sealed by the asbestos rope should extend ≤3mm beyond the surface of the siphon head. The asbestos rope composition by weight percentage should meet the following requirements: MgO: 42.0%, SiO2: 44%, H2O: 10%, density = 2.53g / cm³. 3 Iron pellets are laid above the ingot head, with a thickness of 10mm. The area covered by the iron pellets is larger than the area covered by the asbestos rope, thus completing the ingot sealing operation. S2) Place the cooling frame 1 into the crystallizer. The outer dimensions of the cooling frame 1 are 50mm smaller than the inner wall dimensions of the copper tube of the crystallizer. The straight tie rods 3 are made of φ20mm steel bars and are arranged in a dense manner. The hook at the bottom of the cooling frame 1 is placed into the dovetail groove of the ingot head. The cooling frame 1 includes three rings of circular ribs 2 and parallel straight tie rods 3 welded on the ring ribs 2. S3) Weld U-shaped cold material 4 with the opening facing upwards onto the annular rib 2 of the cooling frame 1, place U-shaped cold material 4 with the opening facing downwards onto the straight tie rib 3, and put straight cold material into the dovetail grooves on both sides of the hook of the cooling frame 1. The U-shaped cold material 4 has a size of φ10mm, and the straight cold material has a size of φ20mm. In this embodiment, the number of cold materials added is as follows: 80 for the outer ring, 62 for the middle ring, 28 for the inner ring, and 98 for the tie rib, for a total of 260, and a total of 65 straight cold materials are added. S4) Set the step program parameters for the opening stopper rod in the continuous casting machine HMI. The step program includes: the first rod large flow stage, the flow reduction and calming stage, the slightly larger flow filling dovetail stage, the rod-carrying stage, the continued flow stage, and the completion of the start-up stage. The stopper rod opening and duration of each stage are preset according to the billet cross-section specifications and the superheat of the molten steel. After the start-up is completed, the stopper rod opening is reduced or increased. After the liquid level in the crystallizer stabilizes, the system switches to automatic control of the stopper rod following the crystallizer liquid level. In this embodiment, the following is adopted: Figure 9 The diagram shows the step size of the stopper rod opening for a φ1200mm cross-section. The first stage of the large flow lasts for T0 cycles (25s), followed by a calming stage for T1 cycles, then a slightly larger flow stage to fill the dovetail for T2 cycles, filling the entire dovetail and completing the box structure with sufficient strength. The next stage is the rod-carrying stage for T3 cycles, followed by a continued flow stage for T4 cycles. The stopper rod opening continues through T5 to T6 cycles, and the start-up is completed in T6 cycles. After the start-up, the stopper rod opening needs to be slightly reduced. After T7 cycles, the liquid level in the crystallizer stabilizes, and the stopper rod is automatically controlled according to the liquid level in the crystallizer. S5) When the molten steel in the tundish reaches the casting tonnage, casting is started. The stopper rod automatically executes the opening degree and duration of each stage according to the set step program. The molten steel is injected into the crystallizer through the submerged entry nozzle. Specifically, in this embodiment, the starting calming time is 230s when the superheat is ≤40℃, 240s when the superheat is 40~60℃, and 260s when the superheat is ≥60℃. S6) After observing that the molten steel has overflowed the upper surface of the cooling frame 1, add a Li-containing protective slag into the crystallizer. The addition of the protective slag should be completed before the casting machine starts to draw speed. In this embodiment, the physicochemical properties of the Li-containing protective slag meet the following weight percentages: SiO2: 33.4%, CaO: 34.5%, Al2O3: 7.4%, F: 10.4%, C: 9.8%, Li2O: 0.44%, R: 1.18%, melting point: 1100℃, viscosity: 0.2 Pa·s; S7) Control the starting speed V0 to start casting, and monitor the billet travel length L, where L = L0 + L t Where L0 is the initial length, which is the length of the crystallizer copper tube minus the distance from the ingot head insertion position to the upper surface of the crystallizer. t This refers to the distance the billet travels after the casting machine starts. Once the billet head has completely exited the crystallizer, the casting speed is adjusted to the crystallizer exit speed V1, where V0 ≤ V1. In this embodiment, the starting speed V0 and the crystallizer exit speed V1 are controlled as follows: when the superheat ≤ 40℃, V0 is 0.04 m / min and V1 is 0.05 m / min; when the superheat 40~60℃, V0 is 0.04 m / min and V1 is 0.04 m / min; when the superheat ≥ 60℃, combined with... Figure 13 As shown, V0 is 0.04 m / min and V1 is 0.04 m / min.

[0029] It should be noted that the above description of the technical solutions is exemplary, and this specification may be embodied in different forms and should not be construed as limiting it to the technical solutions set forth herein. Rather, providing these descriptions will ensure that the disclosure of this invention is thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Furthermore, the technical solutions of this invention are defined only by the scope of the claims.

[0030] The shapes, dimensions, ratios, angles, and figures disclosed in the description of various aspects of this specification and claims are merely examples, and therefore, this specification and claims are not limited to the details shown. In the following description, detailed descriptions of relevant known functions or configurations will be omitted where it would be determined that they unnecessarily obscure the focus of this specification and claims.

[0031] Finally, it should be noted that the above embodiments are merely representative examples of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention should be considered within the protection scope of the present invention.

Claims

1. A method for preventing leaks during continuous casting of extra-large round billets of high-alloy steel, characterized in that: Includes the following steps: S1) Send the siphon head into the crystallizer to the pouring position, seal the gap between the siphon head and the crystallizer wall with asbestos rope, and lay iron pellets above the siphon head to complete the siphon sealing operation. S2) Place the cooling frame (1) into the crystallizer, and place the hook below the cooling frame (1) into the dovetail groove of the ingot head. The cooling frame (1) includes at least three rings of circular ribs (2) and parallel straight ribs (3) welded on the ring ribs (2). S3) Weld U-shaped cold material (4) with opening upward on the annular rib (2) of the cooling frame (1), place U-shaped cold material (4) with opening downward on the straight tie (3), and put straight cold material into the dovetail groove on both sides of the hook of the cooling frame (1). S4) Set the step program parameters for the opening stopper bar opening in the continuous casting machine HMI. The step program includes: the first bar large flow stage, the flow reduction and calming stage, the slightly larger flow filling dovetail stage, the bar stage, the continued flow stage, and the completion start-up stage. The stopper bar opening and duration of each stage are preset according to the billet cross-section specifications and the superheat of the molten steel. S5) When the molten steel in the tundish reaches the casting tonnage, casting is started. The stopper rod automatically executes the stopper rod opening degree and duration of each stage according to the set step program. The molten steel is injected into the crystallizer through the submerged entry nozzle. S6) After observing that the molten steel has overflowed the upper surface of the cooling frame (1), add Li-containing protective slag into the crystallizer and complete the addition of protective slag before the casting machine starts to draw speed. S7) Control the starting speed V0 to start casting, monitor the billet travel length, and adjust the casting speed to the exit speed V1 after the billet head has completely exited the crystallizer, where V0≤V1.

2. The method for preventing leaks during continuous casting of extra-large round billets of high-alloy steel as described in claim 1, characterized in that: In step S1), the ingot head is inserted into the crystallizer at a distance of 350-400mm from the upper surface of the crystallizer. The gap sealed by the asbestos rope extends ≤3mm beyond the surface of the ingot head. The thickness of the iron particles is 8-12mm, and the area covered by the iron particles is greater than or equal to the area covered by the asbestos rope.

3. The method for preventing leaks during continuous casting of extra-large round billets of high-alloy steel as described in claim 1, characterized in that: In step S1), the asbestos rope composition by weight percentage satisfies the following: MgO: 40.0%~45.0%, SiO2: 43%~46%, H2O: 8%~12%, density = 2.5~2.53 g / cm³. 3 .

4. The method for preventing leaks during continuous casting of extra-large round billets of high-alloy steel as described in claim 1, characterized in that: In step S2), the outer dimensions of the cooling frame (1) are 40-60 mm smaller than the inner wall dimensions of the copper tube of the crystallizer, and the straight tie rod (3) is made of φ18-22 mm steel bar.

5. The method for preventing leaks during continuous casting of extra-large round billets of high-alloy steel as described in claim 1, characterized in that: In step S3), the U-shaped cold material (4) has a size of φ10mm, and the straight cold material has a size of φ20mm; the amount of cold material added for different billet cross-sectional specifications is determined as follows: The number of U-shaped cold materials (4) with a cross section of φ900mm is 145~165 pieces, and the number of straight cold materials is 40~50 pieces; The number of U-shaped cold materials (4) with a cross section of φ1000mm is 190~210 pieces, and the number of straight cold materials is 50~60 pieces; The number of U-shaped cold materials (4) with a cross section of φ1100mm is 215~235, and the number of straight cold materials is 55~65; The number of U-shaped cold materials (4) with a cross section of φ1200mm is 250~270 pieces, and the number of straight cold materials is 60~70 pieces.

6. The method for preventing leaks during continuous casting of extra-large round billets of high-alloy steel as described in claim 1, characterized in that: In step S4), after the start-up is completed, the stopper opening is reduced or increased, and after the liquid level in the crystallizer stabilizes, the stopper is switched to automatic control following the liquid level in the crystallizer.

7. The method for preventing leaks during continuous casting of extra-large round billets of high-alloy steel as described in claim 1, characterized in that: In step S5), the initial calming time is controlled according to the billet cross-sectional specifications and the superheat of the molten steel. For a φ900mm cross section, the initial calming time is 130~170s when the superheat is ≤40℃, 150~190s when the superheat is 40~60℃, and 170~210s when the superheat is ≥60℃. For a φ1000mm cross section, the initial calming time is 150~210s when the superheat is ≤40℃, 160~220s when the superheat is 40~60℃, and 180~240s when the superheat is ≥60℃. For a φ1100mm cross section, the initial calming time is 190~230s when the superheat is ≤40℃, 200~240s when the superheat is 40~60℃, and 220~260s when the superheat is ≥60℃. For a φ1200mm cross section, the initial calming time is 210~250s when the superheat is ≤40℃, 220~260s when the superheat is 40~60℃, and 230~290s when the superheat is ≥60℃.

8. The method for preventing leaks during continuous casting of extra-large round billets of high-alloy steel as described in claim 1, characterized in that: In step S6), the physicochemical properties of the Li-containing protective slag, by weight percentage, meet the following requirements: For the P91 series, SiO2: 23.5%~33.5%, CaO: 25%~35%, Al2O3: 0.5%~7.5%, F: 5.5%~10.5%, C: 2.0%~10.0%, Li2O: 0.15%~0.45%, R: 0.90%~1.20%, melting point: 1020℃~1120℃, viscosity: 0.15Pa.s~0.25Pa.s; For the H13 series, SiO2: 22.0%~30.0%, CaO: 25.2%~33.2%, Al2O3: 5.0%~12.0%, F: ≤4.0%, C: 11.0%~19.0%, Li2O: 0.10%~0.20%, R: 1.00%~1.20%, melting point: 1100℃~1200℃, viscosity: 0.50Pa.s~1.00Pa.s.

9. The method for preventing leaks during continuous casting of extra-large round billets of high-alloy steel as described in claim 1, characterized in that: In step S7), the initial casting speed V0 and the casting speed V1 exiting the crystallizer are controlled according to the billet cross-sectional specifications and the superheat of the molten steel in the following manner: For a φ900mm cross-section, V0 is 0.05m / min and V1 is 0.08m / min when the superheat is ≤40℃; V0 is 0.05m / min and V1 is 0.07m / min when the superheat is 40~60℃; and V0 is 0.05m / min and V1 is 0.06m / min when the superheat is ≥60℃. For a φ1000mm cross-section, V0 is 0.05m / min and V1 is 0.07m / min when the superheat is ≤40℃; V0 is 0.05m / min and V1 is 0.06m / min when the superheat is 40~60℃; and V0 is 0.05m / min and V1 is 0.05m / min when the superheat is ≥60℃. For a φ1100mm cross-section, V0 is 0.04m / min and V1 is 0.06m / min when the superheat is ≤40℃; V0 is 0.04m / min and V1 is 0.05m / min when the superheat is 40~60℃; and V0 is 0.04m / min and V1 is 0.04m / min when the superheat is ≥60℃. For a φ1200mm cross section, V0 is 0.04m / min and V1 is 0.05m / min when the superheat is ≤40℃; V0 is 0.04m / min and V1 is 0.04m / min when the superheat is 40~60℃; and V0 is 0.04m / min and V1 is 0.04m / min when the superheat is ≥60℃.

10. The method for preventing leaks during continuous casting of extra-large round billets of high-alloy steel as described in claim 1, characterized in that: In step S7), the billet travel length L is calculated as follows: L = L0 + L t Where L0 is the initial length, which is the length of the crystallizer copper tube minus the distance from the ingot head insertion position to the upper surface of the crystallizer. t This refers to the distance the billet travels after the casting machine starts.

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