Method for improving the tapping self-conductivity of vacuum-treated steel

Abstract

This invention belongs to the field of steelmaking technology and relates to a method for improving the self-priming rate of vacuum-treated steel during casting. The composition of the guiding sand is: Cr2O3: 25%-35%, MgO: 5%-10%, Al2O3: 15%-20%, Fe2O3: 15%-30%, SiO2: 17%-30%, CaO: ≤0.2%. 8%-10% of potassium feldspar is added by weight of the guiding sand. The particle size of the guiding sand is 15% between 0.2-0.4 mm, 75% between 0.4-1.0 mm, and 10% between 1.0-1.2 mm. Based on the specific composition of the guiding sand, this invention, in conjunction with precise control of the guiding sand particle size, the inner cavity size of the ladle's top nozzle, the amount of potassium feldspar, and the ladle's bottom-blowing argon flow rate, effectively prevents adhesion and improves the self-priming rate of steel grades produced in long-process (converter + LF + RH vacuum degassing + continuous casting) steels with long production cycles.

Description

Technical Field

[0001] This invention belongs to the field of steelmaking technology and relates to a method for improving the self-ignition rate of vacuum-treated steel during casting. Background Technology

[0002] Improving the self-priming rate during the opening of the ladle in continuous casting has always been a challenge for steel producers. The success rate is influenced by various factors, such as the quality of the priming sand, the sand-pouring operation, the ladle temperature, and the opening operation. Furthermore, the self-priming rate can vary significantly depending on the steel grade, especially for some grades (such as bearing steel, gear steel, and high-manganese steel), which require both ladle furnace (LF) treatment and vacuum degassing (e.g., RH). This results in a long time for the molten steel in the ladle, typically 2.5-3.5 hours, and sometimes exceeding 4 hours. Prolonged contact between the priming sand and the molten steel can lead to the formation of a thick sintered layer, or the molten steel seeping into the priming sand, creating cold steel that prevents the gate from opening automatically during casting. This necessitates manual oxygen burning to open the gate, causing steel quality contamination and even the risk of interrupted casting. Therefore, compared to steel grades that only require ladle furnace smelting, the self-priming rate for steel grades requiring vacuum treatment is generally lower, typically only 96%-98%.

[0003] In pursuit of higher self-opening rates for vacuum-treated steel, many metallurgical enterprises and researchers have conducted varying degrees of research on key aspects affecting casting self-opening rates. Patent CN201911028737.3 discloses a method to improve the self-opening rate of the guiding sand. This involves adding a nitrogen purging component to the guiding sand addition device to form a sealed space, ensuring the guiding sand is dry and pure. Simultaneously, a positioning bracket is added to the ladle's top nozzle to control the uniform addition of the guiding sand, thereby stabilizing the ladle's self-opening rate. Patent CN201810564619.3 discloses a method to improve the ladle's self-opening rate by adding bottom-blowing inert gas. When the previous heat of steel in the working position is about to finish pouring (5-8 minutes before the end of pouring), inert gas is introduced into the molten steel in the ladle in the standby position through the ventilated nozzle seat brick at the bottom of the ladle. This raises the temperature of the molten steel within 30cm directly above the ventilated nozzle seat brick by 3-5°C, resulting in a more uniform temperature of the molten steel in the ladle. After the ladle rotates to the working position, the sliding gate is opened, the inert gas supply is stopped, and normal pouring begins. This invention effectively prevents the molten steel freezing layer above the sintered layer of the guide sand from thickening, reduces the thickness of the crust layer above the gate, and ensures that the molten steel can break through the crust layer at the gate to achieve automatic pouring, thus improving the self-opening rate of molten steel. Patent CN201910068094.9 discloses a method for controlling the construction of the ladle gate seat bricks, controlling the addition of guide sand, and controlling the hot repair process of the ladle. After the ladle gate seat bricks are constructed, the upper edge of the ladle gate seat bricks is ensured to be at the same level as the bottom of the ladle. Before tapping, after the guide sand is filled in the ladle gate, the guide sand forms a bun-shaped protrusion on the upper surface. The online baking time of the ladle before tapping is ensured to be ≥15min and the temperature ≥800℃. Patent CN201811618664.9 discloses a method for controlling the self-opening rate of a steel ladle, including the selection of chromium-based guiding sand, ladle design process, ladle baking process, ladle repair process, converter smelting process, steel tapping process, and ladle turnover process. The chromium-based guiding sand is made of chromite and additives. The chromite includes the following components by weight percentage: Cr2O3 35%-45%, FeO 12%-15%, MgO 15%-23%, Al2O3 8%-15%, SiO2 2%-12%. The additive is graphite, and the mass of graphite added is 6%-9% of the mass of chromite. Patent CN201721165879.0 discloses a device for improving the self-opening rate of a ladle, including a cover and a hook; the hook is on the top of the cover; the cover is conical or pyramidal, the conical cover is composed of 1-2 steel plates, and the pyramidal cover is composed of 5-8 steel plates, the steel plates being made of steel or iron, which can effectively improve the self-opening rate of the ladle and the quality of the cast billet. Patent CN200720100946.0 discloses a ladle nozzle device that can improve the self-opening rate, used to solve the problem that the guide sand cannot flow down after the slide plate opens during the first two uses of the ladle nozzle.This utility model changes the shape of the ladle's upper nozzle from a top-large, bottom-small shape to a conical hole with a top-small, bottom-large shape, and designs a reasonable size for the hole diameter. After the improvement, the lower diameter is larger, eliminating the problem of drainage sand accumulating at the lower opening and being unable to flow down naturally due to compression. This solves the problem of molten steel not opening on its own in the first two uses. After using this utility model, the self-opening rate of molten steel in the second two uses reaches 98.5%, significantly higher than the 89% level before the improvement. Patent CN202120732832.8 discloses a seat brick structure for improving the self-opening rate of a ladle, including a seat brick component, a bowl brick component, and a bottom casting layer. By adding a bowl brick component to replace the original formwork structure, the height difference between the bottom casting layer and the seat brick component is compensated, making it less likely for steel slag to be generated and flow back into the nozzle seat brick channel, thus improving the self-opening rate of the ladle. Furthermore, since the material and performance of the bowl brick component are similar to those of the seat brick component, the structure of the seat brick component is guaranteed without affecting the normal use effect of the bottom casting layer. Although much research has been conducted on improving the self-opening rate during molten steel casting, the methods described above have several shortcomings: 1. Increasing the self-opening rate by adding equipment or operations increases costs and complicates worker operations; 2. Only a single influencing factor is considered, without a systematic and comprehensive approach addressing the problem from multiple key aspects; 3. Increasing the Cr2O3 content in the quenching sand increases the manufacturing cost of the quenching sand; 4. The problem of low self-opening rate still exists for vacuum-treated steel grades (where the molten steel soaking time is long).

[0004] Patent CN103537661A discloses a chromium-based ladle-opening sand and its production process for improving the ladle self-opening rate. The key points emphasized are: 1. The ladle-opening sand is mainly used for stainless steel production. A typical stainless steel production process is converter + continuous casting, with a short production cycle of approximately 2.5-3.0 hours per heat. However, the ladle-opening sand described in this patent is not suitable for steel grades produced by converter + LF + RH vacuum degassing + continuous casting. This is because such steel grades, such as bearing steel, have a long production cycle of approximately 3.5-4.5 hours per heat. The longer the production cycle, the lower the self-opening rate, and the more difficult it is to improve the self-opening rate. Furthermore, the ladle-opening sand in this patent requires the addition of a certain amount of ultrafine graphite, resulting in a chromium sand (chromium trioxide) content of 60%-75%, which increases the cost. Moreover, a high chromium sand content results in a high melting point for the ladle-opening sand, making it unsuitable for steel grades with long production processes.

[0005] Patent CN104148625A discloses a method for preparing refined chromium-based guiding sand. Although the guiding sand is chromium-based, its chromium trioxide (Cr2O3) content is as high as 60% or more, resulting in high costs. Moreover, the guiding sand has a high melting point and is only suitable for steel grades with a molten steel holding time (i.e., ladle production cycle) of more than 2 hours. However, the current production process for steels such as bearing steel is long, involving converter + LF + RH vacuum degassing + continuous casting, with a molten steel holding time of 3.5-4.5 hours (the longer the time, the lower the self-opening rate). Therefore, the guiding sand in this patent is not suitable for the production needs of special steels that have undergone RH vacuum degassing.

[0006] Patent CN104311049A discloses a method for preparing silica-based guiding sand. The silica-based guiding sand will cause a large volume expansion at temperatures above 1200℃, which will increase the adhesion between the sand and the inner wall of the nozzle, making it difficult for the sand to fall freely during the initial pouring and resulting in poor natural fluidity. This type of guiding sand is only suitable for ordinary steel grades with low self-opening rate (self-opening rate). The self-opening rate is usually low (this type of guiding sand can only reach 93% self-opening rate), and it cannot meet the requirements of high-grade special steel (long production process and long ladle turnover cycle).

[0007] Patent CN110407588A discloses a method for preparing a far-infrared glaze-coated guiding sand. This method involves adding a far-infrared glaze layer to the guiding sand, with components including molybdenum disilicide, 5 parts calcium silicate, 7 parts lithium carbonate, and 50 parts zirconium oxide, which significantly increases the cost of the guiding sand. Secondly, although its self-attraction rate reaches over 99.5%, the molten steel transfer time does not exceed 2 hours, making it impossible to predict the self-attraction rate for longer molten steel transfer times. Summary of the Invention

[0008] This invention provides a method for improving the self-drawing rate of vacuum-treated steel during casting. The guiding sand of this invention is used for steel grades such as bearing steel in converter + LF + RH vacuum degassing + continuous casting. The production cycle is long, about 3.5-4.5 hours per heat. Moreover, the self-drawing rate of vacuum-treated steel grades can be increased from the current 96%-98% to more than 99.5%.

[0009] The guiding sand involved in this invention has the following composition: Cr2O3: 25%-35%, MgO: 5%-10%, Al2O3: 15%-20%, Fe2O3: 15%-30%, SiO2: 17%-30%, CaO: ≤0.2%; 8%-10% potassium feldspar is added by weight of the guiding sand. The particle size of the guiding sand is 15% between 0.2-0.4 mm, 75% between 0.4-1.0 mm, and 10% between 1.0-1.2 mm. The low Cr2O3 content allows the melting point of the guiding sand to be within a more reasonable range, offering advantages such as low cost and low melting point, making it more suitable for steel grades with long ladling times (long production processes), such as bearing steel.

[0010] This invention also provides a method for improving the self-priming rate of vacuum-treated steel during initial casting, comprising:

[0011] 1) The inner dimensions of the ladle nozzle seat brick and the inlet nozzle were optimized, and the slope of the conical inner cavity of the inlet nozzle was increased from 5° to 10°. This makes the downward flow of the diverting sand smoother and avoids blockage in the middle during the falling process.

[0012] 2) Strictly control the baking temperature of the ladle to ensure that the ladle wall temperature reaches 800℃ (preferably above 850℃). If the ladle experiences a long waiting time during operation, it must be taken to the baking station for re-baking to ensure that the temperature meets the requirements.

[0013] 3) After each ladle reaches the hot repair position, clean the cold steel and slag on the nozzle to ensure that the nozzle is a regular trumpet shape.

[0014] 4) After the ladle is moved to the receiving position, turn on the argon gas at the bottom of the ladle to ensure that the argon gas flow rate is not less than 100L / min.

[0015] The properties of the guiding sand vary greatly depending on its composition, which also affects the self-drawing rate. This invention, based on the specific composition of the guiding sand, coordinates precise control of the guiding sand particle size, the inner cavity size of the ladle top nozzle, the amount of potassium feldspar, and the ladle bottom blowing argon flow rate. This can effectively prevent adhesion and improve the self-drawing rate of steel grades with long production cycles in long processes such as converter + LF + RH vacuum degassing + continuous casting.

[0016] Furthermore, the moisture content of the drainage sand is below 0.03%. Specific control methods include: vacuum packaging the drainage sand after manufacturing to prevent moisture from entering and causing the moisture content of the drainage sand to increase; at the same time, the drainage sand is laid flat on the platform of the sand filling position and baked by the heat absorbed by the steel ladle on the platform to further ensure that the moisture content of the drainage sand reaches the minimum, below 0.03%.

[0017] Furthermore, the ladle should be moved to the receiving position with sufficient accuracy to avoid the alloy added to the bottom of the ladle falling directly onto the guide sand, which would damage the sintered layer formed on the surface of the guide sand.

[0018] Furthermore, after the ladle is hoisted to the pouring position, the slide plate is opened quickly in one go, so that the static pressure of the molten steel is applied to the guide sand instantly, avoiding the phenomenon of the guide sand falling unevenly or forming cold steel, and avoiding the formation of sticky cold steel due to insufficient steel flow during the opening of the slide plate.

[0019] For steel grades with long process flows (such as the LF+RH process), the long contact time between molten steel and the guide sand can lead to the formation of a thick sintered layer, preventing the molten steel from automatically breaking under static pressure during casting; or the molten steel may seep into the guide sand, forming cold steel that also prevents automatic opening. This invention adds an appropriate amount of potassium feldspar to the guide sand to prevent the formation of a thick sintered layer on the surface of the guide sand or the seepage of molten steel into the guide sand. Using the guide sand and operating method provided by this invention, the self-priming rate of the ladle during continuous casting can be effectively and stably guaranteed. The self-priming rate of vacuum-treated steel grades is increased from the current 96%-98% to over 99.5%, and the self-priming rate of steel grades without RH treatment is basically 100%. Attached image description:

[0020] Figure 1 The shape of the sprue cavity before and after improvement; Detailed implementation method:

[0021] The present invention will be further described below through specific embodiments, but should not be construed as limiting the invention. Those skilled in the art can make various modifications, substitutions, and alterations based on the above solutions. All modifications, substitutions, and alterations based on the above technical concept fall within the scope of the present invention.

[0022] The guiding sand involved in this invention has the following composition: Cr2O3: 25%-35%, MgO: 5%-10%, Al2O3: 10%-20%, Fe2O3: 15%-30%, SiO2: 17%-30%, CaO: ≤0.2%. An appropriate amount of 8%-10% potassium feldspar is added to form a glassy film on the surface of the guiding sand, preventing the formation of a thick sintered layer or the penetration of molten steel into the guiding sand. The K2O content in the potassium feldspar is not less than 6%. The Cr2O3 content is controlled at 28%-35% to keep the melting point of the guiding sand within a more reasonable range. High-quality carbon black with a flash point below 900℃ is used to form a high-quality sintered layer of moderate thickness on the surface of the guiding sand. The particle size of the guiding sand is 15% between 0.2-0.4 mm, 75% between 0.4-1.0 mm, and 10% between 1.0-1.2 mm.

[0023] The drainage sand is vacuum-packed before leaving the factory. During transportation, the packaging must not be damaged and must not be exposed to rain. After being placed in the sand filling position, it is laid flat on the platform, and the residual heat of the platform is used to bake the drainage sand to ensure that the moisture content of the drainage sand is minimized. The moisture content is sampled and tested to ensure that it is below 0.03%.

[0024] The internal dimensions of the ladle nozzle seat brick and the inlet nozzle were optimized, increasing the slope of the conical inner cavity of the inlet nozzle from 5° to 10°. This makes the channel for the diverting sand flow smoother and prevents blockages during its descent. See the diagram for the internal cavities of the nozzle before and after the improvement. Figure 1.

[0025] The baking process of the steel ladle must be strictly controlled. The baking temperature of the steel ladle during operation must be high. If the waiting time of the steel ladle during operation is long, it must be taken to the baking position for re-baking to ensure that the temperature is not lower than 800℃ (preferably 850℃).

[0026] After each ladle reaches the hot repair position, the cold steel and slag on the nozzle are cleaned to ensure the nozzle is a regular trumpet shape. The cleaned residue is then poured out of the ladle to prevent contamination of the guide sand after the ladle is set up.

[0027] The guide sand poured into the ladle should form a regular "bun" shape, ensuring it is free of impurities. The ladle car should be started and the ladle slowly moved to the receiving position. The ladle must be moved accurately to avoid the added alloy falling directly onto the guide sand, damaging the sintered layer formed on its surface. After the ladle is in the receiving position, the argon gas at the bottom of the ladle should be turned on, ensuring a flow rate of 100-150 L / min. After the steel has passed through the ladle furnace (LF) and vacuum treatment (RH), it should be hoisted onto the ladle turret. Once the ladle is rotated to the pouring position, the slide gate should be opened quickly and in one go, allowing the static pressure of the molten steel to act instantly on the guide sand, preventing insufficient steel flow during the slide gate opening process and thus avoiding the formation of cold, stuck steel.

[0028] Example 1:

[0029] For special steel grades that have undergone converter + LF + RH vacuum degassing + continuous casting, such as bearing steel and gear steel, the composition of the guiding sand is: Cr2O3: 25.4%, MgO: 6%, Al2O3: 17%, Fe2O3: 25%, SiO2: 17.4%, CaO: ≤0.2%; the amount of potassium feldspar added is 10% of the guiding sand mass. High-quality carbon black with an ignition point of less than 900℃ is used. The particle size of the guiding sand is 15% between 0.2-0.4mm, 75% between 0.4-1.0mm, and 10% between 1.0-1.2mm. The guiding sand is vacuum packaged and baked before leaving the factory to ensure that the moisture content is minimized. Moisture content is sampled and tested to ensure that it is below 0.03%. The inclination of the conical inner cavity of the inlet is 10°; the baking temperature is 855℃. After the ladle is moved to the receiving position, the argon gas at the bottom of the ladle should be turned on at a rate of 120 L / min. Statistics show that the self-priming rate during casting is 99.71%.

[0030] Example 2:

[0031] For special steel grades that have undergone converter + LF + RH vacuum degassing + continuous casting, such as bearing steel and gear steel, the composition of the guide sand is: Cr2O3: 31%, MgO: 6%, Al2O3: 17%, Fe2O3: 24%, SiO2: 17%, CaO: ≤0.2%; the amount of potassium feldspar added is 10% of the guide sand mass. High-quality carbon black with an ignition point of less than 900℃ is used. The particle size of the guide sand is 15% between 0.2-0.4mm, 75% between 0.4-1.0mm, and 10% between 1.0-1.2mm. Before leaving the factory, the guide sand is vacuum packaged and baked to ensure that the moisture content is minimized. Moisture content is sampled and tested to ensure that it is below 0.03%. The inclination of the conical inner cavity of the inlet is 10°; the baking temperature is 855℃. After the ladle is moved to the receiving position, the argon gas at the bottom of the ladle should be turned on at 120L / min. Statistics show that the self-priming rate during casting is 99.83%.

[0032] Example 3:

[0033] For special steel grades that have undergone converter + LF + RH vacuum degassing + continuous casting, such as bearing steel and gear steel, the composition of the guiding sand is: Cr2O3: 34.6%, MgO: 6%, Al2O3: 16.3%, Fe2O3: 23.3%, SiO2: 16.7%, CaO: ≤0.2%; the amount of potassium feldspar added is 10% of the guiding sand mass. High-quality carbon black with an ignition point of less than 900℃ is used. The particle size of the guiding sand is 15% between 0.2-0.4mm, 75% between 0.4-1.0mm, and 10% between 1.0-1.2mm. The guiding sand is vacuum packaged and baked before leaving the factory to ensure that the moisture content is minimized. Moisture content is sampled and tested to ensure that it is below 0.03%. The inclination of the conical inner cavity of the inlet is 10°; the baking temperature is 855℃. After the ladle is moved to the receiving position, the argon gas at the bottom of the ladle should be turned on at a rate of 120 L / min. Statistics show that the self-ignition rate during casting is 99.87%.

[0034] Example 4:

[0035] For special steel grades that have undergone converter + LF + RH vacuum degassing + continuous casting, such as bearing steel and gear steel, the composition of the guide sand is: Cr2O3: 29%, MgO: 8%, Al2O3: 18%, Fe2O3: 21%, SiO2: 18%, CaO: ≤0.2%; with 8% potassium feldspar added. High-quality carbon black with an ignition point below 900℃ is used. The particle size of the guide sand is 15% between 0.2-0.4mm, 75% between 0.4-1.0mm, and 10% between 1.0-1.2mm. Before leaving the factory, the guide sand is vacuum packaged and baked to ensure that the moisture content is minimized; the moisture content is sampled and tested to ensure it is below 0.03%. The inclination of the conical inner cavity of the inlet is 10°; the baking temperature is 850℃. After the ladle is moved to the receiving position, the argon gas at the bottom of the ladle should be turned on at 100-150L / min. Statistics show that the self-priming rate during casting is 99.77%.

[0036] Example 5:

[0037] For special steel grades that have undergone converter + LF + RH vacuum degassing + continuous casting, such as bearing steel and gear steel, the composition of the guide sand is: Cr2O3: 29.9%, MgO: 8%, Al2O3: 18.4%, Fe2O3: 20.6%, SiO2: 18%, CaO: ≤0.2%; with 8% potassium feldspar added. High-quality carbon black with an ignition point below 900℃ is used. The particle size of the guide sand is 15% between 0.2-0.4mm, 75% between 0.4-1.0mm, and 10% between 1.0-1.2mm. Before leaving the factory, the guide sand is vacuum packaged and baked to ensure that the moisture content is minimized; the moisture content is sampled and tested to ensure it is below 0.03%. The inclination of the conical inner cavity of the inlet is 10°; the baking temperature is 871℃. After the ladle is moved to the receiving position, the argon gas at the bottom of the ladle should be turned on at 100-150L / min. Statistics show that the self-priming rate during casting is 99.71%.

[0038] Example 6:

[0039] For special steel grades that have undergone converter + LF + RH vacuum degassing + continuous casting, such as bearing steel and gear steel, the composition of the guide sand is: Cr2O3: 28.7%, MgO: 8.2%, Al2O3: 18.1%, Fe2O3: 20%, SiO2: 18%, CaO: ≤0.2%; with 8% potassium feldspar added. High-quality carbon black with an ignition point below 900℃ is used. The particle size of the guide sand is 15% between 0.2-0.4mm, 75% between 0.4-1.0mm, and 10% between 1.0-1.2mm. Before leaving the factory, the guide sand is vacuum packaged and baked to ensure that the moisture content is minimized; the moisture content is sampled and tested to ensure it is below 0.03%. The inclination of the conical inner cavity of the inlet is 10°; the baking temperature is 879℃. After the ladle is moved to the receiving position, the argon gas at the bottom of the ladle should be turned on at 100-150L / min. Statistics show that the self-priming rate during casting is 99.81%.

[0040] Example 7:

[0041] For special steel grades that have undergone converter + LF + RH vacuum degassing + continuous casting, such as bearing steel and gear steel, the composition of the guide sand is: Cr2O3: 28.0%, MgO: 8.0%, Al2O3: 18.1%, Fe2O3: 20%, SiO2: 18%, CaO: ≤0.2%; with 8% potassium feldspar added. High-quality carbon black with an ignition point below 900℃ is used. The particle size of the guide sand is 25% between 0.2-0.4mm, 65% between 0.4-1.0mm, and 10% between 1.0-1.2mm. Before leaving the factory, the guide sand is vacuum packaged and baked to ensure that the moisture content is minimized; the moisture content is sampled and tested to ensure it is below 0.03%. The inclination of the conical inner cavity of the inlet is 10°; the baking temperature is 860℃. After the ladle is moved to the receiving position, the argon gas at the bottom of the ladle should be turned on at 100-150L / min. Statistics show that the self-priming rate during casting is 99.80%.

[0042] Example 8:

[0043] For special steel grades that have undergone converter + LF + RH vacuum degassing + continuous casting, such as bearing steel and gear steel, the composition of the guiding sand is: Cr2O3: 28.3%, MgO: 8.0%, Al2O3: 18.0%, Fe2O3: 20.10%, SiO2: 18%, CaO: ≤0.2%; with 8% potassium feldspar added. High-quality carbon black with an ignition point below 900℃ is used. The particle size of the guiding sand is 15% between 0.2-0.4mm, 65% between 0.4-1.0mm, and 20% between 1.0-1.2mm. The guiding sand is vacuum-packed and baked before leaving the factory to ensure that the moisture content is minimized; the moisture content is sampled and tested to ensure that it is below 0.03%. The inclination of the conical inner cavity of the inlet is 10°; the baking temperature is 860℃. After the ladle is moved to the receiving position, the argon gas at the bottom of the ladle should be turned on at a rate of 100-150 L / min. Statistics show that the self-ignition rate during casting is 99.60%.

[0044] Example 9:

[0045] For special steel grades that have undergone converter + LF + RH vacuum degassing + continuous casting, such as bearing steel and gear steel, the composition of the guide sand is: Cr2O3: 31.0%, MgO: 8.0%, Al2O3: 16.0%, Fe2O3: 18.10%, SiO2: 18%, CaO: ≤0.2%; with 8% potassium feldspar added. High-quality carbon black with an ignition point below 900℃ is used. The particle size of the guide sand is 15% between 0.2-0.4mm, 75% between 0.4-1.0mm, and 10% between 1.0-1.2mm. Before leaving the factory, the guide sand is vacuum packaged and baked to ensure that the moisture content is minimized; the moisture content is sampled and tested to ensure it is below 0.03%. The inclination of the conical inner cavity of the inlet is 10°; the baking temperature is 865℃. After the ladle is moved to the receiving position, the argon gas at the bottom of the ladle should be turned on at a rate of 100-150 L / min. Statistics show that the self-ignition rate during casting is 99.64%.

[0046] Example 10:

[0047] For special steel grades that have undergone converter + LF + RH vacuum degassing + continuous casting, such as bearing steel and gear steel, the composition of the guide sand is: Cr2O3: 31.0%, MgO: 8.4%, Al2O3: 16.0%, Fe2O3: 18.00%, SiO2: 17.5%, CaO: ≤0.2%; with 9% potassium feldspar added. High-quality carbon black with an ignition point below 900℃ is used. The particle size of the guide sand is 15% between 0.2-0.4mm, 75% between 0.4-1.0mm, and 10% between 1.0-1.2mm. The guide sand is vacuum-packed and baked before leaving the factory to ensure that the moisture content is minimized; the moisture content is sampled and tested to ensure that it is below 0.03%. The inclination of the conical inner cavity of the inlet is 10°; the baking temperature is 865℃. After the ladle is moved to the receiving position, the argon gas at the bottom of the ladle should be turned on at a rate of 100-150 L / min. Statistics show that the self-ignition rate during casting is 99.75%.

[0048] Example 11:

[0049] For special steel grades that have undergone converter + LF + RH vacuum degassing + continuous casting, such as bearing steel and gear steel, the composition of the guiding sand is: Cr2O3: 31.4%, MgO: 8.0%, Al2O3: 16.4%, Fe2O3: 18.00%, SiO2: 17.6%, CaO: ≤0.2%; with 10% potassium feldspar added. High-quality carbon black with an ignition point below 900℃ is used. The particle size of the guiding sand is 15% between 0.2-0.4mm, 75% between 0.4-1.0mm, and 10% between 1.0-1.2mm. The guiding sand is vacuum-packed and baked before leaving the factory to ensure that the moisture content is minimized; the moisture content is sampled and tested to ensure that it is below 0.03%. The inclination of the conical inner cavity of the inlet is 10°; the baking temperature is 865℃. After the ladle is moved to the receiving position, the argon gas at the bottom of the ladle should be turned on at a rate of 100-150 L / min. Statistics show that the self-ignition rate during casting is 99.79%.

[0050] Comparative Example 1:

[0051] For special steel grades that undergo converter + LF + RH vacuum degassing + continuous casting, such as bearing steel and gear steel, the composition of the guiding sand is: Cr2O3: 37%, MgO: 6%, Al2O3: 16%, Fe2O3: 20%, SiO2: 19%, CaO: ≤0.2%; no potassium feldspar. Ordinary carbon black is used. The guiding sand particle size is 100% between 0.5-1.2mm, of which: 20% are between 0.2-0.4mm, 70% are between 0.4-1.0mm, and 10% are between 1.0-1.2mm. The moisture content of the guiding sand is approximately 0.5%. The inclination of the conical inner cavity of the upper nozzle is 5°; the baking temperature is 600-700℃. After the ladle is moved to the receiving position, the argon gas at the bottom of the ladle should be turned on, with an argon gas flow rate of 50-100L / min. Statistically, the self-priming rate during casting is 96.33%.

[0052] Comparative Example 2:

[0053] For special steel grades that have undergone converter + LF + RH vacuum degassing + continuous casting, such as bearing steel and gear steel, the composition of the guiding sand is: Cr2O3: 36%, MgO: 7%, Al2O3: 16%, Fe2O3: 22%, SiO2: 20%, CaO: ≤0.2%; free of potassium feldspar. High-quality carbon black with an ignition point below 900℃ is used. 100% of the guiding sand has a particle size between 0.2-0.8mm, of which: 15% is between 0.2-0.4mm, 65% is between 0.4-1.0mm, and 20% is between 1.0-1.2mm. The guiding sand is vacuum-packed and baked before leaving the factory to ensure minimal moisture content; moisture is sampled and tested to ensure it is below 0.03%. The inclination of the conical inner cavity of the inlet is 5°; the baking temperature is 650-700℃. After the ladle is moved to the receiving position, the argon gas at the bottom of the ladle should be turned on at a rate of 100-150 L / min. Statistics show that the self-ignition rate during casting is 97.55%.

[0054] Comparative Example 3: For special steel grades processed by converter + LF + RH vacuum degassing + continuous casting, such as bearing steel and gear steel; the composition of the guiding sand is Cr2O3: 31%, MgO: 7%, Al2O3: 15%, Fe2O3: 21%, SiO2: 20%, CaO: ≤0.2%; with 8% potassium feldspar added. High-quality carbon black with an ignition point below 900℃ is used. 100% of the guiding sand has a particle size between 0.5-1.2mm, of which 15% is between 0.2-0.4mm, 75% is between 0.4-1.0mm, and 10% is between 1.0-1.2mm. The guiding sand is vacuum-packed and baked before leaving the factory to ensure minimal moisture content; moisture is sampled and tested to ensure it is below 0.03%. The inclination of the conical inner cavity of the inlet is 5°; the baking temperature is 650-700℃. After the ladle is moved to the receiving position, the argon gas at the bottom of the ladle should be turned on at a rate of 120 L / min. Statistics show that the self-ignition rate during casting is 98.74%.

[0055] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for improving the self-priming rate of vacuum-treated steel during initial casting, wherein the guiding sand is used for steel grades produced in a converter + LF + RH vacuum degassing + continuous casting process, with a production cycle of 3.5-4.5 hours per heat, characterized in that: The composition of the diversion sand is as follows: Cr2O3: 25%-35%, MgO: 5%-10%, Al2O3: 15%-20%, Fe2O3: 15%-30%, SiO2: 17%-30%, CaO: ≤0.2%; 8%-10% potassium feldspar is added by weight of the diversion sand; the particle size of the diversion sand is 15% between 0.2-0.4 mm, 75% between 0.4-1.0 mm, and 10% between 1.0-1.2 mm. The moisture content of the diversion sand is less than 0.03%; the K2O content in potassium feldspar is not less than 6%; and carbon black with an ignition point of less than 900℃ is used. The methods to improve the self-priming rate of vacuum-treated steel include the following steps: 1) Adjust the inclination of the conical inner cavity of the ladle nozzle seat brick to 10°; 2) Control the baking temperature of the ladle to ensure that the ladle wall temperature reaches above 800℃; 3) After each ladle reaches the hot repair position, clean the cold steel and slag on the nozzle to ensure that the nozzle is a regular trumpet shape; 4) After the ladle is moved to the receiving position, turn on the argon gas at the bottom of the ladle and control the argon gas flow rate to be no less than 100L / min; After the steel has passed through the LF furnace and the RH vacuum treatment, it is hoisted to the ladle turret. After the ladle is rotated to the pouring position, the slide plate is opened quickly in one go, so that the static pressure of the molten steel is applied to the guide sand instantly.

2. The method for improving the self-priming rate of vacuum-treated steel according to claim 1, characterized in that: In step 2), the temperature of the outer wall reaches above 850℃.

3. The method for improving the self-priming rate of vacuum-treated steel according to claim 1, characterized in that: In step 4), the argon flow rate in the ladle is 100-150 L / min.

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