A method for controlling surface and subsurface bubbles of a continuous casting billet for high carbon steel wire rod

Abstract

The present application relates to the technical field of steelmaking continuous casting, and particularly relates to a method for controlling surface and subsurface bubbles of a continuous casting billet for high-carbon steel wire rod, which comprises: in the continuous casting process for producing the continuous casting billet for high-carbon steel wire rod, controlling the total slag layer thickness of the mold powder to be 50-60 mm, the liquid slag layer thickness of the mold powder to be 2-3 mm, the electromagnetic induction intensity of the meniscus position of the molten steel in the mold to be 20-30 mT, and the oxygen content in the molten steel to be less than or equal to 0.0025%. By the method, the CO bubble defects on the surface and subsurface of the high-carbon steel continuous casting billet due to the carbon and oxygen in the molten steel can be significantly reduced without increasing the smelting cost and affecting the metal yield of the continuous casting billet, the surface and subsurface bubble occurrence rate is reduced to less than or equal to 10%, and thus the product quality is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of continuous casting technology in steelmaking, specifically to a method for controlling surface and subcutaneous air bubbles in continuous casting billets for high-carbon steel wire rods. Background Technology

[0002] High-carbon steel wire rods with a carbon content of 0.72-1.00% are widely used in automotive, machinery, bridge, and other technical fields. Due to the special nature of their applications, strict requirements are placed on the surface and subsurface quality of the continuously cast billets used in their production. However, defects such as inclusions, cracks, and bubbles are often found on the surface and subsurface of these billets. Specifically, during the solidification process of molten steel, bubbles are generated when the partial pressures of CO, H, and N gases produced by the reaction of carbon and oxygen in the steel exceed the sum of the static pressure of the molten steel and the atmospheric pressure. If these bubbles are blocked by the solidified surface layer or captured by dendrites, they will form bubbles on the surface and subsurface of the continuously cast billet. Since some of these surface and subsurface bubbles cannot be rolled together during the rolling process, defects such as scale, cracks, and folds will appear on the surface of the wire rod, thus affecting its performance. Therefore, it is necessary to control the surface and subsurface bubbles of the continuously cast billets used for high-carbon steel wire rods.

[0003] Chinese patent document CN102634728A discloses a continuous casting process for small square billets of Fe-Mn-C series high-manganese steel. This process primarily employs a full-process protective casting method to prevent secondary oxidation of the molten steel by air and the resulting defects such as subcutaneous bubbles, slag inclusions, and impurities. Furthermore, electromagnetic stirring in the crystallizer promotes the flotation and removal of gases and inclusions in the molten steel, breaking up dendrites and delaying grain engulfment and growth. However, the controlled bubbles are primarily those caused by secondary oxidation of the molten steel. A key challenge remains to reduce the occurrence of CO bubbles formed by carbon and oxygen in the molten steel itself on the surface and subsurface of the high-carbon steel continuous casting billet, keeping the rate below 10% without increasing smelting costs or affecting the metal yield of the continuous casting billet. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the inability of existing continuous casting production processes to reduce the occurrence of CO bubbles formed by carbon and oxygen in the surface and subsurface of high carbon steel continuous casting billets without increasing smelting costs or affecting the metal yield of continuous casting billets, and to control the occurrence rate to within 10%. Thus, a method for controlling bubbles on the surface and subsurface of high carbon steel wire rod continuous casting billets is provided to solve the above problem.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for controlling surface and subcutaneous air bubbles in continuously cast billets for high-carbon steel wire rod includes: in the continuous casting process for producing continuously cast billets for high-carbon steel wire rod, controlling the total slag layer thickness of the protective slag in the mold to be 50-60 mm, the liquid slag layer thickness of the protective slag in the mold to be 2-3 mm, the electromagnetic induction intensity at the meniscus position of the molten steel in the mold to be 20-30 mT, and the oxygen content in the molten steel to be ≤0.0025%.

[0007] Preferably, the depth of the oscillation marks on the continuously cast billet is 70-180 μm;

[0008] And / or, the solidification hook depth of the continuously cast billet is 180-350μm;

[0009] And / or, the thickness of the protective slag ring on the copper tube wall at the meniscus position of the molten steel in the crystallizer is ≤3mm;

[0010] And / or, the amplitude of the crystallizer is 2-6 mm;

[0011] And / or, the crystallizer has a frequency of 100-160 cpm;

[0012] And / or, the oxygen content of the molten steel is 0.0015-0.0025%.

[0013] Preferably, the depth of the oscillation marks on the continuously cast billet is 80-150 μm;

[0014] And / or, the solidification hook depth of the continuously cast billet is 200-300μm;

[0015] And / or, the amplitude of the crystallizer is 3-5 mm;

[0016] And / or, the frequency of the crystallizer is 120-140 cpm.

[0017] Preferably, the electromagnetic stirring current of the built-in electromagnetic stirrer in the crystallizer is 600-800A;

[0018] And / or, the electromagnetic stirring frequency of the built-in electromagnetic stirrer in the crystallizer is 1-2Hz;

[0019] And / or, the height of the built-in electromagnetic stirrer in the crystallizer is 500 mm;

[0020] And / or, the lower edge of the built-in electromagnetic stirrer in the crystallizer is 100mm higher than the lower edge of the copper tube in the crystallizer.

[0021] Preferably, the immersion nozzle of the crystallizer is an integral four-hole nozzle;

[0022] And / or, the copper tube corner of the crystallizer is opposite to the steel flow outlet;

[0023] And / or, the insertion depth of the immersion nozzle of the crystallizer is 160-180 mm;

[0024] And / or, the copper tube of the crystallizer is 900 mm long;

[0025] And / or, the meniscus of molten steel in the crystallizer is located 80-120 mm below the upper edge of the copper tube.

[0026] Preferably, the protective slag comprises the following components by mass percentage: 30-34% SiO2, 20-23% CaO, 1.0-2.0% MgO, 2.0-4.0% Al2O3, 10-12% Na2O, 7-9% F, 9-11% C, 2-3% Fe2O3, with the remainder being unavoidable impurities;

[0027] And / or, the binary basicity of the protective slag is 0.60-0.70;

[0028] And / or, the melting point of the protective slag is 960-990℃;

[0029] And / or, the viscosity of the protective slag at 1300°C is 0.30-0.40 Pa·s;

[0030] And / or, the melting rate of the protective slag is 10-20 s.

[0031] Preferably, in the continuous casting process, the superheat of molten steel in the tundish is 10-20℃, the continuous casting speed is 0.4-0.8m / min, the flow rate of cooling water in the crystallizer is 2800-3200L / min, and the fluctuation range of the liquid level in the crystallizer is ±1-3mm.

[0032] Preferably, the cross-sectional dimensions of the continuous casting machine used in the continuous casting process are 300mm×390mm~410mm×530mm;

[0033] And / or, the C content of the high-carbon steel wire rod is 0.72-1.00%;

[0034] And / or, a primary smelting process and a refining process are performed sequentially before the continuous casting process.

[0035] Preferably, in the primary smelting process, ferrosilicon, silicomanganese, and a carburizing agent are added sequentially during the tapping process for deoxidation, and lime and silicon carbide are added after tapping for slag formation and slag surface deoxidation.

[0036] Preferably, in the refining process, slag and alloy are added to the molten steel after the primary refining process, the binary basicity of the final refining slag is 2-3, the FeO+MnO content in the final refining slag is ≤2wt%, the smelting time is 40-50min, and the soft stirring time is 15-25min.

[0037] In this invention, the protective slag ring on the copper tube wall at the meniscus of the molten steel inside the crystallizer is formed by the temperature gradient at the high contact point between the liquid slag and the crystallizer wall. This creates a solid slag ring around the crystallizer and adheres to the crystallizer wall. Once the slag ring is formed, due to the difference in wetting degree between the liquid slag and the molten steel and the copper tube wall, a vertically downward capillary channel is formed between the slag ring on the meniscus around the crystallizer and the initial billet shell. Due to the vibration of the crystallizer and capillary action, the liquid slag on the meniscus is continuously drawn into the air gap between the billet shell and the copper tube wall, forming a slag film that provides lubrication.

[0038] The technical solution of this invention has the following advantages:

[0039] 1. A method for controlling surface and subcutaneous bubbles in continuously cast billets for high-carbon steel wire rod, comprising: in the continuous casting process for producing continuously cast billets for high-carbon steel wire rod, controlling the total slag layer thickness of the protective slag in the mold to be 50-60 mm, the liquid slag layer thickness of the protective slag in the mold to be 2-3 mm, the electromagnetic induction intensity at the meniscus of the molten steel in the mold to be 20-30 mT, and the oxygen content in the molten steel ≤0.0025%. This invention strictly controls the total slag layer, liquid slag layer thickness, and electromagnetic induction intensity at the meniscus of the molten steel in the mold during the high-carbon steel production process, thereby avoiding carbon increase on the surface of the continuously cast billet. Simultaneously, combined with the control of oxygen content in the molten steel during the refining process, the occurrence rate of CO bubbles formed by carbon and oxygen in the molten steel on the surface and subcutaneous layer of the high-carbon steel continuously cast billet is reduced to below 10% without increasing smelting costs or affecting the metal yield of the continuously cast billet.

[0040] 2. Based on the C content of the steel grade and the cross-sectional dimensions of the continuous casting machine, this invention controls the thickness of the protective slag ring in the mold by controlling the thickness of the protective slag layer in the mold. If the protective slag layer is too thick, a thick slag ring is easily formed on the copper tube wall at the meniscus of the molten steel in the mold, which hinders the flow of the liquid slag layer into the gap between the copper tube and the continuously cast billet shell, affecting the lubrication performance of the protective slag. If the protective slag layer is too thin, a stable three-layer (powdered slag layer, sintered layer, liquid slag layer) structure cannot be formed above the meniscus of the molten steel in the mold, and the liquid slag layer of the protective slag does not flow in sufficiently, which also affects the lubrication performance and easily causes carbonization on the surface of the continuously cast billet.

[0041] 3. This invention controls the high Fe2O3 content in the protective slag, which acts as a flux to facilitate the formation of the liquid slag layer. Simultaneously, it controls the nozzle insertion depth and the electromagnetic stirring of the crystallizer to increase the temperature of the molten steel at the meniscus, resulting in a stable liquid slag layer thickness. Furthermore, by setting the crystallizer vibration parameters (frequency and amplitude) and combining them with the continuous casting speed, the depth of the oscillation marks and the depth of the solidification hook are controlled, reducing the microscopic segregation of carbon in the overflow zone of the molten steel at the solidification hook location. Finally, by controlling the fluctuation range of the crystallizer liquid surface, it prevents damage to the protective slag structure at the meniscus of the molten steel.

[0042] 4. By adjusting the installation position of the electromagnetic stirrer in the crystallizer and setting the electromagnetic stirring parameters of the crystallizer, the present invention effectively controls the magnetic induction intensity at the meniscus position, thereby breaking the dendritic structure at the solidification front of the continuously cast billet, reducing its capture of bubbles at the solidification interface, promoting the bubbles to rise and be removed, and avoiding excessive disturbance to the molten steel surface that could lead to slag entrainment.

[0043] 5. By controlling the parameters of each step, this invention reduces carbon increase in the continuously cast billet and microscopic segregation of C in the overflow zone of molten steel at the solidification hook position. Combined with the control of oxygen content in the molten steel during the refining process, it can completely eliminate CO bubbles formed on the surface and under the surface of the continuously cast billet for high-carbon steel wire rod. Detailed Implementation

[0044] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0045] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0046] Example 1

[0047] This embodiment provides a method for controlling surface and subcutaneous air bubbles in a continuously cast billet for high-carbon steel wire rod. The steel grade is SWRH72A with a carbon content of 0.72%. The cross-sectional dimensions of the continuous casting machine are 300mm × 390mm. The height of the electromagnetic stirrer in the crystallizer is 500mm. The lower edge of the electromagnetic stirrer is 100mm higher than the lower edge of the copper tube in the crystallizer. The length of the copper tube in the crystallizer is 900mm. The meniscus of molten steel in the crystallizer is 120mm below the upper edge of the copper tube.

[0048] Specifically, the following steps are included:

[0049] 1) In the primary refining process, ferrosilicon, silicomanganese, and carbon raiser are added sequentially during tapping for deoxidation. After tapping, lime and silicon carbide are added for slag formation and slag surface deoxidation. In the subsequent refining process, slag and alloy are added to the molten steel after the primary refining process. The binary basicity of the final refining slag is 2, the FeO+MnO content in the final refining slag is 2%, the smelting time is 40 min, the soft stirring time is 15 min, and the oxygen content in the molten steel is controlled at 0.0025%.

[0050] 2) After the refining process is completed, the molten steel is hoisted to the continuous casting platform for protective pouring. The superheat of the molten steel in the tundish is 20°C. The molten steel flows from the tundish into the crystallizer through the submerged entry nozzle. The submerged entry nozzle is an integral four-hole nozzle. The steel flow outlet corresponds to the corner of the copper tube of the crystallizer. The insertion depth of the submerged entry nozzle of the crystallizer is 160mm. The continuous casting speed is 0.8m / min. The cooling water flow rate of the crystallizer is 2800L / min. The electromagnetic stirring parameters of the crystallizer are 600A and 1Hz. The electromagnetic induction intensity at the meniscus of the molten steel in the crystallizer is 20mT. The fluctuation range of the liquid level in the crystallizer is ±2mm.

[0051] 3) The continuous casting crystallizer uses protective slag casting. The chemical composition of the protective slag, by mass percentage, is: 33% SiO2, 23% CaO, 1.0% MgO, 3.0% Al2O3, 11% Na2O, 8% F, 9% C, 3% Fe2O3, with the remainder being unavoidable impurities. The binary basicity (R) of the protective slag is 0.70, the melting point is 990℃, the viscosity at 1300℃ is 0.35 Pa·s, and the melting rate is 10 s.

[0052] 4) An automatic slag-adding device is used to add protective slag. The total slag layer thickness is 60mm, the liquid slag layer thickness is 3mm, and the protective slag ring thickness is 3mm.

[0053] 5) The crystallizer vibration parameters are: amplitude 5mm, frequency 140cpm;

[0054] 6) The billet exits the crystallizer, is cooled in the secondary cooling zone and flame-cut to obtain a continuously cast billet with a vibration mark depth of 150μm and a solidification hook depth of 300μm.

[0055] Example 2

[0056] This embodiment provides a method for controlling surface and subcutaneous air bubbles in a continuously cast billet for high-carbon steel wire rod. The steel grade is SWRH82A with a carbon content of 0.82%. The cross-sectional dimensions of the continuous casting machine are 350mm × 450mm. The height of the electromagnetic stirrer in the crystallizer is 500mm. The lower edge of the electromagnetic stirrer is 100mm higher than the lower edge of the copper tube in the crystallizer. The length of the copper tube in the crystallizer is 900mm. The meniscus of molten steel in the crystallizer is 100mm below the upper edge of the copper tube.

[0057] Specifically, the following steps are included:

[0058] 1) In the primary refining process, ferrosilicon, silicomanganese, and carburizing agent are added sequentially during tapping for deoxidation. After tapping, lime and silicon carbide are added for slag formation and slag surface deoxidation. In the subsequent refining process, slag and alloy are added to the molten steel after the primary refining process. The binary basicity of the final refining slag is 2.5, the FeO+MnO content in the final refining slag is 1.5%, the smelting time is 45 min, the soft stirring time is 20 min, and the oxygen content in the molten steel is controlled at 0.0020%.

[0059] 2) After the refining process is completed, the molten steel is hoisted to the continuous casting platform for protective pouring. The superheat of the molten steel in the tundish is 15°C. The molten steel flows from the tundish into the crystallizer through the submerged entry nozzle. The submerged entry nozzle is an integral four-hole nozzle. The steel flow outlet corresponds to the corner of the copper tube of the crystallizer. The insertion depth of the submerged entry nozzle of the crystallizer is 170mm. The continuous casting speed is 0.6m / min. The cooling water flow rate of the crystallizer is 3000L / min. The electromagnetic stirring parameters of the crystallizer are 700A and 1.5Hz. The electromagnetic induction intensity at the meniscus of the molten steel in the crystallizer is 25mT. The fluctuation range of the liquid level in the crystallizer is ±1.5mm.

[0060] 3) The continuous casting crystallizer uses protective slag casting. The chemical composition of the protective slag, by mass percentage, is: 30% SiO2, 22% CaO, 1.5% MgO, 4.0% Al2O3, 12% Na2O, 7% F, 11% C, 2.5% Fe2O3, with the remainder being unavoidable impurities. The binary basicity (R) of the protective slag is 0.65, the melting point is 975℃, the viscosity at 1300℃ is 0.40 Pa·s, and the melting rate is 15s.

[0061] 4) An automatic slag-adding device is used to add protective slag. The total slag layer thickness is 55mm, the liquid slag layer thickness is 2mm, and the protective slag ring thickness is 2mm.

[0062] 5) The crystallizer vibration parameters are amplitude 4mm and frequency 130cpm.

[0063] 6) The billet exits the crystallizer, is cooled in the secondary cooling zone and flame-cut to obtain a continuously cast billet with a vibration mark depth of 100μm and a solidification hook depth of 240μm.

[0064] Example 3

[0065] This embodiment provides a method for controlling surface and subcutaneous air bubbles in a continuously cast billet for high-carbon steel wire rod. The steel grade is SWRH92A with a carbon content of 0.92%. The cross-sectional dimensions of the continuous casting machine are 410mm × 530mm. The height of the electromagnetic stirrer in the crystallizer is 500mm. The lower edge of the electromagnetic stirrer is 100mm higher than the lower edge of the copper tube in the crystallizer. The length of the copper tube in the crystallizer is 900mm. The meniscus of molten steel in the crystallizer is 80mm below the upper edge of the copper tube.

[0066] Specifically, the following steps are included:

[0067] 1) In the primary refining process, ferrosilicon, silicomanganese, and carbon raiser are added sequentially during tapping for deoxidation. After tapping, lime and silicon carbide are added for slag formation and slag surface deoxidation. In the subsequent refining process, slag and alloy are added to the molten steel after the primary refining process. The binary basicity of the final refining slag is 3, the FeO+MnO content in the final refining slag is 1%, the smelting time is 50 min, the soft stirring time is 20 min, and the oxygen content in the molten steel is controlled at 0.0015%.

[0068] 2) After the refining process is completed, the molten steel is hoisted to the continuous casting platform for protective pouring. The superheat of the molten steel in the tundish is 10°C. The molten steel flows from the tundish into the crystallizer through the submerged entry nozzle. The submerged entry nozzle is an integral four-hole nozzle. The steel flow outlet corresponds to the corner of the copper tube of the crystallizer. The insertion depth of the submerged entry nozzle of the crystallizer is 180mm. The continuous casting speed is 0.4m / min. The cooling water flow rate of the crystallizer is 3200L / min. The electromagnetic stirring parameters of the crystallizer are 800A and 2.0Hz. The electromagnetic induction intensity at the meniscus of the molten steel in the crystallizer is 30mT. The fluctuation range of the liquid level in the crystallizer is ±1mm.

[0069] 3) The continuous casting crystallizer uses protective slag casting. The chemical composition of the protective slag, by mass percentage, is: 34% SiO2, 21% CaO, 2.0% MgO, 2.0% Al2O3, 10% Na2O, 9% F, 10% C, 2% Fe2O3, with the remainder being unavoidable impurities. The binary basicity (R) of the protective slag is 0.62, the melting point is 963℃, the viscosity at 1300℃ is 0.31 Pa·s, and the melting rate is 19 s.

[0070] 4) An automatic slag-adding device is used to add protective slag. The total slag layer thickness is 60mm, the liquid slag layer thickness is 3mm, and the protective slag ring thickness is 3mm.

[0071] 5) The crystallizer vibration parameters are: amplitude 3mm, frequency 120cpm;

[0072] 6) The billet exits the crystallizer, is cooled in the secondary cooling zone and flame-cut to obtain a continuously cast billet with a vibration mark depth of 80μm and a solidification hook depth of 200μm.

[0073] Example 4

[0074] The difference between this embodiment and Embodiment 1 is that the crystallizer vibration parameters are an amplitude of 2 mm and a frequency of 100 cpm. Other conditions are the same as in Embodiment 1. The billet exits the crystallizer, is cooled in the secondary cooling zone and flame-cut to obtain a continuously cast billet with a vibration mark depth of 70 μm and a solidification hook depth of 180 μm.

[0075] Example 5

[0076] The difference between this embodiment and Embodiment 1 is that the crystallizer vibration parameters are an amplitude of 6 mm and a frequency of 160 cpm. Other conditions are the same as in Embodiment 1. The billet exits the crystallizer, is cooled in the secondary cooling zone and flame-cut to obtain a continuously cast billet with a vibration mark depth of 180 μm and a solidification hook depth of 350 μm.

[0077] Comparative Example 1

[0078] This comparative example provides a method for controlling surface and subcutaneous bubbles in a continuously cast billet for high-carbon steel wire rod. The steel grade is SWRH72A, the C content is 0.72%, the cross-sectional dimensions of the continuous casting machine are 300mm×390mm, the height of the electromagnetic stirrer in the crystallizer is 500mm, the lower edge of the electromagnetic stirrer is 100mm from the lower edge of the copper tube in the crystallizer, the length of the copper tube in the crystallizer is 900mm, and the meniscus of molten steel in the crystallizer is 120mm below the upper edge of the copper tube.

[0079] Specifically, the following steps are included:

[0080] 1) In the primary refining process, ferrosilicon, silicomanganese, and carbon raiser are added sequentially during tapping for deoxidation. After tapping, lime and silicon carbide are added for slag formation and slag surface deoxidation. In the subsequent refining process, slag and alloy are added to the molten steel after the primary refining process. The binary basicity of the final refining slag is 2, the FeO+MnO content in the final refining slag is 2%, the smelting time is 40 min, the soft stirring time is 15 min, and the oxygen content in the molten steel is controlled at 0.0025%.

[0081] 2) After the refining process is completed, the molten steel is hoisted to the continuous casting platform for protective pouring. The superheat of the molten steel in the tundish is 20°C. The molten steel flows from the tundish into the crystallizer through the submerged entry nozzle. The submerged entry nozzle is an integral four-hole nozzle. The steel flow outlet corresponds to the corner of the copper tube of the crystallizer. The insertion depth of the submerged entry nozzle of the crystallizer is 160mm. The continuous casting speed is 0.8m / min. The cooling water flow rate of the crystallizer is 2800L / min. The electromagnetic stirring parameters of the crystallizer are 600A and 1Hz. The electromagnetic induction intensity at the meniscus of the molten steel in the crystallizer is 20mT. The fluctuation range of the liquid level in the crystallizer is ±2mm.

[0082] 3) The continuous casting crystallizer uses protective slag casting. The chemical composition of the protective slag, by mass percentage, is: 33% SiO2, 23% CaO, 1.0% MgO, 3.0% Al2O3, 11% Na2O, 8% F, 9% C, 3% Fe2O3, with the remainder being unavoidable impurities. The binary basicity (R) of the protective slag is 0.70, the melting point is 990℃, the viscosity at 1300℃ is 0.35 Pa·s, and the melting rate is 10 s.

[0083] 4) An automatic slag-adding device is used to add protective slag. The total slag layer thickness is 30mm, the liquid slag layer thickness is 1mm, and the protective slag ring thickness is 1mm.

[0084] 5) The crystallizer vibration parameters are: amplitude 5mm, frequency 140cpm;

[0085] 6) The billet exits the crystallizer, is cooled in the secondary cooling zone and flame-cut to obtain a continuously cast billet with a vibration mark depth of 150μm and a solidification hook depth of 300μm.

[0086] Comparative Example 2

[0087] This comparative example provides a method for controlling surface and subcutaneous bubbles in a continuously cast billet for high-carbon steel wire rod. The steel grade is SWRH72A, the C content is 0.72%, the cross-sectional dimensions of the continuous casting machine are 300mm×390mm, the height of the electromagnetic stirrer in the crystallizer is 500mm, the lower edge of the electromagnetic stirrer is 100mm higher than the lower edge of the copper tube in the crystallizer, the length of the copper tube in the crystallizer is 900mm, and the meniscus of molten steel in the crystallizer is 120mm below the upper edge of the copper tube.

[0088] Specifically, the following steps are included:

[0089] 1) In the primary refining process, ferrosilicon, silicomanganese, and carbon raiser are added sequentially during tapping for deoxidation. After tapping, lime and silicon carbide are added for slag formation and slag surface deoxidation. In the subsequent refining process, slag and alloy are added to the molten steel after the primary refining process. The binary basicity of the final refining slag is 2, the FeO+MnO content in the final refining slag is 2%, the smelting time is 40 min, the soft stirring time is 15 min, and the oxygen content in the molten steel is controlled at 0.0025%.

[0090] 2) After the refining process is completed, the molten steel is hoisted to the continuous casting platform for protective pouring. The superheat of the molten steel in the tundish is 20°C. The molten steel flows from the tundish into the crystallizer through the submerged entry nozzle. The submerged entry nozzle is an integral four-hole nozzle. The steel flow outlet corresponds to the corner of the copper tube of the crystallizer. The insertion depth of the submerged entry nozzle of the crystallizer is 160mm. The continuous casting speed is 0.8m / min. The cooling water flow rate of the crystallizer is 2800L / min. The electromagnetic stirring parameters of the crystallizer are 600A and 1Hz. The electromagnetic induction intensity at the meniscus of the molten steel in the crystallizer is 20mT. The fluctuation range of the liquid level in the crystallizer is ±2mm.

[0091] 3) The continuous casting crystallizer uses protective slag casting. The chemical composition of the protective slag, by mass percentage, is: 33% SiO2, 23% CaO, 1.0% MgO, 3.0% Al2O3, 11% Na2O, 8% F, 9% C, 3% Fe2O3, with the remainder being unavoidable impurities. The binary basicity (R) is 0.70, the melting point is 990℃, the viscosity at 1300℃ is 0.35 Pa·s, and the melting rate is 10 s.

[0092] 4) An automatic slag-adding device is used to add protective slag. The total thickness of the protective slag layer is 80 mm, the thickness of the liquid slag layer is 5 mm, and the thickness of the protective slag ring is 6 mm.

[0093] 5) The crystallizer vibration parameters are: amplitude 5mm, frequency 140cpm;

[0094] 6) The billet exits the crystallizer, is cooled in the secondary cooling zone and flame-cut to obtain a continuously cast billet with a vibration mark depth of 150μm and a solidification hook depth of 300μm.

[0095] Comparative Example 3

[0096] The difference between this comparative example and Example 1 is that the electromagnetic induction intensity at the meniscus of the molten steel in the crystallizer is 0 mT, while other conditions are the same as in Example 1.

[0097] Comparative Example 4

[0098] The difference between this comparative example and Example 1 is that the oxygen content in the molten steel is controlled at 0.0040%, while other conditions are the same as in Example 1.

[0099] Test Example 1

[0100] The surface metallographic structure of the continuous casting billets prepared in Examples 1-5 and Comparative Examples 1-4 was analyzed and statistically analyzed. The statistical method was as follows: the surface and subcutaneous bubble situation of 500 continuous casting billets generated by the corresponding schemes was counted. The results are shown in Table 1 below; where, the surface and subcutaneous bubble occurrence rate (%) = number of continuous casting billets with surface and subcutaneous bubbles / 500 × 100%.

[0101] Table 1

[0102] Example 1 0.0 Example 2 0.0 Example 3 0.0 Example 4 0.5 Example 5 7.5 Comparative Example 1 50.7 Comparative Example 2 43.1 Comparative Example 3 21.2 Comparative Example 4 14.9

[0103] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for controlling surface and subcutaneous air bubbles in continuously cast billets for high-carbon steel wire rod, characterized in that, include: In the continuous casting process for producing high-carbon steel wire rod billets, the total slag layer thickness of the protective slag in the mold is controlled to be 50-60 mm, the molten slag layer thickness of the protective slag in the mold is controlled to be 2-3 mm, the electromagnetic induction intensity at the meniscus of the molten steel in the mold is controlled to be 20-30 mT, and the oxygen content in the molten steel is controlled to be ≤0.0025%; the carbon content of the high-carbon steel wire rod is controlled to be 0.72-1.00%. The oscillation mark depth of the continuously cast billet is 80-150 μm; the solidification hook depth of the continuously cast billet is 200-300 μm; the amplitude of the crystallizer is 3-5 mm; the oscillation frequency of the crystallizer is 120-140 cpm; and the continuous casting speed is 0.4-0.8 m / min. The electromagnetic stirring current of the built-in electromagnetic stirrer in the crystallizer is 600-800 A; The electromagnetic stirring frequency of the built-in electromagnetic stirrer in the crystallizer is 1-2 Hz; The height of the built-in electromagnetic stirrer in the crystallizer is 500 mm. The lower edge of the built-in electromagnetic stirrer in the crystallizer is 100 mm higher than the lower edge of the copper tube in the crystallizer.

2. The control method according to claim 1, characterized in that, The thickness of the protective slag ring on the copper tube wall at the meniscus of the molten steel inside the crystallizer is ≤3 mm. And / or, the oxygen content of the molten steel is 0.0015-0.0025%.

3. The control method according to claim 1 or 2, characterized in that, The immersion inlet of the crystallizer is an integral four-hole inlet; And / or, the copper tube corner of the crystallizer is opposite to the steel flow outlet; And / or, the insertion depth of the immersion nozzle of the crystallizer is 160-180 mm; And / or, the copper tube of the crystallizer is 900 mm long; And / or, the meniscus of molten steel in the crystallizer is located 80-120 mm below the upper edge of the copper tube.

4. The control method according to claim 1 or 2, characterized in that, The protective slag comprises the following components by mass percentage: 30-34% SiO2, 20-23% CaO, 1.0-2.0% MgO, 2.0-4.0% Al2O3, 10-12% Na2O, 7-9% F, 9-11% C, 2-3% Fe2O3, with the remainder being unavoidable impurities; And / or, the binary basicity of the protective slag is 0.60-0.70; And / or, the melting point of the protective slag is 960-990℃; And / or, the viscosity of the protective slag at 1300°C is 0.30-0.40 Pa·s; And / or, the melting rate of the protective slag is 10-20 s.

5. The control method according to claim 1 or 2, characterized in that, In the continuous casting process, the superheat of molten steel in the tundish is 10-20℃, the flow rate of cooling water in the crystallizer is 2800-3200 L / min, and the fluctuation range of the liquid level in the crystallizer is ±1-3 mm.

6. The control method according to claim 1 or 2, characterized in that, The cross-sectional dimensions of the continuous casting machine used in the continuous casting process are 300 mm × 390 mm ~ 410 mm × 530 mm; The continuous casting process is preceded by a primary smelting process and a refining process.

7. The control method according to claim 6, characterized in that, The primary smelting process involves sequentially adding ferrosilicon, silicomanganese, and a carbon raiser during the tapping process for deoxidation. After tapping, lime and silicon carbide are added for slag formation and slag surface deoxidation.

8. The control method according to claim 6, characterized in that, In the refining process, slag and alloy are added to the molten steel after the primary refining process. The binary basicity of the final refining slag is 2-3, the FeO+MnO content in the final refining slag is ≤2 wt%, the smelting time is 40-50 min, and the soft stirring time is 15-25 min.