Method for controlling corner transverse cracks of high carbon steel square billet

Abstract

The present application relates to a kind of high carbon steel square billet corner transverse crack control method, and the molten iron is desulfurized, and after desulfurization is completed, it is handled with slag removal.The pretreated molten iron is mixed into converter, while adding qualified scrap steel;The molten steel is top and bottom combined blowing, and batch adding slag forming agent is carried out in smelting process, and the basicity of slag is controlled;During tapping process, alloy is added to carry out preliminary deoxidation.The molten steel after converter tapping is sent to refining station, argon blowing stirring is carried out, slag forming agent is added to furnace, the basicity of slag is controlled, and calcium wire is fed in later stage of refining.The R angle parameter of the selected crystallizer copper pipe before production is that upper R angle is 14mm and lower R angle is 12mm, the superheat of molten steel is controlled at 20-40 ℃, and the vibration parameter of crystallizer is set as follows: frequency 189 cpm, amplitude ±3.5mm, and the pulling speed is controlled at 2.3m / min constant speed.The present application reduces the generation of square billet corner transverse crack by accurate design and collaborative optimization in whole process, and improves product quality.

Description

Technical Field

[0001] This invention relates to a method for controlling transverse cracks at the corners of high-carbon steel billets, belonging to the field of steel preparation technology. Background Technology

[0002] High-carbon steels with a carbon content of 0.60% or higher, such as spring steel, ball steel, and bearing steel, possess excellent strength, hardness, and wear resistance, making them widely and indispensable in many fields, including machinery manufacturing, the automotive industry, and construction machinery. In the smelting process, hot metal pretreatment, converter smelting, ladle refining, and continuous casting are all crucial steps in the production of high-carbon steel. In particular, the continuous casting of square billets directly determines the performance and yield of subsequent rolled products, significantly impacting the economic efficiency of the entire production chain.

[0003] In the continuous casting of high-carbon steel billets, due to the combined effects of the material's inherent properties and process conditions, the corners of the billets are highly susceptible to quality defects. Among these, transverse tearing cracks at the bottom of the oscillation marks during cooling in the crystallizer are the most typical, and this problem has become a widespread technical challenge in the industry. Specifically, high-carbon steel billets exhibit small volume shrinkage during continuous casting cooling, leading to a significant increase in the pulling resistance experienced by the billet within the crystallizer. Simultaneously, the corners of the billet are two-dimensional cooling zones with a much higher cooling rate than other areas, resulting in substantial thermal stress at the corners. Under the combined effect of pulling resistance and thermal stress, stress concentration easily occurs at the bottom of the oscillation marks at the billet corners, ultimately triggering transverse tearing cracks.

[0004] To address the aforementioned problem of transverse corner cracks, the industry has explored relevant technologies. Currently, the commonly used approach involves selecting crystallizer copper tubes with a small radius and fixed upper and lower R-angles (the conventional R-angle size is 6-10mm), supplemented by optimizing some process parameters such as cooling water flow rate and billet pulling speed. However, practice has shown that the improvement effect of existing technical solutions is very limited, and it is difficult to fundamentally eliminate the transverse corner crack defect in high-carbon steel billets.

[0005] Due to the presence of transverse corner cracks, the industry has had to perform peeling and grinding on all high-carbon steel continuously cast billets or subsequent rolled products to remove cracks and ensure product quality. This additional process not only significantly increases the cost of peeling and flaw detection for billets and rolled products, raising production costs, but also reduces production efficiency. Furthermore, improper operation during peeling and grinding can damage the billet matrix, affecting subsequent processing performance. In addition, existing technologies face the challenge of balancing process parameter adjustments with production stability when attempting to solve the crack problem; optimization of some parameters may adversely affect other process stages, further limiting the effectiveness of the technological solutions.

[0006] Therefore, in response to the problem of transverse cracks at the corners of high-carbon steel billets in continuous casting, developing a technical solution that can fundamentally eliminate this defect without additional peeling and grinding processes, without affecting the stability of existing production processes, and that is simple to operate and easy to promote has become an urgent technical need for the current high-carbon steel production industry. It is of great significance for improving product quality, reducing production costs, and promoting technological progress in the industry. Summary of the Invention

[0007] This invention provides a method for controlling transverse cracks at the corners of high-carbon steel billets. Through precise design and collaborative optimization of the entire process, the generation of transverse cracks at the corners of billets is reduced, thereby improving product quality.

[0008] The technical solution adopted by this invention to solve its technical problem is: A method for controlling transverse cracks at the corner of a high-carbon steel billet includes the following steps: Step S1, molten iron pretreatment: Molten iron is sent to the molten iron pretreatment station for desulfurization. After desulfurization, the sulfur content in the molten iron is ≤0.008%. After desulfurization, slag removal is performed with a slag removal rate ≥95%. Step S2, converter smelting: the pretreated molten iron is added to the converter, along with qualified scrap steel; the molten steel is smelted by top and bottom blowing, controlling the oxygen flow rate and the bottom blowing argon flow rate; slag-forming agent is added in batches during the smelting process, and the slag basicity is controlled at 3.5~4.0; at the end of the smelting process, the carbon content in the molten steel is 0.70~0.80%, the phosphorus content is ≤0.015%, and the temperature of the molten steel is 1650~1760℃; During the steelmaking process, alloys are added for preliminary deoxidation; Step S3, LF refining: The molten steel after tapping from the converter is sent to the refining station, and the electric arc heating system is started to raise and maintain the temperature of the molten steel. During the refining process, argon blowing and stirring are carried out, and slag-forming agents are added into the furnace to control the slag basicity and form a reducing slag atmosphere. In the later stage of refining, calcium wire is fed in to modify the alumina inclusions in the molten steel. The total refining time is controlled at 30~40 minutes. After refining, the temperature of the molten steel is controlled at 1610~1650℃, and the molten steel is allowed to stand for 5~8 minutes. Step S4, continuous casting preparation: Before production, select a crystallizer copper tube with an upper R angle of 12.5~14mm and a lower R angle of 10~12mm. Install the copper tube into the crystallizer assembly and conduct a water flow test on the crystallizer to check for leaks in each cooling water path. At the same time, check and calibrate the continuous casting machine roller table and guide rollers. Step S5, continuous casting: molten steel with qualified smelting composition and temperature is hoisted to the continuous casting ladle turret and poured into the tundish through the ladle's long nozzle; the tundish uses an immersion nozzle for protection during casting; the crystallizer vibration frequency is set to 185~190 cpm, and the amplitude is ±3.5mm; the casting speed is set to 2.2~2.4m / min; the molten steel level is monitored in real time during casting, and the molten steel flow rate is adjusted by the tundish stopper rod; the molten steel temperature in the tundish is monitored in real time to ensure that the molten steel maintains a constant casting speed within the superheat range of 20~40℃. Simultaneously, the high-carbon steel billet production is completed by adjusting the water flow rate in the secondary cooling zone until the entire furnace of molten steel is poured. Furthermore, in step S1, during the desulfurization operation of molten steel, the desulfurization speed is set to 80~90 r / min, and the stirring time lasts for 10~15 min.

[0009] Furthermore, in step S2, the proportion of scrap steel is 15-20%, the oxygen flow rate is controlled at 2800-3200 m³ / h, and the bottom-blown argon flow rate is controlled at 50-80 m³ / h; the alloys added during the steel tapping process are ferrosilicon, ferromanganese silicomanganese, and high-carbon ferrochrome. Furthermore, in step S3, during the refining process, the argon flow rate is controlled in stages when stirring with argon: 80-90 L / min during the heating stage, 70-80 L / min during the composition adjustment stage, and 50-60 L / min during the heat preservation stage. The slag-forming agent includes lime and fluorite, wherein the amount of lime added is 200~300 kg / furnace and the amount of fluorite added is 100~200 kg / furnace; The calcium feeding velocity should be set to 3~5m / s; Furthermore, in step S4, the upper opening radius (R) is 14mm and the lower opening radius (R) is 12mm; Furthermore, in step S5, the crystallizer vibration frequency is set to 189 cpm and the pulling speed is set to 2.3 m / min.

[0010] By employing the above technical solutions, the present invention has the following beneficial effects compared to the prior art: 1. The method for controlling transverse cracks at the corners of high-carbon steel billets provided by this invention achieves deep removal of harmful elements such as sulfur and phosphorus through precise desulfurization in molten iron pretreatment, combined with high-basicity slag making in the converter, slag blocking during steel tapping, and control of the reducing slag atmosphere in LF refining, while reducing the generation of oxide and sulfide inclusions; combined with calcium wire feeding, it reduces the crack sensitivity of high-carbon steel from the perspective of composition and cleanliness, thereby reducing the causes of cracks in high-carbon steel from the source. 2. The method for controlling transverse cracks at the corners of high-carbon steel billets provided by this invention precisely matches the converter end temperature, LF refining end temperature, and superheat of continuous casting molten steel, providing a stable thermal environment for the solidification process. At the same time, the further setting of continuous casting parameters such as constant casting speed and stable liquid level enhances process stability and reduces the problem of uneven solidification of billet shell caused by parameter fluctuations. 3. The method for controlling transverse cracks at the corner of high-carbon steel billet provided by the present invention is specially designed for the special R-angle of the crystallizer, which is aimed at the main causes of transverse cracks at the corner. This avoids cracks caused by excessive two-dimensional cooling intensity at the corner and low corner temperature leading to poor plasticity. At the same time, it reduces the resistance of billet pulling and prevents tearing cracks caused by tensile stress in the weak area at the bottom of the vibration mark valley. 4. The method for controlling transverse cracks at the corners of high-carbon steel billets provided by this invention establishes a full-process control system, promptly detects and adjusts abnormal parameters, improves product quality, and reduces production costs. Attached Figure Description

[0011] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0012] Figure 1 This refers to the surface corner quality of the cast billet obtained using the original process scheme for spring steel 60Si2Mn. Figure 2 This refers to the surface corner quality of the cast billet obtained using the scheme described in this application for spring steel 60Si2Mn; Figure 3 This refers to the surface corner quality of the cast billet obtained using the original process scheme for steel B2 used for grinding balls; Figure 4 This refers to the surface corner quality of the cast billet obtained using the scheme described in this application for steel B2 used for grinding balls. Detailed Implementation

[0013] The invention will now be described in further detail with reference to the accompanying drawings.

[0014] As described in the background section, the quality problem of transverse cracks at the corners of high-carbon steel billets with a carbon content of 0.60% or higher is quite common in the industry. To solve this problem, this application provides a method for controlling transverse cracks at the corners of high-carbon steel billets, forming a complete technical system from source purification → process temperature control → end-stage protection, thereby comprehensively improving the quality and production stability of high-carbon steel billets.

[0015] The most significant innovation in the method for controlling transverse cracks at the corners of high-carbon steel billets lies in the design of the continuous casting stage. This is because the billet pulling resistance is high in the crystallizer, and the corners of the billet undergo two-dimensional cooling with rapid cooling and high stress. Therefore, transverse tearing cracks at the bottom of the oscillation marks are easily generated at the corners of the billet during the cooling process in the crystallizer. However, designing the process solely for the continuous casting stage is insufficient to achieve optimal quality improvement for high-carbon steel billets. Therefore, it is necessary to perform hot metal pretreatment in step S1, converter smelting in step S2, and LF refining assistance in step S3 to purify the composition from the source and to precisely control the temperature and composition throughout the entire process.

[0016] The following is a detailed explanation of each step, including: Step S1, Hot Metal Pretreatment: The molten iron is sent to the hot metal pretreatment station for desulfurization. During the desulfurization operation, the desulfurization speed is set to 80~90 r / min, and the stirring time lasts for 10~15 min. This ensures the desulfurization effect while avoiding excessive stirring that could lead to an excessive drop in molten iron temperature or an increase in inclusions, thus ensuring the stability of subsequent smelting. After desulfurization, the sulfur content in the molten steel is ≤0.008%. After desulfurization, slag removal is performed with a slag removal rate ≥95%. This effectively removes the desulfurization slag, prevents sulfur elements in the slag from dissolving back into the molten steel, avoids a rebound in the sulfur content of the molten steel, and reduces the amount of inclusions carried into the converter, improving the cleanliness of the molten steel.

[0017] Step S2, converter smelting: Pretreated molten iron is added to the converter along with qualified scrap steel, which accounts for 15-20% of the total steel. The scrap steel ratio is carefully controlled to ensure the purity of the molten steel while reducing production costs. Top and bottom blowing are used for the molten steel, with oxygen flow controlled at 2800-3200 m³ / h and bottom blowing argon flow controlled at 50-80 m³ / h. Slagging agents are added in batches during smelting to control the slag basicity at 3.5-4.0. At the final smelting point, the carbon content in the molten steel is 0.70-0.80%, the phosphorus content is ≤0.015%, and the steel temperature is 1650-1760℃. During tapping, alloys are added for preliminary deoxidation. The appropriate final temperature allows for adjustments during subsequent refining. The alloys used during tapping are ferrosilicon, ferromanganese, and high-carbon ferrochrome to reduce the formation of oxide inclusions and prevent inclusions from accumulating at grain boundaries and causing cracks.

[0018] Step S3, LF refining: The molten steel after tapping from the converter is sent to the refining station, and the electric arc heating system is started to heat and hold the molten steel. During the refining process, argon blowing and stirring are carried out, and the argon flow rate is controlled in stages: 80~90 L / min during the heating stage, 70~80 L / min during the composition adjustment stage, and 50~60 L / min during the holding stage. Slagging agents are added to the furnace to control the slag basicity and form a reducing slag atmosphere. The slagging agents include lime and fluorite, with lime added at 200~300 kg / furnace and fluorite added at 100~200 kg / furnace. Calcium wire is fed in during the later stage of refining, and the feeding speed is set at 3~5 m / s. The alumina inclusions in the molten steel are modified. The total refining time is controlled at 30~40 min. After refining, the temperature of the molten steel is controlled at 1610~1650℃, and the molten steel is allowed to stand for 5~8 min.

[0019] Regarding ladle refining, this application uses LF refining instead of RH vacuum refining because LF refining is more suitable for conventional production conditions and can reduce operating costs. At the same time, by controlling the argon flow rate in stages and designing a reasonable refining time, production efficiency is taken into account while ensuring the refining effect.

[0020] Once the aforementioned processes are properly coordinated, the next step is the most significant highlight of this application's design. It fully considers the small volume shrinkage during the continuous casting and cooling process of high-carbon steel billets such as spring steel, ball steel, and bearing steel. This results in high resistance to billet pulling within the crystallizer. Furthermore, the corners of the billets undergo two-dimensional cooling, leading to rapid cooling and high stress. Therefore, the corners of the billets are highly susceptible to transverse tearing cracks at the bottom of the oscillation marks during the cooling process within the crystallizer. Step S4 in this application addresses this by considering that in actual production, continuously cast round billets do not exhibit transverse cracks, and round billets, compared to square billets, do not have corners. Therefore, it considers increasing the radius (R) of the copper tube in the continuous casting crystallizer for square billets. This results in a larger corner radius at the upper meniscus during the steel pouring process, preventing excessive two-dimensional cooling intensity at the corners and avoiding low corner temperatures that could lead to poor plasticity and cracking. Meanwhile, in order to reduce the resistance of billet pulling inside the copper tube, the design considers reducing the taper of the copper tube corners. The R-angle of the copper tube is designed to be larger at the top and smaller at the bottom, thereby reducing the taper of the copper tube corners, which reduces the resistance of billet pulling and prevents tensile stress from forming in the weak area at the bottom of the vibration mark valley, causing tearing cracks.

[0021] Therefore, during the design process, copper tubes with an upper R-angle of 12.5~14mm and a lower R-angle of 10~12mm were selected for the crystallizer. The copper tubes were installed into the crystallizer assembly, and a water flow test was performed to check for leaks in the cooling water channels. Simultaneously, the continuous casting machine's roller conveyor and guide rollers were inspected and calibrated. Preferably, the upper R-angle is 14mm and the lower R-angle is 12mm.

[0022] Step S5, continuous casting: Molten steel with qualified smelting composition and temperature is hoisted to the continuous casting ladle turret and poured into the tundish through the ladle's long nozzle; the tundish uses an immersion nozzle for protection during casting. In practice, using this copper tube significantly reduced the transverse corner cracks of the billet, but some cracks still existed. To further reduce crack defects, the process parameters were further optimized. Observation of the corners of the billet surface revealed that the oscillation marks at the corners were relatively deep. Therefore, the vibration parameters were further optimized to reduce the depth of the oscillation marks. The design adopted high-frequency, small-amplitude crystallizer vibration parameters, which is beneficial for reducing the depth of the oscillation marks. After calculation, the crystallizer vibration frequency was set to 185~190 cpm, and the amplitude to ±3.5mm; the negative slip time can be ≥0.1s to avoid steel leakage during the casting process. To further reduce the resistance during billet pulling, the pulling speed was increased from 2.1 m / min to 2.2~2.4 m / min. During casting, the molten steel level was monitored in real time, and the molten steel flow rate was adjusted using the tundish stopper rod. The molten steel temperature in the tundish was also monitored in real time to ensure a constant pulling speed within a superheat range of 20~40℃. Simultaneously, the water flow rate in the secondary cooling zone was adjusted until the entire furnace of molten steel was poured, completing the production of the high-carbon steel billet. Preferably, the crystallizer vibration frequency was set to 189 cpm, and the pulling speed to 2.3 m / min.

[0023] To verify the feasibility of the above-mentioned method for controlling transverse cracks at the corners of high-carbon steel billets, this application provides examples and comparative examples for two categories of high-carbon steel: spring steel 60Si2Mn and grinding ball steel B2.

[0024] Regarding spring steel 60Si2Mn, the chemical composition by mass percentage is: w[C] = 0.60%, w[Si] = 1.80%, and w[Mn] = 0.80%.

[0025] Comparative Example 1: In the core process, the copper tube's radius (R) is fixed at 10mm at both the top and bottom. The vibration parameters are: frequency 169 cpm, amplitude ±3.8mm, and casting speed 2.1m / min. The resulting billet surface corner quality is as follows: Figure 1 As shown.

[0026] Example 1

[0027] Step S1: Desulfurize the molten iron. During the desulfurization operation, the desulfurization speed is set to 80 r / min, and the stirring time is maintained for 10 min. After desulfurization, the sulfur content in the molten steel is ≤0.008%. After desulfurization, slag removal is performed, with a slag removal rate ≥95%.

[0028] Step S2: The pretreated molten iron is added to the converter, along with qualified scrap steel, which accounts for 15% of the total steel. The molten steel is then subjected to top and bottom blowing, with the oxygen flow rate controlled at 2800 m³ / h and the bottom blowing argon flow rate controlled at 50 m³ / h. Slagging agents are added in batches during the smelting process to control the slag basicity at 3.5. At the final smelting point, the carbon content in the molten steel is 0.70%, the phosphorus content is ≤0.015%, and the steel temperature is 1650~1760℃. Alloys are added during tapping for preliminary deoxidation.

[0029] Step S3: The molten steel after tapping from the converter is sent to the refining station, and the electric arc heating system is started to heat and maintain the temperature of the molten steel. During the refining process, argon blowing and stirring are carried out, and the argon flow rate is controlled in stages: 80 L / min during the heating stage, 70 L / min during the composition adjustment stage, and 50 L / min during the holding stage. A slag-forming agent is added to the furnace to control the slag basicity and form a reducing slag atmosphere. The slag-forming agent includes lime and fluorite, with 200 kg of lime added per furnace and 100 kg of fluorite added per furnace. Calcium wire is fed in during the later stage of refining, and the feeding speed is set to 3 m / s. The alumina inclusions in the molten steel are modified. The total refining time is controlled within 30 minutes. After refining, the temperature of the molten steel is controlled at 1610℃, and the molten steel is allowed to stand for 5-8 minutes.

[0030] Step S4: Select a copper tube for the crystallizer with a 14mm upper radius and a 12mm lower radius. Control the superheat of the molten steel between 20-40℃. Set the crystallizer vibration parameters as follows: frequency 189 cpm, amplitude ±3.5mm, and constant casting speed of 2.3m / min. The resistance to billet casting is significantly reduced, and there is no significant vibration or shaking in the secondary cooling chamber. The resulting billet surface corner quality is as follows... Figure 2 As shown.

[0031] pass Figure 1 and Figure 2 The comparison revealed that, Figure 1 Inspection of the cast billet revealed numerous transverse cracks at the corners. Figure 2 The medium-sized cast billet was inspected and found to be relatively... Figure 1 The surface vibration mark depth of the billet was reduced from 0.31-0.35 mm to 0.22-0.26 mm. After magnetic particle inspection, the transverse crack defect at the corner of the billet was eliminated.

[0032] The steel B2 used for grinding balls has the following chemical composition by mass percentage: w[C] 0.77%, w[Si] 0.23%, w[Mn] 0.75%, and w[Cr] 0.50%.

[0033] Comparative Example 2: In the core process, the copper tube's radius (R) is fixed at 10mm at both the top and bottom. The vibration parameters are: frequency 170 cpm, amplitude ±3.65mm, and casting speed 2.0m / min. The resulting billet surface corner quality is as follows: Figure 3 As shown.

[0034] Example 2

[0035] Step S1: Desulfurize the molten iron. During the desulfurization operation, the desulfurization speed is set to 90 r / min, and the stirring time is maintained for 15 min. After desulfurization, the sulfur content in the molten steel is ≤0.008%. After desulfurization, slag removal is performed, with a slag removal rate ≥95%.

[0036] Step S2: The pretreated molten iron is added to the converter, along with qualified scrap steel, which accounts for 15% of the total steel. The molten steel is then subjected to top and bottom blowing, with the oxygen flow rate controlled at 3200 m³ / h and the bottom blowing argon flow rate controlled at 80 m³ / h. Slagging agents are added in batches during the smelting process to control the slag basicity at 4.0. At the final smelting point, the carbon content in the molten steel is 0.80%, the phosphorus content is ≤0.015%, and the steel temperature is 1650~1760℃. Alloys are added during tapping for preliminary deoxidation.

[0037] Step S3: The molten steel after tapping from the converter is sent to the refining station, and the electric arc heating system is started to heat and maintain the temperature of the molten steel. During the refining process, argon blowing and stirring are carried out, and the argon flow rate is controlled in stages: 90 L / min during the heating stage, 80 L / min during the composition adjustment stage, and 60 L / min during the holding stage. A slag-forming agent is added to the furnace to control the slag basicity and form a reducing slag atmosphere. The slag-forming agent includes lime and fluorite, with 300 kg of lime added per furnace and 200 kg of fluorite added per furnace. Calcium wire is fed in during the later stage of refining, and the feeding speed is set to 5 m / s. The alumina inclusions in the molten steel are modified. The total refining time is controlled within 40 minutes. After refining, the temperature of the molten steel is controlled at 1650℃, and the molten steel is allowed to stand for 5-8 minutes.

[0038] Step S4: Select a copper tube for the crystallizer with a 14mm upper radius and a 12mm lower radius. Control the superheat of the molten steel between 20-40℃. Set the crystallizer vibration parameters as follows: frequency 189 cpm, amplitude ±3.5mm, and constant casting speed of 2.3m / min. The resistance to billet casting is significantly reduced, and there is no significant vibration or shaking in the secondary cooling chamber. The resulting billet surface corner quality is as follows... Figure 4 As shown.

[0039] pass Figure 3 and Figure 4 The comparison revealed that, Figure 3 Inspection of the cast billet revealed numerous transverse cracks at the corners. Figure 4 The medium-sized cast billet was inspected and found to be relatively... Figure 1 The surface vibration mark depth of the billet was reduced from 0.33-0.36 mm to 0.23-0.28 mm. After magnetic particle inspection, the transverse crack defect at the corner of the billet was eliminated.

[0040] In summary, the method for controlling transverse cracks at the corners of high-carbon steel billets provided in this application has proven highly effective in the production of high-carbon steel billets such as spring steel, ball steel, and bearing steel. Previously, numerous transverse cracks existed at the corners of the cast billets, necessitating extensive peeling. After implementation, the method eliminates corner crack defects and the peeling process, thus reducing the cost of peeling and flaw detection for cast billets and rolled products, improving product quality, and demonstrating high practical value in the industry. Furthermore, the proposed solution does not affect other process parameters or production implementation; the production process remains normal, without impacting other quality or equipment aspects. It is easy to implement and promote, possessing significant social application value.

[0041] Those skilled in the art will understand that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0042] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for controlling transverse cracks at the corner of a high-carbon steel billet, characterized in that: Includes the following steps: Step S1, molten iron pretreatment: Molten iron is sent to the molten iron pretreatment station for desulfurization. After desulfurization, the sulfur content in the molten iron is ≤0.008%. After desulfurization, slag removal is performed with a slag removal rate ≥95%. Step S2, converter smelting: the pretreated molten iron is added to the converter, along with qualified scrap steel; the molten steel is smelted by top and bottom blowing, controlling the oxygen flow rate and the bottom blowing argon flow rate; slag-forming agent is added in batches during the smelting process, and the slag basicity is controlled at 3.5~4.0; at the end of the smelting process, the carbon content in the molten steel is 0.70~0.80%, the phosphorus content is ≤0.015%, and the temperature of the molten steel is 1650~1760℃; During the steelmaking process, alloys are added for preliminary deoxidation; Step S3, LF refining: The molten steel after tapping from the converter is sent to the refining station, and the electric arc heating system is started to raise and maintain the temperature of the molten steel. During the refining process, argon blowing and stirring are carried out, and slag-forming agents are added into the furnace to control the slag basicity and form a reducing slag atmosphere. In the later stage of refining, calcium wire is fed in to modify the alumina inclusions in the molten steel. The total refining time is controlled at 30~40 minutes. After refining, the temperature of the molten steel is controlled at 1610~1650℃, and the molten steel is allowed to stand for 5~8 minutes. Step S4, continuous casting preparation: Before production, select a crystallizer copper tube with an upper R angle of 12.5~14mm and a lower R angle of 10~12mm. Install the copper tube into the crystallizer assembly and conduct a water flow test on the crystallizer to check for leaks in each cooling water path. At the same time, check and calibrate the continuous casting machine roller table and guide rollers. Step S5, continuous casting: molten steel with qualified smelting composition and temperature is hoisted to the continuous casting ladle turret and poured into the tundish through the ladle's long nozzle; the tundish uses an immersion nozzle for protection during casting; the crystallizer vibration frequency is set to 185~190 cpm, and the amplitude is ±3.5mm; the casting speed is set to 2.2~2.4m / min; the molten steel level is monitored in real time during casting, and the molten steel flow rate is adjusted by the tundish stopper rod; the molten steel temperature in the tundish is monitored in real time to ensure that the molten steel maintains a constant casting speed within the superheat range of 20~40℃. Simultaneously, the water flow rate in the secondary cooling zone is adjusted until the entire furnace of molten steel is poured, thus completing the production of high-carbon steel billets.

2. The method for controlling transverse cracks at the corner of a high-carbon steel billet according to claim 1, characterized in that: In step S1, during the desulfurization operation of molten steel, the desulfurization speed is set to 80~90 r / min, and the stirring time lasts for 10~15 min.

3. The method for controlling transverse cracks at the corner of a high-carbon steel billet according to claim 1, characterized in that: In step S2, the proportion of scrap steel is 15-20%, the oxygen flow rate is controlled at 2800-3200 m³ / h, and the bottom-blown argon flow rate is controlled at 50-80 m³ / h; the alloys added during the tapping process are ferrosilicon, ferromanganese silicomanganese, and high-carbon ferrochrome.

4. The method for controlling transverse cracks at the corner of a high-carbon steel billet according to claim 1, characterized in that: In step S3, during the refining process, the argon flow rate is controlled in stages when stirring with argon: 80-90 L / min during the heating stage, 70-80 L / min during the composition adjustment stage, and 50-60 L / min during the heat preservation stage. The slag-forming agent includes lime and fluorite, wherein the amount of lime added is 200~300 kg / furnace and the amount of fluorite added is 100~200 kg / furnace; The feeding speed of calcium should be set to 3~5m / s.

5. The method for controlling transverse cracks at the corners of high-carbon steel billets according to claim 1, characterized in that: In step S4, the upper opening radius (R) is 14mm and the lower opening radius (R) is 12mm.

6. The method for controlling transverse cracks at the corner of a high-carbon steel billet according to claim 1, characterized in that: In step S5, the crystallizer vibration frequency is set to 189 cpm and the pulling speed is set to 2.3 m / min.

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