Guide arm spring flat steel surface crack control process method

Abstract

The invention relates to the technical field of guide arm spring flat steel, and discloses a guide arm spring flat steel surface crack control technological method.The guide arm spring flat steel surface crack control technological method comprises the following technological methods of S1, smelting technology optimization, S2, continuous casting technology control, S3, rolling technology optimization and S4, quality detection and feedback adjustment. In the smelting stage, through slag stopping and tapping, LF furnace long-time refining white slag making (the alkalinity is 5.0-7.0, and the white slag retention time is longer than or equal to 30 min) and vacuum deep degassing (the vacuum degree is smaller than or equal to 67 Pa, and the retention time is longer than or equal to 15 min), the content of gas (the hydrogen content is smaller than or equal to 1.5 ppm) and the content of inclusions in steel are remarkably reduced, component fluctuation in the later period is avoided through accurate use of a diffusion deoxidizing agent (the use amount is larger than or equal to 80 kg / furnace), a pure molten steel foundation is laid for the follow-up process, and the production cost is reduced. And crack inducements caused by inclusion and gas are reduced from the source.

Description

Technical Field

[0001] This invention relates to the field of guide arm spring flat steel technology, specifically a process method for controlling surface cracks in guide arm spring flat steel. Background Technology

[0002] Guide arm spring flat steel is a core load-bearing component of automotive suspension systems, primarily responsible for shock absorption, guidance, and force transmission. It needs to operate under alternating load conditions for extended periods, and its surface quality directly determines the product's fatigue life and the overall vehicle's operational safety. With the automotive industry's increasing demand for lightweight and high load-bearing capacity, this type of flat steel is gradually moving towards high alloying. Various strengthening elements are added to improve strength and toughness. However, high alloying also significantly increases the material's susceptibility to cracking, making surface cracks a key issue restricting product quality.

[0003] In existing production processes, the generation of surface cracks involves multiple stages such as smelting, continuous casting, and rolling. In the smelting stage, insufficient deoxidation and poor control of gas and inclusions can easily lead to insufficient purity of molten steel, forming crack initiation points. During continuous casting, factors such as mismatch between the properties of the mold flux and vibration parameters, uneven cooling intensity, and fluctuations in casting speed can cause defects such as deepening of surface vibration marks and longitudinal cracks at corners. In the rolling stage, excessively high heating temperatures or excessively long holding times can easily lead to surface decarburization and grain coarsening. Incomplete descaling can cause iron oxide scale to be pressed in, further inducing cracks. At the same time, the precipitates of high alloying elements at grain boundaries (such as nitrides) can exacerbate stress concentration and easily form intergranular cracks during hot and cold working.

[0004] Traditional processes lack sufficient coordination and control across multiple stages, resulting in poor parameter matching and delayed quality inspection feedback. This leads to a high incidence of surface cracks and low product qualification rates, increasing production costs and posing serious safety hazards. Therefore, developing a comprehensive surface crack control process covering the entire process, achieving end-to-end optimization from molten steel purity to finished product quality, has become a pressing technical challenge for the industry. Summary of the Invention

[0005] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a process for controlling surface cracks in guide arm spring flat steel, which has advantages such as improving the purity of molten steel and reducing crack sources, thus solving the problem of surface cracks restricting product quality.

[0006] (II) Technical Solution To achieve the above-mentioned goals of improving the purity of molten steel and reducing crack sources, the present invention provides the following technical solution: a surface crack control process for guide arm spring flat steel, comprising the following process methods: S1 smelting process optimization, S2 continuous casting process control, S3 rolling process optimization, and S4 quality inspection and feedback adjustment. The S1 smelting process optimization includes S101 converter smelting control, S102 LF furnace refining process, and S103 vacuum treatment process. Among them, the S2 continuous casting process control includes S201 crystallizer parameter optimization, S202 casting speed and cooling control, S203 end and reduction control, and S204 protective slag selection. Among them, the S3 rolling process optimization includes S301 heating process control, S302 descaling and rolling control, and S303 post-rolling treatment; Among them, S4 quality inspection and feedback adjustment includes S401 online inspection, S402 offline analysis and S403 process feedback.

[0007] Preferably, the S101 converter smelting control includes: controlling the carbon content at the tapping endpoint to be ≥0.08%, the phosphorus content to be ≤0.012%, and the tapping temperature to be ≥1580℃; adopting slag-blocking tapping technology to strictly prohibit slag feeding, reducing slag contamination of molten steel; adding deoxidizer, alloy, and slag material along the steel flow when 1 / 4 of the steel is tapped to ensure that the aluminum content entering the LF furnace is ≥0.035%, laying a good foundation for subsequent refining.

[0008] Preferably, the S102 LF furnace refining process is as follows: the total argon blowing time of molten steel in the LF furnace is ≥50min, and deoxidation, desulfurization and inclusion removal are carried out by refining to form white slag. The basicity of the white slag is controlled at 5.0-7.0, the target slag quantity is 13-15kg / t, the white slag holding time is ≥30min, and diffusion deoxidation is carried out using aluminum granules, silicon carbide and carbon powder. The amount of diffusion deoxidizer is ≥80kg / furnace. The aluminum is adjusted to the required level at one time when the refined white slag is formed, and the subsequent feeding of aluminum wire is prohibited to avoid composition fluctuations.

[0009] Preferably, the S103 vacuum treatment process is as follows: the VD furnace in-station time is ≥40 min, the RH furnace in-station time is ≥35 min, and composition adjustment is strictly prohibited after RH and VD furnaces are evacuated. The vacuum is evacuated to below 0.5 tor (67 Pa) and held for ≥15 min. The soft blowing argon time is controlled at 10-25 min. The hydrogen content of the molten steel is controlled at ≤1.5 ppm for each casting. The temperature of the molten steel leaving the station is controlled according to the target superheat of the tundish. The initial casting furnace temperature is <35℃, and the continuous casting furnace temperature is 15-25℃.

[0010] Preferably, the S201 crystallizer parameters are optimized as follows: a small-beveled crystallizer is adopted, with full-process protective casting, and Hengji CrMn-based protective slag is used to ensure that the physical properties of the protective slag match the vibration parameters. The fluctuation of the liquid level in the crystallizer is controlled within ±5mm. If it exceeds the range, the billet is rejected. The electromagnetic stirring parameters of the crystallizer are set to 280-350A and 2.5Hz to enhance the flow of molten steel and refine the grains.

[0011] Preferably, the S202 casting speed and cooling control are as follows: when the billet shape is 280×280mm, the casting speed is controlled at 0.80-0.90m / min, the standard casting speed is 0.82m / min, and the water volume in the crystallizer is dynamically adjusted according to the casting speed. The water volume is 2800L / min when the casting speed is 0.75m / min and 3000L / min when the casting speed is 0.82m / min. The specific water volume is controlled at 0.28-0.34L / kg, with a target of 0.30L / kg, to avoid uneven cooling that could lead to cracks. S203 End-of-line and Reduction Control: The end-of-line electromagnetic stirring parameters are 400A and 5.0-8.0Hz to promote uniform distribution of solute elements. The light reduction + heavy reduction process is activated, and the reduction rollers are used in a total of 10mm for 3-6 stands to reduce center segregation. The continuous casting billets are densely stacked / placed in the pit for slow cooling and heat preservation, with a slow cooling time of ≥24h to reduce internal stress.

[0012] Preferably, the S204 protective slag is selected as follows: Hengji Cr-Mn special protective slag is preferred, with its viscosity controlled at 1.08 Pa・S / 1300℃, melting point at 1178℃, and basicity at 0.60, to ensure good lubrication of the billet surface. During the test phase, the performance of different protective slags can be compared, and the type of protective slag that can reduce surface cracks is preferred.

[0013] Preferably, the S301 heating process control is as follows: when heating 280×280mm billets, the preheating section temperature is ≤650℃, the heating section I temperature is 970-1020℃, the heating section II temperature is 980-1020℃, the soaking section is rapidly heated, the total time in the furnace is ≤160min, the residual oxygen content in the furnace is controlled to <1% throughout the process, maintaining a reducing atmosphere and a slight positive pressure to reduce oxidation loss; S302 Descaling and Rolling Control: High-pressure water descaling pressure ≥28MPa to ensure that iron oxide scale is completely removed. During the rolling process, sharp corners and burrs on the rolling groove, baffle, guide, and roller table are ground clean. Any parts that cannot be ground are replaced in time. Flat steel adopts a slow cooling process. The heat preservation cover is completely closed during the rolling process, and the exit temperature is <500℃ to reduce cracks caused by temperature stress. S303 Post-rolling treatment: The surface and sides of the finished flat steel are not allowed to be ground, the ends must be flat, and burrs and defects must be removed. Rectangular flat steel shall be subjected to ultrasonic testing in accordance with the requirements of GB / T4162 Class B, with a sampling ratio of ≥2 pieces per batch to ensure that the internal quality is qualified.

[0014] Preferably, the S401 online inspection involves taking one sample from each batch of cast billets online for surface pickling inspection, focusing on checking for cracks and inclusion defects. After rolling, the flat steel is subjected to surface magnetic particle testing and ultrasonic testing to promptly detect surface and internal defects. S402 Offline Analysis: Metallographic and electron microscopic analysis are performed on samples with defects to determine the type, depth, and cause of defects, such as checking for grain boundary cracks caused by NbN precipitates.

[0015] Preferably, the S403 process feedback involves dynamically adjusting process parameters based on the test results. If numerous surface cracks are found, the type of protective slag in the crystallizer can be optimized, the electromagnetic stirring parameters adjusted, or the cooling intensity reduced. If decarburization is present, the heating time can be shortened or the heating temperature lowered to ensure continuous process optimization.

[0016] (III) Beneficial Effects Compared with the prior art, the present invention provides a method for controlling surface cracks in guide arm spring flat steel, which has the following beneficial effects: 1. This guide arm spring flat steel surface crack control process improves the purity of molten steel and reduces crack initiation points. During the smelting stage, slag blocking during steel tapping, long-term refining in the LF furnace to create white slag (basicity 5.0-7.0, white slag holding time ≥30min), and deep vacuum degassing (vacuum degree ≤67Pa, holding time ≥15min) significantly reduce the content of gases (hydrogen ≤1.5ppm) and inclusions in the steel. The precise use of diffusion deoxidizer (dosage ≥80kg / furnace) avoids later composition fluctuations, laying a pure molten steel foundation for subsequent processes and reducing crack initiation factors caused by inclusions and gases from the source.

[0017] 2. The method for controlling surface cracks in guide arm spring flat steel optimizes the continuous casting process and suppresses surface cracks in the billet. In the continuous casting stage, a small-beveled crystallizer, dynamically matched protective slag (viscosity 1.08 Pa・S / 1300℃, melting point 1178℃), and electromagnetic stirring parameters (crystallizer 280-350A / 2.5Hz, end 400A / 5.0-8.0Hz) improve the uniformity of the initial billet shell and reduce the depth of vibration marks. Dynamic adaptation of casting speed (0.80-0.90 m / min) and cooling intensity (specific water volume 0.28-0.34 L / kg) prevents the corners of the billet from entering the brittle temperature zone. The light reduction + heavy reduction process (3-6 reduction rollers for a total reduction of 10 mm) and ≥24h slow cooling effectively reduce center segregation and internal stress, reducing the incidence of surface cracks in the billet by more than 60%.

[0018] 3. The surface crack control process for the guide arm spring flat steel is based on precise rolling control, which reduces processing-induced cracks. During the rolling stage, strict control of the heating regime (preheating section ≤650℃, total furnace time ≤160min) and the reducing atmosphere in the furnace (residual oxygen content <1%) reduces surface decarburization and oxidation loss. High-pressure water descaling at ≥28MPa ensures thorough removal of iron oxide scale, preventing the indentation of cracks. Slow cooling after rolling (exit temperature <500℃) and the absence of surface grinding process reduce temperature stress and mechanical damage, further ensuring surface integrity.

[0019] 4. The proposed surface crack control process for guide arm spring flat steel constructs a closed-loop quality control system to ensure process stability. It combines online pickling detection, magnetic particle inspection, and offline metallographic and electron microscopy analysis to achieve precise source tracing of crack defects. Through a process feedback mechanism, it dynamically adjusts the type of protective slag, electromagnetic stirring parameters, and cooling intensity, forming a closed-loop control system of "detection-analysis-optimization." This increases the surface crack pass rate of finished products to over 95%, significantly improves fatigue life stability, and reduces scrap rate and production costs, providing technical support for the large-scale production of high-reliability guide arm spring flat steel. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] This invention provides a technical solution, specifically, a process method for controlling surface cracks in guide arm spring flat steel; Including the following process methods: S1 smelting process optimization: S101 converter smelting control: The carbon content at the end of tapping is controlled to be ≥0.08%, the phosphorus content to be ≤0.012%, and the tapping temperature to be ≥1580℃. Slag-blocking tapping technology is adopted, and slag feeding is strictly prohibited to reduce the pollution of molten steel by slag. Deoxidizer, alloy and slag are added in the flow of steel when 1 / 4 of the steel is tapped to ensure that the aluminum content of the LF furnace entering the station is ≥0.035%, which lays a good foundation for subsequent refining. S102 LF furnace refining process: The total argon blowing time of molten steel in the LF furnace is ≥50min. Deoxidation, desulfurization and inclusion removal are carried out by refining to form white slag. The basicity of the white slag is controlled at 5.0-7.0, the target slag quantity is 13-15kg / t, and the white slag holding time is ≥30min. Aluminum granules, silicon carbide and carbon powder are used for diffusion deoxidation. The amount of diffusion deoxidizer is ≥80kg / furnace. Aluminum is adjusted in one go when the refining white slag is formed. It is forbidden to feed aluminum wire later to avoid composition fluctuations. S103 vacuum treatment process: VD furnace on-site time ≥40min, RH furnace on-site time ≥35min, and composition adjustment operation is strictly prohibited after RH and VD are evacuated. Vacuum is drawn to below 0.5tor (67Pa) and held for ≥15min. Soft blowing argon time is controlled at 10-25min. Hydrogen is drawn for ≥1 furnace per casting. The hydrogen content of molten steel is controlled at ≤1.5ppm. The temperature of molten steel leaving the station is controlled according to the target superheat of the tundish. The temperature of the first casting furnace is <35℃, and the temperature of the continuous casting furnace is 15-25℃. S2 continuous casting process control: S201 crystallizer parameter optimization: A small-beveled crystallizer is adopted, and the entire casting process is protected. Hengji CrMn series protective slag is used to ensure that the physical properties of the protective slag match the vibration parameters. The fluctuation of the liquid level in the crystallizer is controlled within ±5mm. If it exceeds the range, the billet is rejected. The electromagnetic stirring parameters of the crystallizer are set to 280-350A, 2.5Hz to enhance the flow of molten steel and refine the grains. S202 Casting Speed ​​and Cooling Control: When the billet size is 280×280mm, the casting speed is controlled at 0.80-0.90m / min, the standard casting speed is 0.82m / min, and the water flow in the crystallizer is dynamically adjusted according to the casting speed. The water flow is 2800L / min at a casting speed of 0.75m / min and 3000L / min at a casting speed of 0.82m / min. The specific water flow is controlled at 0.28-0.34L / kg, with a target of 0.30L / kg, to avoid uneven cooling that could lead to cracks. S203 End-of-line and Reduction Control: The end-of-line electromagnetic stirring parameters are 400A and 5.0-8.0Hz to promote uniform distribution of solute elements. The light reduction + heavy reduction process is activated, and the reduction rollers are used in a total of 10mm for 3-6 stands to reduce center segregation. The continuous casting billets are densely stacked / placed in the pit for slow cooling and heat preservation, with a slow cooling time of ≥24h to reduce internal stress. S204 protective slag selection: Hengji Cr-Mn special protective slag is preferred, with its viscosity controlled at 1.08Pa・S / 1300℃, melting point 1178℃, and basicity 0.60 to ensure good lubrication of the billet surface. During the test phase, the performance of different protective slags can be compared, and the type of protective slag that can reduce surface cracks should be selected first. S3 rolling process optimization: S301 Heating Process Control: When heating 280×280mm billets, the preheating zone temperature is ≤650℃, the heating zone I temperature is 970-1020℃, the heating zone II temperature is 980-1020℃, the soaking zone is rapidly heated, the total time in the furnace is ≤160min, the residual oxygen content in the furnace is controlled <1% throughout the process, maintaining a reducing atmosphere and slight positive pressure to reduce oxidation loss; S302 Descaling and Rolling Control: High-pressure water descaling pressure ≥28MPa to ensure that iron oxide scale is completely removed. During the rolling process, sharp corners and burrs on the rolling groove, baffle, guide, and roller table are ground clean. Any parts that cannot be ground are replaced in time. Flat steel adopts a slow cooling process. The heat preservation cover is completely closed during the rolling process, and the exit temperature is <500℃ to reduce cracks caused by temperature stress. S303 Post-rolling treatment: The surface and sides of the finished flat steel are not allowed to be ground, the ends must be flat, and burrs and defects must be removed. Rectangular flat steel shall be subjected to ultrasonic testing in accordance with GB / T4162 Grade B requirements, with a sampling ratio of ≥2 pieces per batch to ensure that the internal quality is qualified. S4 Quality Inspection and Feedback Adjustment: S401 Online Inspection: One sample is taken from each batch of billet for surface pickling inspection, focusing on checking for cracks and inclusion defects. After rolling, the flat steel is subjected to surface magnetic particle testing and ultrasonic testing to detect surface and internal defects in a timely manner. S402 Offline Analysis: Metallographic and electron microscopic analysis are performed on samples with defects to determine the type, depth and cause of defects, such as checking for grain boundary cracks caused by NbN precipitates. S403 Process Feedback: Dynamically adjust process parameters based on test results. If many surface cracks are found, optimize the type of mold flux, adjust electromagnetic stirring parameters, or reduce cooling intensity. If decarburization is present, shorten heating time or reduce heating temperature to ensure continuous process optimization. Furthermore, this process improves the purity of molten steel and reduces crack initiation points. During the smelting stage, slag-blocking tapping, long-term refining in the LF furnace to create white slag (basicity 5.0-7.0, white slag holding time ≥30min), and deep vacuum degassing (vacuum degree ≤67Pa, holding time ≥15min) significantly reduce the content of gases (hydrogen ≤1.5ppm) and inclusions in the steel. The precise use of diffusion deoxidizer (dosage ≥80kg / furnace) avoids later compositional fluctuations, laying a pure molten steel foundation for subsequent processes and reducing crack initiation factors caused by inclusions and gases from the source. Furthermore, this process optimizes the continuous casting process and suppresses surface cracks in the billet. In the continuous casting stage, the use of a small-beveled crystallizer, dynamically matched protective slag (viscosity 1.08 Pa·S / 1300℃, melting point 1178℃), and electromagnetic stirring parameters (crystallizer 280-350A / 2.5Hz, end 400A / 5.0-8.0Hz) improves the uniformity of the initial billet shell and reduces the depth of vibration marks. Dynamic adaptation of casting speed (0.80-0.90 m / min) and cooling intensity (specific water volume 0.28-0.34 L / kg) prevents the corners of the billet from entering the brittle temperature zone. The combination of light and heavy reduction (3-6 rollers for a total reduction of 10 mm) and ≥24h slow cooling effectively reduces center segregation and internal stress, resulting in a reduction of the surface crack incidence rate of the billet by more than 60%. Furthermore, this process method features precise rolling control, reducing processing-induced cracks. During the rolling stage, strict control of the heating regime (preheating section ≤650℃, total furnace time ≤160min) and the reducing atmosphere in the furnace (residual oxygen content <1%) reduces surface decarburization and oxidation loss. High-pressure water descaling at ≥28MPa ensures thorough removal of iron oxide scale, preventing the indentation of cracks. Slow cooling after rolling (exit temperature <500℃) and a surface-free grinding process reduce thermal stress and mechanical damage, further ensuring surface integrity. Furthermore, this process constructs a closed-loop quality control system to ensure process stability. The combination of online pickling detection, magnetic particle inspection, and offline metallographic and electron microscopy analysis enables precise tracing of crack defects. Through a process feedback mechanism, the type of protective slag, electromagnetic stirring parameters, and cooling intensity are dynamically adjusted to form a closed-loop control of "detection-analysis-optimization." This increases the surface crack pass rate of finished products to over 95%, significantly improves fatigue life stability, and reduces scrap rate and production costs. This provides technical support for the large-scale production of high-reliability guide arm spring flat steel.

[0022] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for controlling surface cracks in guide arm spring flat steel, comprising the following steps: S1 smelting process optimization, S2 continuous casting process control, S3 rolling process optimization, and S4 quality inspection and feedback adjustment, characterized in that: The S1 smelting process optimization includes S101 converter smelting control, S102 LF furnace refining process and S103 vacuum treatment process. Among them, the S2 continuous casting process control includes S201 crystallizer parameter optimization, S202 casting speed and cooling control, S203 end and reduction control, and S204 protective slag selection. Among them, the S3 rolling process optimization includes S301 heating process control, S302 descaling and rolling control, and S303 post-rolling treatment; Among them, S4 quality inspection and feedback adjustment includes S401 online inspection, S402 offline analysis and S403 process feedback.

2. The method for controlling surface cracks in guide arm spring flat steel according to claim 1, characterized in that: The S101 converter smelting control measures are as follows: at the tapping endpoint, the carbon content is controlled to be ≥0.08%, the phosphorus content to be ≤0.012%, and the tapping temperature to be ≥1580℃. Slag-blocking tapping technology is adopted, and slag feeding is strictly prohibited to reduce slag contamination of the molten steel. When 1 / 4 of the steel is tapped, deoxidizer, alloy, and slag are added along the steel flow to ensure that the aluminum content entering the LF furnace is ≥0.035%, laying a good foundation for subsequent refining.

3. The method for controlling surface cracks in guide arm spring flat steel according to claim 1, characterized in that: The S102 LF furnace refining process is as follows: the total argon blowing time of molten steel in the LF furnace is ≥50min. Deoxidation, desulfurization and inclusion removal are carried out by refining to form white slag. The basicity of the white slag is controlled at 5.0-7.0, the target slag quantity is 13-15kg / t, the white slag holding time is ≥30min, and diffusion deoxidation is carried out using aluminum granules, silicon carbide and carbon powder. The amount of diffusion deoxidizer is ≥80kg / furnace. The aluminum is adjusted to the required level at the time of formation of the refined white slag. It is forbidden to feed aluminum wire later to avoid composition fluctuations.

4. The method for controlling surface cracks in guide arm spring flat steel according to claim 1, characterized in that: The S103 vacuum treatment process is as follows: VD furnace in-station time ≥40min, RH furnace in-station time ≥35min, and composition adjustment is strictly prohibited after RH and VD furnaces are evacuated. Vacuum is evacuated to below 0.5tor (67Pa) and held for ≥15min. Soft blowing argon time is controlled between 10-25min. Hydrogen is evacuated for ≥1 furnace per casting cycle. The hydrogen content of molten steel is controlled to ≤1.5ppm. The temperature of molten steel leaving the station is controlled according to the target superheat of the tundish. For the first casting furnace, the temperature is <35℃, and for the continuous casting furnace, the temperature is 15-25℃.

5. The method for controlling surface cracks in guide arm spring flat steel according to claim 1, characterized in that: The S201 crystallizer parameters were optimized as follows: a small-beveled crystallizer was adopted, and full-process protective casting was carried out. Hengji CrMn-based protective slag was used to ensure that the physical properties of the protective slag matched the vibration parameters. The fluctuation of the liquid level in the crystallizer was controlled within ±5mm. If it exceeded the range, the billet was rejected. The electromagnetic stirring parameters of the crystallizer were set to 280-350A and 2.5Hz to enhance the flow of molten steel and refine the grains.

6. The method for controlling surface cracks in guide arm spring flat steel according to claim 1, characterized in that: The S202 casting speed and cooling control are as follows: When the billet size is 280×280mm, the casting speed is controlled at 0.80-0.90m / min, the standard casting speed is 0.82m / min, and the water volume in the crystallizer is dynamically adjusted according to the casting speed. The water volume is 2800L / min when the casting speed is 0.75m / min and 3000L / min when the casting speed is 0.82m / min. The specific water volume is controlled at 0.28-0.34L / kg, with a target of 0.30L / kg, to avoid uneven cooling that could lead to cracks. S203 End-of-line and Reduction Control: The end-of-line electromagnetic stirring parameters are 400A and 5.0-8.0Hz to promote uniform distribution of solute elements. The light reduction + heavy reduction process is activated, and the reduction rollers are used in a total of 10mm for 3-6 stands to reduce center segregation. The continuous casting billets are densely stacked / placed in the pit for slow cooling and heat preservation, with a slow cooling time of ≥24h to reduce internal stress.

7. The method for controlling surface cracks in guide arm spring flat steel according to claim 1, characterized in that: The selection of S204 protective slag: Hengji Cr-Mn special protective slag is preferred, with its viscosity controlled at 1.08 Pa・S / 1300℃, melting point 1178℃, and basicity 0.60, to ensure good lubrication of the billet surface. During the test phase, the performance of different protective slags can be compared, and the type of protective slag that can reduce surface cracks is preferred.

8. The method for controlling surface cracks in guide arm spring flat steel according to claim 1, characterized in that: The S301 heating process control is as follows: When heating 280×280mm billets, the preheating section temperature is ≤650℃, the heating section I temperature is 970-1020℃, the heating section II temperature is 980-1020℃, the soaking section is rapidly heated, the total time in the furnace is ≤160min, the residual oxygen content in the furnace is controlled to <1% throughout the process, maintaining a reducing atmosphere and a slight positive pressure to reduce oxidation loss; S302 Descaling and Rolling Control: High-pressure water descaling pressure ≥28MPa to ensure that iron oxide scale is completely removed. During the rolling process, sharp corners and burrs on the rolling groove, baffle, guide, and roller table are ground clean. Any parts that cannot be ground are replaced in time. Flat steel adopts a slow cooling process. The heat preservation cover is completely closed during the rolling process, and the exit temperature is <500℃ to reduce cracks caused by temperature stress. S303 Post-rolling treatment: The surface and sides of the finished flat steel are not allowed to be ground, the ends must be flat, and burrs and defects must be removed. Rectangular flat steel shall be subjected to ultrasonic testing in accordance with the requirements of GB / T4162 Class B, with a sampling ratio of ≥2 pieces per batch to ensure that the internal quality is qualified.

9. The method for controlling surface cracks in guide arm spring flat steel according to claim 1, characterized in that: The S401 online inspection: One sample is taken from each batch of billet for surface pickling inspection, focusing on checking for cracks and inclusion defects. After rolling, the flat steel is subjected to surface magnetic particle inspection and ultrasonic inspection to detect surface and internal defects in a timely manner. S402 Offline Analysis: Metallographic and electron microscopic analysis are performed on samples with defects to determine the type, depth, and cause of defects, such as checking for grain boundary cracks caused by NbN precipitates.

10. The method for controlling surface cracks in guide arm spring flat steel according to claim 1, characterized in that: The S403 process feedback: The process parameters are dynamically adjusted based on the test results. If many surface cracks are found, the type of protective slag in the crystallizer can be optimized, the electromagnetic stirring parameters can be adjusted, or the cooling intensity can be reduced. If decarburization issues exist, shorten the heating time or lower the heating temperature to ensure continuous process optimization.