Steelmaking and continuous casting method of high-strength spring flat steel

Abstract

The invention discloses a steelmaking and continuous casting method of high-strength spring flat steel, which comprises the following steps: 1) converter: controlling the end point C to be greater than or equal to 0.15%, and controlling the end point temperature to be greater than or equal to 1640 DEG C; preheating the alloy; lime is added in the tapping process, and argon bottom blowing is kept in the tapping process and after tapping is finished; (2) external refining: refining slag and lime added into a converter are matched for slagging in an LF (Ladle Furnace); 3) vacuum degassing; (4) continuous casting is conducted, specifically, whole-course protection pouring is adopted, an integral tundish and a crystallizer water gap are used, and the tundish has a heating function; electromagnetic stirring and continuous casting soft reduction processes are adopted at the tail end; according to the steelmaking and continuous casting method of the high-strength spring flat steel, the total oxygen content of the spring flat steel can be controlled to be smaller than or equal to 5 ppm, inclusions are controlled to be smaller than or equal to 1.0 grade, Ds type inclusions are controlled to be smaller than or equal to 0.5 grade, the total amount of the inclusions is reduced, the purity of molten steel is high, the fatigue life of the spring flat steel is prolonged, the machining performance of the spring flat steel is effectively improved, and the high strength of the spring flat steel is guaranteed.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, and particularly relates to a method for steelmaking and continuous casting of high-strength spring flat steel. Background Technology

[0002] In recent years, the automotive industry has faced increasingly stringent requirements for energy conservation and emission reduction. Whether it's commercial vehicles or family cars, the demand for lightweighting is also rising. Leaf springs are essential components in commercial vehicles such as heavy trucks, light trucks, and mining trucks, accounting for 5-8% of the vehicle's total weight. Therefore, it is necessary to reduce the weight of leaf springs. However, this weight reduction significantly increases the requirements for the strength and fatigue limit of the spring flat steel.

[0003] With technological advancements, the strength of automotive leaf springs has reached as high as 2000MPa, thus placing increasingly stringent requirements on the heat treatment performance of the raw material for leaf spring production—spring flat steel. To ensure both high strength and high toughness, this type of high-strength spring flat steel is often designed as a medium-carbon, high-alloy steel, requiring extremely high purity of molten steel and uniformity of composition in the continuous casting billet cross-section. Furthermore, increasing the alloy ratio significantly increases the crack sensitivity of the continuous casting billet. Using conventional continuous casting processes, especially during light reduction, the billet is prone to severe intermediate cracks, which cannot be completely eliminated even after rolling, leading to cracking along the cracks during use or fatigue testing. Therefore, the technical problem this invention aims to solve is how to design a technology that can guarantee high strength and high toughness of spring flat steel while reducing intermediate cracks in the continuous casting billet. Summary of the Invention

[0004] The purpose of this application is to provide a steelmaking and continuous casting method for high-strength spring flat steel, which can reduce the generation of intermediate cracks in the continuous casting billet while ensuring the high strength and high toughness of the spring flat steel.

[0005] To solve the above-mentioned technical problems, this application mainly adopts the following technical solutions: In the first aspect, this application provides a method for steelmaking and continuous casting of high-strength spring flat steel, comprising the following steps: Step 1) Converter: The final control of the converter is C≥0.15% and the final temperature≥1640℃; preheat the alloy to ensure that the temperature of the alloy added into the ladle is≥650℃; use the slag washing process, add lime during the tapping process, maintain bottom blowing argon gas in the ladle during the tapping process, and maintain bottom blowing argon gas after the tapping is completed; Step 2) Ladle refining: LF uses refining slag and lime added to the converter to form slag; Step 3) Vacuum degassing; Step 4) Continuous casting: Full-process protective casting is adopted, using an integral tundish and crystallizer nozzle. The casting speed of the continuous casting billet is 0.80-0.90m / min, the electromagnetic stirring frequency of the crystallizer is 3-5Hz, the current is 200-450A, the secondary cooling water flow rate is 0.15-0.25L / kg, and the tundish is equipped with a heating function; the end adopts electromagnetic stirring and continuous casting light reduction process. Step 5) Slow cooling of continuous casting billet: The continuous casting billet is placed in the slow cooling pit for slow cooling. The surface temperature of the billet is ≥600℃ and the surface temperature of the billet is <250℃ when it leaves the slow cooling pit.

[0006] In some embodiments of this application, in step 1), the amount of lime added during the tapping process is 0.7~5.5 kg / t of molten steel, wherein the CaO content in the lime is ≥95%.

[0007] In some embodiments of this application, in step 1), the bottom blowing argon gas is maintained for ≥5 min after the steel tapping is completed.

[0008] In some embodiments of this application, in step 2), the final slag composition is: CaO 45%~55%, SiO2 6%~12%, Al2O3 25%~35%, and R (alkalinity) 4.0~7.0.

[0009] In some embodiments of this application, step 2) further includes continuing slag-preserving refining after the LF component temperature is adjusted, with a current ≤25kA, a voltage ≤120V, and a slag-preserving refining time ≥15min.

[0010] In some embodiments of this application, in step 3), the vacuum degree of vacuum degassing is ≤67Pa and the vacuum holding time is ≥40min.

[0011] In some embodiments of this application, in step 4), a low-temperature casting process is performed, and the superheating requirement of the tundish during continuous casting is 12-20℃ (except for the first heat of the casting cycle), with an increase of 5-8℃ for the first heat of the casting cycle.

[0012] In some embodiments of this application, in step 4), the light pressing process involves pressing rollers 1-9, with a total pressing amount of 4-18mm.

[0013] Compared with the prior art, the advantages and positive effects of this invention are as follows: The steelmaking and continuous casting method for high-strength spring flat steel in this application includes converter, ladle refining, vacuum degassing, continuous casting, and slow cooling of the continuously cast billet. This method can control the total oxygen content of the spring flat steel to ≤5ppm, and the coarseness of various inclusions to ≤1.0 grade, with Ds-type inclusions ≤0.5 grade. This reduces the total amount of inclusions in the spring flat steel while reducing the maximum inclusion size, resulting in high steel purity and significantly improved fatigue life of the produced spring flat steel. The continuous casting light reduction process ensures that the center segregation of the continuously cast billet is ≤1.08 while preventing intermediate cracks. This effectively improves the machinability of the spring flat steel and ensures its high strength. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a cross-sectional view of the continuously cast billet in Embodiment 1 of the present invention; Figure 2 The image shows the metallographic structure of the spring flat steel in Embodiment 1 of the present invention. Figure 3 This is a cross-sectional view of the continuously cast billet in Embodiment 2 of the present invention; Figure 4 The image shows the metallographic structure of the spring flat steel in Embodiment 2 of the present invention; Figure 5 This is a cross-sectional view of the continuously cast billet in Embodiment 3 of the present invention; Figure 6 The image shows the metallographic structure of the spring flat steel in Embodiment 3 of the present invention. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] The following disclosure provides many different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0018] In the first aspect, embodiments of this disclosure provide a method for steelmaking and continuous casting of high-strength spring flat steel, specifically including the following steps: Step 1) Converter: Perform high carbon extraction operation, control C at the converter endpoint to be ≥0.15%, and the endpoint temperature to be ≥1640℃; preheat the alloy to ensure that the temperature of the alloy added to the ladle is ≥650℃; use slag washing process, add lime during the tapping process, maintain bottom blowing argon gas in the ladle during the tapping process, and maintain bottom blowing argon gas after the tapping is completed.

[0019] Specifically, by controlling the carbon content at the converter endpoint to ≥0.15% and by performing high carbon extraction, the oxygen content of the molten steel at the converter endpoint will be relatively low, thus reducing the original inclusions in the molten steel during the alloying process.

[0020] Specifically, preheating the alloy in advance can prevent a significant drop in the temperature of the molten steel.

[0021] Specifically, the alloying elements mainly include elements such as Si, Mn, Cr, and V.

[0022] Specifically, lime is added during the steelmaking process. Lime has a strong physical adsorption capacity, and its main component, calcium oxide, is insoluble in molten steel. The surface charge of the calcium oxide particles interacts with inclusions, agglomerating tiny inclusions into larger particles and increasing the slag formation rate. By systematically removing sulfur, phosphorus impurities, and solid inclusions during the steelmaking process, the cleanliness of the molten steel is ensured.

[0023] Specifically, by continuously blowing argon gas under the bottom during and after the tapping process, the molten steel can be stirred, purified, and its composition homogenized. During the slag floating process, a large amount of impurities in the molten steel will be carried to the surface, which is beneficial to improving the quality of the steel. The slag floating on the surface of the molten steel can also play a role in heat preservation.

[0024] Specifically, in order to ensure the total oxygen content at the converter endpoint and the carbon content at the converter endpoint ≥ 0.15%, the alloy melting efficiency can be guaranteed by setting the converter endpoint temperature ≥ 1640℃.

[0025] In practical use, if the C content and temperature at the converter endpoint do not meet the requirements, the temperature of the molten iron entering the furnace must be ≥1350℃. At the same time, depending on the molten iron conditions, the "double slag method" or "double-linked method" can be used.

[0026] Step 2) Ladle refining: LF uses refining slag and lime added to the converter to form slag.

[0027] In some embodiments of this application, the refining slag used in LF is pre-melted refining slag.

[0028] Specifically, pre-melted refining slag is produced by preheating and melting ordinary refining slag, then cooling it to form a solid of a certain particle size. Pre-melted refining slag is easier to remelt, reducing heat loss and shortening the slag-forming time in the early stage of refining, which helps to improve production efficiency.

[0029] Step 3) Vacuum degassing; Specifically, by performing vacuum degassing, harmful gaseous impurities in molten steel can be removed, preventing defects such as porosity from affecting the quality of the steel. During the vacuum degassing process, non-metallic inclusions in the molten steel undergo morphological changes in a vacuum environment, transforming from harmful free oxides into stable composite oxides, thus making them easier to float and remove from the molten steel.

[0030] In addition, reducing the gas content in molten steel and improving the morphology of inclusions can help improve the strength, toughness, ductility and other properties of steel.

[0031] For example, vacuum degassing includes RH vacuum degassing or VD vacuum degassing.

[0032] Step 4) Continuous casting: Full-process protective casting is adopted, using an integral tundish and crystallizer nozzle. The casting speed of the continuous casting billet is 0.80-0.90m / min, the electromagnetic stirring frequency of the crystallizer is 3-5Hz, the current is 200-450A, the secondary cooling water volume is 0.15-0.25L / kg, and the tundish is equipped with a heating function; the end adopts electromagnetic stirring and continuous casting light reduction process.

[0033] Specifically, by adopting full-process protective casting, it is possible to prevent molten steel from coming into contact with oxygen during the casting process, reduce secondary oxidation of molten steel, thereby significantly reducing the total oxygen content in the steel, improving the quality of continuously cast billets, and reducing production risks.

[0034] Step 5) Slow cooling of continuous casting billet: The continuous casting billet is placed in the slow cooling pit for slow cooling. The surface temperature of the billet is ≥600℃ and the surface temperature of the billet is <250℃ when it leaves the slow cooling pit.

[0035] Specifically, by placing the continuously cast billet in a slow cooling pit for slow cooling, the cooling rate of the continuously cast billet can be effectively controlled, resulting in a smaller internal temperature gradient, thereby reducing the generation of thermal stress, preventing defects such as cracks and delamination from occurring during the cooling process, and improving the internal quality of the continuously cast billet.

[0036] Specifically, the steelmaking and continuous casting methods for high-strength spring flat steel in this embodiment include converter, ladle refining, vacuum degassing, continuous casting, and slow cooling of the continuously cast billet. These methods can control the total oxygen content of the spring flat steel to ≤5ppm, and the coarseness of various inclusions to ≤1.0 grade, with Ds-type inclusions ≤0.5 grade. This reduces the total amount of inclusions in the spring flat steel while minimizing the maximum inclusion size, resulting in high steel purity and significantly improved fatigue life. Furthermore, the continuous casting light reduction process ensures that the center segregation of the continuously cast billet is ≤1.08 while preventing intermediate cracks. This effectively improves the machinability of the spring flat steel and guarantees its high strength.

[0037] In some embodiments of this application, in step 1), the amount of lime added during the tapping process is 0.7~5.5 kg / t of molten steel, wherein the CaO content in the lime is ≥95%.

[0038] Specifically, adding lime during the steelmaking process can remove impurities, adjust slag composition, improve slag fluidity, and remove sulfur from molten steel, thereby improving steel performance. However, if too little lime is added, the surface of the molten steel is easily exposed to air during the refining process, causing secondary oxidation of the molten steel, increasing inclusions, and resulting in low slag basicity, which affects the desulfurization capacity and stability of the slag, thus affecting the smelting effect. If too much lime is added, it will lead to excessively high slag viscosity, which is not conducive to slag-steel separation. Excessive lime will also increase production costs and cause environmental pollution.

[0039] In some embodiments of this application, in step 1), the bottom blowing argon gas is maintained for ≥5 min after the steel tapping is completed.

[0040] Specifically, by maintaining bottom-blowing argon gas after tapping, the argon gas, blown in from the bottom of the ladle, forms a large number of bubbles that rise to the surface, causing intense agitation of the molten steel. This quickly eliminates temperature gradients and alloy oxides generated during tapping, while also promoting lime flotation and ensuring effective slag washing. If the bottom-blowing argon gas duration is insufficient, excessive differences in local composition or temperature in the molten steel may cause alloy agglomeration at the bottom of the ladle, preventing melting and affecting subsequent refining, temperature increases, and composition adjustments.

[0041] In some embodiments of this application, in step 2), the final slag composition is: CaO 45%~55%, SiO2 6%~12%, Al2O3 25%~35%, and R (alkalinity) 4.0~7.0.

[0042] Specifically, within this range, the slag has a strong adsorption capacity for inclusions and maintains good fluidity, preventing inclusions from returning to the molten steel.

[0043] In some embodiments of this application, step 2) further includes continuing slag-preserving refining after the LF component temperature is adjusted, with a current ≤25kA, a voltage ≤120V, and a slag-preserving refining time ≥15min.

[0044] Specifically, by continuing slag-preserving refining after the LF composition temperature adjustment, the purity of molten steel can be improved, the performance of steel can be optimized, and the content of gas and inclusions can be further reduced, thus ensuring the quality of subsequent continuous casting and steel products.

[0045] In some embodiments of this application, in step 3), the vacuum degree of vacuum degassing is ≤67Pa and the vacuum holding time is ≥40min.

[0046] Specifically, by setting the vacuum level of vacuum degassing below 67 Pa, the gas content in the steel can be reduced to an extremely low level; holding the vacuum for more than 40 minutes can ensure that the molten steel is stirred evenly and promote the floating of inclusions.

[0047] In some embodiments of this application, in step 4), a low-temperature casting process is performed, and the superheating requirement of the tundish during continuous casting is 12-20℃ (except for the first heat of the casting cycle), with an increase of 5-8℃ for the first heat of the casting cycle.

[0048] Specifically, by implementing a low-temperature casting process during continuous casting, the superheat of the molten steel can be reduced, the low-magnification microstructure of the billet can be improved, and the microstructure of the billet can be optimized. The lower superheat allows the molten steel to quickly form a stable solidified shell in the crystallizer, reducing the space for columnar crystal growth, promoting the expansion of the equiaxed crystal zone, and effectively reducing the risk of center segregation and porosity.

[0049] In some embodiments of this application, in step 4), the light pressing process involves pressing rollers 1-9, with a total pressing amount of 4-18mm.

[0050] Specifically, the light reduction process can improve the center segregation and porosity of the billet and avoid the formation of black core after rolling.

[0051] Example 1: A method for steelmaking and continuous casting of high-strength spring flat steel, the specific steps of which are as follows: Step 1) Converter: The converter endpoint C is controlled at 0.18%, and the endpoint temperature is controlled at 1648℃; preheat the alloy to ensure that the temperature of the alloy added to the ladle is controlled at 702℃; use the slag washing process, add 200kg of lime to 110t of molten steel during the tapping process, maintain bottom blowing argon gas in the ladle during the tapping process, and maintain bottom blowing argon gas for 6min after the tapping is completed.

[0052] Step 2) Ladle refining: LF uses refining slag and lime added to the converter to form slag. The final slag composition is: CaO 45%, SiO2 6%, Al2O3 28%, R (basicity) 5.0. After the composition and temperature of the LF molten steel are adjusted, slag-preserving refining continues. The current is ≤25kA, the voltage is ≤120V, and the slag-preserving refining time is 15min.

[0053] Step 3) Vacuum degassing, with a vacuum degree ≤ 67 Pa and a vacuum holding time of 45 min.

[0054] Step 4) Continuous casting: A low-temperature casting process is implemented. During continuous casting, the superheat of the tundish is required to be controlled at 12-20℃ for other heats, and the superheat of the first heat is increased by 5-8℃. Production is organized according to 6-8 heats per heat. Full-process protective casting is adopted, and an integral tundish is used. An integral nozzle is used for the crystallizer. The casting speed of the continuous casting billet is 0.86m / min. The electromagnetic stirring frequency of the crystallizer is 4.2Hz, the current is 260A, the secondary cooling water flow rate is 0.23L / kg, and the tundish is equipped with a heating function. The final electromagnetic stirring frequency is 8Hz, the current is 410A, and the 2-9# pressing rollers are used for light pressing, with a total pressing amount of 9.8mm. The cross-sectional dimensions of the continuous casting billet are 240mm×300mm.

[0055] Step 5) Slow cooling of continuous casting billet: The billet after light pressing is transported to the slow cooling pit for slow cooling. The surface temperature of the billet is 631°C when it enters the slow cooling pit and 187°C when it exits the slow cooling pit.

[0056] Example 2: A method for steelmaking and continuous casting of high-strength spring flat steel, the specific steps of which are as follows: Step 1) Converter: The final C of the converter is controlled at 0.22%, and the final temperature is controlled at 1651℃; preheat the alloy to ensure that the temperature of the alloy added to the ladle is controlled at 680℃; use the slag washing process, add 380kg of lime to 110t of molten steel during the tapping process, maintain bottom blowing argon gas in the ladle during the tapping process, and maintain bottom blowing argon gas for 6min after the tapping is completed.

[0057] Step 2) Ladle refining: LF uses refining slag and lime added to the converter to form slag. The final slag composition is: CaO 50%, SiO2 10%, Al2O3 31%, R (basicity) 6.7. After the composition and temperature of the LF molten steel are adjusted, slag-preserving refining continues. The current is ≤25kA, the voltage is ≤120V, and the slag-preserving refining time is 17min.

[0058] Step 3) Vacuum degassing, with a vacuum degree ≤ 67 Pa and a vacuum holding time of 42 min.

[0059] Step 4) Continuous casting: A low-temperature casting process is employed. During continuous casting, the superheat of the tundish is required to be controlled at 12-20℃ for other heats, with a 5-8℃ increase for the first heat. Production is organized according to 3-6 heats per heat. Full-process protective casting is used, employing an integral tundish and an integral nozzle for the crystallizer. The casting speed is 0.82 m / min, the electromagnetic stirring frequency of the crystallizer is 4.2 Hz, the current is 320 A, the secondary cooling water flow rate is 0.19 L / kg, and the tundish is equipped with a heating function. The final electromagnetic stirring frequency is 6.5 Hz, the current is 380 A, and the 1-9# pressing rollers lightly press down, with a total reduction of 13.2 mm. The cross-sectional dimensions of the continuously cast billet are 240 mm × 300 mm.

[0060] Step 5) Slow cooling of continuous casting billet: The billet after light pressing is transported to the slow cooling pit for slow cooling. The surface temperature of the billet is 635°C when it enters the slow cooling pit and 174°C when it exits the slow cooling pit.

[0061] Example 3: A method for steelmaking and continuous casting of high-strength spring flat steel, the specific steps of which are as follows: Step 1) Converter: The final C value of the converter is controlled at 0.23%, and the final temperature is controlled at 1655℃; preheat the alloy to ensure that the temperature of the alloy added to the ladle is controlled at 714℃; use the slag washing process, add 450kg of lime to 110t of molten steel during the tapping process, maintain bottom blowing argon gas in the ladle during the tapping process, and maintain bottom blowing argon gas for 5min after the tapping is completed.

[0062] Step 2) Ladle refining: LF uses refining slag and lime added to the converter to form slag. The final slag composition is: CaO 55%, SiO2 12%, Al2O3 35%, R (basicity) 7.0. After the composition and temperature of the LF molten steel are adjusted, slag-preserving refining continues. The current is ≤25kA, the voltage is ≤120V, and the slag-preserving refining time is 16min.

[0063] Step 3) Vacuum degassing, with a vacuum degree ≤ 67 Pa and a vacuum holding time of 44 min; Step 4) Continuous casting: A low-temperature casting process is employed. During continuous casting, the superheat of the tundish is required to be controlled at 12-20℃ for other heats, with a 5-8℃ increase for the first heat. Production is organized according to 3-6 heats per heat. Full-process protective casting is used, employing an integral tundish and an integral nozzle for the crystallizer. The casting speed is 0.85 m / min, the electromagnetic stirring frequency of the crystallizer is 4.2 Hz, the current is 350 A, the secondary cooling water flow rate is 0.25 L / kg, and the tundish is equipped with a heating function. The final electromagnetic stirring frequency is 6.5 Hz, the current is 370 A, and the 1-9# pressing rollers lightly press down, with a total reduction of 10.0 mm. The cross-sectional dimensions of the continuously cast billet are 240 mm × 300 mm.

[0064] Step 5) Slow cooling of continuous casting billet: The billet after light pressing is transported to the slow cooling pit for slow cooling. When entering the slow cooling pit, the surface temperature of the billet is ≥620℃, and when leaving the slow cooling pit, the surface temperature of the billet is <200℃.

[0065] Experiment 1: The center segregation and porosity of continuously cast billets were inspected according to GB / T 226-2015; the results are as follows: The continuously cast billets of Examples 1, 2, and 3 have good internal quality and no intermediate cracks. The low-magnification and segregation test results of the continuously cast billets of Examples 1-3 are shown in Table 1 below: Table 1 shows the low-magnification and segregation detection indicators of the continuous casting billets in Examples 1-3.

[0066] As shown in Table 1, the center segregation, center porosity, and general porosity of Examples 1, 2, and 3 are all at level 0.5, indicating that the degree of center segregation and center porosity of the billet is low and there are fewer internal defects, which is beneficial to improving the quality of the steel.

[0067] Experiment 2: The inclusions in the spring flat steel prepared in Examples 1, 2 and 3 were rated according to GB / T 10561-2023, and the oxygen content was tested. The test results are shown in Table 2 below. Figure 1 , Figure 3 , Figure 5 Cross-sectional photographs of Examples 1, 2, and 3, respectively; Figure 2 , Figure 4 and Figure 6 The images show metallographic structures of Examples 1, 2, and 3 under a 100x optical microscope.

[0068] Table 2 shows the inclusion detection indicators in the spring flat steel of Examples 1-3.

[0069] The "-" indicates that the sample was not detected.

[0070] Combination Figures 1-6 As can be seen from Table 2, the Class A (sulfide) grade of the spring flat steel prepared in Examples 1 and 3 is 0.5, and the Class A grade of the spring flat steel prepared in Example 2 is 1.0. This indicates that the inclusions are small in size, few in number, and sparsely distributed, and have a relatively minor impact on the properties of the steel.

[0071] The Class B (alumina) grade of the spring flat steel prepared in Examples 1, 2 and 3 is 0.5, indicating that the size of the inclusions is small and the dispersion is low, which can reduce the formation of stress concentration points and help improve the fatigue life of automotive leaf springs.

[0072] No Class C (silicate) inclusions or Class Ds inclusions were detected in the spring flat steel prepared in Examples 1, 2 and 3. The steel exhibited high performance stability, which can reduce the probability of fatigue fracture accidents and quality problems caused by inclusions, thereby enhancing market competitiveness. At the same time, it can improve corrosion resistance and reduce performance degradation caused by corrosion, thereby enhancing the safety and stability of the overall structure.

[0073] In Examples 1, 2, and 3, the coarse grade of the D type (cyclic oxide type) of spring flat steel is 0, indicating the absence of obvious large spherical oxides, thus avoiding the direct damage of fatigue performance by large-sized defects; the fine grade is 0.5, indicating that the size and number of small spherical inclusions are extremely small, which is beneficial to improving the fatigue life, mechanical properties, and processing stability of spring flat steel.

[0074] The oxygen content of the spring flat steel prepared in Examples 1, 2 and 3 was 3.1ppm, 2.3ppm and 2.9ppm, respectively. The low oxygen content means that the content of non-metallic inclusions is low and the overall purity is high. This can enhance the elasticity, toughness, corrosion resistance and wear resistance of the spring flat steel, which is beneficial to extending its service life.

[0075] Experiment 3: Fatigue tests were conducted on the leaf springs prepared in Examples 1, 2, and 3. The experimental results are as follows: Fatigue tests were conducted on Example 1, and the fatigue life was 300,000 cycles without fracture, at which point the experiment was terminated.

[0076] Fatigue tests were conducted on Example 2, and the fatigue life was 280,000 cycles without fracture, at which point the experiment was terminated.

[0077] Fatigue tests were conducted on Example 3, and the fatigue life was 500,000 cycles without fracture, at which point the experiment was terminated.

[0078] It can be seen that the fatigue test counts of the leaf springs prepared by the method of the present invention in Examples 1, 2 and 3 all far exceed 200,000 cycles, indicating that the probability of them breaking within their design life is low, which can reduce safety accidents such as vehicle loss of control and rollover caused by leaf spring failure; and is conducive to extending the service life of vehicles.

[0079] In summary, the steelmaking and continuous casting methods for high-strength spring flat steel in this application include converter, ladle refining, vacuum degassing, continuous casting, and slow cooling of the continuously cast billet. These methods can control the total oxygen content of the spring flat steel to ≤5ppm, the coarseness ratio of various inclusions to ≤1.0 grade, and Ds-type inclusions to ≤0.5 grade. This reduces the total amount of inclusions in the spring flat steel while minimizing the size of the largest inclusion, resulting in high steel purity and significantly improved fatigue life. The continuous casting light reduction process ensures that the center segregation of the continuously cast billet is ≤1.08 while preventing intermediate cracks. This effectively improves the machinability of the spring flat steel and guarantees its high strength.

[0080] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for steelmaking and continuous casting of high-strength spring flat steel, characterized in that, Includes the following steps: Step 1) Converter: The final control of the converter is C≥0.15% and the final temperature≥1640℃; preheat the alloy to ensure that the temperature of the alloy added into the ladle is≥650℃; use the slag washing process, add lime during the tapping process, maintain bottom blowing argon gas in the ladle during the tapping process, and maintain bottom blowing argon gas after the tapping is completed; Step 2) Ladle refining: LF uses refining slag and lime added to the converter to form slag; Step 3) Vacuum degassing; Step 4) Continuous casting: Full-process protective casting is adopted, using an integral tundish and crystallizer nozzle. The casting speed of the continuous casting billet is 0.80-0.90m / min, the electromagnetic stirring frequency of the crystallizer is 3-5Hz, the current is 200-450A, the secondary cooling water flow rate is 0.15-0.25L / kg, and the tundish is equipped with a heating function; the end adopts electromagnetic stirring and continuous casting light reduction process. Step 5) Slow cooling of continuous casting billet: The continuous casting billet is placed in the slow cooling pit for slow cooling. The surface temperature of the billet is ≥600℃ and the surface temperature of the billet is <250℃ when it leaves the slow cooling pit.

2. The steelmaking and continuous casting method for high-strength spring flat steel according to claim 1, characterized in that, In step 1), the amount of lime added during the tapping process is 0.7~5.5 kg / t of molten steel, of which the CaO content in the lime is ≥95%.

3. The steelmaking and continuous casting method for high-strength spring flat steel according to claim 1, characterized in that, In step 1), after the steel tapping is completed, the bottom blowing argon gas is maintained for ≥5 minutes.

4. The steelmaking and continuous casting method for high-strength spring flat steel according to claim 1, characterized in that, In step 2), the final residue composition is: CaO 45%~55%, SiO2 6%~12%, Al2O3 25%~35%, and R (alkalinity) 4.0~7.

0.

5. The steelmaking and continuous casting method for high-strength spring flat steel according to claim 4, characterized in that, In step 2), after the LF component temperature is adjusted, the slag-preserving refining is continued, with a current ≤25kA, a voltage ≤120V, and a slag-preserving refining time ≥15min.

6. The steelmaking and continuous casting method for high-strength spring flat steel according to claim 1, characterized in that, In step 3), the vacuum degree of vacuum degassing is ≤67Pa, and the vacuum holding time is ≥40min.

7. The steelmaking and continuous casting method for high-strength spring flat steel according to claim 1, characterized in that, In step 4), a low-temperature casting process is implemented. The superheating requirement of the tundish during continuous casting is 12-20℃ (except for the first heat of the casting cycle), and the temperature is increased by 5-8℃ for the first heat of the casting cycle.

8. The steelmaking and continuous casting method for high-strength spring flat steel according to claim 1, characterized in that, In step 4), the light pressing process involves pressing rollers 1-9, with a total pressing amount of 4-18mm.

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