Production method for improving segregation banding of high-strength steel for automobiles

Abstract

The invention discloses a production method for improving segregation banding of high-strength steel for automobiles. The production method comprises the following steps and parameter control: molten steel composition, converter tapping, molten steel temperature, desulfurization, continuous casting soft reduction, secondary cooling water amount, hot rolling heating temperature, heating time and reduction rate. The molten steel comprises the following chemical components in percentage by mass: 0.07 to 0.09 percent of C, 0.50 to 0.60 percent of Si, 2.30 to 2.50 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.004 percent of S, 0.025 to 0.055 percent of Als, 0.03 to 0.05 percent of Nb, 0.03 to 0.05 percent of Ti, 0.10 to 0.30 percent of Cr, less than or equal to 0.006 percent of N and the balance of iron and inevitable impurities. Low-segregation, high-homogeneity and high-efficiency production of the high-strength steel is achieved, strength is contributed to high-quality and light-weight development of the automobile industry, and good social reputation is widely won.

Description

Technical Field

[0001] This invention relates to a production method for improving the segregation banding of high-strength steel for automobiles, belonging to the field of steel internal quality improvement production technology. Background Technology

[0002] With the rapid development of new energy vehicles and intelligent driving technologies, and the accompanying trend of lightweighting in the automotive industry, customers are placing higher demands on the high strength, high toughness, and good formability of automotive sheet materials. High-strength steel, due to its high strength, lightweight nature, and excellent collision performance, is widely used in key components such as automotive bodies, chassis, and safety structures, making it a core material for achieving lightweighting and improving safety in automobiles. However, segregation banding significantly affects the processing and welding performance of high-strength steel. In the automotive manufacturing process, high-strength steel undergoes multiple processes such as stamping and welding. Segregation banding can lead to localized cracking or uneven deformation during stamping, affecting the forming accuracy of parts. During welding, segregated banded areas are prone to forming welds with uneven composition, increasing the risk of welding cracks and affecting the integrity and safety of the vehicle body structure.

[0003] Segregation banding is a common phenomenon in metallic materials. It occurs during solidification when solute elements redistribute at the solid-liquid interface, leading to localized compositional inhomogeneity. During rolling, the solute elements extend along the deformation direction, elongating the segregated regions and forming banded distributions. The distribution coefficient and diffusion rate of alloying elements also affect segregation. Elements with slower diffusion rates tend to accumulate locally, and excessively slow cooling rates increase diffusion time, exacerbating segregation; conversely, excessively fast cooling rates can lead to localized compositional inhomogeneity. Furthermore, the segregation of impurities such as sulfur and phosphorus at grain boundaries can reduce the material's toughness.

[0004] Chinese patent application number CN 117721282 A discloses "A heat treatment method for eliminating segregation bands in high alloy steel". This patent focuses on the microstructure analysis of medium carbon high alloy steel in thin plates. It reduces segregation bands in high alloy steel by determining the content level of banded structure and using heat treatment process. However, it does not cover much about the control and optimization of key process parameters such as molten steel temperature and continuous casting light reduction to improve segregation bands.

[0005] Chinese patent application number CN 113642210 B discloses "A method for eliminating banded structures in gear steel by heating process". This patent uses ANSYS to simulate and calculate the temperature change of gear steel billet in heating furnace, and combines the heating process and billet temperature field to accurately select the heating process of heating furnace to achieve the purpose of eliminating banded structures in gear steel. However, it does not study the optimization of steel composition and steelmaking process.

[0006] Chinese patent application number CN 118023492 A discloses "A continuous casting control method to improve segregation of rebar". This patent improves the center segregation of continuous casting billets by preventing deviation and ensuring good centering of the billets, making the secondary cooling spray effect more uniform. However, it does not involve the control of steelmaking composition and the optimization of hot rolling process.

[0007] Chinese patent application CN 116043096 A discloses a steelmaking method for reducing manganese segregation in ship plate steel billets. This patent reduces manganese segregation in ship plate steel billets and improves the banded structure by adjusting the steel composition to control the precipitation temperature of MnS, controlling the superheat of molten steel and the cooling temperature of the billet. However, it does not address the optimization of continuous casting light reduction and rolling process.

[0008] The paper, "Analysis and Improvement Measures for Center Segregation in High-Strength Steel Continuously Casting Slabs," is published in the journal *Continuous Casting*, 2017, No. 5, pages 33-37. The paper analyzes and discusses key parameters such as steel composition, steel purity, steel superheat, continuous casting cooling process, casting machine roll gap control, and light reduction, but does not delve deeply into the optimization of the rolling process. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a production method for improving the segregation banding of high-strength steel for automobiles, which effectively improves the problem of segregation banding in high-strength steel for new energy vehicles.

[0010] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0011] A production method for improving the segregation banding of high-strength steel for automobiles includes the following steps and parameter control: steel composition, converter tapping, steel temperature, desulfurization, continuous casting light reduction, secondary cooling water volume, hot rolling heating temperature, heating time, and reduction rate.

[0012] Preferably, the steel's mass percentage and chemical composition are as follows: C 0.07–0.09%, Si 0.50–0.60%, Mn 2.30–2.50%, P ≤0.015%, S ≤0.004%, Als 0.025–0.055%, Nb 0.03–0.05%, Ti 0.03–0.05%, Cr 0.10–0.30%, and N ≤0.006%. By reducing the content of C, S, and Mn elements in the composition, the risk of MnS chain segregation and central carbon segregation can be reduced during the solidification process of the billet; the addition of a small amount of Nb and Ti alloys can refine the grains, improve the compositional uniformity, and reduce the probability of dendrite segregation.

[0013] Preferably, the converter tapping process employs a dual slag-blocking operation using a "slag-blocking cone" and a "slag-blocking slide." This avoids the risk of phosphorus reversion in molten steel and phosphorus segregation in the cast billet caused by slag discharge during converter tapping.

[0014] Preferably, the converter tapping process involves rapid tapping to reduce temperature drop, with a tapping time of 5-10 minutes and the molten steel temperature controlled at 1570-1630℃. This ensures a rapid connection between the converter tapping-LF-RH process and guarantees low superheat control of the molten steel. The superheat for the first heat is 20-35℃, and for subsequent heats it is 15-30℃. This also reduces the risk of P and S segregation.

[0015] Preferably, the process employs a dual desulfurization process of "molten iron pretreatment desulfurization" + "LF refining desulfurization".

[0016] Preferably, pulverized coal is injected for molten iron pretreatment to control the sulfur content of the molten iron to within 0.006%, thereby reducing the sulfur content in the molten steel from the source and lowering the probability of MnS formation; LF refining uses bottom blowing argon gas for strong stirring in the ladle, and the sulfur content of the finished product is controlled to within 0.004%.

[0017] Preferably, during continuous casting, a light reduction is applied starting at the end of the billet solidification process. Different dynamic light reductions are formulated based on different casting speeds and different degrees of superheat in the molten steel to compensate for shrinkage and reduce center segregation. The formula for calculating the dynamic light reduction is as follows:

[0018] d = a·ΔT + b·V + 5

[0019] Where: d: reduction amount, unit: mm;

[0020] a: Superheat compensation coefficient, unit: mm / ℃; when 15℃≤superheat≤25℃, a is 0.2; when 25℃<superheat≤35℃, a is 0.15;

[0021] ΔT: Superheat of molten steel, unit: °C;

[0022] b: Speed ​​compensation coefficient, unit: mm / m·min -1 When the pulling speed is 0.9 m / min ≤ pulling speed ≤ 1.2 m / min, b is -2; when the pulling speed is 1.2 m / min < pulling speed ≤ 1.3 m / min, b is -2.5; when the pulling speed is 1.3 m / min < pulling speed ≤ 1.5 m / min, b is -3.

[0023] V: Pulling speed, unit: m / min.

[0024] Preferably, the condition of the continuous casting machine is predicted before production. When the roll gap deviation of the fan-shaped section of the casting machine is 0.5 to 0.8 mm, the secondary cooling water volume of the corresponding fan-shaped section is reduced by 10% (by mass); when the roll gap deviation of the fan-shaped section of the casting machine is 0.9 to 1.2 mm, the secondary cooling water volume of the corresponding fan-shaped section is reduced by 15% (by mass) to avoid the risk of increased roll pressure resistance due to overcooling of the billet shell.

[0025] Preferably, the hot rolling heating furnace adopts a high-temperature, long-term homogenization process, with the heating temperature controlled at 1220–1270℃; the heating time in the furnace is controlled at 3.5–4.5 hours to promote the diffusion of solute elements and reduce segregation.

[0026] Preferably, hot rolling employs a large reduction rate, with a single-pass reduction of 20% to 25%, which breaks up the cast dendrites and segregation bands, promoting uniform element distribution.

[0027] Design concept of this invention:

[0028] Segregation bands are a common phenomenon in metallic materials, especially in high-strength steel used for seat rails in new energy vehicles. Due to their high alloy content, solute elements are redistributed at the solidification interface during the solidification process, which can easily lead to uneven local composition and the formation of segregation bands. During the stamping process, these bands can cause local cracking or uneven deformation, which seriously affects the forming accuracy of parts and increases the risk of welding cracks.

[0029] This invention is based on the design concept of low carbon and low sulfur composition, with carbon content controlled in the range of 0.07 to 0.09% and sulfur content ≤ 0.004%, thereby reducing the risk of MnS chain segregation and central carbon segregation from the source.

[0030] By adopting a dual desulfurization process of "hot metal pretreatment desulfurization" + "LF refining desulfurization", the sulfur content of the finished product is controlled within 0.004%, ensuring an extremely low sulfur content level, reducing the sulfur content in the molten steel from the source, and reducing the probability of MnS formation.

[0031] In the design of molten steel composition, adding a small amount of Nb and Ti alloys can refine the grains, improve the uniformity of composition, and suppress dendrite segregation.

[0032] The converter tapping process adopts a dual slag-blocking operation of "slag-blocking cone" + "slag-blocking slide" to avoid the risk of phosphorus return in molten steel and phosphorus segregation in billet caused by slag discharge during converter tapping.

[0033] The converter tapping time is 5-10 minutes, the tapping temperature is 1570-1630℃, and it is quickly connected with the LF-RH process. The superheat of the continuous casting tundish is maintained at 20-35℃ for the first heat and 15-30℃ for other heats to reduce solidification segregation.

[0034] During the continuous casting process, different dynamic light reduction methods are formulated at the end of the billet solidification by combining different casting speeds and molten steel superheat. The reduction amount is adjusted in real time according to the casting speed and molten steel superheat to compensate for shrinkage and dynamically suppress center segregation.

[0035] Pre-production prediction of the continuous casting machine's condition, combined with the casting machine's roll gap deviation, reduces the amount of secondary cooling water in the corresponding area to avoid the risk of roll failure due to overcooling of the billet shell.

[0036] The hot rolling furnace adopts a high-temperature, long-term homogenization process to promote the diffusion and homogenization of solute elements and reduce segregation.

[0037] Hot rolling employs a large reduction rate, with a single-pass reduction of 20% to 25%, which breaks up the cast dendrites and segregation bands, improving the uniformity of the microstructure.

[0038] The beneficial effects of adopting the above technical solution are as follows:

[0039] This invention achieves high-strength steel production with low segregation, high homogeneity, and high efficiency through key process controls such as low-carbon and low-sulfur composition design, double-slag-blocking operation at converter tapping, stable control of low superheat, dual desulfurization process of "hot metal pretreatment desulfurization" + "LF refining desulfurization", dynamic light reduction regulation at the end of billet solidification, high-temperature long-term heating in hot rolling, and high reduction rate. It contributes to the high-quality and lightweight development of the automotive industry and has won widespread social acclaim. Attached Figure Description

[0040] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0041] Figure 1 This is an image of the segregation defect at the center of the sulfur mark on the billet, obtained by conventional methods that only control the steelmaking composition, temperature, and light pressure.

[0042] Figure 2 This is a photograph of the actual appearance of strip-shaped microstructure defects in cold-rolled coils, produced using conventional methods that only control steelmaking composition, temperature, and light reduction.

[0043] Figure 3 This is a photograph of the sulfur stain on the cast billet in Embodiment 1 of the present invention.

[0044] Figure 4 This is a photograph of the actual microstructure of the cold-rolled coil in Embodiment 1 of the present invention;

[0045] Figure 5 This is a photograph of the sulfur stain on the cast billet in Embodiment 2 of the present invention.

[0046] Figure 6 This is a photograph of the actual microstructure of the cold-rolled coil in Embodiment 2 of the present invention;

[0047] Figure 7 This is a photograph of the sulfur stain on the cast billet in Embodiment 3 of the present invention.

[0048] Figure 8 This is a photograph of the actual microstructure of the cold-rolled coil in Embodiment 3 of the present invention. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that what is described herein represents only a small portion of the embodiments of this invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0050] To better illustrate the present invention, the following detailed description is provided in conjunction with specific embodiments.

[0051] Example 1

[0052] A method for improving the formability of segregated bands in high-strength steel for automobiles and its production method, comprising the following steps:

[0053] Five heats of high-strength steel for automobiles were produced. The converter tapping process used a dual slag-blocking operation of "slag-blocking cone" + "slag-blocking slide". No slag discharge or phosphorus return occurred during the converter tapping process.

[0054] The converter adopted rapid tapping to reduce temperature drop. The tapping times were 5, 8, 6, 7 and 6 minutes, and the tapping temperatures were 1602, 1598, 1612, 1570 and 1609℃, respectively.

[0055] The superheat of the first batch of continuously cast steel is 28°C, and the superheat of the other four batches of steel is 15°C, 18°C, 25°C, and 30°C, respectively, to ensure that the steel is cast at a low superheat.

[0056] A dual desulfurization process of "hot metal pretreatment desulfurization" + "LF refining desulfurization" is adopted. Pulverized coal is injected to pretreat the hot metal, and the sulfur content of the hot metal after pretreatment is 0.005%, 0.004%, 0.006%, 0.004%, and 0.003%, respectively, which reduces the sulfur content in the molten steel from the source.

[0057] The molten steel for automotive applications produced in 5 heats features a low-carbon, low-sulfur composition, reducing the risk of MnS chain segregation and central carbon segregation at the source. A small amount of Nb and Ti alloys are added, which refines the grain size, improves compositional uniformity, and suppresses dendritic segregation. The composition of the molten steel for automotive applications in 5 heats is as follows:

[0058]

[0059] Note: The balance is iron and unavoidable impurities.

[0060] Continuous casting was performed at a constant casting speed of 1.2 m / min, with superheats of 28, 15, 18, 25, and 30°C. The light reduction, considering different superheats and casting speeds, was calculated using the formula: d = a·ΔT + b·V + 5, resulting in light reductions of 6.8, 5.6, 6.2, 7.6, and 7.1 mm.

[0061] Furnace a ΔT b V d 1 0.15 28 -2 1.2 6.8 2 0.2 15 -2 1.2 5.6 3 0.2 18 -2 1.2 6.2 4 0.2 25 -2 1.2 7.6 5 0.15 30 -2 1.2 7.1

[0062] During the continuous casting process, the roll gap deviation in the third sector section was 0.5mm, which reduced the secondary cooling water volume in the corresponding sector section area by 10%. The roll gaps in other sector sections were normal.

[0063] Hot rolling adopts a high-temperature, long-duration heating mode, with furnace temperatures of 1238, 1220, 1251, 1270, and 1232℃; and furnace heating times of 3.5, 4.0, 3.5, 4.5, and 3.5 hours.

[0064] Hot rolling employs a large reduction rate, with single-pass reduction rates of 20%, 22%, 23%, 21%, and 25%.

[0065] Experimental results: Sulfur samples were taken from the second billet obtained in the third furnace for sulfur imprint analysis, such as... Figure 3 As shown, no defects such as center segregation or porosity were found after sulfur staining on the slab; subsequent rolling of the slab was monitored, and cross-sectional microstructure of cold-rolled coil samples was observed, revealing no MnS chain segregation or center segregation defects. Figure 4 As shown.

[0066] Example 2

[0067] The converter produced 6 heats of high-strength steel for automobiles. The converter tapping process used a double slag-blocking operation of "slag-blocking cone" + "slag-blocking slide". No slag discharge or phosphorus return occurred during the converter tapping process.

[0068] The converter adopts rapid tapping to reduce temperature drop. The tapping times are 7, 8, 6, 10, 6 and 8 minutes, and the tapping temperatures are 1608, 1592, 1630, 1589, 1619 and 1578℃, respectively.

[0069] The superheat of the first batch of continuously cast steel is 23°C, and the superheat of the other four batches of steel is 27°C, 18°C, 28°C, 35°C, and 25°C, respectively, to ensure that the steel is cast at a low superheat.

[0070] A dual desulfurization process of "hot metal pretreatment desulfurization" + "LF refining desulfurization" is adopted. Pulverized coal is injected to pretreat the hot metal, and the sulfur content of the hot metal after pretreatment is 0.003%, 0.005%, 0.004%, 0.006%, 0.005%, and 0.004%, respectively, thereby reducing the sulfur content in the molten steel from the source.

[0071] The molten steel for automotive applications produced in 6 heats features a low-carbon, low-sulfur composition, reducing the risk of MnS chain segregation and central carbon segregation at the source. A small amount of Nb and Ti alloys are added, which refines the grain size, improves compositional uniformity, and suppresses dendritic segregation. The composition of the molten steel for automotive applications in 6 heats is as follows:

[0072]

[0073]

[0074] Note: The balance is iron and unavoidable impurities.

[0075] The continuous casting process involved a constant casting speed of 1.3 m / min for the first four heats and 1.5 m / min for the last two heats, with superheats of 23, 27, 18, 28, 35, and 25°C, respectively. The light reduction, calculated using the formula d = a·ΔT + b·V + 5, yielded light reductions of 6.6, 6.1, 5.6, 6.2, 6.5, and 6.3 mm for each of the different superheats and casting speeds.

[0076] Furnace a ΔT b V d 1 0.2 23 -2.3 1.3 6.6 2 0.15 27 -2.3 1.3 6.1 3 0.2 18 -2.3 1.3 5.6 4 0.15 28 -2.3 1.3 6.2 5 0.15 35 -2.5 1.5 6.5 6 0.2 25 -2.5 1.5 6.3

[0077] During the continuous casting process, the roll gap deviation of the second sector segment was 0.8 mm, which reduced the secondary cooling water volume of the corresponding sector segment area by 10%; the roll gap deviation of the fifth sector segment was 0.9 mm, which reduced the secondary cooling water volume of the corresponding sector segment area by 15%; the roll gaps of other sector segments were normal.

[0078] Hot rolling adopts a high-temperature, long-duration heating mode, with furnace temperatures of 1248, 1229, 1250, 1236, 1231, and 1235℃; and furnace heating times of 3.5, 3.5, 4.0, 3.5, 4.5, and 3.5 hours.

[0079] Hot rolling employs a large reduction rolling process, with single-pass reduction rates of 23%, 22%, 21%, 20%, 22%, and 21%.

[0080] Experimental results:

[0081] Sulfur samples were taken from the fourth billet obtained from the second furnace for sulfur imprint analysis, such as... Figure 5 As shown, no defects such as center segregation or porosity were found after sulfur staining on the slab; subsequent rolling of the slab was monitored, and cross-sectional microstructure of cold-rolled coil samples was observed, revealing no MnS chain segregation or center segregation defects. Figure 6 As shown.

[0082] Example 3

[0083] Eight heats of high-strength steel for automobiles were produced. The converter tapping process used a dual slag-blocking operation of "slag-blocking cone" + "slag-blocking slide". No slag discharge or phosphorus return occurred during the converter tapping process.

[0084] The converter adopts rapid tapping to reduce temperature drop. The tapping times are 7, 5, 8, 9, 6, 8, 9, and 6 minutes, and the tapping temperatures are 1618, 1596, 1620, 1579, 1611, 1571, 1602, and 1591℃, respectively.

[0085] The superheat of the first batch of continuously cast steel is 35°C, and the superheat of the other 7 batches of steel is 28, 23, 21, 25, 19, 20 and 17°C, respectively, to ensure that the steel is cast at a low superheat.

[0086] A dual desulfurization process of "hot metal pretreatment desulfurization" + "LF refining desulfurization" is adopted. Pulverized coal is injected to pretreat the hot metal, and the sulfur content of the hot metal after pretreatment is 0.004%, 0.003%, 0.004%, 0.005%, 0.004%, 0.005%, 0.004%, and 0.003%, respectively, thereby reducing the sulfur content in the molten steel from the source.

[0087] The molten steel for automotive applications produced in 8 heats features a low-carbon, low-sulfur composition, reducing the risk of MnS chain segregation and central carbon segregation at the source. A small amount of Nb and Ti alloys are added, which refines the grain size, improves compositional uniformity, and suppresses dendritic segregation. The composition of the molten steel for automotive applications in 8 heats is as follows:

[0088]

[0089] Note: The balance is iron and unavoidable impurities.

[0090] The first two heats of continuous casting were at a constant casting speed of 0.9 m / min, and the next six heats were at a constant casting speed of 1.0 m / min, with superheats of 35, 28, 23, 21, 25, 19, 20, and 17℃, respectively. The light reduction, combined with the different superheats and casting speeds, can be calculated using the formula: d = a·ΔT + b·V + 5, resulting in light reductions of 8.4, 7.4, 7.6, 7.2, 8.0, 5.9, 7.0, and 6.4 mm, respectively.

[0091] Furnace a ΔT b V d 1 0.15 35 -2 0.9 8.4 2 0.15 28 -2 0.9 7.4 3 0.2 23 -2 1 7.6 4 0.2 21 -2 1 7.2 5 0.2 25 -2 1 8 6 0.15 19 -2 1 5.9 7 0.2 20 -2 1 7.0 8 0.2 17 -2 1 6.4

[0092] During the continuous casting process, the roll gap deviation of the third sector segment was 1.2 mm, which reduced the secondary cooling water volume of the corresponding sector segment area by 15%; the roll gap deviation of the fifth sector segment was 0.6 mm, which reduced the secondary cooling water volume of the corresponding sector segment area by 10%; the roll gaps of other sector segments were normal.

[0093] Hot rolling adopts a high-temperature, long-duration heating mode, with furnace temperatures of 1228, 1239, 1260, 1236, 1231, 1238, 1221, and 1245℃; and furnace heating times of 3.5, 4.0, 3.5, 3.5, 4.5, 3.5, 4.5, and 4.0 hours.

[0094] Hot rolling employs a large reduction rolling process, with single-pass reduction rates of 21%, 23%, 20%, 22%, 21%, 23%, 21%, and 25%.

[0095] Experimental results: Sulfur imprint samples were taken from the third billet obtained in the fifth heat for sulfur imprint analysis, such as... Figure 7As shown, no defects such as center segregation or porosity were found after sulfur staining on the slab; subsequent rolling of the slab was monitored, and cross-sectional microstructure of cold-rolled coil samples was observed, revealing no MnS chain segregation or center segregation defects. Figure 8 As shown.

[0096] Through the process control described in the above embodiments, high-strength steel for automobiles has achieved low segregation, high homogeneity, and high-efficiency production, contributing to the high-quality and lightweight development of the automotive industry and winning widespread social acclaim. This is in contrast to conventional methods that only control the steel composition, temperature, and continuous casting reduction process, resulting in products (see...). Figure 1 and Figure 2 It represents a significant improvement compared to [previous version].

[0097] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A production method for improving the segregation banding of high-strength steel for automobiles, characterized in that, The control of the following steps and parameters includes: steel composition, converter tapping, steel temperature, desulfurization, continuous casting light reduction, secondary cooling water volume, hot rolling heating temperature, heating time, and reduction rate.

2. The production method for improving the segregation banding of high-strength steel for automobiles according to claim 1, characterized in that, The percentage content and chemical composition of the molten steel are as follows: C 0.07~0.09%, Si 0.50~0.60%, Mn 2.30~2.50%, P≤0.015%, S≤0.004%, Als 0.025~0.055%, Nb 0.03~0.05%, Ti 0.03~0.05%, Cr 0.10~0.30%, N≤0.006%, with the balance being iron and unavoidable impurities.

3. The production method for improving the segregation banding of high-strength steel for automobiles according to claim 1, characterized in that, The converter tapping process employs a dual slag-blocking operation consisting of a slag-blocking cone and a sliding plate.

4. The production method for improving the segregation banding of high-strength steel for automobiles according to claim 1, characterized in that, During the converter tapping process, the tapping time is 5-10 minutes, the temperature of the molten steel tapped from the converter is controlled at 1570-1630℃, the superheat of the first heat is 20-35℃, and the superheat of other heats is 15-30℃.

5. The production method for improving the segregation banding of high-strength steel for automobiles according to claim 1, characterized in that, The process employs a dual desulfurization process: hot metal pretreatment desulfurization followed by LF refining desulfurization.

6. The production method for improving the segregation banding of high-strength steel for automobiles according to claim 5, characterized in that, Pulverized coal is injected to pretreat molten iron, and the sulfur content of the molten iron after pretreatment is controlled to be within 0.006%. LF refining uses bottom-blown argon gas for strong stirring in a steel ladle, and the sulfur content of the finished product is controlled to be within 0.004%.

7. The production method for improving the segregation banding of high-strength steel for automobiles according to claim 1, characterized in that, During continuous casting, a light reduction is applied at the end of the solidification of the billet. The formula for calculating the dynamic light reduction is: d=a·ΔT+b·V+5; Where: d: reduction amount, unit: mm; a: Superheat compensation coefficient, unit: mm / ℃; when 15℃≤superheat≤25℃, a is 0.2; when 25℃<superheat≤35℃, a is 0.15; ΔT: Superheat of molten steel, unit: °C; b: Speed ​​compensation coefficient, unit: mm / m·min -1 ; When the pulling speed is 0.9 m / min ≤ pulling speed ≤ 1.2 m / min, b is -2; When the pulling speed is 1.2 m / min < pulling speed ≤ 1.3 m / min, b is -2.5; when the pulling speed is 1.3 m / min < pulling speed ≤ 1.5 m / min, b is -3. V: Pulling speed, unit: m / min.

8. The production method for improving the segregation banding of high-strength steel for automobiles according to claim 1, characterized in that, Pre-production prediction of the continuous casting machine's condition: when the roll gap deviation of the fan-shaped section of the casting machine is 0.5-0.8mm, reduce the secondary cooling water volume of the corresponding fan-shaped section by 10%; when the roll gap deviation of the fan-shaped section of the casting machine is 0.9-1.2mm, reduce the secondary cooling water volume of the corresponding fan-shaped section by 15%.

9. The production method for improving the segregation banding of high-strength steel for automobiles according to claim 1, characterized in that, The hot rolling heating furnace adopts a high-temperature, long-term homogenization process, with the heating temperature controlled at 1220–1270℃ and the heating time in the furnace controlled at 3.5–4.5 hours.

10. The production method for improving the segregation banding of high-strength steel for automobiles according to claim 1, characterized in that, Hot rolling employs a large reduction rate, with a single-pass reduction of 20% to 25%.

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