Method for reducing banded structure of hot stamping forming steel

Abstract

The invention discloses a method for reducing banded structures of hot stamping formed steel, and belongs to the technical field of steel smelting. The method comprises the following steps: (1) pretreating molten iron; (2) smelting in a decarburization converter; (3) LF furnace refining; and (4) slab continuous casting. Compared with a traditional smelting process, 8-10 ppm of free calcium is additionally added, the higher calcium content is combined with the residual sulfur content in the molten steel to generate CaS, and MnS is prevented from being generated. And the risk that the banded structure is more serious due to plastic deformation of MnS inclusions in the rolling direction is avoided, and the level of the banded structure is effectively reduced from the level 3-4 to the level 1.5-2.5.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and in particular relates to a method for reducing the banded structure of hot stamping formed steel. Background Art

[0002] Hot stamping steel plays an important role in the field of modern automobile manufacturing. It is a raw material that uses metal thermoplastic forming and plays a key role through a unique process.

[0003] First, during the hot stamping process, the steel is heated to the austenitizing temperature, at which point the material has good plasticity. Next, the forming operation is performed in the mold, and the quenching treatment is quickly performed after forming. This series of steps greatly improves the forming performance of the material. On the one hand, hot stamping allows steel to be more easily molded into complex shapes at high temperatures to meet the diverse design requirements of automotive parts; on the other hand, quenching treatment gives the steel ultra-high strength, enabling it to withstand various complex stresses during the use of the car. For this reason, hot stamping steel has greatly expanded the application scope of ultra-high strength steel in automotive parts, providing a strong guarantee for the lightweight and safety of automobiles.

[0004] However, hot stamping steel also faces some challenges. Its relatively complex smelting process determines the high production cost. This complex process requires precise temperature control, strict adjustment of chemical composition, and requires advanced production equipment and professional technicians. This series of factors makes the production cost of hot stamping steel high, limiting its application in some cost-sensitive automotive projects. In addition, the characteristics of the steel grade determine that the microstructure distribution after hot rolling has a certain level of banded structure. The presence of banded structure will affect the mechanical properties and processing properties of steel, reduce its strength and toughness, and increase the risk of failure of parts during use. This problem has been plaguing major domestic steel mills and has become a difficult problem to be solved urgently. In order to solve the problem of banded structure, steel mills need to continuously improve production processes, optimize chemical composition, and improve the uniformity of steel. At the same time, researchers are also actively exploring new heat treatment methods and processing technologies to reduce the generation of banded structure and improve the quality and performance of hot stamping steel. Despite many challenges, the development prospects of hot stamping steel are still broad. With the continuous advancement of technology, it is believed that these problems will be gradually solved, and hot stamping steel will play a more important role in the field of automobile manufacturing. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for reducing the band structure of hot stamping steel.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for reducing the banded structure of hot stamping steel, the method comprising the following steps: (1) Hot metal pretreatment: After the hot metal ladle is desulfurized by spraying magnesium powder and lime, the slag is removed and the S of the hot metal after pretreatment is ≤ 0.008%; (2) Decarbonization converter smelting: the final slag basicity is 3.3-3.6; the mass percentage of the components at the end of smelting is: C: 0.03-0.05%, S≤0.008%, P≤0.020%; the end temperature is 1680-1700℃; the mass percentage of FeO in the final slag is ≤20%; the whole process is argon blowing at the bottom, the steel is tapped without inverting the furnace, the ladle is protected by bottom blowing argon before tapping, the steel flow is rounded during the tapping process, and the oxygen content of the molten steel is controlled at 300-500ppm; (3) LF furnace refining: white slag can be quickly produced within 8 minutes of refining. The smelting process is completely in a reducing atmosphere. The double bottom blowing argon flow rate is 40-50Nm 3 / min, slag layer thickness 10-15mm, FeO+MnO≤1% before leaving the station, calcium treatment is carried out before LF leaves the station, the calcium treatment amount is 8-10ppm higher than the normal calcium treatment, and is controlled at 20-30ppm; (4) Slab continuous casting: adopt ladle slag detection system; ladle casing, stopper rod, water inlet and plate space are protected by argon blowing; the insertion depth of immersion water inlet is 150±5mm; the continuous casting constant casting speed is controlled at 1.2-1.3m / min; the liquid level fluctuation automatic control system is adopted, and the superheat of molten steel in the tundish is 12-18℃; the dynamic light pressure reduction system is adopted, and the pressure reduction is 4-6mm; the vertical section adopts strong cooling, and the temperature of the straightening section is ≥900℃.

[0007] In the step (1) of the present invention, the molten iron is pretreated by a composite blowing method, magnesium powder and lime are added for desulfurization, the desulfurization rate is ≥95%, and slag is removed after desulfurization, and the exposed surface of the molten steel is ≥90%.

[0008] In step (2) of the present invention, argon is blown from the bottom of the ladle for the whole process of smelting, steel is tapped without falling, the service life of the tapping port is 50-100 furnaces, the steel flow is ensured to be complete, argon is blown from the bottom of the ladle before tapping for ≥10 minutes, and the flow rate is 80-100Nm 3 / min, the purpose is to use argon to protect the steel tapping and reduce the nitrogen absorption caused by secondary oxidation during the steel tapping process.

[0009] In step (3) of the present invention, the thickness of the slag layer entering the LF refining station is 10-15 mm, and a foaming agent is added during the process to foam the steel slag, thereby improving thermal efficiency and reducing the nitrogen absorption of the molten steel caused by the violent stirring of the molten steel. The outlet S is ≤0.003%, and the amount of calcium wire fed is controlled according to the calcium content of the molten steel at 20-30 ppm.

[0010] In step (4) of the present invention, the continuous casting tundish adopts a slag retaining wall and a slag retaining weir, the tundish uses a carbon-free magnesium refractory material, an aluminum-carbon argon blowing upper water inlet, uses steel protective slag for hot stamping, the ladle water inlet is argon-sealed for protective casting, an immersion water inlet is adopted, a carbon-free low-silicon covering agent is used, the covering agent thickness is 50 to 100 mm, and slag detection is performed to ensure that the steel slag does not enter the tundish.

[0011] In step (4) of the present invention, ultra-low superheat casting is adopted, and the superheat is 12-18°C; a secondary cooling water segmented cooling process is adopted, and the secondary cooling water ratio of the vertical segment is 1.2-1.5 L / kg, the secondary cooling water ratio of the curved segment is 0.8-1.2 L / kg, and the secondary cooling water ratio of the horizontal segment is 1.2-1.4 L / kg, so as to increase the proportion of equiaxed crystals and shorten the distance between dendrites, while increasing the number of columnar crystals per unit area, reducing the macro and micro segregation levels, and thus improving the banded structure of the plate.

[0012] The method of the present invention also includes a hot rolling process, in which the final rolling temperature control range is 850-870°C, the coiling temperature control range is 620-640°C, the layer cooling adopts front-stage slow cooling, the water valve adopts an open-close-set setting, and the steel coil is stacked and cooled after coiling.

[0013] The chemical composition and mass percentage of the hot stamping steel of the present invention are: C: 0.20-0.25%, Mn: 1.25-1.50%, S≤0.003%, P≤0.025%, Si: 0.20-0.40%, Als: 0.020-0.040%, Ti: 0.020-0.050%, B: 0.0020-0.0050%, Cr: 0.15-0.35%, Ca: 0.002-0.003%, N≤0.0050%, and the balance is iron and unavoidable impurities.

[0014] In step (5) of the present invention, the chemical composition of the carbon-free low-silicon covering agent is: CaO: 40-55%, SiO 2 ≤12.0%,Al 2 O 3 : 35~45%, MgO≤5.0%, F≤5.0%, Fe 2 O 3 ≤5.0%.

[0015] The banded structure level of the continuous casting billet produced by the smelting method of the present invention after being processed into hot-rolled plate is 1.5-2.5, which is lower than the previous banded structure level of 3-4.

[0016] The hot stamping steel ingot obtained by the smelting method of the present invention can be hot-rolled to produce hot-rolled coils, and cold-rolled to produce high-quality annealed or galvanized products.

[0017] Compared with the traditional smelting process, the advantages of the present invention are: 1. It increases the amount of calcium treatment. Calcium treatment is carried out after the LF furnace refining is completed. The amount of calcium treatment is 8-10ppm higher than that of the traditional process. The higher calcium content combines with the residual sulfur content in the molten steel to form CaS to avoid the formation of MnS. MnS is easier to precipitate between grain boundaries. As rolling proceeds, it will be mixed with the banded structure and will undergo plastic deformation in the hot rolling process along the rolling direction to form long strips of MnS inclusions. Fine MnS inclusions will precipitate out of the molten steel during the solidification process, and will form long strips of MnS inclusions in the rolling direction during the hot rolling process. This elongated MnS inclusion band is embedded between the pearlite bands, and the directions of the two are consistent. This situation will aggravate the banded structure of the hot-rolled product. 2. Ultra-low superheat and strong cooling. During the continuous casting process, ultra-low superheat pouring, increasing the cooling rate of the secondary cooling water and using dynamic light pressure reduction and other measures make the columnar crystals dense during the solidification of the ingot, minimize the development of secondary dendrites, and increase the temperature gradient will aggravate the deterioration of the internal quality of the ingot. At the same time, the dynamic light pressure function is used to improve the internal quality of the ingot. The banded structure is the result of selective crystallization during the solidification of the ingot, which causes the rolled material to appear in a banded structure dominated by ferrite and pearlite. It is due to the full development of the secondary dendrites of the ingot and the enrichment of elements between the secondary dendrites, forming a ferrite and pearlite band parallel to the surface of the ingot. Lower superheat combined with a stronger cooling rate can make the columnar crystals grow denser, compress the development space of secondary dendrites, and reduce the level of banded structure from the root.

[0018] The beneficial effects of adopting the above technical solution are: 1. Compared with the traditional smelting process, the present invention adds 8-10ppm more free calcium. The higher calcium content combines with the residual sulfur content in the molten steel to generate CaS to avoid the formation of MnS. The risk of more serious banded structure due to plastic deformation caused by MnS inclusions in the rolling direction is avoided, and the level of banded structure is effectively reduced from level 3-4 to level 1.5-2.5. 2. The present invention reduces the banded structure level of hot-rolled plates through measures such as ultra-low superheat casting process, increasing the cooling speed of secondary cooling water and using a dynamic light reduction model, thereby providing high-quality slab raw materials for subsequent rolling processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The hot-rolled plate strip structure (grade 1.5) produced by the continuous casting slab in Example 1; Figure 2 The hot-rolled plate strip structure (grade 1.5) produced by the continuous casting slab in Example 2; Figure 3 The hot rolled plate band structure (grade 2.0) produced by the continuous casting slab in Example 3; Figure 4 This is the hot-rolled plate strip structure (grade 2.5) produced from the continuous casting slab in Example 4. DETAILED DESCRIPTION

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] 200t converter, 200t LF refining, conventional slab continuous casting machine (230mm), producing hot stamping steel. Example 1

[0022] A method for reducing the banded structure of hot stamping steel comprises the following steps: (1) Hot metal pretreatment: After the hot metal ladle is desulfurized by spraying magnesium powder and lime, the slag is removed and the sulfur content of the hot metal after pretreatment is 0.008%.

[0023] (2) Decarburization converter smelting: final slag basicity is 3.3; the mass percentage of the components at the end of smelting is: C: 0.03%, S: 0.008%, P: 0.020%; the end temperature is 1680℃; the mass percentage of FeO in the final slag is 20%; the whole process is argon-blown smelting, steel is tapped without falling, the life of the tapping port is 50 furnaces, and the ladle is bottom-blown for argon protection before tapping, the argon gas is 18 minutes, and the flow rate is 87Nm 3 / min, the steel flow is round during the steel tapping process, and the oxygen content of the molten steel is 500ppm.

[0024] (3) LF furnace refining: Refining for 8 minutes to achieve rapid white slag production. The smelting process is completely in a reducing atmosphere. The double bottom blowing argon flow rate is 50Nm 3 / min, slag layer thickness 15mm, FeO+MnO=1% at the exit, LF is treated with calcium before leaving the station, and the calcium content in the molten steel is controlled at 30ppm.

[0025] (4) Slab continuous casting: The insertion depth of the immersion nozzle is 155mm; the continuous casting constant casting speed is controlled at 1.3m / min; the superheat of the molten steel in the tundish is 18℃; a dynamic light reduction system is used, and the reduction is 6mm; the vertical section adopts strong cooling, and the temperature of the straightening section is 900℃. The secondary cooling water segmented cooling process is adopted, and the secondary cooling water ratio of the vertical section is 1.2L / kg, the secondary cooling water ratio of the bending section is 0.8L / kg, and the secondary cooling water ratio of the horizontal section is 1.2L / kg.

[0026] (5) Hot rolling: final rolling temperature is 850℃, coiling temperature is 620℃, layer cooling adopts front-end slow cooling, water valve adopts open-close-set setting, and stack cooling is carried out after coiling.

[0027] The chemical composition and mass percentage of the hot stamping steel in this embodiment are shown in Table 1, the covering agent composition is shown in Table 2, and the banded structure grade is 1.5. Figure 1 . Example 2

[0028] (1) Hot metal pretreatment: After the hot metal ladle is desulfurized by spraying magnesium powder and lime, the slag is removed and the sulfur content of the hot metal after pretreatment is 0.007%.

[0029] (2) Decarbonization converter smelting: the final slag basicity is 3.6; the mass percentage of the components at the end of smelting is: C: 0.05%, S: 0.007%, P: 0.018%; the end temperature is 1700℃; the mass percentage of FeO in the final slag is 18%; the whole process is argon-blown smelting, the steel is tapped without falling, the life of the tapping port is 65 furnaces, and the ladle is bottom-blown with argon protection before tapping, the argon gas is 13 minutes, and the flow rate is 95Nm 3 / min, the steel flow is round during the steel tapping process, and the oxygen content of the molten steel is 300ppm.

[0030] (3) LF furnace refining: Refining for 7.5 minutes to achieve rapid white slag production. The smelting process is completely in a reducing atmosphere. The double bottom blowing argon flow rate is 40Nm 3 / min, slag layer thickness 10mm, outgoing FeO+MnO=0.87%, LF is treated with calcium before leaving the station, and the calcium content of molten steel is controlled at 26ppm.

[0031] (4) Slab continuous casting: The insertion depth of the immersion nozzle is 145 mm; the continuous casting constant casting speed is controlled at 1.2 m / min; the superheat of the molten steel in the tundish is 12°C; a dynamic light reduction system is used, with a reduction of 4 mm; strong cooling is used in the vertical section, and the temperature in the straightening section is 940°C. The secondary cooling water segment cooling process is adopted, with a secondary cooling water ratio of 1.5 L / kg in the vertical section, 1.2 L / kg in the bending section, and 1.4 L / kg in the horizontal section.

[0032] (5) Hot rolling: final rolling temperature 870℃, coiling temperature 640℃, layer cooling adopts front-end slow cooling, water valve adopts open-close-set setting, and stack cooling is carried out after coiling.

[0033] The chemical composition and mass percentage of the hot stamping steel in this embodiment are shown in Table 1, the covering agent composition is shown in Table 2, and the banded structure grade is 1.5. Figure 2 . Example 3

[0034] (1) Hot metal pretreatment: After the hot metal ladle is desulfurized by spraying magnesium powder and lime, the slag is removed and the sulfur content of the hot metal after pretreatment is 0.006%.

[0035] (2) Decarbonization converter smelting: the final slag basicity is 3.5; the mass percentage of the components at the end of smelting is: C: 0.04%, S: 0.007%, P: 0.016%; the end temperature is 1690℃; the mass percentage of FeO in the final slag is 15%; the whole process is argon-blown smelting, the steel is tapped without falling, the life of the tapping port is 85 furnaces, and the ladle is bottom-blown with argon protection before tapping, the argon gas is 12 minutes, and the flow rate is 80Nm3 / min, the steel flow is round during the steel tapping process, and the oxygen content of the molten steel is 400ppm.

[0036] (3) LF furnace refining: Refining for 7.6 minutes to achieve rapid white slag production. The smelting process is completely in a reducing atmosphere. The double bottom blowing argon flow rate is 45Nm 3 / min, slag layer thickness 12mm, outgoing FeO+MnO=0.7%, LF is treated with calcium before leaving the station, and the calcium content of molten steel is controlled at 24ppm.

[0037] (4) Slab continuous casting: The insertion depth of the immersion nozzle is 150 mm; the continuous casting constant casting speed is controlled at 1.2 m / min; the tundish molten steel superheat is 15°C; a dynamic light reduction system is used, with a reduction of 5 mm; strong cooling is used in the vertical section, and the temperature in the straightening section is 920°C. The secondary cooling water segmented cooling process is adopted, with a secondary cooling water ratio of 1.3 L / kg in the vertical section, 1.0 L / kg in the bending section, and 1.3 L / kg in the horizontal section.

[0038] (5) Hot rolling: final rolling temperature 860℃, coiling temperature 630℃, layer cooling adopts front-end slow cooling, water valve adopts open-close-set setting, and stack cooling is carried out after coiling.

[0039] The chemical composition and mass percentage of the hot stamping steel in this embodiment are shown in Table 1, the covering agent composition is shown in Table 2, and the banded structure grade is Level 2. Figure 2 . Example 4

[0040] (1) Hot metal pretreatment: After the hot metal ladle is desulfurized by spraying magnesium powder and lime, the slag is removed and the sulfur content of the hot metal after pretreatment is 0.007%.

[0041] (2) Decarbonization converter smelting: the final slag basicity is 3.6; the mass percentage of the components at the end of smelting is: C: 0.04%, S: 0.007%, P: 0.018%; the end temperature is 1695℃; the mass percentage of FeO in the final slag is 17%; the whole process is argon-blown smelting, the steel is tapped without falling, the life of the tapping port is 100 furnaces, and the ladle is bottom-blown with argon protection before tapping, the argon gas is 10 minutes, and the flow rate is 100Nm 3 / min, the steel flow is round during the steel tapping process, and the oxygen content of the molten steel is 350ppm.

[0042] (3) LF furnace refining: Refining takes 7.9 minutes to achieve rapid white slag production. The smelting process is completely in a reducing atmosphere. The double bottom blowing argon flow rate is 42Nm 3 / min, slag layer thickness 14mm, outgoing FeO+MnO=0.60%, LF is treated with calcium before leaving the station, and the calcium content of molten steel is controlled at 20ppm.

[0043] (4) Slab continuous casting: The insertion depth of the immersion nozzle is 145 mm; the continuous casting constant casting speed is controlled at 1.2 m / min; the superheat of the molten steel in the tundish is 14°C; a dynamic light reduction system is used, and the reduction is 45 mm; the vertical section adopts strong cooling, and the temperature of the straightening section is 960°C. The secondary cooling water segmented cooling process is adopted, and the secondary cooling water ratio of the vertical section is 1.4 L / kg, the secondary cooling water ratio of the bending section is 1.1 L / kg, and the secondary cooling water ratio of the horizontal section is 1.3 L / kg.

[0044] (5) Hot rolling: final rolling temperature 865℃, coiling temperature 635℃, layer cooling adopts front-end slow cooling, water valve adopts open-close-set setting, and stack cooling is carried out after coiling.

[0045] The chemical composition and mass percentage of the hot stamping steel in this embodiment are shown in Table 1, the covering agent composition is shown in Table 2, and the banded structure grade is 2.5. Figure 4 .

[0046] Table 1 Chemical composition and mass percentage of low-cost and high-quality hot stamping steel (%)

[0047] Table 2 Chemical composition and mass percentage of carbon-free and low-silicon covering agent (%)

[0048] Compared with the traditional smelting process, the present invention adds 8-10ppm more free calcium. The higher calcium content combines with the residual sulfur content in the molten steel to generate CaS to avoid the generation of MnS. The risk of more serious banded structure due to plastic deformation caused by MnS inclusion in the rolling direction is avoided, and the level of banded structure is effectively reduced from 3-4 to 1.5-2.5. The present invention reduces the banded structure level of the hot-rolled plate through ultra-low superheat casting process, increasing the cooling speed of the secondary cooling water, and using a dynamic light reduction model, providing high-quality slab raw materials for subsequent rolling processes.

[0049] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for reducing the banded structure of hot stamping steel, characterized in that: The method comprises the following steps: (1) Hot metal pretreatment: After the hot metal ladle is desulfurized by spraying magnesium powder and lime, the slag is removed and the S of the hot metal after pretreatment is ≤ 0.008%; (2) Decarbonization converter smelting: the final slag basicity is 3.3-3.6; the mass percentage of the components at the end of smelting is: C: 0.03-0.05%, S≤0.008%, P≤0.020%; the end temperature is 1680-1700℃; the mass percentage of FeO in the final slag is ≤20%; the whole process is argon blowing at the bottom, the steel is tapped without inverting the furnace, the ladle is protected by bottom blowing argon before tapping, the steel flow is rounded during the tapping process, and the oxygen content of the molten steel is controlled at 300-500ppm; (3) LF furnace refining: white slag can be quickly produced within 8 minutes of refining. The smelting process is completely in a reducing atmosphere. The double bottom blowing argon flow rate is 40-50Nm 3 / min, slag layer thickness 10-15mm, FeO+MnO≤1% before leaving the station, calcium treatment is carried out before LF leaves the station, the calcium treatment amount is 8-10ppm higher than the normal calcium treatment, and is controlled at 20-30ppm; (4) Slab continuous casting: adopt ladle slag detection system; ladle casing, stopper rod, water inlet and plate space are protected by argon blowing; the insertion depth of immersion water inlet is 150±5mm; the continuous casting constant casting speed is controlled at 1.2-1.3m / min; the liquid level fluctuation automatic control system is adopted, and the superheat of molten steel in the tundish is 12-18℃; the dynamic light pressure reduction system is adopted, and the pressure reduction is 4-6mm; the vertical section adopts strong cooling, and the temperature of the straightening section is ≥900℃.

2. A method for reducing banded structure of hot stamping steel according to claim 1, characterized in that: In the step (1), the molten iron is pretreated by a composite injection method, magnesium powder and lime are added for desulfurization, the desulfurization rate is ≥ 95%, and slag is removed after desulfurization, and the exposed surface of the molten steel is ≥ 90%.

3. A method for reducing banded structure of hot stamping steel according to claim 1, characterized in that: In the step (2), argon is blown from the bottom of the ladle during the whole process of smelting, steel is tapped without falling down, the service life of the tapping port is 50-100 furnaces, argon is blown from the bottom of the ladle before tapping for ≥10 minutes, and the flow rate is 80-100 Nm 3 / min.

4. A method for reducing the banded structure of hot stamping steel according to any one of claims 1 to 3, characterized in that: In the step (3), the thickness of the slag layer entering the LF refining station is 10-15 mm, the outlet S is ≤0.003%, and the amount of calcium wire fed is controlled according to the calcium content of the molten steel at 20-30 ppm.

5. A method for reducing the banded structure of hot stamping steel according to any one of claims 1 to 3, characterized in that: In the step (4), the continuous casting tundish adopts a slag retaining wall and a slag retaining weir, the tundish uses a carbon-free magnesium refractory material, an aluminum-carbon argon blowing upper water inlet, uses steel protective slag for hot stamping, the ladle water inlet is subjected to argon sealing protection casting, an immersion water inlet is adopted, a carbon-free low-silicon covering agent is used, and the covering agent thickness is 50 to 100 mm, and slag detection is performed to ensure that the steel slag does not enter the tundish.

6. A method for reducing banded structure of hot stamping steel according to any one of claims 1 to 3, characterized in that: The step (4) adopts ultra-low superheat casting, with a superheat of 12 to 18°C; and adopts a secondary cooling water segmented cooling process, with a secondary cooling water ratio of 1.2 to 1.5 L / kg in the vertical segment, 0.8 to 1.2 L / kg in the curved segment, and 1.2 to 1.4 L / kg in the horizontal segment.

7. A method for reducing the banded structure of hot stamping steel according to any one of claims 1 to 3, characterized in that: The method further comprises a hot rolling process, wherein the final rolling temperature of the hot rolling process is controlled within a range of 850-870°C, and the coiling temperature is controlled within a range of 620-640°C.

8. A method for reducing banded structure of hot stamping steel according to any one of claims 1 to 3, characterized in that: The chemical composition and mass percentage of the hot stamping steel are: C: 0.20-0.25%, Mn: 1.25-1.50%, S≤0.003%, P≤0.025%, Si: 0.20-0.40%, Als: 0.020-0.040%, Ti: 0.020-0.050%, B: 0.0020-0.0050%, Cr: 0.15-0.35%, Ca: 0.002-0.003%, N≤0.0050%, and the balance is iron and unavoidable impurities.

9. A method for reducing the banded structure of hot stamping steel according to any one of claims 1 to 3, characterized in that: In the step (5), the chemical composition of the carbon-free and low-silicon covering agent is as follows: CaO: 40-55%, SiO2≤12.0%, Al2O3: 35-45%, MgO≤5.0%, F≤5.0%, Fe2O3≤5.0%.

10. A method for reducing banded structure of hot stamping steel according to any one of claims 1 to 3, characterized in that: The continuous casting billet produced by the smelting method has a banded structure grade of 1.5 to 2.5 after being processed into hot-rolled plates.

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