355MPa strength grade high flatness steel plate and manufacturing method thereof

Abstract

The present invention provides a 355MPa strength grade high-flatness steel plate and a manufacturing method thereof. The chemical composition of the steel plate by weight is as follows: 0.13wt%≤C≤0.15wt%, 0.15wt%≤Si≤0.30wt%, 0.50wt%≤Mn≤0.80wt%, P≤0.02wt%, S≤0.005wt%, 0.018wt%≤Als≤0.045wt%, 0.03wt%≤Ti≤0.04wt%, N≤0.0055wt%, 0.0012wt%≤B≤0.0020wt%, with the remainder being iron and other unavoidable impurities. Furthermore, the 355MPa strength grade high-flatness steel plate has an average internal stress of less than 70MPa. Compared with existing technologies, the steel plate has uniform grains, low average internal stress, good flatness, and high quality stability, and exhibits high processing stability and aesthetics.

Description

Technical Field

[0001] The present invention relates to the field of metal casting, and in particular to a 355MPa strength grade high flatness steel plate and a manufacturing method thereof. Background Art

[0002] 355MPa strength-grade, high-flatness steel plate is a low-alloy structural steel with a relatively low material grade, primarily used for general structural components, and with low quality requirements. However, with the increasing adoption of automation in downstream processing plants, such as laser cutting and automatic welding, steel plates are now required to meet high quality dimensional requirements during use, including warping-free cutting and high dimensional accuracy in welded parts. To meet these requirements, the steel plate must exhibit low internal stress, excellent flatness, and stable mechanical properties to demonstrate both its processing capabilities and aesthetic appeal. Consequently, stringent quality standards must be met for this material, ensuring both high quality and low price.

[0003] However, due to the particularity of the production process, the existing technology for manufacturing coiled flat steel plates is not as good as the single-rolling steel plate rolling production line for controlling the internal stress quality of the product. Nb and Ti micro-alloy control is used in production control, resulting in high production costs and poor quality stability of the steel plates. Summary of the Invention

[0004] The main purpose of the present invention is to provide a 355MPa strength grade high flatness steel plate and a manufacturing method thereof, aiming to solve the problems of poor quality stability and high production cost of the 355MPa strength grade high flatness steel plate produced by the existing technology.

[0005] To achieve the above object, the present invention provides a 355MPa strength grade high flatness steel plate, wherein the chemical composition of the 355MPa strength grade high flatness steel plate is as follows: 0.13wt%≤C≤0.15wt%, 0.15wt%≤Si≤0.30wt%, 0.50wt%≤Mn≤0.80wt%, P≤0.02wt%, S≤0.005wt%, 0.018wt%≤Als≤0.045wt% t%, 0.03wt%≤Ti≤0.04wt%, N≤0.0055wt%, 0.0012wt%≤B≤0.0020wt%, and the rest are iron and other inevitable impurities; and the average internal stress of the 355MPa strength level high-flatness steel plate is less than 70MPa; the metallographic surface layer of the 355MPa strength level high-flatness steel plate has a 30μm decarburized layer structure, and the F+B+P structure of cementite is distributed at its grain boundaries.

[0006] The present invention also provides a method for manufacturing a 355MPa strength grade high-flatness steel plate, comprising the steps of: providing a hot-rolled material; the chemical composition mass percentage of the hot-rolled material is 0.13wt%≤C≤0.15wt%, 0.15wt%≤Si≤0.30wt%, 0.50wt%≤Mn≤0.80wt%, P≤0.02wt%, S≤0.005wt%, 0.018wt%≤Als≤0.045wt%, 0.03wt%≤Ti≤0.04wt%, N≤0.0055wt%, 0.0012wt%≤B≤0.0020wt%, and the rest is iron and other inevitable impurities.

[0007] When the hot-rolled material cools to below 60°C, it is flattened and cut into plates according to the order specifications and thickness, obtaining 355MPa strength grade high flatness steel plates.

[0008] When the order specification thickness a≤12mm, the flatness is ≤2mm / m; when the order specification thickness is 12mm<a≤18mm, the flatness is ≤4mm / 2m; when the order specification thickness is 18mm<a≤25mm, the flatness is ≤5mm / 2m; wherein, the order specification width b is 1800~2000mm.

[0009] Furthermore, the entry pressure reduction of the rough straightening process in the flattening and cutting process is -5mm to -10mm.

[0010] Furthermore, when the straightness does not meet the requirements, the steel plate is subjected to tempering heat treatment and is used as the hot-rolled material again for subsequent operation steps; the temperature of the tempering heat treatment is 550°C; the holding time of the tempering heat treatment is 1.8amin; wherein a is the order specification thickness, in mm.

[0011] Furthermore, the thickness of the hot-rolled material is 230 mm; and the center segregation and center porosity of the slab of the hot-rolled material do not exceed C1.5.

[0012] Furthermore, before the hot-rolled material is cooled, the hot-rolled material is subjected to dephosphorization treatment, rough rolling treatment, finishing rolling treatment and coiling treatment in sequence; wherein the temperature of the finishing rolling treatment is 840-870°C; and the temperature of the coiling treatment is 560-630°C.

[0013] Furthermore, the rough rolling process adopts a rough rolling mill with flat rolls; and the finishing rolling process adopts a finishing mill with CVC rolls.

[0014] Furthermore, after the finishing rolling treatment, the finished rolled material is subjected to laminar cooling to be cooled to the temperature of the coiling treatment; wherein the upper and lower water ratio of the laminar cooling is set to 1:1.1.

[0015] Furthermore, the hot-rolled material is obtained by sequentially subjecting the raw materials to top-bottom combined blowing converter primary refining, LF refining and CC casting to obtain the hot-rolled material.

[0016] Furthermore, the process of cooling to below 60°C is specifically to take the hot-rolled material out of the warehouse for cooling for 24 hours, and then naturally cool it to below 60°C.

[0017] The beneficial effects achieved by the present invention are:

[0018] The metallographic structure of the 355MPa strength-grade, high-flatness steel plate provided by this invention features a 30μm decarburized surface layer and a cementite F+B+P structure (ferrite+bainite+pearlite) distributed at the grain boundaries. The plate exhibits uniform grains, an average internal stress of less than 70MPa, and excellent flatness and quality stability, resulting in high processing stability and aesthetics. The qualified rate for laser cutting exceeds 95%.

[0019] The present invention provides a method for manufacturing a 355MPa strength grade high-flatness steel plate. By introducing the B element into the hot-rolled material and controlling 0.13wt%≤C≤0.15wt%, 0.03wt%≤Ti≤0.04wt%, and 0.0012wt%≤B≤0.0020wt%, the hardenability and mechanical property stability of the 355MPa strength grade high-flatness steel plate are enhanced. Combined with a flattening plate processing process in which the flatness is controlled according to the thickness of the order specification, the 355MPa strength grade high-flatness steel plate with low internal stress, good plate flatness, and high quality stability is produced efficiently and stably, meeting the quality problem of the material not warping or bending after laser cutting. In addition, the manufacturing method has low cost and is suitable for large-scale promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0021] Figure 1 This is a comparison chart of the residual stress of the products obtained in Example 1 and Comparative Example 1;

[0022] Figure 2 This is a material microstructure diagram of the product obtained in Example 1;

[0023] Figure 3 This is the material microstructure diagram of the product prepared in Comparative Example 1.

[0024] The realization of the objectives, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0025] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0026] It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments may be combined with each other. It should also be understood that the terms used in the embodiments of the present invention are intended to describe specific embodiments, rather than to limit the scope of protection of the present invention.

[0027] Unless otherwise defined, all technical and scientific terms used in the present invention are consistent with the prior art knowledge of those skilled in the art and the description of the present invention. The present invention can also be implemented using any methods, equipment and materials in the prior art that are similar or equivalent to the methods, equipment and materials described in the embodiments of the present invention.

[0028] When numerical ranges are given in the examples, it should be understood that unless otherwise specified herein, both endpoints of each numerical range and any value between the two endpoints may be used. The test methods in the following examples, for which specific conditions are not specified, were generally performed under conventional conditions or according to the conditions recommended by the respective manufacturers. The materials or reagents required in the following examples were all commercially available unless otherwise specified.

[0029] In order to solve the problems of poor quality stability and high production cost of 355MPa strength grade high flatness steel plates produced by the prior art, the present invention provides a 355MPa strength grade high flatness steel plate, the chemical composition of the 355MPa strength grade high flatness steel plate is 0.13wt%≤C≤0.15wt%, 0.15wt%≤Si≤0.30wt%, 0.50wt%≤Mn≤0.80wt%, P≤0.02wt%, S≤0.005wt%, 0.018wt%≤Als≤0.045wt%, 0.03wt%≤Ti≤0.04wt%, N≤0.0055wt%, 0.0012wt%≤B≤0.0020wt%, with the remainder being iron and other inevitable impurities; and the average internal stress of the 355MPa strength level high-flatness steel plate is less than 70MPa; the metallographic surface layer of the 355MPa strength level high-flatness steel plate has a 30μm decarburized layer structure, and the F+B+P structure of cementite is distributed at its grain boundaries.

[0030] The 355MPa strength-grade, high-flatness steel plate provided by this invention features a 30μm decarburized surface layer with a cementite F+B+P structure (ferrite+bainite+pearlite) distributed at the grain boundaries. The plate exhibits uniform grains, an average internal stress of less than 70MPa, and excellent flatness and quality stability, resulting in high processing stability and aesthetics. The laser cutting pattern qualification rate exceeds 95%.

[0031] The present invention also provides a method for manufacturing a 355MPa strength grade high-flatness steel plate, comprising the steps of: providing a hot-rolled material; the chemical composition of the hot-rolled material having a mass percentage of 0.13wt%≤C≤0.15wt%, 0.15wt%≤Si≤0.30wt%, 0.50wt%≤Mn≤0.80wt%, P≤0.02wt%, S≤0.005wt%, 0.018wt%≤Als≤0.045wt%, 0.03wt%≤Ti≤0.04wt%, N≤0.0055wt%, 0.0012wt%≤B≤0.0020wt%, and the remainder being iron and other inevitable impurities. Specifically, when 0.13wt%≤C≤0.15wt%, 0.03wt%≤Ti≤0.04wt%, and 0.0012wt%≤B≤0.0020wt%, the yield strength is about 400Mpa, the mechanical properties, reducing the content of Ti element to control the precipitation strengthening effect, better stability performance, and at the same time, the B element has good hardenability, which improves the effect of solid solution strengthening of the material and reduces the fluctuation of the mechanical properties of the material. The relatively low mechanical properties and surface decarburization layer organization are conducive to the control of flatness in the material cutting + straightening process.

[0032] When the hot-rolled material cools to below 60°C, it is flattened and cut into plates according to the order specifications and thickness, obtaining 355MPa strength grade high flatness steel plates.

[0033] When the order specification thickness a≤12mm, the flatness is ≤2mm / m; when the order specification thickness is 12mm<a≤18mm, the flatness is ≤4mm / 2m; when the order specification thickness is 18mm<a≤25mm, the flatness is ≤5mm / 2m; wherein, the order specification width b is 1800~2000mm.

[0034] The present invention provides a method for manufacturing a 355MPa strength grade high-flatness steel plate. By introducing the B element into the hot-rolled material and controlling 0.13wt%≤C≤0.15wt%, 0.03wt%≤Ti≤0.04wt%, and 0.0012wt%≤B≤0.0020wt%, the hardenability and mechanical property stability of the 355MPa strength grade high-flatness steel plate are enhanced. Combined with a flattening plate processing process in which the flatness is controlled according to the thickness of the order specification, the 355MPa strength grade high-flatness steel plate with low internal stress, good plate flatness, and high quality stability is produced efficiently and stably, meeting the quality problem of the material not warping or bending after laser cutting. In addition, the manufacturing method has low cost and is suitable for large-scale promotion and application.

[0035] Furthermore, the rough straightening entrance pressure reduction during the flattening process is -5mm to -10mm. When the rough straightening entrance pressure reduction during the flattening process is -5mm to -10mm, the internal stress of the steel plate can be effectively released, thereby improving the stability of the 355MPa strength grade high flatness steel plate.

[0036] Furthermore, if the flatness does not meet the requirements, the steel plate is subjected to a tempering heat treatment and then used as hot-rolled material for subsequent processing steps. The tempering heat treatment temperature is 550°C and the holding time is 1.8 minutes. Where a is the order thickness in mm. Specifically, if the flatness of the steel plate does not meet the above requirements, the non-compliant steel plate should be tempered at 550°C for 1.8 minutes. After being removed from the tempering furnace, the plate should be naturally cooled on a cooling bed to below 60°C and then re-cut according to the order thickness.

[0037] Furthermore, the thickness of the hot-rolled material is 230 mm, and the center segregation and center porosity of the hot-rolled material slab do not exceed C1.5. Specifically, it is beneficial to control the grain size of the material, and the hot-rolled material has good surface quality and internal quality.

[0038] Furthermore, before the hot-rolled material is cooled, the hot-rolled material is subjected to dephosphorization treatment, rough rolling treatment, finishing rolling treatment and coiling treatment in sequence; wherein the temperature of the finishing rolling treatment is 840-870°C; and the temperature of the coiling treatment is 560-630°C.

[0039] Furthermore, the rough rolling process adopts a rough rolling mill with flat rolls; and the finishing rolling process adopts a finishing mill with CVC rolls.

[0040] Furthermore, after the finishing rolling process, the finished product is subjected to laminar cooling to a coiling temperature, wherein the top and bottom water ratio of the laminar cooling is set to 1:1.1. When the top and bottom water ratio of the laminar cooling is set to 1:1.1, uniform cooling of the top and bottom surfaces of the rolled product is ensured.

[0041] Furthermore, hot-rolled material is obtained by sequentially subjecting raw materials to top-and-bottom combined-blowing converter primary refining, LF refining, and CC casting. Specifically, LF refining involves slag deoxidation, adjusting the molten steel composition, and controlling the molten steel temperature, ultimately producing molten steel with qualified composition, high cleanliness, and an appropriate temperature. CC casting, on the other hand, produces slabs (hot-rolled material) with good surface and internal quality.

[0042] Furthermore, the process of cooling to below 60°C is specifically to take the hot-rolled material out of the warehouse for cooling for 24 hours, and then naturally cool it to below 60°C.

[0043] For further understanding of the present invention, now illustrate with examples:

[0044] Example 1

[0045] (1) Composition of tundish steel liquid: C: 0.143wt%, Si: 0.203wt%, Mn: 0.556wt%, P: 0.0152wt%, S: 0.0032wt%, Als: 0.0256wt%, Ti: 0.0325wt%, N: 0.0045wt%, B: 0.0012wt%, and the rest are iron and unavoidable elements.

[0046] (2) Rolling Process: Finishing rolling temperature 820°C–870°C, coiling temperature 600°C–630°C, laminar water ratio 1:1.1, and laminar water height setting. The slab thickness was 230 mm, the continuous casting furnace discharge temperature was 1195°C, and the total heating time was 242 min. After the slab was heated, controlled rolling was performed in a two-stage process, with flat rolls used in the roughing mill and CVC rolls used in the finishing mill.

[0047] (3) The hot rolling process is controlled and the rolled steel coil is shipped out for 24 hours for cooling. After the steel coil is naturally cooled to below 60℃, it is processed for flattening and cutting. The production specification of the order thickness is 8mm. The pressure reduction at the entrance of the rough straightening is reduced to -4mm. The straightness of the steel plate does not exceed 3mm / 2m.

[0048] Example 2

[0049] (1) Composition of tundish steel liquid: C: 0.135wt%, Si: 0.223wt%, Mn: 0.526wt%, P: 0.0122wt%, S: 0.0022wt%, Als: 0.0326wt%, Ti: 0.0355wt%, N: 0.0052wt%, B: 0.0018wt%, Cr: 0.20%, and the rest are iron and unavoidable elements.

[0050] (2) Rolling Process: The finishing rolling temperature was 820°C to 870°C, the coiling temperature was 560°C to 600°C, the laminar water ratio was 1:1.1, and the laminar water height was set. The slab thickness was 230 mm, the continuous casting slab temperature was 1215°C, and the total heating time was 256 min. After the slab was heated, controlled rolling was performed in a two-stage rolling process, with flat rolls used in the roughing mill and CVC rolls used in the finishing mill.

[0051] (3) The hot rolling process is controlled and the rolled steel coil is shipped out for 24 hours to cool. After the steel coil is naturally cooled to below 60℃, it is processed into flattened plates. The production specification of the order thickness is 20mm. The pressure reduction at the entrance of the rough straightening is reduced to -8mm. The straightness of the steel plate does not exceed 5mm / 2m. The straightness of the steel plate at the end of the coil is 10-15mm / 2m.

[0052] (4) The steel plate is tempered. The tempering process is as follows: temperature 550℃, holding time 36min, then the steel plate is rolled on the cooling bed and naturally cooled to room temperature. The straightness is 2mm / 2m.

[0053] Comparative Example 1

[0054] (1) Composition of tundish steel liquid: C: 0.075wt%, Si: 0.153wt%, Mn: 0.80wt%, P: 0.0132wt%, S: 0.0042wt%, Als: 0.0226wt%, Ti: 0.0425wt%, Nb: 0.0115wt%, N: 0.0062wt%, and the rest are iron and unavoidable elements.

[0055] (2) Rolling Process: Finishing rolling temperature 850°C–870°C, coiling temperature 610–630°C, laminar water ratio 1:1.1, and laminar water height setting. The slab thickness was 230 mm, the continuous casting slab discharge temperature was 1205°C, and the total heating time was 256 min. After the slab was heated, controlled rolling was performed in a two-stage process, with flat rolls in the roughing mill and CVC rolls in the finishing mill.

[0056] (3) Rolling is controlled according to the hot rolling process. The rolled steel coil is placed in the hot coil warehouse for more than 48 hours. The steel coil is naturally cooled to below 60℃ for flattening and cutting. The pressure at the entrance of the rough straightening is reduced to -5mm, and the straightness of the steel plate is 5mm / 2m.

[0057] Comparative Example 2

[0058] (1) Composition of tundish steel liquid: C: 0.065wt%, Si: 0.183wt%, Mn: 0.967wt%, P: 0.0102wt%, S: 0.003wt%, Als: 0.0286wt%, Ti: 0.0455wt%, N: 0.0056wt%, Nb: 0.0215wt%, and the rest are iron and unavoidable elements.

[0059] (2) Rolling Process: Finishing rolling temperature 840°C–860°C, coiling temperature 560–580°C, laminar water ratio 1:1.1, and laminar water height setting. The slab thickness was 230 mm, the continuous casting slab outlet temperature was 1220°C, and the total heating time was 302 minutes. After the slab was heated, controlled rolling was performed in a two-stage process, with flat rolls in the roughing mill and CVC rolls in the finishing mill.

[0060] (3) The hot rolling process is controlled and the rolled steel coil is shipped out for 24 hours to cool. After the steel coil is naturally cooled to below 60°C, it is processed into flattened plates. The production specification of the order thickness is 20mm, and the pressure reduction at the entrance of the rough straightening is reduced to -5mm. The straightness of the steel plate is 7-15mm / 2m, which does not meet the requirements.

[0061] Analysis example 1

[0062] (1) The mechanical properties of the products obtained in Examples 1-2 and Comparative Examples 1-2 were compared and analyzed; the mechanical properties of the products obtained in Examples 1-2 and Comparative Examples 1-2 are shown in Table 1.

[0063] Table 1 Comparative analysis of mechanical properties of products obtained in Examples 1-2 and Comparative Examples 1-2

[0064]

[0065] According to Table 1, the yield strength of the materials in Examples 1 and 2 is about 30 MPa lower than that of the materials in Comparative Examples 1 and 2, and the elongation is increased by 7-10%. The materials have good processing characteristics.

[0066] (2) The residual stress of Example 1 and Comparative Example 1 was detected. The specific results were compared. Figure 1 .

[0067] from Figure 1 It can be seen from the internal stress detection data of Example 1 and Comparative Example 1 that the internal stress of the embodiment is low and the stability is better.

[0068] (3) The metallographic structures of Example 1 and Comparative Example 1 were observed microscopically, and the microscopic structure diagrams of the materials were as follows: Figure 2 、 Figure 3 shown.

[0069] from Figure 2 It can be seen from the figure that the decarburized layer is 30-50um on the surface; the content of B structure gradually increases from the decarburized layer to 1 / 4 of the thickness. The metallographic structure shows that the addition of B element and the reduction of Ti element have achieved the goal of strengthening the structure instead of precipitation strengthening; Figure 3 It can be seen that there is basically no decarburized layer on the surface, and the main structure is ferrite and pearlite. Figure 2 and Figure 3 The microstructure of this 355MPa steel shows a decarburized layer of 30 to 50μm on the surface. This decarburized layer facilitates stress conduction during straightening without affecting mechanical properties. This means that concentrated stress areas are more easily transferred to the ferrite structure through deformation caused by straightening. This decarburized layer facilitates stress uniformity during straightening. By leveraging the hardenability of B and Cr and reducing the precipitation effect of Ti, the addition of B achieves the goal of structural strengthening instead of partial precipitation strengthening.

[0070] In summary, the above technical solutions of the present invention are only preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made by using the contents of the present invention's description and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for manufacturing a 355MPa strength grade high flatness steel plate, characterized in that: Including steps: Providing a hot-rolled material; the chemical composition of the hot-rolled material is as follows: 0.13wt%≤C≤0.15wt%, 0.15wt%≤Si≤0.30wt%, 0.50wt%≤Mn≤0.80wt%, P≤0.02wt%, S≤0.005wt%, 0.018wt%≤Als≤0.045wt%, 0.03wt%≤Ti≤0.04wt%, N≤0.0055wt%, 0.0012wt%≤B≤0.0020wt%, and the remainder is iron and other inevitable impurities; When the hot-rolled material is cooled to below 60°C, it is flattened and cut according to the thickness of the order specifications to obtain 355MPa strength grade high-flatness steel plates; the average internal stress of the 355MPa strength grade high-flatness steel plates is less than 70MPa; the metallographic structure of the 355MPa strength grade high-flatness steel plates has a 30µm decarburized layer structure on the surface, and the F+B+P structure of cementite is distributed at the grain boundaries; When the order specification thickness a≤12mm, the flatness is ≤2mm / m; when the order specification thickness is 12mm<a≤18mm, the flatness is ≤4mm / 2m; when the order specification thickness is 18mm<a≤25mm, the flatness is ≤5mm / 2m; among them, the order specification width b is 1800~2000mm.

2. The manufacturing method according to claim 1, characterized in that The entry reduction of the rough straightening process in the flattening process is -5mm to -10mm.

3. The manufacturing method according to claim 1, characterized in that When the flatness does not meet the requirement, the steel plate is subjected to tempering heat treatment and is used as the hot-rolled material for subsequent operation steps; The temperature of the tempering heat treatment is 550° C.; the holding time of the tempering heat treatment is 1.8 amin; wherein a is the order specification thickness, in mm.

4. The manufacturing method according to claim 1, characterized in that The thickness of the hot-rolled material is 230 mm; and the center segregation and center porosity of the slab of the hot-rolled material do not exceed C1.

5.

5. The manufacturing method according to claim 1, characterized in that The hot rolled material is subjected to dephosphorization treatment, rough rolling treatment, finish rolling treatment and coiling treatment in sequence before the hot rolled material is cooled; The temperature of the finish rolling process is 840-870°C; the temperature of the coiling process is 560-630°C.

6. The manufacturing method according to claim 5, characterized in that The rough rolling process uses a rough rolling mill with flat rolls; the finish rolling process uses a finish rolling mill with CVC rolls.

7. The manufacturing method according to claim 5, characterized in that After the finishing rolling process, the finished product is subjected to laminar cooling to the temperature of the coiling process; The upper and lower water ratio of the laminar cooling is set to 1:1.

1.

8. The manufacturing method according to claim 5, characterized in that The hot-rolled material is obtained by sequentially performing top-bottom combined blowing converter primary refining, LF refining, and CC casting on the raw materials to obtain the hot-rolled material.

9. The manufacturing method according to claim 1, characterized in that The process of cooling to below 60° C. specifically includes taking the hot-rolled material out of the warehouse for cooling for 24 hours, and then naturally cooling it to below 60° C.

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