590mpa grade multi-phase steel sheet for deep drawing and hole expanding part and method for manufacturing the same

Abstract

The application provides a 590MPa grade complex phase steel plate for deep drawing and hole expanding parts and a manufacturing method thereof, and belongs to the field of pickling automobile steel plates.The steel composition comprises Cr, Mo, Nb, C, Si, Mn, P, S, Als, and the balance of Fe and inevitable impurity elements; and satisfies 0.3%<= (Cr+Mo) <=0.4% and Cr / Mo<=2.5.Compared with the prior art, the Si content is relatively low, the surface quality of the steel plate is improved, the Cr-Mo is added in combination, the generation of iron oxide scale is reduced, and the thickness of the iron oxide scale is reduced.The post-rolling adopts a front-stage cooling and medium-temperature coiling process in the production, the process control difficulty is low, the structure and performance stability in the length direction of the steel plate is good.The steel plate has high strength, elongation and hole expanding rate, and can meet the needs of forming of complex parts with high strength, good drawing performance and flanging and hole expanding performance.

Description

Technical Field

[0001] This invention belongs to the field of hot-rolled pickled automotive steel sheets, specifically relating to a 590MPa grade multiphase steel sheet for deep-drawn expanded hole parts and its manufacturing method. Background Technology

[0002] The automotive industry continues to pursue high efficiency, energy conservation, and superior performance, making lightweight chassis a key development direction. Lightweight chassis not only significantly reduces vehicle weight, effectively reducing fuel consumption and improving acceleration performance, but also greatly reduces braking inertia, enhancing driving safety and handling stability. Hot-rolled pickled high-strength steel, with its high strength, surface quality comparable to cold-rolled steel, good plasticity, and lower cost, is widely used in automotive chassis system manufacturing.

[0003] The subframe is a crucial component of the automotive chassis system, directly impacting vehicle handling, comfort, and safety; therefore, it must possess sufficient strength and rigidity. Subframe and other parts have complex shapes, deep stamping depths, and often involve flanging and reaming processes. This necessitates materials with not only high uniform elongation (drawability) to prevent tearing but also high local elongation (reaming rate) to prevent flanging cracking. Existing dual-phase steel (DP) has poor reaming rate, while bainitic steel (FB) has high yield strength but insufficient drawability, making it difficult to achieve a good balance in deep-drawn reamed parts.

[0004] Traditional 590MPa grade hot-rolled pickled duplex steel has an elongation of ≥25% and good drawing performance. However, due to its microstructure of ferrite + martensite, the two phases have a large difference in hardness and contain interfaces with significantly different deformation capacities, resulting in poor flanging and hole-expanding performance, with an expansion rate generally below 40%. This makes it prone to cracking during stretching, flanging, and hole-expanding processes. High-expansion steel typically employs a ferrite + bainite technique. Because bainite and ferrite are similar, the difference in their interfaces is smaller, effectively improving the coordinated deformation capacity of the two phases during local deformation, thus enhancing flanging and hole-expanding performance. However, this approach suffers from high yield strength, leading to generally poor drawing performance.

[0005] With the further development of lightweight chassis, the strength, rigidity, and integration of parts are becoming increasingly demanding, leading to a growing need for high-strength, complex-shaped components. Therefore, hot-rolled pickled steel sheets, which combine high strength, good drawing properties, and flanging and hole-expanding capabilities, will have a broader application prospect.

[0006] In the prior art, Chinese Patent CN111363901A, published on July 3, 2020, discloses a high-surface-quality ferritic-martensitic hot-rolled dual-phase steel and its manufacturing method. Its composition by weight percentage is: C: 0.04-0.08%, Si≤0.1%, Mn: 1.0-1.4%, Al: 0.3-0.8%, Cr: 0.15-0.60%, Nb: 0.01-0.03%, P≤0.015%, S≤0.002%, N≤0.005%. It also contains one or more of the following elements: Ti≤0.03%, V≤0.03%, Ca≤0.005%, with the remainder being Fe and unavoidable impurities, and must simultaneously satisfy: (Si+2Al+Cr)≥1.0; Al / Cr≤2.5. A segmented cooling method is adopted. The final rolled steel plate is cooled to 630-730℃ at a cooling rate of 50-150℃ / s, air-cooled for 3-15 seconds, and then cooled again to below 300℃ at a cooling rate of 60℃ / s or higher before being coiled. The metallographic structure is ferrite + martensite, with a tensile strength ≥600MPa, yield strength ratio ≤0.7, elongation ≥24%, and a porosity of ≥50%, with the optimal porosity in the example being 65%. This scheme incorporates a higher Al content to replace the role of Si and expand the ferrite transformation temperature range, but the high Al content poses a challenge to the control of inclusions. The segmented cooling method of the laminar cooling process makes it difficult to precisely control the air cooling time, resulting in a lower porosity and a tendency to crack during edge-flanging and porosity expansion.

[0007] Therefore, it is essential to provide a hot-rolled pickled steel sheet with better overall performance, combining high strength, good drawing properties, and flanging and hole-expanding properties. Summary of the Invention

[0008] The present invention aims to provide a 590MPa grade multiphase steel plate for deep-drawn expanded hole parts and its manufacturing method. The core of the method lies in combining Cr-Mo-Nb composite microalloying with controlled rolling and controlled cooling processes to obtain a multiphase microstructure dominated by fine-grained ferrite and pearlite, containing dispersed nano-carbide. This microstructure exhibits a small hardness difference and strong coordinated deformation capacity, thereby simultaneously achieving high elongation and high hole expansion rate, making it particularly suitable for manufacturing structural safety parts with complex shapes and large stamping depths. The multiphase steel plate provided by this invention also possesses high surface quality.

[0009] The specific technical solution of this invention is as follows:

[0010] A 590MPa grade multiphase steel sheet for deep-drawing and reaming parts comprises the following components by weight percentage:

[0011] Cr: 0.20%-0.30%, Mo: 0.09%-0.15%, Nb: 0.008%-0.018%, C: 0.07-0.09%, Si: 0.13%-0.17%, Mn: 1.65%-1.75%, P≤0.020%, S≤0.010%, Als: 0.015%-0.040%, balance being Fe and unavoidable impurity elements;

[0012] The composition of the 590MPa grade multiphase steel plate used for deep drawing and reaming parts meets the following requirements: 0.3%≤(Cr+Mo)≤0.4%; Cr / Mo≤2.5.

[0013] Each element represents its content × 100%, which can be calculated by substituting the value before the % sign.

[0014] The metallographic structure of the 590MPa grade multiphase steel plate used for deep drawing and hole expansion parts is ferrite + pearlite + dispersed nano-carbide, wherein the area ratio of ferrite is 72-75% and the ferrite grain size is 11-13.

[0015] The 590MPa grade multiphase steel plate used for deep-drawing and reaming parts has a yield strength ≥470MPa, tensile strength ≥590MPa, and elongation A. 50mm ≥25%, expansion rate ≥70%, surface quality is FB.

[0016] Preferably, the 590MPa grade multiphase steel plate used for deep-drawing and reaming parts has a yield strength of 470-530MPa, a tensile strength of 590-630MPa, and an elongation rate A. 50mm The porosity is 25.5-28.5%, and the porosity is 70-89%.

[0017] The iron oxide scale thickness of the hot-rolled steel coil of the 590MPa grade multiphase steel plate used for deep drawing and reaming parts is ≤10μm.

[0018] The steel banding structure of the 590MPa grade multiphase steel plate used for deep drawing and reaming parts is ≤ grade 2.

[0019] The thickness of the 590MPa grade multiphase steel plate used for deep drawing and reaming parts is 2.0-2.5mm.

[0020] The present invention provides a method for manufacturing the above-mentioned 590MPa grade multiphase steel plate for deep drawing and hole expansion parts, comprising the following processes: steelmaking, continuous casting, billet loading, hot rolling, laminar flow cooling, coiling, and pickling.

[0021] In the process of loading the billet into the furnace, the furnace exit temperature is 1230-1270℃, and the holding time is 180-240 minutes.

[0022] In the hot rolling step, the rough rolling is carried out in 3+3 or 3+5 passes with the descaling water fully open at the inlet, and the rough rolling is carried out to an intermediate billet with a thickness of 30-40mm; the finishing rolling starts at 1000℃-1100℃ and finishes at 870-890℃.

[0023] In the laminar flow cooling step, a front-end cold zone mode is adopted, with a cooling rate of 90-170℃ / s.

[0024] In the winding step, the winding temperature is 590-610℃. The winding temperature is one of the key process parameters to ensure strength and elongation. When the temperature is higher than 610℃, the strength decreases; when the temperature is lower than 590℃, the strength of the material increases.

[0025] In the pickling step, the hot-rolled steel coil is re-coiled on the uncoiler, and after tension leveling and pickling, the finished hot-rolled pickled steel sheet is obtained; the tension leveling elongation is controlled to be 0.5-2.0%.

[0026] The design concept of this invention is as follows:

[0027] This invention effectively suppresses the segregation of elements such as Mn and P by controlling the Cr / Mo ratio and the total (Cr+Mo) content, resulting in a final plate material with a banded microstructure controlled to level 2 or below (according to GB / T 34474.1), significantly improving microstructure uniformity. This provides the microstructure basis for both high elongation and high porosity. The steel plate of this invention also possesses high surface quality.

[0028] C: The most effective element for improving the strength of steel. Taking into account both welding and forming properties, the C content is controlled at 0.07%-0.09%, preferably 0.08%.

[0029] Si: A ferrite solid solution strengthening element that accelerates the segregation of carbon into austenite and has a "removal" and "purification" effect on dissolved carbon in ferrite. High Si content impairs plasticity and easily produces red rust on the surface, affecting surface quality. The content should be controlled at 0.13%-0.17%, preferably 0.15%.

[0030] Mn is a solid solution strengthening element that can also refine ferrite grains. Compared to grain refinement and precipitation strengthening, solid solution strengthening has the lowest rate of increase in yield strength ratio. Therefore, solid solution strengthening is most advantageous for achieving a low yield strength ratio while ensuring strength. However, Mn is a strong center segregation element, which significantly affects molding cracking. The Mn content should be controlled between 1.65% and 1.75%, preferably 1.70%.

[0031] Phosphorus (P): A harmful element in steel, it easily causes severe segregation, reduces the toughness of steel plates, and leads to brittle fracture. Furthermore, excessively high P content significantly reduces the weldability of steel and should generally be removed. Therefore, P should be controlled to ≤0.020%.

[0032] Sulfur (S) is a harmful element in steel. It easily forms sulfide inclusions and segregation with elements such as manganese (Mn) in the steel, reducing the strength and toughness of the steel and worsening fatigue and weldability. Therefore, its content should be minimized. Thus, the S content should be controlled below 0.010%.

[0033] Als has a similar effect on the austenite morphology in the critical heating chamber as Si, and can also form AlN precipitation, which plays a certain role in refining the grains. The Als content is controlled at 0.015%-0.040%.

[0034] Cr: inhibits pearlite transformation, increases the supercooling ability of austenite, thereby refining the microstructure; the high diffusion rate of Cr promotes the uniform distribution of elements such as Mn and P, inhibits the formation of dendrite segregation, and reduces the tendency of banded structures; in addition, it promotes the diffusion of C into austenite, purifies ferrite, and improves plasticity.

[0035] Mo: It strongly delays the transformation of pearlite, providing more time for the nucleation and growth of ferrite. It combines with C to form stable nano-carbides, pinning grain boundaries to inhibit the growth of austenite grains, refining ferrite grains, and improving the strength and toughness of steel. During cooling, molybdenum and carbon form fine nano-carbides. The composite addition of Cr-Mo changes the type and distribution of carbides, thereby optimizing the overall microstructure uniformity, providing a significant precipitation strengthening effect, and improving the strength of steel.

[0036] This invention controls the concentration to 0.3% ≤ (Cr + Mo) ≤ 0.4%, ensuring that Cr and Mo provide sufficient "driving force for alloy carbide formation," achieving a supersaturation ΔC of 0.06–0.08 wt%, without entering the "rapid growth" region due to excessive concentration. During the γ→α phase transition, this results in:

[0037] 1) Nucleation rate Iv∝(ΔC) 5 A surge of 1–2 orders of magnitude;

[0038] 2) High number density (2–4 × 10⁻⁵ nm) is formed in the early stage of precipitation (<5 nm). 22 m -3 (Cr,Mo) X Cᵧ embryonic nucleus, laying the foundation for "fine" size.

[0039] This invention controls the Cr / Mo ratio to be ≤2.5, and the difference in atomic radii between Cr and Mo (Δr≈10%) allows them to simultaneously enter the M7C3 / M2C lattice, thereby reducing the carbide / ferrite interface energy γ from ≈0.9 Jm. -2 Reduced to 0.5–0.6 Jm -2The interface energy decreases, which reduces the critical nucleation work ΔG* by about 30%, further increasing the nucleation rate. The metastable (Cr,Mo)2C or (Cr,Mo)7C3 formed is lenticular or nearly spherical and does not easily grow into a network or rod-like structure.

[0040] This invention utilizes the low diffusion coefficient of Mo to suppress the diffusion coefficient of Mo in ferrite, D_Mo≈4×10 -19 m 2 s -1 It is only 1 / 6–1 / 8 of that of Cr.

[0041] After the formation of high-density small particles in the early stage, the slow diffusion of Mo reduces the Oswald ripening rate constant K to approximately 1 / 3 of that of pure Cr carbides; after medium- and high-temperature encapsulation and cooling, the average particle size can still be maintained at <10 nm, achieving a "diffuse" distribution.

[0042] This invention uses a total Cr+Mo content of ≤0.4% to avoid unstable nucleation of "large-angle grain boundary network". When Cr+Mo >0.5%, carbides tend to preferentially accumulate at the original austenite grain boundaries, forming discontinuous or continuous networks; while controlling it at 0.3–0.4% can suppress the carbon activity a_C to 0.18–0.22, reduce the chemical potential difference between the grain and the grain boundary, force carbides to nucleate uniformly at dislocations and lath boundaries within the grain, and eliminate the tendency for network embrittlement.

[0043] In summary, the design of this invention with 0.3%≤Cr+Mo≤0.4% and Cr / Mo≤2.5 precisely couples the two conditions of "high supersaturation-high nucleation rate" and "low diffusion-low coarsening rate", while suppressing grain boundary instability nucleation and obtaining nanoscale, diffusely distributed (Cr,Mo) carbide particles.

[0044] The composite addition of Cr and Mo in this invention can influence the solidification process of molten steel, altering the solute redistribution coefficient at the solid-liquid interface, thereby reducing the initial segregation of Mn and P between dendrites. Both Cr and Mo atoms tend to segregate towards grain boundaries. By controlling the total amount of (Cr+Mo) within a suitable range (0.3%-0.4%) and using an appropriate ratio (Cr / Mo≤2.5), Cr and Mo atoms can effectively occupy segregation sites at grain boundaries. Controlling Cr / Mo≤2.5 ensures effective synergy between the two elements, avoiding the adverse effects of excessive amounts of either element. If the Mo content is too high, although its carbide strengthening effect is good, the excessive segregation tendency will lead to its own large accumulation at grain boundaries, potentially providing an origin for cracks. Excessive Cr content may also introduce the risk of brittle phases. An appropriate ratio allows Cr and Mo to leverage their respective advantages (such as Cr's diffusion ability and Mo's carbide-forming ability), producing a synergistic effect of "1+1>2," more effectively suppressing the segregation of Mn and P.

[0045] In this invention, Cr and Mo have a synergistic effect in improving the oxidation resistance of steel billets. In high-temperature environments, when steel billets come into contact with oxygen, Cr preferentially reacts with oxygen to form a continuous, dense Cr2O3 oxide film on the billet surface that is firmly bonded to the matrix. This reduces the contact between other elements and oxygen, thus decreasing the formation of iron oxide scale. Mo can dissolve in the Cr2O3 oxide film, forming a Mo-Cr composite oxide with higher stability and lower ion diffusion rate, further improving the protective performance of the oxide film, reducing the thickness of iron oxide scale, and minimizing defects caused by scale indentation.

[0046] Nb: Nb in solid solution can suppress dynamic recrystallization and subsequent static recrystallization during hot deformation, increase the recrystallization termination temperature, increase strain accumulation in the rear stands during hot continuous rolling, promote the transformation of austenite to ferrite, and refine ferrite grains. However, excessive Nb content will have an adverse effect on ferrite phase transformation. Therefore, the Nb content is controlled at 0.008%-0.018%, preferably 0.013%.

[0047] Compared with existing technologies, this invention features a relatively low Si content, resulting in improved surface quality of the steel plate. The composite addition of Cr-Mo helps reduce the formation of iron oxide scale, with a scale thickness ≤10μm. The addition of Cr-Mo, by suppressing component segregation, achieves a banded structure of ≤2 grade in the steel (according to GB / T 34474.1 Evaluation of Banded Structure in Steel Grades Part 1: Standard Rating Chart Method). The thin iron oxide scale of this invention is less likely to detach and be pressed into the matrix, avoiding defects such as pitting and dents on the steel plate surface, resulting in high surface quality. A banded structure of ≤2 grade in the steel indicates a more uniform microstructure, reducing deformation inconsistencies and stress concentration, thereby achieving higher elongation and expansion rates. The addition of Nb increases the recrystallization termination temperature, allowing for higher final rolling temperatures and reducing the mill load. Post-rolling employs a pre-cooling and medium-temperature coiling process, which is easier to control and results in good microstructure and performance stability along the length of the steel plate. The steel plate produced by this invention has high strength, elongation, and hole expansion rate, which can meet the forming requirements of complex parts with high surface quality, high strength, good drawing performance, and flanging and hole expansion performance. Attached Figure Description

[0048] Figure 1 The image shows the microstructure of the hot-rolled pickled steel sheet in Example 1 under a metallographic microscope at 100x magnification. It can be seen that the microstructure consists of ferrite, pearlite, and dispersed nano-carbide.

[0049] Figure 2 The image shows the microstructure of the hot-rolled pickled steel sheet in Example 1 under a metallographic microscope at 500x magnification. It can be seen that fine nano-sized carbides are dispersed inside the ferrite and at the grain boundaries.

[0050] Figure 3The image shows the microstructure of the hot-rolled pickled steel sheet in Example 1 under a scanning electron microscope. The microstructure can be seen more clearly as: polygonal ferrite + pearlite + dispersed nano-carbide.

[0051] Figure 4 The image shows the surface of the hot-rolled pickled steel sheet from Example 1. The surface quality is good, reaching the FB level. Detailed Implementation

[0052] 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 in conjunction with the embodiments of the present invention. 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.

[0053] Examples 1-9

[0054] A 590MPa grade multiphase steel sheet for deep-drawing and reaming parts comprises the following mass percentage composition as shown in Table 1, where the balance not shown in Table 1 is Fe and unavoidable impurities.

[0055] Comparative Example 1 - Comparative Example 2

[0056] A steel plate comprising the following composition by weight percentage as shown in Table 1, wherein the balance not shown in Table 1 is Fe and unavoidable impurities.

[0057] Table 1. Composition and content of steel plates in each embodiment and comparative example

[0058]

[0059] Comparative Example 1 is Example 1 of CN111363901A;

[0060] Comparative Example 2 is Example 1 of CN112779401A;

[0061] Comparative Example 3 is Example 2 of CN106834949B;

[0062] Comparative Example 4 is Example 1 of CN107881430A;

[0063] The manufacturing methods of the steel plates in each embodiment and comparative example include the following processes: steelmaking, continuous casting, billet loading into the furnace, hot rolling, laminar flow cooling, coiling, and pickling.

[0064] In the billet loading process, the billet exit temperature is 1230-1270℃, and the holding time is 180-240 minutes. The main heating parameters of the billets in each embodiment and comparative example are shown in Table 2.

[0065] In the hot rolling process, the roughing rolling is carried out in 3+3 or 3+5 passes with the descaling water fully open at the inlet, and the roughing is carried out to an intermediate billet with a thickness of 30-40 mm; the finishing rolling starts at 1000℃-1100℃ and finishes at 870-890℃. The main parameters of the hot rolling process for each embodiment and comparative example are shown in Table 3.

[0066] In the laminar flow cooling step, a front-end cold zone mode is adopted, with a cooling rate of 90-170℃ / s.

[0067] In the winding step, the winding temperature is 590-610℃. Winding temperature is one of the key process parameters for ensuring strength and elongation. When the temperature is above 610℃, the strength decreases; when the temperature is below 590℃, the material strength increases. Winding temperature is one of the key process parameters for strength. The laminar flow cooling and winding process parameters are shown in Table 4.

[0068] In the pickling step, the hot-rolled steel coil is re-coiled on the uncoiler, and after tension straightening and pickling, the finished hot-rolled pickled steel sheet is obtained; the tension straightening elongation is controlled at 0.5-2.0%, and the specific tension straightening parameters are shown in Table 5.

[0069] The properties of the hot-rolled pickled steel sheets in each embodiment are shown in Table 5.

[0070] Table 2 Heating parameters of the cast billets in each embodiment and comparative example

[0071]

[0072] Table 3 Main hot-rolled parameters for each embodiment and comparative example

[0073]

[0074] Table 4. Laminar flow cooling and winding process parameters for each embodiment and comparative example.

[0075]

[0076] Table 5. Tension-correction parameters and performance of each embodiment and comparative example.

[0077]

[0078] In Table 5, the metallographic structure is represented by F for ferrite, P for pearlite, B for bainite, and M for martensite.

[0079] As can be seen from the data in Table 5, Comparative Example 1 uses a C-Si-Mn-Cr-Al-Nb-Ti segmented cooling and low-temperature coiling process, resulting in an F+M microstructure, which leads to a low porosity in the product. Comparative Example 2 uses a niobium-titanium microalloying, segmented cooling, and medium-temperature coiling process, resulting in a high yield strength in the product, which is not conducive to stamping parts with complex shapes. Comparative Example 3 uses a titanium microalloying, front-end centralized cooling, and medium-temperature coiling process, resulting in a high yield strength in the product, but the amount of Ti added is relatively large, and the Ti precipitation is unstable, leading to a low porosity in the product. Comparative Example 4 uses a C-Si-Mn-Cr-Nb-Ti composition system, a segmented cooling, and a low-temperature coiling process, resulting in an F+M microstructure, which leads to a low porosity in the product.

[0080] The above description of the embodiments is intended to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A 590MPa grade multiphase steel plate for deep-drawing and reaming parts, characterized in that, Its chemical composition, by mass percentage, includes: Cr: 0.20%-0.30%, Mo: 0.09%-0.15%, Nb: 0.008%-0.018%, C: 0.07-0.09%, Si: 0.13%-0.17%, Mn: 1.65%-1.75%, P≤0.020%, S≤0.010%, Als: 0.015%-0.040%, with the balance being Fe and unavoidable impurity elements; and satisfying 0.3%≤(Cr+Mo)≤0.4%, Cr / Mo≤2.5; The iron oxide scale thickness of the hot-rolled steel plate coil is ≤10μm, and the surface quality reaches FB grade; The metallographic structure of the steel plate is ferrite + pearlite + dispersed nano-carbide, wherein the area of ​​ferrite accounts for 72-75%, the ferrite grain size is 11-13, and the banded structure is ≤2. The 590MPa grade multiphase steel plate used for deep-drawing reamed parts has a reaming rate ≥70% and an elongation after fracture A 50mm ≥25%, yield strength is 470-530MPa, tensile strength is 590-630MPa.

2. The 590MPa grade multiphase steel plate for deep-drawing and reaming parts according to claim 1, characterized in that, The elongation A of the steel plate 50mm The porosity is 25.5-28.5%, and the porosity is 70-89%.

3. The 590MPa grade multiphase steel plate for deep-drawing and reaming parts according to claim 1 or 2, characterized in that, The thickness of the steel plate is 2.0-2.5mm.

4. A method for manufacturing a 590MPa grade multiphase steel plate for deep-drawing and reaming parts as described in any one of claims 1-3, characterized in that, The manufacturing method includes the following steps: steelmaking, continuous casting, billet loading into the furnace, hot rolling, laminar flow cooling, coiling, and pickling.

5. The manufacturing method according to claim 4, characterized in that, In the process of loading the billet into the furnace, the furnace exit temperature is 1230-1270℃, and the holding time is 180-240 minutes.

6. The manufacturing method according to claim 4, characterized in that, In the hot rolling step, the rough rolling is carried out in 3+3 or 3+5 passes with the descaling water fully open at the inlet, and the rough rolling is carried out to an intermediate billet with a thickness of 30-40mm; the finishing rolling starts at 1000℃-1100℃ and finishes at 870-890℃.

7. The manufacturing method according to claim 4, characterized in that, In the laminar flow cooling step, a front-end cold zone mode is adopted, with a cooling rate of 90-170℃ / s.

8. The manufacturing method according to claim 4, characterized in that, In the winding step, the winding temperature is 590-610℃.

9. The manufacturing method according to claim 4, characterized in that, In the pickling step, the hot-rolled steel coil is re-coiled on the uncoiler, and after tension leveling and pickling, the finished hot-rolled pickled steel sheet is obtained; the tension leveling elongation is controlled to be 0.5-2.0%.

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