A low yield ratio high-strength weathering steel and a production method thereof

Abstract

The application provides a kind of low yield ratio high-strength weathering steel and its production method, component C:0.055%-0.080%, Si:0.30%-0.50%, Mn:0.60%-0.90%, P:≤0.015%, S:≤0.002%, Cr:0.40%-0.70%, Ni:0.05-0.10%, Cu:0.20%-0.35%, Als:0.020%-0.050%, Ti:0.020%-0.040%, N≤50ppm, the rest is Fe and inevitable impurity element.Compared with prior art, the application is designed by chemical composition, controlled rolling and controlled cooling process and heat treatment process, to obtain fine and uniform quasi-polygonal ferrite and granular bainite, martensite complex organization, with low yield ratio, high strength, high plasticity and toughness and anti-shock property.No addition of Nb and other precious metals, low cost.

Description

Technical Field

[0001] This invention belongs to the field of steel material manufacturing, specifically relating to a low yield strength ratio high strength weathering steel and its production method. Background Technology

[0002] Corrosion is one of the main failure modes of steel materials, causing huge economic losses and resource and energy consumption. Atmospheric corrosion is the most common form of corrosion for steel materials, accounting for more than half. Weathering steel has excellent resistance to atmospheric corrosion and is widely used in the manufacture of steel structures and equipment that are exposed to the atmosphere for a long time, such as buildings, railway vehicles, containers, bridges, and towers, to extend service life and improve service safety. As the application fields of weathering steel continue to expand, the requirements for its comprehensive performance, such as strength, yield strength ratio, and ductility and toughness, are constantly increasing. Especially when used in steel structure buildings, a lower yield strength ratio is required to improve seismic performance.

[0003] Fine-grain strengthening and precipitation strengthening are common strengthening methods to improve the strength of steel materials, but they also increase the yield strength ratio of the material. As the strength of steel increases, it becomes much more difficult to obtain high strength, low yield strength ratio and high ductility and toughness at the same time.

[0004] Patent CN 113201685 A, published on August 3, 2021, discloses an economical low yield strength ratio hot-rolled weathering steel plate and its manufacturing method. Its chemical composition (wt%) is as follows: C: 0.11%-0.13%, Si: 0.20%-0.50%, Mn: 0.20%-0.60%, P: ≤0.015%, S: ≤0.005%, Cr: 0.30%-0.50%, Ni: ≤0.07%, Cu: 0.25%-0.40%, Alt: 0.020%-0.045%, with the balance being Fe and unavoidable impurities. Its yield strength is ≥345MPa, tensile strength is ≥480MPa, yield strength ratio is ≤0.75, and A ≥30.0%. According to the embodiments of this invention patent, the yield strength ratio is actually controlled between 0.72 and 0.74. The yield strength ratio is mainly reduced by increasing the C content and the volume fraction of pearlite. However, with a C content of 0.11%-0.13%, which is in the peritectic region, the slab is prone to longitudinal cracks during continuous casting, leading to steel leakage and affecting industrial production.

[0005] Patent CN112251674A, published on January 22, 2021, discloses a hot-rolled low yield strength ratio high weathering steel for railway passenger cars and its manufacturing method. The chemical composition by mass percentage (wt%) is as follows: C: 0.01%-0.04%, Si: 0.10%-0.30%, Mn: 0.20%-0.50%, P: ≤0.015%, S: ≤0.003%, Cr: 3.5%-5.0%, Ni: 0.20-0.40%, Cu: 0.35%-0.50%, Als: 0.025%-0.050%, Nb: 0.010-0.030%, Ti: 0.010-0.025%, with the balance being Fe and unavoidable impurities. The steel has a yield strength ≥350MPa, tensile strength: 490-690MPa, yield strength ratio ≤0.75, and A ≥30%. According to the embodiments of this invention patent, the yield strength ratio is actually controlled between 0.69 and 0.72. Furthermore, the addition of Nb, and the high content of Cr and Ni, result in a higher alloy cost.

[0006] The patent published on January 8, 2019, with publication number CN 109161793 A, discloses a low yield strength ratio high strength weathering steel and its production method. Its chemical composition and mass percentage are as follows: C: 0.08-0.10%, Si: 0.25-0.30%, Mn: 1.30-1.50%, P≤0.010%, S≤0.010%, Ni: 0.25-0.30%, Cr: 0.45-0.50%, Cu: 0.25-0.35%, Al: 0.02-0.04%, Nb: 0.020-0.030%, Ti: 0.010-0.020%, with the balance being Fe and unavoidable impurity elements. Produced using a medium-thick plate production line, the steel exhibits a yield strength of 428.5-444.3 MPa, a tensile strength of 663.2-673.3 MPa, a yield-to-tensile strength ratio ≤0.66, an elongation after fracture ≥21%, and a longitudinal impact energy at -40℃ ≥66 J. According to the embodiments of this invention patent, the yield-to-tensile strength ratio is actually controlled between 0.65 and 0.66, and the elongation is only 21%-23%. Furthermore, the high Mn and Ni content, along with the addition of Nb, results in a higher alloy cost.

[0007] Patent CN 109234635 A, published on January 18, 2019, discloses a 345MPa grade low yield strength high-weathering steel and its preparation method. Its chemical composition and mass percentage are as follows: C: 0.04-0.12%, Si: 0.50-0.75%, Mn: 0.43-0.50%, P: 0.06-0.09%, S≤0.004%, Ni: 0.15-0.35%, Cr: 0.30-0.60%, Cu: 0.25-0.40%, Al: 0.02-0.04%, Ti: 0.010-0.020%, with the balance being Fe and unavoidable impurity elements. Produced using a medium-thick plate production line and undergoing relaxation treatment, according to the embodiments of this invention patent, the yield strength ratio is actually controlled at 0.69-0.72, which is relatively high.

[0008] The yield strength ratios of the above-mentioned existing materials are all above 0.65, which cannot meet the requirements for low yield strength ratios, and the cost is relatively high. Summary of the Invention

[0009] The purpose of this invention is to provide a high-strength weathering steel with a low yield strength ratio and its production method. Through the synergistic design of chemical composition, controlled rolling and cooling, and heat treatment processes, a high-strength weathering steel plate with an extremely low yield strength ratio (≤0.60) is produced, while also exhibiting excellent plasticity and toughness. The specific technical solution of this invention is as follows:

[0010] A low yield strength ratio high strength weathering steel comprises the following components by mass percentage: C: 0.055%-0.080%, Si: 0.30%-0.50%, Mn: 0.60%-0.90%, P: ≤0.015%, S: ≤0.002%, Cr: 0.40%-0.70%, Ni: 0.05-0.10%, Cu: 0.20%-0.35%, Als: 0.020%-0.050%, Ti: 0.020%-0.040%, N ≤50ppm, with the remainder being Fe and unavoidable impurity elements.

[0011] The composition of the low yield strength ratio high-strength weathering steel also needs to satisfy: Cu + 10 × Ti ≤ 0.6. Cu and Ti can improve the strength of the material through the precipitation of two-phase particles, but the precipitation strengthening effect will increase the yield strength ratio of the material. Therefore, in order to control the yield strength ratio at ≤ 0.60, the chemical composition of the present invention also needs to satisfy: Cu + 10 × Ti ≤ 0.6.

[0012] When calculating using the above formulas, each element represents its content × 100.

[0013] The hot-rolled microstructure of the low yield strength ratio high strength weathering steel consists of ferrite and pearlite, wherein the average grain size of the ferrite is 5.5-8.0 μm and the volume fraction of ferrite is 88-94%.

[0014] The microstructure of the low yield strength ratio high strength weathering steel is a fine and uniform quasi-polygonal ferrite, granular bainite and martensite multiphase structure, wherein the average grain size of ferrite is 4.5-6.5μm, the volume fraction of ferrite is 55-60%, the volume fraction of granular bainite is 5-8%, and the remainder is martensite.

[0015] The yield strength R of the low yield strength ratio high strength weather-resistant steel eL ≥350MPa, tensile strength R m ≥600MPa, elongation A≥24%, yield strength R eL / R m It has a strength of ≤0.60, exhibiting an extremely low yield strength ratio and high strength-plasticity.

[0016] The impact performance of the low yield strength ratio high strength weathering steel is: KV2≥80J at -40℃ (sample size: 10×10×55mm), exhibiting excellent low-temperature toughness.

[0017] This invention provides a method for producing high-strength weather-resistant steel with a low yield strength ratio, comprising the following process flow:

[0018] Converter smelting → refining → continuous casting → heating → controlled rolling → controlled cooling → coiling → heat treatment.

[0019] The heating process involves heating to 1160-1220℃ and holding at that temperature for 140-200 minutes to promote complete solid solution of alloying elements and homogenization of austenite. After the slab exits the heating furnace, high-pressure water is used to remove the surface iron oxide scale, followed by rolling.

[0020] The controlled rolling process includes hot continuous roughing and finishing. The roughing stage involves six passes at a temperature controlled above 1050℃, with a single-pass reduction of 20-30%. Large deformation is achieved at high temperatures in each pass, promoting the recovery and recrystallization of deformed austenite grains and refining the austenite grain size. The finishing stage uses a 7-stand continuous rolling mill with seven passes, an initial rolling temperature ≤1030℃, and a cumulative deformation ≥80%. This cumulative large deformation increases the deformation bands and dislocation density within the deformed austenite, increases the deformation nucleation points of the ferrite phase, and refines the ferrite grains after phase transformation. The finishing temperature is controlled at 840-900℃.

[0021] The controlled cooling process involves rapidly cooling the material to 560-640°C at a rate of 20-40°C / s after finishing rolling, followed by coiling.

[0022] The winding process is carried out at a temperature of 560-640℃. When the winding temperature is below 560℃, the austenite is completely transformed into bainite, resulting in high material strength and a high yield strength ratio. When the winding temperature is above 640℃, the ferrite grains coarsen, resulting in low material strength and insufficient toughness.

[0023] The heat treatment involves heating to 770-830℃ and holding for 25-40 minutes to fully austenitize the pearlite and partially transform proeutectoid ferrite into austenite. Then, water quenching is performed to below 250℃ at a cooling rate ≥65℃ / s to prevent pearlite transformation, resulting in austenite transforming into granular bainite and martensite, thus obtaining a multiphase structure of ferrite, granular bainite, and martensite. Heating temperatures below 770℃ result in incomplete austenitization of the pearlite, leading to a lower proportion of bainite and martensite after heat treatment, insufficient tensile strength, and an increased yield strength ratio. Heating temperatures above 830℃ increase the volume fraction of austenitized proeutectoid ferrite, even achieving complete austenitization, reducing the ferrite content after heat treatment, increasing the yield strength ratio, and decreasing the material's ductility and toughness. Holding times below 25 minutes result in incomplete austenitization of the pearlite, leading to a high yield strength ratio. If the heat preservation time exceeds 40 minutes, the ferrite grains coarsen, reducing the yield strength and toughness of the material.

[0024] The design concept of this invention is as follows:

[0025] Carbon (C): With its small atomic radius, C is interstitially dissolved in the crystal lattice, significantly improving the strength of steel. C also enhances the hardenability of steel, significantly increasing tensile strength after quenching and thus reducing the yield strength ratio. However, excessive C content can worsen the weldability of steel, reduce its ductility and toughness, and increase the crack susceptibility of the cast billet. Therefore, this invention designs the C content to be 0.055%-0.080%.

[0026] Silicon (Si): Si increases the volume fraction of ferrite in steel and enhances material strength through solid solution strengthening. Furthermore, Si helps refine corrosion products and promotes the formation of a dense protective rust layer on the steel surface, thereby improving atmospheric corrosion resistance. However, excessive Si content can deteriorate the weldability and surface quality of the steel. Therefore, this invention designs the Si content to be 0.30-0.50%.

[0027] Manganese (Mn): Mn is one of the important solid solution strengthening elements in steel and also an important deoxidizing element in the steelmaking process. Mn can also expand the austenite phase region, improve the stability of austenite, and promote the transformation of bainite and martensite at low temperatures. However, excessive Mn content will not only increase manufacturing costs but also deteriorate the weldability of steel. Therefore, its content is designed to be 0.60-0.90%.

[0028] Al (aluminum): Al is the main deoxidizing element added to steel. It can also combine with nitrogen to form AlN, which inhibits austenite grain growth during heating and improves strength. However, excessive Al content leads to an increase in oxide inclusions in the steel, reducing the steel's low-temperature toughness and atmospheric corrosion resistance. Therefore, its content is designed to be 0.020-0.050%.

[0029] Cr (chromium): Cr is an important alloying element for improving the atmospheric corrosion resistance of steel. Its enrichment on the steel surface promotes the formation of dense α-FeOOH molecules with good adhesion to the matrix, preventing the diffusion of corrosive media such as oxygen and water into the matrix. Cr also improves the hardenability of materials, promoting the formation of bainitic and martensitic hard phases during quenching. However, excessively high Cr content will worsen the weldability of steel and increase manufacturing costs; therefore, the Cr content is designed to be 0.40-0.70%.

[0030] Cu (copper): Cu enriches in the rust layer of steel, improving its density and promoting anodic passivation, significantly enhancing the material's resistance to atmospheric corrosion. It also improves the hardenability of steel, promoting the formation of bainitic and martensitic hard phases during quenching. However, Cu is a low-melting-point alloying element with a melting point of only 1083℃. Excessive content can easily lead to leaks in continuous casting, copper embrittlement defects on the steel plate surface during hot rolling, and the precipitation of ε-Cu two-phase particles, increasing the material's yield strength ratio. Therefore, the Cu content is designed to be 0.20-0.35%.

[0031] Ni (Ni): Ni can increase the self-corrosion potential of materials, reduce corrosion tendency, and improve atmospheric corrosion resistance; it can also react with Cu to form a high-melting-point Cu-Ni binary alloy phase, effectively preventing copper embrittlement defects caused by Cu and improving the surface quality of weathering steel. However, Ni is a precious metal element, and excessive content will significantly increase the manufacturing cost of steel. Therefore, the Ni content is controlled at 0.05-0.10%.

[0032] Titanium (Ti): Ti is a strong carbonitride forming element. During heat treatment heating and holding, undissolved titanium carbonitride can pin grain boundaries to inhibit grain coarsening and improve strength and toughness. During welding, Ti-containing two-phase particles can inhibit austenite grain coarsening in the coarse-grained region and improve the low-temperature toughness of the heat-affected zone. However, excessively high Ti content leads to excessive precipitation strengthening and grain refinement strengthening, resulting in an increased yield strength ratio. Therefore, its content is controlled between 0.020% and 0.040%.

[0033] Phosphorus (P): P is a harmful residual element in steel, which tends to segregate at grain boundaries, reducing the low-temperature toughness of steel and increasing its susceptibility to weld cracking. Therefore, the P content is designed to be ≤0.015%.

[0034] Sulfur (S): S is a harmful residual element in steel. It readily reacts with Mn to form MnS nonmetallic inclusions, reducing atmospheric corrosion resistance and ductility. S also readily reacts with Ti to precipitate Ti4C2S2 particles at high temperatures, reducing the precipitation of fine titanium carbonitride particles. Therefore, the S content in this invention is designed to be ≤0.002%.

[0035] Nitrogen (N): N readily combines with Ti, precipitating coarse TiN particles at high temperatures, which deteriorates the material's toughness; it also reduces the content of effective Ti, thereby reducing the precipitation of fine titanium carbonitride particles. Therefore, its content should be controlled at ≤50ppm.

[0036] This invention utilizes a synergistic design of C, Mn, Cu, Cr, and Ni to appropriately improve the hardenability of the material, facilitating the transformation of austenite into a hard phase of granular bainite and martensite during heat treatment, thus preventing the transformation of austenite into a single martensite structure and reducing the material's ductility and toughness. Cu, Cr, and Ni simultaneously enhance the material's resistance to atmospheric corrosion. The addition of the microalloying element Ti refines the ferrite grain size during rolling, precipitating fine titanium carbonitride two-phase particles and suppressing ferrite grain coarsening during heat treatment. Through controlled rolling and controlled cooling process design, the ferrite grain size is refined, resulting in a fine-grained ferrite + pearlite microstructure in the hot-rolled steel plate. Because the microstructure is hereditary, this creates conditions for obtaining a multiphase microstructure of fine-grained ferrite, granular bainite, and martensite after heat treatment. By designing a heat treatment process, the complete austenitization of pearlite and the austenitization of a certain volume fraction of proeutectoid ferrite are promoted. Then, rapid cooling to below 250℃ after quenching yields a complex microstructure consisting of fine-grained quasi-polygonal ferrite, granular bainite, and martensite. By controlling the volume fraction ratio of the soft-phase ferrite, hard-phase granular bainite, and martensite, the yield strength of the material is reduced, while the tensile strength is increased, resulting in an extremely low yield-to-tensile ratio, while simultaneously exhibiting high strength and high ductility and toughness.

[0037] Compared with existing technologies, this invention, through the synergistic design of chemical composition, controlled rolling and cooling processes, and heat treatment processes, obtains a fine and uniform quasi-polygonal ferrite and granular bainite-martensite complex structure. The average grain size of the hot-rolled ferrite is 5.5-8.0 μm, with a ferrite volume fraction of 88-94%; after heat treatment, the average grain size of the ferrite is 4.5-6.5 μm, with a ferrite volume fraction of 55-60%. This results in steel with a low yield strength ratio, high strength, high ductility and toughness, and excellent seismic performance. The production process is easy to control. No precious metals such as nitrogen (Nb) are added, resulting in low cost. Attached Figure Description

[0038] Figure 1 The metallographic structures of the hot-rolled state and the heat-treated state are shown in Example 2 of the present invention. Detailed Implementation

[0039] 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.

[0040] Examples 1-4

[0041] A low yield strength ratio high strength weathering steel comprises the following mass percentage composition as shown in Table 1. The balance not shown in Table 1 is Fe and unavoidable impurity elements.

[0042] Comparative Examples 1-5

[0043] A low yield strength ratio high strength weathering steel comprises the following mass percentage composition as shown in Table 1. The balance not shown in Table 1 is Fe and unavoidable impurity elements.

[0044] Table 1 Chemical composition of various embodiments and comparative examples of the present invention

[0045]

[0046] The specific process for steel production in the above embodiments and comparative examples includes: converter smelting → refining → continuous casting → heating → controlled rolling → controlled cooling → coiling → heat treatment.

[0047] Specifically as follows:

[0048] The steel is smelted, refined, and continuously cast according to the above chemical composition. The slab is heated to 1160-1220℃ and held for 140-200 minutes. After exiting the heating furnace, the surface iron oxide scale is removed, and then the slab is rolled. A two-stage rolling process is adopted: the roughing stage consists of six passes, with the rolling temperature controlled above 1050℃ and a single-pass reduction rate of 20-30%. The finishing stage consists of seven passes, with an initial rolling temperature ≤1030℃ and a cumulative deformation ≥80%. The finishing rolling temperature is controlled at 840-900℃, and after finishing rolling, it is rapidly cooled to 560-640℃ at 20-40℃ / s before being coiled. The plate is then heated to 770-830℃ in a box-type resistance furnace, and then placed inside the furnace and held for 25-40 minutes. The plate is then removed from the furnace and water-quenched to below 250℃ at a cooling rate ≥65℃ / s.

[0049] The main process parameters for the production of each of the above embodiments and comparative examples are shown in Table 2.

[0050] Table 2. Main process parameters for controlled rolling, controlled cooling, and heat treatment processes in each embodiment and comparative example.

[0051]

[0052] The mechanical properties, low-temperature toughness, and microstructure of each embodiment and comparative example are shown in Table 3. Tensile properties were tested according to GB / T 228.1-2010 "Metallic materials - Tensile testing - Part 1: Test at room temperature", and impact properties were tested according to GB / T 229 "Metallic materials - Charpy impact test".

[0053] Table 3 Mechanical properties, low-temperature toughness, and microstructure of various embodiments and comparative examples of the present invention.

[0054]

[0055]

[0056] Comparative Example 1 uses 0.12% C and 1.5% Mn, which increases hardenability and quenchability. It is produced and heat-treated according to the process of this invention, but the ferrite volume fraction is reduced, the microstructure is ferrite and martensite, and the plasticity and toughness are poor.

[0057] Comparative Example 2 has a composition that meets the requirements of this invention, but the heat treatment is held at 1000℃, which completely austenitizes the ferrite and pearlite, and the quenching process yields a hard phase structure of granular bainite and martensite, resulting in high strength and yield strength ratio, but poor plasticity and toughness.

[0058] Comparative Example 3 meets the requirements of this invention, but the heat treatment holding time is short, the pearlite is not completely austenitized, and the subsequent cooling rate is slow. The austenite is transformed into pearlite and a small amount of granular bainite, resulting in the microstructure of the steel plate being ferrite, pearlite and a small amount of granular bainite, with a high yield strength ratio.

[0059] Comparative Example 4 meets the requirements of this invention in terms of composition, but it uses air cooling, which results in a slower cooling rate. This causes the austenite to transform into ferrite and pearlite, and the ferrite grains to coarsen, resulting in low strength of the steel plate. The microstructure of the steel plate consists of ferrite and pearlite, and it has a high yield strength ratio.

[0060] Comparative Example 5 meets the requirements of this invention, but Cu+10×Ti>0.6%, and the content of Ti and Cu is relatively high, resulting in a strong precipitation strengthening effect. Even if produced and heat-treated according to the process of this invention, it still results in a high yield strength ratio.

[0061] In summary, the high-strength weather-resistant steel plate prepared according to the chemical composition, controlled rolling and cooling process, and heat treatment technology of this invention has a yield strength ≥350MPa, tensile strength ≥600MPa, elongation ≥24%, yield strength ratio ≤0.60, and KV2 ≥80J at -40℃. It has an extremely low yield strength ratio, high strength, and high plasticity and toughness, and excellent comprehensive performance. It can be used in the manufacture of buildings, bridges, iron towers, etc., to improve seismic performance and service safety.

[0062] The data underlined above do not meet the requirements of this invention.

[0063] 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 low yield strength to high strength weathering steel, characterized in that, The low yield strength ratio high strength weathering steel comprises the following components by mass percentage: C: 0.055%-0.080%, Si: 0.30%-0.50%, Mn: 0.60%-0.90%, P: ≤0.015%, S: ≤0.002%, Cr: 0.40%-0.70%, Ni: 0.05-0.10%, Cu: 0.20%-0.35%, Als: 0.020%-0.050%, Ti: 0.020%-0.040%, N ≤50ppm, with the remainder being Fe and unavoidable impurity elements; The composition of the low yield strength ratio high strength weathering steel must also meet the following requirement: Cu + 10 × Ti ≤ 0.6; The process flow of the production method of the low yield strength ratio high strength weathering steel is as follows: converter smelting → refining → continuous casting → heating → controlled rolling → controlled cooling → coiling → heat treatment. Controlled rolling includes hot continuous roughing and finishing; the hot continuous roughing includes six rolling passes, with the rolling temperature controlled above 1050℃ and a single-pass reduction rate of 20-30%; the finishing includes seven rolling passes, with an initial rolling temperature ≤1030℃, a cumulative deformation ≥80%, and a final finishing temperature controlled at 840-900℃. The controlled cooling process involves rapidly cooling the coil to 560-640°C at a rate of 20-40°C / s after finishing rolling; The heat treatment involves heating to 770-830℃, holding at that temperature for 25-40 minutes, and then rapidly water cooling to below 250℃ at a rate of ≥65℃ / s. The microstructure of the low yield strength ratio high strength weathering steel is a fine and uniform quasi-polygonal ferrite, granular bainite and martensite multiphase structure, wherein the average grain size of ferrite is 4.5-6.5 μm, the volume fraction of ferrite is 55-60%, and the volume fraction of granular bainite is 5-8%. The low yield strength R eL ≥ 350 MPa, tensile strength R m ≥ 600 MPa, elongation A ≥ 24%, yield strength ratio R eL / R m ≤ 0.60; -40°C KV2 ≥ 80 J.

2. A method for producing low yield strength ratio high-strength weathering steel according to claim 1, characterized in that, The production process is as follows: converter smelting → refining → continuous casting → heating → controlled rolling → controlled cooling → coiling → heat treatment; rolling includes hot continuous roughing and finishing; the hot continuous roughing includes six rolling passes, with the rolling temperature controlled above 1050℃ and a single-pass reduction rate of 20-30%; the finishing includes seven rolling passes, with an initial rolling temperature ≤1030℃, a cumulative deformation ≥80%, and a final finishing temperature controlled at 840-900℃; the controlled cooling involves rapid cooling to 560-640℃ at 20-40℃ / s after finishing and coiling; the heat treatment involves heating to 770-830℃, holding for 25-40 minutes, and then rapidly water cooling to below 250℃ at ≥65℃ / s.

3. The production method according to claim 2, characterized in that, The heating process involves heating to 1160-1220℃ and holding at that temperature for 140-200 minutes.

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