1300MPa-grade medium-manganese high-strength steel plate with ultralow yield ratio and manufacturing method thereof

Abstract

The invention discloses a 1300MPa-grade medium-manganese high-strength steel plate with an ultralow yield ratio and a manufacturing method thereof. The 1300MPa-grade medium-manganese high-strength steel plate comprises the following components in percentage by weight: 0.1-0.2% of C, 0.2-0.4% of Si, 3-7% of Mn, less than or equal to 0.1% of Al, less than or equal to 0.01% of P, less than or equal to 0.01% of S, 0.2-0.6% of Cr, 0.02-0.06% of Nb, 0.02-0.08% of V, 0.01-0.04% of Ti and the balance of Fe and inevitable impurities. The manufacturing method comprises the steps of smelting, casting, controlled rolling, controlled cooling, air cooling after rolling and the like. The tensile strength is larger than or equal to 1300 MPa, the yield strength is larger than or equal to 830 MPa, the ductility is larger than or equal to 12%, the Charpy impact energy at the room temperature is larger than or equal to 30 J, the yield ratio is smaller than or equal to 0.7, the addition amount of precious metal is small, the process is simple, and the method is suitable for wide popularization.

Description

Technical Field

[0001] This invention belongs to the field of high-strength steel plate technology, specifically relating to a 1300MPa grade ultra-low yield strength ratio medium-manganese high-strength steel plate and its manufacturing method. Background Technology

[0002] In the field of engineering machinery steel, the performance requirements for thick plates are constantly increasing to meet the demands of maintaining extremely high safety performance while reducing equipment weight and energy consumption. This is to adapt to the development trend of high-strength and weight-reducing equipment and structures. Currently, the production process of high-strength steel plates for engineering machinery still mainly relies on traditional offline quenching and tempering treatment.

[0003] However, there are several problems with high-strength steel that uses offline quenching and tempering: First, traditional quenched and tempered high-strength steel often adds a certain amount of precious metal alloying elements such as Cr, Ni, and Mo to the steel. The metal carbides precipitate and strengthen the steel during high-temperature tempering, which reduces the softening of the steel plate during high-temperature tempering, resulting in higher alloy costs for the steel plate.

[0004] Secondly, steel plates subjected to traditional offline quenching and tempering heat treatment have a higher yield strength and lower tensile strength due to the high-temperature tempering process. This results in a higher yield strength-to-tensile strength ratio. In actual service, steel plates with a high yield strength-to-tensile strength ratio are less resistant to deformation and impact. Once the stress reaches the yield strength of the steel plate, the steel structure is more likely to reach its fracture strength, leading to cracking and other safety hazards.

[0005] Finally, traditional offline quenching and tempering heat treatment requires reheating and quenching of the steel plate after rolling, as well as high-temperature tempering. These two heat treatment processes consume a significant amount of energy, leading to increased carbon emissions during the actual steel production process. In the current context, reducing carbon emissions per ton of steel produced will inevitably become a new direction for the future development of the steel industry. Therefore, it is necessary to develop a low yield strength ratio high-strength steel product that can meet the requirements of online production.

[0006] Currently, medium-manganese steel products are widely used in automotive steel sheet manufacturing. Through appropriate heat treatment processes, the steel sheet's matrix structure can be a multiphase structure consisting of bainite, martensite, and retained austenite, resulting in high strength while maintaining good ductility and toughness. Furthermore, by rationally altering the heat treatment regime, different proportions of the aforementioned microstructures can be obtained, thereby regulating the steel sheet's mechanical properties. However, medium-manganese steel products are currently mainly used in thin-gauge products such as automotive steel. This is because thin sheets undergo significant cold deformation during production, which helps refine the internal microstructure and achieve higher strength. After cold deformation, the steel sheet often requires continuous annealing to ensure the microstructure meets design requirements. However, these processes are not feasible for medium-thick plate materials. Due to the greater thickness of the steel sheet, the rolling compression ratio is low during actual production. Steel sheets are typically produced using controlled rolling and controlled cooling methods. Traditional high-strength steel sheets require subsequent quenching and tempering heat treatment after rolling, reducing production efficiency.

[0007] Chinese patent CN102181790A discloses a "steel for automotive safety components with a tensile strength of 1300MPa and its production method." The chemical composition of this steel plate, by weight percentage, is: C: 0.12–0.22%, Si: 0.10–0.40%, Mn: 1.00–1.60%, Cr: 0.10–0.45%, Ti: 0.01–0.10%, B: 0.0005–0.005%, A… ls: 0.01~0.06%, P≤0.025%, S≤0.010%, N≤0.008%; its production steps include converter smelting, alloying, vacuum treatment and composition fine adjustment, continuous casting, heating the billet to 1220~1280℃, rough rolling, fine rolling, laminar flow cooling, coiling, pickling, cold rolling, annealing, leveling, finishing, shearing, heating austenitizing under nitrogen protective atmosphere, mold forming, quenching, tempering and other processes.

[0008] Chinese patent CN104946997A discloses "a 1300MPa grade ultra-high strength steel and its preparation method", characterized in that the chemical composition by weight percentage is: C: 0.15-0.20%; Si: 0.10-0.30%; Mn: 1.00-1.30%; Cr: 0.40-0.60%; Mo: 0.40-0.60%; Ni: 0.40-0.60%; Nb: 0.02-0.04%; V: 0.04-0.06%; Ti: 0.010-0.020%; Alt: 0.025-0.050%; B: 0.0010-0.0030%; P≤0.012%; S≤0.005%; Ceq: 0.55-0.60%; the remainder being Fe and unavoidable impurities. The preparation method mainly includes slab smelting, slab casting, slab heating, steel plate rolling and heat treatment.

[0009] Chinese patent CN106868398A discloses "1300MPa grade ultrafine ferrite / low-temperature bainitic duplex steel and its preparation method". Its chemical composition by weight percentage is: C: 0.28-0.32%, Si: 1.7-2.1%, Mn: 1.5-1.7%, Cr: 1.1-1.4%, Ni: 0.8-1.2%, W: 0.6-0.8%, P≤0.02%, S≤0.02%, with the remainder being Fe and unavoidable impurities. Its metallographic structure consists of ultrafine ferrite and low-temperature bainite, wherein the grain size of the ultrafine ferrite is 0.5-2μm and the volume content is 20-35%. The medium-carbon silicon-containing low-alloy steel is quenched and martensitic, then heated to a temperature below Ac1, held at that temperature, and then rolled and deformed. It is then heated to partially austenitize the "α+γ" two-phase region and placed in a salt bath furnace at a temperature slightly higher than the martensite initiation point of the two-phase region for isothermal bainite transformation, and then air-cooled to room temperature.

[0010] From the perspective of current technology, 1300MPa grade ultra-high strength steel is currently divided into two categories. One category is cold-rolled thin-gauge steel plates, which mainly achieve their mechanical properties through hot rolling, cold rolling, and subsequent continuous heat treatment. Steel plates produced using this method can meet a relatively low yield strength ratio, but their composition and production process are unsuitable for medium and heavy plate production. The other category is hot-rolled steel plates, which are produced by adding large amounts of precious metals such as Cr, Ni, and Mo, followed by quenching and tempering after rolling to produce ultra-high strength steel. These steel plates often achieve a strength level of 1300MPa, but due to the quenching and tempering process, their yield strength ratio is often high. Furthermore, the high amount of alloying elements added and the subsequent quenching and tempering process result in lower production costs and efficiency. Therefore, developing low-yield-strength-ratio, short-process 1300MPa grade ultra-high strength steel suitable for medium and heavy plate production lines is essential for the structural upgrading of materials in the engineering machinery industry and also responds to the current trend of reducing carbon emissions in the steel industry. Summary of the Invention

[0011] The purpose of this invention is to provide a 1300MPa grade ultra-low yield strength ratio medium-manganese high-strength steel plate and its manufacturing method, obtaining a non-quenched and tempered medium-thick plate high-strength steel with a tensile strength ≥1300MPa, elongation ≥12%, Charpy impact at room temperature ≥30J, and yield strength ratio ≤0.7. Compared with quenched and tempered steel of the same grade, it reduces the amount of precious metal elements such as Cr, Ni, and Mo, lowers the yield strength ratio of the steel plate, and improves the weldability of the steel plate. The non-quenched and tempered process can significantly shorten the production cycle of the steel plate, improve production efficiency, and reduce production costs compared with the traditional quenched and tempered process.

[0012] To achieve the above objectives, the technical solution of the present invention is as follows:

[0013] A 1300MPa grade ultra-low yield strength ratio medium-manganese high-strength steel plate has the following composition by weight percentage: C: 0.1-0.2%, Si: 0.2-0.4%, Mn: 3-7%, Al≤0.1%, P≤0.01%, S≤0.01%, Cr: 0.2-0.6%, Nb: 0.02-0.06%, V: 0.02-0.08%, Ti: 0.01-0.04%, with the balance including Fe and unavoidable impurities.

[0014] Furthermore, the balance consists of Fe and unavoidable impurities.

[0015] The microstructure of the steel plate described in this invention includes ferrite, bainite, martensite, and retained austenite.

[0016] The steel plate of the present invention has a tensile strength ≥1300MPa, a yield strength ≥830MPa, an elongation ≥12%, a Charpy impact energy at room temperature ≥30J, and a yield strength ratio ≤0.7.

[0017] The thickness of the steel plate described in this invention is 4 to 20 mm.

[0018] In the composition design of the 1300MPa grade ultra-low yield strength ratio medium manganese high-strength steel plate of this invention:

[0019] Carbon (C): Ensures material strength; as carbon content increases, the strength of the steel plate significantly improves. However, excessive carbon content leads to decreased toughness and increased susceptibility to weld cracking. This invention employs a low-carbon design, enhancing the steel plate's strength through the TRIP effect of retained austenite during deformation and the dispersed precipitation of Nb. This allows the steel plate to possess both high strength and excellent ductility and toughness. Therefore, the carbon content in this invention is controlled between 0.1% and 0.2%.

[0020] Silicon (Si): Silicon has a solid solution strengthening effect, which can improve the corrosion resistance and high-temperature oxidation resistance of steel. The addition of Si can also effectively increase the elastic modulus of the steel plate. However, excessive Si content can lead to severe decarburization on the steel surface, resulting in a decrease in the effective protective thickness of the steel plate and also reducing weldability. Therefore, the silicon content in this invention is controlled at 0.2% to 0.4%.

[0021] Manganese (Mn): Manganese is the main element stabilizing austenite in steel. Adding a large amount of manganese can significantly lower the austenite quenching transformation temperature of steel. Even after quenching to room temperature, some austenite remains intact, forming retained austenite. This retained austenite does not decompose during subsequent tempering and remains at room temperature. During the deformation of the steel plate, the martensite deforms, creating stress concentration points. To alleviate this stress concentration, the surrounding retained austenite undergoes a phase transformation, improving the actual deformability of the steel plate. However, excessively high Mn content in the steel can cause the martensitic transformation temperature to approach or fall below room temperature, increasing the retained austenite content and reducing the steel plate's strength. Therefore, the manganese content in this invention is controlled at 3-7%.

[0022] Aluminum (Al): Aluminum effectively prevents the formation of carbides in steel, promotes the solid solution of carbon in austenite, and improves the stability of austenite during cooling. Simultaneously, aluminum also refines grain size, which is highly beneficial for improving the toughness of steel plates. However, if the aluminum content in steel is too high, it increases the difficulty of smelting and casting, raises manufacturing costs, and leads to excessive oxide formation, deteriorating the quality of the steel plate. Therefore, this invention controls the Al content to ≤0.1%.

[0023] Chromium (Cr): Chromium increases the hardenability of steel, significantly delays the ferrite-pearlite transformation, lowers the critical temperature for ferrite phase transformation during air cooling after water cooling, and thus refines ferrite grains. Simultaneously, its ability to delay the pearlite-ferrite transformation, combined with controlled cooling temperature, reduces the amount of ferrite transformation in the steel, allowing the steel plate to maintain high strength while possessing a certain degree of toughness. However, excessively high chromium content can lead to the precipitation of effective carbon elements in the steel, reducing the number of dissolved carbon atoms in low-carbon steel and increasing the brittleness tendency of the steel plate during tempering. Therefore, the chromium content in this invention is controlled at 0.2–0.6%.

[0024] Niobium (Nb): Niobium is a strong carbide-forming element. In steel, during high-temperature rolling deformation, it can refine rolled austenite grains through deformation-induced precipitation. Simultaneously, the precipitated carbides pin dislocations, resulting in precipitation strengthening. During cooling, niobium carbide precipitation further enhances precipitation strengthening, increasing the matrix strength. The strengthening effect increases with increasing niobium content, but when the niobium content is too high, its precipitation strengthening and grain refinement effects become less pronounced. Therefore, the niobium content in this invention is controlled at 0.02–0.06%.

[0025] Vanadium (V): Vanadium is a strong carbide-forming element, playing a role in precipitation strengthening and grain refinement in materials. Because excessive Mn content in steel easily leads to grain coarsening, adding trace amounts of vanadium helps refine the microstructure and improve alloy strength. Simultaneously, V carbide precipitation has a dispersion strengthening effect, further enhancing the strength of the steel. Therefore, the vanadium content in this invention is controlled at 0.02–0.08%.

[0026] Titanium (Ti): Titanium is a strong carbide-forming element, capable of forming TiN in steel. As a nucleation site for austenite, it refines the austenite grains. In this invention, the addition of trace amounts of Ti primarily serves to refine the austenite grains. Excessive Ti content leads to the precipitation of TiC, consuming carbon (C) in the steel, reducing the solid solubility of C in austenite, and consequently decreasing austenite stability. Therefore, the Ti content in this invention is controlled at 0.01–0.04%.

[0027] P and S are unavoidable harmful elements in steel and should be controlled to be as low as possible. Therefore, this invention controls P ≤ 0.01% and S ≤ 0.01%.

[0028] In terms of composition design, this invention employs a low-C, medium-Mn composition, combined with the addition of microalloying elements such as Cr, Nb, V, and Ti, resulting in a steel plate with a good balance of strength and plasticity. Furthermore, the lower alloying element content of this invention reduces the aluminum content of the steel plate. c1 and A c3 Temperature helps steel plates form a microstructure dominated by bainite, but also containing proeutectoid ferrite, martensite, and a certain amount of retained austenite during the actual slow cooling process. Because of its low strength, ferrite in steel reaches its yield point first and begins plastic deformation as stress increases during actual deformation, resulting in a low yield strength and a low yield-to-tensile ratio. As deformation increases, the dislocation density in ferrite continuously increases, and its strength also continuously improves. When the strength reaches the yield strength of bainite and martensite, bainite and martensite begin to yield. As stress levels continue to rise, local stress concentration begins to occur after the martensite deformation reaches a certain extent. At this point, the surrounding retained austenite can alleviate local stress concentration, allowing the material to undergo further plastic deformation, thereby improving the material's deformability.

[0029] The manufacturing method of the 1300MPa grade ultra-low yield strength ratio medium-manganese high-strength steel plate of the present invention includes the following steps:

[0030] 1) Smelting and casting

[0031] The above-mentioned components are smelted and cast into steel ingots or continuously cast billets;

[0032] 2) Slab heating

[0033] After the obtained steel ingot is rolled into a slab, the slab or billet is heated to a temperature of 1200-1250℃ for a heating time of t = 1-2H. The heating time t is in min and H is the thickness of the slab or billet in mm.

[0034] 3) Controlled rolling

[0035] Two-stage rolling is adopted. The first stage rolling temperature is 1100-1150℃, and the rolling is carried out to 3-5 times the thickness of the finished steel plate.

[0036] The second stage of rolling is at a temperature of 840–880℃, and the steel plate is rolled to a thickness of 4–20 mm.

[0037] 4) Online water cooling

[0038] The initial cooling temperature of the steel plate is 820-860℃, the final cooling temperature is 630-660℃, and then it is air-cooled to room temperature.

[0039] Preferably, in step 3), after the first stage of rolling is completed, the steel plate is naturally cooled or water-cooled to the second stage rolling temperature.

[0040] Preferably, in step 4), the cooling rate is 5 to 10 °C / s.

[0041] This invention employs a two-stage rolling process. In the first stage of rolling, the initial rolling temperature is 1100–1150°C. Since the temperature of the steel plate is above the recrystallization temperature, deformation allows the steel plate to fully complete dynamic recrystallization at the recrystallization temperature, forming refined original austenite grains. The principle of microstructure inheritance is used to effectively refine the subsequent microstructure.

[0042] The second-stage rolling temperature is 840–880℃. This second-stage rolling temperature must be maintained so that it does not drop below temperature A throughout the entire rolling process. c1 Below the temperature, avoid generating proeutectoid ferrite during the rolling process.

[0043] The subsequent cooling temperature of the steel plate is controlled at A. c1The temperature is above the required level to ensure that the steel plate does not have the supercooling conditions to form proeutectoid ferrite before being immersed in water. After rolling, the steel plate is directly cooled to a relatively high temperature of 630-660℃ at a cooling rate of 5-10℃ / s. The temperature after water cooling is above the bainite transformation temperature. During the subsequent air cooling process, proeutectoid ferrite will preferentially precipitate in the steel. During the continued cooling process, as the temperature continues to decrease, bainite, martensite, and finally untransformed retained austenite will form in the steel. Because the steel contains a certain amount of ferrite, its yield strength is relatively low. In the actual deformation process, ferrite is relatively soft and will undergo plastic deformation first, which will reduce the yield strength of the steel. However, because the amount of ferrite formed during the cooling process is small, after yield deformation, when the stress concentration caused by the deformation of ferrite reaches the condition for bainite and martensite to begin yielding, the bainite and martensite in the steel will begin to undergo plastic deformation. Finally, with the continuous increase of deformation and stress, the steel plate reaches the fracture strength. Compared to traditional quenched and tempered and bainitic high-strength steels, this steel contains a small amount of ferrite, thus enabling it to achieve a lower yield strength ratio.

[0044] Compared to traditional cooling to 300-500℃, the final cooling temperature is easier to control, shortening the cooling time of the steel plate. Afterward, the steel plate can be directly air-cooled to room temperature, reducing the cooling time on the cooling bed and saving space resources. Moreover, the cooling process is easier to operate and implement, and there is no need to track and control the air cooling process, which improves the process operability of steel plate production and increases the production efficiency of steel plates. It is very suitable for stable mass production on medium and heavy plate production lines.

[0045] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0046] The chemical composition of the steel plate of this invention is based on traditional low-carbon alloy steel. Through the addition of manganese and supplemented with small amounts of microalloying elements Cr, Nb, V, and Ti, the steel plate achieves several improvements. Firstly, manganese stabilizes austenite, significantly delaying the ferrite-pearlite transformation temperature. This reduces the formation of proeutectoid ferrite during cooling and directs it towards lower temperatures, refining the size of the proeutectoid ferrite and improving the solid solution strengthening effect, thereby enhancing the steel plate's strength. Secondly, the addition of manganese increases the stability of austenite. During cooling, as the steel plate temperature decreases to the bainite transformation temperature range, the austenite in the steel undergoes a bainite transformation. However, since the actual transformation temperature is not isothermal but continuously decreases, the bainite transformation also shifts towards lower temperatures as the steel plate temperature decreases, resulting in a good balance of strength and toughness. Existing strength levels reaching 1300 MPa often require the addition of higher contents of Cr, Ni, and Mo, which significantly improves ductility and toughness but effectively reduces the yield strength ratio of the steel plate.

[0047] This invention, based on compositional design, employs a non-quenching and tempering process. Through two-stage controlled rolling and subsequent cooling, the final cooling temperature is controlled within a relatively high range of 630–660°C, preferentially precipitating proeutectoid ferrite. During continued cooling, the steel plate forms a mixed microstructure of bainite, martensite, and retained austenite as the temperature continues to decrease, thus achieving a low yield strength ratio (≤0.7). In contrast, traditional TMCP production processes often avoid the ferrite transformation region during cooling, directly cooling the steel plate to the lower bainite transformation temperature region, resulting in a bainite matrix structure and often a similarly high yield strength ratio. Traditional quenching and tempering processes, when producing high-strength steel, contain a high content of alloying elements. While precipitation strengthening during tempering improves the strength and toughness of the steel plate, the yield strength generally increases while the tensile strength decreases during tempering, resulting in a high final yield strength ratio, typically above 0.95. Furthermore, the quenching and tempering process has a longer workflow and higher energy consumption.

[0048] This invention utilizes a non-quenched and tempered process to achieve thicknesses ranging from 4 to 20 mm, with tensile strength ≥1300 MPa, yield strength ≥830 MPa, elongation ≥12%, Charpy impact energy at room temperature ≥30 J, and yield strength ratio ≤0.7, achieving both high strength and a low yield strength ratio. Compared to cold-rolled manganese steel, it reduces the need for cold rolling and continuous annealing processes, while allowing for higher final cooling temperatures in online water cooling, thus improving rolling production efficiency and reducing subsequent heat treatment energy consumption. Compared to current quenched and tempered alloy high-strength steels of the same strength level, it eliminates the post-rolling quenching and tempering heat treatment process, shortening the steel plate production cycle and further reducing heating energy consumption during production, thereby improving production efficiency. Attached Figure Description

[0049] Figure 1 This is a photograph of the microstructure of the steel plate in Embodiment 1 of the present invention. Detailed Implementation

[0050] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0051] The following will further illustrate the 1300MPa grade ultra-low yield strength ratio medium-manganese high-strength steel plate and its manufacturing method according to specific embodiments. However, the present invention is not limited to the following embodiments, and various technical solutions derived therefrom should be within the protection scope of the present invention.

[0052] The components of the embodiments of the present invention are shown in Table 1, and Table 2 shows the process control parameters of the embodiments of the present invention.

[0053] Mechanical properties were tested. For tensile testing, plate-shaped tensile specimens were taken. For V-shaped Charpy impact specimens, standard specimens of 10*10*55mm were used (7.5*10*55mm impact specimens for 8-10mm steel plates and 2.5*10*55mm impact specimens for 4mm steel plates). The test results are shown in Table 3 below.

[0054] Figure 1 The image shows a typical scanning electron microscope (SEM) morphology of a steel plate obtained in an embodiment of the present invention. The smooth black area in the image represents proeutectoid ferrite, while the grayish-white area represents a mixed structure of bainite and martensite laths. The retained austenite is difficult to observe from the SEM due to its small size, but it can be detected by X-ray diffraction.

[0055] As can be seen from Tables 1, 2, and 3, the low-carbon, medium-manganese, high-strength steel plate produced by the manufacturing method described in this invention has a tensile strength ≥1300MPa, yield strength ≥830MPa, elongation ≥12%, Charpy impact energy at room temperature ≥30J, and yield strength ratio ≤0.7. It exhibits excellent plastic deformation capacity and can meet the requirements of conventional cold working processes such as cutting and bending. The Charpy impact energy at room temperature ≥30J also indicates good impact resistance.

[0056] In summary, the 1300MPa grade ultra-low yield strength ratio medium manganese high-strength steel plate involved in this invention can significantly simplify the production process compared with traditional quenched and tempered high-strength steel, and the production process space is easier to control. At the same time, it has good strength and toughness matching performance, making it suitable for mass production on medium and heavy plate production lines.

[0057]

[0058]

[0059]

Claims

1. A 1300 MPa grade ultra-low yield ratio medium-manganese high-strength steel plate, having the following composition by weight percentage: C: 0.1-0.2%, Si: 0.2-0.4%, Mn: 3-7%, Al≤0.1%, P≤0.01%, S≤0.01%, Cr: 0.2-0.6%, Nb: 0.02-0.06%, V: 0.02-0.08%, Ti: 0.01-0.04%, and the balance consisting of Fe and inevitable impurities.

2. The 1300 MPa grade ultra-low yield ratio medium-manganese high-strength steel plate of claim 1, characterized in that, The balance consists of Fe and inevitable impurities.

3. The 1300 MPa grade ultra-low yield ratio medium-manganese high-strength steel plate according to claim 1 or 2, characterized in that, The microstructure of the steel plate comprises ferrite, bainite, martensite and residual austenite.

4. The 1300 MPa grade ultra-low yield ratio medium-manganese high-strength steel plate according to claim 1 or 2 or 3, characterized in that, The steel plate has a tensile strength≥1300 MPa, a yield strength≥830 MPa, an elongation≥12%, a Charpy impact energy at room temperature≥30 J and a yield ratio≤0.

7.

5. The 1300 MPa grade ultra-low yield ratio medium-manganese high-strength steel plate according to claim 1 or 2 or 3 or 4, characterized in that, The thickness of the steel plate is 4-20 mm.

6. The method of producing a 1300 MPa grade ultra-low yield ratio medium-manganese high-strength steel sheet according to any one of claims 1 to 5, characterized by, The method comprises the following steps: 1) Smelting and casting Smelting and casting an ingot or a continuous casting billet according to the composition of claim 1 or 2; 2) Slab heating The obtained ingot is broken down to form a slab, and the slab or the continuous casting billet is heated at a temperature of 1200-1250 °C for a time t = 1-2H, where t is the heating time in minutes and H is the thickness of the slab or the continuous casting billet in millimeters; 3) Controlled rolling Two-stage rolling is adopted, the first stage is rolling at a temperature of 1100-1150 °C to 3-5 times the thickness of the finished steel plate; The second stage is rolling at a temperature of 840-880 °C to a thickness of 4-20 mm; 4) On-line water cooling The slab is cooled at a temperature of 820-860 °C and a final cooling temperature of 630-660 °C, and then air-cooled to room temperature.

7. The production method according to claim 6, wherein In step 3), the steel plate is naturally cooled or water-cooled to the second-stage rolling temperature after the first-stage rolling is completed.

8. The production method according to claim 6, wherein In step 4), the cooling rate is 5-10 °C / s.

Images