Steel plate and production method thereof

Abstract

The present application provides a steel plate and a production method thereof, wherein the rough rolling temperature is controlled at 900-1100° C., the thickness of the warm billet is ≥1.5t, the start temperature of the finishing rolling is ≤870° C., the final rolling temperature is T1-20-T1+20° C., the final cooling temperature is 660-700° C., and T1=836-0.64×t; the target thickness of the steel plate is t≤100 mm, the normalizing temperature is 880-900° C., the furnace time is 1.8t-2.0t min, the steel plate is cooled in water after being taken out of the furnace, and the red-return temperature is T2-20-T2+20° C., and T2=752-2.66×t+0.007×t 2 Alternatively, the target plate thickness is t≤50mm, the normalizing temperature is 850-870°C, the furnace time is 1.6t-1.7t min, and the plate is air-cooled after exiting the furnace; t is the target plate thickness in mm. The controlled rolling + normalizing process reduces the strength and toughness degradation of the steel plate caused by the forming, heat treatment, and PWHT process chain.

Description

Technical Field

[0001] The present application relates to the technical field of steel smelting, and in particular to a steel plate and a production method thereof. Background Art

[0002] Current trends in oil and gas exploration and development are: 1. The maturity of resource exploration in onshore and shallow-water areas continues to increase; 2. Deepwater reserves are abundant but the proven rate is low (the global average proven rate is <30%), making it a key replacement for oil and gas reserves and production. Deepwater development, driven by larger equipment and increasingly demanding operating conditions, places higher demands on the performance of steel materials.

[0003] Specifically, the following are the key issues: 1. In terms of forming and processing, key components such as cargo holds, fuel tanks, and pressure vessel heads of large liquefied petroleum gas / liquid ammonia carriers must withstand ≥5% cold-forming plastic deformation. Due to the limited capabilities of forming equipment, thick-gauge steel plates (t ≥ 50 mm) require high-temperature, high-deformation processes, which degrade the material's original properties and necessitate subsequent heat treatment for restoration. 2. Performance restoration requires secondary heat treatment that matches the original steel plate production process. 3. Welded components must undergo multiple rounds of local / global post-weld heat treatment (PWHT) to eliminate residual stresses, stabilize structural dimensional tolerances, and improve the microstructure of the weld heat-affected zone (HAZ) to ensure safe operation throughout the equipment's lifecycle. This process chain (forming → restoration heat treatment → PWHT) results in a significant reduction in the steel plate's strength and toughness. Therefore, the development of new low-temperature steels that combine adaptability to large-deformation cold forming or high-temperature forming with tolerance to multi-stage heat treatment has become a critical technical bottleneck in deepwater oil and gas equipment manufacturing. Summary of the Invention

[0004] The purpose of this application is to provide a method for producing steel plates, which solves the problem in the prior art that the strength and toughness indicators of the steel plates are greatly attenuated due to the process chain of forming → performance recovery heat treatment → PWHT through the combination of rolling and normalizing heat treatment.

[0005] In order to achieve one of the above-mentioned objects of the invention, an embodiment of the present application provides a method for producing a steel plate, comprising converter smelting, LF refining, RH refining, continuous casting, heating, rolling, and normalizing heat treatment in sequence, wherein:

[0006] In the rolling process, the rough rolling temperature is 900-1100°C, the thickness of the warm billet is ≥1.5t, the start rolling temperature of the finishing rolling is ≤870°C, the final rolling temperature is T1-20~T1+20°C, the final cooling temperature is 660-700°C, and T1=836-0.64×t;

[0007] Normalizing heat treatment process: when the target thickness of the steel plate is t≤100mm, the normalizing temperature is 880~900℃, the furnace time is 1.8t~2.0t min, the steel plate is cooled in water after being taken out of the furnace, and the red-return temperature is T2-20~T2+20℃, T2=752-2.66×t+0.007×t 2 ;

[0008] Alternatively, the normalizing heat treatment process is as follows: when the target thickness of the steel plate is t≤50mm, the normalizing temperature is 850~870℃, the furnace time is 1.6t~1.7t min, and the steel plate is air-cooled after leaving the furnace;

[0009] Where, t is the target thickness of the steel plate, in mm.

[0010] In one embodiment of the present application, in the heating process, the soaking section temperature is 1100-1150°C, the furnace time is ≥st+80min, and st is the thickness of the slab obtained in the continuous casting process, in mm.

[0011] In one embodiment of the present application, in the converter process, alloy and slag are added in the order of ferrosilicon, metallic manganese, aluminum blocks, and lime when the converter is tapping steel, wherein the amount of aluminum added is 0.65+15[O]kg / t, wherein [O] is one hundred times the oxygen content measured before tapping.

[0012] In one embodiment of the present application, lime is added in the LF refining process, and the amount of lime added is 0.9+40[O]kg / t, wherein [O] is one hundred times the oxygen content measured before tapping the converter.

[0013] In one embodiment of the present application, after the LF refining process is completed, the calcium wire is fed at a speed of 92+845[Al]m at a feeding speed of 1.0-2.0m / s, wherein [Al] is one hundred times the aluminum content measured after the LF refining process is completed.

[0014] In one embodiment of the present application, after the calcium feeding line is completed, the soft stirring time is ≥8 minutes, the soft stirring time of the RH refining process is ≥12 minutes, and the addition of Al is strictly prohibited in the RH refining process.

[0015] The present application also provides a steel plate obtained by the above-mentioned steel plate production method, wherein the chemical composition of the steel plate comprises, by mass percentage, C: 0.16-0.19%, Si: 0.30-0.40%, Mn: 1.35-1.45%, P≤0.015%, S≤0.005%, Ni: 0.15-0.25%, Nb: 0.010-0.020%, V: 0.020-0.030%, Ti: 0.010-0.020%, Alt: 0.02-0.05%, and the balance is iron and unavoidable impurities;

[0016] The microstructure of the steel plate is ferrite and pearlite. In the normalizing heat treatment process, the pearlite of the steel plate that is water-cooled after normalizing is dispersed; the banded structure of the pearlite of the steel plate that is air-cooled after normalizing is rated ≤ level 2.

[0017] In one embodiment of the present application, the yield strength of the steel plate is ≥355 MPa, the tensile strength is 540~620 MPa, the elongation after fracture is ≥30%, the low-temperature impact energy of -51°C is ≥100 J, and the Z-direction tensile section shrinkage is ≥65%.

[0018] In one embodiment of the present application, after the steel plate is subjected to large deformation cold forming or hot forming, normalizing recovery performance, and post-weld heat treatment, the yield strength is ≥300 MPa, the tensile strength is 485~540 MPa, the elongation after fracture is ≥30%, the low-temperature impact energy of -51°C is ≥100 J, and the Z-direction tensile section shrinkage rate is ≥65%.

[0019] In one embodiment of the present application, the strain of the large deformation cold forming process is 5~10%; the temperature of the hot forming process is 920±10℃, the holding time is 1.6t±0.2t min, the heating rate is ≤50℃ / h, and the cooling is natural cooling in the air; the normalizing recovery performance process is the same as the normalizing heat treatment process of the steel plate; the post-weld heat treatment process has a temperature of 635±15℃, a holding time of 360min, a heating and cooling rate of ≤50℃ / h, and undergoes 4 cycles.

[0020] One or more technical solutions provided in this application have at least the following technical effects or advantages:

[0021] The steel plate production method provided in this application establishes a uniform initial microstructure by controlling the refinement of the original austenite grains during rolling, suppressing the formation of banded structure. Controlled normalizing heat treatment refines the grains, disperses the pearlite, eliminates banded structure, reduces internal stress, and ensures dimensional and visual stability during subsequent processing (cutting, welding, etc.). The "controlled rolling + normalizing" process meets the requirements of a comprehensive process chain: large-deformation cold forming / hot forming → performance recovery heat treatment → PWHT (Preformed Warming Heat Treatment). This method has promising applications in shipbuilding, marine engineering, and pressure vessel steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the metallographic structure diagram of the steel plate at 1 / 2 thickness of Example 1.

[0023] Figure 2 This is the metallographic structure diagram of the steel plate at 1 / 2 thickness of Example 2.

[0024] Figure 3 This is the metallographic structure diagram of the steel plate of Example 6 at 1 / 4 thickness.

[0025] Figure 4 This is the metallographic structure diagram of the steel plate of Example 6 at 1 / 2 thickness. DETAILED DESCRIPTION

[0026] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0027] The embodiment of the present application provides a method for producing a steel plate, comprising converter smelting, LF refining, RH refining, continuous casting, heating, rolling, and normalizing heat treatment in sequence, wherein:

[0028] In the rolling process, the rough rolling temperature is 900℃~1100℃, the thickness of the warm billet is ≥1.5t, the start rolling temperature of the finishing rolling is ≤870℃, the final rolling temperature is T1-20~T1+20℃, the final cooling temperature is 660~700℃, and T1=836-0.64×t;

[0029] Normalizing heat treatment process: when the target thickness of the steel plate is t≤100mm, the normalizing temperature is 880~900℃, the furnace time is 1.8t~2.0t min, the steel plate is cooled in water after being taken out of the furnace, and the red-return temperature is T2-20~T2+20℃, T2=752-2.66×t+0.007×t 2 ;

[0030] Alternatively, the normalizing heat treatment process is as follows: when the target thickness of the steel plate is t≤50mm, the normalizing temperature is 850~870℃, the furnace time is 1.6t~1.7t min, and the steel plate is air-cooled after leaving the furnace;

[0031] Where, t is the target thickness of the steel plate, in mm.

[0032] It should be noted that all formulas referring to target plate thickness t in this article are numerical values ​​for the target plate thickness in mm. The thickness of the warmed billet refers to the thickness of the billet after it has been rolled to a certain thickness and then the finish rolling temperature has been reached before finishing rolling begins. This certain thickness is the thickness of the warmed billet.

[0033] Rolling in the austenite recrystallization zone during the rough rolling stage can fully recrystallize and refine the original austenite grains, laying the foundation for a uniform initial structure. Rolling in the non-recrystallization zone during the finishing rolling stage can flatten the austenite grains through deformation induction, increase deformation energy storage, form a highly refined rolled structure, effectively inhibit the formation of banded structure, create an ideal precursor structure for subsequent heat treatment, and improve low-temperature toughness.

[0034] The finishing temperature is precisely controlled according to the target thickness of the steel plate to ensure sufficient deformation energy storage in the steel plate and to avoid phase change at this temperature. After rolling, a multifunctional intermittent cooling system is used for water cooling at a controlled cooling rate of 6-10°C / s. After cooling to 660-700°C, air cooling is performed. The faster cooling rate refines the grain size in the steel plate.

[0035] During the normalizing heat treatment process, when the first normalizing heat treatment is used (steel plate target thickness t≤100mm), water cooling is performed after exiting the furnace, with a controlled cooling rate of 6-10°C / s. This refines the grains, disperses the pearlite, eliminates banded structure, and improves strength and toughness, allowing the steel plate to withstand long-term post-weld heat treatment. Controlling the re-red temperature during cooling can maintain the steel plate's microstructure, reduce internal stress, and ensure dimensional and appearance stability during subsequent processing (cutting, welding, etc.).

[0036] When the second type of normalizing heat treatment is adopted (the target thickness of the steel plate is t≤50mm), air cooling is performed after the furnace. On the one hand, it can reduce the dependence on heat treatment equipment (cooling device, straightening machine); on the other hand, it can simplify the downstream manufacturing process. When heat treatment is performed to restore performance after large deformation, there is no need for water cooling process, which significantly reduces the production difficulty of manufacturing enterprises.

[0037] Furthermore, during the converter process, alloy and slag are added in the order of ferrosilicon, manganese metal, aluminum blocks, and lime. The aluminum addition is 0.65 + 15 [O] kg / t, where [O] is one hundred times the oxygen content measured before tapping. For example, if the O content is 0.0544%, then [O] = 0.0544. This can also be understood as the value of the O content without the % notation.

[0038] The unit for aluminum addition and lime addition (kg / t) is the weight of aluminum and lime added per ton of molten steel. In the converter process, the lime addition rate is 0.995-1.005 kg / t.

[0039] Ferrosilicon is first added to the converter for deoxidation to prevent the oxygen in the molten steel from oxidizing the alloy. At the same time, the amount of aluminum added is accurately calculated based on the oxygen content, effectively inhibiting the formation of high-melting-point Al2O3 inclusions while saving resources.

[0040] Ferrosilicon, metallic manganese, aluminum blocks and lime are added in the early stage of steel tapping. For example, ferrosilicon, metallic manganese, aluminum blocks and lime can be added in sequence when the steel is 1 / 8 to 1 / 6 tapped.

[0041] In one embodiment of the present application, lime is added in the LF refining process, and the amount of lime added is 0.9+40[O]kg / t, where [O] is one hundred times the oxygen content measured before tapping the converter.

[0042] In the LF refining process, the amount of lime added is accurately controlled by measuring the oxygen content, which is beneficial to adsorb inclusions in the molten steel and purify the molten steel.

[0043] Furthermore, after the LF refining process is completed, the calcium wire is fed at 92+845[Al]m with a feeding speed of 1.0~2.0m / s, wherein [Al] is one hundred times the aluminum content measured after the LF refining process is completed.

[0044] Dynamically adjust the calcium wire feed rate based on the Al content to avoid overfeeding and conserve resources. Controlling the wire feed speed allows the calcium wire to completely dissolve and be consumed during the rising calcium bubbles, improving calcium absorption and allowing inclusions in the molten steel to be fully modified and removed by floating. This ensures the crystallinity and castability of the molten steel, while also laying the foundation for the low-temperature toughness of the finished steel plate.

[0045] Furthermore, after the calcium feeding line is completed, the soft stirring time should be ≥8 minutes, and the soft stirring time in the RH refining process should be ≥12 minutes. The addition of Al is strictly prohibited during the RH refining process. Multiple soft stirring cycles give inclusions in the molten steel ample time to float, improving the purity of the molten steel.

[0046] The remaining alloying elements, such as Ni, are added in the converter smelting stage, Nb and V are added after the ladle is in place in the LF refining process, and Ti is added after lime is added.

[0047] In one embodiment of the present application, during the heating process, the soaking zone temperature is 1100-1150°C, and the furnace time is ≥ st + 80 min, where st is the thickness of the slab obtained during the continuous casting process, in mm. The slab thickness is used when calculating the furnace time.

[0048] Heating in this temperature range can effectively inhibit the growth of austenite grains, which is beneficial to improving the low-temperature toughness of the steel plate; calculating the furnace time by the thickness of the slab can ensure that the slab temperature is fully uniform, so that the plate shape during the rolling process is good.

[0049] The present application also provides a steel plate obtained by the aforementioned steel plate production method, wherein the chemical composition of the steel plate comprises, by mass percentage, the following: C: 0.16-0.19%, Si: 0.30-0.40%, Mn: 1.35-1.45%, P≤0.015%, S≤0.005%, Ni: 0.15-0.25%, Nb: 0.010-0.020%, V: 0.020-0.030%, Ti: 0.010-0.020%, Alt: 0.02-0.05%, and the balance being iron and unavoidable impurities;

[0050] The microstructure of the steel plate is ferrite and pearlite. In the normalizing heat treatment process, the pearlite of the steel plate that is water-cooled after normalizing is dispersed; the banded structure of the pearlite of the steel plate that is air-cooled after normalizing is rated ≤ level 2.

[0051] The use of C, Si, Mn, Ni matrix, combined with Nb, V, Ti, Al multi-element microalloying composition system reduces alloy cost and smelting difficulty compared with the traditional composition system with Cu / Mo alloy added and strictly limited P / S content.

[0052] The following describes the role of each chemical component in the steel plate of the present invention and the selection of its dosage:

[0053] Carbon (C): is a key strengthening element. When the C content is low, the steel plate cannot withstand long-term post-weld heat treatment. When the C content exceeds 0.19%, the low-temperature toughness of the steel plate deteriorates and the surface hardness is high, which is not conducive to large cold forming deformation. In the present invention, the C content is controlled at 0.16-0.19%, combined with the overall design of other elements and processes, while ensuring the strengthening effect, the low-temperature toughness and cold formability are improved.

[0054] Silicon (Si): A deoxidizing and solid solution strengthening element, it increases carbon activity, making it insoluble in carbides, thereby inhibiting carbide coarsening and reducing strength loss during long post-weld heat treatments. However, high Si content can reduce the steel's low-temperature toughness. In this invention, the Si content is controlled at 0.30-0.40%. Combined with other elements and the overall process design, this ensures deoxidation and reduces oxide inclusions in the steel, fully maximizing its strengthening effect without compromising low-temperature toughness.

[0055] Manganese (Mn): It is a solid solution and fine grain strengthening element, but it is also an element that is easily segregated and easily forms inclusions, which will affect the low-temperature impact toughness of the core of the steel plate. In the present invention, the Mn content is controlled within a range of 1.35-1.45%, which can ensure the strength of the steel plate on the one hand, and reduce segregation and avoid the degradation of the low-temperature impact toughness of the core of the steel plate caused by MnS inclusions on the other hand.

[0056] Nickel (Ni): It smoothes and disperses cementite edges, making dislocations more easily slippable at low temperatures. It's an effective element for improving the low-temperature toughness of steel plates, but the alloy costs are high. This invention controls the Ni content to 0.15-0.25%, ensuring the steel plate's low-temperature toughness while also minimizing alloy costs.

[0057] Niobium (Nb): It reduces steel's overheat sensitivity and temper brittleness, minimizing strength loss during prolonged post-weld heat treatment. However, excessive Nb content weakens the strengthening effect. In this invention, the Nb content is controlled within a range of 0.01-0.02% to ensure a strengthening and toughening effect.

[0058] Vanadium (V): Reduces the area of ​​pearlite clusters, increases the number of cementite breakpoints and fragmentation within the pearlite lamellae, and improves the strength and toughness of the steel plate. It also provides a certain degree of precipitation strengthening during long post-weld heat treatments. However, excessive V content can negatively impact weldability. In this invention, controlling the V content to 0.02-0.03% ensures this strengthening and toughening effect.

[0059] Titanium (Ti): It is a nitrogen-fixing and deoxidizing element, but it is easy to form large Ti (C, N) particles in the core of the steel plate, affecting the low-temperature impact toughness at 1 / 2 of the thickness. In the present invention, the Ti content is controlled at 0.01-0.02%.

[0060] Aluminum (Al): It is a deoxidizing and grain-refining element. Excessive aluminum can easily increase Al2O3 inclusions in steel, affecting the low-temperature toughness of the steel. In the present invention, the content of Al is controlled within 0.02-0.05%.

[0061] Phosphorus and sulfur (P and S) are unavoidable impurity elements in steel. P tends to segregate in the center of the steel plate, while S easily combines with Mn to form MnS inclusions, affecting the low-temperature toughness at half the thickness of the steel plate. During production, P and S contents should be minimized, but removing P and S increases the difficulty and cost of the steelmaking process. This invention controls P to ≤ 0.015% and S to ≤ 0.005%, combining overall chemical composition design with process control schemes. This effectively controls the level of center segregation and the content of non-metallic inclusions, ensuring excellent low-temperature impact toughness of the steel plate. It also avoids the increased difficulty and cost associated with overly stringent P and S content control requirements.

[0062] The pearlite of the steel plate after the above two normalizing heat treatments (water cooling after normalizing and air cooling after normalizing) is dispersed or slightly banded, making the steel plate strong and tough and able to withstand long-term post-weld heat treatment.

[0063] Furthermore, the steel plate must have a yield strength of 355 MPa or greater, a tensile strength of 540-620 MPa, an elongation of 30% or greater, a low-temperature impact energy of 100 J at -51°C, and a Z-axis tensile reduction in area of ​​65% or greater. The steel plate must be tested using NB / T 47013.3 and must meet Level I standards. The Z-axis is the thickness of the steel plate.

[0064] Furthermore, after large deformation cold forming or hot forming, normalizing recovery performance, and post-weld heat treatment, the steel plate has a yield strength ≥300MPa, a tensile strength of 485~540MPa, an elongation after fracture ≥30%, a low-temperature impact energy of -51℃ ≥100J, and a Z-direction tensile section shrinkage rate ≥65%.

[0065] Furthermore, the strain of the large deformation cold forming process is 5~10%; the temperature of the hot forming process is 920±10℃, the holding time is 1.6t±0.2t min, the heating rate is ≤50℃ / h, and the cooling is natural cooling in the air; the normalizing recovery process is the same as the normalizing heat treatment process of the steel plate; the post-weld heat treatment process has a temperature of 635±15℃, a holding time of 360min, a heating and cooling rate of ≤50℃ / h, and undergoes 4 cycles.

[0066] The technical solution of the present application is further described below with reference to some specific embodiments.

[0067] Table 1 Chemical composition of steel plates of Examples 1 to 6

[0068]

[0069] Table 2 Parameters of converter smelting, LF refining, and RH refining processes

[0070]

[0071] Table 3 Parameters of heating, rolling and normalizing heat treatment processes

[0072]

[0073] The steel plates of Examples 1 to 6 were tested according to NB / T 47013.3, and all of Examples 1 to 6 met the requirements of Level I. Samples were taken according to ASME SA-20 / SA-20M standards to test the metallographic structure and mechanical properties. The specific test methods and test results are as follows:

[0074] (1) Metallographic structure: Take a 15cm×15cm sample and make a metallographic sample along the rolling direction. After mechanical grinding and nitric acid etching, put it under a metallographic microscope for tissue observation. The metallographic structures of Examples 1 to 6 are all ferrite + pearlite structures. The pearlite of Examples 1, 3, 5, and 6 is diffusely distributed without obvious banded structure. The pearlite of Examples 2 and 4 is slightly banded. According to GB / T 34474.1, Examples 2 and 4 are graded for banded structure, and the rating results are 1 and 1.5 respectively. The metallographic structure pictures of the steel plates of Examples 1, 2, and 6 are shown as follows: Figures 1 to 4 The figures shown in FIG. 1 can represent the metallographic structure of the steel plate in each embodiment, and the other embodiments are omitted.

[0075] (2) Mechanical properties: The tensile and impact properties of the steel plates of the above embodiment were tested with reference to the ASTM A370 standard, and the Z-direction tensile properties of the steel plates of the above embodiment were tested with reference to the ASTM A770 standard. The test results are shown in Table 4.

[0076] Table 4 Mechanical properties of Examples 1 to 6

[0077]

[0078] The steel plates of Examples 1-4 were subjected to simulated large-deformation cold forming, recovery heat treatment, and post-weld heat treatment using a tensile testing machine and a box-type resistance furnace. Specifically, the following steps were performed: ① The pre-deformation tensile strains of the steel plates of Examples 1-4 were 8%, 7%, 9%, and 6%, respectively; ② The recovery heat treatment process requirements were the same as the normalizing heat treatment process for the steel plates; ③ The simulated post-weld heat treatment temperature was 635±15°C, the holding time was 360 minutes, and the heating and cooling rate was ≤50°C / h, for four cycles. After the treatment, tensile, impact, and Z-axis tensile properties were tested. The test results are shown in Table 5.

[0079] The steel plates of Examples 5 and 6 were subjected to simulated high-temperature forming, recovery heat treatment, and post-weld heat treatment in a box-type resistance furnace. Specifically, the following steps were performed: ① The simulated high-temperature forming temperature was 920±10°C, the holding time was 1.5 min, the heating rate was ≤50°C / h, and the temperature was naturally cooled in air; ② The recovery heat treatment process was the same as the normalizing heat treatment process for the steel plates; ③ The simulated post-weld heat treatment temperature was 635±15°C, the holding time was 360 min, and the heating rate was ≤50°C / h, for four cycles. After the treatment, tensile, impact, and Z-axis tensile properties were tested. The test results are shown in Table 5.

[0080] Table 5 Mechanical properties of steel plates after large deformation cold forming / hot forming → recovery performance heat treatment → post-weld heat treatment

[0081]

[0082] It should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each implementation method can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0083] The series of detailed descriptions listed above are only specific descriptions of feasible implementation methods of this application. They are not intended to limit the scope of protection of this application. Any equivalent implementation methods or changes that do not deviate from the technical spirit of this application should be included in the scope of protection of this application.

Claims

1. A method for producing a steel plate, characterized in that: The chemical composition of the steel plate includes, by mass percentage, C: 0.16-0.19%, Si: 0.30-0.40%, Mn: 1.35-1.45%, P≤0.015%, S≤0.005%, Ni: 0.15-0.25%, Nb: 0.010-0.020%, V: 0.020-0.030%, Ti: 0.010-0.020%, Alt: 0.02-0.05%, and the balance is iron and unavoidable impurities; the production method includes converter smelting, LF refining, RH refining, continuous casting, heating, rolling, and normalizing heat treatment in sequence, wherein, In the rolling process, the rough rolling temperature is 900-1100°C, the thickness of the warm billet is ≥1.5t, the start rolling temperature of the finishing rolling is ≤870°C, the final rolling temperature is T1-20~T1+20°C, the final cooling temperature is 660-700°C, and T1=836-0.64×t; Normalizing heat treatment process: when the target thickness of the steel plate is t≤100mm, the normalizing temperature is 880~900℃, the furnace time is 1.8t~2.0t min, the steel plate is cooled in water after being taken out of the furnace, the water cooling rate is 6~10℃ / s, and the red-return temperature is T2-20~T2+20℃, T2=752-2.66×t+0.007×t 2 ; Where, t is the target thickness of the steel plate, in mm.

2. The method for producing a steel plate according to claim 1, wherein: In the heating process, the soaking zone temperature is 1100-1150° C., and the furnace time is ≥st+80 min, where st is the thickness of the slab obtained in the continuous casting process, in mm.

3. The method for producing a steel plate according to claim 1, wherein: In the converter process, alloy and slag are added in the order of ferrosilicon, metallic manganese, aluminum blocks, and lime when the converter is tapping steel, wherein the amount of aluminum added is 0.65+15[O]kg / t, wherein [O] is one hundred times the oxygen content measured before tapping.

4. The method for producing a steel plate according to claim 1, wherein: In the LF refining process, lime is added in an amount of 0.9+40[O]kg / t, wherein [O] is one hundred times the oxygen content measured before tapping the converter.

5. The method for producing a steel plate according to claim 4, wherein: After the LF refining process is completed, the calcium wire is fed at 92+845[Al]m at a feeding speed of 1.0-2.0m / s, wherein [Al] is one hundred times the aluminum content measured after the LF refining process is completed.

6. The method for producing a steel plate according to claim 5, wherein: After the calcium feeding line is completed, the soft stirring time is ≥8min, the soft stirring time of the RH refining process is ≥12min, and it is strictly forbidden to add Al in the RH refining process.

7. The steel plate obtained by the method for producing a steel plate according to claim 1, characterized in that: The chemical composition of the steel plate includes, by mass percentage, C: 0.16-0.19%, Si: 0.30-0.40%, Mn: 1.35-1.45%, P≤0.015%, S≤0.005%, Ni: 0.15-0.25%, Nb: 0.010-0.020%, V: 0.020-0.030%, Ti: 0.010-0.020%, Alt: 0.02-0.05%, and the balance is iron and unavoidable impurities; The structure of the steel plate is ferrite and pearlite. In the normalizing heat treatment process, the pearlite of the steel plate after water cooling after normalizing is dispersed.

8. The steel plate according to claim 7, characterized in that The yield strength of the steel plate is ≥355MPa, the tensile strength is 540~620MPa, the elongation after fracture is ≥30%, the low-temperature impact energy at -51℃ is ≥100J, and the Z-direction tensile section shrinkage is ≥65%.

9. The steel plate according to claim 8, characterized in that After large deformation cold forming or hot forming, normalizing recovery and post-weld heat treatment, the steel plate has a yield strength ≥300MPa, a tensile strength of 485~540MPa, an elongation at break ≥30%, a low-temperature impact energy of -51℃ ≥100J, and a Z-direction tensile section shrinkage ≥65%.

10. The steel plate according to claim 9, characterized in that The strain of the large deformation cold forming process is 5~10%; the temperature of the hot forming process is 920±10℃, the holding time is 1.6t±0.2t min, the heating rate is ≤50℃ / h, and the cooling is natural cooling in the air; the normalizing recovery process is the same as the normalizing heat treatment process of the steel plate; the post-weld heat treatment process has a temperature of 635±15℃, a holding time of 360min, a heating and cooling rate of ≤50℃ / h, and undergoes 4 cycles.

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