High-strength high-toughness steel plate and method of manufacturing

Abstract

The application relates to a high-strength and high-toughness steel plate and a preparation method thereof, and belongs to the technical field of steel plate preparation. The steel plate comprises the following chemical components: C: 0.12-0.16%, Si: 0.8-1.5%, Mn: 1.5-2.5%, Nb: 0.02-0.05%, Ti: 0.01-0.03%, Mo: 0.05-0.1%, Al: 0.02-0.06%, Cr: 0.3-0.8%, B: 0.0035-0.005%, P<=0.02%, S<=0.01%, and the balance of Fe and inevitable impurities. The application can inhibit the precipitation of carbides, retain residual austenite to improve toughness, improve hardenability through Mn, Cr, Mo and B, ensure that the required hard phase structure is obtained under a reasonable cooling speed, refine grains and precipitate strengthening through Nb and Ti, further improve the strength and toughness, can have good toughness and formability while ensuring high strength, can be used for manufacturing automobile chassis and bottom plate structural parts, and meets the requirements of light weight and safety performance.

Description

Technical Field

[0001] This invention belongs to the technical field of metallic materials, and more specifically, relates to a high-strength and high-toughness steel plate and its preparation method. Background Technology

[0002] With the rapid development of automotive materials technology, the composition of materials used in modern automobile manufacturing is constantly changing. Taking modern sedans as an example, steel accounts for 55-60% of the car's weight by weight. The application of steel in automotive parts is quite extensive, such as in car body, chassis, suspension, and steering components, and this will continue to see significant growth.

[0003] The advantages of steel in automotive parts are mainly reflected in two aspects: (1) Using high-strength steel plates can achieve the purpose of reducing the thickness and weight of the body panels, which increases safety performance while reducing weight. (2) Steel has a lower yield strength ratio, better strain distribution capability and higher strain hardening characteristics. At the same time, the mechanical properties of high-strength steel plates are more uniform, thus having better collision characteristics and higher fatigue life.

[0004] Since steel remains the primary material in automobiles, and with the automotive industry's increasing demands for energy conservation, emission reduction, and collision safety, automotive steel is trending towards higher strength and lighter weight. Therefore, developing high-strength, lightweight automotive steel sheets has become an important task for the metallurgical industry.

[0005] As a critical load-bearing component, the automotive floor panel withstands complex loads and impacts, requiring it to possess high strength, high toughness, good formability, and corrosion resistance simultaneously. Currently, the steel used for automotive floor panels on the market has the following shortcomings:

[0006] Poor strength-toughness matching: Traditional high-strength steel often leads to a decrease in toughness while improving strength, and the elongation is generally less than 15%, which is difficult to meet the requirements of complex forming and impact energy absorption.

[0007] Insufficient corrosion resistance: Conventional pickled steel plates have poor surface corrosion resistance and are prone to rusting in humid environments, which affects their service life;

[0008] Technological limitations: Existing ultra-high strength steels mostly rely on complex alloy systems or special production equipment, resulting in excessively high costs and making large-scale application difficult.

[0009] Therefore, it is of great significance to develop a pickled steel sheet for automotive flooring that combines high strength, high toughness, excellent corrosion resistance, and controllable cost. Summary of the Invention

[0010] The purpose of this invention is to provide a high-strength and high-toughness steel plate and its preparation method, which achieves a synergistic improvement in strength and toughness by optimizing alloy composition and process parameters.

[0011] The objective of this invention can be achieved through the following technical solutions:

[0012] A high-strength, high-toughness steel plate, comprising the following chemical components by weight percentage:

[0013] C: 0.12-0.16%;

[0014] Si: 0.8-1.5%;

[0015] Mn: 1.5-2.5%;

[0016] Nb: 0.02-0.05%;

[0017] Ti: 0.01-0.03%;

[0018] Mo: 0.05-0.1%;

[0019] Al: 0.02-0.06%;

[0020] Cr: 0.3-0.8%;

[0021] B: 0.0035-0.005%;

[0022] P≤0.02%;

[0023] S≤0.01%;

[0024] The balance consists of Fe and unavoidable impurities.

[0025] In the technical solution of this invention, carbon (C) is a basic element for improving the strength of steel. The strength of the matrix is ​​enhanced by solid solution strengthening and the formation of hard phases such as carbides and martensite.

[0026] Silicon (Si) is a strong solid solution strengthening element that can improve the yield strength and tensile strength of steel. At the same time, silicon can inhibit the precipitation of carbides in steel, which is conducive to the formation of fine ferrite and bainite structures during hot rolling and cooling, and promotes the stable existence of retained austenite, thereby improving strength and toughness.

[0027] Manganese (Mn) is an important alloying element in steel, possessing solid solution strengthening properties and significantly improving the hardenability of steel. It promotes the formation of martensite or bainite structures, thereby increasing strength. Manganese can also combine with sulfur to form MnS, mitigating the harmful effects of sulfur.

[0028] Niobium (Nb) and titanium (Ti) are microalloying elements that form carbonitrides in steel, refining grain size and providing precipitation strengthening. Niobium significantly inhibits austenite grain growth and recrystallization, resulting in fine ferrite grains after hot rolling, thus improving strength and toughness. Titanium forms TiN, fixing nitrogen in the steel and preventing grain coarsening during heating. This invention, through the combined addition of trace amounts of niobium and titanium, achieves grain refinement and precipitation strengthening during hot rolling, further improving the strength of the steel without significantly reducing toughness.

[0029] Molybdenum (Mo) is a strong carbide-forming element. Adding molybdenum helps to form fine carbide precipitation during the coiling process to strengthen the steel and improve the strength and toughness of the steel. It can maintain high strength when tempered at higher temperatures and prevent temper brittleness of type II. It can refine the grain and improve the hardenability and tempering stability of the steel.

[0030] Aluminum (Al) is typically added to steel as a deoxidizer. In this invention, by adding an appropriate amount of aluminum, a certain amount of retained austenite is formed during cooling, improving the toughness and formability of the steel. Aluminum can also refine the grains, further enhancing the toughness of the steel. In addition, similar to silicon, aluminum can inhibit carbide formation and promote carbon enrichment into austenite during bainite transformation, thereby stabilizing the retained austenite.

[0031] Chromium (Cr) is an element that improves hardenability, promoting the formation of bainite or martensite structures in steel during cooling, thereby increasing strength and hardness while maintaining a certain level of toughness. Chromium also improves the corrosion resistance and wear resistance of steel.

[0032] Boron (B) is an extremely effective hardenability element. Trace amounts of boron can ensure that the core of the steel plate can be fully hardened during the cooling process after hot rolling, so as to obtain the required high-strength structure. This can significantly improve the hardenability of steel, allowing the steel plate to form bainite or martensite structure even under slower cooling conditions, thereby increasing strength.

[0033] Phosphorus (P) and sulfur (S) are impurity elements in steel, and their content should be minimized.

[0034] This invention achieves grain refinement, precipitation strengthening, and retained austenite stabilization by precisely controlling the contents of C, Mn, Si, and Al, combined with microalloying elements such as Nb, Ti, Mo, Cr, and B. This significantly improves toughness and ductility while maintaining high strength, and also provides good pickling adaptability. Furthermore, existing steel plate manufacturing processes typically include Ni, a relatively expensive alloying element. This solution directly removes Ni, significantly reducing raw material costs. Simultaneously, Mo, another expensive element, is controlled at a content of 0.05-0.10%, further reducing the use of costly alloying elements and saving costs. The Nb content is 0.02-0.05%, similarly reducing the input of expensive elements and achieving cost control.

[0035] A method for preparing a high-strength, high-toughness steel plate as described above includes the following steps:

[0036] S1. Smelting and casting: After pretreatment of molten steel, it is smelted in a converter, alloy fine-tuning is added, and then LF refining and RH vacuum treatment are carried out in sequence. Finally, the molten steel is continuously cast into a continuous casting billet.

[0037] S2. Heating: Heat the continuously cast billet to the austenitizing temperature and hold for 2-3 hours to allow Nb and Ti to be completely dissolved.

[0038] S3. Rolling: The heated slab is hot rolled in multiple passes, with the roughing rolling temperature at 1030-1050℃ and the finishing rolling temperature at 840-920℃. After hot rolling, the steel plate is cooled to 520-570℃ by laminar flow cooling and then coiled.

[0039] S4. Pickling: Using a composite pickling solution, the coiled hot-rolled steel sheet is pickled at 50-90℃, and then leveled.

[0040] S5. Continuous Annealing: Heat the steel plate to 770-850℃ and hold for 1-3 minutes to obtain an austenitic structure; then quench the steel plate at a cooling rate of 150-300℃ / min to 320-380℃ and hold at 340-360℃ for 3-4 minutes for partitioning treatment. During the quenching stage, some austenite is transformed into martensite, and during the partitioning stage, carbon in the martensite diffuses into the untransformed austenite; finally, cool the plate at a cooling rate of 4-6℃ to 180-220℃ and hold for 2-3 minutes for tempering treatment to eliminate internal stress in the martensite while retaining stable residual austenite.

[0041] S6. Cooling: Cool the steel plate to room temperature at a cooling rate of 20-30℃ / min. Slow cooling can avoid secondary martensitic transformation, and the final retained austenite accounts for 8-12% of the steel plate and is distributed in a thin film between the martensite laths.

[0042] Furthermore, in step S1, the thickness of the continuously cast billet is 200-230 mm.

[0043] Furthermore, in step S2, the austenitizing temperature is 1150-1250℃. This heating temperature range helps ensure uniform internal temperature of the slab and appropriate austenite grain size; proper holding time allows the austenite grains to grow sufficiently and have a uniform composition, without excessive coarsening.

[0044] Preferably, in step S2, a mixture of nitrogen and hydrogen gas is introduced during the heating process, which can reduce the oxidation loss of Al elements and create conditions for subsequent surface treatment.

[0045] Furthermore, in step S3, the laminar cooling rate is 30-45℃ / s.

[0046] In this technical solution, the purpose of hot rolling in step S3 is to promote grain refinement and specific phase transformations, such as the formation of bainite or martensite, in order to obtain a fine and uniform initial structure, laying the foundation for subsequent heat treatment.

[0047] The coiling temperature is higher than the martensitic transformation initiation temperature (Ms point), so the steel mainly undergoes bainitic transformation during coiling, without forming a large amount of martensite. By controlling the coiling temperature, the steel sheet completes the bainitic transformation during coiling, while retaining some untransformed austenite. These retained austenite are preserved at room temperature, thus providing a transformation-induced plasticity (TRIP) effect in the final microstructure, improving the toughness and formability of the steel sheet.

[0048] Furthermore, in step S3, before coiling, the cooling rate of the steel plate is controlled at 5-15℃ / s, and the plate is held for 2-5 seconds. Appropriately slowing down the cooling or using isothermal cooling is beneficial for the formation of fine bainite and the retention of a certain amount of retained austenite, resulting in good weldability and fatigue resistance. This invention, by controlling the cooling and coiling processes, optimizes the content of retained austenite, thereby balancing strength and toughness.

[0049] Further, in step S4, the composite pickling solution comprises, by volume percentage, 30-45% hydrochloric acid, 1-5% sulfuric acid, 0.2-0.5% ethylenediaminetetraacetic acid, 1-3% propyl sulfide, 0.5-0.8% octyl epoxy acid, 0.5-1.5% dicycloalkylamine nitrite, 3-4% ethanol, and the balance being water; wherein the concentration of the hydrochloric acid is 30-50 wt%, and the concentration of the sulfuric acid is 70-80 wt%.

[0050] The steel plate of this invention contains appropriate amounts of easily oxidized elements such as Si and Al, which may form a small amount of silicon-aluminum oxides on its surface. Therefore, pickling is mainly to remove the oxide scale formed during hot rolling. Pickled steel plates retain the high strength and low cost of the hot-rolled state, while having better surface quality and formability than ordinary hot-rolled plates, and have advantages such as smooth surface, high dimensional accuracy, and good formability.

[0051] Furthermore, in step S4, the pickling time is 5-15 seconds, and the pickling line speed is 30-100 mpm, preferably 40-70 mpm.

[0052] Furthermore, in step S4, the sample is rinsed with a pretreatment solution containing nano-titanium dioxide and sodium dodecyl sulfonate before pickling.

[0053] Furthermore, after pickling and before leveling, the steel plate is rinsed with water 3-5 times until the pH value of the rinsing water reaches 6.5-7; then the steel plate is dried. Drying is performed using hot air circulation or infrared drying at a temperature of 80-120℃.

[0054] Furthermore, after drying, applying rust-preventive oil to the surface of the steel plate can effectively prevent rusting during short-term storage and transportation.

[0055] Furthermore, after pickling, leveling is carried out using a rolling force mode with a rolling force of 100-200 tons, and demineralized water is used as the leveling liquid. The leveling elongation is 0.4-2%, preferably 0.6-1%.

[0056] In the steel plate manufacturing process, leveling refers to the process of lightly rolling the steel plate after pickling or annealing, which is a key step in finishing.

[0057] In step S5, the purpose of continuous annealing is to optimize the proportion and distribution of multiphase microstructures such as ferrite, martensite, retained austenite and / or bainite, so as to achieve a balance between strength and toughness while improving strength and ductility.

[0058] Furthermore, after step S5, a surface treatment stage is also included, specifically: under argon protection, a Cr2O3-Al2O3-TiO2 layer is clad on the surface of the steel plate by laser cladding technology, wherein the coating thickness is 1-2mm, the laser power is 1800-2300W, and the scanning speed is 12-18mm / s.

[0059] The pickled steel sheet obtained by this invention has a fine and uniform multiphase microstructure. Specifically, it consists of ferrite (F), bainite (B), and retained austenite (RA), and may also contain a small amount of martensite (M). Ferrite provides certain plasticity and toughness, bainite and martensite provide high strength, while retained austenite undergoes a martensitic transformation during deformation, improving work hardening and toughness. Compared with the ferrite-pearlite microstructure commonly found in traditional hot-rolled pickled steel sheets, the multiphase microstructure of this invention has significant advantages in terms of strength and toughness.

[0060] Furthermore, the content of retained austenite is 5-15%.

[0061] As mentioned above, the high-strength and high-toughness steel plate is used in the manufacture of automotive parts. The steel plate is prepared by the above-described method and is used to manufacture automotive floor panels.

[0062] The steel sheet of this invention can be widely used in automotive chassis and body panel parts, such as frame longitudinal beams, cross beams, chassis reinforcements, suspension brackets, and subframes. Manufacturing these parts using the high-strength, high-toughness pickled steel sheet of this invention allows for a reduction in steel sheet thickness while maintaining part strength and safety performance, thereby reducing overall vehicle weight and improving fuel economy. Furthermore, due to the excellent toughness and formability of the steel sheet of this invention, cracking is less likely to occur during part stamping and service, improving part reliability and service life.

[0063] The beneficial effects of this invention are:

[0064] (1) This invention improves toughness by suppressing carbide precipitation with Si and Al and retaining residual austenite; it enhances hardenability with Mn, Cr, Mo, and B to ensure the desired hard phase structure is obtained at a reasonable cooling rate; and it further improves strength and toughness by refining grains and precipitation strengthening with Nb and Ti. Through the above-mentioned composition optimization, this invention ensures that the steel has sufficient strength while minimizing harmful elements and adding beneficial elements to improve toughness and processability. Through specific hot rolling, cooling, and coiling processes, as well as pickling treatment, a fine and uniform multiphase structure is obtained, which can ensure high strength while having good toughness and formability. It can be used to manufacture automotive chassis and floor structure components, meeting the requirements of lightweight and safety performance.

[0065] (2) The preparation method of this invention first adopts the process route of molten iron pretreatment, converter smelting, alloy fine-tuning, LF refining, RH vacuum treatment, and continuous casting, which effectively reduces the adverse effects of impurities on the toughness of steel plates and lays a good material foundation for subsequent rolling and heat treatment processes. In the heating step, the continuously cast billet is heated at 1200-1254℃ for 2-3 hours, which solves the problem of insufficient solid solution of microalloying elements caused by insufficient heating temperature in traditional methods, thus affecting the precipitation strengthening effect. In the rolling process, by controlling the final rolling temperature in the non-recrystallized austenite region, the grain refinement during the rolling process is achieved by utilizing the inhibitory effect of Nb element on austenite recrystallization. In the pickling process, the specific acid temperature and concentration can efficiently remove the iron oxide scale on the surface of the steel plate, and at the same time, the acid temperature causes the steel plate surface to form a Si-rich layer, solving the problem of insufficient surface toughness of high-strength steel in traditional pickling processes. Finally, through the synergistic effect of quenching-partitioning-tempering, the optimized ratio of martensite and retained austenite is achieved. The preparation steps cooperate and work together to form an organic whole. Continuous casting provides high-quality billets for subsequent processes; the heating step ensures sufficient solid solution of microalloying elements; the rolling step achieves grain refinement and microstructure homogenization; the pickling step improves surface quality and formability; and the continuous annealing step ultimately endows the steel plate with excellent strength, toughness, and comprehensive properties. This synergistic effect enables the steel plate prepared by this invention to comprehensively surpass steel plates prepared by traditional processes in terms of strength, toughness, and corrosion resistance. Detailed Implementation

[0066] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with embodiments, is provided below.

[0067] Example 1

[0068] A high-strength, high-toughness steel plate, comprising the following chemical components by weight percentage:

[0069] C: 0.14%, Si: 1%, Mn: 2%, P: 0.015%, S: 0.005%, Al: 0.04%, Cr: 0.5%, Mo: 0.08%, Nb: 0.03%, Ti: 0.02%, B: 0.0042%, with the remainder being Fe and unavoidable impurities.

[0070] Its preparation method includes the following steps:

[0071] S1. Smelting and Casting: According to the above chemical composition design, the molten steel is smelted in a converter. After being refined by LF and degassed by RH vacuum, the molten steel is continuously cast into slabs with a thickness of 200mm.

[0072] S2. Heating: Heat the slab to 1200℃ and hold for 2 hours to allow Nb and Ti to be completely dissolved.

[0073] S3. Rolling: The heated slab is hot rolled in multiple passes, with the roughing rolling starting temperature at 1040±2℃ and the finishing rolling finishing temperature at 850±2℃. The total reduction rate of roughing and finishing rolling is about 90%, and the final rolling thickness is 4mm. After hot rolling, the steel plate is sent to a cooling device for immediate laminar flow cooling. The laminar flow cooling is divided into two stages: the first stage cools to 550℃ at a rate of about 40℃ / s, and the second stage cools to 530℃ at a rate of about 10℃ / s. Then, it is coiled into a steel coil.

[0074] S4. Pickling: After the steel coil is cooled at room temperature, it is pickled at 70°C using a composite pickling solution, followed by leveling to obtain a smooth pickled steel sheet. The composite pickling solution comprises: 35% hydrochloric acid, 3% sulfuric acid, 0.3% ethylenediaminetetraacetic acid, 2% propyl sulfide, 0.6% octyl epoxy acid, 1% dicycloalkylamine nitrite, 3.5% ethanol, and the balance being water; wherein the concentration of the hydrochloric acid is 40 wt% and the concentration of the sulfuric acid is 75 wt%.

[0075] S5. Continuous Annealing: Heat the steel plate to 820℃ and hold for 2 minutes to obtain an austenitic structure; then quench the steel plate to 350℃ at a cooling rate of 250℃ / min and hold at 350℃ for 3-4 minutes for partitioning treatment. During the quenching stage, some austenite is transformed into martensite, and during the partitioning stage, carbon in the martensite diffuses into the untransformed austenite; finally, cool to 200℃ at a cooling rate of 5℃ and hold for 2-3 minutes for tempering treatment to eliminate internal stress in the martensite while retaining stable residual austenite.

[0076] S6. Cooling: Cool the steel plate to room temperature at a cooling rate of 25℃ / min.

[0077] Example 2

[0078] A high-strength, high-toughness steel plate, comprising the following chemical components by weight percentage:

[0079] C: 0.12%, Si: 0.8%, Mn: 1.5%, P: 0.01%, S: 0.004%, Al: 0.02%, Cr: 0.3%, Mo: 0.05%, Nb: 0.02%, Ti: 0.01%, B: 0.0035%, with the remainder being Fe and unavoidable impurities.

[0080] Its preparation method includes the following steps:

[0081] S1. Smelting and Casting: According to the above chemical composition design, the molten steel is smelted in a converter. After being refined by LF and degassed by RH vacuum, the molten steel is continuously cast into slabs with a thickness of 200mm.

[0082] S2. Heating: Heat the slab to 1180℃ and hold for 2 hours to allow Nb and Ti to be completely dissolved.

[0083] S3. Rolling: The heated slab is hot rolled in multiple passes, with the roughing rolling starting temperature at 1040±2℃ and the finishing rolling finishing temperature at 830±2℃. The total reduction rate of roughing and finishing rolling is about 90%, and the final rolling thickness is 3mm. After hot rolling, the steel plate is sent to a cooling device for immediate laminar flow cooling. The laminar flow cooling is divided into two stages: the first stage cools to 550℃ at a rate of about 50℃ / s, and the second stage cools to 530℃ at a rate of about 10℃ / s. Then, it is coiled into a steel coil.

[0084] S4. Pickling: After the steel coil is cooled at room temperature, it is pickled at 50-90℃ using a composite pickling solution, followed by leveling to obtain a smooth pickled steel sheet. The composite pickling solution comprises: 30% hydrochloric acid, 1% sulfuric acid, 0.2% ethylenediaminetetraacetic acid, 1% propyl sulfide, 0.5% octyl epoxy acid, 0.5% dicycloalkylamine nitrite, 3% ethanol, and the balance being water; wherein the concentration of the hydrochloric acid is 30 wt% and the concentration of the sulfuric acid is 70 wt%.

[0085] S5. Continuous Annealing: Heat the steel plate to 820℃ and hold for 2 minutes to obtain an austenitic structure; then quench the steel plate to 350℃ at a cooling rate of 250℃ / min and hold at 350℃ for 3-4 minutes for partitioning treatment. During the quenching stage, some austenite is transformed into martensite, and during the partitioning stage, carbon in the martensite diffuses into the untransformed austenite; finally, cool to 200℃ at a cooling rate of 5℃ and hold for 2-3 minutes for tempering treatment to eliminate internal stress in the martensite while retaining stable residual austenite.

[0086] S6. Cooling: Cool the steel plate to room temperature at a cooling rate of 25℃ / min.

[0087] S7. Surface treatment: Under argon protection, a Cr2O3-Al2O3-TiO2 layer is clad on the surface of the steel plate by laser cladding technology. The coating thickness is 1mm, the laser power is 2000W, the scanning speed is 15mm / s, the defocusing distance is 80mm, and the coating composition includes 40%Cr2O3, 30%Al2O3, 20%TiO2 and 10%SiC. The powder feeding flow rate is 15g / min, and the argon flow rate is 20L / min.

[0088] Example 3

[0089] A high-strength, high-toughness steel plate, comprising the following chemical components by weight percentage:

[0090] C: 0.16%, Si: 1.5%, Mn: 2.5%, P: 0.02%, S: 0.01%, Al: 0.06%, Cr: 0.8%, Mo: 0.1%, Nb: 0.05%, Ti: 0.03%, B: 0.005%, with the remainder being Fe and unavoidable impurities.

[0091] Except for step S4, the composite pickling solution comprises: 45% hydrochloric acid, 5% sulfuric acid, 0.5% ethylenediaminetetraacetic acid, 3% propyl sulfide, 0.8% octyl epoxy acid, 1.5% dicycloalkylamine nitrite, 4% ethanol, and the balance being water; wherein the concentration of the hydrochloric acid is 50 wt% and the concentration of the sulfuric acid is 80 wt%. The remaining preparation methods are the same as in Example 1.

[0092] Comparative Example 1

[0093] The difference between this comparative example and Example 1 is that the amount of Nb and Ti added in this comparative example is 0, while the other components, preparation steps and parameters are the same.

[0094] Comparative Example 2

[0095] The difference between this comparative example and Example 1 is that the amount of Mo added in this comparative example is 0, while the other components, preparation steps and parameters are the same.

[0096] Comparative Example 3

[0097] The difference between this comparative example and Example 1 is that the amount of Cr and B added in this comparative example is 0, while the other components, preparation steps and parameters are the same.

[0098] Comparative Example 4

[0099] The difference between this comparative example and Example 1 is that in step S5 of this comparative example, the steel plate is heated to 820°C and held for 2 minutes to obtain an austenitic structure; then the steel plate is quenched to 150°C at a cooling rate of 250°C / min and held for 3-4 minutes to transform the austenite into martensite; finally, the temperature is raised to 220°C at a heating rate of 5°C and held for 2-3 minutes for tempering treatment.

[0100] The following performance tests were conducted on Examples 1-3 and Comparative Examples 1-4 respectively:

[0101] (1) Tensile property test

[0102] The test was conducted in accordance with GB / T228.1-2021 "Metallic Materials - Tensile Testing - Part 1: Tests at Room Temperature". The specimen thickness was 3 mm, and the gauge length was 50 mm. The specimen axis was parallel to the rolling direction of the steel plate, and the surface was ground to a roughness Ra ≤ 1.6 μm to avoid stress concentration. A universal testing machine with an accuracy class of 0.5 and an extensometer with a gauge length of 50 mm and an accuracy class of 1 was used. The test temperature was 23±5℃, the tensile rate in the elastic stage was 5 mm / min, and the tensile rate from yield to fracture was 20 mm / min. The yield strength Rp0.2, tensile strength Rm, and elongation at fracture A of the specimen were tested. 80 Each sample was tested three times, and the arithmetic mean was taken as the result.

[0103] (2) Impact toughness test

[0104] The test was conducted in accordance with GB / T229-2020 "Charpy Pendulum Impact Test Method for Metallic Materials". V-notch impact specimens were used, with dimensions of 10mm × 10mm × 55mm. The notch was located at half the thickness of the steel plate, with a bottom roughness Ra ≤ 1.6μm and a notch depth of 2mm. A pendulum impact testing machine with an energy range of 300J and an accuracy of ±1% was used, equipped with a low-temperature constant temperature bath. The impact absorbed energy (KV², J) was tested at 23±5℃ and -40±2℃. The specimens were held at the target temperature for 1 hour, ensuring a temperature fluctuation error ≤ ±2℃. Three specimens were tested at each temperature point, and the average value was taken after removing outliers.

[0105] (3) Neutral salt spray test

[0106] The test was conducted in accordance with GB / T10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test", using a salt spray test chamber with a temperature controlled at 35±2℃ and a salt spray deposition rate of 1.0~2.0 mL / ( The sample size was 150mm × 70mm, retaining its original surface condition, with the edges sealed with anti-corrosion paint. A 5% NaCl solution with a pH of 6.5-7.2 was used for continuous spraying for 144 hours, with surface corrosion observed every 48 hours. The weight of the samples before and after testing was obtained by weighing. The samples were weighed after rust removal, cleaning, and drying, with an accuracy of 0.1mg, to calculate the 144-hour salt spray corrosion protection rate. ).

[0107] The test results are shown in Table 1.

[0108] Table 1

[0109]

[0110] As can be seen from the test results in Table 1, compared with Comparative Examples 1-4, the performance of Examples 1-3 is significantly better than that of Comparative Examples 1-4, and meets the requirements for use of automotive floor panels.

[0111] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for producing a high-strength high-ductility steel sheet, characterized by comprising: The high-strength and high-ductility steel plate comprises the following chemical components in percentage by weight: ​ C：0.12-0.16%； Si: 0.8-1.5%; Mn: 1.5-2.5%; Nb: 0.02-0.05%; Ti: 0.01-0.03%; Mo: 0.05-0.1%; Al：0.02-0.06%； Cr：0.3-0.8%； B：0.0035-0.005%； P≤0.02%； S≤0.01%； the balance being Fe and inevitable impurities; The preparation method comprises the following steps: S1, smelting and casting: after pretreatment of the molten steel, converter smelting is performed, alloy fine adjustment is added, LF refining is performed in sequence, RH vacuum treatment is performed, and then the molten steel is continuously cast into a continuous casting billet; S2, heating: the continuous casting billet is heated to an austenitizing temperature, and is kept for 2-3 hours to make Nb and Ti completely solid-solute; S3, rolling: the heated slab is subjected to multi-pass hot rolling, wherein the rough rolling opening temperature is 1030-1050℃, and the finish rolling final rolling temperature is 840-920℃; after hot rolling, the steel plate is subjected to laminar cooling to 520-570℃ for coiling; S4, pickling: using a composite pickling solution, the hot-rolled steel plate after coiling is subjected to pickling treatment at 50-90℃, and then is subjected to skin pass; S5, continuous annealing: the steel plate is heated to 770-850℃ and is kept for 1-3 minutes; then the steel plate is quenched at a cooling rate of 150-300℃ / min to 320-380℃, and is kept at 340-360℃ for 3-4 minutes for partitioning treatment; finally, the steel plate is cooled at a cooling rate of 4-6℃ / min to 180-220℃ and is kept for 2-3 minutes for tempering treatment; S6, cooling: the steel plate is cooled to room temperature at a cooling rate of 20-30℃ / min.

2. The method of producing a high-strength high-ductility steel sheet according to claim 1, characterized by, In step S1, the thickness of the continuous casting billet is 200-230mm.

3. The method of producing a high-strength high-ductility steel sheet according to claim 1, characterized by, In step S2, the austenitizing temperature is 1150-1250℃.

4. The method of producing a high-strength high-ductility steel sheet according to claim 1, characterized by, In step S3, the laminar cooling speed is 30-45℃ / s.

5. The method of producing a high-strength high-ductility steel sheet according to claim 1, characterized by, In step S4, the composite pickling solution comprises, in percentage by volume, 30-45% of hydrochloric acid, 1-5% of sulfuric acid, 0.2-0.5% of ethylenediaminetetraacetic acid, 1-3% of propyl sulfide, 0.5-0.8% of epoxy acid octyl, 0.5-1.5% of dicycloalkylamine nitrite, 3-4% of ethanol, and the balance of water; wherein the concentration of the hydrochloric acid is 30-50wt%, and the concentration of the sulfuric acid is 70-80wt%.

6. The method of producing a high-strength high-ductility steel sheet according to claim 1, characterized by, In step S4, the pickling time is 5-15 seconds, and the pickling line speed is 30-100mpm.

7. The method of producing a high-strength high-ductility steel sheet according to claim 1, characterized by, After pickling is completed and before skin pass, the steel plate is subjected to 3-5 times of water flushing until the pH value of the flushing water reaches 6.5-7; and then the steel plate is dried.

8. The method of producing a high-strength high-ductility steel sheet according to claim 1, characterized by, After pickling, skin pass is performed by using a rolling force mode, the rolling force is 100-200 tons, and desalted water is used as the skin pass liquid, and the skin pass elongation is 0.4-2%.

9. Use of a steel sheet produced by the method according to any one of claims 1 to 8 for producing an automobile component, characterized in that, The steel plate is used for preparing an automobile floor panel.

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