High-strength and high-toughness steel plate and preparation method thereof

Abstract

The invention relates to a high-strength and high-toughness steel plate and a preparation method, and belongs to the technical field of steel plate preparation. Comprising the following chemical components of 0.12%-0.16% of C, 0.8%-1.5% of Si, 1.5%-2.5% of Mn, 0.02%-0.05% of Nb, 0.01%-0.03% of Ti, 0.05%-0.1% of Mo, 0.02%-0.06% of Al, 0.3%-0.8% of Cr, 0.0035%-0.005% of B, smaller than or equal to 0.02% of P, smaller than or equal to 0.01% of S and the balance Fe and inevitable impurities. The precipitation of carbides is inhibited through Si and Al, and retained austenite is retained to improve the toughness; the hardenability is improved through Mn, Cr, Mo and B, and it is ensured that a needed hard-phase structure is obtained at the reasonable cooling speed; through Nb and Ti grain refinement and precipitation strengthening, the toughness is further improved, the high strength can be guaranteed, meanwhile, good toughness and formability are achieved, the alloy can be used for manufacturing automobile chassis and bottom plate structural parts, and the requirements for light weight and safety performance are met.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal materials, and more particularly relates to a high-strength and high-toughness steel plate and a preparation method. BACKGROUND

[0002] With the rapid development of automobile material technology, the composition of modern automobile manufacturing materials is also changing. Taking modern car materials as an example, according to the weight conversion, steel accounts for 55-60% of the self-weight of the automobile. The application of steel in automobile parts is relatively extensive, such as automobile body, chassis, suspension, steering and other parts, which will continue to grow.

[0003] The application advantages of steel in automobile parts mainly reflect in two aspects: (1) the use of high-strength steel plate can achieve the purpose of reducing the thickness and weight of the body plate, while lightening, the safety performance is increased. (2) Steel has a lower yield ratio, better strain distribution ability and higher strain hardening characteristics, and the mechanical properties of high-strength steel plate are more uniform, thereby having better crash characteristics and higher fatigue life.

[0004] Since most of the automobile materials are still dominated by steel, with the increasing requirements of the automobile industry for energy saving and collision safety, automobile steel is developing towards high strength and light weight. Therefore, the development of high-strength and light-weight automobile steel plate has become an important task in the metallurgical industry.

[0005] As a key load-bearing component, the automobile bottom plate needs to have high strength, high toughness, good formability and corrosion resistance at the same time. The automobile bottom plate steel on the market has the following shortcomings: Poor matching of strength and toughness: traditional high-strength steel often leads to a decrease in toughness while improving strength, and the elongation is generally lower than 15%, which is difficult to meet the requirements of complex forming and collision energy absorption; Insufficient corrosion resistance: the surface corrosion resistance of conventional pickling steel plate is poor, and rusting easily occurs in a humid environment, affecting the service life; Process limitations: existing ultra-high-strength steel relies on a complex alloy system or special production equipment, resulting in high cost and difficult large-scale application.

[0006] Therefore, it is of great significance to develop a pickling steel plate for automobile bottom plate with high strength, high toughness, excellent corrosion resistance and controllable cost. SUMMARY

[0007] The purpose of the present application is to provide a high-strength and high-toughness steel plate and a preparation method, which realizes the synergistic improvement of strength and toughness by optimizing the alloy composition and process parameters.

[0008] The purpose of the present application can be achieved by the following technical solutions: A high-strength and high-toughness 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.

[0009] In the technical solution of the present application, carbon (C) is a basic element for improving the strength of the steel, which enhances the strength of the matrix by solid solution strengthening and forming hard phases such as carbides and martensite.

[0010] Silicon (Si) is a strong solid solution strengthening element, which can improve the yield strength and tensile strength of the steel. At the same time, silicon can inhibit the precipitation of carbides in the steel, which is beneficial to the formation of fine ferrite and bainite structure during hot rolling and cooling, and promotes the stable existence of residual austenite, thereby improving the strength and toughness.

[0011] Manganese (Mn) is an important alloying element in steel, which has a solid solution strengthening effect and can significantly improve the hardenability of the steel, promoting the formation of martensite or bainite structure, thereby improving the strength. Manganese can also form MnS with sulfur, reducing the harmful effects of sulfur.

[0012] Niobium (Nb) and titanium (Ti) are micro-alloying elements that form carbonitrides in steel, which play a role in grain refinement and precipitation strengthening. Niobium can significantly inhibit austenite grain growth and recrystallization, thereby obtaining fine ferrite grains after hot rolling, improving strength and toughness. Titanium can form TiN, fixing nitrogen in the steel, and preventing grain coarsening during heating. The present application adds trace amounts of niobium and titanium to achieve grain refinement and precipitation strengthening during hot rolling, further improving the strength of the steel without significantly reducing the toughness.

[0013] Molybdenum (Mo) is a strong carbide-forming element, and the addition of molybdenum helps to form fine carbide precipitation strengthening during coiling and improve the strength and toughness of the steel; it can maintain high strength at higher temperature tempering and prevent second type temper brittleness; it can refine the grain and improve the hardenability and tempering stability of the steel.

[0014] Aluminum (Al) is usually added to steel as a deoxidizer. In the present application, the appropriate addition of aluminum helps to form a certain amount of residual austenite during the cooling process, thereby improving the toughness and formability of the steel. Aluminum can also refine the grain and improve the toughness of the steel. In addition, similar to silicon, aluminum can inhibit the formation of carbides and promote the enrichment of carbon in austenite during bainite transformation, thereby stabilizing the residual austenite.

[0015] Chromium (Cr) is an element that improves hardenability, which can promote the formation of bainite or martensite structure in steel during cooling, thereby improving the strength and hardness while maintaining a certain toughness. Chromium can also improve the corrosion resistance and wear resistance of steel.

[0016] Boron (B) is a very effective hardening element. A small amount of boron can ensure that the core of the steel plate is fully hardened during the cooling process after hot rolling, thereby obtaining the required high-strength structure, significantly improving the hardenability of the steel, and enabling the steel plate to form bainite or martensite structure under slower cooling conditions, thereby improving the strength.

[0017] Phosphorus (P) and sulfur (S) are impurity elements in steel, and their content should be minimized.

[0018] In one aspect, the present application precisely controls the content of C, Mn, Si, Al, and combines with Nb, Ti, Mo, Cr, B, and other micro-alloying elements to achieve grain refinement, precipitation strengthening, and residual austenite stabilization, thereby maintaining high strength while significantly improving toughness and ductility, and having good pickling adaptability. On the other hand, the steel plate prepared in the prior art generally contains Ni element, which is a high-priced alloy element. The present solution directly removes Ni, significantly reducing the cost of raw materials. At the same time, Mo is a high-priced element, and the content of Mo is controlled to be 0.05-0.10% in the present solution, reducing the use of expensive alloy elements, further saving costs. The content of Nb element is 0.02-0.05%, which also reduces the input of expensive elements, achieving the effect of controllable cost.

[0019] A method for preparing a high-strength and high-toughness steel plate as described above, comprising 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 austenitizing temperature and kept for 2-3 hours to ensure complete solid solution of Nb and Ti; 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 temperature is 840-920℃; after hot rolling, the steel plate is subjected to laminar cooling to 520-570℃ and coiled; S4, pickling: using a composite pickling solution, the hot-rolled steel plate after coiling is pickled at 50-90℃, and then is leveled; S5, continuous annealing: the steel plate is heated to 770-850℃ and kept for 1-3 minutes to obtain austenite structure; then the steel plate is quenched at a cooling rate of 150-300℃ / min to 320-380℃ and kept at 340-360℃ for 3-4 minutes for partitioning treatment, the quenching stage converts part of the austenite into martensite, and the partitioning stage diffuses carbon in the martensite into the unconverted austenite; finally, the temperature is lowered to 180-220℃ at a cooling rate of 4-6℃ / min and kept for 2-3 minutes for tempering treatment to eliminate the stress in the martensite while retaining stable residual austenite; S6, cooling: the steel plate is cooled to room temperature at a cooling rate of 20-30℃ / min. Slow cooling can avoid secondary martensite transformation, and the final residual austenite accounts for 8-12% in the steel plate and is distributed in the form of thin films between the martensite laths.

[0020] Further, in step S1, the thickness of the continuous casting billet is 200-230mm.

[0021] Further, in step S2, the austenitizing temperature is 1150-1250℃. With this heating temperature range, the internal temperature of the slab is uniform and the austenite grain size is moderate; appropriate holding time can make the austenite grains grow fully and uniformly without excessive coarsening.

[0022] Preferably, in step S2, nitrogen and hydrogen mixed gas is introduced during heating, which can reduce the oxidation loss of Al element and create conditions for subsequent surface treatment.

[0023] Further, in step S3, the speed of laminar cooling is 30-45℃ / s.

[0024] In the technical solution, in step S3, the purpose of hot rolling is to promote grain refinement and specific phase transformation, such as bainite or martensite formation, to obtain a fine and uniform initial structure to lay the foundation for subsequent heat treatment.

[0025] The coiling temperature is higher than the martensite transformation start temperature (Ms point), so the steel mainly undergoes bainite transformation when coiling, without forming a large amount of martensite. By controlling the coiling temperature, the steel plate completes bainite transformation during coiling and retains part of the unconverted austenite. These residual austenites are retained at room temperature, thereby providing a transformation-induced plasticity (TRIP) effect in the final structure to improve the toughness and formability of the steel plate.

[0026] Further, in step S3, before coiling, the cooling speed of the steel plate is controlled to be 5-15℃ / s and stays for 2-5 seconds. Among them, appropriate cooling or isothermal is conducive to the formation of fine bainite and the retention of a certain amount of residual austenite, which has good welding performance and fatigue resistance. The present application controls the cooling and coiling process to make the content of residual austenite reach the optimal range, so as to balance the strength and toughness.

[0027] 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% epoxy acid octane, 0.5-1.5% dicycloalkylamine nitrite, 3-4% ethanol and water in remainder; wherein the concentration of the hydrochloric acid is 30-50wt%, and the concentration of the sulfuric acid is 70-80wt%.

[0028] Among them, the steel plate of the present application contains appropriate amount of Si, Al and other easily oxidized elements in the composition, which may form a small amount of silicon aluminum oxide on the surface. Therefore, pickling is mainly to remove the oxide scale formed during hot rolling. The pickled steel plate retains the high strength and low cost of the hot rolled state, and the surface quality and forming performance are better than those of ordinary hot rolled plates, with the advantages of smooth surface, high dimensional accuracy and good formability.

[0029] Further, in step S4, the pickling time is 5-15 seconds, and the pickling line speed is 30-100mpm, preferably 40-70mpm.

[0030] Further, in step S4, a pretreatment solution containing nanometer titanium dioxide and sodium dodecyl sulfonate is used for rinsing before pickling.

[0031] Further, after pickling is completed and before leveling, the steel plate is rinsed with water for 3-5 times until the pH value of the rinsing water reaches 6.5-7; and then the steel plate is dried. Among them, the drying adopts hot air circulation drying or infrared drying, and the drying temperature is 80-120℃.

[0032] Further, after drying, antirust oil is coated on the surface of the steel plate, which can effectively prevent rusting during short-term storage and transportation.

[0033] Further, after pickling, the leveling is carried out by using rolling force mode, the rolling force is 100-200 tons, and desalted water is used as leveling liquid, the leveling elongation is 0.4-2%, preferably 0.6-1%.

[0034] In the steel plate preparation process, leveling refers to the process of slightly rolling the steel plate after pickling or annealing, which is a key link of finishing machining.

[0035] In step S5, the purpose of continuous annealing is to optimize the proportion and distribution of multi-phase structures such as ferrite, martensite, residual austenite and / or bainite, to achieve a strength-toughness balance while improving strength and ductility.

[0036] Further, after step S5, a surface treatment stage is further included, specifically: under the protection of argon, a Cr2O3-Al2O3-TiO2 layer is cladded on the surface of the steel plate by laser cladding technology, wherein the coating thickness is 1-2 mm, the laser power is 1800-2300 W, and the scanning speed is 12-18 mm / s.

[0037] The pickled steel plate obtained by the application has fine and uniform multi-phase microstructure, specifically: ferrite (F), bainite (B) and residual austenite (RA), and possibly a small amount of martensite (M). The ferrite provides certain plasticity and toughness, the bainite and martensite provide high strength, and the residual austenite undergoes martensite transformation when deformed, thereby improving work hardening and toughness. Compared with the traditional ferrite-pearlite structure of hot-rolled pickled steel plates, the multi-phase structure of the application has significant advantages in strength and toughness.

[0038] Further, the content of residual austenite is 5-15%.

[0039] The application of the high-strength and high-toughness steel plate as described above in the preparation of automobile parts, the steel plate is prepared by the preparation method described above, and the steel plate is used to prepare an automobile bottom plate.

[0040] The steel plate of the application can be widely used in automobile chassis and body bottom plate parts, such as frame longitudinal beams, cross beams, chassis reinforcing parts, suspension supports, auxiliary frames, etc. The high-strength and high-toughness pickled steel plate of the application is used to manufacture the above-mentioned parts, which can thin the thickness of the steel plate under the premise of ensuring the strength and safety performance of the parts, thereby reducing the weight of the whole vehicle and improving fuel economy. At the same time, since the steel plate of the application has good toughness and formability, it is not easy to crack during the stamping forming and service process of the parts, thereby improving the reliability and service life of the parts.

[0041] The beneficial effects of the application are: (1) The present application inhibits the precipitation of carbides by Si and Al, retains residual austenite to improve toughness, improves hardenability by Mn, Cr, Mo and B, ensures the required hard phase structure under reasonable cooling speed, and further improves strength and toughness by Nb and Ti grain refinement and precipitation strengthening. The present application optimizes the above-mentioned components to reduce harmful elements and add beneficial elements to improve toughness and process performance while ensuring sufficient strength of the steel, and through specific hot rolling, cooling and coiling processes, and pickling treatment, a fine and uniform multiphase structure is obtained, which can have good toughness and formability while ensuring high strength, and can be used to manufacture automobile chassis and floor structure parts to meet the requirements of lightweight and safety performance.

[0042] (2) The preparation method of the present application first adopts the process route of molten iron pretreatment, converter smelting, alloy fine adjustment, LF refining, RH vacuum treatment and continuous casting, effectively reduces the adverse effects of impurities on the toughness of the steel plate, and lays a good material foundation for the subsequent rolling and heat treatment process; in the heating step, the continuous casting blank is heated at 1200-1254℃ for 2-3 hours, solving the problem of insufficient solid solution of micro-alloy elements caused by insufficient traditional heating temperature, and further affecting the precipitation strengthening effect. In the rolling process, the finish rolling temperature is controlled in the non-recrystallization region of austenite, and the Nb element is used to inhibit the recrystallization of austenite, realizing grain refinement during rolling. 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 the acid temperature can form a Si-rich layer on the surface of the steel plate, solving the problem of insufficient surface toughness of high-strength steel in traditional pickling process. Finally, through the synergistic effect of quenching, partitioning and tempering, the optimal ratio of martensite and residual austenite is realized. Each preparation step cooperates and synergizes to form an organic whole. The smelting and continuous casting provide high-quality casting blanks for the subsequent process; the heating step ensures sufficient solid solution of micro-alloy elements; the rolling step realizes grain refinement and uniformization of the structure; the pickling step improves the surface quality and formability; and the continuous annealing step finally endows the steel plate with excellent strength and toughness and comprehensive performance. This synergistic effect makes the steel plate prepared by the present application surpass the steel plate prepared by the traditional process in strength, toughness, corrosion resistance and other aspects. DETAILED DESCRIPTION

[0043] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined object, the specific embodiments, structures, features and effects according to the present application are described in detail as follows in combination with examples.

[0044] Example 1 A high-strength and high-toughness steel plate, by mass percentage, comprises the following chemical components: 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%, the rest being Fe and inevitable impurities.

[0045] The preparation method comprises the following steps: S1, smelting and casting: according to the chemical composition design described above, the molten steel is smelted by a converter, the molten steel is refined by an LF, and then is degassed by an RH, and then is continuously cast into a slab with a thickness of 200 mm.

[0046] S2, heating: the slab is heated to 1200℃ and is kept for 2 hours, so that Nb and Ti are completely solid-solved.

[0047] S3, rolling: the heated slab is subjected to multi-pass hot rolling, wherein the rough rolling opening temperature is 1040±2℃, the finish rolling final rolling temperature is 850±2℃, the total reduction of rough rolling and finish rolling is about 90%, and the final rolling thickness is 4 mm; after hot rolling, the steel plate is immediately subjected to laminar cooling in a cooling device, the laminar cooling is divided into two stages, the first stage is cooled to 550℃ at a speed of about 40℃ / s, then the second stage is cooled to 530℃ at a speed of about 10℃ / s, and then is coiled into a steel coil.

[0048] S4, pickling: after the steel coil is cooled at room temperature, a composite pickling solution is used to perform pickling treatment on the steel coil at 70℃, and then is flattened to obtain a pickled steel plate with a smooth surface. The composite pickling solution comprises: hydrochloric acid 35%, sulfuric acid 3%, ethylenediaminetetraacetic acid 0.3%, propyl sulfide 2%, epoxy acid octane 0.6%, dicycloalkylamine nitrite 1%, ethanol 3.5%, and water in a remainder amount; wherein the concentration of the hydrochloric acid is 40wt%, and the concentration of the sulfuric acid is 75wt%.

[0049] S5, continuous annealing: the steel plate is heated to 820℃ and is kept for 2 minutes to obtain an austenite structure; then the steel plate is quenched and cooled to 350℃ at a cooling rate of 250℃ / min, and is kept at 350℃ for 3-4 minutes for partitioning treatment, the quenching stage converts part of the austenite into martensite, and the partitioning stage diffuses the carbon in the martensite into the unconverted austenite; finally, the steel plate is cooled to 200℃ at a cooling rate of 5℃ / min and is kept for 2-3 minutes for tempering treatment to eliminate the stress in the martensite and at the same time to retain stable residual austenite; S6, cooling: the steel plate is cooled to room temperature at a cooling rate of 25℃ / min.

[0050] Example 2 A high-strength and high-toughness steel plate comprises the following chemical components in percentage by mass: 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%, the rest Fe and inevitable impurities.

[0051] The preparation method comprises the following steps: S1, smelting and casting: according to the chemical composition design described above, the molten steel is smelted by converter, the molten steel is refined by LF, and then is degassed by RH, and then is continuously cast into a slab with a thickness of 200 mm.

[0052] S2, heating: the slab is heated to 1180℃ and kept for 2 hours to make Nb and Ti completely solid solution.

[0053] S3, rolling: the heated slab is subjected to multi-pass hot rolling, wherein the rough rolling opening temperature is 1040±2℃, and the finish rolling final rolling temperature is 830±2℃; the total reduction of rough rolling and finish rolling is about 90%, and the final rolling thickness is 3mm; after hot rolling, the steel plate is immediately subjected to laminar cooling in a cooling device, the laminar cooling is divided into two stages, the first stage is cooled to 550℃ at a speed of about 50℃ / s, and then the second stage is cooled to 530℃ at a speed of about 10℃ / s, and then is coiled into a steel coil.

[0054] S4, pickling: after the steel coil is cooled at room temperature, a composite pickling solution is used to pickle the steel coil at 50-90℃, and then is flattened to obtain a pickled steel plate with a smooth surface. The composite pickling solution comprises: 30% hydrochloric acid, 1% sulfuric acid, 0.2% ethylenediaminetetraacetic acid, 1% propyl sulfide, 0.5% epoxy acid octyl, 0.5% dicycloalkylamine nitrite, 3% ethanol and water in residual amount; wherein the concentration of the hydrochloric acid is 30wt%, and the concentration of the sulfuric acid is 70wt%.

[0055] S5, continuous annealing: the steel plate is heated to 820℃ and kept for 2 minutes to obtain austenite organization; then the steel plate is quenched and cooled to 350℃ at a cooling rate of 250℃ / min, and kept at 350℃ for 3-4 minutes for partitioning treatment, the quenching stage converts part of the austenite into martensite, and the partitioning stage diffuses the carbon in the martensite to the unconverted austenite; finally, the temperature is lowered to 200℃ at a cooling rate of 5℃ / min and kept for 2-3 minutes for tempering treatment to eliminate the stress in the martensite and at the same time retain stable residual austenite; S6, cooling: the steel plate is cooled to room temperature at a cooling rate of 25℃ / min.

[0056] S7, surface treatment: under the protection of argon, a Cr2O3-Al2O3-TiO2 layer is cladded on the surface of the steel plate by laser cladding technology, wherein the coating thickness is 1 mm, the laser power is 2000 W, the scanning speed is 15 mm / s, the defocusing amount is 80 mm, the coating composition includes 40% Cr2O3, 30% Al2O3, 20% TiO2 and 10% SiC, the powder feeding flow is 15 g / min, and the argon flow is 20 L / min.

[0057] Example 3 A high-strength and high-ductility steel plate includes the following chemical components in percentage by mass: 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%, and the rest Fe and unavoidable impurities.

[0058] In step S4, the composite pickling solution includes: hydrochloric acid 45%, sulfuric acid 5%, ethylenediaminetetraacetic acid 0.5%, propyl sulfide 3%, epoxy acid octane 0.8%, dicycloalkylamine nitrite 1.5%, ethanol 4%, and water in the remainder; wherein the concentration of the hydrochloric acid is 50wt%, the concentration of the sulfuric acid is 80wt%. The rest of the preparation method is the same as that in Example 1.

[0059] Comparative Example 1 This comparative example is different from Example 1 in that the addition amount of Nb and Ti in the comparative example is 0, and the rest of the components, preparation steps and parameters are consistent.

[0060] Comparative Example 2 This comparative example is different from Example 1 in that the addition amount of Mo in the comparative example is 0, and the rest of the components, preparation steps and parameters are consistent.

[0061] Comparative Example 3 This comparative example is different from Example 1 in that the addition amount of Cr and B in the comparative example is 0, and the rest of the components, preparation steps and parameters are consistent.

[0062] Comparative Example 4 This comparative example is different from Example 1 in that in step S5 of the comparative example, the steel plate is heated to 820℃ and held for 2 minutes to obtain an austenitic structure; then the steel plate is quenched at a cooling rate of 250℃ / min to 150℃ and held for 3-4 minutes to convert the austenite into martensite; finally, the temperature is raised to 220℃ at a heating rate of 5℃ and held for 2-3 minutes for tempering treatment.

[0063] The following performance tests were performed on Examples 1-3 and Comparative Examples 1-4: (1) Tensile properties test Refer to GB / T228.1-2021 "Tensile test of metallic materials Part 1: Room temperature test method" standard, the specimen thickness is 3mm, the gauge length is 50mm), the specimen axis is parallel to the rolling direction of the steel plate, and the surface is polished to a roughness of Ra≤1.6μm to avoid stress concentration. A universal material testing machine with an accuracy level of 0.5 is used, equipped with an extensometer with a gauge length of 50mm and an accuracy level of 1. The test temperature is 23±5℃, the tensile rate in the elastic stage is 5mm / min, and the tensile rate from yield to fracture is 20mm / min. The yield strength Rp0.2, tensile strength Rm and elongation after fracture A of the test specimens are tested. 80 Each sample was tested 3 times and the arithmetic mean was taken as the result.

[0064] (2) Impact toughness test The test was conducted in accordance with the GB / T229-2020 "Charpy Pendulum Impact Test Method for Metallic Materials" standard, using a V-notched impact specimen measuring 10mm × 10mm × 55mm. The notch was located at 1 / 2 of the steel plate thickness, with a bottom roughness Ra ≤ 1.6μm and a notch depth of 2mm. A pendulum impact tester 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°C and a low temperature of -40±2°C. The specimens were kept at the target temperature for one hour, ensuring a temperature fluctuation error of ≤±2°C. Three specimens were tested at each temperature point, and the average value was calculated after removing outliers.

[0065] (3) Neutral salt spray test Refer to GB / T10125-2021 "Artificial Atmosphere Corrosion Test Salt Spray Test" standard, use salt spray test chamber, temperature control is 35±2℃, salt spray deposition volume is 1.0~2.0mL / ( ), the sample size was 150mm×70mm, the original surface state was retained, and the edges were sealed with anti-corrosion paint. A 5% mass fraction NaCl solution with a pH value of 6.5-7.2 was used for continuous spraying for 144 hours, and the surface corrosion state was observed every 48 hours. The weight of the sample before and after the test was obtained by weighing. The sample was derusted, cleaned, and dried before and after the test, and then weighed to the nearest 0.1mg, and the 144-hour salt spray corrosion rate ( ).

[0066] The test results are shown in Table 1.

[0067] Table 1 From the test results in Table 1, it can be seen that the performance of Examples 1-3 is significantly better than that of Comparative Examples 1-4, and meets the use requirements of automobile floor parts.

[0068] The above merely describes preferred embodiments of the present application, and is not intended to limit the present application in any form. Although the present application has been described above with reference to preferred embodiments, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above disclosed technical content to obtain equivalent embodiments with equivalent changes, without departing from the technical solution of the present application. Any modification, equivalent change and modification of the above embodiments made according to the technical essence of the present application, without departing from the technical solution of the present application, still belongs to the scope of the technical solution of the present application.

Claims

1. A high-strength and high-toughness steel plate, comprising the following chemical components 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 is Fe and inevitable impurities.

2. A method for preparing a high-strength and high-toughness steel plate according to claim 1, characterized in that: The preparation method comprises the following steps: S1. Smelting and casting: After pre-treatment, the molten steel is smelted in a converter, alloy is added for fine adjustment, LF refining and RH vacuum treatment are carried out in sequence, and then the molten steel is continuously cast into continuous casting billets; S2. Heating: Heat the continuous casting billet to the austenitizing temperature and keep it at this temperature for 2-3 hours to completely dissolve Nb and Ti; S3, rolling: the heated slab is subjected to multiple hot rolling passes, wherein the rough rolling start temperature is 1030-1050°C and the finishing rolling temperature is 840-920°C; after hot rolling, the steel plate is laminar cooled to 520-570°C and coiled; S4. Pickling: Use a composite pickling solution to pickle the coiled hot-rolled steel plate at 50-90°C, and then level it; S5. Continuous annealing: Heat the steel plate to 770-850°C and hold for 1-3 minutes; then quench and cool the steel plate to 320-380°C at a cooling rate of 150-300°C / min, hold at 340-360°C for 3-4 minutes, and perform partitioning treatment; finally, cool the steel plate to 180-220°C at a cooling rate of 4-6°C and hold for 2-3 minutes, and perform tempering treatment; S6. Cooling: Cool the steel plate to room temperature at a cooling rate of 20-30°C / min.

3. The method for preparing a high-strength and high-toughness steel plate according to claim 2, wherein: In step S1, the thickness of the continuous casting billet is 200-230 mm.

4. The method for preparing a high-strength and high-toughness steel plate according to claim 2, wherein: In step S2, the austenitizing temperature is 1150-1250°C.

5. The method for preparing a high-strength and high-toughness steel plate according to claim 2, wherein: In step S3, the laminar cooling speed is 30-45°C / s.

6. The method for preparing a high-strength and high-toughness steel plate according to claim 2, wherein: In step S4, the composite pickling solution includes, 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% octanol epoxide, 0.5-1.5% dicycloalkylamine nitrite, 3-4% ethanol, and the balance water; wherein the concentration of the hydrochloric acid is 30-50wt%, and the concentration of the sulfuric acid is 70-80wt%.

7. The method for preparing a high-strength and high-toughness steel plate according to claim 2, wherein: In step S4, the pickling time is 5-15 seconds, and the pickling line speed is 30-100 mpm.

8. The method for preparing a high-strength and high-toughness steel plate according to claim 2, wherein: After pickling, and before leveling, the steel plate is rinsed with water 3-5 times until the pH value of the rinse water reaches 6.5-7; then the steel plate is dried.

9. The method for preparing a high-strength and high-toughness steel plate according to claim 2, wherein: After pickling, the steel is leveled using a rolling force mode with a rolling force of 100-200 tons. Desalted water is used as the leveling fluid, and the leveling elongation is 0.4-2%.

10. Use of the high-strength and high-toughness steel plate according to claim 1 in the preparation of automobile parts, characterized in that: The steel plate is produced by the production method according to any one of claims 2 to 9, and the steel plate is used for producing automobile floor panels.

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