High-strength steel sheet having good formability and method for manufacturing the same

Abstract

This application discloses a high-strength steel plate with good formability and its preparation method. The high-strength steel plate with good formability comprises the following chemical composition by mass percentage: C: 0.14%–0.18%, Si: ≤0.10%, Mn: 1.30%–1.50%, P: ≤0.010%, S: ≤0.0008%, Cr: 0.30%–0.40%, Nb: 0.02%–0.04%, Ti: 0.010%–0.030%, V: 0.03%–0.05%, Mo… The composition of the high-strength steel plate is as follows: 0.30%~0.50%, B: 0.0008%~0.0018%, Ca: 0.0010%~0.0020%, N: ≤0.004%, O: ≤0.0015%, Als: 0.010%~0.040%, with the balance being iron and unavoidable impurities. The carbon equivalent is ≤0.57, and 0.8≤([Ca]–0.75*[O]) / [S]≤1.5, where [Ca], [O], and [S] represent the mass content of Ca, O, and S elements in the high-strength steel plate, respectively. The high-strength steel plate with good formability of the embodiments of this application combines good mechanical properties and cold bending forming performance, and does not crack when forming at small angles.

Description

Technical Field

[0001] This application belongs to the field of steel plate preparation technology, specifically relating to a high-strength steel plate with good formability and its preparation method. Background Technology

[0002] As the engineering equipment industry continues to develop towards larger and lighter sizes, the strength grade of steel plates used in its core structural components has generally increased from the traditional 345MPa to 700MPa to 900MPa and even 2500MPa levels. This trend is particularly evident in key load-bearing components such as concrete pump truck booms, aerial work platform booms, telescopic booms of large truck cranes, and track plates of crawler cranes, where high-strength steel plates of 900MPa grade and above have become key materials for achieving weight reduction and efficiency improvement.

[0003] However, the increasing complexity of equipment structures poses more stringent challenges to material processing performance. Especially in the manufacturing of critical components with compact structures, limited space, or extremely high assembly precision requirements, the design of their load-bearing structure and external dimensions often necessitates high-strength steel plates with extremely small cold-forming bending radii. If the material's plastic forming capacity is insufficient, cracking is highly likely to occur during actual bending processing.

[0004] Therefore, there is an urgent need to develop a high-strength steel plate that maintains ultra-high strength while also possessing excellent cold bending forming performance and effectively solving the problem of cracking during small-angle forming. Summary of the Invention

[0005] In view of this, this application provides a high-strength steel plate with good formability and a method for preparing the same, aiming to provide a high-strength steel plate that takes into account both mechanical properties and excellent cold bending forming performance, and can effectively solve the problem of small-angle forming cracking.

[0006] In a first aspect, embodiments of this application provide a high-strength steel plate with good formability. The high-strength steel plate comprises the following chemical composition by mass percentage: C: 0.14%–0.18%, Si: ≤0.10%, Mn: 1.30%–1.50%, P: ≤0.010%, S: ≤0.0008%, Cr: 0.30%–0.40%, Nb: 0.02%–0.04%, Ti: 0.010%–0.030%, V: 0.03%–0.05%, Mo: 0. 30%~0.50%, B: 0.0008%~0.0018%, Ca: 0.0010%~0.0020%, N: ≤0.004%, O: ≤0.0015%, Als: 0.010%~0.040%, the balance being iron and unavoidable impurities, carbon equivalent ≤0.57, and 0.8≤([Ca]–0.75*[O]) / [S]≤1.5, where [Ca], [O] and [S] represent the mass content of Ca, O and S elements in the high-strength steel plate, respectively.

[0007] In some embodiments, the metallographic structure of the high-strength steel plate is a single tempered sorbite, and the average size of the tempered sorbite is 3 to 5 micrometers.

[0008] In some embodiments, the thickness of the high-strength steel plate is 3.0 to 10.0 mm.

[0009] In some embodiments, the unevenness of the high-strength steel plate is ≤2mm / m.

[0010] In some embodiments, the mechanical properties of the quenched and tempered steel plate of the high-strength steel plate satisfy: yield strength R eL ≥960MPa, tensile strength R m ≥1000MPa, elongation A: ≥13%; impact energy KV2 at -40℃ ≥140J, impact energy aspect ratio ≥0.8; forming performance R ≥2.5a, 90° bending qualified.

[0011] Secondly, embodiments of this application provide a method for preparing a high-strength steel plate with good formability, the method comprising: Refined steel is continuously cast to obtain a billet, which comprises the following chemical composition by mass percentage: C: 0.14%–0.18%, Si: ≤0.10%, Mn: 1.30%–1.50%, P: ≤0.010%, S: ≤0.0008%, Cr: 0.30%–0.40%, Nb: 0.02%–0.04%, Ti: 0.010–0.030%, V: 0.03–0.05%, Mo: 0.30–0.50%, B: 0.0008–0.0018%, Ca: 0.0010–0.0020%, N: ≤0.004%, O: ≤0.0015%, Als: 0.010%–0.040%, with the balance being iron and unavoidable impurities, and a carbon equivalent ≤0.57. The billet is subjected to heating, hot rolling, laminar flow cooling, coiling, leveling, quenching and tempering to obtain a high-strength steel plate. The holding time for quenching is (1.6*t+k) min, where k is 8~12 and t is the thickness of the steel plate in mm. The quenching adopts a roll-pressing quenching method. The roll gap setting value for quenching is equal to the thickness of the high-strength steel plate. The water pressure for quenching is 0.8MPa, and the water ratio applied to the upper and lower surfaces of the high-strength steel plate is 1:(1.2~1.5).

[0012] In some embodiments, the tempering temperature is 580±10℃, and the tempering holding time is (1.6*t+Q)min, where Q is 28~35.

[0013] In some embodiments, before continuously casting the refined molten steel to obtain a billet, the method further includes: smelting the molten iron in a converter, refining it in an LF furnace, vacuum treating it in an RH furnace, and treating it with Si-Ca, so that the chemical composition of the refined molten steel meets the following requirements: O≤0.0015%, S≤0.0008%, N≤0.004%, Ca:0.001%~0.002%.

[0014] In some embodiments, the Si-Ca treatment includes feeding pure calcium wire into molten steel using a wire feeder at a feeding speed ≥2m / min.

[0015] In some embodiments, the temperature of the refined molten steel is 1540°C to 1560°C.

[0016] The present application has at least the following advantageous effects: The high-strength steel plate with excellent formability provided in this application embodiment achieves good tensile strength and yield strength through the combination of various elements contained in the high-strength steel plate. Furthermore, it strictly controls the content of harmful elements, such as S, N, and O, within the aforementioned content ranges, and controls the quantity, morphology, and size of inclusions such as MnS, TiN, and TiO2. The addition of calcium at the aforementioned content reduces the amount of phosphorus, sulfides, and nitrides. This solves the problem of segregation at the center of the cast billet, thereby reducing the probability of crack initiation and improving the performance of the high-strength steel plate. It is stable and not prone to cracking; at the same time, by controlling 0.8≤([Ca]–0.75*[O]) / [S]≤1.5, more spherical calcium sulfide is generated, reducing the amount of manganese sulfide. Moreover, calcium sulfide has high hardness, which reduces the specific surface area of ​​inclusions and the contact area between inclusions and the matrix, thereby reducing the risk of cracking when high-strength steel plates are bent; the elements contained in high-strength steel plates are within the above range, and the carbon equivalent is within the above range, which is conducive to making high-strength steel plates take into account mechanical properties, hardenability, weldability, ductility and toughness and cold workability. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the implementation regulations of this application, the drawings used in the embodiments of this application will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 The metallographic structure of the high-strength steel plate with good formability according to Embodiment 1 of this application is shown. Figure 2 The image shows the calcium sulfide morphology of the high-strength steel sheet with good formability of Embodiment 1 of this application; Figure 3 The energy spectrum of the high-strength steel plate containing calcium sulfide with good formability, as shown in Embodiment 1 of this application, is illustrated. Figure 4 The diagram shows the forming effect of the high-strength steel sheet with good formability of Embodiment 1 of this application under condition 2.5a. Figure 5 The image shows the morphology of manganese sulfide in the high-strength steel plate with good formability in Comparative Example 1 of this application; Figure 6 The energy spectrum of a high-strength steel plate containing manganese sulfide, as shown in Comparative Example 1 of this application, is illustrated. Figure 7 The diagram shows the forming effect of the high-strength steel plate of Comparative Example 2 of this application under condition 2.5a. Detailed Implementation

[0019] To make the purpose, technical solution, and beneficial technical effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the implementation details described in this specification are merely for illustrative purposes and are not intended to limit the scope of this application.

[0020] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, although not explicitly stated, every point or individual value between the endpoints of the range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit and combined with any other point or individual value or with other lower or upper limits to form a range not explicitly stated.

[0021] In the description of this application, it should be noted that, unless otherwise stated, "above" and "below" include the stated number, and "multiple" in "one or more" means two or more.

[0022] The foregoing description of this application is not intended to describe every disclosed implementation or method. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments, which can be used in various combinations. The examples listed are representative only and should not be construed as exhaustive.

[0023] In a first aspect, embodiments of this application provide a high-strength steel plate with good formability. The high-strength steel plate comprises the following chemical composition by mass percentage: C: 0.14%–0.18%, Si: ≤0.10%, Mn: 1.30%–1.50%, P: ≤0.010%, S: ≤0.0008%, Cr: 0.30%–0.40%, Nb: 0.02%–0.04%, Ti: 0.010%–0.030%, V: 0.03%–0.05%, Mo: 0.3%. 0%~0.50%, B: 0.0008%~0.0018%, Ca: 0.0010%~0.0020%, N: ≤0.004%, O: ≤0.0015%, Als: 0.010%~0.040%, with the balance being iron and unavoidable impurities, carbon equivalent ≤0.57, and 0.8≤([Ca]–0.75*[O]) / [S]≤1.5, where [Ca], [O] and [S] represent the mass content of Ca, O and S elements in the high-strength steel plate, respectively.

[0024] The high-strength steel plate provided in this application embodiment, through the combination of various elements contained in the high-strength steel plate, enables the high-strength steel plate to have good tensile strength and yield strength. Furthermore, the content of harmful elements, such as S, N, and O, is strictly controlled within the aforementioned content range. The quantity, morphology, and size of inclusions such as MnS, TiN, and TiO2 are also controlled. The addition of calcium at the aforementioned content reduces the quantity of phosphorus, sulfides, and nitrides, thereby solving the problem of agglomeration at the center of the billet and reducing the probability of crack initiation, making the high-strength steel plate stable and less prone to cracking. Simultaneously, controlling 0.8≤([Ca]–0.75*[O]) / [S]≤1.5 generates more spherical calcium sulfide, reducing the quantity of manganese sulfide. Moreover, the high hardness of calcium sulfide reduces the specific surface area of ​​inclusions and the contact area between inclusions and the matrix, thereby reducing the risk of cracking during bending. The carbon equivalent being within the aforementioned range is beneficial for the high-strength steel plate to balance mechanical properties, hardenability, weldability, ductility, toughness, and cold workability.

[0025] Optionally, in the chemical composition of the high-strength steel plate, the ratio of ([Ca]–0.75*[O]) / [S] can be any value or range of its composition from 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 and 1.5.

[0026] Optionally, the carbon equivalent in the high-strength steel plate can be 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, or 0.3. 3. Any value or a range thereof from 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.40, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, and 0.57.

[0027] The technical concept of the high-strength steel plate in this application embodiment, comprising the following chemical composition by mass percentage, is as follows: C: Carbon, as an important alloying element in steel, plays a crucial role in improving the strength of steel plates and promoting the precipitation of the second phase. However, excessive carbon content can affect weldability, and the banded structure caused by center segregation has a fatal impact on forming. This patent uses a medium carbon content, which satisfies the hardness required for quenching martensite and the carbon required for the precipitation of the second phase microalloy, while controlling the carbon equivalent to a low content. Therefore, the mass content of carbon is used in the range of 0.14% to 0.18%.

[0028] Silicon (Si): Silicon offers advantages such as increasing the strength of steel plates, expanding the mid-temperature phase transformation zone, and inhibiting carbide precipitation. However, excessively high levels can negatively impact the surface quality of the steel plates. Furthermore, as a deoxidizer, excessively low levels of silicon make it difficult to control the oxygen content in the steel. Therefore, a range of ≤0.10% is adopted.

[0029] Mn: Manganese is a major solid solution strengthening element in steel, a typical austenite stabilizing element, and plays a role in refining ferrite grains. It also has a good effect on delaying the pearlite transformation. Therefore, a range of 1.30% to 1.50% is adopted.

[0030] P: Phosphorus, as a harmful inclusion in steel, has a significant detrimental effect on the low-temperature impact toughness, cold formability, weldability, and fatigue crack propagation resistance of steel, and the lower the better; however, considering the operability and cost of steelmaking, the P content is controlled at ≤0.010%.

[0031] S: Sulfur, as a harmful inclusion in steel, has a significant detrimental effect on the low-temperature toughness and fatigue crack propagation resistance (mainly long strip-shaped sulfides) of steel. More importantly, S combines with Mn in steel to form MnS inclusions. During hot rolling, the plasticity of MnS causes MnS to extend along the rolling direction, forming MnS inclusion bands along the rolling direction, which seriously impairs the fatigue crack propagation resistance of the steel plate. Taking into account the operability of steelmaking, the S content is controlled at ≤0.0008%.

[0032] O: Oxygen is a harmful element in steel. It reacts with elements such as Ti and Ca to form various inclusions, affecting the effective composition of these elements. Therefore, the lower its content, the better. However, excessively low oxygen content will significantly increase steelmaking costs and affect production schedules.

[0033] Niobium (Nb): The microalloying element niobium exhibits significant grain-refining strengthening and moderate precipitation strengthening effects, which are beneficial for improving the strength of steel plates. Furthermore, the products formed by Nb with C and N will re-dissolve during heating and precipitate during cooling. Nb does not react with elements such as S and O, resulting in high yield and stable strengthening effect. Experimental results show that in ultra-high strength steel, an increase in Nb content > 0.04% does not significantly contribute to strength. Considering both cost and strength, Nb content is controlled between 0.02% and 0.04%.

[0034] Ti: Titanium also contributes significantly to strength, especially after the addition of Ti combined with Mo, which can form (Ti x Mo 1、x C y N 1、yThe coefficients 0 < x < 1 and 0 < y < 1 contribute very steadily to the strength. Furthermore, the TiN particles formed by titanium and nitrogen effectively suppress the grain structure of the weld heat-affected zone, thereby improving weldability. This patent uses trace amounts of Ti, primarily to improve the performance of the quenched and tempered steel; therefore, the Ti content is controlled at 0.01%~0.03%. Vanadium (V) is also a steel element with moderate precipitation strengthening and fine grain strengthening. Moreover, V has a low precipitation temperature, and adding an appropriate amount of vanadium can promote the precipitation strengthening effect of V(CN). Therefore, in this invention, the V content is controlled at 0.03%~0.05%.

[0035] Mo (Mo): Molybdenum (Mo) contributes significantly to strength. It can form complex carbonitrides with Nb and Ti, promoting their interphase precipitation and greatly enhancing the strength of the ferrite matrix. Furthermore, Mo improves hardenability, inhibits pearlite formation, and promotes the formation of strong and tough structures such as bainite. However, Mo is a precious metal, and excessive amounts can cause the formation of M / A islands in the steel, affecting its formability. Considering both cost and performance, the Mo content is controlled between 0.30% and 0.50%.

[0036] Cr: Cr element can improve the hardenability of steel and reduce the adhesion of iron oxide scale on the surface of strip steel, reduce the pulverization of iron oxide scale on the surface of steel plate, and improve the surface quality of steel plate. Therefore, the Cr content in this application is set to 0.30%~0.40%.

[0037] B: B is an element with a strong hardenability in steel. Even a trace amount of B can greatly improve the hardenability of steel. Therefore, the B content in this application is set to 0.0008%~0.0018%.

[0038] Ca: Ca can form spherical CaS with S, thereby modifying sulfides and reducing the surface area of ​​flat sulfides, thus reducing anisotropy. However, excessive Ca content can lead to the formation of inclusions such as calcium aluminates. Therefore, the Ca content in this application is set at 0.0010%~0.0020%.

[0039] N: Nitrogen is a harmful element in steel. Ti has a strong affinity for N, and the presence of N will greatly increase the risk of TiN inclusions. Therefore, the N content is controlled at ≤0.004%.

[0040] Als: As a major deoxidizing element, aluminum's content in steel determines the oxygen content. However, excessive Al content will generate Al2O3, which is the core for TiN heterogeneous nucleation, leading to excessive TiN inclusions. Therefore, Als should be controlled between 0.010% and 0.040%.

[0041] In some embodiments, the metallographic structure of the high-strength steel plate is a single tempered sorbite, and the average size of the tempered sorbite is 3 to 5 micrometers.

[0042] The single microstructure of tempered sorbite is beneficial to improving the coordinated deformation ability of the microstructure of high-strength steel plates during the forming process, thus giving high-strength steel plates good processing performance.

[0043] In some embodiments, the thickness of the high-strength steel plate is 3.0 to 10.0 mm. Optionally, the thickness of the high-strength steel plate can be any value or a range of combinations thereof from 3.0 mm, 3.5 mm, 4.0 mm, 4.5 mm, 5.0 mm, 5.1 mm, 5.2 mm, 5.3 mm, 5.4 mm, 5.5 mm, 6.0 mm, 6.5 mm, 7.0 mm, 7.5 mm, 8.0 mm, 8.5 mm, 9.0 mm, 9.5 mm, and 10.0 mm.

[0044] In some embodiments, the unevenness of the high-strength steel plate satisfies ≤2mm / m. Optionally, the unevenness of the high-strength steel plate can be any value or a range of combinations thereof from 0.1mm / m, 0.2mm / m, 0.3mm / m, 0.4mm / m, 0.5mm / m, 0.6mm / m, 0.7mm / m, 0.8mm / m, 0.9mm / m, 1.0mm / m, 1.1mm / m, 1.2mm / m, 1.3mm / m, 1.4mm / m, 1.5mm / m, 1.6mm / m, 1.7mm / m, 1.8mm / m, 1.9mm / m, and 2.0 mm / m.

[0045] There are various methods for detecting the flatness of steel plates, mainly divided into contact measurement and non-contact measurement. For example, a mechanical probe or probe is used to directly contact the surface of the steel plate, and a displacement sensor records the height change. The formula for calculating the flatness of a steel plate is (h1-h2) / d, where h1 represents the thickness of the steel plate at the first position, h2 represents the thickness of the steel plate at the second position, and d represents the distance between the first and second positions.

[0046] In some embodiments, the mechanical properties of the quenched and tempered steel plate of the high-strength steel plate satisfy: yield strength R eL ≥960MPa, tensile strength R m ≥1000MPa, elongation A: ≥13%; impact energy KV2 at -40℃ ≥140J, impact energy aspect ratio ≥0.8; forming performance R ≥2.5a, 90° bending qualified.

[0047] Optionally, the mechanical properties of the quenched and tempered steel plate of high-strength steel plate meet the following requirements: yield strength R eL The tensile strength is 980~1050MPa, and the tensile strength R is... mThe strength is 1000~1060MPa, the elongation A is 13%~15%; the impact energy KV2 at -40℃ is 140J~210J, the impact energy ratio is ≥0.8; the forming performance R is 2.5a~3.0a, and the 90° bending is qualified.

[0048] Secondly, embodiments of this application provide a method for preparing a high-strength steel plate with good formability, the method comprising: Refined steel is continuously cast to obtain a billet, which comprises the following chemical composition by mass percentage: C: 0.14%–0.18%, Si: ≤0.10%, Mn: 1.30%–1.50%, P: ≤0.010%, S: ≤0.0008%, Cr: 0.30%–0.40%, Nb: 0.02%–0.04%, Ti: 0.010–0.030%, V: 0.03–0.05%, Mo: 0.30–0.50%, B: 0.0008–0.0018%, Ca: 0.0010–0.0020%, N: ≤0.004%, O: ≤0.0015%, Als: 0.010%–0.040%, with the balance being iron and unavoidable impurities, and a carbon equivalent ≤0.57. In this step, the refined steel is an ultra-low sulfur and ultra-low nitrogen steel, which is beneficial for controlling impurity elements and inclusions in high-strength steel plates in the subsequent process.

[0049] The billet is subjected to heating, hot rolling, laminar flow cooling, coiling, leveling, quenching and tempering to obtain a high-strength steel plate. The holding time for quenching is (1.6*t+k) min, where k is 8~12, which can be selected as 10, and t is the thickness of the steel plate in mm. The quenching adopts a roll-pressing quenching method. The roll gap setting value for quenching is equal to the thickness of the high-strength steel plate. The water pressure for quenching is 0.8MPa, and the water ratio applied to the upper and lower surfaces of the high-strength steel plate is 1:(1.2~1.5).

[0050] Optionally, the water ratio applied to the upper and lower surfaces of the high-strength steel plate can be any ratio or a range of combinations thereof from (1:0.8), (1:0.9), (1:1.0), (1:1.1), and (1:1.2).

[0051] The preparation method of this embodiment strictly controls the content of harmful elements in the chemical composition of the refined steel and adds an appropriate amount of calcium, which reduces the amount of phosphorus, sulfides, and nitrides in the billet and reduces the aggregation of these elements or inclusions in the center of the billet, thereby reducing the probability of crack initiation. Calcium reacts with sulfur to form spherical calcium sulfide, which not only reduces the amount of manganese sulfide, but also has high hardness and will not deform during hot rolling, reducing the specific surface area of ​​inclusions and the contact area between inclusions and the billet matrix, thus reducing the risk of cracking during bending.

[0052] The preparation method in this embodiment employs a roll-press quenching method. The roller conveyors operate at differential speeds, using different rotational speeds of the front and rear sets of rollers to achieve tension on the steel plate, reducing deformation during quenching and thus minimizing free elongation. Simultaneously, the water ratio between the upper and lower plates of the quenching machine is set within the aforementioned range, ensuring a greater water volume on the lower plate than the upper plate. This evens out the internal stress on both plates, achieving uniform cooling during quenching, optimizing the quenched plate shape, and reducing the adverse effects of quenching on the plate shape. The roller gap setting is equal to the thickness of the high-strength steel plate. This allows the roller gap to constrain deformation during quenching, resulting in good flatness and a uniform internal stress distribution within the steel plate. This gives the high-strength steel plate good flatness, for example, flatness ≤2mm / m.

[0053] In some embodiments, the quenching temperature is 870~890℃. Optionally, the quenching temperature can be any value or a range of combinations thereof from 870℃, 871℃, 872℃, 873℃, 874℃, 875℃, 876℃, 877℃, 878℃, 879℃, 880℃, 881℃, 882℃, 883℃, 884℃, 885℃, 886℃, 887℃, 888℃, 889℃, and 890℃.

[0054] Generally, the preparation method of high-strength steel plates includes the following steps in sequence: smelting molten iron in a converter, refining, Si-Ca treatment, continuous casting, billet heating, hot rolling, laminar flow cooling, coiling, leveling, quenching, tempering, and straightening.

[0055] Electromagnetic stirring during continuous casting helps to homogenize the composition of the refined steel used in continuous casting, reduces the segregation of these elements or inclusions in the center of the billet, and thus reduces the probability of crack initiation.

[0056] In some embodiments, the heating temperature during billet heating can be 1150~1200℃. Optionally, the heating temperature can be 1150℃, 1151℃, 1152℃, 1153℃, 1154℃, 1155℃, 1156℃, 1157℃, 1158℃, 1159℃, 1160℃, 1161℃, 1162℃, 1163℃, 1164℃, 1165℃, 1166℃, 1167℃, 1168℃, 1169℃, 1170℃, 1171℃, 1172℃, 1173℃, 1174℃, 117... Any value or a range thereof from 5℃, 1176℃, 1177℃, 1178℃, 1179℃, 1180℃, 1181℃, 1182℃, 1183℃, 1184℃, 1185℃, 1186℃, 1187℃, 1188℃, 1189℃, 1190℃, 1191℃, 1192℃, 1193℃, 1194℃, 1195℃, 1196℃, 1197℃, 1198℃, 1199℃, and 1200℃.

[0057] Hot rolling of cast billets can include roughing and finishing rolling.

[0058] In some embodiments, the roughing temperature is ≥1080±20℃ and the final rolling temperature is ≥860±20℃. Optionally, the roughing temperature can be ≥1060℃ and ≤1100℃, for example, any value or a range of combinations of 1060℃, 1061℃, 1062℃, 1080℃, 1099℃, and 1100℃.

[0059] Optionally, the final rolling temperature can be ≥840℃ and ≤880℃, for example, any value or a range of combinations of 840℃, 841℃, 842℃, 850℃, 860℃, 879℃, and 880℃.

[0060] In some embodiments, the finishing rolling temperature is 860~900℃; optionally, the finishing rolling temperature can be any value or a range of combinations thereof from 860℃, 861℃, 862℃, 863℃, 864℃, 865℃, 866℃, 867℃, 868℃, 869℃, 870℃, 871℃, 872℃, 873℃, 874℃, 875℃, 876℃, 877℃, 878℃, 879℃, 880℃, 881℃, 882℃, 883℃, 884℃, 885℃, 886℃, 887℃, 888℃, 889℃, 890℃, 891℃, 892℃, 893℃, 894℃, 895℃, 896℃, 897℃, 898℃, 899℃, and 900℃.

[0061] In some embodiments, the winding temperature is 580~620°C. Optionally, the winding temperature can be any value or a range of combinations thereof from 580°C, 581°C, 582°C, 583°C, 584°C, 585°C, 586°C, 587°C, 588°C, 589°C, 590°C, 591°C, 592°C, 593°C, 594°C, 595°C, 596°C, 597°C, 598°C, 599°C, 600°C, 601°C, 602°C, 603°C, 604°C, 605°C, 606°C, 607°C, 608°C, 609°C, 610°C, 611°C, 612°C, 613°C, 614°C, 615°C, 616°C, 617°C, 618°C, 619°C, and 620°C.

[0062] In some embodiments, the tempering temperature is 580±10℃, and the tempering holding time is (1.6*t+Q) min, where Q is 28~35, optionally 30. Optionally, the tempering temperature can be any value or a range of combinations thereof from 570℃, 571℃, 572℃, 573℃, 574℃, 575℃, 576℃, 577℃, 578℃, 579℃, 580℃, 581℃, 582℃, 583℃, 584℃, 585℃, 586℃, 587℃, 588℃, 589℃, and 590℃.

[0063] In some embodiments, before continuously casting the refined molten steel to obtain a billet, the method further includes: smelting the molten iron in a converter, refining it in an LF furnace, vacuum treating it in an RH furnace, and treating it with Si-Ca, so that the chemical composition of the refined molten steel meets the following requirements: O≤0.0015%, S≤0.0008%, N≤0.004%, Ca:0.001%~0.002%.

[0064] In converter smelting, molten iron is desulfurized at the KR desulfurization station to obtain pre-desulfurized molten iron; low-sulfur clean scrap steel and pre-desulfurized molten iron are charged into the converter and smelted by oxygen blowing to obtain converter steel; during the tapping process of the converter steel, deoxidation is carried out to obtain converter steel with an oxygen content ≤0.005%; In the LF furnace refining process, the converter steel is heated and desulfurized to obtain desulfurized steel with a sulfur content ≤0.001%. In the heating and desulfurization steps, LF furnace electrodes are used for heating, and lime is added during the heating process to form slag; the amount of lime added meets the requirements that TFe in the slag is ≤1.5% and the basicity R is ≥5.

[0065] After refining in the LF furnace, the desulfurized molten steel has the following composition: O≤0.005%, S≤0.0008%, N≤0.004%, and the temperature is 1560℃-1580℃.

[0066] In the vacuum treatment of the RH furnace, the desulfurized molten steel is subjected to deep deoxidation to obtain deep deoxidized molten steel with an oxygen content ≤0.0015%; the deep deoxidized molten steel is then subjected to calcium treatment to obtain calcium-treated molten steel with a calcium content of 0.0010%~0.0020%.

[0067] Deep deoxidation operation uses RH furnace vacuum treatment, with vacuum chamber pressure maintained at ≤133Pa and pure circulation time ≥20min; The composition of the deep deoxidized steel is O≤0.0015%, S≤0.0008%, N≤0.004%, and the temperature is 1540℃~1560℃.

[0068] After vacuum treatment in the RH furnace and before continuous casting, the preparation method also includes: transferring the deeply deoxidized molten steel to the tundish for calcium treatment to obtain tundish molten steel.

[0069] In the calcium treatment operation, pure calcium wire is fed into the molten steel through a wire feeder at a feeding speed of ≥2m / min. After calcium treatment, the molten steel composition is O≤0.0015%, S≤0.0008%, N≤0.004%, Ca:0.001%~0.002%, and the temperature is 1540℃~1560℃.

[0070] In some embodiments, the calcium treatment includes feeding pure calcium wire or calcium wire containing silicon into molten steel using a wire feeder at a feeding speed ≥2m / min.

[0071] In some embodiments, the temperature of the refined molten steel is 1540°C to 1560°C.

[0072] The refined molten steel is the molten steel transferred from the ladle to the continuous casting crystallizer.

[0073] Examples The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0074] Examples 1-8 and Comparative Examples 1-3 This embodiment provides a high-strength steel and its preparation method. The preparation method mainly includes the following steps: converter, argon station, LF furnace, RH (Si-Ca treatment), continuous casting, slab inspection, heating, rough rolling, finish rolling, laminar flow cooling, coiling, leveling, quenching, tempering, and surface quality inspection.

[0075] The chemical composition of the examples and comparative examples is shown in Table 1 below.

[0076] The main process parameters for the examples and comparative examples are shown in Table 2 below.

[0077] The performance test results of the steel plates obtained in the examples and comparative examples are shown in Table 3 below. Table 1 shows the mass percentage of the chemical composition of the high-strength steels in each embodiment and comparative example.

[0078] The portion of the high-strength steel that is 100% short in the table is due to Fe and unavoidable impurity elements.

[0079] Table 2 shows the main process parameters for the preparation methods of high-strength steel in each embodiment and comparative example.

[0080] Test section The high-strength steel plates obtained in the examples and comparative examples were tested.

[0081] 1. Testing of the mechanical properties of high-strength steel plates: The high-strength steel plates prepared in the examples were sampled according to GB / T228.1-2021 "Metallic materials - Tensile testing - Part 1 - Room temperature test method"; Tensile tests were conducted using a German Zwick tensile testing machine with a load range of 50 to 1500 kN and a displacement speed of 2 mm / min. The tensile strength, yield strength, elongation, and other test data of the materials were obtained by computer-generated graphs. The test results are shown in Table 3.

[0082] 2. Impact energy testing of high-strength steel plates: The samples were tested according to GB / T229-2020 "Metallic materials Charpy pendulum impact test method".

[0083] 3. Test method for the qualified proportion of high-strength steel plates with R≥2.5a and 90° bend: The test specimens shall be tested in accordance with GB / T 232-2024 "Metallic Materials - Test Method for Bending".

[0084] 4. The test method for the shape of high-strength steel plates is to measure the shape according to GB / T 709-2019 "Dimensions, shape, weight and permissible deviations of hot-rolled steel plates and strips".

[0085] Table 3 shows the performance test results of the products made from high-strength steel in each embodiment and comparative example.

[0086] The " / " in the table indicates that the impact energy of the finished high-strength steel was not measured. The thickness of this high-strength steel is relatively small and it is not considered a necessary test indicator.

[0087] The performance parameters measured above are taken as average values.

[0088] Figure 1 The metallographic structure diagram of the high-strength steel plate of Embodiment 1 of this application is shown; from Figure 1 The steel plate of Example 1 exhibits a uniform and fine tempered sorbite structure, which has good structural uniformity and provides a basis for high strength and good ductility.

[0089] Figure 2 This paper shows a calcium sulfide morphology diagram of the high-strength steel plate of Embodiment 1 of this application; from Figure 2 It can be observed that the CaS inclusions in the steel plate of Example 1 should appear as fine, dispersed, spherical or near-spherical particles, uniformly distributed in the steel plate matrix.

[0090] Figure 3 The energy spectrum of a high-strength steel plate containing calcium sulfide according to Embodiment 1 of this application is shown; by Figure 3 Energy dispersive spectroscopy (EDS) analysis of the steel plate from Example 1 confirmed that the main components of the inclusion were calcium (Ca) and sulfur (S), thus identifying it as calcium sulfide (CaS). In summary... Figure 2 and Figure 3 This demonstrates that calcium treatment technology can modify harmful, easily deformable, elongated manganese sulfide (MnS) inclusions in traditional steel into harmless, non-deformable spherical calcium sulfide (CaS) inclusions. Therefore, controlling the S, N, and O content in refined steel can control the quantity, morphology, and size of inclusions such as MnS, TiN, and TiO2, reducing the cracking risk of high-strength steel plates. Adding an appropriate amount of Ca to modify sulfides, transforming banded sulfides into spherical shapes, significantly improves the longitudinal formability of high-strength steel plates, which is beneficial for balancing the impact energy ratio.

[0091] Figure 4 The diagram shows the forming effect of the high-strength steel plate of Embodiment 1 of this application under condition 2.5a; from Figure 4 It can be observed that the steel plate of Example 1, under extremely harsh bending conditions with a mold radius only 2.5 times the plate thickness, remained intact at the bend without any cracks. This demonstrates that the product of Example 1 has excellent forming capability with ultra-small bending radius, meeting the customer's stringent requirements for forming performance R2.5~3.0a.

[0092] Figure 5 The image shows the morphology of manganese sulfide in the high-strength steel plate of Comparative Example 1 of this application; from Figure 5 It can be observed that the inclusions in the steel plate of Comparative Example 1 are slender strips or spindle shapes, distributed along the rolling direction.

[0093] Figure 6 The energy spectrum of a high-strength steel plate containing manganese sulfide, as shown in Comparative Example 1 of this application, is illustrated; Figure 6 Energy dispersive spectroscopy (EDS) analysis of the steel plate in Comparative Example 1 confirmed that the main components of the inclusion were manganese (Mn) and sulfur (S), which is a typical manganese sulfide (MnS) inclusion. Figure 5 and Figure 6 The combination demonstrates the inclusion state of traditional high-strength steel without calcium treatment. These elongated MnS inclusions become stress concentration points and crack initiation points when the plate is under stress, especially lateral stress or bending, severely deteriorating the lateral plasticity, toughness, and bending properties of the steel plate.

[0094] Figure 7 The diagram shows the forming effect of the high-strength steel plate of Comparative Example 2 of this application under condition 2.5a; from Figure 7 In the study, it can be observed that under the same bending condition of d=2.5a, the steel plate exhibits obvious cracks or even complete fracture at the bend. This demonstrates that if traditional techniques are used, whether due to improper inclusion control or an incompatible quenching process, the steel plate cannot meet the stringent forming requirement of r=2.5a.

[0095] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any skillful means or substitutions should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A high-strength steel plate with good formability, characterized in that, The high-strength steel plate comprises the following chemical composition by mass percentage: C: 0.14%–0.18%, Si: ≤0.10%, Mn: 1.30%–1.50%, P: ≤0.010%, S: ≤0.0008%, Cr: 0.30%–0.40%, Nb: 0.02%–0.04%, Ti: 0.010%–0.030%, V: 0.03%–0.05%, Mo: 0.30%–0.50%, B:

0. 0.0008%~0.0018%, Ca: 0.0010%~0.0020%, N: ≤0.004%, O: ≤0.0015%, Als: 0.010%~0.040%, with the balance being iron and unavoidable impurities, carbon equivalent ≤0.57, and 0.8≤([Ca]–0.75*[O]) / [S]≤1.5, where [Ca], [O] and [S] represent the mass content of Ca, O and S elements in the high-strength steel plate, respectively.

2. The high-strength steel plate according to claim 1, characterized in that, The high-strength steel plate has a single tempered sorbite microstructure with an average size of 3-5 micrometers.

3. The high-strength steel plate according to claim 1, characterized in that, The thickness of the high-strength steel plate is 3.0 to 10.0 mm.

4. The high-strength steel plate according to claim 1, characterized in that, The unevenness of the high-strength steel plate is ≤2mm / m.

5. The high-strength steel plate according to claim 1, characterized in that, The mechanical properties of the quenched and tempered steel plate of the high-strength steel plate meet the following requirements: yield strength R eL ≥960MPa, tensile strength R m ≥1000MPa, elongation A: ≥13%; impact energy KV2 at -40℃ ≥140J, impact energy aspect ratio ≥0.8; forming performance R ≥2.5a, 90° bending qualified.

6. A method for preparing a high-strength steel plate with good formability, characterized in that, The method includes: Refined steel is continuously cast to obtain a billet, which comprises the following chemical composition by mass percentage: C: 0.14%–0.18%, Si: ≤0.10%, Mn: 1.30%–1.50%, P: ≤0.010%, S: ≤0.0008%, Cr: 0.30%–0.40%, Nb: 0.02%–0.04%, Ti: 0.010–0.030%, V: 0.03–0.05%, Mo: 0.30–0.50%, B: 0.0008–0.0018%, Ca: 0.0010–0.0020%, N: ≤0.004%, O: ≤0.0015%, Als: 0.010%–0.040%, with the balance being iron and unavoidable impurities, and a carbon equivalent ≤0.

57. The billet is subjected to heating, hot rolling, laminar flow cooling, coiling, leveling, quenching and tempering to obtain a high-strength steel plate. The holding time for quenching is (1.6*t+k) min, where k is 8~12 and t is the thickness of the steel plate in mm. The quenching adopts a roll-pressing quenching method. The roll gap setting value for quenching is equal to the thickness of the high-strength steel plate. The water pressure for quenching is 0.8MPa, and the water ratio applied to the upper and lower surfaces of the high-strength steel plate is 1:(1.2~1.5).

7. The method according to claim 6, characterized in that, The tempering temperature is 580±10℃, and the tempering holding time is (1.6*t+Q)min, where Q is 28~35.

8. The production method according to claim 6, characterized in that, Before continuously casting the refined molten steel to obtain the billet, the method further includes: smelting the molten iron in a converter, refining it in an LF furnace, vacuum treating it in an RH furnace, and treating it with Si-Ca, so that the chemical composition of the refined molten steel meets the following requirements: O≤0.0015%, S≤0.0008%, N≤0.004%, Ca:0.001%~0.002%.

9. The method according to claim 8, characterized in that, The Si-Ca treatment involves feeding pure calcium wire into molten steel using a wire feeder at a feeding speed ≥2m / min.

10. The method according to any one of claims 6 to 9, characterized in that, The temperature of the refined molten steel is 1540℃~1560℃.

Images