A thin-gauge high-strength steel with a tensile strength greater than or equal to 750 MPa and a preparation method thereof

Abstract

This application provides a thin-gauge high-strength steel with a tensile strength greater than or equal to 750 MPa and a method for preparing the same. The thin-gauge high-strength steel with a tensile strength greater than or equal to 750 MPa comprises the following components by mass percentage: C: 0.05%–0.07%, Si: 0.05%–0.15%, Mn: 1.5%–1.7%, Nb: 0.05%–0.07%, Ti: 0.1%–0.13%, Alt: 0.01%–0.03%, P: ≤0.013%, S: ≤0.001%, N: ≤0.003%, with the remainder being iron and unavoidable impurities. This allows the thin-gauge high-strength steel to achieve a balance of high strength, high toughness, and good formability.

Description

Technical Field

[0001] This application relates to the field of steel technology, specifically to a thin-gauge high-strength steel with a tensile strength greater than or equal to 750 MPa and its preparation method. Background Technology

[0002] With economic development and increasing environmental awareness, many industries are demanding thinner structural components and preferring to use relatively cheaper hot-rolled steel instead of cold-rolled steel. This demand is particularly strong in heavy-duty trucks, special containers, and automotive parts, where the need for high-strength, ultra-thin hot-rolled steel is growing daily. These sectors require steel with thinner or even ultra-thin specifications, high strength, excellent elongation, and good cold bending and welding properties.

[0003] Replacing some thick-gauge plain carbon steel with ultra-thin high-strength hot-rolled steel can reduce the weight of transportation equipment, thereby saving energy; it can also replace some cold-rolled sheets of the same specifications, greatly improving formability and reducing procurement costs. The existing technologies described above all suffer from one or more of the following problems: 1) They mainly rely on adding large amounts of alloying elements, such as Cu, Cr, V, and Mo, to improve mechanical properties, resulting in high costs; 2) Ultra-thin high-strength cold-rolled steel requires cold rolling and annealing processes to obtain, leading to high process costs and low elongation. Summary of the Invention

[0004] This application provides a thin-gauge high-strength steel with a tensile strength greater than or equal to 750 MPa and its preparation method, aiming to reduce the problems of high loss and high production cost of non-oriented electrical steel.

[0005] In a first aspect, embodiments of this application provide a thin-gauge high-strength steel with a tensile strength greater than or equal to 750 MPa, comprising the following components by mass percentage: C: 0.05%-0.07%, Si: 0.05%-0.15%, Mn: 1.5%-1.7%, Nb: 0.05%-0.07%, Ti: 0.1%-0.13%, Alt: 0.01%-0.03%, P: ≤0.013%, S: ≤0.001%, N: ≤0.003%, with the remainder being iron and unavoidable impurities.

[0006] In some embodiments, the elongation A of the high-strength steel is greater than or equal to 16%.

[0007] In some embodiments, the thickness of the high-strength steel is 1.5mm-3mm.

[0008] Secondly, embodiments of this application provide a method for preparing thin-gauge high-strength steel with a tensile strength greater than or equal to 750 MPa, including hot metal desulfurization, converter blowing, refining, continuous casting, rotary descaling, soaking furnace, high-pressure water descaling, finishing rolling, laminar flow cooling, and coiling processes; wherein, the high-strength steel comprises the following components by mass percentage: C: 0.05%-0.07%, Si: 0.05%-0.15%, Mn: 1.5%-1.7%, Nb: 0.05%-0.07%, Ti: 0.1%-0.13%, Alt: 0.01%-0.03%, P: ≤0.013%, S: ≤0.001%, N: ≤0.003%, with the remainder being iron and unavoidable impurities.

[0009] In some embodiments, in the soaking furnace process, the temperature at which the soaking furnace exits is 1150°C-1250°C.

[0010] In some embodiments, the final rolling temperature in the finishing rolling process is 870°C-930°C.

[0011] In some embodiments, the finishing rolling process includes 7-stand finishing rolling, wherein the pass reduction rates from the 1st to the 7th pass in the finishing rolling are, in sequence: 55%-65%, 50%-60%, 40%-50%, 30%-40%, 25%-35%, 20%-35%, and 10%-20%; and the rolling temperatures from the 1st to the 7th pass are, in sequence: 1040℃-1080℃, 1000℃-1050℃, 960℃-1030℃, 940℃-990℃, 930℃-980℃, 910℃-960℃, and 870℃-930℃.

[0012] In some embodiments, during the continuous casting process, liquid core pressing is used to reduce the billet thickness from 70mm-90mm to 50mm-55mm.

[0013] In some embodiments, during the laminar flow cooling process, the average cooling rate is 20°C / s-50°C / s.

[0014] In some embodiments, during the laminar flow cooling process, the first 10m-15m of the finished strip is not cooled, while the strip beyond 10m-15m undergoes laminar flow cooling.

[0015] In some embodiments, the descaling pressure in the high-pressure water descaling process is 30MPa-38MPa.

[0016] Compared with the prior art, this application has at least the following beneficial effects: (1) This application takes advantage of the characteristics of the short process of continuous casting and rolling of thin slabs. Based on the principle of grain refinement and nano-sized precipitate precipitation strengthening of steel, it does not add precious metals such as Cu, Cr, Mo, and V, but only uses Nb and Ti micro-alloying technology to produce high-performance steel plates with tensile strength ≥750MPa.

[0017] (2) Since Ti is a highly reactive element, it will react with elements such as O, N, and S in the molten steel first, thereby reducing the effective Ti content and affecting the strengthening effect of TiC. Therefore, the technical solution of this application can effectively reduce the reaction consumption of Ti element by strictly controlling the content of S, N, and O elements within an extremely low range, thereby improving the strengthening effect of TiC.

[0018] (3) The method for preparing thin-gauge high-strength steel with a tensile strength greater than or equal to 750MPa provided in this application adopts a high-temperature steel burning and high-temperature rolling process, which reduces the rolling mill load; the load distribution of each stand of the finishing mill and the laminar flow cooling method are adjusted to obtain high-performance steel plates with good plate shape, thickness as low as 1.5mm and tensile strength ≥750MPa.

[0019] (4) The preparation method of thin-gauge high-strength steel with tensile strength greater than or equal to 750 MPa provided in this application can give full play to the uniform temperature of the thin slab continuous casting and rolling process, effectively solve the problem of large performance fluctuation of Ti microalloyed steel, and make the fluctuation range of yield strength and tensile strength in the whole coil direction and plate width direction within 50 MPa.

[0020] (5) The thin-gauge high-strength steel with a tensile strength greater than or equal to 750 MPa provided in this application has a simpler process and a significant cost advantage compared to cold-rolled materials; compared to hot-rolled materials, it can be "strengthened and thinned", which also has a cost advantage. Detailed Implementation

[0021] 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 embodiments described in this specification are merely for explaining this application and are not intended to limit it.

[0022] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, just as any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an undefined range.

[0023] In this description, 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.

[0024] 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 this application, guidance is provided through a series of embodiments that can be combined in various forms.

[0025] As described in the background art, the prior art uses thin-gauge hot-rolled high-strength steel to replace thick-gauge ordinary carbon steel, and also replaces some cold-rolled steel of the same specifications. However, this thin-gauge hot-rolled high-strength steel requires the addition of a large amount of alloying elements such as Cu, Cr, V, and Mo to improve the mechanical properties of the steel, which leads to an increase in the cost of the steel. For cold-rolled thin-gauge steel, it is necessary to go through cold rolling and annealing processes to obtain cold-rolled steel with the required strength. The process cost is high, and the elongation of the thin-gauge steel obtained is low, which does not meet the performance requirements of some scenarios.

[0026] In view of this, the embodiments of this application provide thin-gauge high-strength steel with a tensile strength greater than or equal to 750MPa. By designing the chemical composition and preparation method of the steel, the steel can achieve thin gauge, high strength, and high elongation while reducing costs and improving production efficiency.

[0027] In a first aspect, embodiments of this application provide thin-gauge high-strength steel with a tensile strength greater than or equal to 750 MPa, comprising the following components by mass percentage: C: 0.05%-0.07%, Si: 0.05%-0.15%, Mn: 1.5%-1.7%, Nb: 0.05%-0.07%, Ti: 0.1%-0.13%, Alt: 0.01%-0.03%, P: ≤0.013%, S: ≤0.001%, N: ≤0.003%, with the remainder being iron and unavoidable impurities.

[0028] The following describes in detail the role of each chemical element in the thin-gauge high-strength steel with a tensile strength greater than or equal to 750 MPa provided in the embodiments of this application: Carbon (C): Carbon is a fundamental strengthening element. Through solid solution strengthening, it integrates into the ferrite matrix, providing basic strength support for steel to achieve a tensile strength ≥750MPa. This application adopts a low-carbon design, with the core objective of balancing strength and high elongation: on the one hand, it avoids the decrease in plasticity and increased cold brittleness caused by high carbon content, enabling thin-gauge steel to possess good formability and elongation properties, meeting the plasticity requirements of subsequent processing and application scenarios; on the other hand, the low-carbon design can reduce the crack sensitivity of steel during hot rolling, adapting to the stable production of thin-gauge steel, while eliminating the need to rely on a large amount of expensive alloying elements to compensate for strength, indirectly reducing alloy costs. In addition, the low carbon content can also work synergistically with microalloying elements to create favorable conditions for fine-grain strengthening and precipitation strengthening, achieving a balance between strength and plasticity. Therefore, the carbon mass fraction in this application is controlled at 0.05%-0.07%.

[0029] Silicon (Si): Silicon primarily functions as a weak solid solution strengthening element and a deoxidizer. Firstly, as a weak solid solution strengthening element, silicon can moderately supplement the strength of the steel matrix, helping to achieve the tensile strength target of 750 MPa without excessively damaging the steel's plasticity. Secondly, silicon is an effective deoxidizer, capable of removing free oxygen from molten steel, reducing the formation of oxide inclusions, improving steel cleanliness, and preventing inclusions from becoming fracture sources under stress, thereby ensuring and improving the high elongation and mechanical property stability of dimensional steel. Therefore, the mass fraction of silicon in this application is controlled at 0.05%-0.15%.

[0030] Manganese (Mn): Manganese is a core strengthening element in steel. It possesses extremely strong solid solution strengthening capabilities, significantly enhancing the strength of the steel matrix. Furthermore, manganese is far less expensive than precious alloying elements such as Cu, Cr, V, and Mo, allowing it to replace a large number of expensive alloys in existing technologies, significantly reducing alloy costs. Manganese also refines steel grains, improving both strength and plasticity / toughness through grain refinement, achieving a synergistic effect of "high strength + high elongation," addressing the pain point of "high strength inevitably leading to low elongation" in existing thin-gauge steel. Additionally, manganese lowers the brittle-cold transition temperature of steel, improving the low-temperature toughness and formability of thin-gauge steel. It also promotes the stabilization of austenite during hot rolling, enabling steel to achieve a tensile strength of 750 MPa in the hot-rolled state without the need for subsequent processes such as cold rolling and annealing, significantly reducing process costs and improving production efficiency. Therefore, the mass fraction of manganese in this application is controlled at 1.5%-1.7%.

[0031] Niobium (Nb): As a trace microalloying element, niobium works synergistically with manganese to exert both grain refinement and precipitation strengthening effects, making it a key auxiliary element for achieving "high strength and high ductility" in thin-gauge steel. On the one hand, niobium can inhibit austenite grain growth during hot rolling, promoting the formation of an ultra-fine and uniform grain structure in the steel. This grain refinement strengthening not only further enhances the strength of the steel but also effectively improves its plasticity, enabling thin-gauge steel to possess good elongation on top of high strength. Simultaneously, it improves the uniformity of mechanical properties along the thickness direction, reducing performance fluctuations caused by grain inhomogeneity in thin-gauge steel. On the other hand, niobium can combine with C and N in molten steel to form nanoscale Nb(C,N) precipitates. This precipitation strengthening further enhances the strength of the steel, and the precipitate has minimal impact on the plasticity of the steel, achieving a balance between strength and plasticity. Furthermore, niobium requires only trace amounts to achieve a significant strengthening effect, with dosages far lower than those of expensive alloys such as Cu and Cr in existing technologies, without incurring excessive additional costs, thus balancing strengthening effect and economy. Therefore, the mass fraction of niobium in this application is controlled at 0.05%-0.07%.

[0032] Titanium (Ti): Titanium, in synergy with niobium, is an important microalloying element for improving the stability of mechanical properties and high elongation of steel. Titanium is a strong carbide-nitride forming element, capable of fully combining with free C and N in molten steel to form fine and uniform Ti(C,N) precipitates. This precipitation strengthening enhances the steel's strength, helping to achieve the 750 MPa tensile strength target. Titanium can also fix free N in molten steel, preventing age hardening, decreased plasticity, and deterioration of elongation caused by free N, thus improving the plastic stability of thin-gauge steel. Simultaneously, it reduces the ineffective consumption of niobium, allowing niobium to more fully exert its grain-refining and precipitation strengthening effects, forming a synergistic strengthening effect with niobium and further optimizing the performance matching of "high strength + high elongation". Compared with the large amounts of expensive alloys added in existing technologies, titanium is less expensive, and significant effects can be achieved with minimal addition. Therefore, the mass fraction of titanium in this application is controlled at 0.1%-0.13%.

[0033] Acid-soluble aluminum (Alt): Acid-soluble aluminum primarily functions as a final deoxidizer and grain refiner, ensuring high elongation and performance stability of steel. As a final deoxidizer, acid-soluble aluminum can further remove residual trace oxygen in molten steel, reduce the formation of oxide inclusions, improve steel cleanliness, and prevent inclusions from disrupting the continuity of the steel, thereby reducing the risk of fracture under stress and improving the high elongation of thin-gauge steel. Simultaneously, acid-soluble aluminum can promote grain refinement, improve the toughness and plasticity of the steel, and ensure good uniformity of mechanical properties in thin-gauge states, meeting the production and application requirements of thin-gauge steel. This application controls the acid-soluble aluminum content to a low range, reducing the increase in alumina inclusions caused by excessive aluminum, balancing deoxidation effect and steel cleanliness. Therefore, the mass fraction of Alt in this application is controlled at 0.01%-0.03%.

[0034] Phosphorus (P): Phosphorus is a harmful impurity element that needs to be strictly controlled in the steel used in this application. Its negative impact on the performance of steel is mainly reflected in the following aspects: Phosphorus tends to segregate at the grain boundaries of steel, leading to a decrease in grain boundary bonding strength, causing cold brittleness of the steel, and significantly reducing the plasticity and elongation of the steel. Thin-gauge steel is more sensitive to brittleness, and even trace amounts of phosphorus can cause cracking and fracture during processing or use. Therefore, this application strictly controls the phosphorus content to ≤0.013% to reduce the damage of phosphorus to the plasticity and elongation of steel, and improve the mechanical property stability and safety of thin-gauge high-strength steel.

[0035] Sulfur (S): Sulfur is another harmful impurity element that needs to be strictly limited in the steel used in this application. Its harm mainly stems from the fact that sulfur combines with manganese in molten steel to form MnS plastic inclusions. These inclusions cause anisotropy in the steel, significantly reducing its transverse elongation and formability. Furthermore, during the hot rolling process of thin-gauge steel, MnS inclusions easily induce cracking and delamination, affecting the surface quality and mechanical integrity of the steel. This application employs extremely low sulfur control, limiting the sulfur content to ≤0.001%, which can effectively reduce the formation of MnS inclusions and ensure the uniformity of the mechanical properties and the reliability of forming of the steel.

[0036] Nitrogen (N): As a harmful impurity element, excessive nitrogen content can adversely affect the properties of steel. Free nitrogen combines with microalloying elements (Nb, Ti) in the steel, consuming some Nb and Ti and reducing the strengthening efficiency of microalloying elements. Simultaneously, free nitrogen causes age hardening in the steel, leading to decreased plasticity and deterioration of elongation. Furthermore, excessive nitrogen can cause defects such as bubbles and porosity in the steel, affecting the density and mechanical property stability of thin-gauge steel. Therefore, this application strictly controls the nitrogen content to ≤0.003% to reduce the presence of free nitrogen, allowing Nb and Ti to fully exert their strengthening effects while ensuring the plasticity and density of the steel, thus meeting the performance requirements of thin-gauge high-strength steel.

[0037] According to the embodiments of this application, by controlling the chemical composition of thin-gauge high-strength steel within the above-mentioned range, when the steel thickness is in the range of 1.5mm-3mm, the tensile strength of thin-gauge high-strength steel can be above 750MPa, and the elongation A can be greater than or equal to 16%.

[0038] An embodiment of the second aspect of this application provides a method for preparing thin-gauge high-strength steel with a tensile strength greater than or equal to 750 MPa, including hot metal desulfurization, converter blowing, refining, continuous casting, rotary descaling, soaking furnace heating, high-pressure water descaling, finishing rolling, laminar flow cooling, and coiling processes; wherein, the high-strength steel comprises the following components by mass percentage: C: 0.05%-0.07%, Si: 0.05%-0.15%, Mn: 1.5%-1.7%, Nb: 0.05%-0.07%, Ti: 0.1%-0.13%, Alt: 0.01%-0.03%, P: ≤0.013%, S: ≤0.001%, N: ≤0.003%, with the remainder being iron and unavoidable impurities.

[0039] In some embodiments, during the soaking furnace heating process, the furnace outlet temperature is 1150℃-1250℃. For example, it can be 1150℃, 1160℃, 1170℃, 1180℃, 1190℃, 1200℃, 1210℃, 1220℃, 1230℃, 1240℃, 1250℃, or any range of the above values.

[0040] The core of the soaking furnace heating process is to heat the descaled billet to a suitable temperature, providing good rolling plasticity and microstructure conditions for the subsequent finishing rolling process. In this embodiment, controlling the soaking furnace exit temperature within the range of 1150℃-1250℃ ensures that the billet is fully heated, guaranteeing that microalloying elements such as Nb and Ti in the molten steel are fully dissolved into austenite, creating conditions for precipitation strengthening and grain refinement strengthening in the subsequent finishing rolling process. If the temperature is too low, Nb and Ti cannot be fully dissolved, and sufficient nanoscale precipitates cannot be formed during the subsequent finishing rolling process, resulting in insufficient strengthening effect; if the temperature is too high, it will cause excessive growth of austenite grains, making it difficult to refine the grains through finishing rolling, leading to a decrease in the plasticity of the steel and failing to meet the high elongation requirements. At the same time, excessively high temperatures will increase energy consumption and costs, and may also lead to a thickening of the iron oxide scale on the billet surface, increasing the descaling load.

[0041] In some embodiments, the final rolling temperature in the finishing rolling process is 870°C-930°C. For example, it can be 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, or any range of the above values.

[0042] According to the embodiments of this application, by controlling the final rolling temperature at 870℃-930℃, the final rolling process can be completed in the austenite region, avoiding the decrease in plasticity caused by rolling in the ferrite region. Simultaneously, it can reduce excessive austenite grain growth, ensuring stable grain size after refinement. During the cooling process of the steel after final rolling, austenite rapidly transforms into ferrite, while Nb and Ti further precipitate, forming a large number of nanoscale precipitates. This fully leverages the synergistic effect of grain refinement strengthening and precipitation strengthening, improving the tensile strength of the steel. If the final rolling temperature is too high, it will lead to austenite grain growth, resulting in poor refinement and insufficient strength. If the final rolling temperature is too low, it will enter the ferrite rolling region, reducing the plasticity of the steel and failing to meet the high elongation requirements, while also easily leading to rolling cracks.

[0043] In some embodiments, the winding temperature in the winding process can be 600°C-650°C. For example, it can be 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, or any range of the above values.

[0044] In some embodiments, the finishing rolling process includes 7-stand finishing rolling, wherein the pass reduction rates from the 1st to the 7th pass in the finishing rolling are, in sequence: 55%-65%, 50%-60%, 40%-50%, 30%-40%, 25%-35%, 20%-35%, and 10%-20%; and the rolling temperatures from the 1st to the 7th pass are, in sequence: 1040℃-1080℃, 1000℃-1050℃, 960℃-1030℃, 940℃-990℃, 930℃-980℃, 910℃-960℃, and 870℃-930℃.

[0045] According to the embodiments of this application, the rolling temperature adopts a "gradient cooling" design, with the final rolling temperature controlled at 870℃-930℃. The gradient cooling design works in conjunction with the pass reduction rate. The first three passes have higher temperatures (1040℃-1080℃ to 960℃-1030℃), corresponding to a high reduction rate. The higher temperature ensures the plasticity of the billet and reduces cracking caused by high deformation. At the same time, the austenite grains have good stability at high temperatures, and grain refinement can be achieved through high deformation. The middle two passes gradually decrease in temperature (940℃-990℃ to 930℃-980℃). The temperature reduction promotes the precipitation of Nb and Ti from austenite, forming fine precipitates that play a preliminary precipitation strengthening role. At the same time, the temperature reduction inhibits austenite grain growth, preserving the refined grains.

[0046] In some embodiments, during the continuous casting process, liquid core pressing is used to reduce the billet thickness from 70mm-90mm to 50mm-55mm.

[0047] According to the embodiments of this application, the liquid core reduction process is used to reduce the billet thickness from 70mm-90mm to 50mm-55mm, which can reduce the rolling load of subsequent finishing rolling processes. Pre-thinning the billet through liquid core reduction helps reduce problems such as steel cracking and surface quality deterioration caused by excessive reduction during finishing rolling, while also shortening finishing rolling time and improving production efficiency. During liquid core reduction, the billet is in a semi-solidified state, and the reduction action can break up the columnar crystals inside the billet, promoting grain refinement and laying the foundation for fine grain strengthening in subsequent soaking furnace heating and finishing rolling processes. In addition, liquid core reduction can reduce defects such as porosity and shrinkage cavities inside the billet, increase the billet density, avoid fluctuations in mechanical properties caused by internal defects in thin-gauge steel, and improve tensile strength.

[0048] In some embodiments, the average cooling rate in the laminar flow cooling process is 20℃ / s-50℃ / s. For example, it can be 20℃ / s, 21℃ / s, 22℃ / s, 23℃ / s, 24℃ / s, 25℃ / s, 26℃ / s, 27℃ / s, 28℃ / s, 29℃ / s, 30℃ / s, 31℃ / s, 32℃ / s, 33℃ / s, 34℃ / s, 35℃ / s, 36℃ / s, 37℃ / s, 38℃ / s, 39℃ / s, 40℃ / s, 41℃ / s, 42℃ / s, 43℃ / s, 44℃ / s, 45℃ / s, 46℃ / s, 47℃ / s, 48℃ / s, 49℃ / s, 50℃ / s, or any range of the above values.

[0049] In some embodiments, during the laminar flow cooling process, the first 10m-15m of the finished steel strip is not cooled, while the strip beyond 10m-15m undergoes laminar flow cooling. This helps to produce thin-gauge steel with good sheet shape and reduces steel accumulation.

[0050] In some embodiments, to ensure that the strip after laminar flow cooling has a precise red-hot temperature, different laminar flow cooling methods can be adopted according to the thickness of the strip. For example, for strips with a thickness of less than 2 mm, a slow cooling process in the front section can be adopted; for strips with a thickness of more than 2 mm, a fast cooling process in the front section can be adopted.

[0051] In some embodiments, the descaling pressure in the high-pressure water descaling process is 30MPa-38MPa. For example, it can be 30MPa, 31MPa, 32MPa, 33MPa, 34MPa, 35MPa, 36MPa, 37MPa, 38MPa, or any range of the above values.

[0052] According to the embodiments of this application, by controlling the descaling pressure in the high-pressure water descaling process within the aforementioned range, it is beneficial to better remove iron oxide scale, reduce the embedding of iron oxide scale into the steel surface during subsequent finishing rolling, and improve the surface precision and quality of thin-gauge steel. Simultaneously, it can reduce the consumption of alloying elements by iron oxide scale, and improve the strengthening efficiency of elements such as Mn, Nb, and Ti. When the descaling pressure is too low, it is difficult to effectively remove iron oxide scale, and the residual iron oxide scale will lead to surface defects and a decrease in mechanical properties of the steel. When the descaling pressure is too high, it may impact the surface of the billet, causing microcracks on the billet surface. These microcracks in thin-gauge billets will further expand during subsequent finishing rolling, causing the steel to crack. Furthermore, excessively high pressure will increase energy consumption and raise costs.

[0053] Example 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.

[0054] Example 1 S10, the chemical composition (mass fraction) of thin-gauge high-strength steel is shown in Table 1, and it is prepared according to the following method: S20 is used to obtain refined steel by desulfurizing molten iron, smelting it in a converter, blowing it with argon, and refining it in an LF furnace. S30 involves continuously casting refined molten steel to obtain a billet; the continuous casting adopts an electromagnetic stirring alternating stirring mode, with the alternation time changing every 30 seconds, a current of 250A, a frequency of 10Hz, and a strong cooling mode for cooling, with a liquid level fluctuation range of ±3mm. S40, after the billet is descaled by rotation, it is heated in a soaking furnace, where the outlet temperature of the soaking furnace is 1200℃. S50 involves high-pressure water descaling of the cast billet after soaking in a heating furnace at a pressure of 35 MPa; followed by 7-stand finishing rolling to obtain a slab. The reduction rate and temperature for each pass during the finishing rolling process are as follows: F1: 60%, 1060℃; F2: 55%, 1020℃; F3: 46%, 990℃; F4: 34%, 970℃; F5: 30%, 950℃; F6: 28%, 930℃; F7: 15%, 900℃. S60 involves laminar flow cooling of the slab at an average cooling rate of 35℃ / s, followed by coiling to obtain thin-gauge high-strength steel at a coiling temperature of 630℃.

[0055] Examples 2-6 The chemical composition of the high-strength steel is shown in Table 1, and the preparation method parameters of the high-strength steel are also shown in Table 1. The rest are the same as the preparation method in Example 1.

[0056] Comparative Example 1 - Comparative Example 2 The chemical composition of the high-strength steel is shown in Table 1, the preparation parameters of the high-strength steel are shown in Table 1, and the rest are the same as the preparation method in Example 1.

[0057] Table 1 Table 2 The performance data of the high-strength steel in Examples 1 to 6 and Comparative Examples 1 to 2 are shown in Table 3.

[0058] Table 3 As shown in Table 3, by controlling the chemical composition and preparation process of high-strength steel within a specific range, it is beneficial to ensure that the tensile strength and yield strength of thin-gauge high-strength steel are both within a high range, while the steel can also have high elongation and cold bending performance.

[0059] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered 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 thin-gauge high-strength steel with a tensile strength greater than or equal to 750 MPa, characterized in that, It includes the following components by mass percentage: C: 0.05%-0.07%, Si: 0.05%-0.15%, Mn: 1.5%-1.7%, Nb: 0.05%-0.07%, Ti: 0.1%-0.13%, Alt: 0.01%-0.03%, P: ≤0.013%, S: ≤0.001%, N: ≤0.003%, with the remainder being iron and unavoidable impurities.

2. The high-strength steel according to claim 1, characterized in that, The elongation A of the high-strength steel is greater than or equal to 16%; and / or, The thickness of the high-strength steel is 1.5mm-3mm.

3. A method for preparing thin-gauge high-strength steel with a tensile strength greater than or equal to 750 MPa, characterized in that, It includes processes such as hot metal desulfurization, converter blowing, refining, continuous casting, rotary descaling, soaking furnace heating, high-pressure water descaling, finishing rolling, laminar flow cooling, and coiling. The high-strength steel comprises the following components by mass percentage: C: 0.05%-0.07%, Si: 0.05%-0.15%, Mn: 1.5%-1.7%, Nb: 0.05%-0.07%, Ti: 0.1%-0.13%, Alt: 0.01%-0.03%, P: ≤0.013%, S: ≤0.001%, N: ≤0.003%, with the remainder being iron and unavoidable impurities.

4. The preparation method according to claim 3, characterized in that, In the heating process of the soaking furnace, the temperature of the soaking furnace exiting the furnace is 1150℃-1250℃.

5. The preparation method according to claim 3, characterized in that, In the finishing rolling process, the final rolling temperature is 870℃-930℃.

6. The preparation method according to claim 3, characterized in that, The finishing rolling process includes 7-stand finishing rolling, wherein the reduction rates of the 1st to 7th passes in the finishing rolling are, in order: 55%-65%, 50%-60%, 40%-50%, 30%-40%, 25%-35%, 20%-35%, and 10%-20%; and the rolling temperatures of the 1st to 7th passes are, in order: 1040℃-1080℃, 1000℃-1050℃, 960℃-1030℃, 940℃-990℃, 930℃-980℃, 910℃-960℃, and 870℃-930℃.

7. The preparation method according to claim 3, characterized in that, In the continuous casting process, liquid core pressing is used to reduce the billet thickness from 70mm-90mm to 50mm-55mm.

8. In the preparation method according to claim 3, the average cooling rate in the laminar flow cooling process is 20℃ / s-50℃ / s.

9. The preparation method according to claim 8, characterized in that, In the laminar flow cooling process, the first 10m-15m of the finished steel strip is not cooled, while the steel strip beyond 10m-15m undergoes laminar flow cooling treatment.

10. The preparation method according to claim 3, characterized in that, In the high-pressure water descaling process, the descaling pressure is 30MPa-38MPa.

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