A 900MPa high-strength steel, its preparation method and application

Abstract

This application relates to a 900MPa grade high-strength steel, its preparation method, and its application. The method includes: obtaining a slab with a set chemical composition; heating the slab and controlling the heating process parameters to refine the grains in the slab, followed by hot rolling, cooling, and coiling to obtain a hot-rolled coil; pickling the hot-rolled coil, followed by cold rolling using a reciprocating rolling mode, and controlling the reduction rate of the cold rolling to ensure sufficient recrystallization driving force inside the pickled hot-rolled coil to obtain a cold-hardened coil; continuously and fully annealing the cold-hardened coil, and controlling the process parameters of the soaking section of the continuous full annealing to eliminate the fibrous structure in the microstructure of the cold-hardened coil, followed by leveling to obtain the 900MPa grade high-strength steel. The 900MPa grade high-strength steel prepared by this application has excellent formability.

Description

Technical Field

[0001] This application relates to the field of steel preparation technology, and in particular to a 900MPa grade high-strength steel, its preparation method and application. Background Technology

[0002] To meet the demands of energy conservation, emission reduction, and lightweight vehicles, the automotive industry is increasingly using advanced high-strength steels (AHSS) such as transformation-strengthened ultra-high-strength DP, CP, and QP steels, which combine high strength and good formability, in vehicle bodies and numerous complex components. While these ultra-high-strength steels have seen rapid development, not all components are suitable for their use. For example, automotive seat frames and sliding rails, while meeting strength requirements, emphasize local formability, such as bending at lower bending radii, hole enlargement, and local flanging. Therefore, the local stress-strain behavior of the material during forming is particularly important. These components are better suited for manufacturing with low-alloy high-strength (HSLA) steels, which offer excellent local formability.

[0003] Car seat rails are critical safety components in automobiles, requiring high strength, high dimensional accuracy, and no cracks, as well as excellent bending performance. Currently, there are few ultra-high-strength low-alloy steels of 900MPa and above available on the market that meet the requirements for automotive seat frames and rails. Most are hot-rolled or semi-annealed products, and their overall quality, including cold bending performance, dimensional accuracy, and sheet shape, can no longer meet the demands of lightweighting and ensuring the safety and reliability of seats in automobiles. Therefore, there is an urgent need to develop a low-alloy high-strength steel with higher strength, better formability, and superior performance. Summary of the Invention

[0004] This application provides a 900MPa grade high-strength steel, its preparation method and application, to solve the following technical problem: how to improve the formability of 900MPa grade high-strength steel.

[0005] In a first aspect, this application provides a method for preparing 900MPa grade high-strength steel, the method comprising:

[0006] A slab with a specified chemical composition is obtained;

[0007] The slab is heated and the heating process parameters are controlled to refine the grains in the slab. Then, it is hot rolled, cooled, and coiled to obtain a hot-rolled coil.

[0008] The hot-rolled coil is pickled and then cold-rolled using a reciprocating rolling mode, and the reduction rate of the cold rolling is controlled so that the interior of the pickled hot-rolled coil has sufficient recrystallization driving force to obtain a cold-hardened coil.

[0009] The cold-hardened coil is subjected to continuous full annealing, and the process parameters of the soaking zone of the continuous full annealing are controlled to eliminate the fibrous structure in the microstructure of the cold-hardened coil. After leveling, a 900MPa grade high-strength steel is obtained.

[0010] Optionally, the heating process parameters include: a holding temperature of 1190℃~1270℃ and a holding time of ≥150min.

[0011] Optionally, the cold rolling reduction rate is 50% to 80%.

[0012] Optionally, the process parameters of the heat exchange section include: a temperature of 700℃~800℃ and a time of 60s~100s.

[0013] Optionally, the rolling force is 6000KN to 10000KN.

[0014] Optionally, the 900MPa grade high-strength steel meets the following mechanical properties: yield strength ≥900MPa, tensile strength ≥950MPa, elongation after fracture ≥8.0%, minimum mandrel diameter for 180° cold bending 0.5T, where T represents the thickness of the 900MPa grade high-strength steel.

[0015] Optionally, the specified chemical composition includes: C, Si, Mn, P, S, Al, Nb, Ti, N, H, and Fe; wherein, by mass fraction,

[0016] The C content is 0.06%–0.12%, the Si content is 0.15%–0.45%, and the Mn content is 1.20%.

[0017] The content of phosphorus is ≤1.70%, the content of phosphorus is ≤0.015%, the content of sulfur is ≤0.0030%, the content of al is 0.020% to 0.060%, the content of nitrogen is 0.02% to 0.08%, the content of titanium is 0.03% to 0.15%, the content of nitrogen is ≤0.005%, and the content of hydrogen is ≤2.0 ppm.

[0018] Optionally, obtaining a slab with a set chemical composition includes:

[0019] The molten iron is smelted using a "full three-stage desulfurization" process, followed by LF refining, RH refining, and continuous casting to obtain a slab with a set chemical composition.

[0020] Secondly, this application provides a 900MPa grade high-strength steel prepared by the method described in any embodiment of the first aspect.

[0021] Thirdly, this application provides the application of 900MPa high-strength steel as described in any embodiment of the second aspect in the manufacture of automotive seat slide rails.

[0022] The technical solutions provided in this application have the following advantages compared with the prior art:

[0023] The method for preparing the 900MPa-grade high-strength steel provided in this application includes: obtaining a slab with a set chemical composition; heating the slab and controlling the heating process parameters to refine the grains in the slab, followed by hot rolling, cooling, and coiling to obtain a hot-rolled coil; pickling the hot-rolled coil, followed by cold rolling using a reciprocating rolling mode, and controlling the reduction rate of the cold rolling to ensure sufficient recrystallization driving force inside the pickled hot-rolled coil to obtain a cold-hardened coil; continuously and fully annealing the cold-hardened coil, and controlling the process parameters of the soaking section of the continuous full annealing to eliminate the fibrous structure in the microstructure of the cold-hardened coil, followed by leveling to obtain the 900MPa-grade high-strength steel. Using a slab with a predetermined chemical composition ensures its high cleanliness and quality. Simultaneously, carefully designed heating process parameters guarantee the full dissolution of Nb and Ti microalloying elements in the austenite, preventing austenite grain growth and refining the grain size within the slab. Hot rolling, cooling, and coiling of the heated slab further refine the grain size. Pickling the hot-rolled coil imparts a good surface quality, facilitating subsequent cold rolling. Cold rolling the pickled hot-rolled coil using a reciprocating rolling process, with controlled reduction, provides sufficient recrystallization driving force for subsequent continuous full annealing, promoting a homogenized microstructure. Continuous full annealing of the cold-hardened coil, with controlled process parameters in the soaking zone, effectively eliminates fibrous structures. Leveling the cold-hardened coil after continuous annealing improves its shape and enhances its formability. In summary, the above-mentioned preparation method for 900MPa grade high-strength steel fully realizes the effects of fine grain strengthening, precipitation strengthening and dislocation strengthening, thereby improving the formability of 900MPa grade high-strength steel. Attached Figure Description

[0024] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 A schematic flowchart illustrating a method for preparing 900MPa high-strength steel according to an embodiment of this application;

[0027] Figure 2 Microstructure of a 900MPa high-strength steel provided in an embodiment of this application. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0030] In this application, the terms "including" or "comprising" mean "including but not limited to".

[0031] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0032] Firstly, this application provides a method for preparing 900MPa grade high-strength steel. Figure 1 A schematic flowchart illustrating a method for preparing 900MPa high-strength steel according to an embodiment of this application; please refer to [link / reference]. Figure 1 The method includes:

[0033] S1. Obtain a slab with a set chemical composition;

[0034] In some embodiments, the specified chemical composition includes: C, Si, Mn, P, S, Al, Nb, Ti, N, H, and Fe; wherein, by mass fraction,

[0035] The content of C is 0.06%–0.12%, the content of Si is 0.15%–0.45%, the content of Mn is 1.20%–1.70%, the content of P is ≤0.015%, the content of S is ≤0.0030%, the content of Al is 0.020%–0.060%, the content of Nb is 0.02%–0.08%, the content of Ti is 0.03%–0.15%, the content of N is ≤0.005%, and the content of H is ≤2.0ppm.

[0036] In this embodiment, carbon (C) is the most important solid solution strengthening element in high-strength steel, and is crucial for improving steel strength. During heat treatment, it forms carbonitrides with microalloyed Nb and Ti, playing a role in grain refinement and precipitation strengthening. However, excessively high C content (above 0.12%) may affect weldability and forming quality; excessively low C content (below 0.06%) may adversely affect strength. For example, the C content can be 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, etc.

[0037] Si is one of the solid solution strengthening elements. In steel, it does not form carbides but dissolves in ferrite or austenite in solid solution form, thus reducing the austenite phase region. Increasing Si content can improve the hardness, strength, and high-temperature fatigue strength of steel. However, excessively high Si content, exceeding 0.45%, may deteriorate the weldability of the steel. For example, the Si content mentioned above can be 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, etc.

[0038] Manganese (Mn) is also an important element for solid solution strengthening and expanding the austenite region. It can form MnS with sulfur, which can prevent hot brittleness caused by sulfur, thereby improving the hot working properties of steel. Mn forms a solid solution with Fe, increasing the hardness and strength of ferrite and austenite in steel. Mn also plays a role in refining pearlite by lowering the critical transformation temperature in steel, indirectly improving the strength of pearlitic steel. However, Mn easily causes microstructure segregation. When the Mn content is too high and exceeds 1.2%, it can easily lead to forming cracks in steel, deteriorating the overall properties of the steel, and also affecting weldability. For example, the Mn content mentioned above can be 1.20%, 1.30%, 1.40%, 1.50%, 1.60%, 1.70%, etc.

[0039] Phosphorus (P) also plays a role in solid solution strengthening, but while increasing strength, it significantly reduces plasticity and impact toughness, especially at low temperatures, making steel noticeably brittle—a phenomenon known as "cold brittleness." Furthermore, P tends to segregate at grain boundaries, deteriorating the material's mechanical properties. For example, the P content mentioned above can be 0.015%, 0.013%, 0.011%, 0.009%, etc.

[0040] Sulfur (S) originates from molten iron, steelmaking ores, and raw materials. It is a harmful element. FeS forms low-melting-point (985℃) compounds with Fe, while the hot working temperature of steel is generally above 1150℃. Therefore, during hot working of steel, the premature melting of FeS compounds leads to cracking of the workpiece, a phenomenon known as "hot brittleness." Sulfur reduces the ductility and toughness of steel, causing cracks during forging and rolling. It also negatively impacts weldability and reduces corrosion resistance. For example, the S content can be 0.003%, 0.0025%, 0.002%, etc.

[0041] Al is a major deoxidizing alloy in steelmaking. When added to steel as an alloying element, it can refine grains and fix nitrogen in the steel, thereby inhibiting aging of low-carbon steel and improving its toughness at low temperatures. For example, the Al content can be 0.020%, 0.030%, 0.040%, 0.050%, 0.060%, etc.

[0042] Ti is one of the commonly used microalloying elements in the metallurgical industry. In low-alloy steels, Ti can improve plasticity and toughness. Because Ti fixes nitrogen and sulfur and forms titanium carbide nanoprecipitates, it plays a role in refining grains and precipitation strengthening. The formation of carbides significantly improves the plasticity and impact toughness of steel. Alloy steels containing Ti have good mechanical and processing properties. However, Ti is easily oxidized and has a complex morphology. Excessive Ti content, exceeding 0.15%, can easily affect performance stability. For example, the aforementioned Ti content can be 0.03%, 0.05%, 0.07%, 0.09%, 0.11%, 0.13%, 0.15%, etc.

[0043] Nitrogen (Nb) is also a microalloying element. Nb mainly exists in the form of carbides, refining the grain size and improving the impact toughness of steel while lowering its brittle transition temperature. However, excessively high Nb content (above 0.08%) leads to a significant increase in cost. For example, the Nb content could be 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, or 0.08%.

[0044] Like carbon (C), nitrogen (N) can dissolve in iron to form interstitial solid solutions. However, while increasing strength and hardness, it decreases the toughness of steel and increases notch sensitivity. The brittle properties of steel caused by nitrogen are also a major cause of blue brittleness in steel. For example, the nitrogen content can be 0.005%, 0.004%, 0.003%, 0.002%, etc.

[0045] At the same time, the hydrogen (H) content should be limited. H generates numerous cracks in steel, significantly reducing its plasticity and toughness, leading to sudden breakage of parts during use. To prevent hydrogen embrittlement and subsequent cracking, the H content is limited to ≤2.0 ppm. For example, the H content could be 2.0%, 1.8%, 1.6%, 1.4%, etc.

[0046] In some embodiments, obtaining a slab with a predetermined chemical composition includes:

[0047] The molten iron is smelted using a "full three-stage desulfurization" process, followed by LF refining, RH refining, and continuous casting to obtain a slab with a set chemical composition.

[0048] In the embodiments of this application, the steelmaking adopts the "full three-stage desulfurization" smelting mode to obtain low S and low P molten steel. After LF+RH refining, deep desulfurization and degassing, and removal of inclusions, it is continuously cast to obtain a high-cleanliness slab with low P, low S, low N, and low H.

[0049] S2. The slab is heated and the heating process parameters are controlled to refine the grains in the slab. Then, it is hot rolled, cooled, and coiled to obtain a hot-rolled coil.

[0050] In some embodiments, the heating process parameters include: a holding temperature of 1190℃~1270℃ and a holding time of ≥150min.

[0051] In this embodiment of the application, the heating process parameters are defined as follows: the holding temperature is 1190℃~1270℃, and the holding time is ≥150min. This ensures that the Nb and Ti microalloying elements in the slab are fully dissolved in the austenite, preventing austenite grain growth and thus refining the grains. For example, the holding temperature can be 1190, 1200, 1210, 1220, 1230, 1240, 1250, 1260, 1270℃, etc., and the holding time can be 160min, 170min, 180min, etc.

[0052] The rolling process includes roughing and finishing rolling, with a final rolling temperature of 850–900°C. The cooling process includes a front-end centralized water cooling mode, where the temperature is cooled to 500–600°C at a cooling rate of 50–70°C / s before coiling.

[0053] S3. Pickle the hot-rolled coil, then cold-roll it using a reciprocating rolling mode, and control the reduction rate of the cold rolling to ensure that the interior of the pickled hot-rolled coil has sufficient recrystallization driving force to obtain a cold-hardened coil.

[0054] In some embodiments, the cold rolling reduction rate is 50% to 80%.

[0055] In the embodiments of this application, the cold-rolled coils in the above-mentioned cold rolling process are rolled by an 18-roll single stand with ≥3 passes of reciprocating rolling, and the reduction rate reaches 50-80%. The main purpose is to provide sufficient recrystallization driving force for subsequent full annealing to ensure the uniformity of the microstructure, while avoiding the use of high annealing temperatures, thereby reducing costs.

[0056] The pickling process parameters mentioned above include: pickling concentration of 30 g / L to 60 g / L, and pickling speed of 150 m / min to 350 m / min.

[0057] S4. The cold-hardened coil is continuously annealed, and the process parameters of the soaking zone of the continuous full annealing are controlled to eliminate the fibrous structure in the microstructure of the cold-hardened coil. After that, it is leveled to obtain 900MPa grade high-strength steel.

[0058] In some embodiments, the process parameters of the heat soaking section include: a temperature of 700℃~800℃ and a time of 60s~100s.

[0059] In this embodiment, the cold-rolled coil undergoes continuous full annealing, and the process parameters of the soaking zone during continuous full annealing are controlled to have a temperature of 700℃~800℃ and a time of 60s~100s, which can eliminate fibrous structures in the microstructure of the cold-rolled coil. For example, the temperature in the soaking zone during continuous annealing can be 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 780℃, 790℃, 800℃, etc., and the time can be 60s, 70s, 80s, 90s, 100s, etc.

[0060] The aforementioned continuous annealing includes a heating section, a soaking section, a slow cooling section, a rapid cooling section, an over-aging section, and a final cooling section. For example, the cold-rolled coil is heated to 700℃ to 800℃ at a rate of 2.5 to 3.5℃ / s and held for 60s to 100s. After holding, it is slowly cooled to 600℃ to 700℃ at a rate of 1℃ / s to 7℃ / s, and then rapidly cooled to 350℃ to 450℃ at a cooling rate of 8℃ / s to 20℃ / s. The over-aging temperature is 350℃ to 450℃, and the over-aging time is 240s to 350s. The final cooling temperature is 140℃ to 180℃.

[0061] In some embodiments, the rolling force is 6000KN to 10000KN.

[0062] In this embodiment, the leveling process employs a constant rolling force mode, which reduces rolling force fluctuations, avoids sheet shape problems, improves the accuracy of thickness difference in the width direction, and eliminates yield plateaus, thereby improving forming performance. When the rolling force is too small and below 6000KN, it is difficult to improve sheet shape and eliminate yield plateaus, and stamping is prone to orange peel defects. When the rolling force exceeds 10000KN, it deteriorates sheet shape and dimensional accuracy while increasing equipment load. For example, the aforementioned rolling force can be 6000KN, 7000KN, 8000KN, 9000KN, 10000KN, etc.

[0063] In some embodiments, the 900MPa grade high-strength steel meets the following mechanical properties: yield strength ≥900MPa, tensile strength ≥950MPa, elongation after fracture ≥8.0%, and minimum mandrel diameter of 0.5T for 180° cold bending, where T represents the thickness of the 900MPa grade high-strength steel.

[0064] Secondly, this application provides a 900MPa grade high-strength steel prepared by the method described in any embodiment of the first aspect.

[0065] In the embodiments of this application, the preparation method of the above-mentioned 900MPa grade high-strength steel fully utilizes the fine grain strengthening, precipitation strengthening and dislocation strengthening effects of microalloying to obtain high-strength steel with high strength level and good formability.

[0066] The 900MPa-grade high-strength steel is realized based on the above-described preparation method for 900MPa-grade high-strength steel. The specific steps of the preparation method for 900MPa-grade high-strength steel can be referred to the above embodiments. Since the 900MPa-grade high-strength steel adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated here.

[0067] Thirdly, this application provides the application of 900MPa high-strength steel as described in any embodiment of the second aspect in the manufacture of automotive seat slide rails.

[0068] In this embodiment, the 900MPa high-strength steel has uniform structure and stable performance, and a minimum bending diameter of 0.5T (T is the thickness of the high-strength steel) when cold-bent 180°. It is used in the manufacture of automotive seat slide rails to meet the requirements of lightweighting and seat slide rail forming in the automotive industry.

[0069] The application of the 900MPa high-strength steel in the manufacturing of automotive seat slide rails is based on the aforementioned 900MPa high-strength steel. The specific steps for using the 900MPa high-strength steel can be referred to in the above embodiments. Since the application of the 900MPa high-strength steel in the manufacturing of automotive seat slide rails adopts some or all of the technical solutions in the above embodiments, it has at least all the beneficial effects brought about by the technical solutions in the above embodiments, which will not be elaborated here.

[0070] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0071] A method for preparing 900MPa grade high-strength steel includes the following steps:

[0072] (1) The molten steel is smelted by “full three-stage desulfurization” and refined by LF+RH, and then continuously cast to obtain a high-cleanliness slab with low P, low S, low N and low H. The actual chemical composition of the slab is shown in Table 1 below (wt%).

[0073] Table 1 shows the chemical composition (wt%) of the slab, with the remainder being Fe and unavoidable impurities.

[0074] Serial Number C％ Si% Mn% P％ S％ Al％ Nb% Ti% N％ H / ppm Example 1 0.06 0.45 1.70 0.012 0.0018 0.020 0.03 0.15 0.0032 1 Example 2 0.09 0.38 1.66 0.011 0.0009 0.037 0.06 0.06 0.0036 1.5 Example 3 0.08 0.39 1.51 0.008 0.0018 0.025 0.068 0.06 0.0039 1.3 Example 4 0.08 0.32 1.53 0.011 0.0017 0.036 0.42 0.10 0.0046 0.9 Example 5 0.08 0.20 1.48 0.008 0.0018 0.032 0.028 0.13 0.0039 0.8 Example 6 0.08 0.30 1.39 0.007 0.0012 0.034 0.049 0.10 0.0032 1 Example 7 0.10 0.39 1.40 0.007 0.0006 0.036 0.03 0.14 0.0036 1.1 Example 8 0.09 0.42 1.30 0.011 0.0021 0.036 0.059 0.10 0.0029 1.2 Example 9 0.12 0.15 1.25 0.012 0.0018 0.058 0.07 0.03 0.0039 0.9 Example 10 0.11 0.19 1.21 0.011 0.0009 0.060 0.06 0.12 0.0032 1.1 Comparative Example 1 0.06 0.45 1.70 0.018 0.007 0.020 0.03 0.15 0.0035 3.0 Comparative Example 2 0.05 0.45 1.75 0.018 0.007 0.020 0.01 0.15 0.0035 1.0 Comparative Example 3 0.06 0.45 1.70 0.012 0.0018 0.020 0.03 0.15 0.0032 1

[0075] (2) The slab obtained above is heated to 1190-1270℃ and held for 160-196 min, and then rolled (roughing and finishing). The final rolling temperature is 850-900℃. The front section of the finishing plate is cooled to the coiling temperature of 500-600℃ by centralized water cooling mode to obtain a hot-rolled coil with a thickness of 2.5-5.0 mm. The specific preparation process parameters of the hot-rolled coil are shown in Table 2 below.

[0076] Table 2. Process parameters for hot-rolled coil preparation

[0077]

[0078]

[0079] (3) The hot-rolled coil obtained above is further pickled with acid solution concentration of 30-60 g / l and speed of 150-350 m / min to remove surface oxides. After pickling, the steel coil is reciprocated and rolled on an 18-roll single stand for 3-6 passes with a total reduction rate of 50-80% to obtain a cold-hardened steel coil of the target thickness. The specific pickling and cold rolling process parameters are shown in Table 3 below.

[0080] Table 3. Preparation process parameters for pickling and cold rolling

[0081] Serial Number Pickling concentration (g / l) Pickling speed (m / min) (Reciprocating) rolling passes reduction rate % Cold rolled thickness / mm Example 1 58 300 6 80.00％ 0.5 Example 2 46 285 5 63.64％ 1.0 Example 3 38 198 3 50.00％ 2.5 Example 4 60 350 4 57.50％ 1.7 Example 5 35 220 4 60.00％ 1.2 Example 6 40 260 3 55.56％ 2.0 Example 7 55 310 4 60.00％ 1.2 Example 8 45 150 4 62.67％ 1.4 Example 9 50 320 3 55.56％ 2.0 Example 10 30 250 3 55.00％ 1.8 Comparative Example 1 58 300 6 80％ 0.5 Comparative Example 2 58 300 6 70％ 0.7 Comparative Example 3 58 300 (One direction) 6 80.00％ 0.5

[0082] (4) The above-mentioned cold-hardened roll is subjected to continuous full annealing to obtain the finished roll, and the specific continuous annealing process parameters are shown in Table 4 below.

[0083] Table 4 Process parameters for continuous annealing

[0084]

[0085]

[0086] (5) The mechanical properties of the above-mentioned 900MPa grade high-strength steel finished products are shown in Table 4 below.

[0087] Table 4 Mechanical properties of finished high-strength steel products of 900MPa grade

[0088]

[0089]

[0090] Table 4 shows that the high-strength steel obtained using the preparation method for 900MPa grade high-strength steel meets the following requirements: yield strength.

[0091] With a tensile strength ≥940MPa and an elongation after fracture ≥8.0%, it possesses high strength and plasticity. It does not crack when cold-bent 180° with a minimum longitudinal bending diameter of 0T (T is the thickness of high-strength steel). For specifications with a transverse thickness <2.0mm, it does not crack when the minimum bending diameter is 0T. For specifications with a transverse thickness ≥2.0mm, it does not crack when the minimum bending diameter is 0.5T. Its performance meets the standard requirements and satisfies the forming needs of steel for automotive seat slide rails. In Comparative Example 1, the P, H, and S contents are not within the scope of the embodiments of this application, and the high-strength steel obtained by cold bending at 180°C has a minimum bending diameter of 1.5T without cracking, but the bending effect is not as good as that of the embodiments. In Comparative Example 2, the C and Nb contents are not within the scope of the embodiments of this application, and the yield strength of the high-strength steel obtained is 859MPa. In Comparative Example 3, the rolling method and the homogenization temperature of the continuous annealing in the cold rolling process are not within the scope of the embodiments of this application, and the high-strength steel obtained has increased strength but low elongation after fracture, and does not crack when cold bent at 180°C with a minimum bending diameter of 1.5T. Figure 2 A microstructure image of a 900MPa grade high-strength steel provided for an embodiment of this application; please refer to [link / reference]. Figure 2 This indicates that the microstructure of the 900MPa grade high-strength steel provided in this application is uniform and mainly consists of ferrite, pearlite and carbides.

[0092] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing 900MPa grade high-strength steel, characterized in that, The method includes: A slab with a specified chemical composition is obtained; The slab is heated and the heating process parameters are controlled to refine the grains in the slab. Then, it is hot rolled, cooled, and coiled to obtain a hot-rolled coil. The hot-rolled coil is pickled and then cold-rolled using a reciprocating rolling mode, with the reduction rate of the cold rolling controlled at 50% to 80% to ensure that the interior of the pickled hot-rolled coil has sufficient recrystallization driving force, thus obtaining a cold-hardened coil. The cold-hardened coil is subjected to continuous full annealing, and the process parameters of the soaking zone of the continuous full annealing are controlled to eliminate the fibrous structure in the microstructure of the cold-hardened coil and obtain a uniform recrystallized structure. After leveling, a 900MPa grade high-strength steel is obtained. The specified chemical composition is: C, Si, Mn, P, S, Al, Nb, Ti, N, H, and Fe; wherein, by mass fraction, the content of C is 0.06%~0.12%, the content of Si is 0.15%~0.45%, the content of Mn is 1.20%~1.70%, the content of P is ≤0.015%, the content of S is ≤0.0030%, the content of Al is 0.020%~0.060%, the content of Nb is 0.02%~0.08%, the content of Ti is 0.03%~0.15%, the content of N is ≤0.005%, the content of H is ≤2.0ppm, and the remainder is Fe and unavoidable impurities; The heating process parameters include: holding temperature of 1190℃~1270℃, and holding time ≥150min; The process parameters of the heat spreader include: temperature of 700℃~800℃ and time of 60s~100s; The 900MPa grade high-strength steel meets the following mechanical properties: yield strength ≥ 900MPa, tensile strength ≥ 950MPa, elongation after fracture ≥ 8.0%, minimum mandrel diameter for 180° cold bending 0.5T, where T represents the thickness of the 900MPa grade high-strength steel.

2. The method according to claim 1, characterized in that, The leveling rolling force is 6000KN~10000KN.

3. The method according to claim 1, characterized in that, The process of obtaining a slab with a specified chemical composition includes: The molten iron is smelted using a "full three-stage desulfurization" process, followed by LF refining, RH refining, and continuous casting to obtain a slab with a set chemical composition.

4. A 900MPa grade high-strength steel prepared by the method according to any one of claims 1 to 3.

5. The application of the 900MPa grade high-strength steel as described in claim 4 in the manufacture of automotive seat slide rails.

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