900MPa-grade high-strength steel as well as preparation method and application thereof

Abstract

The invention relates to 900MPa-grade high-strength steel as well as a preparation method and application thereof. The method comprises the following steps: obtaining a plate blank with set chemical components; heating the plate blank, controlling technological parameters of heating to refine grains in the plate blank, and then performing hot rolling, cooling and coiling to obtain a hot-rolled coil; the hot-rolled coil is subjected to acid pickling, then cold rolling is conducted in a reciprocating rolling mode, the reduction rate of cold rolling is controlled, so that the interior of the hot-rolled coil subjected to acid pickling has sufficient recrystallization driving force, and a cold hard coil is obtained; and the cold hard coil is subjected to continuous complete annealing, technological parameters of a soaking section of continuous complete annealing are controlled so as to eliminate fibrous structures in the structure of the cold hard coil, then flattening is conducted, and the 900MPa-grade high-strength steel is obtained. The 900MPa-grade high-strength steel prepared by the preparation method disclosed by the invention has excellent forming performance.

Description

Technical Field

[0001] The present application relates to the technical field of steel preparation, and in particular to a 900MPa grade high-strength steel and a preparation method and application thereof. Background Art

[0002] In order to achieve energy conservation, emission reduction, and lightweight requirements, the automotive industry has increasingly used advanced high-strength steels (AHSS) for automobiles, such as phase-transformation-strengthened ultra-high-strength DP, CP, and QP steels, which have both high strength and good formability, in car bodies. They are also increasingly used in many complex parts. Although such ultra-high-strength steels have been booming, not all parts are suitable for phase-transformation-strengthened ultra-high-strength steels. For example, for car seat frames and slide rails, while the strength is met, more emphasis is placed on the local formability of the material, such as bending at a lower bending radius, expanding holes, and local flanging. Therefore, the local stress-strain behavior of material forming is particularly important, and such parts are more suitable for manufacturing with low-alloy high-strength (HSLA) steels with excellent local formability.

[0003] Car seat slides are key safety components of cars, requiring high strength, high dimensional accuracy, no cracks, and good bending performance. Currently, there are few ultra-high-grade low-alloy high-strength steels on the market that meet the requirements of car seat frames and slides of 900MPa and above. Most of them are hot-rolled products or semi-annealed products. The comprehensive quality of cold bending performance, dimensional accuracy, plate shape, etc. can no longer meet the needs of lightweight cars and seat safety and reliability. Therefore, it is urgent to develop a low-alloy high-strength steel with higher strength level, better forming performance, and better performance. Summary of the invention

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

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

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

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

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

[0009] The chilled coil is subjected to continuous full annealing, and the process parameters of the soaking section of the continuous full annealing are controlled to eliminate the fibrous structure in the structure of the chilled coil, and then flattened to obtain 900 MPa grade high-strength steel.

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

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

[0012] Optionally, the process parameters of the soaking section include: temperature of 700° C. to 800° C., and time of 60s to 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%, and a minimum bending core diameter of 0.5T for 180° cold bending, where T represents the thickness of the 900MPa grade high-strength steel.

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

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

[0017] ~1.70%, the P content is ≤0.015%, the S content is ≤0.0030%, the Al content is 0.020%~0.060%, the Nb content is 0.02%~0.08%, the Ti content is 0.03%~0.15%, the N content is ≤0.005%, and the H content is ≤2.0ppm.

[0018] Optionally, obtaining a slab having a set chemical composition comprises:

[0019] The molten iron is smelted in the "full three-removal" mode, followed by LF refining, RH refining and continuous casting to obtain slabs with set chemical composition.

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

[0021] In a third aspect, the present application provides an application of the 900 MPa grade high-strength steel described in any embodiment of the second aspect in the manufacture of automobile seat slide rails.

[0022] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0023] The preparation method of the 900MPa grade high-strength steel provided in an embodiment of the present application comprises: obtaining a slab with a set chemical composition; heating the slab and controlling the process parameters of the heating to refine the grains in the slab, and then hot rolling, cooling and coiling to obtain a hot-rolled coil; pickling the hot-rolled coil, and then cold rolling it in a reciprocating rolling mode, and controlling the reduction rate of the cold rolling so that the interior of the hot-rolled coil after pickling has sufficient recrystallization driving force to obtain a chilled coil; continuously and fully annealing the chilled coil, and controlling the process parameters of the soaking section of the continuous full annealing to eliminate the fibrous structure in the structure of the chilled coil, and then flattening it to obtain a 900MPa grade high-strength steel. The use of a slab with a set chemical composition can ensure the high cleanliness quality of the slab; at the same time, the design of the heating process parameters can ensure that the Nb and Ti microalloying elements are fully dissolved back into the austenite to prevent the austenite grains from growing, thereby refining the grains in the slab; the heated slab is hot rolled, cooled and coiled, which can further refine the grains of the slab; the hot-rolled coil is pickled, which can make the hot-rolled coil have good surface quality, thereby facilitating the smooth subsequent cold rolling; the hot-rolled coil after pickling is cold rolled in a reciprocating rolling mode, and the reduction rate of the cold rolling is controlled, which can provide sufficient recrystallization driving force for the subsequent continuous full annealing, so as to promote the homogenization of the structure of the hot-rolled coil after pickling; the chilled coil is continuously fully annealed, and the process parameters of the soaking section of the continuous annealing are controlled, which can effectively eliminate the fibrous structure in the structure of the chilled coil; the chilled coil after continuous annealing is flattened, which can improve the plate shape, thereby improving the forming performance. In summary, the above-mentioned preparation method of 900MPa grade high-strength steel fully realizes the effects of fine grain strengthening, precipitation strengthening and dislocation strengthening, and improves the formability of 900MPa grade high-strength steel. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0025] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0026] Figure 1 A schematic diagram of a process for preparing a 900 MPa grade high-strength steel according to an embodiment of the present application;

[0027] Figure 2 A microstructure diagram of a 900 MPa grade high-strength steel provided in an embodiment of the present application. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0029] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have 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., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

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

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

[0032] In a first aspect, the present application provides a method for preparing 900MPa grade high-strength steel. Figure 1 A schematic diagram of a process for preparing a 900 MPa grade high-strength steel according to an embodiment of the present application; see Figure 1 , the method comprising:

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

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

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

[0036] In the embodiments of the present application, the C element is the most important solid solution strengthening element in high-strength steel and an important element for improving the strength of steel. At the same time, it forms carbonitrides with microalloying elements Nb and Ti during heat treatment, which plays a role in fine grain strengthening and precipitation strengthening. However, if the C content is too high and exceeds 0.12%, it may affect the welding performance and forming quality; if the C content is too low and is lower than 0.06%, it may have an adverse effect on the strength. Exemplarily, the above-mentioned 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. It does not form carbides in steel, but dissolves in ferrite or austenite in the form of solid solution, which can reduce the austenite phase area. Increasing Si can improve the hardness, strength and high temperature fatigue strength of steel. However, when the Si content is too high and exceeds 0.45%, the welding performance of steel may be deteriorated. For example, the above Si content can be 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, etc.

[0038] Mn is also an important element for solid solution strengthening and expansion of austenite area. It can form MnS with sulfur, which can prevent hot brittleness caused by sulfur, thereby improving the hot working performance of steel; Mn forms a solid solution with Fe to improve the hardness and strength of ferrite and austenite in steel. Mn in steel plays a role in refining pearlite by reducing the critical transformation temperature, and also indirectly plays a role in improving the strength of pearlite steel. However, Mn is easy to cause structural segregation. When the Mn content is too high and exceeds 1.2%, it is easy to cause steel forming cracks, deteriorate the comprehensive performance of steel, and also affect welding performance. Exemplarily, the above-mentioned Mn content can be 1.20%, 1.30%, 1.40%, 1.50%, 1.60%, 1.70%, etc.

[0039] P also plays a role in solid solution strengthening, but while P increases strength, it causes a significant decrease in plasticity and impact toughness, especially at low temperatures, it makes the steel material significantly brittle, a phenomenon known as "cold brittleness". In addition, P tends to segregate at grain boundaries, deteriorating the mechanical properties of the material. For example, the P content can be 0.015%, 0.013%, 0.011%, 0.009%, etc.

[0040] S comes from molten iron, steelmaking ore and raw materials, and is a harmful element. FeS and Fe form a low melting point (985°C) compound, and the hot working temperature of steel is generally above 1150°C. Therefore, when the steel is hot-worked, the workpiece cracks due to the premature melting of the FeS compound. This phenomenon is called "hot brittleness". It reduces the ductility and toughness of the steel, causing cracks during forging and rolling. At the same time, sulfur is not good for welding performance and reduces corrosion resistance. Exemplarily, the above-mentioned S content can be 0.003%, 0.0025%, 0.002%, etc.

[0041] Al is the main deoxidizing alloy for steelmaking. When added to steel as an alloying element, it can refine the grains and fix nitrogen in the steel, thereby inhibiting the aging of low-carbon steel and improving the toughness of steel 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. Ti can improve plasticity and toughness in low alloy steel. Since Ti fixes nitrogen and sulfur and forms titanium carbide nano-precipitation phase, it plays a role in grain refinement and precipitation strengthening. The precipitation of carbides can significantly improve the plasticity and impact toughness of steel. Alloy steel containing Ti elements has good mechanical properties and process properties, but Ti is easily oxidized and has a complex morphology. When the Ti content is too high and exceeds 0.15%, it is easy to affect the performance stability. Exemplarily, the above-mentioned Ti content can be 0.03%, 0.05%, 0.07%, 0.09%, 0.11%, 0.13%, 0.15%, etc.

[0043] Nb is also a microalloying element. Nb mainly exists in the form of carbides. It refines the grains, improves the impact toughness of steel and reduces its brittle transition temperature. However, when the Nb content is too high and exceeds 0.08%, the cost increases significantly. For example, the Nb content can be 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, etc.

[0044] Like C, N can be dissolved in iron to form an interstitial solid solution. However, while the strength and hardness are improved, the toughness of the steel decreases and the notch sensitivity increases. The brittleness of the steel caused by N is also the main reason for the blue brittleness of the steel. For example, the N content can be 0.005%, 0.004%, 0.003%, 0.002%, etc.

[0045] At the same time, the H content should be limited. H will cause a large number of cracks in the steel, significantly reducing the plasticity and toughness of the steel, causing the parts to break suddenly during use. In order to prevent the "hydrogen embrittlement" phenomenon from causing steel cracking, the H content is limited to ≤2.0ppm. For example, the H content can be 2.0%, 1.8%, 1.6%, 1.4%, etc.

[0046] In some embodiments, obtaining a slab having a set chemical composition comprises:

[0047] The molten iron is smelted in the "full three-removal" mode, followed by LF refining, RH refining and continuous casting to obtain slabs with set chemical composition.

[0048] In the embodiment of the present application, steelmaking adopts the "full three-removal" smelting mode to obtain low S, low P molten steel, and then undergoes LF+RH refining deep desulfurization and degassing, and removal of inclusions, and then continuous casting is performed to obtain low P, low S, low N, low H high-cleanliness slabs.

[0049] S2, heating the slab and controlling the heating process parameters to refine the grains in the slab, and then hot rolling, cooling and coiling to obtain a hot-rolled coil;

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

[0051] In the embodiment of the present application, the heating process parameters are limited to a holding temperature of 1190°C to 1270°C and a holding time of ≥150min, which can ensure that the Nb and Ti microalloying elements in the slab are fully dissolved back into the austenite to prevent the austenite grains from growing and play a role in refining the grains. Exemplarily, the above holding temperatures 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 includes rough rolling and finish rolling, and the final rolling temperature can be 850-900° C. The cooling includes a front-stage concentrated water cooling mode, cooling to 500-600° C. at a cooling rate of 50-70° C. / s for coiling.

[0053] S3, pickling the hot-rolled coil, and then cold-rolling it in a reciprocating rolling mode, and controlling the reduction rate of the cold rolling so that the interior of the hot-rolled coil after pickling has sufficient recrystallization driving force to obtain a chilled coil;

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

[0055] In the embodiment of the present application, the cold-rolled coil in the above-mentioned cold rolling process adopts an eighteen-roll single frame to carry out reciprocating rolling for ≥3 passes, and the reduction rate reaches 50-80%. The main purpose is to provide sufficient recrystallization driving force for subsequent full annealing to ensure the homogenization of the structure, while avoiding the use of high annealing temperature to achieve the effect of reducing costs.

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

[0057] S4, continuously annealing the chilled coil, and controlling the process parameters of the soaking section of the continuous full annealing to eliminate the fibrous structure in the structure of the chilled coil, and then flattening to obtain 900 MPa grade high-strength steel.

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

[0059] In the embodiment of the present application, the cold hard coil is subjected to continuous full annealing, and the temperature in the soaking section of the continuous full annealing is controlled to be 700°C to 800°C and the time is 60s to 100s, so as to eliminate the fibrous structure in the structure of the cold hard coil. Exemplarily, in the soaking section of the continuous annealing, the temperature can be 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 780°C, 790°C, 800°C, etc., and the time can be 60s, 70s, 80s, 90s, 100s, etc.

[0060] The above-mentioned continuous annealing includes a heating section, a soaking section, a slow cooling section, a fast cooling section, an over-aging section and a final cooling section; illustratively, the cold hard coil is heated to 700°C to 800°C at 2.5 to 3.5°C / S, and kept warm for 60s to 100s; after keeping warm, it is slowly cooled to 600°C to 700°C at a rate of 1°C / s to 7°C / s, and then quickly cooled to 350°C to 450°C at a cooling rate of 8°C / s to 20°C / s; the over-aging temperature is 350°C to 450°C, and the over-aging time is 240s to 350s; the final cooling temperature is 140°C to 180°C.

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

[0062] In the embodiment of the present application, the constant rolling force mode is used for leveling, which can reduce the fluctuation of rolling force, avoid plate shape problems, improve the thickness difference accuracy in the width direction, eliminate the yield platform, and improve the forming performance. When the rolling force is too small and lower than 6000KN, it is difficult to improve the plate shape and eliminate the yield platform, and the risk of orange peel is prone to occur in stamping forming; when the rolling force exceeds 10000KN, the plate shape and dimensional accuracy will deteriorate, and the equipment load will increase. Exemplarily, the above rolling force can be 6000KN, 7000KN, 8000KN, 9000KN, 10000KN, etc.

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

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

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

[0066] The 900MPa-grade high-strength steel is realized based on the preparation method of the above-mentioned 900MPa-grade high-strength steel. The specific steps of the preparation method of the 900MPa-grade high-strength steel can refer to the above-mentioned embodiment. Since the 900MPa-grade high-strength steel adopts part or all of the technical solutions of the above-mentioned embodiments, it at least has all the beneficial effects brought by the technical solutions of the above-mentioned embodiments, which will not be repeated here one by one.

[0067] In a third aspect, the present application provides an application of the 900 MPa grade high-strength steel described in any embodiment of the second aspect in the manufacture of automobile seat slide rails.

[0068] In the embodiment of the present application, the above-mentioned 900MPa grade high-strength steel has uniform structure, stable performance, and a minimum bending diameter of 0.5T (T is the thickness of high-strength steel) for cold bending of 180°. It is used in the manufacture of automobile seat slide rails to meet the lightweight and seat slide rail parts forming needs of the automobile industry.

[0069] The application of the 900MPa-grade high-strength steel in the manufacture of automobile seat slides is based on the above-mentioned 900MPa-grade high-strength steel. The specific steps of the 900MPa-grade high-strength steel can refer to the above-mentioned embodiments. Since the application of the 900MPa-grade high-strength steel in the manufacture of automobile seat slides adopts part or all of the technical solutions of the above-mentioned embodiments, it at least has all the beneficial effects brought by the technical solutions of the above-mentioned embodiments, which will not be repeated here one by one.

[0070] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to national standards. If there is no corresponding national standard, then the conditions recommended by the manufacturer are followed.

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

[0072] (1) The molten steel is subjected to "full three-removal" smelting, LF+RH refining, and continuous casting to obtain a low P, low S, low N, low H and high cleanliness slab. The actual chemical composition is as shown in Table 1 below: Chemical composition (wt%) of the slab.

[0073] Table 1 Chemical composition of slab (wt%), the rest is 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° C., kept at this temperature for 160-196 min, and then rolled (rough rolling and finish rolling), wherein the final rolling temperature is 850-900° C., and the front section of the finished rolled plate is cooled to a coiling temperature of 500-600° C. in a centralized water cooling mode to obtain a hot rolled coil with a thickness of 2.5-5.0 mm. The specific process parameters for preparing the hot rolled coil are shown in Table 2 below.

[0076] Table 2 Preparation process parameters of hot rolled coil

[0077]

[0078]

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

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

[0081] Serial number Pickling concentration g / l Pickling speed m / min (Reciprocating) rolling pass 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 cold hardened coil is subjected to continuous full annealing treatment to obtain a finished coil. The specific process parameters of the continuous annealing are shown in Table 4 below.

[0083] Table 4 Continuous annealing process parameters

[0084]

[0085]

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

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

[0088]

[0089]

[0090] From Table 4, it can be seen that the high-strength steel obtained by the preparation method of 900MPa grade high-strength steel meets the following requirements: yield strength

[0091] ≥940MPa, tensile strength ≥970MPa, elongation after break ≥8.0%, with high strength and plasticity, cold bending 180° longitudinal minimum bending diameter 0T does not crack (T is the thickness of high-strength steel), transverse thickness <2.0mm specification minimum bending diameter 0T does not crack, transverse thickness ≥2.0mm specification minimum bending diameter 0.5T does not crack, the performance meets the standard requirements and meets the forming needs of steel for automotive seat slides. In Comparative Example 1, the P content, H content, and S content are not within the scope of the embodiments of the present application, and the high-strength steel obtained is cold bent at 180°C, with a minimum bending diameter of 1.5T without cracking, and the bending effect is not as good as the embodiment; in Comparative Example 2, the C and Nb contents are not within the scope of the embodiments of the present application, and the yield strength of the high-strength steel obtained is 859MPa; in Comparative Example 3, the rolling method in the cold rolling process and the soaking temperature of the continuous annealing are not within the scope of the embodiments of the present application, and the strength of the high-strength steel obtained is increased, while the elongation after fracture is low, and the cold bending is 180°C, with a minimum bending diameter of 1.5T without cracking. Figure 2 A microstructure diagram of a 900MPa grade high-strength steel provided in the embodiment of the present application; see Figure 2 , indicating that the microstructure of the 900MPa grade high-strength steel provided in the present application is uniform, and is mainly composed of ferrite, pearlite and carbide.

[0092] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A method for preparing 900MPa grade high-strength steel, characterized in that: The method comprises: A slab with a set chemical composition is obtained; The slab is heated and the process parameters of the heating are controlled to refine the grains in the slab, and then hot-rolled, cooled and coiled to obtain a hot-rolled coil; The hot-rolled coil is pickled, and then cold-rolled in a reciprocating rolling mode, and the reduction rate of the cold rolling is controlled so that the interior of the hot-rolled coil after pickling has sufficient recrystallization driving force to obtain a chilled coil; The chilled coil is subjected to continuous full annealing, and the process parameters of the soaking section of the continuous full annealing are controlled to eliminate the fibrous structure in the structure of the chilled coil, and then flattened to obtain 900 MPa grade high-strength steel.

2. The method according to claim 1, characterized in that The heating process parameters include: a holding temperature of 1190° C. to 1270° C., and a holding time of ≥150 min.

3. The method according to claim 1, characterized in that: The cold rolling reduction ratio is 50% to 80%.

4. The method according to claim 1, characterized in that The process parameters of the soaking section include: temperature of 700° C. to 800° C. and time of 60s to 100s.

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

6. The method according to claim 1, characterized in that The 900MPa grade high-strength steel meets the following mechanical properties: yield strength ≥900MPa, tensile strength ≥950MPa, elongation after fracture ≥8.0%, and a minimum bending core diameter of 0.5T for 180° cold bending, where T represents the thickness of the 900MPa grade high-strength steel.

7. The method according to claim 1, characterized in that The set chemical composition includes: C, Si, Mn, P, S, Al, Nb, Ti, N, H and Fe; wherein, in terms of mass fraction, The content of C is 0.06% to 0.12%, the content of Si is 0.15% to 0.45%, and the content of Mn is 1.20% to 1.70%. The content of P is ≤0.015%, the content of S is ≤0.0030%, the content of Al is 0.020% to 0.060%, the content of Nb is 0.02% to 0.08%, the content of Ti is 0.03% to 0.15%, the content of N is ≤0.005%, and the content of H is ≤2.0ppm.

8. The method according to claim 1, characterized in that: The method of obtaining a slab having a set chemical composition comprises: The molten iron is smelted in the "full three-removal" mode, followed by LF refining, RH refining and continuous casting to obtain slabs with set chemical composition.

9. A 900 MPa grade high strength steel prepared by the method according to any one of claims 1 to 8.

10. Use of the 900 MPa high-strength steel according to claim 9 in the manufacture of automobile seat slide rails.

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