1800MPa-grade hot forming steel and preparation method thereof

Abstract

The invention relates to 1800MPa-grade hot forming steel and a preparation method thereof, and belongs to the technical field of steel preparation. The product / method comprises the following steps: obtaining a cold hard roll with set chemical components; the cold hard coil is subjected to continuous annealing treatment, and a hot-formed steel raw material coil is obtained; the hot-formed steel raw material roll is subjected to flattening, blanking and hot stamping treatment, and the 1800 MPa-grade hot-formed steel is obtained; the continuous annealing treatment specifically comprises the steps that the cold hard coil is heated, and the heating rate and the final temperature are controlled; the heated cold hard coil is subjected to soaking, and the soaking duration time is controlled; cooling the uniformly heated cold hard coil, and controlling the final temperature of cooling; and the cooled cold hard coil is subjected to overaging treatment, so that the cold hard coil is subjected to continuous annealing treatment. The annealing process of heating, soaking, cooling and overaging is adopted, high-efficiency and low-cost production of high-performance hot forming steel can be achieved, and enterprise benefits are maximized.

Description

Technical Field

[0001] This application relates to the technical field of steel preparation, and particularly to an 1800 MPa grade hot forming steel and a preparation method thereof. Background Art

[0002] The 1800 MPa grade hot forming steel is a kind of ultra-high strength steel, mainly used in the fields of automobiles, aerospace, etc., and has excellent strength, toughness and lightweight characteristics.

[0003] The existing preparation process mainly includes hot metal desulfurization → smelting → LF refining → RH refining → continuous casting → hot rolling → pickling → cold rolling → bell annealing → blanking → hot forming to obtain 1800 MPa hot forming steel. Among them, the bell annealing has a long cycle and many equipment, resulting in low production efficiency and high cost. Therefore, an economical and efficient production method is needed. Summary of the Invention

[0004] This application provides an 1800 MPa grade hot forming steel and a preparation method thereof to solve the following technical problem: how to improve the preparation efficiency of the 1800 MPa grade hot forming steel.

[0005] In the first aspect, an embodiment of this application provides a preparation method of an 1800 MPa grade hot forming steel, including the following steps:

[0006] Obtain a cold-rolled coil with a set chemical composition;

[0007] Perform continuous annealing treatment on the cold-rolled coil to obtain a raw coil of hot forming steel;

[0008] Perform leveling, blanking and hot stamping on the raw coil of hot forming steel to obtain an 1800 MPa grade hot forming steel;

[0009] The performing continuous annealing treatment on the cold-rolled coil specifically includes:

[0010] Heat the cold-rolled coil and control the heating rate and the end temperature;

[0011] Soak the heated cold-rolled coil and control the soaking duration;

[0012] Cool the soaked cold-rolled coil and control the end temperature of the cooling;

[0013] Perform over-aging treatment on the cooled cold-rolled coil to perform continuous annealing treatment on the cold-rolled coil.

[0014] Optionally, the end temperature of the heating is 720 °C to 780 °C; and / or, the heating rate is 2 °C / min to 5 °C / min.

[0015] Optionally, the soaking duration is 1.5 min to 2 min; and / or, the end temperature of cooling is 420°C to 470°C; the overaging treatment time is 5 min to 10 min.

[0016] Optionally, obtaining the cold-rolled coil with a set composition specifically includes:

[0017] Obtaining a continuous casting billet with a set chemical composition;

[0018] Performing hot rolling on the continuous casting billet to obtain a hot-rolled coil;

[0019] Performing pickling and cold rolling on the hot-rolled coil to obtain a cold-rolled coil with a set chemical composition.

[0020] Optionally, the set chemical composition includes a C content of 0.29% to 0.34%, a P content ≤ 0.02%, and an S content ≤ 0.003%. Among them, the C element can form a solid solution structure, improving the strength, hardness, and hardenability of the steel. However, the C element needs to be controlled within a certain range. If the carbon content is too high, the plasticity and toughness of the steel will be significantly reduced. The P element can improve the strength and hardness of the steel matrix. If it is too high, the plasticity and impact toughness will be significantly reduced, resulting in "cold brittleness" and poor cold working and weldability of the steel. An increase in the S element will reduce the plasticity and toughness of the steel matrix and cause "cold brittleness" at low temperatures, increasing the brittleness of the steel matrix.

[0021] Optionally, the set chemical composition by mass fraction includes: C: 0.29% to 0.34%, Si: 0.12% to 0.42%, Mn: 1.1% to 1.4%, P: ≤ 0.02%, S: ≤ 0.003%, Al: 0.01% to 0.06%, Cr: 0.15% to 0.35%, Nb: 0.04% to 0.06%, V: 0.01% to 0.04%, Ti: 0.02% to 0.05%, B: 0.002% to 0.004%, and Fe.

[0022] Optionally, performing hot rolling on the continuous casting billet to obtain a hot-rolled coil specifically includes:

[0023] Heating and soaking the continuous casting billet;

[0024] Performing rough rolling and finish rolling on the heated continuous casting billet and coiling to obtain a hot-rolled coil;

[0025] The target temperature of the heating is 1100°C to 1300°C; the soaking time is 160 min to 200 min; and / or, the finish rolling temperature of the finish rolling is 860°C to 930°C; and / or, the coiling temperature is 600°C to 700°C.

[0026] Optionally, the hot-formed steel raw material coil is leveled, blanked, and hot-stamped to obtain 1800 MPa grade hot-formed steel, which specifically includes:

[0027] Level the hot-formed steel raw material coil;

[0028] Preheat the leveled hot-formed steel raw material coil to a set temperature and hold for heat preservation to achieve austenitization;

[0029] Hot-stamp the austenitized hot-formed steel raw material coil, and then perform pressure-holding quenching to achieve complete martensite transformation, obtaining 1800 MPa grade hot-formed steel.

[0030] Optionally, the set temperature is 850°C to 950°C, and the heat preservation time is 5 min to 8 min; and / or,

[0031] The target temperature of the hot stamping is greater than 800°C; and / or,

[0032] The pressure-holding pressure for the pressure-holding quenching is 5000 KN to 10000 KN, and the pressure-holding time is 10 s to 15 s.

[0033] In a second aspect, the embodiments of the present application provide 1800 MPa grade hot-formed steel prepared by using the preparation method described in the first aspect. The properties of the 1800 MPa grade hot-formed steel at least meet one of the following: the yield strength R P0.2 is 1200 MPa to 1350 MPa; the tensile strength Rm is 1800 MPa to 1950 MPa; the elongation after fracture A50 is greater than 4%.

[0034] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0035] The embodiment of the present application provides a preparation method for 1800MPa grade hot forming steel, including the following steps: obtaining a cold rolled coil with a set chemical composition, ensuring that the chemical composition of the cold rolled coil meets the element requirements of 1800 grade steel; heating the cold rolled coil and controlling the heating rate and end temperature; adjusting the hardness, plasticity and toughness of the material by controlling the annealing temperature and time; soaking the heated cold rolled coil and controlling the soaking duration to eliminate the residual stress of the cold rolled coil. Cooling the soaked cold rolled coil and controlling the end temperature of the cooling; reaching this temperature can refine and evenly distribute the crystal grains of the 1800 grade hot forming steel structure. The cooled cold rolled coil is subjected to over-aging treatment. After the aging treatment, the internal structure and stress state are more stable, and subsequent dimensional changes and deformations can be effectively reduced, ensuring the dimensional accuracy and stability of the product. Through continuous annealing treatment of the cold rolled coil, the raw material coil of the hot forming steel is obtained; the raw material coil of the hot forming steel is subjected to leveling, blanking and hot stamping treatments to obtain 1800MPa grade hot forming steel.

[0036] In this method, continuous annealing is used instead of batch annealing. The annealing time is short, the efficiency is high, the required equipment is simple, and the production cost is low. The obtained 1800MPa grade hot forming steel product has a yield strength R P0.2 of 1200MPa - 1350MPa; the tensile strength Rm is 1800MPa - 1950MPa; the elongation after fracture A50 is greater than 4%. The performance is excellent. It can be seen that the method provided in the present application can achieve high-efficiency, high-efficiency and low-cost production of high-value-added 1800MPa grade hot forming steel products. Description of the Drawings

[0037] The drawings here are incorporated into the specification and form a part of this specification, showing the embodiments in line with the present application, and are used together with the specification to explain the principles of the present application.

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0039] Figure 1 It is a schematic flow chart of a preparation method for 1800MPa grade hot forming steel according to some embodiments of the present application. Detailed Embodiments

[0040] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Apparently, the described embodiments are only a part rather than all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the scope of protection of the present application.

[0041] The various embodiments of the present application may exist 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 construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and single 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, and this applies regardless of the range; in addition, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0042] In this document, terms such as "including" mean "including but not limited to". Relative terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. "And / or" describes the associated relationship of associated objects and indicates that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone; where A and B may be singular or plural. "At least one" means one or more, and "multiple" means two or more; "at least one kind", "at least one of the following items (pieces)" or similar expressions refer to any combination of these items, including any combination of single item (piece) or plural items (pieces); for example, "at least one of a, b, or c", or "at least one of a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively. The "parts representation method" such as parts by weight, parts by mass, etc. represents the proportional relationship between each component. In the proportional relationships involved in this document, the parameters that need to be described by proportion should be understood as the antecedents of the proportional formula in the order of description, and the proportional numbers should be understood as the consequents of the proportional formula. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one by one with the proportional numbers in the proportional formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0043] Unless otherwise specified, all kinds of raw materials, reagents, instruments, equipment, etc. used in this article can be obtained through market purchase or can be prepared by existing methods.

[0044] Figure 1 It is a schematic flow chart of a preparation method of a 1800MPa grade hot-formed steel according to some embodiments of the present application;

[0045] As Figure 1 shown, in the first aspect, the embodiments of the present application provide a preparation method of a 1800MPa grade hot-formed steel, including the following steps:

[0046] Obtain a cold-rolled coil with a set chemical composition;

[0047] Perform continuous annealing treatment on the cold-rolled coil to obtain a hot-formed steel raw material coil;

[0048] Perform leveling, blanking, and hot stamping on the hot-formed steel raw material coil to obtain a 1800MPa grade hot-formed steel;

[0049] The specific steps of performing continuous annealing treatment on the cold-rolled coil include:

[0050] Heat the cold-rolled coil and control the heating rate and end temperature;

[0051] Soak the heated cold-rolled coil and control the soaking duration;

[0052] Cool the soaked cold-rolled coil and control the end temperature of the cooling;

[0053] Perform over-aging treatment on the cooled cold-rolled coil to perform continuous annealing treatment on the cold-rolled coil.

[0054] In the above embodiment, the preparation method includes: obtaining a cold-rolled coil with a set chemical composition to meet the composition requirements of the 1800 grade hot-formed steel and providing a basic material for subsequent annealing and hot forming. Perform continuous annealing treatment on the cold-rolled coil to improve the structure and properties of the cold-rolled coil and obtain a hot-formed steel raw material coil; perform leveling on the hot-formed steel raw material coil to eliminate internal stress and ensure a flat surface; according to the shape of the part, cut the flattened steel plate into blanks, and then perform hot stamping treatment to make the martensite transformation complete, and finally obtain a 1800MPa grade hot-formed steel.

[0055] As an optional embodiment, the end temperature of the heating is 720°C to 780°C.

[0056] In the above-described embodiment, the reason for controlling the final temperature of the heating section during the continuous annealing process to be 720°C to 780°C is that the annealing temperature within this temperature range can make the grains in the alloy more uniform. Exemplarily, the annealing temperature can be 720°C, 725°C, 730°C, 735°C, 740°C, 745°C, 750°C, 755°C, 760°C, 765°C, 770°C, 775°C or 780°C.

[0057] As an alternative embodiment, the heating rate is 2°C / min to 5°C / min.

[0058] In the above-described embodiment, the reason for controlling the heating rate is that at this heating rate, it helps to avoid the strip deformation caused by the sudden temperature rise. Exemplarily, the heating rate can be 2°C / min, 3°C / min, 4°C / min or 5°C / min.

[0059] As an alternative embodiment, the soaking duration is 1.5 min to 2 min;

[0060] In the above-described embodiment, the function of soaking is to keep the cold-rolled and hardened strip steel at a set temperature for a period of time to ensure the homogenization of the internal structure of the material, eliminate internal stress, and achieve the required mechanical properties and microstructure. The reason for controlling the soaking time to be 1.5 min to 2 min is that it can eliminate the internal stress of the material with the highest efficiency, promote the recrystallization of the deformed grains after cold rolling, and form new, stress-free equiaxed grains. Exemplarily, the soaking duration can be 1.5 min, 1.6 min, 1.7 min, 1.8 min, 1.9 min or 2.0 min.

[0061] As an alternative embodiment, the final temperature of the cooling is 420°C to 470°C; the overaging treatment time is 5 min to 10 min.

[0062] In the above-described embodiment, the reason for controlling the final temperature of the cooling to be 420°C to 470°C is that at this cooling temperature, the grains of the 1800-grade hot-formed steel structure can be refined and evenly distributed; Exemplarily, the final temperature of the cooling can be 420°C, 425°C, 430°C, 435°C, 440°C, 445°C, 450°C, 455°C, 460°C, 465°C or 470°C.

[0063] As an alternative embodiment, the cooling method can adopt rapid cooling, or adopt slow cooling first and then rapid cooling, or rapid cooling first and then slow cooling and other cooling methods.

[0064] As an alternative embodiment, obtaining the cold-rolled and hardened strip with a set composition specifically includes:

[0065] Obtain a continuous casting billet with a set chemical composition;

[0066] Perform hot rolling on the continuous casting billet to obtain a hot rolled coil;

[0067] Perform pickling and cold rolling on the hot rolled coil to obtain a cold hard coil with a set chemical composition.

[0068] As an alternative embodiment, the set chemical composition includes a C content of 0.29% to 0.34%, a P content

[0069] ≤0.02%, and an S content ≤0.003%.

[0070] In the above embodiment, controlling the chemical composition of the continuous casting billet or the cold hard coil to satisfy a C content of 0.29% to 0.34% is because the C element can form a solid solution structure, improving the strength, hardness, and hardenability of the steel. If it exceeds this range, the carbon content of the cold hard coil will be too high, significantly reducing the plasticity and toughness of the steel. Exemplarily, in the chemical composition of the continuous casting billet or the cold hard coil, the content of the C element can be 0.29%, 0.30%, 0.31%, 0.32%, 0.33%, or 0.34%.

[0071] Controlling the chemical composition of the continuous casting billet or the cold hard coil to satisfy a P content ≤0.02% is because the P element within this range can improve the strength and hardness of the steel matrix. Excessively high levels will cause a significant reduction in plasticity and impact toughness, resulting in "cold brittleness" and poor cold working and weldability of the steel. Exemplarily, the content of the P element can be 0.05%, 0.01%, 0.15%, or 0.02%.

[0072] Controlling the chemical composition of the continuous casting billet or the cold hard coil to satisfy an S content ≤0.003% is because an increase in the S element will reduce the plasticity and toughness of the steel matrix, and cause "cold brittleness" to increase the brittleness of the steel matrix at low temperatures. Exemplarily, the S element is 0.0005%, 0.001%, 0.0015%, 0.002%, 0.0025%, or 0.003%.

[0073] As an alternative embodiment, the set chemical composition by mass fraction includes: C: 0.29% to 0.34%, Si: 0.12% to 0.42%, Mn: 1.1% to 1.4%, P: ≤0.02%, S: ≤0.003%, Al: 0.01% to 0.06%, Cr: 0.15% to 0.35%, Nb: 0.04% to 0.06%, V: 0.01% to 0.04%, Ti: 0.02% to 0.05%, B: 0.002% to 0.004%, and Fe.

[0074] In the above embodiments, by way of example, the content of the Si element may be 0.12%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40% or 0.42%; the content of the Mn element may be 1.1%, 1.2%, 1.3% or 1.4%; the content of the Al element may be 0.01%, 0.02%, 0.03%, 0.04%, 0.05% or 0.06%; the content of the Cr element may be 0.15%, 0.20%, 0.25%, 0.30% or 0.35%; the content of the Nb element may be 0.04%, 0.045%, 0.05%, 0.055% or 0.06%; the content of the V element may be 0.01%, 0.02%, 0.03% or 0.04%; the content of the Ti element may be 0.02%, 0.03%, 0.04% or 0.05%, and the content of the B element may be 0.002%, 0.003% or 0.004%.

[0075] As an alternative embodiment, the continuous casting billet is hot-rolled to obtain a hot-rolled coil, which specifically includes:

[0076] heating and insulating the continuous casting billet;

[0077] rough-rolling and finish-rolling the heated continuous casting billet, and coiling to obtain a hot-rolled coil;

[0078] The target temperature of the heating is 1100°C to 1300°C; the insulation time is 160 min to 200 min.

[0079] In the above embodiments, the hot-rolling process causes dynamic recrystallization of the continuous casting billet, and the grains are refined, thereby improving the strength and toughness of the material. The reason for controlling the hot-rolling temperature to be 1100°C to 1300°C and the insulation time to be 160 min to 200 min is that the metal billet is heated above the recrystallization temperature and insulated to soften it, facilitating the subsequent rolling process. By way of example, the target temperature of the heating may be 1100°C, 1150°C, 1200°C, 1250°C or 1300°C, and the insulation time may also be 160 min, 170 min, 180 min, 190 min or 200 min.

[0080] As an alternative embodiment, the finish-rolling final rolling temperature is 860°C to 930°C; the reason for controlling this final rolling temperature is that its temperature is in the austenitizing temperature range, which is beneficial for rolling. By way of example, the final rolling temperature may be 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C or 930°C.

[0081] As an alternative embodiment, the coiling temperature is 600°C to 700°C.

[0082] In the above embodiment, the reason for controlling the coiling temperature to be 600°C to 700°C is that the coiling temperature directly affects the microstructure, properties, and surface quality of the hot-rolled strip steel. In this temperature range, it ensures that the hot-formed steel products at the 1800 MPa level have good mechanical properties, formability, and processability. Exemplarily, the coiling temperature can be 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, 660°C, 670°C, 680°C, 690°C, or 700°C.

[0083] As an alternative embodiment, the pickling and cold rolling of the hot-rolled coil specifically include:

[0084] The hot-rolled coil is pickled conventionally and then cold-rolled. The cold rolling undergoes 18-high rolling. According to the different thicknesses of the strip steel, the rolling deformation rate is different. When the thickness specification is in the range of 0.8 mm to 2.5 mm, the 18-high rolling deformation rate is controlled within the range of 45% to 70%.

[0085] As an alternative embodiment, the leveling, blanking, and hot stamping of the hot-formed steel raw material coil to obtain the hot-formed steel at the 1800 MPa level specifically include:

[0086] Level the hot-formed steel raw material coil;

[0087] Preheat the leveled hot-formed steel raw material coil to a set temperature and hold for heat preservation to achieve austenitization;

[0088] Perform hot stamping on the austenitized hot-formed steel raw material coil, and then perform pressure holding and quenching to achieve complete martensite transformation to obtain the hot-formed steel at the 1800 MPa level.

[0089] In the above embodiment, leveling the hot-formed steel raw material coil ensures surface flatness and elimination of internal stress; preheating and holding for heat preservation to achieve complete austenitization of the microstructure of the raw material coil; transferring the preheated (fully austenitized) sheet to the stamping device quickly, with the transfer time being 3 s to 5 s, pre-cooling to the hot stamping target temperature and then performing hot stamping. After hot stamping, a stamped part is obtained through pressure holding and quenching + natural cooling, enabling complete martensite transformation of the material and achieving a strength of 1800 MPa. As an alternative embodiment, the set temperature is 850°C to 950°C, and the heat preservation time is 5 min to 8 min.

[0090] In the above embodiments, the reason for controlling the set temperature of the preheating to be 850°C to 950°C and the heat preservation time to be 5 min to 8 min is that the structure of the raw material coil is completely austenitized within this temperature range, ensuring the uniformity of the structure. Exemplarily, the set temperature can be 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C or 950°C, and the heat preservation time can be 5 min, 6 min, 7 min or 8 min.

[0091] As an alternative embodiment, the target temperature of the hot stamping is greater than 800°C;

[0092] In the above embodiments, the reason for controlling the target temperature of the hot stamping to be greater than 800°C is that this temperature is the lowest point of the austenitization temperature.

[0093] As an alternative embodiment, the holding pressure of the pressure holding quenching is 5000 KN to 10000 KN, and the holding time is 10 s to 15 s.

[0094] In the above embodiments, the reason for controlling the holding pressure of the pressure holding quenching to be 5000 KN to 10000 KN and the holding time to be 10 s to 15 s is to complete the martensite transformation of the material. Exemplarily, the holding pressure can be 5000 KN, 6000 KN, 7000 KN, 8000 KN, 9000 KN or 10000 KN. The holding time can be 10 s, 11 s, 12 s, 13 s, 14 s or 15 s.

[0095] In a second aspect, based on a general inventive concept, the embodiments of the present application provide a 1800 MPa grade hot formed steel prepared by using the preparation method described in the first aspect, and the performance of the 1800 MPa grade hot formed steel satisfies at least one of the following: the yield strength R P0.2 is 1200 MPa to 1350 MPa; the tensile strength Rm is 1800 MPa to 1950 MPa; the elongation after fracture A50 is greater than 4%.

[0096] The 1800 MPa grade hot formed steel is realized based on the above preparation method, and the specific steps of the preparation method can refer to the above embodiments. Since the 1800 MPa grade hot formed steel adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be elaborated herein one by one.

[0097] The present application will be further elaborated below in conjunction with specific embodiments. For the experimental methods without specific conditions indicated in the following embodiments, they are generally determined in accordance with national standards / industry standards; if there are no corresponding national standards / industry standards, they are carried out in accordance with general international standards, conventional conditions or the conditions recommended by the manufacturer.

[0098] Example 1

[0099] This example provides a hot-formed steel of 1800 MPa grade, and its preparation method is as Figure 1 shown, including the following steps:

[0100] S1. Obtain a continuous casting billet with a set chemical composition, and the specific chemical composition is shown in Table 1;

[0101] S2. Subject the continuous casting billet to hot rolling treatment to obtain a hot-rolled coil; the hot rolling parameters are shown in Table 2;

[0102] S3. Subject the hot-rolled coil to pickling and cold rolling treatments to obtain a cold-rolled and hardened coil;

[0103] S4. Heat the cold-rolled and hardened coil and control the heating rate and end temperature;

[0104] Subject the heated cold-rolled and hardened coil to soaking and control the soaking duration;

[0105] Cool the soaked cold-rolled and hardened coil and control the end temperature of the cooling;

[0106] Subject the cooled cold-rolled and hardened coil to over-aging treatment to conduct continuous annealing treatment on the cold-rolled and hardened coil to obtain a raw coil of hot-formed steel;

[0107] S5. Subject the raw coil of hot-formed steel to skin pass rolling, blanking and hot stamping treatments to obtain a hot-formed steel of 1800 MPa grade. The experimental parameters are shown in Table 2.

[0108] Perform performance tests on the obtained hot-formed steel of 1800 MPa grade, and the results are shown in Table 4.

[0109] Examples 2 to 7

[0110] The same preparation method as in Example 1 is used for preparation, with the difference being the chemical composition and specific preparation parameters, as detailed in Table 1 and Table 2. And perform performance tests on the obtained hot-formed steel of 1800 MPa grade respectively, and the results are shown in Table 4.

[0111] Comparative Examples 1 to 3

[0112] This comparative example provides a hot-formed steel of 1800 MPa grade, and the preparation method includes the following steps:

[0113] S1. Obtain a continuous casting billet with a set chemical composition. The specific chemical composition is shown in Table 1.

[0114] S2. Subject the continuous casting billet to hot rolling to obtain a hot rolled coil. The hot rolling parameters are shown in Table 3.

[0115] S3. Subject the hot rolled coil to pickling and cold rolling to obtain a cold rolled and hardened coil.

[0116] S4. Subject the cold rolled and hardened coil to bell annealing to obtain a raw coil of hot forming steel.

[0117] S5. Subject the raw coil of hot forming steel to leveling, blanking, and hot stamping to obtain 1800 MPa grade hot forming steel. The experimental parameters are shown in Table 3.

[0118] Perform performance tests on the obtained 1800 MPa grade hot forming steel. The results are shown in Table 4.

[0119] Table 1 List of chemical compositions of 1800 MPa grade hot forming steel in Examples 1 - 7 and Comparative Examples 1 - 3

[0120] Serial number C Si Mn P S Cr Al Nb V Ti B Fe Example 1 0.31 0.24 1.3 0.012 0.001 0.21 0.04 0.04 0.01 0.03 0.003 Bal. Example 2 0.32 0.25 1.3 0.010 0.002 0.28 0.03 0.05 0.02 0.04 0.002 Bal. Example 3 0.32 0.23 1.4 0.012 0.001 0.19 0.03 0.04 0.01 0.03 0.002 Bal. Example 4 0.33 0.26 1.2 0.016 0.003 0.20 0.02 0.06 0.03 0.03 0.003 Bal. Example 5 0.30 0.22 1.1 0.017 0.002 0.25 0.05 0.05 0.02 0.03 0.004 Bal. Example 6 0.32 0.20 1.3 0.012 0.001 0.29 0.03 0.04 0.04 0.04 0.002 Bal. Example 7 0.33 0.26 1.2 0.016 0.003 0.32 0.03 0.05 0.03 0.03 0.003 Bal. Comparative example 1 0.31 0.25 1.3 0.015 0.002 0.22 0.04 0.04 0.02 0.03 0.002 Bal. Comparative example 2 0.32 0.24 1.2 0.014 0.003 0.24 0.06 0.06 0.02 0.04 0.003 Bal. Comparative example 3 0.33 0.24 1.3 0.012 0.001 0.25 0.03 0.05 0.03 0.02 0.004 Bal.

[0121] Table 2 List of main process parameters of Examples 1 - 7

[0122]

[0123]

[0124] Table 3 List of main process parameters of Comparative Examples 1 - 3

[0125]

[0126] Table 4 List of performances of 1800 MPa grade hot forming steel obtained in Examples 1 - 7 and Comparative Examples 1 - 3

[0127] Serial number Yield strength / MPa Tensile strength / MPa Elongation after fracture A50 / % Example 1 1287 1908 6.0 Example 2 1294 1901 5.5 Example 3 1290 1893 5.5 Example 4 1294 1906 5.0 Example 5 1293 1912 5.5 Example 6 1310 1925 5.5 Example 7 1323 1931 5.0 Comparative example 1 1314 1925 5.0 Comparative example 2 1284 1897 5.5 Comparative example 3 1296 1912 5.2

[0128] From the results of the list of performances of dual - phase steel obtained in Examples 1 - 7 and Comparative Examples 1 - 3 given in Table 4, although the performance of 1800 MPa grade hot forming steel prepared by continuous annealing is comparable to that prepared by traditional bell annealing, the time for traditional bell annealing is generally 3 - 4 days per furnace, and each furnace can only accommodate 3 - 4 cold rolled and hardened coils. The continuous annealing process adopted in this application requires simple equipment, and the annealing time for each cold rolled and hardened coil is only 10 min - 15 min, greatly improving the production efficiency and reducing the production cost.

[0129] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined in the present application 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 these embodiments shown in the present application, but rather to the broadest scope consistent with the principles and novel features claimed in the present application.

Claims

1. A method for preparing 1800MPa grade hot-formed steel, characterized in that: The following steps are involved: A chilled coil with a set chemical composition is obtained; The chilled steel coil is subjected to continuous annealing treatment to obtain a hot-formed steel raw material coil; The hot-formed steel raw material coil is flattened, blanked and hot stamped to obtain 1800 MPa grade hot-formed steel; The continuous annealing treatment of the cold hardened coil specifically includes: Heating the chilled coil and controlling the heating rate and the end point temperature; The heated cold coil is subjected to soaking, and the duration of the soaking is controlled; Cooling the soaked chilled coil and controlling the cooling end point temperature; The cooled chilled coil is subjected to an over-aging treatment to perform a continuous annealing treatment on the chilled coil.

2. The preparation method according to claim 1, characterized in that: The end point temperature of the heating is 720° C. to 780° C.; and / or the heating rate is 2° C. / min to 5° C. / min.

3. The preparation method according to claim 1, characterized in that: The duration of the soaking is 1.5 min to 2 min; and / or the terminal temperature of the cooling is 420° C. to 470° C.; the time of the over-aging treatment is 5 min to 10 min.

4. The preparation method according to claim 1, characterized in that: The method of obtaining a cold-hardened coil having a set composition specifically comprises: Obtaining a continuous casting billet with a set chemical composition; Hot rolling the continuous casting billet to obtain a hot rolled coil; The hot rolled coil is pickled and cold rolled to obtain a chilled coil with a set chemical composition.

5. The preparation method according to claim 1, characterized in that: The set chemical composition includes a C content of 0.29% to 0.34%, a P content of ≤0.02%, and a S content of ≤0.003%.

6. The preparation method according to claim 5, characterized in that: The set chemical composition, calculated by mass fraction, includes: C: 0.29% to 0.34%, Si: 0.12% to 0.42%, Mn: 1.1% to 1.4%, P: ≤0.02%, S: ≤0.003%, Al: 0.01% to 0.06%, Cr: 0.15% to 0.35%, Nb: 0.04% to 0.06%, V: 0.01% to 0.04%, Ti: 0.02% to 0.05%, B: 0.002% to 0.004%, and Fe.

7. The preparation method according to claim 4, characterized in that: The hot rolling of the continuous casting billet to obtain a hot rolled coil specifically comprises: Heating and keeping the continuous casting billet warm; The heated continuous casting slab is subjected to rough rolling and finish rolling, and is coiled to obtain a hot-rolled coil; The target temperature of the heating is 1100° C. to 1300° C.; the insulation time is 160 min to 200 min; and / or, The final rolling temperature of the finish rolling is 860°C to 930°C; and / or the coiling temperature is 600°C to 700°C.

8. The preparation method according to claim 1, characterized in that: The hot-formed steel raw material coil is flattened, blanked and hot stamped to obtain 1800MPa grade hot-formed steel, which specifically includes: Flattening the hot-formed steel raw material coil; Preheating the flattened hot-formed steel raw material coil to a set temperature and keeping it warm to achieve austenitization; The austenitized hot-formed steel raw material coil is hot stamped and then press-quenched to achieve complete martensitic transformation to obtain 1800MPa grade hot-formed steel.

9. The preparation method according to claim 8, characterized in that: The set temperature is 850°C to 950°C, and the holding time is 5min to 8min; and / or, The target temperature of the hot stamping is greater than 800° C.; and / or, The holding pressure of the pressure-holding quenching is 5000KN to 10000KN, and the holding time is 10s to 15s.

10. 1800MPa grade hot-formed steel prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The properties of the 1800MPa grade hot-formed steel at least meet one of the following requirements: yield strength R P0.2 It is 1200MPa~1350MPa; the tensile strength Rm is 1800MPa~1950MPa; the elongation after break A50 is greater than 4%.

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