A hot-formed steel with high strength and hydrogen embrittlement resistance and its application

Abstract

The present invention provides a hot-formed steel with high strength and hydrogen embrittlement resistance and its application, belonging to the technical field of alloy materials. The hot-formed steel with high strength and hydrogen embrittlement resistance, by weight percentage, comprises the following components: C 0.22 - 0.28%, Mn 0.8 - 1.4%, Nb 0.01 - 0.08%, Cr 0.2 - 0.8%, B 0.001 - 0.005%, Ti 0.01 - 0.06%, V 0 - 0.5%, Si 0 - 0.5%, Mo 0 - 1.0%, Ni 0 - 2.0%, W 0 - 1.0%, and the balance is Fe and inevitable impurities. The ratio between the weight percentage of Cr and the weight percentage of Nb is greater than 8. The hot-formed steel with high strength and hydrogen embrittlement resistance can have both excellent strength and hydrogen embrittlement resistance, and can greatly improve the safety performance of vehicles and achieve the purpose of lightweighting.

Description

Technical Field

[0001] The present invention belongs to the technical field of alloy materials, and particularly relates to a hot-forming steel with high strength and hydrogen embrittlement resistance and its application. Background Art

[0002] Due to excellent properties such as high strength, low springback and high dimensional accuracy, hot-forming steels are widely used in structural parts related to vehicle safety, and can achieve the effect of reducing vehicle weight and saving energy while improving vehicle body safety. The production process of hot-forming steels mainly includes steps such as smelting, casting, hot rolling, pickling, cold rolling, annealing and hot stamping forming, etc. The hot stamping forming step generally includes steps such as blank heating, stamping forming, pressure holding quenching and laser trimming.

[0003] Currently, on structural parts related to vehicle safety, the 22MnB5 hot-forming steel with a strength of 1500 MPa is the most widely used. The main reason is its excellent combination of strength and hydrogen embrittlement delayed cracking resistance. On the premise of ensuring safety performance requirements, vehicle lightweighting has become one of the most direct and effective solutions for energy conservation and emission reduction. Based on this, in related technologies, hot-forming steels with higher strength levels (1600 - 2000 MPa) are being studied in order to partially or completely replace the 1500 MPa level hot-forming steel. However, although this 1600 - 2000 MPa grade hot-forming steel has very high strength, it is also accompanied by the risk of hydrogen embrittlement cracking and cannot meet the SEP1970 standard, that is, under the four-point bending loading condition, pickling in acid (0.1 mol / L HCl), presetting 100% yield strength, and not cracking for 120 hours. If it is used in structural parts related to vehicle safety, it is difficult to ensure vehicle safety performance. Therefore, how to balance its hydrogen embrittlement resistance while increasing the strength of hot-forming steels is an urgent problem to be solved. Summary of the Invention

[0004] The present invention aims to solve at least to some extent the difficult problems in related technologies. For this purpose, an embodiment of the present invention provides a hot-forming steel with high strength and hydrogen embrittlement resistance and its application.

[0005] The hot-forming steel with high strength and hydrogen embrittlement resistance according to the embodiment of the present invention, by weight percentage, comprises the following components: C 0.22 - 0.28%, Mn 0.8 - 1.4%, Nb 0.01 - 0.08%, Cr 0.2 - 0.8%, B 0.001 - 0.005%, Ti 0.01 - 0.06%, V 0 - 0.5%, Si 0 - 0.5%, Mo 0 - 1.0%, Ni 0 - 2.0%, W 0 - 1.0%, the balance being Fe and unavoidable impurities, and the ratio between the weight percentage of Cr and the weight percentage of Nb is greater than 8.

[0006] The advantages and technical effects brought by the hot-forming steel according to the embodiment of the present invention are as follows:

[0007] (1) The hot-formed steel in the embodiment of the present invention contains a specified amount of C, Mn, Cr, Mo, and B, which can improve the hardenability of the hot-formed steel, reduce the critical cooling rate, ensure that the final structure contains more than 95% martensite, and thus improve the tensile strength of the hot-formed steel.

[0008] (2) The hot-formed steel in the embodiment of the present invention contains a specified amount of Cr and Nb at the same time, and the ratio between the weight percentage of Cr and the weight percentage of Nb is greater than 8. Based on the limited precipitation content of Nb carbide, by adding a small amount of Cr, it can promote the precipitation of Nb-containing complex carbide, form the complex carbide of Cr and Nb. Even when the Nb content is insufficient, it can still ensure that a large number of nano-scale precipitation particles exist in the structure, thereby significantly improving the precipitation strengthening effect. At the same time, more importantly, a large number of complex carbides of Cr and Nb can be used as hydrogen traps to improve the hydrogen embrittlement resistance of the hot-formed steel, ensuring that the hydrogen embrittlement resistance is not lost while the strength is increased. It should be noted that the Cr content cannot be lower than 0.2% nor higher than 0.8%. When the Cr content is lower than 0.2%, it will reduce the precipitation kinetics of Cr promoting the complex carbide of Cr and Nb, while when the Cr content is higher than 0.8%, it will cause Cr to precipitate alone in the form of Cr-rich carbide, reducing the content of the complex carbide of Cr and Nb, thereby reducing the hydrogen embrittlement resistance of the hot-formed steel.

[0009] (3) The hot-formed steel in the embodiment of the present invention contains a specified amount of Ti. The main function of Ti is to fix the N element to form TiN, avoiding the formation of BN by N and B, so as to fully exert the role of B in improving hardenability.

[0010] (4) The hot-formed steel in the embodiment of the present invention also contains a specified amount of V. V can refine the grain size, making the original austenite grain size of the hot-formed steel smaller, ensuring that the toughness is not reduced or even increased while the strength is increased. At the same time, its carbide can also be used as a hydrogen trap to increase the hydrogen embrittlement resistance of the hot-formed steel.

[0011] (5) The hot-formed steel in the embodiment of the present invention also contains a specified amount of Si. During self-tempering after hot stamping die quenching, Si can hinder carbon diffusion, inhibit the decomposition of martensite and the growth rate of carbide aggregation, and significantly improve the tempering stability and strength of the hot-formed steel.

[0012] (6) The hot-formed steel in the embodiment of the present invention also contains a specified amount of Ni. Ni can ensure that the strength of the hot-formed steel is increased without significantly reducing its toughness.

[0013] (7) The hot-formed steel in the embodiment of the present invention also contains a specified amount of W. W forms carbide, which can improve the strength of the hot-formed steel and its toughness at the same time.

[0014] In some embodiments, 710 MPa < 3000 MPa × weight percentage of C + 65 MPa × weight percentage of Mn < 900 MPa.

[0015] In some embodiments, the weight percentage of Mn is 0.8 - 1.3%.

[0016] In some embodiments, the ratio between the weight percentage of Cr and the weight percentage of Nb is greater than 12.

[0017] In some embodiments, the weight percentage of Nb is 0.02 - 0.04%.

[0018] In some embodiments, the content of impurity N is less than 100 ppm, and the contents of impurities P, S, and O are all less than 200 ppm.

[0019] In some embodiments, the critical cooling rate of the hot - formed steel is 50 °C / s or less, and / or the metallographic structure of the hot - formed steel is more than 95% martensite, preferably 100% martensite.

[0020] In some embodiments, the original austenite grain size of the hot - formed steel is 3 - 15 μm, and / or in the VDA238 - 100 standard test, the bending angle of a 1.4 - mm - thick steel plate is greater than 50°.

[0021] In some embodiments, the tensile strength of the hot - formed steel is 1600 MPa or more, and at the same time, in the SEP1970 standard test, under the four - point bending loading condition, after pickling in acid, with a preset 100% yield strength, it does not crack within 120 hours.

[0022] In addition, the embodiments of the present invention also provide an application of the high - strength hydrogen - embrittlement - resistant hot - formed steel in vehicles.

[0023] The advantages and technical effects brought by the application of the embodiments of the present invention are as follows:

[0024] Since the hot - formed steel of the embodiments of the present invention has excellent strength and hydrogen - embrittlement - resistant performance, it can be used in parts such as seat cross - beams, A / B pillars, door anti - collision beams, front and rear bumpers, sill beams, and center tunnels of vehicles, which can greatly improve the safety performance of vehicles and achieve the purpose of lightweighting. Brief Description of the Drawings

[0025] Figure 1 is a schematic flow chart of the preparation method of the high - strength hydrogen - embrittlement - resistant hot - formed steel of the present invention;

[0026] Figure 2 is a schematic flow chart of the hot stamping forming steps of the high - strength hydrogen - embrittlement - resistant hot - formed steel of the present invention;

[0027] Figure 3 It is the hot stamping process diagram of the high-strength hydrogen embrittlement-resistant hot forming steel of Embodiment 3 of the present invention;

[0028] Figure 4 It is the transmission electron microscope image and energy spectrum diagram of the high-strength hydrogen embrittlement-resistant hot forming steel of Embodiment 3 of the present invention; the substance within the circle in the left figure is the composite carbide of Cr and Nb. Specific embodiments

[0029] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention, and should not be construed as a limitation to the present invention.

[0030] The embodiments of the present invention provide a high-strength hydrogen embrittlement-resistant hot forming steel, which is characterized in that, by weight percentage, it includes the following components: C 0.22 - 0.28%, Mn 0.8 - 1.4%, Nb 0.01 - 0.08%, Cr 0.2 - 0.8%, B 0.001 - 0.005%, Ti 0.01 - 0.06%, V 0 - 0.5%, Si 0 - 0.5%, Mo 0 - 1.0%, Ni 0 - 2.0%, W 0 - 1.0%, and the balance is Fe and unavoidable impurities, and the ratio between the weight percentage of Cr and the weight percentage of Nb is greater than 8.

[0031] In the hot forming steel of the embodiments of the present invention, the weight percentage of C is 0.22 - 0.28%, such as 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, etc. The role of C is to improve the strength and hardenability of the hot forming steel. When the weight percentage of C is lower than 0.22%, the strength of the hot forming steel is lower than 1600 MPa, and compared with the commonly used 22MnB5 hot forming steel, the improvement in strength cannot be achieved; when the weight percentage of C is higher than 0.28%, the toughness of the hot forming steel is significantly reduced. Considering the matching of strength and toughness, the weight percentage of C is selected to be 0.22 - 0.28%. Preferably, in some embodiments, the weight percentage of C is 0.24 - 0.28%.

[0032] In the hot forming steel of the embodiments of the present invention, the weight percentage of Mn is 0.8 - 1.4%, such as 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, etc. Mn can increase the hardenability of the steel and reduce the austenite formation temperature. When the weight percentage of Mn is lower than 0.8%, the hardenability of the steel is poor and the austenite formation temperature is high; when the weight percentage of Mn is higher than 1.4%, it is not conducive to welding. Therefore, the weight percentage of Mn is 0.8 - 1.4%. Preferably, in some embodiments, the weight percentage of Mn is 0.8 - 1.3%.

[0033] In some embodiments, 710 MPa < 3000 MPa × weight percentage of C + 65 MPa × weight percentage of Mn < 900 MPa. C and Mn have a solid solution strengthening effect. In the foregoing relationship, 3000 MPa is the solid solution strength of C, 65 MPa is the solid solution strength of Mn, 3000 MPa × weight percentage of C is the contribution value from the solid solution strengthening effect of C, 65 MPa × weight percentage of Mn is the contribution value from the solid solution strengthening effect of Mn. When the contents of C and Mn satisfy the foregoing relationship, it is possible to control the welding C equivalent while increasing the strength, and avoid the deterioration of the welding performance.

[0034] In the hot-formed steel according to the embodiments of the present invention, the weight percentage of Nb is 0.01-0.08%, such as 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, etc. Nb forms carbides during the hot stamping process, which can refine the grain size, making the original austenite grain size of the hot-formed steel smaller and increasing the toughness of the hot-formed steel; at the same time, the carbides can also act as hydrogen traps, increasing the hydrogen embrittlement resistance of the hot-formed steel. When the weight percentage of Nb is lower than 0.01%, the toughness and hydrogen embrittlement resistance of the hot-formed steel are both poor; when the weight percentage of Nb is higher than 0.08%, the grain refinement and precipitation strengthening effects are not significant. Therefore, the weight percentage of Nb is 0.01-0.08%. Preferably, in some embodiments, the weight percentage of Nb is 0.02-0.04%.

[0035] In the hot-formed steel according to the embodiments of the present invention, the weight percentage of Cr is 0.2-0.8%, such as 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, etc. Since the hot-formed steel requires a lower critical cooling rate to ensure that all austenite transforms into martensite during the cooling process. However, reducing the original austenite grain size will increase the critical cooling rate. Therefore, a specified amount of Cr needs to be added to improve the hardenability of the steel and reduce its critical cooling rate. When the weight percentage of Cr is lower than 0.2%, the critical cooling rate of the steel is relatively high, and other soft phases such as ferrite and pearlite may be generated, greatly reducing the strength of the hot-formed steel; when the weight percentage of Cr is higher than 0.8%, 2 O 3 oxide scale will be produced, which is not easy to be pickled clean, affecting the hot-dip plating effect. Therefore, the weight percentage of Cr is 0.2-0.8%. Preferably, in some embodiments, the weight percentage of Cr is 0.4-0.7%.

[0036] It is found in the present invention that when Cr and Nb are within their respective defined ranges and satisfy the condition that the ratio of the weight percentage of Cr to the weight percentage of Nb is greater than 8, for example, the ratio is 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, etc., Cr and Nb will form fine complex carbides, which can play the role of precipitation strengthening, improve the mechanical properties of hot-formed steel; at the same time, the complex carbides of Cr and Nb can also be used as hydrogen traps to improve the hydrogen embrittlement resistance of hot-formed steel. Cr and Nb cooperate with each other, and the above two effects together improve the mechanical properties and hydrogen embrittlement resistance of hot-formed steel. The tensile strength of the hot-formed steel can reach more than 1600 MPa, and it does not crack after 120 h at 100% yield strength.

[0037] If there is only Cr or only Nb, it is impossible to form the complex carbides of Cr and Nb, which will affect the mechanical properties and hydrogen embrittlement resistance of hot-formed steel. If the content of Cr is higher than the range of the embodiments of the present invention, mainly Cr 23 C 6 、Cr 7 C 3 and other coarse carbides (above 100 nm or even micron level) will deteriorate the mechanical properties, and both toughness and strength will decrease. It will also consume a large amount of carbon and reduce the strength. At the same time, the content of the complex carbides of Cr and Nb will be greatly reduced, and the effect of capturing hydrogen is not obvious, making the hot-formed steel prone to hydrogen embrittlement cracking at 100% yield strength. If the ratio of the weight percentage of Cr to the weight percentage of Nb is less than or equal to 8, it will also deteriorate the hydrogen embrittlement resistance of hot-formed steel, and it is prone to hydrogen embrittlement cracking at 100% yield strength.

[0038] Preferably, in some embodiments, the ratio of the weight percentage of Cr to the weight percentage of Nb is greater than 12. When the weight percentage ratio of Cr and Nb is preferably within the above range, it is beneficial to further improve the mechanical properties and hydrogen embrittlement resistance of hot-formed steel.

[0039] In the hot-formed steel of the embodiments of the present invention, the weight percentage of B is 0.001 - 0.005%, such as 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, etc. The role of B is to improve the hardenability of the steel and reduce the critical cooling rate of the steel, so that the steel material transforms from the austenite phase to the martensite phase in the hot stamping forming step, thereby improving the strength of the hot-formed steel. When the weight percentage of B is lower than 0.001%, the critical cooling rate of the steel is relatively high, and other soft phases such as ferrite and pearlite may be produced, greatly reducing the strength of the hot-formed steel; when the weight percentage of B is higher than 0.005%, the hardenability effect is not significant. Therefore, the weight percentage of B is 0.001 - 0.005%. Preferably, in some embodiments, the weight percentage of B is 0.002 - 0.004%.

[0040] In the hot-formed steel of the embodiment of the present invention, the weight percentage of Ti is 0.01-0.06%, such as 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, etc. After adding Ti, precipitates in the form of TiN will be formed, which can fix N element and avoid consuming B element, so as to give full play to the role of B in improving hardenability. Preferably, in some embodiments, the weight percentage of Ti is 0.02-0.05%.

[0041] V will form carbides during the hot stamping process, which can refine the grain size, making the original austenite grain size of the hot-formed steel smaller and increasing the toughness of the hot-formed steel; at the same time, its carbides can also act as hydrogen traps to increase the hydrogen embrittlement resistance of the hot-formed steel. When the weight percentage of V is higher than 0.5%, the grain refinement and precipitation strengthening are not significant. Therefore, the weight percentage of V is 0-0.5%. Preferably, in some embodiments, the weight percentage of V is 0-0.05%.

[0042] In the hot-formed steel of the embodiment of the present invention, the weight percentage of Si is 0-0.5%, such as 0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, etc. The role of Si is to improve the self-tempering resistance during the hot stamping process and prevent the reduction of strength. When the weight percentage of Si is higher than 0.5%, more SiO 2 will be easily formed in the scale, which is not conducive to improving the surface quality of the hot-rolled strip. Therefore, the weight percentage of Si is 0-0.5%. Preferably, in some embodiments, the weight percentage of Si is 0-0.4%.

[0043] In the hot-formed steel of the embodiment of the present invention, the weight percentage of Mo is 0-1.0%, such as 0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc. The role of Mo is to improve hardenability. When the weight percentage of Mo is higher than 1.0%, the hardenability is not significant. Therefore, the weight percentage of Mo is 0-1.0%. Preferably, in some embodiments, the weight percentage of Mo is 0-0.5%.

[0044] In the hot-formed steel of the embodiment of the present invention, the weight percentage of Ni is 0-2.0%, such as 0, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, etc. The role of Ni is to improve strength while ensuring that the toughness does not decrease significantly. When the weight percentage of Ni is higher than 2.0%, the strength improvement is not significant. Therefore, the weight percentage of Ni is 0-2.0%. Preferably, in some embodiments, the weight percentage of Ni is 0-0.2%.

[0045] In the hot-formed steel of the embodiment of the present invention, the weight percentage of W is 0-1.0%, such as 0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc. The function of W is to improve hardenability and play a role in solid solution strengthening. When the weight percentage of W is higher than 1.0%, the strength improvement is not obvious. Therefore, the weight percentage of W is 0-1.0%. Preferably, in some embodiments, the weight percentage of W is 0-0.3%.

[0046] Preferably, in some embodiments, the content of impurity N is less than 100 ppm, and the contents of impurities P, S, and O are all less than 200 ppm. N, P, S, and O are all inevitable impurities, and their existence will reduce the toughness of the hot-formed steel. Therefore, the lower the contents of N, P, S, and O, the better. In the embodiment of the present invention, controlling the content of N to be less than 100 ppm and controlling the contents of P, S, and O to be less than 200 ppm can prevent the toughness of the hot-formed steel from being reduced.

[0047] Preferably, in some embodiments, the critical cooling rate of the hot-formed steel is 50°C / s or less, and / or the metallographic structure of the hot-formed steel is more than 95% martensite. When the critical cooling rate of the hot-formed steel is too high, it is not conducive to the transformation of austenite to martensite, and thus not conducive to improving the strength of the hot-formed steel. When the proportion of martensite in the metallographic structure of the hot-formed steel is too low, the proportion of other soft phases such as ferrite and pearlite is too high, which is not conducive to improving the strength of the hot-formed steel.

[0048] Preferably, in some embodiments, the original austenite grain size of the hot-formed steel is 3-15 μm; and / or, in the VDA238-100 standard test of the hot-formed steel, the bending angle of the 1.4 mm thick steel plate is greater than 50°. When the original austenite grain size of the hot-formed steel is too large, the bending angle decreases, indicating a decrease in toughness.

[0049] Preferably, in some embodiments, the tensile strength of the hot-formed steel is 1600 MPa or more, such as 1600 MPa, 1660 MPa, 1700 MPa, 1750 MPa, 1770 MPa, 1780 MPa, 1800 MPa, etc. At the same time, in the SEP1970 standard test of the hot-formed steel, under the four-point bending loading condition, pickling in acid, presetting 100% yield strength, and no cracking in 120 hours.

[0050] In addition, the embodiment of the present invention also provides a preparation method of a high-strength hydrogen embrittlement-resistant hot-formed steel, such as Figure 1 and Figure 2As shown, it includes the following steps: smelting, casting, hot rolling, coiling, pickling, cold rolling, continuous annealing, and hot stamping forming. The hot stamping forming step includes the following steps: blank heating, stamping forming, and pressure holding quenching.

[0051] In some embodiments, the final rolling temperature in the hot rolling step is 780 - 900 °C, and / or the coiling temperature is 450 - 600 °C, which is convenient for obtaining a hot rolled coil with no or low internal oxidation.

[0052] In some embodiments, the dew point of the continuous annealing is -16 - 31 °C, and / or the temperature of the continuous annealing is 740 - 800 °C, which is convenient for obtaining a uniform structure and properties.

[0053] In some embodiments, coating is also included between continuous annealing and hot stamping forming. After obtaining the bare steel plate by continuous annealing, an aluminum-silicon layer or a zinc layer can be coated on the surface of the bare steel plate in advance to prevent the bare steel plate from being oxidized during the subsequent hot stamping forming process.

[0054] In addition, the embodiments of the present invention also provide the application of the hot forming steel with high strength and hydrogen embrittlement resistance in the embodiments of the present invention in vehicles.

[0055] Due to the excellent strength and hydrogen embrittlement resistance of the hot forming steel in the embodiments of the present invention, it can be used in parts such as seat crossbeams, A / B pillars, door anti-collision beams, front and rear bumpers, sill beams, and center channels of vehicles, which can greatly improve the safety performance of vehicles and achieve the purpose of lightweight.

[0056] The present invention will be described in detail below with reference to the embodiments and the drawings.

[0057] Example 1

[0058] A kind of hot forming steel with high strength and hydrogen embrittlement resistance, and its chemical composition is shown in Table 1.

[0059] The preparation method of this hot forming steel includes the following steps:

[0060] (1) Smelting: Charge materials according to the chemical composition of the hot forming steel and smelt them into molten steel;

[0061] (2) Cast the molten steel to obtain a steel billet;

[0062] (3) Hot roll the steel billet, with the final rolling temperature being 870 °C, to obtain a thick steel plate with a thickness of 4 mm;

[0063] (4) Coil the hot rolled thick steel plate, with the coiling temperature being 550 °C, to obtain a hot rolled coil;

[0064] (5) Pickle the hot rolled coil to obtain a pickled plate;

[0065] (6) Cold roll the pickled sheet at room temperature to obtain a thin steel sheet with a thickness of 1.4 mm;

[0066] (7) Continuously anneal the thin steel sheet at a dew point of -23 °C and a temperature of 780 °C for 10 min to obtain a bare steel sheet;

[0067] (8) Coat an aluminum-silicon layer on the bare steel sheet;

[0068] (9) Heat the steel sheet with an aluminum-silicon layer in a roller hearth furnace to 920 °C, then put it into a hot stamping die, and then perform hot stamping forming under a constant pressure of about 30 °C, and directly quench in the hot stamping die to obtain the final stamped part.

[0069] Comparative Example 1

[0070] A hot-formed steel, the chemical composition of which is shown in Table 1. The preparation method of this hot-formed steel is the same as that of Example 1.

[0071] Comparative Example 2

[0072] A hot-formed steel, the chemical composition of which is shown in Table 1. The preparation method of this hot-formed steel is the same as that of Example 1.

[0073] Example 2

[0074] A high-strength hydrogen embrittlement-resistant hot-formed steel, the chemical composition of which is shown in Table 1. The preparation method of this hot-formed steel is the same as that of Example 1.

[0075] Comparative Example 3

[0076] A hot-formed steel, the chemical composition of which is shown in Table 1. The preparation method of this hot-formed steel is the same as that of Example 1.

[0077] Example 3

[0078] A high-strength hydrogen embrittlement-resistant hot-formed steel, the chemical composition of which is shown in Table 1. The preparation method of this hot-formed steel is the same as that of Example 1.

[0079] Comparative Example 4

[0080] A hot-formed steel, the chemical composition of which is shown in Table 1. The preparation method of this hot-formed steel is the same as that of Example 1.

[0081] Example 4

[0082] A high-strength hydrogen embrittlement-resistant hot-formed steel, the chemical composition of which is shown in Table 1. The preparation method of this hot-formed steel is the same as that of Example 1.

[0083] Comparative Example 5

[0084] A hot-formed steel, the chemical composition of which is shown in Table 1. The preparation method of this hot-formed steel is the same as that of Example 1.

[0085] Comparative Example 6

[0086] A hot-formed steel, the chemical composition of which is shown in Table 1. The preparation method of this hot-formed steel is the same as that of Example 1.

[0087] Example 5

[0088] A high-strength hydrogen embrittlement-resistant hot-formed steel, the chemical composition of which is shown in Table 1. The preparation method of this hot-formed steel is the same as that of Example 1.

[0089] Comparative Example 7

[0090] A hot-formed steel, the chemical composition of which is shown in Table 1. The preparation method of this hot-formed steel is the same as that of Example 1.

[0091] Performance test

[0092] Bending angle test: According to the VDA238-100 test standard, test the bending angles of the 1.4 mm thick hot-formed steel sheet in the TD and RD directions, and take the minimum value.

[0093] Hydrogen embrittlement resistance: According to the SEP1970 test standard, soak in acid (0.1 mol / L HCl) under four-point bending loading conditions, preset 100% yield strength, and observe whether cracking occurs within 120 hours. If there is no cracking in hydrogen embrittlement at 100% yield strength within 120 hours, it proves that the hydrogen embrittlement resistance is qualified; if cracking occurs in hydrogen embrittlement at 100% yield strength, it proves that the hydrogen embrittlement resistance is unqualified.

[0094] Table 1. Chemical compositions of the hot-formed steels of Examples 1-5 and Comparative Examples 1-7

[0095] C Mn Nb Cr B Ti V Si Mo Ni W Example 1 0.27 1.25 0.030 0.40 0.003 0.034 - 0.32 - - - Comparative Example 1 0.27 1.25 0.030 0.10 0.003 0.034 - 0.32 - - - Comparative Example 2 0.27 1.25 0.030 1.30 0.003 0.034 - 0.32 Example 2 0.26 1.35 0.032 0.60 0.003 0.034 - 0.20 - - - Comparative Example 3 0.26 1.35 0.032 0.10 0.003 0.034 - 0.20 - - - Example 3 0.24 1.23 0.035 0.70 0.003 0.035 - 0.28 - - - Comparative Example 4 0.24 1.23 0.035 0.15 0.003 0.035 - 0.28 - - - Example 4 0.27 1.20 0.030 0.45 0.003 0.036 0.05 0.25 0.42 - - Comparative Example 5 0.27 1.20 0.030 0.15 0.003 0.036 0.05 0.20 - - - Comparative Example 6 0.27 1.20 0.07 0.45 0.003 0.036 0.05 0.25 0.42 - - Example 5 0.24 1.28 0.043 0.50 0.003 0.035 0.05 0.20 0.40 0.2 0.3 Comparative Example 7 0.24 1.28 0.043 0.12 0.003 0.034 0.05 0.20 - - -

[0096] Table 2. Properties of the hot-formed steels of Examples 1-5 and Comparative Examples 1-7

[0097]

[0098] As can be seen from Table 1 and Table 2, the hot-formed steels of Examples 1-5 of the present invention have excellent tensile strength and hydrogen embrittlement resistance. Specifically, the tensile strength is above 1600 MPa, and there is no cracking in hydrogen embrittlement at 100% yield strength within 120 hours.

[0099] From the comparison between Example 1 and Comparative Example 1, Example 2 and Comparative Example 3, Example 3 and Comparative Example 4, Example 4 and Comparative Example 5, and Example 5 and Comparative Example 7, it can be seen that the Cr content in Comparative Examples 1, 3, 4, 5, and 7 is lower than the range defined by the present invention, and the ratio between the weight percentage of Cr and the weight percentage of Nb is less than 8, and the hot-formed steel obtained exhibits hydrogen embrittlement cracking at 100% yield strength.

[0100] From the comparison between Example 4 and Comparative Example 6, it can be seen that the ratio between the weight percentage of Cr and the weight percentage of Nb in Comparative Example 6 is less than 8, and the hot-formed steel obtained exhibits hydrogen embrittlement cracking at 100% yield strength.

[0101] From the comparison between Example 1 and Comparative Example 2, it can be seen that the Cr content in Comparative Example 2 is higher than the range defined by the present invention, and the hot-formed steel obtained exhibits hydrogen embrittlement cracking at 100% yield strength. Moreover, an increase in the Cr content will also increase the production cost of the hot-formed steel.

[0102] In the present invention, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0103] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A hot-formed steel with high strength and resistance to hydrogen embrittlement, characterized in that, by weight percentage, it includes the following components: C 0.22 - 0.28%, Mn 0.8 - 1.4%, Nb 0.02 - 0.04%, Cr 0.4 - 0.8%, B 0.001 - 0.005%, Ti 0.01 - 0.06%, V 0 - 0.5%, Si 0 - 0.5%, Mo 0 - 1.0%, Ni 0 - 2.0%, W 0 - 1.0%, and the balance is Fe and unavoidable impurities. The ratio between the weight percentage of Cr and the weight percentage of Nb is greater than 10. The tensile strength of the hot-formed steel is above 1600 MPa. At the same time, in the SEP1970 standard test, under the four-point bending loading condition, pickling in acid, presetting 100% yield strength, it does not crack in 120 hours.

2. The hot-formed steel with high strength and resistance to hydrogen embrittlement according to claim 1, characterized in that, 710 MPa < 3000 MPa × weight percentage of C + 65 MPa × weight percentage of Mn < 900 MPa.

3. The hot-formed steel with high strength and resistance to hydrogen embrittlement according to claim 1 or 2, characterized in that, the weight percentage of Mn is 0.8 - 1.3%.

4. The hot-formed steel with high strength and resistance to hydrogen embrittlement according to claim 1, characterized in that, the ratio between the weight percentage of Cr and the weight percentage of Nb is greater than 12.

5. The hot-formed steel with high strength and resistance to hydrogen embrittlement according to claim 1, characterized in that, the content of impurity N is less than 100 ppm, and the contents of impurities P, S, and O are all less than 200 ppm.

6. The hot-formed steel with high strength and resistance to hydrogen embrittlement according to claim 1, characterized in that, the critical cooling rate of the hot-formed steel is below 50 °C / s, and / or the metallographic structure of the hot-formed steel is more than 95% martensite.

7. The hot-formed steel with high strength and resistance to hydrogen embrittlement according to claim 6, characterized in that, the metallographic structure of the hot-formed steel is 100% martensite.

8. The hot-formed steel with high strength and resistance to hydrogen embrittlement according to claim 1, characterized in that, the original austenite grain size of the hot-formed steel is 3 - 15 μm, and / or in the VDA238 - 100 standard test, the bending angle of a 1.4 mm thick steel plate is greater than 50°.

9. Application of the hot-formed steel with high strength and resistance to hydrogen embrittlement according to any one of claims 1 - 8 in vehicles.

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