Preparation method of high-oxidation-resistance hot forming steel part

Abstract

The invention discloses a preparation method of a high-oxidation-resistance hot-formed steel part, and belongs to the technical field of hot-formed steel, the preparation method comprises the following steps: removing a surface oxide layer of a hot-rolled hot-formed steel billet by adopting an acid pickling process to obtain a hot-formed steel plate, and then putting the hot-formed steel plate subjected to acid pickling into a molybdate solution for soaking and passivating treatment to obtain the high-oxidation-resistance hot-formed steel part. A layer of nano-scale passivation film is formed on the surface of the hot-formed steel, the passivated hot-formed steel plate is heated to be completely austenitized, heat preservation is conducted, and finally the completely austenitized hot-formed steel plate is rapidly transferred into a stamping die to be stamped and quenched. According to the method, the surface oxidation problem of the hot-formed steel plate in the austenitizing process is solved in a surface passivation mode, and a thin and compact oxidation layer which is better combined with a base body is formed on the surface of a part, so that the abrasion problem of a mold is reduced, meanwhile, shot blasting treatment can be omitted, and the service life of the part is prolonged. And the production cost of hot-formed steel parts is further reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of hot-formed steel materials, and in particular relates to a method for preparing a hot-formed steel part with high oxidation resistance. Background Art

[0002] The rapid development of the automobile industry has led to an increasing demand for lightweight and safety. In order to alleviate the pollution caused by automobile exhaust emissions to the environment, the application of high-strength thin steel plates in white bodies is the main development direction of the automobile manufacturing industry. Statistics show that for every 10% reduction in vehicle mass, fuel consumption can be reduced by 6% to 8%, and exhaust emissions can be reduced by 5% to 6%. The use of high-strength thin steel plates in white bodies can not only effectively reduce the weight of the body and reduce fuel consumption, but also improve the safety and comfort of the car. It is the best way to achieve lightweight and improve collision safety at the same time. However, the plastic deformation range of high-strength thin steel plates becomes narrower during the manufacturing process, the punching pressure increases, the forming rebound of parts is serious, the size and shape stability deteriorates, and the formability and weldability of the material are adversely affected, making conventional cold stamping very difficult, and increasing the processing difficulty and manufacturing cost of automobile manufacturers. Hot-formed steel is widely used in white bodies due to its advantages such as high ductility, small rebound, and low manufacturing difficulty, such as A-pillars, B-pillars, front and rear bumpers, and door anti-collision beams.

[0003] At present, the most widely used hot-formed steel is 22MnB5. The manufacturing process of parts is to put the steel plate containing ferrite and pearlite into a heating furnace above the austenitizing temperature and keep it for a period of time to obtain a complete austenite phase; quickly transfer the fully austenitized steel plate from the heating furnace to the stamping tool, pressurize and close the mold to deform the steel plate into the required shape; in order to obtain high-strength martensitic structure, it is necessary to use the cooling system equipped with the mold to quickly cool it while closing the mold to obtain an ultra-high-strength product. Compared with cold forming technology, it has the advantages of eliminating the impact of springback, high precision and good quality of formed parts, greatly improving the crash resistance and overall safety of the car body, and reducing the steel plate to achieve lightweight and save consumables.

[0004] During the austenitization process, hot-formed steel plates will produce an oxide layer with a loose structure and easy to fall off from the matrix. This oxide layer will damage the mold in the subsequent stamping stage and affect the surface quality of the final parts. Although the production cost of bare plates is low, the surface of the steel plate is prone to form an oxide layer with poor bonding with the matrix during the austenitization process. It is easy to fall off during the stamping process and damage the mold and parts. The production process has to be stopped for cleaning, affecting the production rhythm and production efficiency. At present, in order to improve the oxidation resistance of bare plates, the existing technology mainly adopts the method of surface coating of steel plates, including aluminum silicon coating, aluminum zinc coating, etc., but the preparation cost of the coating is relatively expensive, the process is complicated, special equipment is required for production, and it is highly dependent on the equipment. There are also problems such as cracking and sticking to the roller. In addition, thicker oxide layers usually need to be removed by shot peening, but shot peening cannot guarantee dimensional accuracy, and the process cost is high, which will cause large changes in product size and affect subsequent use. Therefore, the thickness of the oxide layer on the surface of hot-formed parts and the bonding force between it and the matrix have a significant impact on the size and cost of the final product. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a method for preparing hot-formed steel parts with high oxidation resistance. The present invention adopts surface passivation to solve the surface oxidation problem of hot-formed steel plates during the austenitization process, and forms a thin and dense oxide layer on the surface of the parts with better bonding with the matrix, which is beneficial to reducing the wear problem of the mold, and also can avoid shot peening, further reducing the production cost of hot-formed steel parts.

[0006] In order to achieve the above object, the present invention provides the following technical solutions: The present invention provides a method for preparing a hot-formed steel part with high oxidation resistance, comprising the following steps: (1) A pickling process is used to remove the surface oxide layer of the hot-formed steel billet after hot rolling to obtain a hot-formed steel plate; (2) The pickled hot-formed steel plate is immersed in a molybdate solution for passivation treatment to form a nano-scale passivation film on the surface of the hot-formed steel; (3) heating the passivated hot-formed steel plate until it is completely austenitized and then keeping it warm; (4) The fully austenitized hot-formed steel plate is quickly transferred to the stamping die for press quenching.

[0007] Based on the above technical solution, further, the chemical composition of the hot-formed steel is as follows by mass percentage: C: 0.18~0.35%, Mn: 1.0~2.0%, Si: 0.2~1.0%, S≤0.01%, P≤0.015%, Al: 0.05~0.1%, Cr≤1.0%, Nb≤0.01%, V≤0.01%, Ti: 0.01~0.03%, B≤0.01%, La+Ce≤0.015%, and the balance is Fe and unavoidable impurities.

[0008] Based on the above technical solution, further, the chemical composition of the hot-formed steel is as follows by mass percentage: C: 0.20~0.30%, Mn: 1.3~1.8%, Si: 0.2~0.4%, S: 0.001~0.010%, P: 0.001~0.010%, Al: 0.05~0.1%, Cr: 0.3~0.7%, Nb: 0.001~0.010%, V: 0.001~0.010%, Ti: 0.01~0.03%, B: 0.001~0.005%, La+Ce: 0.0005~0.015%, and the balance is Fe and unavoidable impurities.

[0009] Based on the above technical solution, further, the thickness of the hot-formed steel plate described in step (1) is 2.0~4.0 mm.

[0010] Based on the above technical solution, further, the molybdate solution described in step (2) includes Na2MoO4 and K2MoO4.

[0011] Based on the above technical solution, further, the passivation treatment conditions described in step (2) are room temperature, the concentration of the molybdate solution is 0.5~2g / L, and the passivation treatment time is not less than 15min.

[0012] Based on the above technical solution, further, the concentration of the molybdate solution in step (2) is 0.8-1.5 g / L, and the passivation treatment time is 15-60 min.

[0013] Based on the above technical solution, further, in step (3), the austenitizing temperature is 920-950°C, and the holding time is controlled to be more than 5 minutes.

[0014] Based on the above technical solution, further, the insulation time in step (3) is controlled within 5 to 20 minutes.

[0015] Based on the above technical solution, further, the cooling rate of the stamping quenching in step (4) is not less than 20°C / s, and the mold opening temperature is not higher than 200°C.

[0016] Based on the above technical solution, further, the cooling rate of stamping quenching in step (4) is 20~50℃ / s.

[0017] The present invention also provides a hot-formed steel part obtained by the preparation method.

[0018] Based on the above technical solution, further, the yield strength of the hot-formed steel part is 1000~1200MPa, the tensile strength is 1400~1600MPa, the elongation after fracture is 12~17%, and the volume percentage of martensite is 95~99%.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. The method of the present invention can effectively replace the current main steel plate surface coating method, significantly improve the oxidation resistance of hot-formed steel plates, and further reduce production costs.

[0020] 2. The method of the present invention can form a thin and dense oxide layer on the surface of the hot-formed steel substrate during the austenitizing process stage. The main component of the passivation film is Fe2(MoO4)3 with a dense structure. The passivation film can effectively prevent the oxidation reaction during the austenitizing stage, and ultimately reduce the thickness of the oxide layer, improve the physical structure of the oxide layer, and enhance the surface oxidation resistance of the hot-formed steel, effectively solving the problems of reduced production efficiency and final product performance caused by excessive thickness of the oxide layer.

[0021] 3. The method of the present invention can promote the formation of Si-rich phase on the surface oxide layer of hot-formed steel close to the substrate, which is beneficial to enhance the adhesion between the oxide layer and the substrate, making it difficult to fall off during stamping and quenching, reducing damage to the mold and the impact on the surface quality of the final product.

[0022] 4. The method of the present invention avoids the shot peening treatment on the surface of the final product, which is conducive to further reducing the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention, the drawings related to the embodiments are briefly introduced below.

[0024] Figure 1 These are the results of surface phase detection of the hot-formed steel plate after passivation in Example 1, where (a) is the total spectrum, (b) is the Fe 2p spectrum, (c) is the O 1s spectrum, and (d) is the Mo 3d spectrum.

[0025] Figure 2 This is a comparison chart of the oxidation weight gain of the hot-formed steel plates in Example 1 and Comparative Example 1 during the austenitizing stage.

[0026] Figure 3This is a comparison of the macroscopic morphology of the oxide layer surface of the hot-formed steel plates in Example 1 and Comparative Example 1 after austenitization and high-temperature oxidation.

[0027] Figure 4 The graphs are comparisons of the surface microstructures of the oxide layers of the hot-formed steel plates after austenitization and high-temperature oxidation in Example 1 and Comparative Example 1, wherein (a) is unpassivated, (b) is passivated for 15 minutes, and (c) is passivated for 30 minutes.

[0028] Figure 5 The figures are comparison diagrams of the cross-sectional microstructures of the oxide layers of the hot-formed steel plates after austenitization and high-temperature oxidation in Example 1 and Comparative Example 1, wherein (a) is unpassivated, (b) is passivated for 15 minutes, and (c) is passivated for 30 minutes.

[0029] Figure 6 1 is a comparison diagram of the phase composition of the oxide layer of the hot-formed steel plates after austenitization and high-temperature oxidation in Example 1 and Comparative Example 1, wherein (a) is unpassivated, (b) is passivated for 15 minutes, and (c) is passivated for 30 minutes.

[0030] Figure 7 This is a schematic diagram showing the principle of changing the oxide layer structure by passivation on the surface of hot-formed steel in Examples 1-3. DETAILED DESCRIPTION

[0031] The present invention is described in detail below with reference to the embodiments, but the embodiments of the present invention are not limited thereto. Obviously, the embodiments described below are only partial embodiments of the present invention. For those skilled in the art, other similar embodiments obtained without creative labor all fall within the protection scope of the present invention.

[0032] Example 1 The present embodiment provides a method for preparing a hot-formed steel part with high oxidation resistance. The chemical composition of the hot-formed steel used is as follows by mass percentage: C: 0.24%, Mn: 1.5%, Si: 0.24%, S: 0.0035%, P: 0.005%, Al: 0.08%, Cr: 0.45%, Nb: 0.005%, V: 0.003%, Ti: 0.02%, B: 0.002%, La+Ce: 0.0008%, and the balance is Fe and unavoidable impurities.

[0033] The steps include: (1) After hot rolling, the hot-formed steel billet has a thick oxide layer on its surface. The surface oxide layer caused by hot rolling is completely removed by pickling process to obtain a hot-formed steel plate with a pure iron surface (plate thickness 2.5 mm); (2) The hot-formed steel plates after pickling were subjected to room temperature immersion passivation treatment using Na2MoO4 solution. The concentration of the Na2MoO4 solution was 1g / L, and the passivation treatment time was set to 15min and 30min respectively. After passivation, the surface was air-dried to form a nano-scale passivation film on the surface of the bare hot-formed steel plate. This passivation film is beneficial to reduce the direct contact between oxygen and the steel plate in the initial stage of subsequent austenitization, effectively hindering the oxidation reaction, and improving the oxidation behavior of the hot-formed steel plate during the austenitization process; (3) The passivated hot-formed steel plate is placed in a heating furnace for austenitization at a temperature of 930°C. In order to completely austenitize the hot-formed steel plate, the holding time is 8 minutes. (4) The fully austenitized hot-formed steel plate is taken out and quickly transferred to a stamping die for press quenching. The cooling rate of press quenching is 38°C / s and the die opening temperature is 182°C.

[0034] The yield strength of the prepared hot-formed steel stamping parts is 1048MPa, the tensile strength is 1404MPa, the elongation after fracture is 13.64%, and the volume percentage of martensite is 98%.

[0035] Comparative Example 1 The experimental process of this comparative example is the same as that of Example 1, except that the hot-formed steel plate after pickling is not subjected to room temperature immersion passivation treatment (no passivation treatment) in a Na2MoO4 solution, but is directly placed in a heating furnace for austenitization.

[0036] The yield strength of the prepared hot-formed steel stamping parts is 1075MPa, the tensile strength is 1438MPa, the elongation after fracture is 14.13%, and the volume percentage of martensite is 98%.

[0037] Example 2 The present embodiment provides a method for preparing a hot-formed steel part with high oxidation resistance. The chemical composition of the hot-formed steel used is as follows by mass percentage: C: 0.23%, Mn: 1.5%, Si: 0.25%, S: 0.004%, P: 0.0045%, Al: 0.09%, Cr: 0.51%, Nb: 0.004%, V: 0.002%, Ti: 0.02%, B: 0.002%, La+Ce: 0.005%, and the balance is Fe and unavoidable impurities.

[0038] The steps include: (1) After hot rolling, the hot-formed steel billet has a thick oxide layer on its surface. The surface oxide layer caused by hot rolling is completely removed by pickling process to obtain a hot-formed steel plate with a pure iron surface (plate thickness 2.5 mm); (2) The hot-formed steel plate after pickling was subjected to room temperature immersion passivation treatment using Na2MoO4 solution. The concentration of the Na2MoO4 solution was 0.8 g / L, and the passivation treatment time was set to 35 min. The surface was air-dried after passivation, and a nano-scale passivation film was formed on the surface of the bare hot-formed steel plate. This passivation film is beneficial to reduce the direct contact between oxygen and the steel plate in the initial stage of subsequent austenitization, effectively hindering the oxidation reaction, and improving the oxidation behavior of the hot-formed steel plate during the austenitization process; (3) The passivated hot-formed steel plate is placed in a heating furnace for austenitization at a temperature of 920°C. In order to completely austenitize the hot-formed steel plate, the holding time is 6.5 min. (4) The fully austenitized hot-formed steel plate is taken out and quickly transferred to a stamping die for press quenching. The cooling rate of press quenching is 28°C / s and the die opening temperature is 191°C.

[0039] The yield strength of the prepared hot-formed steel stamping parts is 1100MPa, the tensile strength is 1451MPa, the elongation after fracture is 14.67%, and the volume percentage of martensite is 98%.

[0040] Example 3 The present embodiment provides a method for preparing a hot-formed steel part with high oxidation resistance. The chemical composition of the hot-formed steel used is as follows by mass percentage: C: 0.24%, Mn: 1.6%, Si: 0.24%, S: 0.005%, P: 0.004%, Al: 0.08%, Cr: 0.48%, Nb: 0.003%, V: 0.003%, Ti: 0.02%, B: 0.002%, La+Ce: 0.012%, and the balance is Fe and unavoidable impurities.

[0041] The steps include: (1) After hot rolling, the hot-formed steel billet has a thick oxide layer on its surface. The surface oxide layer caused by hot rolling is completely removed by pickling process to obtain a hot-formed steel plate with a pure iron surface (plate thickness 2.5 mm); (2) The hot-formed steel plate after pickling was subjected to room temperature immersion passivation treatment using Na2MoO4 solution. The concentration of the Na2MoO4 solution was 1.5 g / L, and the passivation treatment time was set to 30 min. The surface was air-dried after passivation, and a nano-scale passivation film was formed on the surface of the bare hot-formed steel plate. This passivation film is beneficial to reduce the direct contact between oxygen and the steel plate in the initial stage of subsequent austenitization, effectively hindering the oxidation reaction, and improving the oxidation behavior of the hot-formed steel plate during the austenitization process; (3) The passivated hot-formed steel plate is placed in a heating furnace for austenitization at a temperature of 950°C. In order to completely austenitize the hot-formed steel plate, the holding time is 6 minutes. (4) The fully austenitized hot-formed steel plate is taken out and quickly transferred to a stamping die for press quenching. The cooling rate of press quenching is 23°C / s and the die opening temperature is 152°C.

[0042] The yield strength of the prepared hot-formed steel stamping parts is 1181 MPa, the tensile strength is 1538 MPa, the elongation after fracture is 15.44%, and the volume percentage of martensite is 99%.

[0043] Comparative Example 2 This comparative example provides a method for preparing a hot-formed steel part with high oxidation resistance. The chemical composition of the hot-formed steel used is as follows by mass percentage: C: 0.23%, Mn: 1.58%, Si: 0.25%, S: 0.004%, P: 0.003%, Al: 0.07%, Cr: 0.40%, Nb: 0.003%, V: 0.003%, Ti: 0.02%, B: 0.003%, and the amount is Fe and unavoidable impurities.

[0044] The steps include: (1) After hot rolling, the hot-formed steel billet has a thick oxide layer on its surface. The surface oxide layer caused by hot rolling is completely removed by pickling process to obtain a hot-formed steel plate with a pure iron surface (plate thickness 2.5 mm); (2) The hot-formed steel plate after pickling was subjected to room temperature immersion passivation treatment using Na2MoO4 solution. The concentration of the Na2MoO4 solution was 1.5 g / L, and the passivation treatment time was set to 30 min. The surface was air-dried after passivation, and a nano-scale passivation film was formed on the surface of the bare hot-formed steel plate. This passivation film is beneficial to reduce the direct contact between oxygen and the steel plate in the initial stage of subsequent austenitization, effectively hindering the oxidation reaction, and improving the oxidation behavior of the hot-formed steel plate during the austenitization process; (3) The passivated hot-formed steel plate is placed in a heating furnace for austenitization at a temperature of 950°C. In order to completely austenitize the hot-formed steel plate, the holding time is 6 minutes. (4) The fully austenitized hot-formed steel plate is taken out and quickly transferred to a stamping die for press quenching. The cooling rate of press quenching is 24°C / s and the die opening temperature is 162°C.

[0045] The yield strength of the prepared hot-formed steel stamping parts is 1175MPa, the tensile strength is 1488MPa, the elongation after fracture is 10.2% (due to the lack of addition of rare earth La+Ce, the elongation after fracture failed to reach the target of 12%), and the volume percentage of martensite is 95%.

[0046] After the hot-formed steel plate of the present invention is passivated by Na2MoO4 solution, the phase composition test results of the surface passivation film are as follows: Figure 1As shown in Figure 1, according to the XPS test results, the phase composition of the passivation film is mainly Fe2(MoO4)3 and a small amount of FeO, Fe2O3, and FeOOH. The passivation film containing Fe2(MoO4)3 has a relatively dense microstructure and will have a better protective effect on the steel substrate.

[0047] When the hot-formed steel plate is heated to a specified temperature in the austenitizing process stage, as the high-temperature oxidation reaction proceeds, the relationship between the weight gain per unit area of ​​the hot-formed steel plate without passivation treatment (Comparative Example 1) and after different passivation treatment times (Example 1) is as follows: Figure 2 As shown in the figure, as the oxidation reaction continues, the oxidation weight gain of the passivated hot-formed steel plate is significantly reduced, and the oxidation weight gain of the hot-formed steel plate with extended passivation time shows a further downward trend. The passivation of the hot-formed steel surface helps to hinder the oxidation reaction, reduce the thickness of the oxide layer on the steel plate surface, and reduce the degree of surface oxidation.

[0048] Figure 3 This is a comparison of the macroscopic morphology of the oxide layer surface of the hot-formed steel plate after austenitization and high-temperature oxidation. The integrity of the oxide layer on the surface of the hot-formed steel passivation plate using the method of the present invention is relatively intact, with almost no shedding phenomenon, and the oxide layer has good bonding with the substrate. This is conducive to avoiding equipment wear problems caused by the shedding of the oxide layer during the stamping and quenching stage of hot-formed steel and the problem of controlling the surface quality of the final parts, which can better ensure the production rhythm and promote the smooth progress of the production process.

[0049] In order to further investigate the effect of the method of the present invention on improving the oxidation resistance of hot-formed steel, the surface and cross-sectional SEM observations were performed on the oxide layers of hot-formed steel plates without passivation treatment (Comparative Example 1) and after different passivation treatment times (Example 1). Figure 4 and Figure 5 ). Figure 4 The SEM test of the oxide layer surface of different hot-formed steel plates shows that the oxide layer on the surface of the unpassivated hot-formed steel plate has a large number of deep network cracks, such as Figure 4 (a) is shown. After magnification, the cracks are deep and dense, which makes the overall density of the oxide layer poor. The presence of deep network cracks aggravates the oxidation degree of the steel plate. However, there are no deep network cracks on the oxide layer surface of the hot-formed steel passivated plate. There are only some discontinuous cracks in the gullies of the "walnut-like" structure, such as Figure 4 As shown in (b) and 4(c), the overall density of the oxide layer is relatively good. Figure 5The SEM test of the cross section of the oxide layer of different hot-formed steel plates is used to observe the structure and phase composition of the oxide layer of different steel plates. The oxide layer of the unpassivated hot-formed steel plate is separated from the substrate, and the adhesion of the oxide layer is poor. This is mainly due to the low Si content in the Si-rich phase on the side of the oxide layer close to the substrate, and the poor continuity and density. Figure 5 Compared with the hot-formed steel passivated plate (b)-5(c), the oxide layer thickness is further reduced, and the adhesion of the oxide layer is higher. The surface scanning results between the oxide layer and the substrate also show that the passivation of the hot-formed steel surface is conducive to the formation of Si-rich phase.

[0050] Combination Figure 6 According to the XRD phase detection results of the surface oxide layers of different steel plates, the phases in the Si-rich phase are mainly FeO-Fe2SiO4. The characteristic peak intensity of the Fe2SiO4 phase in the surface oxide layer of the hot-formed steel plate after passivation treatment is higher, indicating that the Fe2SiO4 content in the Si-rich phase is higher. Because Fe2SiO4 has a dense microstructure, it can effectively hinder the penetration of oxygen into the matrix, reduce the degree of oxidation on the surface of the steel plate, and significantly improve the oxidation resistance of the steel plate. At the same time, the Si-rich phase with a higher Fe2SiO4 content is also conducive to enhancing the adhesion between the oxide layer and the matrix, making it difficult for the hot-formed steel plate to separate from the matrix during stamping and quenching, resulting in the phenomenon of oxide layer shedding.

[0051] Figure 7 This is the principle of how passivation treatment of hot-formed steel changes the structure and phase composition of the oxide layer. After passivation treatment, the oxidation behavior of hot-formed steel during the austenitizing process stage will be changed, prompting the oxide layer to form a thicker and denser Si-rich phase on the side close to the substrate, thereby inducing further thinning of the oxide layer and enhancing the adhesion between the oxide layer and the substrate.

[0052] In summary, the preparation method of high oxidation resistance hot-formed steel parts of the present invention can effectively slow down the oxidation degree of the hot-formed steel plate during the austenitizing process stage, and form an oxide layer with a thin thickness, dense structure and good bonding with the matrix on the surface of the hot-formed steel, thereby effectively solving the problems of stamping die wear and part surface quality control caused by the shedding of the oxide layer.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a hot-formed steel part with high oxidation resistance, characterized in that: The steps include: (1) The surface oxide layer of the hot-formed steel billet after hot rolling is removed by pickling process to obtain a hot-formed steel plate; (2) The pickled hot-formed steel plate is immersed in a molybdate solution for passivation treatment to form a passivation film on the surface of the hot-formed steel; (3) heating the passivated hot-formed steel plate until it is completely austenitized and then keeping it warm; (4) Rapidly transfer the fully austenitized hot-formed steel plate to the stamping die for press quenching; The chemical composition of the hot-formed steel is as follows by mass percentage: C: 0.18-0.35%, Mn: 1.0-2.0%, Si: 0.2-1.0%, S≤0.01%, P≤0.015%, Al: 0.05-0.1%, Cr≤1.0%, Nb≤0.01%, V≤0.01%, Ti: 0.01-0.03%, B≤0.01%, La+Ce≤0.015%, and the balance is Fe and unavoidable impurities; the yield strength of the hot-formed steel parts is 1000-1200MPa, the tensile strength is 1400-1600MPa, the elongation after fracture is 12-17%, and the volume percentage of martensite is 95-99%; The molybdate described in step (2) includes Na2MoO4 and K2MoO4; the passivation treatment condition is room temperature, the concentration of the molybdate solution is 0.5~2g / L, and the passivation treatment time is not less than 15min.

2. The preparation method according to claim 1, characterized in that: The thickness of the hot-formed steel plate described in step (1) is 2.0-4.0 mm.

3. The preparation method according to claim 1, characterized in that: In step (3), the austenitizing temperature is 920-950°C, and the holding time is controlled to be more than 5 minutes.

4. The preparation method according to claim 1, characterized in that: The cooling rate of the stamping quenching in step (4) is not less than 20°C / s, and the mold opening temperature is not higher than 200°C.

5. The preparation method according to claim 4, characterized in that: The cooling rate of the stamping quenching in step (4) is 20-50°C / s.

6. A hot-formed steel part obtained by the preparation method according to any one of claims 1 to 5.

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