A hot-formed steel part and a method of manufacturing the same

Abstract

The application relates to a hot-formed steel part and a preparation method thereof, which comprises the following steps: obtaining a first austenitizing heat treatment holding time according to the thickness of a first steel plate, performing austenitizing heat treatment, then performing stamping and pressure holding by using a die with holes to obtain a first hot-formed steel part semi-product, then spraying water to the first hot-formed steel part semi-product through the holes, setting a water spraying time according to the shape characteristics of the first hot-formed steel part semi-product, then detecting the organization and mechanical properties, when the organization or the mechanical properties do not meet the expected requirements, gradually increasing the first austenitizing heat treatment holding time as the austenitizing heat treatment holding time of an n-th steel plate until the detection meets the expected requirements, and determining the austenitizing heat treatment holding time of the n-th steel plate as a target austenitizing heat treatment holding time to prepare a target hot-formed steel part. The application solves the technical problem that the mechanical properties of the existing hot-formed steel part are poor.

Description

Technical Field

[0001] This application relates to the field of hot stamping technology for hot-formed steel, and in particular to a hot-formed steel part and its preparation method. Background Technology

[0002] The application of hot-formed steel enables the lightweighting of vehicles while improving their crashworthiness. This is because hot-formed steel is formed at high temperatures, resulting in strong formability. After forming, it is quenched in a mold, leading to high strength in the finished parts.

[0003] With the widespread application of hot-formed steel, its use in commercial vehicles is also gradually increasing, for parts such as saddles. However, because the hot-formed steel used in commercial vehicles is relatively thick, incomplete austenitization can easily occur during austenitizing heat treatment. This can result in insufficient heat penetration or insufficient time, leaving banded structures within the matrix. In production, it has also been found that as the thickness of the hot-formed steel sheet increases, incomplete quenching during die hardening can easily occur, such as insufficient quenching rate or uneven quenching. Insufficient quenching rate can lead to inadequate part performance. Uneven quenching can result in uneven property distribution. Summary of the Invention

[0004] This application provides a hot-formed steel part and a method for preparing the same, in order to solve the technical problem of poor mechanical properties of existing hot-formed steel parts.

[0005] In a first aspect, this application provides a method for preparing hot-formed steel parts, the method comprising:

[0006] The holding time for the first austenitizing heat treatment is determined based on the thickness of the first steel plate.

[0007] The first steel plate is subjected to austenitizing heat treatment according to the first austenitizing heat treatment holding time to obtain the first austenitizing steel plate.

[0008] The first austenitized steel plate is stamped and held under pressure using a mold with holes to obtain a first hot-formed steel part semi-finished product. Water is then sprayed onto the first hot-formed steel part semi-finished product through the holes, and the spraying time is set according to the shape characteristics of the first hot-formed steel part semi-finished product to obtain the first hot-formed steel part finished product.

[0009] The microstructure and mechanical properties of the first hot-formed steel part are tested. When the microstructure does not meet the expected microstructure requirements or the mechanical properties do not meet the expected mechanical property requirements, the holding time of the first austenitizing heat treatment is gradually increased to serve as the holding time of the austenitizing heat treatment of the nth steel plate until the microstructure of the nth hot-formed steel part meets the expected microstructure requirements and the mechanical properties of the nth hot-formed steel part meet the expected mechanical property requirements. The holding time of the austenitizing heat treatment of the nth steel plate is then determined as the target austenitizing heat treatment holding time to prepare the target hot-formed steel part.

[0010] Optionally, the holding time of the first austenitizing heat treatment satisfies the following relationship:

[0011] T1≥(1.5~2)H

[0012] In the formula, T1 represents the holding time of the first austenitizing heat treatment, and H represents the thickness of the first steel plate.

[0013] Optionally, the holding time of the first austenitizing heat treatment satisfies the following relationship:

[0014] When H < 3 mm, T1 ≥ 2 * H, and T1 ≥ 4 min;

[0015] When H≥3mm, T1≥1.5*H, and T1≥6min;

[0016] In the formula, T1 represents the holding time of the first austenitizing heat treatment, and H represents the thickness of the first steel plate.

[0017] Optionally, the step of testing the microstructure and mechanical properties of the first hot-formed steel part, when the microstructure does not meet the expected microstructure requirements or the mechanical properties do not meet the expected mechanical property requirements, involves gradually increasing the holding time of the first austenitizing heat treatment as the holding time of the austenitizing heat treatment of the nth steel plate, until the microstructure of the nth hot-formed steel part meets the expected microstructure requirements and the mechanical properties of the nth hot-formed steel part meet the expected mechanical property requirements, and determining the holding time of the austenitizing heat treatment of the nth steel plate as the target austenitizing heat treatment holding time to prepare the target hot-formed steel part, includes:

[0018] The microstructure and mechanical properties of the first hot-formed steel part are tested. When the microstructure does not meet the expected microstructure requirements, or the mechanical properties do not meet the expected mechanical property requirements, the following applies: T n =T1*(1.1) n-1The holding time of the first austenitizing heat treatment is gradually increased in a stepwise manner to serve as the holding time for the austenitizing heat treatment of the nth steel plate, until the microstructure of the nth hot-formed steel part meets the expected microstructure requirements and the mechanical properties of the nth hot-formed steel part meet the expected mechanical property requirements. The holding time for the austenitizing heat treatment of the nth steel plate is then determined as the target austenitizing heat treatment holding time to prepare the target hot-formed steel part. Wherein, T1 represents the holding time of the first austenitizing heat treatment, and T... n This represents the holding time for the austenitizing heat treatment of the nth steel plate, where n is a positive integer.

[0019] Optionally, the step of using a mold with holes to stamp and hold the first austenitized steel plate to obtain a first hot-formed steel part semi-finished product, and then spraying water onto the first hot-formed steel part semi-finished product through the holes, and setting the water spraying time according to the shape characteristics of the first hot-formed steel part semi-finished product, to obtain the first hot-formed steel part finished product, includes:

[0020] The first austenitized steel plate is stamped and held under pressure using a mold with holes, and the first set of cooling water channels inside the mold is in a water-flow state to obtain a first hot-formed steel part semi-finished product.

[0021] The first and second cooling channels within the mold are both in a water-flow state. The cooling water from the second cooling channel is sprayed onto the first hot-formed steel part semi-finished product through the holes. The spraying time is set according to the shape characteristics of the first hot-formed steel part semi-finished product to obtain the first hot-formed steel part finished product.

[0022] Optionally, setting the water spraying time based on the shape characteristics of the first hot-formed steel part semi-finished product includes:

[0023] The water spraying time is set according to the minimum draft angle of the first hot-formed steel part semi-finished product.

[0024] Optionally, the expression for the water spraying time is:

[0025] t w = k / (|a|+1)

[0026] In the formula, t w The value of k represents the water spraying time, 'a' represents the minimum draft angle, and 'k' represents the model parameter. The value of k is set according to the thickness of the steel plate.

[0027] Optionally, setting the value of k based on the thickness of the steel plate includes:

[0028] When the thickness of the steel plate is <6mm, k is 50, and 6≤t w≤16;

[0029] When the thickness of the steel plate is ≥6mm, k is 60, and 8≤t w ≤18.

[0030] Optionally, the diameter of the hole and the diameter of the second set of cooling water channels satisfy the following relationship:

[0031] D k ≤0.25*D w

[0032] In the formula, D k D represents the diameter of the hole. w This indicates the diameter of the second set of cooling water channels.

[0033] Secondly, this application provides a hot-formed steel part, which is prepared by the method described in the first aspect.

[0034] The technical solutions provided in this application have the following advantages compared with the prior art:

[0035] The method for preparing hot-formed steel parts provided in this application involves determining the austenitizing heat treatment holding time based on the thickness of the steel plate. By gradually increasing the austenitizing heat treatment holding time until the microstructure of the hot-formed steel part meets the expected microstructure requirements and the mechanical properties of the hot-formed steel part meet the expected mechanical property requirements, the steel plate achieves complete austenitization, thereby avoiding the defect of insufficient austenitization in the hot-formed steel parts. Furthermore, a mold with holes is used, and the water spraying time through the holes is reasonably set to achieve complete quenching of the hot-formed steel parts, thereby avoiding the defect of insufficient quenching. In summary, this method solves the technical problem of poor mechanical properties in existing hot-formed steel parts. Attached Figure Description

[0036] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0037] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 A schematic flowchart illustrating a method for preparing a hot-formed steel part provided in an embodiment of this application;

[0039] Figure 2Microstructure of a hot-formed steel part with a banded structure provided in this application embodiment;

[0040] Figure 3 A microstructure diagram of a uniformly structured hot-formed steel part provided in an embodiment of this application. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0042] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0043] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, terms such as "comprising" and "including" mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than one" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0044] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0045] Figure 1 A schematic flowchart illustrating a method for preparing a hot-formed steel part according to an embodiment of this application; please refer to [link / reference]. Figure 1 This application provides a method for preparing hot-formed steel parts, the method comprising:

[0046] S1. The holding time for the first austenitizing heat treatment is obtained based on the thickness of the first steel plate.

[0047] S2. Perform austenitizing heat treatment on the first steel plate according to the first austenitizing heat treatment holding time to obtain the first austenitized steel plate.

[0048] In some embodiments, the holding time of the first austenitizing heat treatment satisfies the following relationship:

[0049] T1≥(1.5~2)H

[0050] In the formula, T1 represents the holding time of the first austenitizing heat treatment, and H represents the thickness of the first steel plate.

[0051] In some embodiments, the holding time of the first austenitizing heat treatment satisfies the following relationship:

[0052] When H < 3 mm, T1 ≥ 2 * H, and T1 ≥ 4 min;

[0053] When H≥3mm, T1≥1.5*H, and T1≥6min;

[0054] In the formula, T1 represents the holding time of the first austenitizing heat treatment, and H represents the thickness of the first steel plate.

[0055] In this embodiment, the austenitizing temperature is above Ac3. The test sheet used for the steel plate can be a small-sized material sheet, typically 150mm*300mm, or 100mm*300mm. This size ensures that the material can be quenched easily through a flat die. Here, Ac3 is the complete austenitizing temperature. To ensure thorough heating and uniform microstructure during heating, achieving complete austenitization, when the heating temperature is above Ac3, the holding time (in minutes) must be at least 1.5 to 2 times the thickness of the steel plate. If the holding time is too short, complete heating of the plate is unlikely to be achieved. Optionally, when H < 3mm, T1 ≥ 2*H, and T1 ≥ 4min; that is, when T1 is below 4, T1 = 4. When H ≥ 3mm, T1 ≥ 1.5*H, and T1 ≥ 6min; that is, when T1 is below 6, T1 = 6.

[0056] S3. The first austenitized steel plate is stamped and held under pressure using a mold with holes to obtain a first hot-formed steel part semi-finished product. Water is then sprayed onto the first hot-formed steel part semi-finished product through the holes, and the spraying time is set according to the shape characteristics of the first hot-formed steel part semi-finished product to obtain the first hot-formed steel part finished product.

[0057] In this embodiment, quenching is performed using a flat plate mold. Since the test specimens are typically small, quenching with a flat plate mold is sufficient to achieve the required quenching rate. If the laboratory lacks the facilities for flat plate mold quenching, water quenching can also be used to quench the material.

[0058] In some embodiments, the process of stamping and holding the first austenitized steel plate using a perforated mold to obtain a first hot-formed steel part semi-finished product, followed by spraying water through the perforations onto the first hot-formed steel part semi-finished product, and setting the water spraying time according to the shape characteristics of the first hot-formed steel part semi-finished product, to obtain the first hot-formed steel part finished product, includes:

[0059] The first austenitized steel plate is stamped and held under pressure using a mold with holes, and the first set of cooling water channels inside the mold is in a water-flow state to obtain a first hot-formed steel part semi-finished product.

[0060] The first and second cooling channels within the mold are both in a water-flow state. The cooling water from the second cooling channel is sprayed onto the first hot-formed steel part semi-finished product through the holes. The spraying time is set according to the shape characteristics of the first hot-formed steel part semi-finished product to obtain the first hot-formed steel part finished product.

[0061] In some embodiments, setting the water spraying time based on the shape characteristics of the first hot-formed steel part semi-finished product includes:

[0062] The water spraying time is set according to the minimum draft angle of the first hot-formed steel part semi-finished product.

[0063] In some embodiments, the expression for the water spraying time is:

[0064] t w = k / (|a|+1)

[0065] In the formula, t w The value of k represents the water spraying time, 'a' represents the minimum draft angle, and 'k' represents the model parameter. The value of k is set according to the thickness of the steel plate.

[0066] In some embodiments, setting the value of k based on the thickness of the steel plate includes:

[0067] When the thickness of the steel plate is <6mm, k is 50, and 6≤t w ≤16; that is, if the spraying time t is found through calculation... w If t is less than 6, then take 6. w If the value is greater than 16, then take 16;

[0068] When the thickness of the steel plate is ≥6mm, k is 60, and 8≤t w ≤18. That is, if the spraying time t is found through calculation... w If t is less than 8, then take 8. w If the value is greater than 18, then take 18.

[0069] In some embodiments, the diameter of the hole and the diameter of the second cooling water channel satisfy the following relationship:

[0070] D k ≤0.25*D w

[0071] In the formula, D k D represents the diameter of the hole. w This indicates the diameter of the second set of cooling water channels.

[0072] In this embodiment, because thick-gauge hot-formed steel absorbs a significant amount of heat after heating, temperature reduction is difficult. Traditional hot stamping die designs struggle to achieve complete material quenching, making complete martensitic transformation challenging. Therefore, optimization and improvement of traditional hot stamping dies are necessary. Traditional hot stamping dies utilize cooling water channels to remove heat transferred from the sheet metal. For thick-gauge hot stamping dies, openings in the die are required for water flow.

[0073] Two cooling channels need to be designed within the mold. One channel is used to cool the mold itself and does not allow water to flow through the mold surface. The other channel has holes on its side close to the mold surface, allowing water to be sprayed directly onto the part. During operation, the first channel continuously flows water to cool the mold, while the second channel remains closed. When the sheet metal is heated and transferred to the mold, it is stamped. After stamping, pressure is maintained. After pressure maintenance, water flows through the second channel, spraying onto the part surface through the holes. The pressure maintenance time is typically 6-15 seconds. After pressure maintenance, the mold is lifted, and water continues to flow through the second channel, spraying onto the part through the holes in the mold. The spraying time through the holes needs to be determined based on the shape characteristics of the part to avoid being too short or too long. Too short a spraying time results in insufficient quenching, while too long a spraying time wastes time and resources. When thick-gauge hot-formed steel is hot-stamped, traditional hot-stamping dies often struggle to meet cooling requirements due to the sheet thickness. This can easily lead to insufficient cooling capacity and performance discrepancies. Parts with small draft angles are particularly prone to insufficient cooling at the sidewalls. Therefore, the minimum draft angle of the part is crucial for determining its shape characteristics. A smaller absolute draft angle results in greater difficulty in cooling the sidewalls and a longer water spraying time. The minimum draft angle of hot-stamped parts can be determined using 3D design softening and simulation software. Water spraying through the die enables rapid cooling of the part, allowing thick-gauge hot-stamped parts to complete the martensitic transformation. The timing of the cooling water spraying should be scientifically determined.

[0074] S4. Detect the microstructure and mechanical properties of the first hot-formed steel part. If the microstructure does not meet the expected microstructure requirements or the mechanical properties do not meet the expected mechanical property requirements, gradually increase the holding time of the first austenitizing heat treatment as the holding time of the austenitizing heat treatment of the nth steel plate until the microstructure of the nth hot-formed steel part meets the expected microstructure requirements and the mechanical properties of the nth hot-formed steel part meet the expected mechanical property requirements. Determine the holding time of the austenitizing heat treatment of the nth steel plate as the target austenitizing heat treatment holding time to prepare the target hot-formed steel part.

[0075] In some embodiments, the step of testing the microstructure and mechanical properties of the first hot-formed steel part, when the microstructure does not meet the expected microstructure requirements or the mechanical properties do not meet the expected mechanical property requirements, involves gradually increasing the holding time of the first austenitizing heat treatment as the holding time of the austenitizing heat treatment of the nth steel plate, until the microstructure of the nth hot-formed steel part meets the expected microstructure requirements and the mechanical properties of the nth hot-formed steel part meet the expected mechanical property requirements. The holding time of the austenitizing heat treatment of the nth steel plate is then determined as the target austenitizing heat treatment holding time to prepare the target hot-formed steel part. This includes:

[0076] The microstructure and mechanical properties of the first hot-formed steel part are tested. When the microstructure does not meet the expected microstructure requirements, or the mechanical properties do not meet the expected mechanical property requirements, the following applies: T n =T1*(1.1) n-1 The holding time of the first austenitizing heat treatment is gradually increased in a stepwise manner to serve as the holding time for the austenitizing heat treatment of the nth steel plate, until the microstructure of the nth hot-formed steel part meets the expected microstructure requirements and the mechanical properties of the nth hot-formed steel part meet the expected mechanical property requirements. The holding time for the austenitizing heat treatment of the nth steel plate is then determined as the target austenitizing heat treatment holding time to prepare the target hot-formed steel part. Wherein, T1 represents the holding time of the first austenitizing heat treatment, and T... n This represents the holding time for the austenitizing heat treatment of the nth steel plate, where n is a positive integer.

[0077] In this embodiment, thick-gauge hot-formed steel requires more energy to achieve austenitization during heating, while ensuring the uniformity of austenitization. Excessively increasing the heating temperature and extending the holding time can easily lead to energy waste. Therefore, a step-wise approach to increasing the holding time during austenitization heat treatment is proposed, with material microstructure testing and mechanical property testing used as feedback to determine the optimal holding time for austenitization heat treatment. The finished hot-formed steel part undergoes material microstructure testing to observe the presence of banded structures, and mechanical property strength testing is performed. Banded structures are primarily detected using optical microscopy for metallographic analysis, but can also be detected using electron microscopy, EBSD, etc. The expected microstructure requirement is the absence of banded structures, and the expected mechanical properties are: yield strength ≥ 950 MPa, tensile strength ≥ 1300 MPa, elongation after fracture ≥ 5%, and Vickers hardness HV ≥ 400. Strength can be determined by testing tensile strength or hardness. Hardness is primarily tested using a Vickers hardness tester; the Vickers hardness of the material is analyzed to determine whether the material's performance after heat treatment meets the required strength. If testing reveals the absence of banded structures and the hardness meets requirements, then the heating parameters are satisfactory. If banded structures are present and the hardness is insufficient, it indicates inadequate austenitization, necessitating an increase in austenitization time. Figure 2 Microstructure of a hot-formed steel part with a banded structure provided in this application embodiment; Figure 3 A microstructure diagram of a uniformly structured hot-formed steel part provided in this application embodiment; please refer to... Figures 2-3 When increasing the austenitizing holding time, a method based on T was adopted. n =T1*(1.1) n-1 The heating is carried out in a stepped manner, that is, the second steel plate T2 = T1*(1.1), the third steel plate T3 = T1*(1.1). 2 The fourth steel plate, T4, is equal to T1*(1.1). 3 And so on, for the nth steel plate T n =T1*(1.1) n-1 All steel plates are of identical dimensions, and after quenching, the banded microstructure is inspected. The holding time is determined until the banded microstructure disappears, meeting the expected microstructure requirements, and the strength meets the expected mechanical property requirements. If the heating time is too long, the energy consumption is too high. Therefore, after obtaining the critical holding time, the holding time can be appropriately extended, but not excessively. This determines the holding time for the material, achieving complete austenitization of the part.

[0078] As one implementation method in the finished product of the target hot-formed steel part:

[0079] Simulation and blanking of parts for hot stamping: First, simulation analysis can be used to optimize sheet metal dimensions and hot stamping process parameters. Simulation can reveal the thinning and thickening rates at different locations on the part. Typically, the thinning rate should not exceed -15%, and the thickening rate should not exceed 10%. Based on the simulation results, sheet metal optimization can be performed; excessively large sheet metal dimensions lead to material waste, while excessively small dimensions can result in insufficient forming. Simultaneously, the hot stamping process parameters can be optimized based on the simulation results. These parameters mainly include stamping speed, blank holder force (when a blank holder ring is present), and coefficient of friction. For some parts requiring a blank holder ring during hot stamping, the influence of the blank holder force on the part's formability must be considered; otherwise, a blank holder ring is not needed, and therefore, no blank holder force is required. Hot stamping processes typically do not require lubrication. However, in the hot stamping preparation of some parts, high-temperature resistant lubricating oil is sometimes applied, in which case the influence of the coefficient of friction must be considered. Furthermore, because hot-formed steel has different surface states, such as bare sheet, aluminum-silicon coated sheet, and zinc-based coated sheet, the coating state affects the coefficient of friction during the stamping process. Meanwhile, the thickness of the coating also affects the coefficient of friction in hot stamping. Therefore, the coefficient of friction is an important parameter that needs to be considered in the hot stamping process.

[0080] Once the sheet metal outline and process parameters are determined, the sheet metal can be blanked according to the outline. Blanking is typically done using a blanking die or laser cutting. The sheet metal is then fed into the next process.

[0081] Austenitizing heat treatment of parts: The furnace parameters are set according to the aforementioned austenitizing temperature and the determined target austenitizing holding time. Because thick-gauge hot-formed steel parts are large in size and heavy in weight, box furnaces are usually used for heating treatment. If equipment conditions permit, roller hearth furnaces can also be used for heating. Alternatively, induction heating or other methods can be employed. After heating, the sheet metal is removed from the furnace and transferred to a hot stamping die using a robotic arm.

[0082] Hot stamping and water spraying: After the sheet metal is transferred to the hot stamping die, the press is started for hot stamping. During hot stamping, the process parameters used in the simulation analysis are followed. After the hot stamping die is closed, water spraying is performed through the second set of water channels in the die. At this time, the die and water simultaneously quench and cool the part, allowing the part to quickly complete the martensitic transformation. After the holding pressure time is reached, the upper die of the hot stamping die is lifted, and then water spraying continues for a period of time according to the continued water spraying time determined in the previous steps.

[0083] Part Performance Testing: After stamping, the performance of the parts is tested. Different parts have different performance requirements. For commonly used 1500MPa grade hot-formed steel, the required strength range is: yield strength: 950-1300MPa, tensile strength: 1300-1800MPa, elongation after fracture ≥5%.

[0084] Secondly, this application provides a hot-formed steel part, which is prepared by the method described in the first aspect.

[0085] This hot-formed steel part is realized based on the above-described method for preparing hot-formed steel parts. The specific steps of the method for preparing hot-formed steel parts can be referred to in the above embodiments. Since this hot-formed steel part adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated here.

[0086] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0087] This application provides a method for preparing hot-formed steel parts, the method comprising:

[0088] S11. The holding time for the first austenitizing heat treatment is obtained based on the thickness of the first steel plate.

[0089] S21. The first steel plate is subjected to austenitizing heat treatment according to the first austenitizing heat treatment holding time to obtain the first austenitizing steel plate.

[0090] S31. The first austenitized steel plate is stamped and held under pressure using a mold with holes to obtain a first hot-formed steel part semi-finished product. Water is then sprayed onto the first hot-formed steel part semi-finished product through the holes, and the spraying time is set according to the shape characteristics of the first hot-formed steel part semi-finished product to obtain the first hot-formed steel part finished product.

[0091] S41. Inspect the microstructure and mechanical properties of the first hot-formed steel part. If the microstructure does not meet the expected microstructure requirements, or the mechanical properties do not meet the expected mechanical property requirements, gradually increase the holding time of the first austenitizing heat treatment as the holding time of the austenitizing heat treatment of the nth steel plate, until the microstructure of the nth hot-formed steel part meets the expected microstructure requirements, and the mechanical properties of the nth hot-formed steel part meet the expected mechanical property requirements. Determine the holding time of the austenitizing heat treatment of the nth steel plate as the target austenitizing heat treatment holding time to prepare the target hot-formed steel part. See Table 1 for specific process parameters.

[0092] Table 1. Manufacturing process parameters for hot-formed steel parts

[0093]

[0094] The mechanical properties of the target hot-formed steel parts prepared in Examples 1-3 and Comparative Example 1 were tested, and the results are shown in Table 2.

[0095] Table 2 Mechanical properties of hot-formed steel parts

[0096] Example 1 1081 1508 14 466 Example 2 1030 1486 15 461 Example 3 1016 1480 8 458 Comparative Example 1 650 1200 13 376

[0097] Through the above embodiments 1 to 3 and Comparative Example 1, and in conjunction with Tables 1 and 2, it is shown that the method for preparing hot-formed steel parts provided in this application can ensure the strength of the material, so that the hot-formed parts have good strength. However, the hot-formed steel parts in Comparative Example 1 have a large thickness, and the austenitizing heat treatment holding time is insufficient and not sufficiently cooled, resulting in the mechanical properties of the steel plate after hot forming not meeting the standards.

[0098] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing hot-formed steel parts, characterized in that, The method includes: The holding time for the first austenitizing heat treatment is determined based on the thickness of the first steel plate. The first steel plate is subjected to austenitizing heat treatment according to the first austenitizing heat treatment holding time to obtain the first austenitizing steel plate. The first austenitized steel plate is stamped and held under pressure using a mold with holes to obtain a first hot-formed steel part semi-finished product. Water is then sprayed onto the first hot-formed steel part semi-finished product through the holes, and the spraying time is set according to the shape characteristics of the first hot-formed steel part semi-finished product to obtain the first hot-formed steel part finished product. The microstructure and mechanical properties of the first hot-formed steel part are tested. When the microstructure does not meet the expected microstructure requirements, or the mechanical properties do not meet the expected mechanical property requirements, the following applies: T n =T1*(1.1) n-1 The holding time of the first austenitizing heat treatment is gradually increased in a stepwise manner to serve as the holding time for the austenitizing heat treatment of the nth steel plate, until the microstructure of the nth hot-formed steel part meets the expected microstructure requirements and the mechanical properties of the nth hot-formed steel part meet the expected mechanical property requirements. The holding time for the austenitizing heat treatment of the nth steel plate is then determined as the target austenitizing heat treatment holding time to prepare the target hot-formed steel part. Wherein, T1 represents the holding time of the first austenitizing heat treatment, and T... n This represents the holding time for the austenitizing heat treatment of the nth steel plate, where n is a positive integer; The step of setting the water spraying time based on the shape characteristics of the first hot-formed steel part semi-finished product includes: The water spraying time is set according to the minimum draft angle of the first hot-formed steel part semi-finished product; The expression for the water spraying time: In the formula, t w The time for water spraying is indicated, 'a' represents the minimum draft angle, and 'k' represents the model parameters, which are based on the steel plate. The thickness is set by the value of k; Setting the value of k based on the thickness of the steel plate includes: When the thickness of the steel plate is <6mm, k is 50, and ; When the thickness of the steel plate is ≥6mm, k is 60, and .

2. The method according to claim 1, characterized in that, The holding time for the first austenitizing heat treatment satisfies the following relationship: T1≥(1.5~2)H In the formula, T1 represents the holding time of the first austenitizing heat treatment, and H represents the thickness of the first steel plate.

3. The method according to claim 2, characterized in that, The holding time for the first austenitizing heat treatment satisfies the following relationship: When H < 3 mm, T1 ≥ 2 * H, and T1 ≥ 4 min; When H≥3mm, T1≥1.5*H, and T1≥6min; In the formula, T1 represents the holding time of the first austenitizing heat treatment, and H represents the thickness of the first steel plate.

4. The method according to claim 1, characterized in that, The process involves stamping and holding the first austenitized steel plate using a perforated mold to obtain a first hot-formed steel part semi-finished product. Water is then sprayed onto the first hot-formed steel part semi-finished product through the perforations, and the spraying time is set according to the shape characteristics of the first hot-formed steel part semi-finished product to obtain the first hot-formed steel part finished product. This process includes: The first austenitized steel plate is stamped and held under pressure using a mold with holes, and the first set of cooling water channels inside the mold is in a water-flow state to obtain a first hot-formed steel part semi-finished product. The first and second cooling channels within the mold are both in a water-flow state. The cooling water from the second cooling channel is sprayed onto the first hot-formed steel part semi-finished product through the holes. The spraying time is set according to the shape characteristics of the first hot-formed steel part semi-finished product to obtain the first hot-formed steel part finished product.

5. The method according to claim 4, characterized in that, The diameter of the hole and the diameter of the second set of cooling water channels satisfy the following relationship: In the formula, D k D represents the diameter of the hole. w This indicates the diameter of the second set of cooling water channels.

6. A hot-formed steel part, characterized in that, The hot-formed steel part is prepared by the method described in any one of claims 1 to 5.

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