A plated hot stamped steel part and a method of making the same

Abstract

The application relates to the technical field of preparation and stamping forming manufacturing of plated hot stamping steel, in particular to a plated hot stamping steel part and a preparation method thereof. The method comprises the following steps: a single heat preservation step is arranged to perform first mode austenitizing heat treatment on a first plate, so that a first austenitizing plate is obtained; the ratio of the interdiffusion layer thickness to the surface alloy layer thickness in the first austenitizing plate is obtained; according to the ratio, it is judged whether the mode of gradually increasing the number of heat preservation steps is adopted to perform different mode austenitizing heat treatment on a plurality of plates until when n heat preservation steps are arranged to perform n mode austenitizing heat treatment on the nth plate, so that the ratio of the interdiffusion layer thickness to the surface alloy layer thickness in the nth plate reaches a preset ratio, then stamping and pressure holding are performed, and a plated hot stamping steel part is obtained. The application solves the technical problem that the existing plated hot stamping steel is prone to the phenomenon of plated layer sticking to a roller during heating.

Description

Technical Field

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

[0002] Lightweighting of automobiles has become a major trend in modern development, leading to the widespread application of hot stamping technology. In hot stamping, the hot-formed steel sheet needs to be heated to above its austenitizing temperature before stamping. Because stamping bare steel sheets easily results in severe oxide scale buildup, subsequent shot peening can affect the shape accuracy of the parts. Therefore, coated hot-stamping steel has been proposed.

[0003] However, hot-stamped steel with a coating is prone to coating sticking to the rollers during the heating process. Roller sticking affects both the lifespan of the furnace rollers and the coating quality of the steel sheet, negatively impacting subsequent use. Therefore, it is necessary to propose new methods to reduce roller sticking. Summary of the Invention

[0004] This application provides a coated hot-stamped steel part and its preparation method to solve the technical problem that coated hot-stamped steel is prone to sticking to the rollers during the heating process.

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

[0006] A single insulation step is set to perform a first mode of austenitizing heat treatment on the first plate to obtain the first austenitizing plate.

[0007] The first austenitic sheet material is sampled and tested to obtain the ratio of the thickness of the interdiffusion layer to the thickness of the surface alloy layer in the first austenitic sheet material.

[0008] Based on the ratio of the interdiffusion layer thickness to the surface alloy layer thickness in the first austenitized sheet, it is determined whether to perform austenitizing heat treatment of several sheets in different modes by gradually increasing the number of insulation steps, until the nth sheet is subjected to the nth mode of austenitizing heat treatment with n insulation steps, so that the ratio of the interdiffusion layer thickness to the surface alloy layer thickness in the nth sheet reaches the preset ratio, and the target austenitized sheet is obtained.

[0009] The target austenitic sheet material is stamped and held under pressure to obtain coated hot stamped steel parts.

[0010] Optionally, the step of determining whether to perform austenitizing heat treatment of several plates in different modes by gradually increasing the number of insulation steps based on the ratio of the interdiffusion layer thickness to the surface alloy layer thickness in the first austenitized sheet material, until the nth plate material is subjected to the nth mode of austenitizing heat treatment with n insulation steps, so that the ratio of the interdiffusion layer thickness to the surface alloy layer thickness in the nth plate material reaches a preset ratio, and obtaining the target austenitized sheet material, includes:

[0011] If the ratio of the thickness of the interdiffusion layer to the thickness of the surface alloy layer in the first austenitized sheet is ≤0.1, then the austenitizing heat treatment of several sheets in different modes is carried out by gradually increasing the number of insulation steps until the nth sheet is subjected to the nth mode of austenitizing heat treatment with n insulation steps, so that the ratio of the thickness of the interdiffusion layer to the thickness of the surface alloy layer in the nth sheet reaches the preset ratio, and the target austenitized sheet is obtained.

[0012] If the ratio of the thickness of the interdiffusion layer to the thickness of the surface alloy layer in the first austenitic sheet is >0.1, the target austenitic sheet is obtained.

[0013] Optionally, the preset ratio is >0.1.

[0014] Optionally, the final holding temperature in the nth mode austenitizing heat treatment is >840℃.

[0015] Optionally, the austenitizing heat treatment time for the nth mode is <12 min.

[0016] Optionally, the final holding temperature in the nth mode austenitizing heat treatment is 933℃, the time of the nth mode austenitizing heat treatment is 4min, and the ratio of the thickness of the interdiffusion layer to the thickness of the surface alloy layer in the target austenitized sheet is >0.2.

[0017] Optionally, in each of the austenitizing heat treatment modes, the sheet metal absorbs the same amount of energy.

[0018] Optionally, the temperature of the stamping die is <100°C.

[0019] Optionally, the step of stamping and holding the target austenitized sheet to obtain coated hot-stamped steel parts includes:

[0020] The target austenitic sheet is stamped and held under pressure, and the cooling rate of the target austenitic sheet is controlled to obtain coated hot stamped steel parts; wherein the cooling rate is >27℃ / s.

[0021] Secondly, this application provides a coated hot-stamped steel part, which is prepared by the method described in any embodiment of the first aspect.

[0022] The technical solutions provided in this application have the following advantages compared with the prior art:

[0023] The method for preparing coated hot-stamped steel parts provided in this application involves austenitizing heat treatment of the sheet metal and detecting the ratio of interdiffusion layer to surface alloy layer in the coating of the heat-treated material. If the ratio meets the requirements, stamping is performed; if the ratio does not meet the requirements, the heat treatment method is adjusted until the requirements are met. This improves the formability of coated hot-stamped steel and avoids coating sticking to the rolls. Furthermore, it improves energy utilization and production efficiency. Attached Figure Description

[0024] 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.

[0025] 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.

[0026] Figure 1 A schematic flowchart illustrating a method for preparing a coated hot-stamped steel part according to an embodiment of this application;

[0027] Figure 2 A graph showing the relationship between time and temperature in the austenitizing heat treatment method for a single insulating step provided for the implementation case of this application;

[0028] Figure 3 A graph showing the relationship between time and temperature in the austenitizing heat treatment method for two insulating steps provided in this application implementation case;

[0029] Figure 4 A graph showing the relationship between time and temperature in the austenitizing heat treatment method for three insulating steps provided in this application implementation case;

[0030] Figure 5 This is a graph showing the relationship between time and temperature in the austenitizing heat treatment method of the comparative case of this application;

[0031] Figure 6 These are microscopic morphology images of the sheet metal in the comparative cases of this application;

[0032] Figure 7The microstructure diagram of the sheet metal provided for Implementation Example 1 of this application; wherein, Implementation Example 1-1 corresponds to Figure 7 A, Implementation Cases 1-2 correspond Figure 7 B, corresponding to implementation cases 1-3 Figure 7 C;

[0033] Figure 8 This is a diagram showing the location of the microhardness test on the sample provided in Implementation Example 1 of this application;

[0034] Figure 9 This is a diagram showing the martensite microstructure distribution of sheet metal provided in Implementation Example 1 of this application; wherein, Implementation Example 1-1 corresponds to... Figure 9 A, Implementation Cases 1-2 correspond Figure 9 B, corresponding to implementation cases 1-3 Figure 9 C;

[0035] Figure 10 This is a diagram showing the martensite microstructure distribution of sheet metal provided in Implementation Example 2 of this application; wherein, Implementation Example 2-2 corresponds to Figure 10 A, corresponding to implementation cases 2-4 Figure 10 B, corresponding to implementation cases 2-6 Figure 10 C;

[0036] Figure 11 Characterization diagram of the high-temperature mechanical properties of the sheet metal provided for Implementation Example 2 of this application; wherein, Implementation Example 2-1 corresponds to working condition 1, Implementation Example 2-3 corresponds to working condition 3, and Implementation Example 2-5 corresponds to working condition 5;

[0037] Figure 12 The microstructure of the sheet metal provided in Implementation Example 3 of this application; wherein, Implementation Example 3-2 corresponds to Figure 12 A, corresponding to Implementation Case 3-3 Figure 12 B;

[0038] Figure 13 Characterization diagram of the high-temperature mechanical properties of the sheet metal provided for Implementation Example 3 of this application; wherein, Implementation Example 3-1 corresponds to working condition 1#, Implementation Example 3-4 corresponds to working condition 4#, and Implementation Example 3-5 corresponds to working condition 5#;

[0039] Figure 14 Microscopic morphology diagram of the sheet metal provided for the implementation case of this application. Detailed Implementation

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] Firstly, this application provides a method for preparing coated hot-stamped steel parts, please refer to [link to relevant documentation]. Figure 1 The above includes:

[0045] S1. Set a single insulation step to perform the first mode austenitizing heat treatment on the first plate to obtain the first austenitizing plate;

[0046] In the embodiments of this application, considering economy and practicality, the chemical composition of the sheet metal, by mass fraction, includes: C: 0.1-0.55%, Si: 0.2-0.8%, Mn: 1.2-3.1%, Cr: 0.2-1.5%, Al: 0.02-0.16%, and B: 0.0003-0.09%.

[0047] More preferably, C: 0.2-0.25%, Si: 0.2-0.4%, Mn: 1.2-1.4%, Cr: 0.2-0.5%, Al: 0.04-0.1%, and B: 0.003-0.005%.

[0048] To ensure the material's high-temperature oxidation resistance, a coating is applied to the surface of the substrate. This coating mainly consists of aluminum and silicon, along with unavoidable impurities, wherein the aluminum content by weight is greater than 50% and the silicon content is not less than 5%. More preferably, the recommended coating solution composition is approximately 90% Al and approximately 10% Si by weight.

[0049] Sheet metal: Based on the shape of the part to be stamped, the shape of the sheet metal is determined through analysis and design, and then blanking is carried out.

[0050] The first mode of austenitizing heat treatment includes: heating the sheet metal to temperature Ta at a heating rate v1, with a heating time of ta, and holding at that temperature to tb. The sheet metal is then held at temperature Ta for a holding time of tb-ta. The energy absorbed by the sheet metal during heating and holding is S1, where S1 is the area of ​​oabtb. (See [reference needed]). Figure 2 .

[0051] S2. Sample and test the first austenitic sheet material to obtain the ratio of the thickness of the interdiffusion layer to the thickness of the surface alloy layer in the first austenitic sheet material.

[0052] After austenitization, the material is sampled and tested. The main tests are the microstructure of the coating and the thickness of each layer. The aluminum-silicon coated steel coating produced by this patent mainly consists of an interdiffusion layer and a surface alloy layer. Metallographic methods can be used to process the material. Electron microscopy can be used to observe the delamination of the coating.

[0053] S3. Based on the ratio of the thickness of the interdiffusion layer to the thickness of the surface alloy layer in the first austenitized sheet, determine whether to perform austenitizing heat treatment of several sheets in different modes by gradually increasing the number of insulation steps, until the nth sheet is subjected to austenitizing heat treatment in the nth mode with n insulation steps, so that the ratio of the thickness of the interdiffusion layer to the thickness of the surface alloy layer in the nth sheet reaches the preset ratio, and the target austenitized sheet is obtained.

[0054] In some embodiments, determining whether to perform austenitizing heat treatment on several plates using different modes by gradually increasing the number of insulation steps, based on the ratio of the interdiffusion layer thickness to the surface alloy layer thickness in the first austenitized sheet material, until n insulation steps are set to perform austenitizing heat treatment on the nth sheet material in the nth mode, so that the ratio of the interdiffusion layer thickness to the surface alloy layer thickness in the nth sheet material reaches a preset ratio, and obtaining the target austenitized sheet material, includes:

[0055] If the ratio of the thickness of the interdiffusion layer to the thickness of the surface alloy layer in the first austenitized sheet is ≤0.1, then the austenitizing heat treatment of several sheets in different modes is carried out by gradually increasing the number of insulation steps until the nth sheet is subjected to the nth mode of austenitizing heat treatment with n insulation steps, so that the ratio of the thickness of the interdiffusion layer to the thickness of the surface alloy layer in the nth sheet reaches the preset ratio, and the target austenitized sheet is obtained.

[0056] If the ratio of the thickness of the interdiffusion layer to the thickness of the surface alloy layer in the first austenitic sheet is >0.1, the target austenitic sheet is obtained.

[0057] By measuring the diffusion layer thickness and alloy layer thickness in the electron microscope field of view, the ratio of the diffusion layer thickness to the alloy layer thickness at a certain location is obtained. The ratios of the diffusion layer thickness to the alloy layer thickness at multiple locations are then averaged. If the ratio is greater than 0.1, it indicates that the alloying degree of the material is good during the austenitization process, and the coating sticking to the roller is low. If the ratio is less than 0.1, it indicates that the alloying degree of the material is poor during the austenitization process, leading to severe coating sticking to the roller. Therefore, different modes of austenitizing heat treatment are performed on several plates by gradually increasing the number of heat preservation steps.

[0058] If a single heat-insulating step is used to perform a first-mode austenitizing heat treatment on the first plate, and the ratio of the diffusion layer to the alloy layer in the resulting sample does not exceed 0.1, then two heat-insulating steps are added to perform a second-mode austenitizing heat treatment on the second plate. This step includes: heating the plate to Tc at v2, holding for td-tc, and then heating to Ta at v3, holding for tb-ta. Increasing the heat-insulating step reduces the value of tb-ta. Using time in seconds and temperature in degrees Celsius as a coordinate system, the coordinates of temperature and time in the first heating mode are located at coordinates O(0s, 0℃), c(tc s, Tc℃), d(td s, Td℃), a(ta s, Ta℃), b(tb s, Ta℃), and tb(tb s, 0℃), which sequentially connect to enclose an area S2, where S2 is equal to S1. Please refer to [link to relevant documentation]. Figure 3 .

[0059] If a second-mode austenitizing heat treatment is performed on the second sheet material using a two-stage holding step, and the ratio of the diffusion layer to the alloy layer in the resulting sample does not exceed 0.1, then a third-mode austenitizing heat treatment is performed on the third sheet material using a three-stage holding step. This step includes: heating the sheet material to Te at v4, holding for tf-te, heating to Tc at v5, holding for td-tc, and then heating to Ta at v6, holding for tb-ta. In this mode, tb-ta and tc-td can differ from the single-stage and two-stage austenitizing heat treatments described above. Using time (in seconds) and temperature (in degrees Celsius) as a coordinate system, the coordinates of temperature and time in the first heating mode are located within a closed area S3 enclosed by the coordinates O(0s, 0°C), e(te s, Te°C), f(tf s, Tf°C), c(tc s, Tc°C), d(td s, Td°C), a(ta s, Ta°C), b(tb s, Ta°C), and tb(tb s, 0°C) connected sequentially. S3 is equal to S1. Please refer to [link to relevant documentation]. Figure 4 .

[0060] If the third plate is subjected to austenitizing heat treatment in the third mode with three insulation steps, and the ratio of diffusion layer to alloy layer of the obtained sample does not exceed 0.1, then the number of insulation steps is increased one by one to perform austenitizing heat treatment in different modes on several plates until the nth plate is subjected to austenitizing heat treatment in the nth mode with n insulation steps, so that the ratio of the thickness of the interdiffusion layer to the thickness of the surface alloy layer in the nth plate reaches the preset ratio, and the target austenitized plate is obtained.

[0061] In some implementations, the preset ratio is >0.1.

[0062] In hot-formed coated steel, excessively high temperatures in the heating furnace can easily lead to roller sticking (because the coating softens and melts due to heat, causing the coating material to adhere to the rollers inside the furnace). Roll sticking affects both the lifespan of the furnace rollers and the coating quality of the steel sheet, negatively impacting subsequent use. The magnitude of this ratio is related to the degree of alloying.

[0063] If this ratio is less than 0.1, it indicates that the alloying degree of the material is poor during the austenitization process, leading to severe coating sticking to the rollers. Therefore, a method of gradually increasing the number of insulation steps is adopted to perform different modes of austenitizing heat treatment on several plates until the nth plate is subjected to the nth mode of austenitizing heat treatment with n insulation steps. This ensures that the ratio of the interdiffusion layer thickness to the surface alloy layer thickness in the nth plate reaches >0.1, thereby achieving a better degree of alloying and a lower coating sticking to the rollers, resulting in the target austenitized plate. (See [reference needed]). Figure 14 The microstructure of the target austenitic sheet metal.

[0064] In some embodiments, the final holding temperature in the nth mode austenitizing heat treatment is >840°C.

[0065] The positive effect of controlling the final holding temperature in the nth mode austenitizing heat treatment to >840℃ is that it ensures complete austenitization. Specifically, the final holding temperature in this nth mode austenitizing heat treatment can be 880℃, 900℃, etc.

[0066] In some embodiments, the time for the nth mode austenitizing heat treatment is <12 min.

[0067] The positive effect of controlling the austenitizing heat treatment time of the nth mode to <12 min is energy saving. Specifically, the time of the austenitizing heat treatment of the nth mode can be 10 min, 8 min, 6 min, 4 min, etc.

[0068] In some embodiments, the final holding temperature in the nth mode austenitizing heat treatment is 933°C, the time of the nth mode austenitizing heat treatment is 4 min, and the ratio of the interdiffusion layer thickness to the surface alloy layer thickness in the target austenitized sheet is >0.2; where n is determined according to the actual working conditions and is an integer.

[0069] In some embodiments, the sheet metal absorbs the same amount of energy in each of the austenitizing heat treatment modes.

[0070] In this embodiment, by Figures 2-4 This ensures that the energy absorbed during the heating and insulation process of the sheet material is S1=S2=S3=........=Sn.

[0071] S4. The target austenitic sheet material is stamped and held under pressure to obtain coated hot stamped steel parts.

[0072] In some embodiments, the temperature of the stamping die is <100°C.

[0073] The positive effect of controlling the die temperature of stamping to <100℃ is that it ensures the quenching effect of the die. Specifically, the die temperature of stamping can be 90℃, 85℃, 80℃, etc.

[0074] In some embodiments, the step of stamping and holding the target austenitized sheet to obtain coated hot-stamped steel parts includes:

[0075] The target austenitic sheet is stamped and held under pressure, and the cooling rate of the target austenitic sheet is controlled to obtain coated hot stamped steel parts; wherein the cooling rate is >27℃ / s.

[0076] The positive effect of controlling the cooling rate to >27℃ / s is to ensure the quenching effect of the mold. Specifically, this cooling rate can be 28℃ / s, 30℃ / s, etc.

[0077] The heated sheet metal is rapidly transferred from the furnace to a hot stamping die for stamping and pressure holding. The pressure holding pressure is determined based on the shape and thickness of the part, and the holding time is typically 10 seconds to ensure sufficient cooling of the part.

[0078] Secondly, this application provides a coated hot-stamped steel part, which is prepared by the method described in any embodiment of the first aspect.

[0079] The coated hot-stamped steel part is realized based on the above-described method for preparing coated hot-stamped steel parts. The specific steps of the method for preparing coated hot-stamped steel parts can be referred to the above embodiments. Since the coated hot-stamped 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.

[0080] 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.

[0081] Comparative Case: Figure 5 The heating method shown is a comparative case. Figure 6 This is a microscopic morphology image of the coated steel sheet using this method.

[0082] Example 1: Austenitizing heat treatment was performed at a heating temperature lower than that in the comparative case;

[0083] Example 2: Austenitizing heat treatment was performed at a heating temperature higher than that in the comparative case;

[0084] Example 3: Austenitizing heat treatment using multiple insulation steps;

[0085] Implementation Case 1:

[0086] The samples were hot-formed steel with an aluminum-silicon coating of 1.2 mm thickness. Example 1-1 involved holding the steel at 850℃ for 4 min, Example 1-2 involved holding it at 850℃ for 8 min, and Example 1-3 involved holding it at 850℃ for 12 min. The samples were then rapidly water-quenched to preserve the austenitized microstructure. The morphology and composition of the coatings were then compared.

[0087] From its morphology, please refer to [the original text]. Figure 7 Among them, implementation case 1-1 corresponds to Figure 7 A, Implementation Cases 1-2 correspond Figure 7 B, corresponding to implementation cases 1-3 Figure 7 C. The material coating consists of two main layers: an "interdiffusion layer" and a "surface alloy layer." The morphology differs from that in the comparative case. Compositional tests were performed on samples taken from each layer, and the results were compared with the compositional ranges in the comparative case. See the table below.

[0088] Table 1 Material composition of the test specimens

[0089]

[0090] The comparative case and the implementation case are different in composition and appearance.

[0091] To test the material's strength, microhardness was measured on the sample surface. Five points were marked on each sample, and the average value was taken. The tensile strength was converted from the measured HV0.2 hardness value, as shown in Table 2. Figure 8 The diagram shows the locations of the microhardness tests on the sample. Please refer to [link / reference]. Figure 9 Martensite microstructure distribution diagram of sheet metal; where, implementation case 1-1 corresponds to... Figure 9 A, Implementation Cases 1-2 correspond Figure 9 B, corresponding to implementation cases 1-3 Figure 9 C.

[0092] Table 2 shows the microhardness values ​​and corresponding tensile strength values ​​of the samples.

[0093] Serial Number HV0.2 average hardness Corresponding tensile strength (MPa) Implementation Case 1-1 556 1831 Implementation Cases 1-2 555 1827.5 Implementation Cases 1-3 555.2 1828.2

[0094] As shown in Table 2, the sheet material in Implementation Case 1 has higher strength, as indicated by its microhardness.

[0095] Implementation Case 2

[0096] Thermal simulation tests were conducted on the materials using a Gleeble 2000 thermal simulation testing machine. The temperature was first raised to 933℃ and held for 4 minutes. Heating was then stopped, and the material was allowed to cool to the tensile deformation temperature before tensile deformation was performed. Three tensile deformation temperatures were selected; please refer to Table 2.

[0097] Table 2. Process parameters for thermal simulation test in Implementation Case 4

[0098]

[0099]

[0100] See Figure 10 Microscopic morphology images of the sheet metal, with Example 2-2 corresponding to... Figure 10 A, corresponding to implementation cases 2-4 Figure 10 B, corresponding to implementation cases 2-6 Figure 10 C. The obtained material microstructure diagram differs from that of the material protected in the comparative case. Furthermore, the temperature of 933℃ for 4 minutes is outside the protection range of the comparative case.

[0101] In the comparative case, the equation of the EH line is y = -16x + 1004; therefore, the holding time at 933℃ is 4.4375 min, and at 931℃ it is 4.5 min. Therefore, the 933℃ and 4 min used in this experiment are not within the protection range of the comparative case.

[0102] Table 3 Material composition of the test specimens

[0103]

[0104] As shown in Table 3 above, the different layers of the material in Implementation Case 4 have different compositions.

[0105] according to Figure 11 In the high-temperature mechanical properties of the implementation cases 2-1 (corresponding to condition 1), 2-3 (corresponding to condition 3), and 2-5 (corresponding to condition 5), the strain rate is 1 / s; the stress of the aluminum-silicon coated hot-formed steel decreases with increasing deformation temperature. The limiting true strain value is approximately 0.25. Note: Subsequent measurements will be taken to determine the microhardness and martensitic microstructure of the test specimen.

[0106] Implementation Case 3

[0107] A segmented heating method with an increased number of insulation steps was used for austenitizing heat treatment of the material. Table 4 below shows the test scheme for the segmented heating test.

[0108] Table 4 Heating process parameters for the segmented heating method with multiple insulation steps

[0109]

[0110]

[0111] Table 5 Material composition of the test specimens

[0112]

[0113] Depend on Figure 12 As can be seen, the microstructure of the sheet metal provided in Implementation Example 3 of this application; wherein, Implementation Example 3-2 corresponds to Figure 12 A, corresponding to Implementation Case 3-3 Figure 12 B; The coating of the material is mainly divided into three layers, which is different from the comparison case.

[0114] Depend on Figure 13 It can be seen that, in Implementation Case 3-1 corresponding to Working Condition 1#, Implementation Case 3-4 corresponding to Working Condition 4#, and Implementation Comparison Case 3-5 corresponding to Working Condition 5#, the ultimate true strain of the material at high temperature can reach 0.25 or higher. The multi-stage austenitizing heat treatment with multiple insulation steps can ensure the high-temperature mechanical properties of the material.

[0115] In summary, the holding temperature can be determined to be 933℃, the austenitizing heat treatment time is 4 minutes, and the ratio of the interdiffusion layer thickness to the surface alloy layer thickness in the target austenitized sheet material is >0.2. Staged heating can further achieve a ratio of the interdiffusion layer thickness to the surface alloy layer thickness in the sheet material >0.1, which can solve the problem of sticking to the rollers.

[0116] 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 coated hot-stamped steel parts, characterized in that, The method includes: A single insulation step is set to perform a first mode of austenitizing heat treatment on the first plate to obtain the first austenitizing plate. The first austenitic sheet material is sampled and tested to obtain the ratio of the thickness of the interdiffusion layer to the thickness of the surface alloy layer in the first austenitic sheet material. Determine whether the ratio of the interdiffusion layer thickness to the surface alloy layer thickness in the first austenitic sheet material is greater than 0.1; If the ratio is not greater than 0.1, the austenitizing heat treatment of several plates is carried out by gradually increasing the number of insulation steps. After each increase in the number of insulation steps, the heat-treated plates are sampled and tested to obtain the ratio of the interdiffusion layer thickness to the surface alloy layer thickness. This process continues until the nth plate is subjected to the nth mode of austenitizing heat treatment with n insulation steps. If the ratio of the interdiffusion layer thickness to the surface alloy layer thickness in the nth plate is found to be greater than 0.1, then the nth plate is taken as the target austenitizing plate. If the ratio of the thickness of the interdiffusion layer to the thickness of the surface alloy layer in the first austenitized sheet material is greater than 0.1, then the first austenitized sheet material is taken as the target austenitized sheet material. The target austenitic sheet material is stamped and held under pressure to obtain coated hot stamped steel parts.

2. The method according to claim 1, characterized in that, The final holding temperature in the nth mode austenitizing heat treatment is >840℃.

3. The method according to claim 1, characterized in that, The austenitizing heat treatment time for the nth mode is <12 min.

4. The method according to claim 1, characterized in that, The final holding temperature in the nth mode austenitizing heat treatment is 933℃, the time of the nth mode austenitizing heat treatment is 4min, and the ratio of the thickness of the interdiffusion layer to the thickness of the surface alloy layer in the target austenitized sheet is >0.

2.

5. The method according to claim 1, characterized in that, In each of the austenitizing heat treatment modes, the sheet metal absorbs the same amount of energy.

6. The method according to claim 1, characterized in that, The temperature of the stamping die is <100℃.

7. The method according to claim 1, characterized in that, The process of stamping and holding the target austenitized sheet metal to obtain coated hot-stamped steel parts includes: The target austenitic sheet is stamped and held under pressure, and the cooling rate of the target austenitic sheet is controlled to obtain coated hot stamped steel parts; wherein the cooling rate is >27℃ / s.

8. A coated hot-stamped steel part, characterized in that, The coated hot-stamped steel part is prepared by the method described in any one of claims 1-7.

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