A plated hot-formed steel part and a method for producing the same

Abstract

The application relates to a plated hot-formed steel part and a preparation method thereof, and belongs to the technical field of steel preparation; the method comprises the following steps: selecting aluminum-silicon plated hot-formed steel according to part design; heating the aluminum-silicon plated hot-formed steel to obtain a steel to be punched; performing punch forming on the steel to be punched, and then performing pressure holding quenching to obtain the part; wherein the heating comprises a pre-alloying stage, an austenitizing stage and a temperature rising stage; the pre-alloying stage is pre-alloyed at a relatively low temperature, so that the base body iron element can diffuse into the plating layer, and the melting point of the plating layer is improved. Meanwhile, because the temperature is relatively low, the plating layer cannot be excessively melted, so that the roll sticking phenomenon can be relieved or even avoided. The aluminum-silicon plated hot-formed steel is fully austenitized in the austenitizing stage, and then the performance of the part is improved. The temperature rising stage can ensure the tapping temperature of the aluminum-silicon plated hot-formed steel, and is beneficial to subsequent punch forming.

Description

Technical Field

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

[0002] Aluminum-silicon coated hot-formed steel is widely used in the hot stamping field, and various coating thicknesses are currently available. However, some problems exist in the heating stage of the hot stamping process. For example, because the sheet metal has an aluminum-silicon coating, it is prone to sticking to the rollers when moving in the roller hearth furnace. After the coating melts, it adheres to the rollers, causing buildup, which in severe cases requires machine shutdown for repair and roller replacement.

[0003] Simultaneously, austenitization of the sheet metal needs to be achieved during the heating process. After austenitization, the components within the sheet metal must diffuse evenly and the microstructure must be uniform. Only a uniform microstructure during heating can prevent the presence of banded structures and ensure uniform performance of the stamped parts. The degree of austenitization is directly affected by the heating temperature and heating time. After heating and removing from the furnace, the sheet metal needs to be transferred to a die for stamping. During stamping, there is a risk of breakage. If the sheet metal temperature is low during stamping, its formability will decrease, making it prone to breakage. Summary of the Invention

[0004] This application provides a coated hot-formed steel part and its preparation method to improve the problems that occur in the heating and hot stamping process mentioned above.

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

[0006] The aluminum-silicon coated hot-formed steel is selected based on the part design;

[0007] The aluminum-silicon coated hot-formed steel is heated to obtain steel to be stamped;

[0008] The steel to be stamped is stamped into shape, and then subjected to pressure holding and quenching to obtain the part;

[0009] The heating process includes a pre-alloying stage to diffuse iron from the matrix of the aluminum-silicon coated hot-formed steel into the coating, an austenitizing stage to fully austenitize the aluminum-silicon coated hot-formed steel, and a heating stage to facilitate the stamping process.

[0010] As an optional implementation, the temperature T1 of the pre-alloying stage satisfies: 598℃ ≤ T1 < 860℃; and / or

[0011] The temperature T2 of the austenitizing stage satisfies: 860 ≤ T2 < 930 °C; and / or

[0012] The temperature T3 during the heating stage satisfies: 930≤T3≤960℃.

[0013] As an optional implementation, the relationship between the pre-alloying stage time t1 and the total heating time t satisfies: 0% < t1 / t ≤ 47%; and / or

[0014] The relationship between the austenitizing stage time t2 and the total heating time t satisfies: 0% < t2 / t ≤ 40%; and / or

[0015] The relationship between the heating phase time t3 and the total heating time t satisfies: 20% ≤ t3 / t ≤ 45%; and / or

[0016] The relationship between the total heating time t, the time t1 of the pre-alloying stage, the time t2 of the austenitizing stage, and the time t3 of the heating stage satisfies: t = t1 + t2 + t3.

[0017] As an optional implementation, the total heating time t is 180 to 1200 s.

[0018] As an optional implementation, the method further includes: performing a crack detection on the part; if a crack is found, adjusting the temperature during the heating stage.

[0019] When the part has visible cracks, the temperature T3 of the heating stage should be adjusted to satisfy: 950≤T3≤960℃;

[0020] If the part has cracks that are not visible to the naked eye, the thinning condition is checked;

[0021] When the maximum thinning rate x of the part satisfies x≥30%, the temperature T3 of the heating stage is adjusted to 950℃.

[0022] When the maximum thinning rate x of the part satisfies 15% ≤ x < 30%, the temperature T3 of the heating stage is adjusted to 940-950℃.

[0023] When the maximum thinning rate x of the part satisfies 12% ≤ x < 15%, the temperature T3 of the heating stage is adjusted to 930-940℃.

[0024] When the maximum thinning rate x of the part satisfies x < 12%, the temperature T3 of the heating stage is adjusted to 930℃.

[0025] As an optional implementation, when the maximum thinning rate x of the part satisfies 15% ≤ x < 30%, the temperature T3 of the heating stage is adjusted to satisfy T3 = (200 / 3)x + 930; and / or

[0026] When the maximum thinning rate x of the part satisfies 12% ≤ x < 15%, the temperature T3 of the heating stage is adjusted to satisfy T3 = (1000 / 3)x + 890.

[0027] As an optional implementation, the method further includes: the aluminum-silicon coated hot-formed steel is in the form of a one-piece, patch plate, or welded type.

[0028] As an optional implementation, when the aluminum-silicon coated hot-formed steel is in the form of a welded type, the welding method is selected according to the coating thickness of the aluminum-silicon coated hot-formed steel.

[0029] When the coating thickness H of the aluminum-silicon coated hot-formed steel meets the requirement of H≤10μm, the welding method is direct laser welding;

[0030] When the coating thickness H of the aluminum-silicon coated hot-formed steel meets the requirement of 10 < H ≤ 20 μm, the welding method is direct laser welding or direct laser filler wire welding.

[0031] When the coating thickness H of the aluminum-silicon coated hot-formed steel satisfies 20<H≤35μm, the welding method is direct laser filler wire welding or indirect laser filler wire welding.

[0032] When the coating thickness H of the aluminum-silicon coated hot-formed steel satisfies H>35μm, the welding method is indirect laser filler wire welding.

[0033] As an optional implementation, the cooling rate of the pressure holding quenching is not less than 27°C / s.

[0034] Secondly, this application provides a coated hot-formed steel part, which is manufactured using the method for preparing coated hot-formed steel parts described in the first aspect.

[0035] The technical solutions provided in this application have the following advantages compared with the prior art:

[0036] The method provided in this application involves heating in stages, including a pre-alloying stage, an austenitizing stage, and a heating stage. The pre-alloying stage uses relatively low-temperature pre-alloying to allow the iron elements in the base material to diffuse into the coating, increasing the melting point of the coating. Simultaneously, because the temperature is relatively low, excessive melting of the coating is avoided, thus mitigating or even preventing roller sticking. The austenitizing stage fully austenitizes the aluminum-silicon coated hot-formed steel, allowing the base material to completely transform into martensite during subsequent stamping and quenching processes, thereby improving the performance of the parts. The heating stage ensures the furnace exit temperature of the aluminum-silicon coated hot-formed steel and also serves to continue austenitizing. Increasing the furnace exit temperature ensures that the sheet metal remains at a relatively high temperature when transferred to the die, which is beneficial for subsequent stamping and forming. Attached Figure Description

[0037] 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.

[0038] 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.

[0039] Figure 1 A flowchart illustrating the method provided in the embodiments of this application;

[0040] Figure 2 This is a first topographic view of the coating on a part provided in an embodiment of this application;

[0041] Figure 3 This is a second topographic view of the coating on a part provided in an embodiment of this application;

[0042] Figure 4 This is a third topographic view of the coating on a part provided in an embodiment of this application. Detailed Implementation

[0043] 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.

[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 flowchart of the method provided in the embodiments of this application is shown below. Figure 1 As shown in the figure, this application provides a method for preparing a hot-formed steel part with a coating, the method comprising:

[0046] S1. Select aluminum-silicon coated hot-formed steel according to the part design;

[0047] In some embodiments, the design of hot-stamped parts with aluminum-silicon coatings requires the selection of hot-formed steel materials for aluminum-silicon coatings, as well as the design of the strength and strength zones of the parts.

[0048] After the strength zoning design is completed, the specific shape details of the parts need to be determined. Aluminum-silicon coated hot-formed steel is mainly divided into one-piece, patch plate, and welded types. One-piece type involves hot stamping from a single sheet of material. Patch plate type refers to adding a reinforcing plate (also called a patch plate) to the original one-piece material to enhance the local strength of the part. The patch plate is usually connected to the original sheet material by spot welding before hot stamping. Welded type involves laser welding two hot-formed steel sheets of different strengths or thicknesses into one piece before hot stamping.

[0049] Laser welding into a single stamping unit is an effective means to improve strength and impact resistance. This method proposes a classification of hot-formed steel with aluminum-silicon coatings of different thicknesses, and selects welding methods for different categories. The specific classification method and welding methods proposed in this method are as follows:

[0050] Before heating and hot stamping, the coating thickness of the sheet metal is tested: when the coating thickness is less than or equal to 10 μm, it is a Class A sheet, and the welding method is direct laser welding; when the coating thickness is greater than 10 μm and less than or equal to 20 μm, it is a Class B sheet, and the welding method is direct laser welding or direct laser filler wire welding; when the coating thickness is greater than 20 μm and less than or equal to 35 μm, it is a Class C sheet, and the welding method is direct laser filler wire welding or indirect laser filler wire welding; when the coating thickness is greater than 35 μm, it is a Class D sheet, and the welding method is indirect laser filler wire welding.

[0051]

[0052]

[0053] S2. The aluminum-silicon coated hot-formed steel is heated to obtain steel to be stamped; wherein the heating includes a pre-alloying stage to diffuse iron elements in the matrix of the aluminum-silicon coated hot-formed steel into the coating, an austenitizing stage to fully austenitize the aluminum-silicon coated hot-formed steel, and a heating stage to facilitate the stamping process.

[0054] Specifically, in this embodiment, the aluminum-silicon coated hot-formed steel needs to be heated before hot stamping. Currently, the heating equipment in hot stamping production lines mainly uses roller hearth furnaces. When using a roller hearth furnace for heating, a robotic arm clamps the aluminum-silicon coated hot-formed steel and places it into the furnace from one end. The aluminum-silicon coated hot-formed steel moves to the other end of the roller hearth furnace and then exits from the other end. The robotic arm then clamps the heated aluminum-silicon coated hot-formed steel and transfers it to a hot stamping die for hot stamping. The roller hearth furnace heating process is divided into three stages (that is, three zones in sequence), according to the time order: pre-alloying stage, austenitizing stage, and heating stage.

[0055] The pre-alloying stage is primarily to prevent the coating from sticking to the rollers. By pre-alloying at a relatively low temperature, the iron elements in the base material diffuse into the coating, increasing its melting point. Simultaneously, because the heating temperature in this stage is relatively low, excessive melting of the coating is avoided, thus mitigating or even preventing the sticking phenomenon.

[0056] The austenitizing stage is mainly to ensure that the matrix of the part is fully austenitized, so that the matrix can be completely transformed into martensite during subsequent stamping and quenching processes.

[0057] The heating stage is designed to maintain the furnace exit temperature of the aluminum-silicon coated hot-formed steel, while also ensuring continued austenitization. Increasing the exit temperature ensures that the aluminum-silicon coated hot-formed steel remains at a relatively high temperature when transferred to the die, which is beneficial for subsequent stamping. At higher temperatures, the aluminum-silicon coated hot-formed steel has lower deformation resistance and is prone to deformation. If the temperature is too low during the forming process, cracking is likely to occur, leading to part failure.

[0058] In some embodiments, the temperature T1 of the pre-alloying stage satisfies: 598℃ ≤ T1 < 860℃; the temperature T2 of the austenitizing stage satisfies: 860℃ ≤ T2 < 930℃; and the temperature T3 of the heating stage satisfies: 930℃ ≤ T3 ≤ 960℃. The relationship between the time t1 of the pre-alloying stage and the total heating time t satisfies: 0% < t1 / t ≤ 47%; the relationship between the time t2 of the austenitizing stage and the total heating time t satisfies: 0% < t2 / t ≤ 40%; the relationship between the time t3 of the heating stage and the total heating time t satisfies: 20% ≤ t3 / t ≤ 45%; and the relationship between the total heating time t, the time t1 of the pre-alloying stage, the time t2 of the austenitizing stage, and the time t3 of the heating stage satisfies: t = t1 + t2 + t3. The total heating time needs to be specifically set according to the specific part; typically, the total heating time t is 180–1200 s.

[0059] Because the temperature during the heating stage directly affects the temperature at which the aluminum-silicon coated hot-formed steel enters the mold, and thus affects the formability of the part, this method proposes to determine the temperature during the heating stage based on the forming quality of the stamped part in order to ensure forming quality. In some embodiments, the method further includes: performing a crack detection on the part; if a crack is found, adjusting the temperature of the heating stage; when the part has visible cracks, adjusting the temperature T3 of the heating stage to satisfy: 950 ≤ T3 ≤ 960 °C; when the part has invisible cracks, detecting thinning; when the maximum thinning rate x of the part satisfies x ≥ 30%, adjusting the temperature T3 of the heating stage to 950 °C; when the maximum thinning rate x of the part satisfies 15% ≤ x < 30%, adjusting the temperature T3 of the heating stage to 940–950 °C; when the maximum thinning rate x of the part satisfies 12% ≤ x < 15%, adjusting the temperature T3 of the heating stage to 930–940 °C; when the maximum thinning rate x of the part satisfies x < 12%, adjusting the temperature T3 of the heating stage to 930 °C. Furthermore, when the maximum thinning rate x of the part satisfies 15% ≤ x < 30%, the temperature T3 of the heating stage is adjusted to satisfy T3 = (200 / 3)x + 930; when the maximum thinning rate x of the part satisfies 12% ≤ x < 15%, the temperature T3 of the heating stage is adjusted to satisfy T3 = (1000 / 3)x + 890.

[0060] S3. The steel to be stamped is stamped and then subjected to pressure holding and quenching to obtain the part;

[0061] In some embodiments, the cooling rate of the pressure-holding quenching is not less than 27°C / s.

[0062] Specifically, in this embodiment, after the aluminum-silicon coated hot-formed steel is heated, it is removed from the furnace and then quickly clamped by a machine and transferred to a hot stamping die for stamping. After stamping, it undergoes pressure holding and quenching. The pressure holding and quenching process is mainly to convert the austenite in the aluminum-silicon coated hot-formed steel into martensite. Typically, the cooling rate of the hot-formed steel during pressure holding and quenching needs to be no less than 27°C / s. To ensure the cooling rate of the hot-stamped parts, corresponding cooling channels are designed in the hot stamping die for water cooling during production. After the pressure holding and quenching of the parts, the die is opened, and then a robot arm clamps the parts and moves them out of the hot stamping die. Typically, the robot arm places the parts on a conveyor belt, which then delivers them to a worktable. Workers inspect and analyze the parts. The main forming quality checks include cracking, thinning, and part performance.

[0063] Based on a general inventive concept, embodiments of this application also provide a coated hot-formed steel part, which is manufactured using the method for preparing coated hot-formed steel parts as described above.

[0064] The coated hot-formed steel parts system is prepared based on the above method. The specific steps of the method can be referred to the above embodiments. Since the coated hot-formed steel parts adopt some or all of the technical solutions of the above embodiments, they have at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be elaborated here.

[0065] 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.

[0066] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the orientation shown in the accompanying drawings. Furthermore, in the description of this application, the terms "comprising," "including," etc., mean "including but not limited to."

[0067] In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, without necessarily requiring or implying any actual relationship or order between these entities or operations. In this document, "and / or" describes the association 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" 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 represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0068] 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 a hot-formed steel part with a coating, characterized in that, The method includes: The aluminum-silicon coated hot-formed steel is selected based on the part design; The aluminum-silicon coated hot-formed steel is heated to obtain steel to be stamped; The steel to be stamped is stamped into shape, and then subjected to pressure holding and quenching to obtain the part; The heating includes a pre-alloying stage to diffuse iron from the matrix of the aluminum-silicon coated hot-formed steel into the coating, an austenitizing stage to fully austenitize the aluminum-silicon coated hot-formed steel, and a heating stage to facilitate the stamping process. The temperature T1 of the pre-alloying stage satisfies: 598℃≤T1<860℃; the temperature T2 of the austenitizing stage satisfies: 860≤T2<930℃; the temperature T3 of the heating stage satisfies: 930≤T3≤960℃. The relationship between the pre-alloying stage time t1 and the total heating time t satisfies: 0% < t1 / t ≤ 47%; The relationship between the austenitization stage time t2 and the total heating time t satisfies: 0% < t2 / t ≤ 40%; The relationship between the heating phase time t3 and the total heating time t satisfies: 20%≤t3 / t≤45%; The relationship between the total heating time t, the time t1 of the pre-alloying stage, the time t2 of the austenitizing stage, and the time t3 of the heating stage satisfies: t = t1 + t2 + t3; The total heating time t is 180~1200s.

2. The method for preparing coated hot-formed steel parts according to claim 1, characterized in that, The method further includes: performing a crack detection on the part; if a crack is found, adjusting the temperature during the heating stage. If the part has visible cracks, the temperature T3 during the heating stage should be adjusted to satisfy: 950≤T3≤960℃; If the part has cracks that are not visible to the naked eye, the thinning condition is checked; When the maximum thinning rate x of the part satisfies x≥30%, the temperature T3 of the heating stage is adjusted to 950℃. When the maximum thinning rate x of the part satisfies 15%≤x<30%, the temperature T3 of the heating stage is adjusted to 940~950℃. When the maximum thinning rate x of the part satisfies 12%≤x<15%, the temperature T3 of the heating stage is adjusted to 930~940℃. When the maximum thinning rate x of the part satisfies x < 12%, the temperature T3 of the heating stage is adjusted to 930℃.

3. The method for preparing coated hot-formed steel parts according to claim 1, characterized in that, When the maximum thinning rate x of the part satisfies 15% ≤ x < 30%, the temperature T3 of the heating stage is adjusted to satisfy T3 = (200 / 3)x + 930; and / or When the maximum thinning rate x of the part satisfies 12%≤x<15%, the temperature T3 of the heating stage is adjusted to satisfy T3=(1000 / 3)x+890.

4. The method for preparing coated hot-formed steel parts according to claim 1, characterized in that, The method further includes the following: the aluminum-silicon coated hot-formed steel can be in the form of a single piece, a patch plate, or a welded type.

5. The method for preparing coated hot-formed steel parts according to claim 1, characterized in that, When the aluminum-silicon coated hot-formed steel is of the form of welded type, the welding method shall be selected according to the coating thickness of the aluminum-silicon coated hot-formed steel. When the coating thickness H of the aluminum-silicon coated hot-formed steel meets the requirement of H≤10μm, the welding method is direct laser welding; When the coating thickness H of the aluminum-silicon coated hot-formed steel meets the requirement of 10 < H ≤ 20 μm, the welding method is direct laser welding or direct laser filler wire welding. When the coating thickness H of the aluminum-silicon coated hot-formed steel satisfies 20<H≤35μm, the welding method is direct laser filler wire welding or indirect laser filler wire welding. When the coating thickness H of the aluminum-silicon coated hot-formed steel satisfies H>35μm, the welding method is indirect laser filler wire welding.

6. The method for preparing coated hot-formed steel parts according to claim 1, characterized in that, The cooling rate of the pressure-holding quenching is not less than 27℃ / s.

7. A hot-formed steel part with a coating, characterized in that, The part is prepared by the method for preparing coated hot-formed steel parts according to any one of claims 1 to 6.

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