Aluminum-silicon plated hot-stamped formed member, method for producing the same, and use thereof

Abstract

This invention provides an aluminum-silicon coated hot-stamped component, its preparation method, and its application. The component includes a steel plate substrate and an aluminum-silicon coating disposed on at least one surface of the steel plate substrate. The aluminum-silicon coating includes a low-aluminum ferrite layer with an aluminum content of less than 5 wt%, and the thickness of the low-aluminum ferrite layer is greater than 5 μm. The maximum bending angle of the aluminum-silicon coated hot-stamped component is greater than 65°. This invention significantly increases the thickness of the low-aluminum, tough ferrite layer in the aluminum-silicon coating after hot stamping, reaching 5-100 μm, by improving the hot stamping process. This effectively prevents the formation or propagation of surface or coating cracks, improving the bending performance of the pre-coated steel plate after hot stamping. Simultaneously, the hot stamping process of this invention takes into account or optimizes the microstructure of the steel matrix, further enhancing the overall bending and tensile properties of the material.

Description

Technical Field

[0001] This invention relates to a hot-stamped component with an aluminum-silicon coating, its preparation method and application, and particularly to a method for improving the bending performance of a hot-stamped steel sheet with an aluminum-silicon coating and a hot-stamped component obtained by the method. Background Technology

[0002] With the goals of "carbon peaking" and "carbon neutrality" being proposed, energy conservation and emission reduction in the automotive industry have become a top priority, and lightweighting of vehicles is an effective way to implement energy conservation and emission reduction. Among many lightweight materials, ultra-high strength steel is an ideal material for achieving vehicle lightweighting while ensuring vehicle safety due to its advantages such as high strength, low cost, and mature technology.

[0003] Hot stamping is a forming process that involves stamping and deforming fully austenitic steel sheets at high temperatures while simultaneously cooling them rapidly to obtain ultra-high-strength steel components. Hot stamping offers advantages such as high forming precision and significant weight reduction, making it particularly suitable for processing complex, integrated, thin-walled parts, such as A-pillars, B-pillars, and roof beams of automotive bodies. The global market for hot-stamped steel (PHS) exceeds 6 million tons annually.

[0004] In actual hot stamping processes, to avoid oxidation and decarburization on the steel surface caused by high temperatures, a pre-coating treatment is usually performed on the steel plate surface. Among them, the most widely used is the high-temperature resistant Al-Si coating patent (CN101583486B) invented by ArcelorMittal in 1999. The PHS of this pre-coated Al-Si coating was commercialized in 2007. According to CN101583486B, the hot stamping parameters are as follows: when the steel plate thickness is between 0.7-1.5 mm, the heating temperature and time are limited to the quadrilateral formed by (3 minutes, 930℃), (6 minutes, 930℃), (13 minutes, 880℃), and (4.5 minutes, 880℃); when the steel plate thickness is between 1.5-3 mm, the temperature and time are limited to the quadrilateral formed by (4 minutes, 940℃), (8 minutes, 940℃), (13 minutes, 900℃), and (6.5 minutes, 900℃); the thickness of the pre-coated Al-Si layer is 20 to 33 μm. Currently, Al-Si coating remains the only commercially available protective layer for PHS. ArcelorMittal produces more than 3 million tons of Al-Si coated PHS annually, and this number is still increasing significantly. Therefore, it is crucial to develop alternative pre-coating technologies for global automotive and steel companies.

[0005] Furthermore, another drawback of Al-Si pre-coating technology is that it inevitably compromises the flexibility of PHS, which severely impacts the safety of PHS applications in automobiles. For example,Figure 1 The results of VDA 238-100 standard bending tests on PHS with and without Al-Si coating are shown, indicating that Al-Si coating significantly reduces the bending performance of steel after hot stamping. Figure 2 The image shows the bending deformation of a car's B-pillar after a real traffic accident, highlighting the importance of the B-pillar's flexibility in protecting passenger space during such accidents. Because the flexibility of automotive components is crucial for protecting passenger lives in accidents, the low flexibility of Al-Si coated PHS is one of the biggest limitations to its application in the automotive industry.

[0006] Recent research papers and patent documents have reported several methods for improving the fracture toughness of hot-stamped Al-Si coated components:

[0007] Yucaitang (Suzhou)'s patent CN108588612B involves a thin Al-Si coating with a thickness between 6-26 μm, a heating temperature between 900℃ and 940℃, and a holding time between 2 min and 5 min. The thin Al-Si coating improves the fracture toughness of hot-stamped steel parts. However, the brittleness of the Al-Si coating still exists, and this technology does not optimize the hot-stamping parameters for the steel substrate.

[0008] ArcelorMittal's patent application CN104769138A discloses a technique for decarburizing a steel substrate before Al-Si coating, thereby improving the overall fracture toughness of Al-Si coated steel. However, compared to traditional hot stamping techniques, this decarburization technique is complex and requires additional capital and energy costs.

[0009] Baosteel's patent CN106466697B provides another series of hot stamping parameters for aluminum-silicon coated steel: optimal temperatures of 935 to 950°C or 945 to 950°C, with holding times of 2.5 to 5 minutes. It is worth noting that Baosteel's hot stamping parameter range is slightly higher than ArcelorMittal's. However, in practice, Baosteel's hot stamping parameters may result in coarse austenite grains in the steel matrix, leading to poor fracture toughness in the steel components. This confirms that in traditional hot stamping technology, hot stamping parameters can only be limited to a very narrow range.

[0010] A paper titled "Influence of Al-Si Coating Structure on Bending Properties and Hydrogen Embrittlement Resistance of 1.5-GPa Grade Hot-Formed Steel" published in *Acta Materialia* investigated how to improve the bending properties of 1.5-GPa grade PHS. However, this paper neglected the difference between high-alumina ferrite and low-alumina ferrite, resulting in highly unstable bending properties of the obtained products. Furthermore, the hot stamping method proposed in this paper can only be applied to 1.5-GPa grade PHS and cannot improve the bending properties of 2-GPa grade PHS. Most importantly, this method still uses a traditional one-step hot stamping process, which cannot address the problem of primary austenite grain size (PAGS) coarsening.

[0011] CN107614733A discloses a hot-pressed forming (HPF) component with excellent peel resistance and its manufacturing method. The invention lies in improving the peel resistance of a hot-dip aluminized steel sheet with a hot-dip aluminized coating by controlling the heat treatment conditions to form only a soft, single diffusion layer during alloying heat treatment. The hot forming process involves heating the hot-dip aluminized steel sheet at 900-990℃ for 2-30 minutes to alloy the hot-dip aluminized layer on its surface; simultaneously, the alloyed hot-dip aluminized steel sheet is rapidly cooled to below 300℃ during hot forming. However, although this method improves the peel resistance of the coating by forming a soft diffusion layer composed of dissolved Al α-ferrite through controlling the austenitization temperature and duration, this heat treatment process can cause a large pre-austenite grain size in the steel sheet matrix, thereby reducing the overall bending and ultimate tensile strength of the material.

[0012] In summary, although pre-coating with aluminum or aluminum alloy can prevent decarburization and surface oxidation in hot-stamped steel, the coating as a whole exhibits brittleness, significantly reducing the bending performance of the steel after hot stamping. Therefore, there is an urgent need to investigate how to compensate for the bending performance loss caused by Al-Si coatings. Recent reported processes have improved the bending performance of traditional aluminum-silicon coated hot-stamped steel sheets, but the bending toughness of Al-Si coated parts is still lower than that of parts without Al-Si coatings. CN107614733A proposes a method to remove the brittle layer on the surface by controlling heat treatment conditions to improve the coating's peel resistance; however, this method leads to severe coarsening of the austenite grains in the steel substrate, impairing the bending performance of the steel substrate. Therefore, to meet the increasingly stringent standards of the automotive industry, more research and development is needed to improve the bending toughness of Al-Si coated parts. Summary of the Invention

[0013] To address the problem that pre-coating leads to a decrease in the bending performance of steel sheets, the present invention aims to provide an improved hot-stamped steel sheet and its preparation process to improve the bending performance of pre-coated steel sheets after hot stamping.

[0014] The inventors have disclosed a method for hot stamping of pre-coated steel sheets in an unpublished prior application CN202111226071.X. This method specifically includes a pre-heat treatment of the pre-coated steel sheet prior to hot stamping, which mainly includes a heating and holding step and a cooling step. The pre-heat treatment can improve the alloying degree of the pre-coated layer, reduce the carbide structure in the steel sheet substrate, and obtain a martensitic and / or bainitic substrate structure. This reduces the wear of the pre-coated layer on the stamping die during high-temperature stamping deformation, refines the grain size, and improves the fracture performance of the final hot-stamped component.

[0015] The interdiffusion zone between the coating and the PHS substrate is ferrite, and its thickness is related to the austenitizing time. Although ferrite is generally considered to be softer than martensitic matrix and can effectively improve the bending properties of Al-Si coated PHS, many attempts to manufacture thicker ferrite layers to improve the bending properties of Al-Si coated PHS have failed. Through meticulous research, the inventors of this invention discovered that only ferrite with low Al content (Al weight percentage equal to or less than 5%, preferably equal to or less than 3%) can limit crack tip propagation, thereby improving the bending properties of Al-Si coated PHS. Based on this new discovery, the hot stamping method of this invention increases the austenitizing temperature and duration, successfully increasing the thickness of the low-Al-content ferrite layer, thus significantly improving the bending properties of Al-Si coated PHS. Furthermore, the inventors of this invention also propose for the first time a second-step heat treatment through grain refinement to compensate for the damage to the bending properties of the steel substrate caused by the first-step high-temperature austenitizing heat treatment, thereby obtaining an aluminum-silicon coated hot-stamped component with improved overall bending properties.

[0016] A first aspect of the present invention provides an aluminum-silicon coated hot-stamped component comprising a steel plate substrate and an aluminum-silicon coating disposed on at least one surface of the steel plate substrate, the aluminum-silicon coating comprising a low-aluminum-content ferrite layer having an aluminum content of less than 5 wt% formed by interdiffusion between the steel plate substrate and the aluminum-silicon pre-coating layer, wherein the thickness of the low-aluminum-content ferrite layer is greater than 5 μm, and wherein the maximum bending angle of the aluminum-silicon coated hot-stamped component is greater than 65°, wherein the maximum bending angle is measured by a VDA 238-100 standard bending test.

[0017] In a preferred embodiment of the present invention, the thickness of the low-aluminum-content ferrite layer is greater than 8 μm, for example greater than 10 μm, or greater than 15 μm, more preferably greater than 20 μm.

[0018] In various embodiments of the present invention, in order to fully prevent the formation and propagation of surface or coating cracks, the thickness of the low-aluminum-content ferrite layer can be 5-100 μm, preferably 5-25 μm.

[0019] In a preferred embodiment of the present invention, the low-aluminum-content ferrite layer comprises an ultra-low-aluminum-content ferrite layer with an aluminum content of less than 3 wt%, and the thickness of the ultra-low-aluminum-content ferrite layer is greater than 4.7 μm, preferably greater than 8 μm, for example greater than 10 μm, or greater than 15 μm, more preferably greater than 20 μm. In some embodiments of the present invention, the thickness of the ultra-low-aluminum-content ferrite layer can be 4.7-100 μm, preferably 5-25 μm.

[0020] In various embodiments of the present invention, the thickness of the low-aluminum-content ferrite layer accounts for 20%-98.5% of the thickness of the aluminum-silicon coating.

[0021] In some embodiments of the present invention, the maximum bending angle of the aluminum-silicon coated hot stamping member is greater than 70°, most preferably about 75°, wherein the maximum bending angle is measured by a VDA 238-100 standard bending test.

[0022] In various embodiments of the present invention, the aluminum-silicon coating may further include a high-aluminum-content ferrite layer with an aluminum content higher than 5 wt%, formed by interdiffusion between the steel substrate and the aluminum-silicon pre-coating layer. However, in order to reduce the impact of the brittleness of the aluminum-silicon coating on the bending properties of the steel after hot stamping, the thickness of the high-aluminum-content ferrite layer should be as small as possible. That is, the aluminum-silicon pre-coating layer in the raw material should form as many low-aluminum-content ferrite layers or ultra-low-aluminum-content ferrite layers as possible.

[0023] In some embodiments of the present invention, in addition to iron, the steel plate substrate may also contain the following components expressed in weight percent: carbon 0.2-0.4%; manganese 0.5-1.5%; boron 0-0.005%; not more than 1% of one or more alloying elements selected from aluminum, silicon, chromium, molybdenum, niobium, and vanadium; and other unavoidable impurity elements.

[0024] In other embodiments of the invention, in addition to iron, the steel plate substrate may also contain the following components expressed in weight percent: 0.3-0.5% carbon; 0.5-2.5% manganese; 0-0.005% boron; not more than 3% of one or more alloying elements selected from aluminum, silicon, chromium, molybdenum, niobium, and vanadium; and other unavoidable impurity elements.

[0025] Increasing the carbon, manganese, and silicon content can improve the hardenability of the steel substrate and facilitate the formation of martensite after the pre-heat treatment, achieving a grain refinement effect. However, excessive carbon, manganese, and silicon content can adversely affect the fracture properties of the steel substrate. Adding a very small amount of boron can improve the hardenability of the steel substrate without affecting fracture properties. Aluminum can deoxidize during smelting while protecting the effectiveness of boron. Other elements such as chromium and molybdenum can also improve hardenability, but disadvantageously, they significantly increase the cost of the steel plate. Vanadium and niobium can refine austenite grains and produce precipitation strengthening, improving the strength of hot-stamped components. As a preferred example, the steel substrate can be commercially available 22MnB5 or 34MnB5 steel.

[0026] In embodiments of the present invention, the thickness of the steel plate substrate can be 0.5-3 mm, and the thickness of the aluminum-silicon pre-coating layer can be 5-50 μm, preferably 6-25 μm, for example 6-15 μm. In the aluminum-silicon coated hot-stamped forming component provided by the present invention, the thickness of the steel plate substrate can be 0.5-3 mm; the thickness of the aluminum-silicon coating can be 10-100 μm, preferably 20-70 μm. In some specific embodiments, the thickness of the aluminum-silicon coated hot-stamped forming component is 1.0-1.3 mm, which is a typical thickness for steel plates used in vehicle body safety components.

[0027] According to the aluminum-silicon coated hot stamping forming component provided by the present invention, the ultimate tensile strength of the hot stamping forming component is 1400-2000 MPa.

[0028] Furthermore, the austenite grain size in the microstructure of the steel substrate of the aluminum-silicon coated hot-stamped component provided by the present invention does not exceed 18 μm. As a preferred embodiment, the austenite grain size in the microstructure of the above-mentioned hot-stamped component does not exceed 10 μm. The higher the degree of grain refinement, the better the fracture performance of the hot-stamped steel.

[0029] In some specific embodiments, the aluminum-silicon pre-coating layer contains, by weight, 8-11% Si, 2-4% Fe, 85-90% Al, and unavoidable impurities. Al primarily provides the coating with high-temperature stability and oxidation resistance; however, disadvantageously, Al can alloy with the steel substrate at high temperatures, forming brittle intermetallic compounds. Si can inhibit the growth of intermetallic compounds, reducing the harmful effects of brittle intermetallic compounds on the fracture performance of the steel plate.

[0030] As an example, commercially available 22MnB5 steel with a pre-coated Al-Si layer can be used. The 22MnB5 steel substrate has a C content of 0.20-0.23% (by weight), a Mn content of 0.9-1.4%, and a Si content of 0.20-0.28%. Furthermore, the thickness of the pre-coated Al-Si layer is approximately 25 μm.

[0031] A second aspect of the present invention provides a method for preparing an aluminum-silicon coated hot-stamped component, comprising hot stamping after two heat treatments, wherein the two heat treatments include:

[0032] The first step, austenitization: heat the aluminum-silicon pre-coated steel plate substrate to 951-1100℃ and hold for 5 to 60 minutes, then cool it to below 300℃ at a rate of not less than 5℃ / s.

[0033] The second step is grain refinement: reheat to 800-870℃ and hold for 3 to 20 minutes, then cool at a rate of not less than 50℃ / s.

[0034] The hot stamping process includes: performing hot stamping at a temperature of not less than 600°C during the cooling process, followed by cooling to room temperature at a rate of not less than 50°C / s.

[0035] Figure 3 This diagram illustrates a comparison between an existing one-step heat treatment process and the two-step heat treatment process provided by this invention. According to the preparation method provided by this invention, the first and second heat treatment steps can be performed continuously or discontinuously. This adds greater flexibility to the manufacture of hot-stamped steel sheets.

[0036] According to the preparation method provided by the present invention, the first step of austenitization process causes the steel plate substrate and the aluminum-silicon pre-coating layer to diffuse into each other to form an aluminum-silicon coating, and the aluminum-silicon coating includes a low-aluminum-content ferrite layer with an aluminum content of less than 5 wt%, and the thickness of the low-aluminum-content ferrite layer is greater than 5 μm.

[0037] Compared to existing one-step heat treatment processes, the first austenitizing step in the preparation method of this invention involves a higher temperature and a longer duration. This results in a larger pre-austenite grain size (PAGS) in the steel substrate, thus affecting the material's flexural strength and ultimate tensile strength (UTS). This is the main reason why researchers avoid increasing the austenitizing temperature and duration during hot stamping. This invention creatively introduces a two-step hot stamping process to overcome this problem. The second heating step in the preparation method of this invention effectively refines the PAGS, resulting in a significantly smaller PAGS in the steel substrate after the second heating step compared to conventional hot stamping processes with lower austenitizing temperatures.

[0038] In a preferred embodiment of the preparation method of the present invention, the heating temperature of the first step of austenitization is 980-1100℃, and the holding time is 10-30 minutes; the heating temperature of the second step of grain refinement is 830-850℃, and the holding time is 4-7 minutes.

[0039] Preferably, the hot stamping temperature is 650-850℃.

[0040] In a preferred embodiment of the preparation method of the present invention, the holding time for the first step of austenitization is longer than the holding time for the second step of grain refinement.

[0041] A third aspect of the invention provides the application of the hot-stamped component in automotive safety structural components, reinforcing structural components, wheel components, or high-strength and tough automotive structural components, preferably, the hot-stamped component is used as the A-pillar, B-pillar, or roof crossbeam of the automotive body-in-white.

[0042] This invention improves the bending performance of pre-coated steel sheets after hot stamping by modifying the hot stamping process. In traditional hot stamping processes, although the pre-coated aluminum or aluminum alloy layer can prevent decarburization and surface oxidation of the hot-stamped steel, the overall coating exhibits brittleness, significantly reducing the bending performance of the steel after hot stamping. In this invention, after hot stamping, the thickness of the low-aluminum, tough ferrite layer (Al weight percentage less than or equal to 5%) in the coating is significantly increased to 5-100 μm, preferably 5-20 μm, effectively preventing the formation or propagation of surface or coating cracks. Simultaneously, the hot stamping process of this invention can consider or optimize the microstructure of the steel matrix, further improving the bending and tensile properties of the material. The aluminum-silicon coated hot-stamped steel obtained by this invention has 10% to 60% better bending performance than the same steel treated by traditional hot stamping methods. This invention is applicable to, but not limited to, high-strength hot-stamped steel with tensile strengths of 1500 MPa and 2000 MPa. Attached Figure Description

[0043] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:

[0044] Figure 1 The results of VDA 238-100 standard bending tests on PHS with and without Al-Si coating are shown.

[0045] Figure 2 It shows the bending and deformation of the B-pillar of a car after a real traffic accident;

[0046] Figure 3 This is a comparative schematic diagram of the existing one-step heat treatment process and the two-step heat treatment process provided by the present invention.

[0047] Figure 4 This is a diagram showing the pre-coated layer and the original microstructure of the 22MnB5 steel plate used in this embodiment of the invention.

[0048] Figure 5 This is a comparison diagram of the microstructure of the steel plate substrate before and after the grain refinement step in Embodiment 5 of the present invention;

[0049] Figure 6 This is a comparison diagram of the cross-sectional microstructure of the hot-stamped components prepared in Comparative Example 1 and Example 1;

[0050] Figure 7 This is a comparison diagram of the original austenite grain size (PAGS) of the hot stamping formed components obtained in Comparative Example 1 and Example 1;

[0051] Figure 8 The maximum bending angle of Al-Si coated 1500MPa 22MnB5 hot-stamped components from Examples 1-3 and Comparative Examples 1, 2 and 6 is compared.

[0052] Figure 9 The maximum bending angle of the Al-Si coated 2000MPa 22MnB5 hot-stamped components of Examples 4 and 5 and Comparative Examples 3 and 4 is shown in comparison.

[0053] Figure 10 The results of tensile tests on hot-stamped components prepared in Example 1 are shown in comparison with those of Comparative Examples 1, 5, and 6. Detailed Implementation

[0054] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0055] The pre-coated Al-Si layer and the original microstructure of the 22MnB5 steel plate used in the examples are as follows: Figure 4 As shown, the pre-coating layer, starting from the steel substrate side, consists of a Si-rich intermetallic compound layer and an Al layer, which is a typical pre-coating structure for commercially available 22MnB5 steel. The steel substrate mainly consists of ferrite, pearlite, and carbides. The lamellar pearlite particles can reach sizes of 2 μm or more, and the spherical carbide particles can reach sizes of 0.5 μm or more.

[0056] Example 1

[0057] Aluminum-silicon coated hot-stamped components with a strength of 1500 MPa were prepared using the method of this invention.

[0058] The aluminum-silicon pre-coated steel plate (1500MPa 22MnB5) used in this embodiment was purchased from Ansteel ThyssenKrupp Automotive Steel Co., Ltd., TA1500-B10NC4, with a thickness of 1.22mm, wherein the thickness of the steel plate substrate is about 1.2mm and the thickness of the aluminum-silicon pre-coating layer is about 11μm.

[0059] S1. Austenitization: The aluminum-silicon pre-coated steel plate is heated to 980°C at a heating rate of 10°C / s, held for 20 minutes, and then cooled to below 300°C at a rate of 5°C / s.

[0060] S2. Grain refinement: The cooled steel plate is reheated to 830°C at a heating rate of 10°C / s and held for 7 minutes.

[0061] S3: When the heat preservation is completed, immediately transfer the hot steel plate to the mold, ensuring that the temperature of the steel plate is above 600℃ when it is transferred to the mold, and hot stamp the steel plate in the mold to obtain the final hot stamped component, and then cool it to room temperature at a rate of 50℃ / s.

[0062] Example 2

[0063] The aluminum-silicon pre-coated steel plate (1500MPa 22MnB5) used in this embodiment was purchased from Ansteel ThyssenKrupp Automotive Steel Co., Ltd., TA1500-B10NC4, with a thickness of 1.23mm, wherein the thickness of the steel plate substrate is about 1.2mm and the thickness of the aluminum-silicon pre-coating layer is about 15μm.

[0064] Aluminum-silicon coated hot stamping components with a strength of 1500 MPa were prepared using a method similar to that in Example 1, except that the austenitizing conditions in step S1 were: temperature 1030°C and holding time 10 minutes; and the grain refinement conditions in step S2 were: temperature 840°C and holding time 5 minutes.

[0065] Example 3

[0066] The aluminum-silicon pre-coated steel plate (1500MPa 22MnB5) used in this embodiment was purchased from Ansteel ThyssenKrupp Automotive Steel Co., Ltd., TA1500-B10NC4, with a thickness of 1.22mm, wherein the thickness of the steel plate substrate is about 1.2mm and the thickness of the aluminum-silicon pre-coating layer is about 11μm.

[0067] Aluminum-silicon coated hot stamping components with a strength of 1500 MPa were prepared using a method similar to that in Example 1, except that the austenitizing conditions in step S1 were: temperature 1030°C and holding time 20 minutes; and the grain refinement conditions in step S2 were: temperature 850°C and holding time 6 minutes.

[0068] Example 4

[0069] Preparation of hot-stamped aluminum-silicon coated components with a strength of 2000 MPa

[0070] The aluminum-silicon pre-coated steel plate (2000MPa) used in this embodiment was purchased from Ansteel ThyssenKrupp Automotive Steel Co., Ltd., TA2000-B10ZBG, with a thickness of 1.22mm, wherein the thickness of the steel plate substrate is about 1.2mm and the thickness of the aluminum-silicon pre-coating layer is about 10μm.

[0071] S1. Austenitization: The aluminum-silicon pre-coated steel plate is heated to 1100℃ at a heating rate of 50℃ / s, held for 15 minutes, and then cooled to below 300℃ at a rate of 5℃ / s.

[0072] S2. Grain refinement: The cooled steel plate is reheated to 870°C at a heating rate of 50°C / s and held for 4 minutes.

[0073] S3: After the heat preservation is completed, the hot steel plate is immediately transferred to the mold. When the steel plate is transferred to the mold, the temperature of the steel plate is above 600℃. The steel plate is then hot-stamped in the mold to obtain the final hot-stamped component. Then, it is cooled to room temperature at a rate of 50℃ / s.

[0074] Example 5

[0075] The aluminum-silicon pre-coated steel plate (2000MPa) used in this embodiment was purchased from Ansteel ThyssenKrupp Automotive Steel Co., Ltd., TA2000-B10ZBG, with a thickness of 1.23mm, wherein the thickness of the steel plate substrate is about 1.2mm and the thickness of the aluminum-silicon pre-coating layer is about 13μm.

[0076] Aluminum-silicon coated hot stamping components with a strength of 2000 MPa were prepared using a method similar to that in Example 4, except that the austenitizing conditions in step S1 were: temperature 1100°C and holding time 30 minutes; and the grain refinement conditions in step S2 were: temperature 850°C and holding time 5 minutes.

[0077] Comparative Example 1

[0078] Aluminum-silicon coated hot-stamped components with a strength of 1500 MPa were prepared using existing methods.

[0079] The aluminum-silicon pre-coated steel sheet (1500MPa 22MnB5) used in this comparative example was purchased from Ansteel ThyssenKrupp Automotive Steel Co., Ltd., TA1500-B10NB1, with a thickness of 1.22mm, of which the thickness of the steel sheet substrate is about 1.15mm and the thickness of the aluminum-silicon pre-coating layer is about 35μm.

[0080] S1. Austenitization: The aluminum-silicon pre-coated steel plate is heated to 930℃ at a heating rate of 10℃ / s and held for 7 minutes;

[0081] S2: When the heat preservation is completed, immediately transfer the hot steel plate to the mold, ensuring that the temperature of the steel plate is above 600℃ when it is transferred to the mold, and hot stamp the steel plate in the mold to obtain the final hot stamped component, and then cool it to room temperature at a rate of 50℃ / s.

[0082] Comparative Example 2

[0083] Thin aluminum-silicon coated hot-stamped components with a strength of 1500 MPa are prepared using existing methods.

[0084] The aluminum-silicon pre-coated steel plate (1500MPa 22MnB5) used in this embodiment was purchased from Ansteel ThyssenKrupp Automotive Steel Co., Ltd., TA1500-B10NC4, with a thickness of 1.24mm, wherein the thickness of the steel plate substrate is approximately 1.22mm and the thickness of the aluminum-silicon pre-coating layer is approximately 11μm.

[0085] S1. Austenitization: The aluminum-silicon pre-coated steel plate is heated to 930℃ at a heating rate of 10℃ / s and held for 7 minutes;

[0086] S3: When the heat preservation is completed, immediately transfer the hot steel plate to the mold, ensuring that the temperature of the steel plate is above 600℃ when it is transferred to the mold, and hot stamp the steel plate in the mold to obtain the final hot stamped component, and then cool it to room temperature at a rate of 50℃ / s.

[0087] Comparative Example 3

[0088] Aluminum-silicon coated hot-stamped components with a strength of 2000 MPa were prepared using existing methods.

[0089] The aluminum-silicon pre-coated steel plate (2000MPa) used in this embodiment was purchased from Ansteel ThyssenKrupp Automotive Steel Co., Ltd., TA2000-B10NBG, with a thickness of 1.27mm, wherein the thickness of the steel plate substrate is about 1.2mm and the thickness of the aluminum-silicon pre-coating layer is about 35μm.

[0090] S1. Austenitization: The aluminum-silicon pre-coated steel plate is heated to 930℃ at a heating rate of 50℃ / s and held for 7 minutes;

[0091] S2: After the heat preservation is completed, the hot steel plate is immediately transferred to the mold. When the steel plate is transferred to the mold, the temperature of the steel plate is above 600℃. The steel plate is then hot-stamped in the mold to obtain the final hot-stamped component. Then, it is cooled to room temperature at a rate of 50℃ / s.

[0092] Comparative Example 4

[0093] Thin aluminum-silicon coated hot-stamped components with a strength of 2000 MPa are prepared using existing methods.

[0094] The aluminum-silicon pre-coated steel plate (2000MPa) used in this embodiment was purchased from Ansteel ThyssenKrupp Automotive Steel Co., Ltd., TA1500-B10ZBG, with a thickness of 1.22mm, wherein the thickness of the steel plate substrate is about 1.2mm and the thickness of the aluminum-silicon pre-coating layer is about 10μm.

[0095] S1. Austenitization: The aluminum-silicon pre-coated steel plate is heated to 930℃ at a heating rate of 50℃ / s and held for 7 minutes;

[0096] S2: After the heat preservation is completed, the hot steel plate is immediately transferred to the mold. When the steel plate is transferred to the mold, the temperature of the steel plate is above 600℃. The steel plate is then hot-stamped in the mold to obtain the final hot-stamped component. Then, it is cooled to room temperature at a rate of 50℃ / s.

[0097] Comparative Example 5

[0098] This comparative example uses the same aluminum-silicon pre-coated steel sheet as Example 1, but only performs step S1 austenitization and step S3 hot stamping, without performing step S2 grain refinement.

[0099] Comparative Example 6

[0100] This comparative example involves heat-treating the aluminum-silicon pre-coated steel sheet from Example 1 according to the conditions described in CN107614733A.

[0101] Aluminum-silicon pre-coated steel sheet (1500MPa 22MnB5) is heated at 990℃ for 10 minutes and then immediately transferred to a mold, ensuring that the temperature of the steel sheet is above 600℃ when it is transferred to the mold. The steel sheet is then hot-stamped in the mold to obtain the final hot-stamped component, and then cooled to room temperature at a rate of 50℃ / s.

[0102] Characterization and Testing

[0103] 1. Figure 5 The images show a comparison of electron backscatter diffraction (EBSD) of the microstructure of the steel plate substrate before and after the grain refinement step in Example 5. It can be observed that after the grain refinement step, the original austenite grains in the microstructure are significantly refined, and the original austenite grain size is reduced from more than 50 μm before the grain refinement step to 6-7 μm after the grain refinement step.

[0104] 2. Figure 6This is a comparison of the cross-sectional microstructure of the hot-stamped components prepared in Comparative Example 1 and Example 1. As can be seen from the figures, compared to the Comparative Example, the coating in Example 1 lacks an aluminum-rich intermetallic compound layer, reducing the overall brittleness of the coating. The thickness of the low-aluminum ferrite layer in Example 1 reaches 13 micrometers, higher than the 4 micrometers in Comparative Example 1. The thickness of the ultra-low aluminum content ferrite layer in Example 1 is 5.9 micrometers. Because only the low-aluminum ferrite layer (including the ultra-low aluminum content ferrite layer) possesses high toughness, it can hinder crack propagation during bending. Therefore, Example 1 exhibits better bending toughness than Comparative Example 1, with a bending angle reaching 65 degrees, higher than the 56 degrees in Comparative Example 1.

[0105] 3. Figure 7 This is a comparison diagram of the original austenite grain size (PAGS) of the hot stamped components prepared in Comparative Example 1(a) and Example 1(b). It can be observed that the PAGS obtained by the hot stamping method using the two-step heat treatment process of the present invention is much smaller than that obtained by the conventional hot stamping process using a low austenitizing temperature.

[0106] 4. The maximum bending angle of the hot-stamped components of Examples 1-5 and Comparative Examples 1-4 was measured by bending test according to VDA 238-100 standard.

[0107] Figure 8 The comparison shows the maximum bending angle of hot-stamped components with Al-Si coating of 1500MPa 22MnB5 from Examples 1-3 and Comparative Examples 1, 2, and 6, where: (A) represents the Al-Si coating of 1500MPa 22MnB5 from Comparative Example 1; (B) represents the Al-Si coating of 1500MPa 22MnB5 from Comparative Example 2; (C) represents the Al-Si coating of 1500MPa 22MnB5 from Comparative Example 6 after heat treatment according to CN107614733A; (D) represents the Al-Si coating of 1500MPa 22MnB5 from Example 1 (austenitizing parameters: 980℃, 20 minutes); (E) represents the Al-Si coating of 1500MPa 22MnB5 from Example 2 (austenitizing parameters: 1030℃, 10 minutes); (F) represents the Al-Si coating of 1500MPa 22MnB5 from Example 3. 22MnB5 (austenitizing parameters: 1030℃, 20 minutes).

[0108] Figure 9The maximum bending angle of the hot-stamped components with Al-Si coating of 2000MPa 22MnB5 from Examples 4 and 5 and Comparative Examples 3 and 4 is compared, where: (A) represents Al-Si coating of 2000MPa 22MnB5 from Comparative Example 3; (B) represents Al-Si coating of 2000MPa 22MnB5 from Comparative Example 4; (C) represents Al-Si coating of 2000MPa 22MnB5 from Example 4 (austenitizing parameters: 1100℃, 15 minutes); (D) represents Al-Si coating of 2000MPa 22MnB5 from Example 5 (austenitizing parameters: 1100℃, 30 minutes).

[0109] Figure 8 and Figure 9 The experimental results of the VDA 238-100 standard bending test show that the bending performance of the Al-Si coating PHS is significantly improved after the hot stamping process of the present invention, which includes two-step heat treatment.

[0110] 5. Tensile tests were conducted on the hot-stamped components prepared in Example 1 and Comparative Examples 1, 5, and 6 using the uniaxial quasi-static tensile method. The results are as follows: Figure 10 As shown. Figure 10 The experimental results show that the embodiments of the present invention have essentially the same yield strength as comparative examples 1, 5 (without grain refinement), and 6 (using the heat treatment method in CN107614733A), but the maximum tensile strength of the present invention is higher. The heat treatment method of the present invention does not negatively affect the tensile mechanical properties of the material; on the contrary, it enhances the plasticity of the material. Compared with comparative examples 1, 5, and 6, the plasticity of embodiment 1 of the present invention is increased by 22.5%, 14%, and 28.9%, respectively. Combined with the significantly increased maximum bending angle of the embodiments of the present invention compared to the comparative examples, it can be concluded that the embodiments of the present invention have superior mechanical properties compared to the comparative examples.

[0111] The above embodiments are merely preferred embodiments of the present invention and do not constitute any limitation on the present invention. Any equivalent substitutions or modifications made by those skilled in the art to the technical solutions and content disclosed in the present invention without departing from the scope of the present invention shall not depart from the technical solutions of the present invention and shall still fall within the protection scope of the present invention.

Claims

1. A hot-stamped component with an aluminum-silicon coating, comprising a steel plate substrate and an aluminum-silicon coating disposed on at least one surface of the steel plate substrate, the aluminum-silicon coating comprising a low-aluminum-content ferrite layer with an aluminum content of less than 5 wt% formed by interdiffusion between the steel plate substrate and the aluminum-silicon pre-coating, the low-aluminum-content ferrite layer limiting the propagation of crack tips. in, The thickness of the low-aluminum-content ferrite layer is greater than 10 μm, wherein the low-aluminum-content ferrite layer includes an ultra-low-aluminum-content ferrite layer with an aluminum content of less than 3 wt%, and the thickness of the ultra-low-aluminum-content ferrite layer is greater than 5 μm. The maximum bending angle of the aluminum-silicon coated hot-stamped component is greater than 65°, and the maximum bending angle is measured by the VDA 238-100 standard bending test; and The original austenite grain size of the microstructure of the steel plate substrate does not exceed 18 μm.

2. The aluminum-silicon coated hot-stamped component according to claim 1, wherein, The thickness of the low-aluminum-content ferrite layer is greater than 15 μm.

3. The aluminum-silicon coated hot-stamped component according to claim 2, wherein, The thickness of the low-aluminum-content ferrite layer is greater than 20 μm.

4. The aluminum-silicon coated hot-stamped component according to claim 1, wherein, The thickness of the low-aluminum-content ferrite layer is 10-100µm.

5. The aluminum-silicon coated hot-stamped component according to claim 1, wherein, The thickness of the low-aluminum-content ferrite layer is 10-25µm.

6. The aluminum-silicon coated hot-stamped component according to claim 1, wherein, The thickness of the ultra-low aluminum content ferrite layer is greater than 8 μm.

7. The aluminum-silicon coated hot-stamped component according to claim 1, wherein, The thickness of the ultra-low aluminum content ferrite layer is greater than 10 μm.

8. The aluminum-silicon coated hot-stamped component according to claim 7, wherein, The thickness of the ultra-low aluminum content ferrite layer is greater than 15 μm.

9. The aluminum-silicon coated hot-stamped component according to claim 8, wherein, The thickness of the ultra-low aluminum content ferrite layer is greater than 20 μm.

10. The aluminum-silicon coated hot-stamped component according to claim 1, wherein, The thickness of the ultra-low aluminum content ferrite layer is 5-100µm.

11. The aluminum-silicon coated hot-stamped component according to claim 10, wherein, The thickness of the ultra-low aluminum content ferrite layer is 5-25µm.

12. The aluminum-silicon coated hot-stamped component according to claim 1, wherein, The thickness of the low-aluminum-content ferrite layer accounts for 20%-98.5% of the thickness of the aluminum-silicon coating.

13. The aluminum-silicon coated hot-stamped component according to claim 1, wherein, The maximum bending angle of the aluminum-silicon coated hot-stamped component is greater than 70°.

14. The aluminum-silicon coated hot-stamped component according to claim 13, wherein, The maximum bending angle of the aluminum-silicon coated hot-stamped component is approximately 75°.

15. The aluminum-silicon coated hot-stamped component according to any one of claims 1 to 14, wherein, The thickness of the steel plate substrate is 0.5-3 mm; the thickness of the aluminum-silicon coating is 10-100 μm.

16. The aluminum-silicon coated hot-stamped component according to claim 15, wherein, The thickness of the aluminum-silicon coating is 20-70 μm.

17. The aluminum-silicon coated hot-stamped component according to any one of claims 1 to 14, wherein, The ultimate tensile strength of the hot-stamped component is 1400-2000 MPa.

18. The aluminum-silicon coated hot-stamped component according to claim 1, wherein, The original austenite grain size of the microstructure of the steel plate substrate does not exceed 10 μm.

19. The aluminum-silicon coated hot-stamped component according to claim 1, wherein, The aluminum-silicon coating also includes a high-aluminum-content ferrite layer with an aluminum content higher than 5 wt%, formed by the mutual diffusion between the steel plate substrate and the aluminum-silicon pre-coating.

20. A method for preparing an aluminum-silicon coated hot-stamped component according to any one of claims 1 to 19, comprising hot stamping after two heat treatments, wherein the two heat treatments include: The first step, austenitization: heat the aluminum-silicon pre-coated steel plate substrate to 951-1100℃ and hold for 5 to 60 minutes, then cool it to below 300℃ at a rate of not less than 5℃ / s. The second step is grain refinement: reheat to 800-870℃ and hold for 3 to 20 minutes, then cool at a rate of not less than 50℃ / s. The hot stamping process includes: performing hot stamping at a temperature of not less than 600°C during the cooling process, followed by cooling to room temperature at a rate of not less than 50°C / s.

21. The preparation method according to claim 20, wherein, The heating temperature for the first step of austenitization is 980-1100℃, and the holding time is 10-30 minutes.

22. The preparation method according to claim 20, wherein, The second step of grain refinement involves heating at 830-850℃ and holding for 4-7 minutes.

23. The preparation method according to claim 20, wherein, The hot stamping temperature is 650-850℃.

24. The preparation method according to claim 20, wherein, The holding time for the first step of austenitization is longer than the holding time for the second step of grain refinement.

25. The application of the hot-stamped forming component according to any one of claims 1 to 19 in the safety structural components of automobiles.

26. The use of the hot-stamped forming component according to any one of claims 1 to 19 in the reinforcing structural parts of automobiles.

27. The use of the hot-stamped component according to any one of claims 1 to 19 in the wheel components of an automobile.

28. The application of the hot-stamped forming component according to any one of claims 1 to 19 in high-strength and tough automotive structural components.

29. The hot-stamped component of any one of claims 1 to 19 is used as an A-pillar, B-pillar, or roof crossbeam of an automobile body-in-white.

Images